Rozprawy doktorskie na temat „Seismic Shaking”

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.
"June 2004."
Includes bibliographical references (leaf 73).
The thesis presents a remotely accessible system for controlling a shaker table laboratory experiment. The Shake Table WebLab is implemented at MIT's Civil Engineering Department under the Microsoft-sponsored iLab initiative for the development of educationally-oriented virtual experiments. Facilitated accessibility, safe operation and expandability are essentials at the root of the design and implementation of the Shake Table WebLab. The fully functional system allows students and researchers to excite a two-story structure, which is three feet high, by vibrating its base while receiving accelerometer readings from its three levels. Registered Internet users may upload their own input data, such as the seismic ground acceleration of a newly occurring earthquake, and therefore study the corresponding behavior of a real structure. The system is designed with an expandable architecture which enables future researchers to add functionalities that suit their fields of interest. Relevant fields of study include real-time signal processing and filtering techniques that would provide an understanding of how earthquakes affect a structure and therefore provide insight on means to minimize encountered damage in large-scale structures. An already developed tool utilizes frequency domain transfer functions to compare the measured structural response at the upper levels with a predictable result based on seismic vibrations applied at the structure's base. Two main characteristics of the web-based application are interactivity, provided through synchronized control/response processes, and sensor-based monitoring of the experiment.
(cont.) The system is built on the Microsoft .Net Framework through server-hosted Active Server Pages and browser-embedded Windows Form Controls. Web Service methods are implemented for initiating remote processes. Throughout the thesis, I state the motivations for conducting this project, the different online activities and generic administrative features, and a description of the implemented technologies and system components.
by Mazen Manasseh.
S.M.

In this research, the dynamic behavior of a seismic isolation system composed of high strength geotextile placed over an ultra-high molecular weight polyethylene (UHMWPE) geomembrane (together called as composite liner) beneath the structure is investigated experimentally. The results of the shaking table experiments which were performed on model structures both under harmonic and modified earthquake motions with and without the seismic isolation (composite liner system), are presented in the thesis. The main focus is given on the potential improvement obtained by use of the composite liner system as compared to the unisolated cases. Based on the performed experiments, it is observed that the utilization of composite liner system provides significant reduction in the accelerations and interstorey drift ratios of structures under harmonic motions while signifant drop is obtained in the spectral accelerations under earthquake motions which provide noticeable improvement in the durability of structures under dynamic effects at the expense of increased translational displacements.

Reinforced concrete frames constructed before the introduction of modern seismic codes have performed poorly during past earthquakes. Such frames have primarily been designed for gravity load effects, leading to light transverse reinforcement in the columns, unconfined beam-column joints, and generally a lack of seismic details required for ductile post-yield behaviour. It has been demonstrated in literature that light transverse reinforcement in a column may result in shear and axial failure. Furthermore, lack of confinement may cause shear failure at joints. However, interaction of vulnerable components and their contribution to the collapse behaviour of existing reinforced concrete frames is not well understood. This research project was initiated to provide a better understanding of the factors contributing to collapse of the frames with non-seismic detailing. In the experimental phase of this study, four 1:2.25 scale, two-bay-two-story specimens were designed with non-seismic details and tested on a shaking table. The target failure mode was intended to be damage leading to collapse that would enable examination of gravity load redistribution during the test. The tests provide unique benchmark data for both qualitative and quantitative assessment of the factors influencing the behaviour of reinforced concrete frames up to the point of collapse. Based on the results from the shaking table tests, this dissertation will evaluate the influence of axial load on shear and axial behaviour of non-ductile columns and the effects of unconfined joints on overall behaviour of a frame near the point of collapse. The analytical phase of the research included evaluation of existing models for predicting shear and axial failure of non-ductile columns and collapse of frames. The currently available models for shear and axial failure of non-ductile columns are mainly drift-based. The results of the current study suggest that these models should be refined using the column ends rotation demand. While results from comprehensive nonlinear models of the four specimens were compared with the test data, simplified models that can be easily employed in engineering practice for assessing existing frames were also evaluated. A refinement to provision from ASCE-41 on column effective stiffness was also proposed in this dissertation.

Il fenomeno di liquefazione sismo-indotta dei terreni può causare danni rilevanti alle strutture interrate. Nella progettazione di tubazioni interrate non è sempre possibile evitare le zone ad elevata sismicità con un alto rischio di liquefazione. Questo aspetto è evidente se si pensa alla lunghezza dei tracciati e all’estensione sul territorio, legata alla necessità di garantire l’approvvigionamento di servizi essenziali in maniera diffusa. Nello specifico, le tubazioni costituiscono un mezzo di trasporto per fluidi di varia natura, dal petrolio greggio al gas naturale, dall’acqua alle acque reflue. La progettazione di queste strutture è complessa e necessita di tenere debitamente in conto i rischi naturali e le relative conseguenze. Tra le diverse manifestazioni associate al fenomeno, in caso di tubazioni leggere quali ad esempio le tubazioni per il trasporto di gas naturale, può verificarsi una risalita del tubo. Casi di risalita di tubazioni interrate si sono avuti ad esempio in occasione del terremoto di Kushiro-Oki nel 1993, del terremoto di Hokkaido-Toho-Oki nel 1994, del terremoto di Niigata nel 2004 o del terremoto di Tohoku nel 2011. Manifestazioni di liquefazione con conseguenti danni alle infrastrutture interrate si sono avuti durante la sequenza sismica di Christchurch del 2010-2011, inoltre, ingenti perdite di gas da tubazioni interrate con conseguente innesco e propagazione di incendi si sono osservati con il terremoto di Kobe nel 1995. Le metodologie tradizionali per contrastare gli effetti del fenomeno di liquefazione sono state ampiamente utilizzate e sono sufficientemente consolidate in termini di implementazione e risultati. Tuttavia, la loro efficacia nella mitigazione della liquefazione per i problemi specifici legati alle condotte interrate non è altrettanto consolidata. In linea generale, le tecnologie e i materiali attualmente in fase di studio sembrano fornire risultati promettenti per applicazioni future ma non esistono ancora, ad oggi, soluzioni standardizzate. Nella proposta di opportune metodologie di mitigazione che facciano fronte al problema della risalita, bisogna considerare diversi fattori quali, ad esempio, la variabilità delle caratteristiche dei terreni attraversati, il tempo necessario alla soluzione adottata per diventare efficace in sito, nonché la sua durabilità in rapporto alla vita nominale dell’opera, quantità e costo dei materiali e semplicità di realizzazione e installazione. Questa attività di ricerca si pone l’obiettivo di esplorare soluzioni alternative per il problema specifico di risalita delle condotte interrate che si verifica in caso di liquefazione sismo-indotta. La ricerca è stata sviluppata presso il laboratorio di geotecnica dell’Università di Tokyo, mediante prova su tavola vibrante effettuate su modelli in scala 1:10. Questa tesi illustra i risultati di undici prove, eseguite durante due periodi distinti di permanenza all’estero. Le prove sono incentrate sullo studio del comportamento della sezione trasversale del tubo, in un deposito di terreno sabbioso mediamente addensato, all’applicazione di una serie di storie temporali sinusoidali di accelerazione. Alcune delle prove sono basate sulla quantificazione dello spostamento verticale del tubo in relazione al diverso peso apparente, le restanti prove mirano invece allo studio delle metodologie di mitigazione per la stabilità del sistema. Tubi drenanti, sacco di ghiaia e geogriglie sono stati utilizzati come metodologie di mitigazione durante la sperimentazione. Un sacco di ghiaia disposto al di sopra della tubazione è risultato soddisfacente nella mitigazione della risalita. Questo sistema rappresenta una soluzione alternativa a basso costo e semplicità di realizzazione e posa in opera, indipendentemente dalle caratteristiche del terreno del sito specifico e che può essere utilizzata con l’ulteriore beneficio di un eventuale drenaggio dell’acqua grazie alle caratteristiche di permeabilità dei materiali ghiaiosi.
Liquefaction of soil deposit can impose deformations on the structures interacting with it with consequent damages. In the design of lifelines, it is not always possible to avoid areas with high seismicity in which the liquefaction hazard is consistent, due to the very long route of these infrastructures and the necessity to provide essential services in different areas. Specifically, pipeline systems provide a medium of transportation for fluids which could vary from crude oil or natural gas to water or sewage fluids. Their construction is challenging due to natural hazards that might cause loss of functionality and possible danger to the environment. The loss of soil shear strength can produce permanent ground deformation which can lead to lateral movements, flotation or subsidence of buried pipeline in case of liquefaction. Uplift of underground structures might also occur, mostly in case of very light structures which could be the pipelines transporting natural gas. Numerous cases of uplift of buried pipelines have been observed over years for example during the 2004 Niigata Earthquake, the 2011 Tohoku Earthquake, 1993 Kushiro-Oki Earthquake and 1994 Hokkaido-Toho-Oki Earthquake. In addition, the 2010-2011 Christchurch Earthquake sequence induced liquefaction on a vast area and massive damage to buried infrastructure has been accounted for. Kobe Earthquake in 1995 caused extensive gas leakage from buried pipelines with subsequent fires ignition. Conventional methods to prevent liquefaction have been widely used worldwide and are enough consolidated in terms of implementation and results but their effectiveness in the mitigation of liquefaction for buried pipelines is less known. Different solutions have been investigated over years to assess this problem and recently new techniques are developing to satisfy engineering economy, environmental impact, technical performances and durability criteria. For the specific problem of pipelines, various aspects need to be considered such as different soils characteristics for the length of the pipeline track, time for the solution to start being effective on site, life of the solution when compared with the design life of the pipe, amounts and costs of the materials and simplicity of realization. Overall new technologies and new materials seem to have satisfactory results promising for future applications but there are not yet solutions which can be considered as a standard. To assess this specific problem, accounting for all the above-mentioned factors, this research work wants to investigate alternative solutions for the specific problem of seismic-liquefaction induced uplift of onshore gas buried pipelines. The research is conducted by means of 1-g shaking table tests in a model scale of 1:10 performed in the geotechnical laboratory of the University of Tokyo. This thesis presents the results of eleven shaking table tests, executed in two different time periods, with reference to the transversal cross-section of the pipe embedded in a homogenous medium-dense sandy soil deposit by applying series of input motion. Some of the tests deal with the quantification of the vertical displacement by changing the pipe apparent unit weight and the remaining tests study the effectiveness of new remedial measures to increase the stability of the system. Drain pipes, gravel bags, and geogrids are used as testing countermeasures and the experimental results will be presented in the thesis. A gravel bag installed above the pipeline has been proven effective in mitigating the uplift. This represents an innovative protection system with low-cost technology and easiness of realization and installation in every kind of soil condition and which can be used with the support of the additional benefit of drainage systems not accounted for in this research. Please note that this thesis does not provide considerations on the longitudinal development of the pipelines, which would have required specific studies.

The presented research investigated the viability of a double-braided synthetic fiber rope for providing improved performance of steel moment frames subjected to earthquake-induced ground motions. A series of experimental tests, including a 1:3-scale dynamic test and 1:6-scale shaking table tests, was conducted using Northridge ground-motion input. A series of nonlinear dynamic analytical studies, using DRAIN-2DX, was conducted to develop the experimental tests. Throughout experimental testing, the ropes exhibited a hyper-elastic loading response and a reduced-stiffness unloading response. A conditioning cycle was defined as a loading cycle induced in the rope above the highest load expected to be experienced by the rope, and was determined to be requisite for ropes intended to be used for the stated objectives of the research program. After experiencing a conditioning cycle, the rope response returned to initial conditions without permanent deformation, demonstrating repeatability of response through several loading cycles below the conditioning load. In the 1:6-scale shaking-table experiments, the ropes drastically improved the performance of the steel moment frames. Maximum and residual drift were reduced significantly, with a corresponding minimal increase to the maximum base shear. Base shear was reduced at several peaks subsequent to the initial pulse of the Northridge ground-motion input. The analytical model developed was excellent for predicting elastic response of the 1:6-scale shaking table experiments and adequate for the purpose of planning shaking table studies. Correlation of peak rope forces between the analytical model and experimental results was poor, and was attributed to limitations of the pre-defined elements used to represent the rope devices in the software program. The inability of the elements to capture the complex unloading response of the rope was specifically noted.
Ph. D.

The present thesis is part of the wide work required by the SEBESMOVA3D (SEeismic BEhavior of Scaled MOdels of groin VAults made by 3D printers) project whose first motivation is the preservation of the cultural heritage in case of seismic events. Therefore, the main topic of the thesis is the analysis of the seismic response of scaled models of groin vaults, made of plastic 3D printed bricks filled with mortar, and subjected to shaking table tests performed at the EQUALS laboratory of the University of Bristol. The work has been developed on two parallel binaries: the processing of the displacement data acquired in situ and the calibration of a FEM model.

This research employs a deterministic seismic risk assessment methodology to assess the potential damage and loss at meshblock level in the Christchurch CBD and Mount Pleasant primarily due to building damage caused by earthquake ground shaking. Expected losses in terms of dollar value and casualties are calculated for two earthquake scenarios. Findings are based on: (1) data describing the earthquake ground shaking and microzonation effects; (2) an inventory of buildings by value, floor area, replacement value, occupancy and age; (3) damage ratios defining the performance of buildings as a function of earthquake intensity; (4) daytime and night-time population distribution data and (5) casualty functions defining casualty risk as a function of building damage. A GIS serves as a platform for collecting, storing and analyzing the original and the derived data. It also allows for easy display of input and output data, providing a critical functionality for communication of outcomes. The results of this study suggest that economic losses due to building damage in the Christchurch CBD and Mount Pleasant will possibly be in the order of $5.6 and $35.3 million in a magnitude 8.0 Alpine fault earthquake and a magnitude 7.0 Ashley fault earthquake respectively. Damage to non-residential buildings constitutes the vast majority of the economic loss. Casualty numbers are expected to be between 0 and 10.

2008/2009
È stato affrontato il problema della definizione della pericolosità sismica utilizzando il metodo neo-deterministico (NDSHA), che si basa sul calcolo di sismogrammi sintetici realistici. Considerando modelli strutturali medi e un set di sorgenti distribuite internamente alle zone sismogenetiche, possono essere definite delle mappe di scuotimento al bedrock complementari alla mappa di pericolosità di tipo probabilistico (PSHA) sulla quale è basata la normativa antisismica italiana. L’analisi di stabilità effettuata ha dimostrato che l’informazione disponibile sui terremoti del passato può non essere rappresentativa per i futuri terremoti, anche se si hanno a disposizione cataloghi estesi nel tempo (∼ 1000 anni). Ciò non è sorprendente se si tiene presente la scala dei tempi dei processi geologici, ma tale consapevolezza è spesso ignorata in PSHA. NDSHA permette di superare questo limite mediante l’uso di indicatori indipendenti sul potenziale sismico di un’area (e.g. nodi sismogenetici e faglie attive) che consentono di colmare le lacune nella sismicità osservata. Il confronto tra le mappe di pericolosità PSHA e NDSHA sul territorio italiano ha evidenziato che NDSHA fornisce valori maggiori di PSHA nelle aree caratterizzate da forti terremoti osservati e in corrispondenza dei nodi sismogenetici. I valori massimi di NDSHA sono confrontabili con quelli di PSHA per lunghi periodi di ritorno (T≥2475 anni). D’altro canto, PSHA tende a sovrastimare, rispetto a NDSHA, la pericolosità sismica in aree a bassa sismicità. È quindi auspicabile una revisione della normativa che tenga conto di questi fatti. Gli scenari di scuotimento sono utili sia per la ricostruzione delle caratteristiche di sorgente dei terremoti del passato (es. terremoto del 1117) che per la previsione degli effetti degli eventi futuri. Quest’ultimo aspetto, importante per le azioni di prevenzione della Protezione Civile, è stato sviluppato nell’ambito del progetto ASI-SISMA mediante la generazione di scenari dipendenti dal tempo a diversa scala di dettaglio. L’applicazione della tecnica analitica di calcolo dei sismogrammi sintetici in mezzi anelatici tridimensionali, per la cui è stata messa a punto una subroutine per la gestione automatica dell’input, è stata applicata allo studio di eventi di profondità intermedia, avvenuti in Vrancea (Romania), considerando sia serie temporali registrate (accelerogrammi) che intensità osservate.
The problem of the definition of the neo-deterministic seismic hazard assessment (NDSHA), based on the computation of realistic synthetic seismograms, has been capably addressed. Considering average structural models and a set of sources distributed within the seismogenic zones, ground shaking maps at the bedrock, complementary to the probabilistic seismic hazard (PSHA) map on which the Italian seismic code is based, can be defined. The stability analysis performed showed that the available information from past events may not be well representative of future earthquakes, even if long earthquake catalogues (< 1000 years) are available. This is not surprising if we consider the geological times, but this awareness is often ignored in PSHA. NDSHA can easily overcome this limit since it allows to take into account, in a formally well defined way, not only the observed seismicity but also independent indicators of the seismogenic potential of a given area like the seismogenic nodes and active faulting data. The comparison between PSHA and NDSHA maps over the Italian territory evidenced that NDSHA provides values larger than those given by PSHA in areas where large earthquakes are observed and in areas identified as prone to large earthquakes (i.e. seismogenic nodes). The maximum values of NDSHA are consistent with those of PSHA for long return periods (T≥2475 years). Comparatively smaller values are obtained in low-seismicity areas. Therefore a revision of the code taking into account these facts is desirable. Ground shaking scenarios are useful in order to detect the main characteristics of the past earthquakes (e.g. the 1117 earthquake) and to predict the expected ground shaking associated with future earthquakes. The last aspect, which constitutes a useful tool for the rescue actions of the Civil Protection, has been developed in the framework of the ASI-SISMA Project by means of the generation of multi-scale time-dependent seismic hazard scenarios. The application of the analytical technique for the computation of synthetic seismograms in three-dimensional anelastic models, for which a subroutine for the automatic generation of the input has been developed, has been applied to the study of intermediate-depth Vrancea (Romania) earthquakes, considering both recorded time series (accelerograms) and observed macroseismic intensities.
XXII Ciclo
1982

Hospitals are regarded as some of the most important structures in society due to the service that they provide. Knowing this, governments spend large amounts of money on these facilities. Also, codes of design require to provide them more reserve capacity than that for conventional structures. However, large damages (such as collapses and permanent or temporary interruptions of their functionality) have still been observed in hospitals during strong earthquakes. Unfortunately, it is precisely after this type of event that their service is in high demand and failure in providing that service could lead to further disastrous or fatal consequences. Therefore, the use of protective technologies, combined with rational procedures of design, would help to reduce damage and probable losses of functionality in hospital structures. In this thesis, a procedure for seismic design of structures equipped with a type of protective technology, namely, buckling-restrained braces (BRBs), is proposed. Then, the results of experimental and numerical studies are presented to understand the benefits of using BRBs in structures. This study highlights that BRBs are very effective to dissipate seismic energy and can act as structural fuses, i.e. disposable devices that may be replaced after an earthquake without interruptions in the functionality of the structure. One of the advantages of the proposed procedure is that it takes into account explicitly the characteristics and contributions of both, the main structure and the BRBs. It is based on the assumption that a structure protected with BRBs can rationally be represented by a dual SDOF system whose parts yield at different displacement levels. Other advantages include: 1) better control of the displacement demands on the structure; 2) achievement of the fuse concept beforehand; and 3) rapid assessment of the probabilistic performance of the structure. The experimental studies consisted of testing steel and concrete models, with and without BRBs, on a shaking table. In addition to calibrate and validate the proposed method of design, the tests have helped to find that, due to BRBs: 1) the damping ratio is increased significantly; and 2) the dynamic response, to ground motions characteristic of the lakebed zone of Mexico City, is reduced in terms of lateral displacements, inter-storey drifts, floor velocities and floor accelerations. The numerical studies are: 1) a study of the response of typical hospitals improved with BRBs; 2) a study of residual displacements in conventional and dual systems; and 3) evaluation of the economic benefits of using BRBs in structures. On these studies, hypothetical hospitals located in the lakebed zone of Mexico City were considered. The results show that the use of BRBs is very beneficial in medium- and low-rise buildings, while adverse effects may be observed in high-rise structures.

The city of Wellington has a high population concentration and lies within a geologically active landscape at the southern end of the North Island, New Zealand. Wellington has a high seismic risk due to its close proximity to several major fault systems, with the active Wellington Fault located in the north-western central city. Varying soil depth and properties in combination with the close proximity of active faults mean that in a large earthquake rupture event, ground shaking amplification is expected to occur in Thorndon, Te Aro and around the waterfront. This thesis focuses on the area bounded by Thorndon Overbridge in the north, Wellington Hospital in the south, Kelburn in the west, and Oriental Bay in the east. It includes many of the major buildings and infrastructural elements located within the central Wellington commercial area. The main objectives were to create an electronic database which allows for convenient access to all available data within the study area, to create a 3D geological model based upon this data, and to define areas of different seismic subsoil class and depth to rock within the study area at a scale that is useful for preliminary geotechnical analysis (1:5,000. Borelogs from 1025 holes with accompanying geological and geotechnical data obtained from GNS Science and Tonkin & Taylor were compiled into a database, together with the results from SPAC microtremor testing at 12 sites undertaken specifically for this study. This thesis discusses relevant background work and defines the local Wellington geology. A 3D geological model of the central Wellington commercial area, along with ten ArcGIS maps including surficial, depth to bedrock, site period, Vs30, ground shaking amplification hazard and site class (NZS 1170.5:2004) maps were created. These outputs show that a significant ground shaking amplification risk is posed on the city, with the waterfront, Te Aro and Thorndon areas most at risk.

This doctoral project aims to contribute to advancement of the research in the field of innovative and resilient timber buildings with high seismic performance and minimum environmental impact in a green and sustainable way. Recent seismic events have raised questions about the adequacy of the current seismic design in code provisions. In modern seismic codes, the performance objectives are expressed in terms of life safety of the occupants and according to capacity design rules a certain damage level of structures is accepted under strong earthquakes. The resultant seismic damages are often difficult and financially prohibitive to repair. In order to significantly reduce structural and non-structural damage and avoid high economic loss, in the last decades research studies focused on the development of low damage design and technologies. In this thesis, seismic design and performance of multi-storey post-tensioned timber framed buildings with different dissipative systems have been investigated in order to develop new low-damage construction systems for high seismic areas. An extensive experimental campaign was performed at the structural laboratory of the University of Basilicata (Italy), in collaboration with the University of Canterbury (New Zealand), considering a three-dimensional, two-third scale, three-storey, post-tensioned glulam timber frame building. Different testing configurations were considered: i) the bare timber frame with post-tensioning only at the beam-column connections (free rocking); ii) the post-tensioned timber frame with dissipative devices at the beam-column and column-foundation connections (dissipative rocking); and iii) the post-tensioned timber frame with dissipative bracing systems at all storey (dissipative bracing). The seismic response of test specimen was investigated through unidirectional shaking table tests under consecutive ground motions at increasing PGA intensities, while the cyclic behaviour of hysteretic dampers was characterized by means of quasi-static tests. In particular, the testing configuration with dissipative bracing, which had not been previously implemented in post-tensioned glulam timber structures, has been deeply investigated in this research. The estimation of equivalent viscous damping has been proposed in order to optimize the displacement-based design procedure for sizing the hysteretic dissipative devices of the bracing systems. The experimental seismic response of the braced model is evaluated in terms of global and local behaviour and nonlinear numerical analysis have been carried out within two different FEM software (Sap 2000 and OpenSees). The comparison of the results obtained from all configurations demonstrated that the dissipative bracing system improved the seismic performance of post-tensioned timber buildings reducing inter-storey drift with full re-centring capability. During all seismic tests no damages were observed to structural elements, only localized breakage of external replaceable devices occurred during the test with strongest earthquake. More than one hundred inelastic cycles were experimentally recorded from dynamic tests before the failure of devices. The reliability of quasi-static testing procedures proposed by current seismic and guidelines codes for type tests and factory production control tests was also investigated. The number of cycles estimated from shaking table tests and non-linear dynamic analyses shows a decreasing trend with the increase of ductility demand in line with American standards testing requirements.

The Italian and European regions are characterized by a wide diffusion of structures in the minor historical centres. The decay condition, in which part these buildings are, makes often necessary structural interventions to preserve they integrity. This way, during last decades several new intervention methodologies were developed, employing both innovative and traditional materials, with the aim to avoid further damages, particularly those induced by seismic events. However, these new materials and techniques are often commercialized and employed without any preliminary exhaustive study to verify their applicability and their effectiveness. The present research joins in this contest considering the multi-leaf stone masonries, one of the most diffuse structural systems widely employed on minor historical buildings. This masonry typology is constituted by more approached leaves and it is characterized by a high percentage of internal voids. Furthermore, the employment of hydraulic lime-based grout injection is also considered as strengthening technique suitable for this masonry typology. This study aims to validate the application of this intervention methodology, widely applied since many years employing materials different for chemical composition, trough an extensive experimental campaign and a subsequent numerical modelling. First experimental phase involves a series of dynamic tests on whole building models, considering a reducing scale factor, realized with multi-leaf stone masonry, subsequently strengthened trough injection of grout. The execution of these shaking table tests allowed to evaluate the influence of the considered strengthening technique on the overall dynamic behaviour of the injected structure. Furthermore, also the increasing of strength and the seismic response of the building models could be evaluated. A complementary experimental phase involved several further quasi-static laboratory tests tests on single structural elements. Compression tests allowed to study the strength increasing of this elements as well as their failure mechanisms after the grout injection. Further shear compression tests provided important informations about the mechanical behaviour of single structural elements subjected to in-plane cyclic forces. Finally, a numerical modelling of the mechanical behaviour of specimens subjected to compression load was developed. This analysis allowed to deepen the study of the stress distribution and of the failure mechanisms of single structural elements subjected to strengthening trough grout injection.
Il territorio italiano, così come quello europeo, è caratterizzato da un’ampia diffusione di strutture appartenenti all’edilizia storica minore. Lo stato di degrado, in cui talvolta si trovano tali edifici, rende spesso necessari interventi strutturali volti a garantirne l’integrità. In tale senso, negli ultimi decenni sono state sviluppate nuove metodologie d’intervento, sfruttando sia di materiali tradizionali che innovativi, per preservare tali strutture da ulteriori danni, in particolare quelli indotti da eventi sismici. Tuttavia, nuovi materiali e tecniche d’intervento vengono spesso commercializzati ed applicati senza l’esecuzione di un esaustivo studio preliminare che ne verifichi l’applicabilità e l’efficacia. La presente ricerca si inserisce in questo contesto prendendo in considerazione le murature multi-strato in pietra, una delle tipologie costruttive maggiormente impiegate nell’edilizia storica minore. Tale muratura è costituita da più paramenti accostati ed è caratterizzata da un’alta percentuale di vuoti interni. Inoltre, si considera l’impiego dell’iniezione di miscela, a base di calce idraulica naturale, come tecnica di consolidamento applicabile a tale tipologia muraria. Lo studio si propone di validare l’impiego di questa metodologia d’intervento, già da tempo ampiamente utilizzata sfruttando materiali di diversa composizione chimica, mediante la realizzazione di un’ampia campagna sperimentale e di una successiva modellazione numerica. La prima fase sperimentale comprende una serie di prove dinamiche su modelli di edificio, in scala ridotta, realizzati in muratura multi-strato di pietra, successivamente sottoposta ad iniezione di miscela. L’esecuzione di tali prove su tavola vibrante ha permesso di valutare l’influenza della tecnica di consolidamento considerata sul comportamento dinamico globale della struttura su cui si interviene. Inoltre, si è potuto valutare l’incremento di resistenza oltre che la variazione della risposta sismica dei modelli di edificio. Una complementare fase sperimentale ha coinvolto numerose ed ulteriori prove di laboratorio, realizzate in ambito quasi-statico, su singoli elementi strutturali.L’esecuzione di prove di compressione ha permesso di verificare sia l’incremento di resistenza di tali elementi strutturali che la variazione delle loro modalità di rottura a seguito dell’iniezione di miscela legante. Ulteriori prove di taglio e compressione hanno fornito importanti indicazioni riguardo al comportamento meccanico di singoli elementi strutturali soggetti a forze cicliche nel piano. Infine, si è sviluppata una modellazione numerica del comportamento meccanico di campioni sottoposti a carico di compressione monoassiale. Quest'analisi ha dunque permesso di approfondire lo studio della distribuzione delle tensioni e delle modalità di rottura di singoli elementi strutturali, soggetti ad intervento di consolidamento mediante iniezioni di miscela legante.

Les séismes constituent une source d’aléas importante pour l’étude de la vulnérabilité d’unbâtiment. Le comportement parasismique des bâtiments à ossatures en bois est particulièrementintéressant. Deux familles de structure à ossature en bois peuvent être distinguées : les ossaturesutilisant les produits industriels que sont les panneaux en bois reconstitué servant à contreventerla structure et les connecteurs métalliques, et les ossatures traditionnelles avec remplissage reposantsur des techniques de construction anciennes et dépendantes du contexte local. L’efficacitédu comportement parasismique des bâtiments à ossature en bois traditionnels avec remplissagereste encore peu reconnue en raison du manque de résultats issus des travaux de recherche.Les travaux présentés dans cette thèse visent ainsi à améliorer les connaissances sur le comportementparasismique de cette typologie constructive. Partant de l’hypothèse selon laquellece comportement est gouverné par la réponse des assemblages par connecteurs métalliques, uneapproche multi-échelles, couplant études expérimentales et études numériques est développée.Elle détaille l’analyse à l’échelle 1 de la connexion, en passant par l’échelle 2 des cellules élémentaires,constitutives des murs, par l’échelle 3 des murs de contreventement pour se finaliserà l’échelle 4 du bâtiment dans son ensemble.Sur le plan expérimental, cette approche permet d’une part, de réaliser des études paramétriqueset ainsi d’appréhender l’influence de la réponse de chaque élément (bois, clous, feuillard,remplissage, contreventement, ouvertures) sur le comportement local (échelles 1 et 2) et global(échelles 3 et 4) de la structure. D’autre part, elle permet de fournir une base de données pourla validation des modélisations numériques aux différentes échelles.Sur le plan de la modélisation numérique, cette approche multi-échelles est fondée sur la priseen compte du comportement non-linéaire hystérétique des assemblages à l’échelle supérieure, parl’intermédiaire d’un macro-élément, développé dans la cadre de la méthode des éléments finis.Ainsi, grâce à une modélisation simplifiée (assemblage des macro-éléments), le calcul est rapide,aussi bien à l’échelle du mur qu’à celle du bâtiment, et intègre les phénomènes non-linéaire locaux.Le modèle peut ainsi prédire de manière relativement précise le comportement dynamique de lastructure complète à l’échelle 4, testée sur table vibrante.L’étude présentée dans ce manuscrit fait partie des travaux précurseurs relatifs à l’analysede la vulnérabilité sismique des ossatures bois avec remplissage. Cette étude débouche sur denombreuses perspectives pour l’analyse de cette typologie constructive. Elle confirme que les bâtimentsà ossatures en bois avec remplissage ont un comportement parasismique très performant
The seismic vulnerabilty is an important issue in the design of a building. The seismicresistant behavior of timber-framed structures is particularly relevant. Two types of timberframedstructures can be distinguished : the timber-framed structures using industrial products,such as wood-products panels used to brace the structure or metal fasteners, and traditionaltimber-framed structures included infill made of natuarl materials (earth or stones masonry).The seismic resistant behavior efficiency of traditional structures remains poorly recognizedbecause of the lack of research results on this kind of construction.Therefore, the thesis aims at improving the seismic behavior knowledge of timber-framedmasonry. Based on the assumption that their behavior is driven by the response of the metalfasteners connections, a multi-scale approach is proposed. It couples experimental and numericalstudies. At the scale 1 of the connection, at the scale 2 of the elementary constitutive cell ofwalls, at the scale 3 of structural elements such as shear walls and finally at the scale 4 of theentire building.In regards to the experimental work, this method allows, on the one hand, to perform parametricstudies and to analyze the influence of each element (wood member, nails, steel strip,infill, bracing, openings) on the local behavior (scales 1 and 2) and on the global behavior(scales 3 and 4) of the structure. On the other hand, it allows to provide a database to validatethe numerical modeling at each scale.In regards to the numerical work, this multi-scale approach allows to take into account thehysteretic behavior of joints in the development of a macro-element at the scale 2. Thus, thanksto a simplified finite element modeling (macro-element assembly), the computational cost islimited and it allows to take into account the local phenomena. The model is able to predictrelatively accurately the dynamic behavior at the scale 4 of the building, tested on a shakingtable.The study, presented herein, is one of the pioneer work that deals with the analysis of theseismic vulnerability of timber-framed structures with infill panels. This study provides outlookfor the analysis of this type of buildings. It confirms that the timbered masonry structures havea relevant seismic resistant behavior

碩士
國立臺灣大學
土木工程學研究所
94
Abstract The Chi-Chi earthquake struck Taiwan in 1999. Causing many people dead and injured, buildings destroyed and also inducing numerous landslides . The pseudo static and sliding block analysis for seismic analysis slope usually involve many assumptions. In order to understand the behavior of slope subjected to earthquake, Wang (2003) used large shaking table to perform large scale model slope test in NCREE to observe the dynamic behavior of slope. The small shaking table was developed in laboratory in 2004 to facilitate the laboratory slope model test and which has advantage of easy operation and specimen preparation. The aim of this study is to take advantage of the convenience of the small shaking table to simulate and study the seismic slope behavior. The control factors such as slope angle and slope height have been changed during tests. The development of sliding initiated from the slope crest and moving toward the slope toe causing heave when the control factor is slope angle. As the control slope height increases , the slope became more unstable with ,and development of the failure obvious when the dynamic force is applied the specimen. The images of model slope behavior were recorded during tests and image analysis using PIV is performed to tract the displacement vectors when landslide initiates. The infrared rays were used to scan the surface of specimen, which measured the differences in geometry of specimen before and after test. The deformation of slope was measured according to the average height to two curves. The FLAC program was used to simulate the displacement vector and shear strain increment and the results good consistence with test results.

碩士
國立臺灣大學
土木工程學研究所
95
The Chi-Chi earthquake struck Taiwan in 1999 which induced numerous landslides.Using pseudo static and sliding block analysis for seismic slope analysis usually involve simplitied assumptions. In order to understand the behavior of slope subjected to earthquake, Wang (2003) used large shaking table to perform large scale model slope test in NCREE to observe the dynamic behavior of slope. The small shaking table was developed in laboratory in 2004 to facilitate the laboratory slope model test with the advantage of easy operation and specimen preparation. The aim of this study is to take advantage of the small shaking table to simulate and study the seismic slope behavior. The control factors such as slope height and slope angle have been changed during tests. The development of sliding initiated from the slope crest and moved toward the toe causing heave when the slope angle. Varies as the slope height increases , the slope became more unstable with rapid development of failure. The images of model slope behavior were recorded during tests and image analysis where performed using PIV to tract the displacement vectors when landslide initiated. The infrared rays were used to scan the surface of specimen, which measured the differences in geometry of specimen before and after test. The deformation of slope was measured based on the average height of two curves. The FLAC program was used to simulate displacements of the slopes in laboratory tests and a good agreement between the the results of numerical models and the measurements analyzed by PIV was achieved.

博士
國立成功大學
建築學系碩博士班
92
Seismic analysis is the essential of seismic strategy for building structures. It can help researchers and engineers to recognize the characteristics and weakness of a structure, and determine proper measures for resisting earthquake. School buildings in Taiwan usually have typical plan and structure system; therefore result in typical failure patterns, which have been qualified in the investigations of past earthquakes. In this dissertation, a series of shaking table tests of typical school building structure models is employed to simulate earthquakes, thus the dynamic behaviors and damage details of specimens can be observed and analyzed quantitatively. The test results also provide the basis for modification of a present seismic analysis method for low-rise RC building structures. It is expected that the improved method could be further used to related applications such like rapid seismic estimation and retrofitting after earthquake. 　　The results of shaking table tests of three 1/3-scaled RC school building models with different structure systems show a common “weak-column-strong-beam” failure mode. It is due to the underestimation of performance of beam, which in the present design methodology in Taiwan is usually improperly considered as a rectangular section without linked slabs or windowsills. According to the “weak-column-strong-beam” behavior, this dissertation presents a nonlinear pushover analysis method for low-rise RC building structures, which can calculate story shear-displacement curve by summing lateral force-deflection curve of each individual vertical member. Then base on concept of energy dissipation, hysteretic behaviors of RC material, and experiential factors obtained from shaking table tests with repeated excitation, a deterioration rule for RC column after multiple earthquakes is established. According to the failure mode and damage condition in previous earthquake, the rule makes lateral force-deflection curve of RC column deteriorated by reducing stiffness and strength. Finally, a practical seismic analysis method is presented. Through a reasonable assumed distribution of lateral forces, the capacity curve can be derived from the story shear-displacement curves. And by using equations suggested by ATC-40, the corresponding capacity spectrum, period, damping ratio and PGA can also be obtained. This method can provide not only collapse PGA of a low-rise RC building structure, but also damage conditions of members at a specific PGA. Combining with the deterioration rule for RC column after multiple earthquakes, it can also be applied to seismic analysis for after-earthquake or aged buildings. 　　The test results of new-built and retrofitted specimens’ show that well constructed and properly positioned wing-walls can increase the seismic performance of low-rise RC school building structures; likewise a separation with sufficient width between windowsill and column can prevent short-column effect. The structural responses, damage progress, and dynamic characteristics vary relatively to each other. However, an attempt to derive quantitative relationship between damage index and fundamental period just results in an unclear quadratic fitting. After modification of: biaxial bending effect, shear contribution of hoops, interaction of bending and shear, reducing factor for flexural stiffness before yielding, extra deflection due to bond slip, limitation of allowable maximum deflection, P-D effect, and RC walls’ contribution in out-of-plane direction, the modified analytical curves approximately match the test results. The comparison of analytical results of the practical seismic analysis method and results from shaking table test as well as two school buildings damaged in past earthquake also shows reasonable accuracy.

Experiences from recent earthquake records all over the world suggest that reinforced soil slopes provide better resistance to the seismic forces and possess higher yield accelerations compared to unreinforced slopes. While the design and practice of geosynthetic reinforced soil slopes has reached a level where the basics are well established and the procedures are standardized, the seismic designs still lack complete understanding of concepts and principles that alter the performance of the slope during seismic episodes. This thesis presents results from shaking table tests on geosynthetic reinforced soil slopes subjected to cyclic base shaking to understand the influence of various parameters that govern the performance of these slopes during seismic events. A uniaxial shaking table was used in the study and reduced scale model slopes were built in a laminar box and were subjected to sinusoidal base shaking, varying the frequency and acceleration of base shaking in different tests. Various series of shaking table tests were carried out to study the effects of shaking acceleration, frequency of shaking, fines content in soil, type and quantity of reinforcement and slope inclination on the response of model slopes in terms of acceleration amplifications and horizontal displacements. Acceleration of shaking was varied between 0.1g - 0.3g and frequency was varied between 1Hz - 16Hz in different tests. The frequency of testing was much below the natural frequency of the slopes. Two soils, a clayey sand with 44% fines content and a poorly graded sand with no fines were used to study the effect of fines content on the slope response. A geotextile and a biaxial geogrid were used to study the effect of type of reinforcement and reinforcement was placed in single, two and three layers in different tests to study the effect of quantity of reinforcement. Slope inclination was varied as 45, 60 and 75. While understanding the influence of reinforcement parameters, soil gradation and slope angle, tests were carried out at different accelerations and frequencies, to investigate the influence of these parameters under different ground shaking conditions. Results from shaking table tests revealed that among all the parameters studied, soil gradation has greater influence on the seismic response of the unreinforced as well as reinforced soil slopes. Slopes made of sand without fines showed highest acceleration amplifications and displacements. While the slopes made of clayey sand showed higher displacements at higher frequency levels, exhibiting progressive failure, slopes built with cohesionless sand showed higher seismic response at low-frequency high-amplitude motions, exhibiting sudden flowslide type of failure. Inclusion of reinforcement did not have significant influence on the acceleration amplifications, but the displacements were drastically reduced by reinforcing the slopes, the beneficial effect more pronounced in case of slopes made of sand without fines. Among the two types of geosynthetics used in the study, both were equally effective in reducing the deformations, the different being not significant. Results showed that reinforcement saturation occurred in the models at 2 layers, beyond which further increase in reinforcement did not influence the response of the slope. The catastrophic flowslide occurred in unreinforced slope at low frequency shaking in case of sand without fines is completely arrested by reinforcing the slope with three layers of geotextile and the deformations were reduced by about 92% for that case, indicating the importance of soil reinforcement in mitigating seismic hazards. Increase in slope angle resulted in increase in deformations but the acceleration amplifications remained unaffected. Steeper slopes benefitted more by the inclusion of reinforcing layers. Displacements computed using Newmark’s sliding block method agreed reasonably well with the experimental measurements.

Tese de doutoramento em Estruturas - Engenharia Civil
Ancient masonry buildings were built for many centuries taking into account only vertical static loads, without reference to any particular seismic code. The different types of masonry present common features that are directly related to the high seismic vulnerability of this type of buildings, such as the high specific mass, the low tensile strength, low to moderate shear strength and low ductility (brittle behaviour). Besides the material properties, the seismic behaviour of ancient masonry buildings depends on other factors, such as geometry of the structure, connection between orthogonal walls, connections between structural walls and floors, connections between walls and roof, foundation strength, stiffness of the floors and strength of the non-structural elements. The Portuguese housing stock consists of several building typologies in which some of them present construction features associated with poor seismic performance. Thus, it is necessary to intervene in these types of buildings with the purpose of reducing their seismic vulnerability. The “gaioleiro” buildings correspond to a Portuguese building typology, built between the 19th century and the beginning of the 20th century, with the highest seismic vulnerability of the housing stock of Portugal. These buildings are, generally, four to six stories high, with stone masonry walls, timber floors and roof, and still remain in use nowadays. Motivated by the above reasons, this thesis aims at evaluating the seismic vulnerability of the “gaioleiro” buildings and proposing a strengthening technique to reduce it. The study involved shaking table tests and several types of numerical analysis. The tests were carried out on the shaking table of the National Laboratory for Civil Engineering (Lisbon). The experimental program involved the definition of a prototype representative of the average features of the “gaioleiro” buildings, which was later used for the construction of the mock-ups. Due the size and payload capacity of the shaking table, two mock-ups were built using a reduce scale: non-strengthened and strengthened mock-ups. The seismic load is composed by two orthogonal and uncorrelated accelerograms which induce, simultaneously, in-plane and out-of-plane behaviour of the mock-ups. In the strengthened mock-up steel elements were used to improve the connection between walls and floors, and ties in the upper storeys. Through the experimental program the dynamic properties of the mock-ups, the vulnerability curves, the crack patterns and the collapse mechanisms were obtained, and the efficiency of the strengthening technique adopted to reduce the seismic vulnerability of the “gaioleiro” buildings was evaluated. The experimental results were used for validating the numerical model of the nonstrengthened mock-up, which was later used in non-linear dynamic with time integration and pushover analyses. Furthermore, a sensitivity analysis varying the proprieties of the numerical model was carried out. The seismic vulnerability curves obtained from the dynamic identification tests show that the strengthened mock-up presents a reduction of the damage indicator of about 46% with respect to the non-strengthened mock-up. The results of the seismic tests show that the damage of the non-strengthened mock-up concentrates at the facades and the strengthening technique adopted improved significantly the seismic behaviour of the mock-up, leading to the conclusion that the strengthening technique was efficient in the reduction of its seismic vulnerability. Finally, the sensitivity analysis shows that the Young’s modulus of the masonry walls, the Young’s modulus of the timber floors and the compressive non-linear properties are the parameters that most influence the seismic behaviour of the numerical model. The stiffness of the floors influences significantly the capacity strength and the collapse mechanism of the structure. Thus, the strengthening of the floors is also an effective solution for reducing of the seismic vulnerability of the “gaioleiro” buildings, namely by improving the out-of-plane response of the walls.
Os edifícios antigos de alvenaria foram construídos durante muitos séculos tendo em consideração apenas ações estáticas e verticais, sem referência a qualquer regulamento sísmico. Os diferentes tipos de alvenaria apresentam caraterísticas comuns que estão relacionadas diretamente com a grande vulnerabilidade sísmica deste tipo de edifícios, tais como a elevada massa específica, a baixa resistência à tração, a baixa a moderada resistência ao corte e a baixa ductilidade (comportamento frágil). Além das propriedades dos materiais, o comportamento sísmico dos edifícios antigos de alvenaria depende de outros fatores, tais como: geometria da estrutura, ligação entre paredes ortogonais, ligação entre paredes e pavimentos, ligação entre paredes e cobertura, resistência da fundação, rigidez dos pavimentos e resistência dos elementos não estruturais. O parque habitacional de Portugal é constituído por várias tipologias de edifícios, entre as quais algumas apresentam características de construção associadas a um mau desempenho sísmico. Assim, torna-se necessário intervir nestas tipologias de edifícios, tendo por objetivo reduzir a sua vulnerabilidade sísmica. Os edifícios gaioleiros correspondem à tipologia de edifícios construídos no final do século XIX e inícios do século XX que apresenta a maior vulnerabilidade sísmica do edificado de Portugal. Estes edifícios têm, geralmente, quatro a seis pisos, paredes de alvenaria de pedra, pavimentos e cobertura em estrutura de madeira e encontram-se ainda em utilização nos dias de hoje. Tendo em consideração o anteriormente referido, a presente tese tem como principais objetivos a avaliação e redução da vulnerabilidade sísmica dos edifícios gaioleiros. O estudo envolveu ensaios em plataforma sísmica e diferentes tipos de análises numéricas. Os ensaios foram realizados na plataforma sísmica do Laboratório Nacional de Engenharia Civil (Lisboa). O programa experimental envolveu a definição de um protótipo representativo das características correntes dos edifícios gaioleiros, que posteriormente foi utilizado para a construção dos modelos experimentais. Devido às dimensões e limite de capacidade de carga da plataforma sísmica, foram ensaiados dois modelos experimentais à escala reduzida: modelo não reforçado e reforçado. A ação sísmica aplicada é composta por dois acelerogramas ortogonais e não correlacionáveis que induzem, simultaneamente, comportamento no plano e para fora do plano dos modelos experimentais. No modelo reforçado utilizaram-se elementos metálicos para melhorar a ligação entre as paredes e os pavimentos, e tirantes nos pisos superiores. O programa experimental permitiu obter as propriedades dinâmicas dos modelos, as curvas de vulnerabilidade, os padrões de fendilhação e os mecanismos de colapso, bem como concluir sobre a eficiência da técnica de reforço adotada na redução da vulnerabilidade dos edifícios gaioleiros. Os resultados experimentais foram utilizados na calibração de modelos numéricos. Estes foram, posteriormente, utilizados em análise não lineares dinâmicos e estáticas. Além disso, foi realizada uma análise de sensibilidade variando as propriedades do modelo numérico. Como principais conclusões sobre os ensaios em plataforma sísmica, as curvas de vulnerabilidade sísmica obtidas através dos ensaios de identificação dinâmica demostraram que o modelo reforçado apresenta uma redução do indicador de dano de cerca de 46% relativamente ao modelo não reforçado. Os resultados dos ensaios sísmicos demostraram que o dano do modelo não reforçado concentra-se nas fachadas e que a técnica de reforço adotada melhorou significativamente o comportamento sísmico do modelo, concluindo-se que a técnica de reforço foi eficiente na redução da sua vulnerabilidade sísmica. Por último, os resultados da análise de sensibilidade demostraram que o módulo de elasticidade das paredes, o módulo de elasticidade dos pavimentos e as propriedades não-lineares em compressão são os parâmetros com maior influência no comportamento sísmico do modelo numérico. A rigidez dos pavimentos tem influência significativa na capacidade resistente e no mecanismo de colapso da estrutura. Assim, o reforço dos pavimentos é também uma solução efetiva para a redução da vulnerabilidade sísmica dos edifícios gaioleiros, melhorando sobretudo a resposta para fora do plano das paredes.
Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/32190/2006

Use of soil retaining walls for roads, embankments and bridges is increasing with time and reinforced soil retaining walls are found to be very efficient even under critical conditions compared to unreinforced walls. They offer competitive solutions to earth retaining problems associated with less space and more loads posed by tremendous growth in infrastructure, in addition to the advantages in ease and cost of construction compared to conventional retaining wall systems. The study of seismic performance of reinforced soil retaining walls is receiving much attention in the light of lessons learned from past failures of conventional retaining walls. Laboratory model studies on these walls under controlled seismic loading conditions help to understand better how these walls actually behave during earthquakes. The objective of the present study is to investigate the seismic response of geosynthetic reinforced soil wall models through shaking table tests. To achieve this, wrap faced and rigid faced reinforced soil retaining walls of size 750 × 500 mm in plan and 600 mm height are built in rigid and flexible containers and tested under controlled dynamic conditions using a uni-axial shaking table. The effects of frequency and acceleration of the base motion, surcharge pressure on the crest, number of reinforcing layers, container boundary, wall structure and reinforcement layout on the seismic performance of the retaining walls are studied through systematic series of shaking table tests. Results are analyzed to understand the effect of each of the considered parameters on the face displacements, acceleration amplifications and soil pressures on facing at different elevations of the walls. A numerical model is developed to simulate the shaking table tests on wrap faced reinforced soil walls using a computer program FLAC (Fast Lagrangian Analysis of Continua). The experimental data are used to validate the numerical model and parametric studies are carried out on 6 m height full-scale wall using this model. Thus, the study deals with the shaking table tests, dynamic response of reinforced walls and their numerical simulation. The thesis presents detailed description of various features and various parts of the shaking table facility along with the instrumentation and model containers. Methodology adopted for the construction of reinforced soil model walls and testing procedures are briefly described. Scaling and stability issues related to the model wall size and reinforcement strength are also discussed. From the study, it is observed that the displacements are decreasing with the increase in relative density of backfill, increase in surcharge pressure and increase in number of reinforcing layers; In general, accelerations are amplified to the most at the top of the wall; Behaviour of model walls is sensitive to model container boundary. The frequency content is very important parameter affecting the model response. Further, it is noticed that the face displacements are significantly affected by all of the above parameters, while the accelerations are less sensitive to reinforcement parameters. Even very low strength geonet and geotextile are able to reduce the displacements by 75% compared to unreinforced wall. The strain levels in the reinforcing elements are observed to be very low, in the order of ±150 micro strains. A random dynamic event is also used in one of the model tests and the resulted accelerations and displacements are presented. Numerical parametric studies provided important insight into the behaviour of wrap faced walls under various seismic loading conditions and variation in physical parameters.

Use of soil retaining walls for roads, embankments and bridges is increasing with time and reinforced soil retaining walls are found to be very efficient even under critical conditions compared to unreinforced walls. They offer competitive solutions to earth retaining problems associated with less space and more loads posed by tremendous growth in infrastructure, in addition to the advantages in ease and cost of construction compared to conventional retaining wall systems. The study of seismic performance of reinforced soil retaining walls is receiving much attention in the light of lessons learned from past failures of conventional retaining walls. Laboratory model studies on these walls under controlled seismic loading conditions help to understand better how these walls actually behave during earthquakes. The objective of the present study is to investigate the seismic response of geosynthetic reinforced soil wall models through shaking table tests. To achieve this, wrap faced and rigid faced reinforced soil retaining walls of size 750 × 500 mm in plan and 600 mm height are built in rigid and flexible containers and tested under controlled dynamic conditions using a uni-axial shaking table. The effects of frequency and acceleration of the base motion, surcharge pressure on the crest, number of reinforcing layers, container boundary, wall structure and reinforcement layout on the seismic performance of the retaining walls are studied through systematic series of shaking table tests. Results are analyzed to understand the effect of each of the considered parameters on the face displacements, acceleration amplifications and soil pressures on facing at different elevations of the walls. A numerical model is developed to simulate the shaking table tests on wrap faced reinforced soil walls using a computer program FLAC (Fast Lagrangian Analysis of Continua). The experimental data are used to validate the numerical model and parametric studies are carried out on 6 m height full-scale wall using this model. Thus, the study deals with the shaking table tests, dynamic response of reinforced walls and their numerical simulation. The thesis presents detailed description of various features and various parts of the shaking table facility along with the instrumentation and model containers. Methodology adopted for the construction of reinforced soil model walls and testing procedures are briefly described. Scaling and stability issues related to the model wall size and reinforcement strength are also discussed. From the study, it is observed that the displacements are decreasing with the increase in relative density of backfill, increase in surcharge pressure and increase in number of reinforcing layers; In general, accelerations are amplified to the most at the top of the wall; Behaviour of model walls is sensitive to model container boundary. The frequency content is very important parameter affecting the model response. Further, it is noticed that the face displacements are significantly affected by all of the above parameters, while the accelerations are less sensitive to reinforcement parameters. Even very low strength geonet and geotextile are able to reduce the displacements by 75% compared to unreinforced wall. The strain levels in the reinforcing elements are observed to be very low, in the order of ±150 micro strains. A random dynamic event is also used in one of the model tests and the resulted accelerations and displacements are presented. Numerical parametric studies provided important insight into the behaviour of wrap faced walls under various seismic loading conditions and variation in physical parameters.

碩士
國立臺灣大學
土木工程學研究所
104
Earthquakes can affect the stability of slope and trigger landslides. In this study, both theoretical and experimental analysis are used to comprehend the flows behavior of the slope under seismic conditions. Though theory, we develop a depth-integrated equations with the assumption of conservation of kinetic energy, mass and momentum. To solve the granular flow equations, we derive the numerical models from the local equations and the depth-integrated equations. A series of experiments is conducted on a shaking table, which can simulate the seismic vibration. We use the images from experiments and the particle tracking velocimetry (PTV) method to acquire the velocity fields, the depth of flow layer and the time-evolving variables. Using these approach, we develop a model that can be used to estimate the behavior of slope under seismic conditions. Through the theory and experiment results, we can know more about the mechanism of landslides once the shaking conditions are given.

Vertical inclusions of expanded polystyrene (EPS) placed behind rigid retaining walls were investigated as geofoam seismic buffers to reduce earthquake-induced loads. A numerical model was developed using the program FLAC and the model validated against 1-g shaking table test results of EPS geofoam seismic buffer models. Two constitutive models for the component materials were examined: elastic-perfectly plastic with Mohr-Coulomb (M-C) failure criterion and non-linear hysteresis damping model with equivalent linear method (ELM) approach. It was judged that the M-C model was sufficiently accurate for practical purposes. The mechanical property of interest to attenuate dynamic loads using a seismic buffer was the buffer stiffness defined as K = E/t (E = buffer elastic modulus, t = buffer thickness). For the range of parameters investigated in this study, K ≤ 50 MN/m3 was observed to be the practical range for the optimal design of these systems. Parametric numerical analyses were performed to generate design charts that can be used for the preliminary design of these systems. A new high capacity shaking table facility was constructed at RMC that can be used to study the seismic performance of earth structures. Reduced-scale models of geosynthetic reinforced soil (GRS) walls were built on this shaking table and then subjected to simulated earthquake loading conditions. In some shaking table tests, combined use of EPS geofoam and horizontal geosynthetic reinforcement layers was investigated. Numerical models were developed using program FLAC together with ELM and M-C constitutive models. Physical and numerical results were compared against predicted values using analysis methods found in the journal literature and in current North American design guidelines. The comparison shows that current Mononobe-Okabe (M-O) based analysis methods could not consistently satisfactorily predict measured reinforcement connection load distributions at all elevations under both static and dynamic loading conditions. The results from GRS model wall tests with combined EPS geofoam and geosynthetic reinforcement layers show that the inclusion of a EPS geofoam layer behind the GRS wall face can reduce earth loads acting on the wall facing to values well below those recorded for conventional GRS wall model configurations.
Thesis (Ph.D, Civil Engineering) -- Queen's University, 2011-04-28 16:56:57.084

碩士
國立高雄第一科技大學
營建工程所
90
Presently, there are thousands of base isolated structures constructed worldwide. The number of the isolated structures has been increasing rapidly in the last few years primarily due to the maturity of the isolation technology itself and also human awareness of earthquake risk. Some of these constructed cases were even subjected to real-live earthquakes and proved the effectiveness of the technology. However, very few of them were ever subjected to near-fault ground waves that possess very different characteristics and response spectra from those of far-field waves. The response of a sliding isolated structure subjected to a set of near-fault and far-field earthquakes are simulated and compared. It is shown that the isolator displacement can be considerably enlarged in a near-fault earthquake due to the long-period velocity pulse possessed in the near-fault earthquake. Furthermore, in order to improve the performance of near-fault seismic isolation, three types of sliding isolators with the sliding surfaces of different geometry are studied and their advantages and disadvantages are discussed. The effect of using supplemental viscous damping together with these isolators is also investigated. The study shows that for a near-fault earthquake, sliding isolation with supplemental damping is beneficial in reducing both maximum base drift and structural acceleration, although the damping may have a negative effect in the isolation for far-field earthquakes. In order to study the effect of a near-fault ground motion on a sliding isolated structure, in this paper, a shaking-table test was conducted. Both near-fault and far-field ground accelerations were imposed on a full-scale model isolated by a friction pendulum system, so the structural response can be compared. Also, a set of artificially simulated pulse waves with variable pulse periods was also imposed on the isolated structure, in order to study the effect of pulse periods. Furthermore, in order to reduce the isolator displacements, a supplement viscous damper was added to the isolation system. The study shows that for a near-fault earthquake, sliding isolation with supplemental damping is beneficial in reducing both maximum base drift, even though the damping may increase the structural acceleration in a far-field earthquake.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1988.
Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 273-281).

Concrete highway bridges are important elements of our country's transportation infrastructure; however, only few studies that address their seismic behavior using data collected from instrumented structures are available in the literature. This gap of knowledge impairs full exploitation of structural health monitoring techniques for seismic damage assessment, and improvement of design recommendations. This research is particularly concerned with curved concrete box-girder highway bridges, whose seismic behavior is still widely unexplored due to lack of field monitoring data. By taking advantage of vibration records collected during six earthquake events at the West Street on Ramp, a curved concrete box-girder highway bridge located in Anaheim, California, this research aims at advancing knowledge about the seismic behavior of these bridges. Modal identification of the bridge during the earthquakes is conducted, and sensitivity analysis is carried out to reconcile the observed dynamic characteristics of the bridge with the behavior of its structural elements. Data collected from an instrumented large-scale bridge specimen during shaking table tests are also analyzed to gain insight about the response of the bridge bents during the earthquakes, and propose a strategy to model their seismic behavior. Information from modal identification and the shaking table tests analyses are instrumental in developing a nonlinear finite element model of the bridge, calibrated employing a multistage finite element model updating strategy. In order to evaluate the significance of using the structural-health-monitoring-informed structural model obtained, seismic performance assessment through incremental dynamic analysis is conducted, and results are compared with the predicted performance estimated with a conventional finite element model of the bridge. By advancing knowledge about the seismic behavior of concrete highway bridges, this research may ultimately contribute to improve structural health monitoring practices and design guidelines for this type of structures.

Communities on Vancouver Island, British Columbia face significant exposure to damaging earthquakes. This seismic risk arises not only from the Island’s proximity to crustal, sub-crustal and subduction earthquake sources in the Cascadia Subduction Zone and from their associated aftershock sequences, but also from environmental (natural and human-made) and social vulnerabilities in Vancouver Island communities and their current capacities to respond and recover from a large seismic event. Seeking to 1) assist community officials and the general public to better understand the scope of the earthquake risk on Vancouver Island; 2) raise awareness of the gaps in Vancouver Island’s risk assessment; 3) encourage and facilitate comprehensive seismic risk discussions at all levels of governance; and 4) offer quantitative data on which to base sound funding and policy decisions, this dissertation offers three new studies, presented in paper format, toward the comprehensive management of seismic risk on Vancouver Island. The first paper, reviews the components of risk and, building on international risk management standards and best practices, develops a new, comprehensive Disaster Risk Management (DRM) Framework for practitioners. This DRM Framework is then used to review existing knowledge of Vancouver Island’s seismic risk. A number of information gaps are identified, and two in particular, mainshock and aftershock hazard assessment, are targeted for further analysis.
Graduate

Considering the seismic behaviour of cultural heritage buildings, an influential role is played by masonry vaults, often representing the most vulnerable part of the construction. Despite their long-lasting history and the damage observation following the Italian earthquakes of the recent past, research in this area is still limited. In this regard, the present thesis is devoted to the study of the seismic behaviour of masonry groin vaults, considered as one of the most diffused vault type in European seismic prone areas in cloisters, palaces and churches. Groin vaults are resulting from the intersection at a right angle of two semi-cylindrical shells on a square bay, and can be addressed as the simplest form of cross vaults, defined as a combination (compound) of curved shells whose thrust converges along the diagonals to isolated abutments. The goal of this work is met via an integration of laboratory tests and numerical analyses. The first part of the thesis reviews the historical developments of the cross vault, the structural methods adopted by the scientific community and the damage evidences after laboratory experiments and post-seismic observation. The subsequent part deals with shaking table tests on a scaled arch built with dry-joint 3D printed voussoirs. The experimental campaign had a twofold purpose. On the one hand it gave insight into the seismic behaviour of masonry arches and, on the other hand, thanks to the tracking motion system employed to record the tests, it provided valuable information to calibrate a three-dimensional numerical model. The physical model was studied using a commercially available FEM software, namely DIANA (from TNO Delft), assuming rigid-infinitely resistant blocks and Coulomb friction interfaces. The nonlinear analyses regarded both the static and dynamic behaviour, shading light on the influence of interface stiffness and damping. The numerical model was subsequently extended to the study of the three-dimensional behaviour of groin vaults. In particular, the analyses focused on the results available in literature following a recent experimental campaign on a 1:5 scaled vault. The model was able to properly catch the maximum strength and the failure mechanism recorded in the quasi-static tests. Analogies between the nonlinear behaviour of the vault and the free-standing rigid block undergoing incremental horizontal force are also discussed. The last part of the thesis is dedicated to a sensitivity analysis aimed at evaluating the influence of the main geometrical and mechanical parameters on the seismic capacity and failure mechanisms of groin vaults. A non-commercial code implemented in Matlab, based on the upper bound approach of standard limit analysis, was used. The results were finally processed through a multiple linear regression analysis in order to get simplified analytical equations for expedite seismic evaluation of existing groin vaults.

Οι κατασκευές εδαφικής αντιστήριξης εξακολουθούν να βρίσκονται σε ευρύτατη χρήση, με διαρκώς αυξανόμενο ενδιαφέρον λόγω των απαιτήσεων των σύγχρονων έργων υποδομής αλλά και των αναγκών δόμησης σε πυκνό αστικό περιβάλλον. Το ενδιαφέρον εστιάζεται σε κατασκευαστικές λύσεις και μεθόδους σχεδιασμού που συνδυάζουν ασφάλεια και οικονομία. Η ανάλυση των συγκεκριμένων κατασκευών αντιμετωπίζει πλήθος δυσεπίλυτων προβλημάτων στο αντικείμενο της αλληλεπίδρασης εδάφους-κατασκευής που συχνά καθορίζουν τη συμπεριφορά του έργου. Η κατανόηση αυτών των μηχανισμών επιτρέπει το σχεδιασμό με μικρότερα περιθώρια αβεβαιότητας που οδηγούν σε οικονομικότερες και ορθολογικότερες λύσεις. Στην κατεύθυνση αυτή συμβάλει η παρούσα Διατριβή, με την ανάπτυξη αναλυτικών εργαλείων και θεωρητικών ευρημάτων που βοηθούν στην κατανόηση των μηχανισμών της αλληλεπίδρασης και στην εκτίμηση της συμπεριφοράς των τοίχων αντιστήριξης υπό συνδυασμένη βαρυτική και σεισμική φόρτιση. Έμφαση δίνεται στην παραγωγή απλών κλειστών λύσεων και μεθοδολογιών για τον υπολογισμό των εδαφικών ωθήσεων και τη στατική ανάλυση του συστήματος τοίχου εδάφους. Συγκεκριμένα, παράγονται λύσεις άνω και κάτω ορίου για ενδόσιμους τοίχους, οι οποίες, παρότι προσεγγιστικές, πλεονεκτούν έναντι των κλασικών εξισώσεων Coulomb και Mononobe-Okabe τις οποίες μπορούν να αντικαταστήσουν. Σε ειδικές περιπτώσεις, όπως η περίπτωση τοίχων προβόλων με πεπλατυσμένο πέλμα, οι προτεινόμενες λύσεις οδηγούν σε ακριβή αποτελέσματα που βασίζονται σε ένα γενικευμένο πεδίο τάσεων Rankine. Επίσης παρουσιάζονται επεκτάσεις τους οι οποίες επιτρέπουν τον υπολογισμό μη-υδροστατικών κατανομών ωθήσεων γαιών λαμβάνοντας υπόψη την κυματική διάδοση της σεισμικής διέγερσης στο επίχωμα, σύμφωνα με μια ορθότερη παραλλαγή της ιδέας των Steedman & Zeng και τις διαφορετικές κινηματικές συνθήκες που προέρχονται από την απόκριση του τοίχου με περιστροφή περί την κορυφή ή τη βάση σύμφωνα με την τεχνική της Dubrova. Για την περίπτωση ανένδοτων τοίχων παρουσιάζεται μεθοδολογία για τη δραστική απλοποίηση των διαθέσιμων ελαστοδυναμικών, κυματικών λύσεων, όπως αυτή των Veletsos & Younan, η οποία καταλήγει σε κλειστές μαθηματικές εκφράσεις για τον υπολογισμό των ωθήσεων. Τέλος, παρουσιάζονται νέα ευρήματα στην κατεύθυνση της μαθηματικής αντιμετώπισης του δυσεπίλυτου προβλήματος της οριακής ισορροπίας ριπιδίου τάσεων σε εδαφικό μέσο στο οποίο ενεργούν βαρυτικές και αδρανειακές δυνάμεις πεδίου. Η παρούσα εργασία συμβάλλει στην περαιτέρω διερεύνηση του προβλήματος το οποίο θεμελίωσαν θεωρητικά οι Levy, Boussinesq, von Karman και Caquot, μέσω της δραστικής (αλλά ακριβούς) απλοποίησης του σε μία μη-γραμμική συνήθη διαφορική εξίσωση, η οποία επιτρέπει την επίλυση με απλές αριθμητικές και ημιαναλυτικές τεχνικές. Πέρα από τα ακριβή αριθμητικά αποτελέσματα, η προτεινόμενη ανάλυση προσφέρει μια βαθύτερη εποπτεία στο πρόβλημα και ανοίγει το δρόμο για περαιτέρω διερεύνηση ή και επέκταση της μεθόδου πέρα από τα όρια της κλασικής οριακής ανάλυσης. Η αξιοπιστία των προτεινόμενων λύσεων ελέγχεται μέσω συγκρίσεων με καθιερωμένες λύσεις και πειραματικά δεδομένα από τη βιβλιογραφία, αλλά και πρόσφατα πειραματικά αποτελέσματα που παρήχθησαν από τον συγγραφέα και ερευνητές στη σεισμική τράπεζα του Πανεπιστημίου του Bristol του Ηνωμένου Βασιλείου.
Earth retaining structures are still in widespread use, with growing interest due to the demands of modern infrastructure and building needs in a dense urban environment. Building solutions and design methodologies that combine safety and economy are the objectives of modern research. Significant difficulties in the analysis of retaining structures arise from the soil-structure interaction nature of the problem that often prescribes its behavior. Understanding these mechanisms allows design under smaller uncertainties, leading to economical and rational solutions. The contribution of the present thesis consists of the development of analytical tools and theoretical findings, helpful in understanding the mechanisms of interaction and the behavior of walls under combined gravity and seismic loading. Emphasis is given to the derivation of simple closed-form solutions and methodologies for the calculation of earth pressures and the static analysis of wall-soil system. Specifically, approximate Lower and Upper Bound solutions are produced for the case of yielding walls, which are advantageous compared to the classical equations Coulomb and Mononobe-Okabe. In special cases, such as the L-shaped cantilever walls, these solutions lead to exact results, pertaining to a generalized Rankine stress field. Extensions of the above solutions are presented allowing the calculation of non-hydrostatic earth pressure distributions, due to the wave propagation of the seismic excitation in the backfill, according to a better variant of the Steedman & Zeng approach and different kinematic conditions of the wall rotating around the top or bottom, according to the technique of Dubrova. For the case of non-yielding walls, a new methodology for the drastic simplification of available wave solutions, such as the Veletsos & Younan, is presented which leads to closed-form expressions for the dynamic pressure calculation. Finally, new theoretical findings are presented for the mathematical treatment of the intractable problem of plastic limit equilibrium in soil medium subjected to gravitational and inertial forces field. This work contributes to the further investigation of the problem which is founded theoretically by Levy, Boussinesq, von Karman and Caquot, through the significant (but accurate) simplification to a single, non-linear ordinary differential equation, easier to handle by simple numerical and semi-analytical techniques. Apart from the exact numerical results, the proposed analysis provides a deeper physical insight, leading the way to further investigation or extension of the method beyond the classical limit analysis assumptions. The reliability of the proposed solutions is checked through comparisons with established solutions and experimental data from the literature and recent experimental results obtained by the author and researchers in the shake table laboratory of the University of Bristol, UK.