Дисертації з теми "RC FRAMED BUILDING"

Mitigation of progressive collapse after an initial failure has become a primary concern of engineers in recent years. Often alternative load paths are sought to redistribute load from the damaged area. It has been recognised for some time that the omission of compressive membrane action (CMA), also termed ‘arching action’, can lead to a significant underestimation of load capacity. An investigation has been conducted to ascertain whether the additional load carrying capacity from CMA can provide an inherent alternative load path to aid robustness. A series of scaled specimens with industry standard detailing have been designed for an experimental investigation. Reinforced concrete elements were modelled in the double span scenario once an intermediate column has been removed. The test rig used allows the central support to be removed followed by the application of a point load applied at midspan; the system is determinate including measurement of the horizontal reaction. Subsequent to the flexural response two modes of membrane action are induced, initially compressive until tensile membrane extends load capacity at high values of deflection. The response during the latter tensile phase is outside the scope of this research. Comparisons of experimental data with analytical methods inclusive of CMA have demonstrated that whilst conservative the method by Merola (2009) provides a reasonable prediction. This method has been utilised in a study of a series of flat slab structures with a range of column spacings. The inherent restraint stiffness provided by the surrounding slab and frame has been quantified using FEA and has allowed for the extent to which CMA can improve the robustness of a structure to be determined.

Thesis (MScIng)--Stellenbosch University, 2005.
Some digitised pages may appear illegible due to the condition of the original hard copy.
ENGLISH ABSTRACT: Reinforced concrete (RC) frames with unreinforced masonry infill form the structural system of many buildings and this is also true for South Africa. It is common practice to consider the masonry infill as a non-structural component and therefore it does not contribute to the performance of the Re frame buildings under lateral loading such as earthquake loading. This is done by leaving a sufficient gap between the Re frame and the infill. This ensures that there is no contact between the frame and the infill during an earthquake event. However, it has been suggested that masonry infill can play a significant role in the performance of a Re frame building under lateral loading. The first part of the study focuses on the South African situation. The relevance of shear walls in these Re frame buildings as well as the size of the gap (between frame and infill) left in practice, are investigated. This is done by finite element analysis. The second part of the study focuses on the effects that the infill can have on the global performance of the structure when there is full contact between the Re frames and infill. The effect of openings in the infill to the response of the frame is also investigated. Finite element models of single span Re frames with infill is built and analyzed in order to investigate possible damage to the infill, frame infill interaction and to obtain the non linear stiffness of the frame with infill as a whole. This obtained non linear stiffness can be modelled in Diana as a non linear spring that will be used in the development of a simplified analysis method. The simplified method developed consists of a frame and two such non linear springs, placed diagonally, and which have the same force versus displacement behaviour as the original frame with infill. These single span frames can be added together to model a whole frame. In a first step to generalise the simplified method, various geometries of infills are considered, varying span and height, as well as opening percentage, representing windows and doors of varying total area and positioning. However, in this study a single masonry type, namely solid baked clay bricks set in a general mortar, is considered. To generalise the approach further, other masonry types can be considered in the same way. The use of these springs in a simplified model saves computational time and this means that larger structures can be modelled in Diana to investigate response of'Rf' frame buildings with infill. The work reported in this thesis considers only in-plane action. Out-of-plane-action of the masonry infill has been reported in the literature to be considerable, under the condition that it is sufficiently tied to the frame to prevent mere toppling over, causing life risking hazards in earthquake events. This matter should be studied in continuation of the current research to generalise the simple approach to three dimensions.
AFRIKAANSE OPSOMMING: Gewapende betonrame (GBR-e) met ongewapende messelwerk invulpanele (invul) vorm die strukturele ruggraat van vele geboue en dit geld ook vir geboue in Suid-Afrika. Dit is algemene praktyk om die invulpaneel in sulke geboue as 'n nie-strukturele komponent te beskou. Daarvolgens dra dit nie by tot die gedrag van 'n GBR gebou onderhewig aan 'n aarbewing nie. Dit word bereik deur 'n groot genoeg gaping tussen die betonraam en die invul te los. Die gevolg is dat daar geen kontak tussen die betonraam en die invul plaasvind indien daar 'n aardbewing sou voorkom nie. Dit is egter voorgestel dat invul 'n noemenswaardige rol kan speel in die gedrag van 'n GBR gebou onderwerp aan 'n horisontale las. Die eerste deel van die studie fokus op die Suid-Afrikaanse situasie. Die relavansie van skuifmure in GBR geboue asook die grootte van die gaping (tussen die raam en invul) wat in die praktyk gebruik word, word ondersoek. Dit word gedoen met behulp van eindige element analises. Die tweede deel van die studie fokus op die effek wat invul kan hê op die globale gedrag van 'n struktuur wanneer daar volle kontak tussen die GBR en die invul is. Die effek wat die teenwoordigheid van openinge in die invul kan hê op die gedrag van 'n GBR is ook ondersoek. Eindige element modelle van enkelspan GBR met invul is gemodelleer en geanaliseer om die moontlike skade aan die invul, die interaksie tussen die GBR en die invul asook die nie-lineêre styfheid van die raam en invul as 'n geheel, te ondersoek. Hierdie nielineêre styfheid kan in Diana as 'n nie-lineêre veer gemodelleer word en word gebruik in die ontwikkeling van 'n vereenvoudigde metode. Hierdie vereenvoudigde metode wat ontwikkel is, bestaan uit 'n raam en twee sulke nielineêre vere (diagonaal geplaas). Die raam met vere het dieselfde krag teenoor verplasingsgedrag as die van die oorspronklike raam met invul wat dit voorstel. Hierdie rame kan saamgevoeg word om 'n raam uit 'n gebou as 'n geheel te modelleer. Verskeie invul geometrieë word gebruik in die analises in 'n eerste stap om die vereenvoudigde metode te veralgemeen. Die span en hoogte asook opening persentasie van die invul word gevariëer om vensters en deure van veskeie grootte en posisie voor te stel. In die studie, 'n enkel messelwerk tipe, naamlik solied klei bakstene geset in algemene mortar, word gebruik. Ander messelwerk tipes kan gebruik word om die metode verder te veralgemeen. Die gebruik van die vere in die vereenvoudigde metode spaar berekenings tyd en dit beteken dat groter strukture in Diana gemodelleer kan word om die gedrag van GBR geboue met invul te ondersoek. Die werk gedoen in die tesis neem slegs in-vlak aksie in ag. Literatuurstudie dui daarop dat goeie uit-vlak-aksie van messelwerk invul bestaan, mits dit goed geanker is aan die raam om te verseker dat dit nie kan omval en 'n gevaar vir lewens in 'n aardbewing inhou nie. Dit behoort verder bestudeer te vord in die vervolging van die huidige ondersoek om die vereenvoudige metode na drie dimensies te veralgemeen.

The seismic assessment of existing structures is considered the fundamental step to (i) estimate the seismic capacity of the initial structure (ii) predict the collapse mechanism and the structural weakness, (iii) select the most appropriate seismic retrofitting technique and determine the improved capacity of the upgraded building. Nonlinear dynamic analysis is widely recognised as the most accurate tool to predict the seismic behaviour of structures. However, this type of analysis has a high computational cost, and it is not an approach that can be extensively applied for professional purposes yet. To provide a tool that predicts the seismic behaviour of structures with a good accuracy but with a lower computational burden, nonlinear static methods of analysis were developed. The Capacity Spectrum Method (CSM) proposed by Freeman and the N2 Method proposed by Fajfar were pioneering methods and were recommended by the American and the European seismic code, respectively. Although these methods of analysis are generally reliable for the assessment of plane frames, however they neglect the contribution of higher modes of vibration to the seismic response and do not consider the progressive reduction of the structural stiffness due to the nonlinear behaviour of the structure. To improve the level of accuracy, advanced nonlinear static methods of analysis were developed, such as the Multimodal Pushover Analysis by Chopra et al., the Displacement Adaptive Puhover by Pinho et al. and the Advanced N1 method by Ghersi et al. Despite the innovative character of these methods, however they still present shortcomings. Another important aspect regarding existing structures is the presence of infill panels. Although infill panels provide the structure with a much larger stiffness and their location and mechanical properties influence the dissipative mechanism of the structure, however they are considered nonstructural elements, and their contribution to the seismic response is neglected. This thesis aims at the development of a nonlinear static method of analysis that can accurately estimate the seismic response of RC frames, with and without infill panels, keeping acceptable computation costs. To this end, the thesis proposes a multimodal adaptive procedure named overDamped Displacement Adaptive Procedure (D-DAP). This method has been developed from the combination of the approaches proposed by Pinho et al. and by Ghersi et al. The multimodal adaptive procedure to update the load vector is taken from the first, while the method for the association of the peak ground acceleration to the displacement demand without the SDOF approximation is drawn from the second. In addition, the D-DAP is equipped with an equivalent damping to consider the increase of the energy dissipation due the cumulated damage in the structure. To this end, the value of the equivalent damping is updated at each step according to a new damping law that has been properly calibrated in this work for RC frames with and without infill panels. The accuracy of the D-DAP in the seismic assessment of rc frames was compared to that of the DAP by Pinho, the MPA by Chopra, the N2 method (EC8) and the CSM (FEMA 440). To this end, a set of 54 RC frames was designed to be representative of existing buildings with various levels of seismic deficiencies, and their seismic responses were predicted by those aforementioned methods of analysis. These comparisons showed that the D-DAP applied with the proposed damping law demonstrated an accuracy in predicting the seismic response of RC frames, with and without infills, generally higher than the other nonlinear static methods of analysis. In particular, the D-DAP provided a significant improvement with respect to the other existing methods in the prediction of the response of RC frames with infill panels.

The construction of reinforced concrete buildings with unreinforced infill is common practice even in seismically active country such as Bhutan, which is located in high seismic region of Eastern Himalaya. All buildings constructed prior 1998 were constructed without seismic provisions while those constructed after this period adopted seismic codes of neighbouring country, India. However, the codes have limited information on the design of infilled structures besides having differences in architectural requirements which may compound the structural problems. Although the influence of infill on the reinforced concrete framed structures is known, the present seismic codes do not consider it due to the lack of sufficient information. Time history analyses were performed to study the influence of infill on the performance of concrete framed structures. Important parameters were considered and the results presented in a manner that can be used by practitioners. The results show that the influence of infill on the structural performance is significant. The structural responses such as fundamental period, roof displacement, inter-storey drift ratio, stresses in infill wall and structural member forces of beams and column generally reduce, with incorporation of infill wall. The structures designed and constructed with or without seismic provision perform in a similar manner if the infills of high strength are used.

The construction of reinforced concrete buildings with unreinforced infill is common practice even in seismically active country such as Bhutan, which is located in high seismic region of Eastern Himalaya. All buildings constructed prior 1998 were constructed without seismic provisions while those constructed after this period adopted seismic codes of neighbouring country, India. However, the codes have limited information on the design of infilled structures besides having differences in architectural requirements which may compound the structural problems. Although the influence of infill on the reinforced concrete framed structures is known, the present seismic codes do not consider it due to the lack of sufficient information. Time history analyses were performed to study the influence of infill on the performance of concrete framed structures. Important parameters were considered and the results presented in a manner that can be used by practitioners. The results show that the influence of infill on the structural performance is significant. The structural responses such as fundamental period, roof displacement, inter-storey drift ratio, stresses in infill wall and structural member forces of beams and column generally reduce, with incorporation of infill wall. The structures designed and constructed with or without seismic provision perform in a similar manner if the infills of high strength are used.

This thesis presents a high fidelity numerical model developed to investigate the seismic performance and structural robustness of an original and retrofitted 10-storey reinforced concrete (RC) framed building. The analysed structure represents a typical existing building in Catania, Italy, that was designed to resist only gravity and wind loading according to the design regulation allowed until the 1981 in that area. The proposed numerical description adopts beam-column elements for beams and columns and special purpose shell elements for modelling RC floor slabs, both allowing for geometric and material nonlinearity. In order to model masonry infills, a novel macro-element is implemented within a FE framework based on an already published discrete formulation. 3D nonlinear dynamic simulations are performed considering sets of natural accelerograms acting simultaneously along all the three space directions and compatible with the design spectrum for the Near Collapse Limit State. To improve computational efficiency, which is critical when investigating the nonlinear dynamic behaviour of large structures, the partitioning approach previously developed at Imperial College is adopted, enabling effective parallelisation on HPC systems. The numerical results obtained from the 3D nonlinear dynamic simulations are presented and discussed, focusing on the variation in time of the deformed shape, inter-storey drifts, plastic deformations and internal force distribution, considering or neglecting the infill panel contribution. The original structure showed a very poor seismic performance, even though the infill panel contribution leads to significant variation in the response it is not sufficient to preserve the structure from the collapse. A never adopted strengthening solution that utilises the synergetic contribution of concentric steel bracing and eccentric steel bracings with dissipative shear links is illustrated and employed to retrofit the original structure. A detailed model of the retrofitting components is implemented within the detailed model for the original building. The results of numerical simulations for the retrofitted structure confirm that the proposed solution significantly enhances the response under earthquake loading, allowing the structure to resist the design earthquake with only limited damage in the original RC beams and columns, highlighting the feasibility of retrofitting for this typical multi-storey RC building structure.

Prior to this study, to our best knowledge, no cast-in-place, older-type RC building has ever been subjected to near-field strong ground motions from three major earthquakes. This happened in an indirect way in Turkey over a time span of eleven years. Three identical buildings belonging to Ministry of Public Works and Resettlement (MPWR) that had been built to the same design templates, experienced March 13th 1992 Erzincan earthquake in Erzincan, November 12th 1999 Dü
zce earthquake in Bolu and May 1st 2003 Bingö
l earthquake in Bingö
l, respectively. The ground motion sensor stations were fortuitously nearby in an adjacent single-story building in Bolu and Bingö
l. The station in Erzincan was in a single-story building about 2 km away from the case study building but we assume that the record applies to the building there. These three data represent characteristics of near-field ground motions and the distance of the sensor stations to the nearest fault trace was less than 10 km. The buildings sustained varying degrees of damage during the earthquakes and their damage survey was employed through site investigations. Given that the damage information, input motions, design drawings and material properties of the buildings are all known, this provided an opportunity to predict the structural damage to these buildings by proper modeling using the tools of current computational performance assessment procedures. In this circumstance, three dimensional (3D) analytical models of the MPWR buildings have been performed. Bi-directional excitations have been applied to the models by nonlinear time history analyses (NTHA). The results illustrate that NTHA are capable of indicating the occurrence of shear failure in captive columns
however, they overestimate the global damage level for all buildings. The overestimation is more significant in Erzincan case where the building sustained a pulse-type motion without significant distress.

[EN] A simplified analytical method ("FAST") for the estimation of large-scale vulnerability of Reinforced Concrete (RC) Moment Resisting Frames with masonry infills is proposed and subsequently tested by using real damage scenario caused by the 2011 Lorca earthquake as a benchmark. FAST is a spectral-based approach that allows predicting the average non-structural Damage State expected for each class of building (defined by number of storeys, age of construction, infills ratio in plan and location) for a given demand level. It accounts for non-uniformity of infills in elevation, i.e. a reduction of infills ratio of the ground floor. FAST is based on: (i) the definition of approximated capacity curves of the infilled building, assuming that the RC frame is designed according to the corresponding seismic code; and on (ii) the assumption of "a priori" deformed shapes in accordance with the attainment of each non-structural damage state at 1st storey, estimated through experimental and numerical correlations. Two versions of FAST are proposed: a "simplified" approach aimed at the evaluation of uniformly infilled frames; and a "generalised" version which can account for any intermediate situation between uniformly infilled frames and pilotis frames (i.e. without infills at 1st storey). Also, some extensions of the method are highlighted. Aimed at testing FAST, the real damage scenario after the earthquake of Lorca (2011) is used as a benchmark, despite its impulsivity and directivity. In order to define the specific input parameters for the case study, information regarding ground motion, post-earthquake damage scenario and also building design practice must be collected. Hence, a detailed review of historical Spanish seismic codes and a critical analysis of current Spanish seismic code NCSE-02 in comparison with current reference performance-based codes such as Eurocode 8 are provided. Special emphasis is placed on provisions which can prevent a proper capacity design and that, in turn, can cause brittle failures or favour the interaction with infills. Also, the prescription of lower behaviour factor for wide-beam frames with respect to deep-beam frames -which is not present in most codes¿ is discussed; outcomes of several case studies suggest that such prescription is obsolete. Finally, FAST is applied to Lorca earthquake and predicted damage scenarios are obtained, considering different assumptions for input values. Results show proper agreement between predicted and real damages. Structural collapses were rarely observed, even though the PGA was three times higher than the typical acceleration of design, so FAST proves that masonry infills provided additional strength to RC frames.
[ES] Se propone un método analítico simplificado ("FAST") para la estimación de la vulnerabilidad a gran escala de edificios porticados de hormigón armado con tabiquería de fábrica, posteriormente testeado mediante la adopción del escenario de daño real correspondiente al terremoto de Lorca de 2011 como patrón de comparación. FAST es un procedimiento espectral que permite predecir el nivel de daño no estructural medio esperado para cada clase de edificio (definido por su número de plantas, año de construcción, densidad de tabiquería en planta y localización geográfica), considerando un nivel de demanda dado. El método tiene en cuenta la irregularidad de la tabiquería en alzado, es decir, la posible reducción relativa de tabiquería en planta baja. FAST se basa en: (i) la definición de curvas de capacidad aproximadas para los edificios tabicados, asumiendo que la estructura de HA se ha proyectado según la norma sísmica correspondiente en cada caso; y en (ii) la asunción de deformadas "apriorísticas" coherentes con cada grado de daño (suponiendo que éste se alcanza siempre en planta baja), estimadas a través de correlaciones experimentales y numéricas. Se proponen dos versiones de FAST: una "simplificada" para la evaluación de edificios uniformemente tabicados en altura, y otra "generalizada", que es capaz de tener en cuenta cualquier situación intermedia entre el prototipo uniformemente tabicado y el de planta baja diáfana. Además, se proponen ciertas extensiones al método. A fin de validar FAST, se elige el escenario de daño real correspondiente al terremoto de Lorca (2011) como patrón de comparación, a pesar de su impulsividad y directividad. Para definir los parámetros de input correspondientes al caso de estudio, es necesario recopilar previamente la información concerniente a la señal sísmica, el escenario de daño y las características del parque construido. Por tanto, se lleva a cabo una revisión exhaustiva de las normas sísmicas históricas en España y un análisis crítico de la norma sísmica española actual NCSE-02 en comparación con otras normas actuales de referencia basadas en el desempeño, como el Eurocódigo 8, haciendo énfasis en las provisiones que no garantizan el diseño por capacidad y que por tanto pueden provocar mecanismos frágiles o favorecer la excesiva influencia de la tabiquería. Además, se discute sobre la restricción del coeficiente de ductilidad en estructuras de vigas planas, cuestión que no se refleja en otras normas. Los resultados obtenidos mediante análisis de casos de estudio muestran que dicha prescripción resulta obsoleta para normas actuales. Finalmente, FAST se aplica al caso del terremoto de Lorca, obteniéndose predicciones de daño medio para diferentes asunciones. Los resultados muestran una coincidencia aceptable entre la predicción y los daños reales. FAST confirma que la causa principal de la práctica ausencia de colapsos (ante un terremoto con PGA triple que la típica de proyecto) hay que buscarla en la contribución estructural de la tabiquería de fábrica.
[CAT] Es proposa un mètode analític simplificat ("FAST") per a l'estimació de la vulnerabilitat a gran escala d'edificis porticats de formigó armat amb envans de fàbrica. Posteriorment, el mètode ha estat testejat mitjançant l'adopció de l'escenari de dany real corresponent al terratrèmol de Lorca de 2011 com a patró de comparació. FAST és un procediment espectral que permet predir el nivell de dany no estructural mitjà esperat per a cada classe d'edifici (definit pel seu nombre de plantes, any de construcció, densitat d'envans en planta i localització geogràfica), considerant un determinat nivell de demanda. El mètode té en compte la irregularitat de la distribució de envans al llarg de les diferents plantes del edifici. Es a dir, es pot tenir en compte que, freqüentment, hi ha una menor quantitat de d'envans a la planta baixa. FAST es fonamenta en: (i) la definició de corbes de capacitat aproximades que tenen en compte no sols la estructura del edifici sinó també els envans i assumint que l'estructura de HA s'ha projectat segons la norma sísmica corresponent en cada cas; (ii) l'assumpció de deformades "apriorístiques" coherents amb cada grau de dany (suposant que aquest es dona sempre a la planta baixa) que han estat estimades a través de correlacions experimentals i numèriques. Es proposen dues versions de FAST: una "simplificada" per a l'avaluació d'edificis amb envans uniformement repartits per totes les plantes, i una altra "generalitzada", que és capaç de tenir en compte qualsevol situació intermèdia entre el prototip uniformement paredat i el de planta baixa diàfana. A més, es proposen certes extensions al mètode. Per tal de validar FAST, es tria l'escenari de dany real corresponent al terratrèmol de Lorca (2011) com a patró de comparació, malgrat la seva impulsivitat i directivitat. Per definir els paràmetres de entrada corresponents al cas d'estudi, cal recopilar prèviament la informació concernent al senyal sísmica, l'escenari de dany i les característiques del parc construït. Per tant, es porta a terme una revisió exhaustiva de les normes sísmiques històriques a Espanya i una anàlisi crítica de la norma sísmica espanyola actual (NCSE-02) comparant-la amb altres normes actuals de referència, com l'Eurocodi 8, fonamentat en el concepte d'acompliment. També es fa èmfasi a les provisions que no garanteixen el disseny per capacitat i que, per tant, poden provocar mecanismes de col·lapse fràgils o afavorir la interacció de la estructura amb els envans. A més, es discuteix sobre la restricció del coeficient de ductilitat de les estructures de bigues planes ja que es una qüestió que no aborden la majoria de les normes. Els resultats obtinguts mitjançant l'anàlisi de casos d'estudi mostren que aquesta restricció resulta obsoleta a les normes actuals. Finalment, FAST s'aplica al cas del terratrèmol de Lorca, obtenint prediccions de dany mitjà per a diferents combinacions del paràmetres de entrada. Els resultats mostren una coincidència acceptable entre la predicció i els danys reals. FAST confirma que la causa principal de la pràctica absència de col·lapses (davant un terratrèmol amb PGA triple que la típica de projecte) cal buscar-la en la contribució estructural dels envans.
Gómez Martínez, F. (2015). FAST simplified vulnerability approach for seismic assessment of infilled RC MRF buildings and its application to the 2011 Lorca (Spain) earthquake [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/54780
TESIS
Premiado

Subject of the solution master´s thesis is new civil building. It is five floors building with underground floor. The structual system is made by combination of RC frame and loadbearing masonry with monoplane roof. In underground floor is a garage. In First floor is designed for commercial and comunal activities. In next floors there is always 8 flats. Building is located in straight terrain in the development area of new houses in Zlin in area Bartosova.

The subject of this project is a new building of a shooting range and lasergame arena in Brno, district Královo pole. The aim of the thesis is to create a documentation for realization of a shooting range and lasergame arena. It is a stand-alone two-storey building without the basement. The building is based on piled foundations, the construction system is reinforced concrete frame, infill material is light concrete brick. There is an exception: in the tunnel shooting range, there are monolithic reinforced concrete walls. The ceilings above the first floor are made also of reinforced concrete, the ceiling above the second floor / roof is made of pre-stressed reinforced concrete roof panels of spiroll type. There is flat, single-layer roof. The walls are designed as double-layered, contact-insulated with fiber-cement cladding.

The diploma thesis deals with project of a new building of university dormitories in the city center of Brno. It is detached building with basement and four above-ground floors with the irregular rectangular shape. Dormitories can be divided into three fundamental parts. The underground garages can be considered as the first part. Parking places are designed only for students, occasional visitors, and employees. In the underground floor, technical rooms and large warehouse can be found. The second part is designed to the general public including association areas such as reception, coffee-house with outdoor terrace, copy center and tobacco shop. Rooms for students, manager offices, repairman’s room, and laundry can be found in the third part. In total there are 44 two-person rooms and one room for a disabled person on the second floor. The structural system of the building is a cast-in-place concrete frame with a filling of ceramic fittings. The external wall is insulated with mineral wool with a ventilated facade and fiber-cement facade tiles. The building is based on base piles with a pile under each pillar. Vegetation covers a flat roof as well as a part of the north side of the facade. There will also be a public park and two volleyball fields in the area.

Major portion of urban building is irregular. Sometime the building is designed irregular and many time it become irregular due to different circumstances like change of use of building or reconstruction. In the present study, an effort is made to understand the behaviour of a building which becomes vertical irregular by non uniform distribution of mass along height. A four storey building is modelled in STADD PRO V8i for studying the effect of mass irregularity on the behaviour of building structure. Seismic load is applied on the building model as per IS 1893 (PART 1): 2002. In each storey, seven case of different loading condition is formulated by changing the ratio of mass of that storey to that of adjacent storey to 1, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0.This process is repeated for each floor. A total of 28 cases is analysed and change in various output parameter like roof drift, storey drift, base shear, frequency etc is studied. Based on the present study, it can be concluded that whenever mass is increased on lower and/or top storey, large variation is observed in studied output parameter than those occur when mass is changed in middle floor. Most critical location is top storey as drift is increased by 70% than that of original building when maximum loading is applied on top storey.
MR. ALOK VERMA ASSOCIATE PROFESSOR

In the present study, behaviour of multi-storey building in which there is non uniform variation of stiffness along height i.e. soft storey characteristic is analysed for different storey of the building. In the event of earthquake, it becomes of prime importance to take into account the effects arising from the soft storey for better performance of building. If these irregularity effects are not taken into account, severe damage will occur to the building during earthquake. For the fulfilment of above objective, the effect of soft storey on building has been studied. A five storey building in STAAD PRO V8i and seismic load is applied in accordance with IS 1893 (Part-1):2002. A total of five cases has been formulated in each storey by varying total stiffness of that storey to 90%, 80%,70%, 60% and 50% of base case (original building). Above step are repeated for all storey amounting to total of twenty five cases. Each case is studied carefully and effect on different output parameter is noted down. It can be conclude from the present study that whenever stiffness decreases in lower storey, the large variation is observed in output parameter than those occurs while decreasing stiffness in middle or upper storey. By changing the stiffness of a particular storey appreciable variation occurs only in that storey.

Under seismic loading the structural systems that should be designed to ensure proper energy dissipation capacity are Reinforced concrete moment resisting frames (RCMRF). “Strong-column - weak-beam” design is currently in practice, demands to have collapse mechanism in the structure. RC column-beam connections display ductile behavior, when the response of a structure is controlled by the flexural strength of beams. The failure mode where the beams forms hinges is considered as most recommended mode for guaranteeing good global energy -dissipation without much degradation of capacity at the connections. In spite of the fact that numerous universal codes prescribe the moment capacity ratio at beam column joint to be more than one, still there are many errors among these codes and Indian standard is quiet on this viewpoint. The objective of this project work is to compare the design and resulting performances of framed building for various MCRs recommended in international codes and its effect on design (BOQ). In the present work using SAP 2000, pushover analysis is done for increasing moment capacity ratio at column beam joints and the effect on design (BOQ) and the resulting performances of the building are studied.

Reinforced concrete moment resisting frames (RCMRF) are structural systems that should be designed to ensure proper energy dissipation capacity when subjected to seismic loading. In this design philosophy the capacity design approach that is currently used in practice demands “strong-column / weak-beam” design to have good ductility and a preferable collapse mechanism in the structure. When only the flexural strength of longitudinal beams controls the overall response of a structure, RC beam-column connections display ductile behaviour (with the joint panel region essentially remaining elastic). The failure mode where in the beams form hinges is usually considered to be the most favourable mode for ensuring good global energy-dissipation without much degradation of capacity at the connections. Though many international codes recommend the moment capacity ratio at beam column joint to be more than one, still there are lots of discrepancies among these codes and Indian standard is silent on this aspect. So in the present work pushover analysis is being done using SAP 2000 for increasing moment capacity ratio at beam column joints and its effect on the global ductility and lateral strength of the structure is studied. To incorporate the uncertainties in material properties, a probabilistic approach is followed to observe the effect of ground motion intensity on probability of exceedance of any specific damage state for structures designed considering different moment capacity ratios (MCR) at the connections. For this objective fragility curves are developed considering the pushover curves obtained from the nonlinear static analysis. Ductility of the structure increases with increase of MCR. Also the buildings designed with lesser MCR values are found to be more fragile compared to the building with higher MCR.

The area of vertically irregular type of building is now having a lot of interest in seismic research field. Vertical irregularity arises in the buildings due to the significant change in stiffness and strength. The typical OGS and stepped types of irregularities are considered in the present study. For OGS buildings, the Magnification factors (MF) are suggested by the design codes. The present study focus on the performance of typical OGS buildings designed considering various magnification factors as well as the stepped type buildings with different geometry configurations using fragility analysis. The critical inter-storey drift is considered as an intensity measure. Various heights (6, 8 &10 stories) are considered for the present study. Fragility curves are developed for each type of buildings as per the methodology introduced by Cornell (2002). PSDM models are developed for each frames and the corresponding fragility curves are generated. It is observed that in terms of performance, a building with infill walls in all stories is equally comparable with an OGS framed building with MF of about 1.5. Performance of the OGS frame increases with the increase in MF, but it makes the adjacent storey vulnerable. The study is extended to the seismic reliability for all the considered buildings. The reliability is found out by combining a fragility curve with a seismic hazard curve of the region. The seismic hazard curve for the present study is chosen from the study conducted by Pallav et. al (2012). The performance of the buildings is assessed by comparing the reliabilities achieved with the target reliabilities suggested as per ISO 2394 (1998). It is observed that the frames without any infill walls failed to achieve the target reliabilities whereas the buildings with infill walls achieved the target reliabilities. The stiffness of infill walls is a significant factor that improves the performance of buildings during earthquakes.

Nine RC framed building with brick masonry infill were designed for same seismic hazard in accordance with IS code taking in to consideration of effect of Masonry. Generally these buildings are analysed as RC framed structures with regards to structural action of masonry infill walls present and investigation has been made to study the behaviour of RC frames with various arrangement of infill when subjected to dynamic earthquake (dynamic) loading. The result of bare frame and frame with infill effect are compared and conclusion are made in view of IS -1893(2002) code. Based on the present study, it can be concluded that It the performance of fully masonry infill panels was significantly superior to that of bare frame. Brick infill walls present in RC frame building reduce the structural drift but increases strength and stiffness. Therefore it is essential for the structural systems selected, to be thoroughly investigated and well understood by Engineers.

Setback buildings with geometric irregularity (both in elevation and plan) are now increasingly encountered in modern urban construction. Setback buildings are characterised by staggered abrupt reductions in floor area along the height of the building, with consequent drops in mass, strength and stiffness. Height-wise changes in stiffness and mass render the dynamic characteristics of these buildings different from the ‘regular’ building. This paper presents the design code perspective of this building category. Almost all the major international design codes recommend dynamic analysis for design of setback buildings with scaled up base shear corresponding to the fundamental period as per the code specified empirical formula. However, the empirical equations of fundamental period given in these codes are a function of building height, which is ambiguous for a setback building. It has been seen from the analysis that the fundamental period of a setback building changes when the configuration of the building changes, even if the overall height remains the same. Based on modal analysis of 90 setback buildings with varying irregularity and height, this study proposes a correction factor to the empirical code formula for fundamental period, to render it applicable for stepped buildings

A regular building is defined as a building with uniformly distributed mass, stiffness, strength and structural form. When one or more of these properties is non-uniformly distributed, either individually or in combination with other properties in the vertical direction, the building is referred to as being vertically irregular. There are many examples of the failure of such buildings in past earthquakes due to non-uniform distribution of structural properties. Major international codes including ASCE/SEI 7 (2016) recognize five different classes of vertical irregularity in multi-storeyed buildings that need special design considerations. Most inter-national design codes either prohibit construction or recommend alternative seismic analysis and design of vertically irregular buildings depending on the degree of irregularity and site hazard. Force-based quantities such as mass, stiffness, and strength or geometrical quantities such as plan dimensions are used by design codes as measures (irregularity indicators) for assessing the degree of vertical irregularity present in buildings. Previous literature have proposed different methodologies to quantify the vertical irregularity of buildings in terms of their elastic mode properties. However, the definition of vertical irregularity of buildings mentioned in the codes and standards appears to be not supported by their associated seismic risk. Present study reviews the existing provisions of quantifying vertical irregularity in the context of seismic risk and found that all the vertically irregular buildings listed in the design codes do not pose higher seismic risk. Seismic risks of these buildings are evaluated in terms of fragility function, drift hazard, probability of failure and design confidence level. A concept of ‘vulnerability indicator’ in RC moment resisting vertically irregular framed buildings is proposed to replace the existing ‘irregularity indicator’. A good correlation between the proposed indicator and associated seismic risk is observed for different types of vertically irregular buildings. The design codes recommend five different irregularity quantifier, one for each of the five categories of vertically irregular building. If there is no correlation between ‘irregularity measures’ and ‘seismic safety’ exists the purpose of estimating ‘irregularity measures’ is lost. Therefore, a direct performance indicator of seismic risk is essential for the design code to impose special design requirement in place of presently used indirect irregularity indicator. This study also concludes that vertical geometric irregular buildings exhibit seismic risks lower than even a reference regular building and can be excluded from the list of special design group of building codes. Vertically irregular infill framed buildings are conventionally built with burnt clay brick masonry. However, with growing environmental concern for conservation of natural resources and disposal of waste, fly ash bricks, Autoclaved Aerated Concrete (AAC) and Cellular Lightweight Concrete (CLC) blocks are emerging as a substitute to burnt clay bricks for the construction of masonry infill. AAC and CLC blocks have been widely used as infilled masonry all over the world as a potential infill material due to various advantages. A study on the effect of such modern infill materials in the seismic performance of the vertically irregular building can be useful to ensure the safety of such buildings. However, the variability of mechanical properties related to the modern infill masonry materials are not readily available unlike the conventional building material like steel, concrete, clay and fly ash bricks. For this purpose, an extensive experimental programme was carried out to determine various physical and mechanical properties of AAC and CLC block masonry and best-fit probability distribution models are proposed. Higher order analyses such as XRD and field emission scanning electron microscope (FESEM) are conducted to understand the morphological and microstructural differences in block unit leading to variation in its properties. The proposed probability distributions are used to study performance of typical vertically irregular buildings made of modern infill masonry. The seismic risk of a vertically irregular building with AAC and CLC infill is found to be lower than that with conventional infill materials like clay and fly ash bricks. Although clay and fly ash brick masonry have higher strength and stiffness properties, the lightweight properties may be attributed to the lower seismic risk of buildings with AAC and CLC block masonry. This study concludes that the use of modern lightweight infill materials can improve the building performance in seismically active areas.

This paper is concerned with the effects of various vertical irregularities on the seismic response of a structure. The objective of the project is to carry out Response spectrum analysis (RSA) and Time history Analysis (THA) of vertically irregular RC building frames and to carry out the ductility based design using IS 13920 corresponding to Equivalent static analysis and Time history analysis.. Three types of irregularities namely mass irregularity, stiffness irregularity and vertical geometry irregularity were considered. According to our observation, the storey shear force was found to be maximum for the first storey and it decreases to minimum in the top storey in all cases. The mass irregular structures were observed to experience larger base shear than similar regular structures. The stiffness irregular structure experienced lesser base shear and has larger inter-storey drifts. The absolute displacements obtained from time history analysis of geometry irregular structure at respective nodes were found to be greater than that in case of regular structure for upper stories but gradually as we moved to lower stories displacements in both structures tended to converge. Lower stiffness results in higher displacements of upper stories. In case of a mass irregular structure, time history analysis gives slightly higher displacement for upper stories than that in regular structures whereas as we move down lower stories show higher displacements as compared to that in regular structures. High rise structure subjected to high frequency ground motion results in small displacements. Similarly, if a low rise structure is subjected to high frequency ground motion it results in larger displacements whereas small displacements occur when the high rise structure is subjected to low frequency ground motion

碩士
國立屏東科技大學
土木工程系所
105
Several studies have indicated that enhancing seismic resistance may benefit the progressive collapse resistance for building frames under column loss. This ongoing study intends to investigate the relationship between the column-loss and seismic shear resistances by using beam-column sub-assemblages. The resistance ratio is defined and used as a measure for quantifying the relationship. An analytical expression of the ratio is derived based on the strong column and weak beam mechanism and plastic analysis technique. Three dimensional RC building models with different structural parameters are designed. Nonlinear static analyses are performed to evaluate the influences of the design parameters on the resistance ratio. The analysis results indicate that the span length or span-to-height ratio is the most important factor for the resistance ratio. Lower resistance ratios are observed with increased span length, which implied a higher collapse potential. Although larger seismic design force can increase both the seismic shear and column-loss resistances, the resistance ratio slightly decreases with increased seismic coefficient. An opposite trend is observed for the effect of story numbers. An approximate resistance ratio can be obtained with the analytical expression.

The Open Ground Storey buildings are very commonly found in India due to provision for very much needed parking space in urban areas. However, seismic performance of this type of buildings is found to be consistently poor as demonstrated by the past earthquakes. Some of the literatures indicate that use of shear walls may enhance the performance of this kind of buildings without obstructing the free movement of vehicles in the parking lot. The present study is an attempt in this direction to study the performance of Open Ground Storey buildings strengthened with shear walls in a bay or two. In addition to that, the study considers a different scenarios of Open Ground storey buildings strengthened by applying various schemes of multiplication factors in line with the approach proposed by IS 1893 (2002) for the comparison purpose. Study shows that the shear walls significantly increases the base shear capacity of OGS buildings however the comparative cost is slightly on the higher side.

碩士
國立屏東科技大學
土木工程系所
106
Progressive collapse response of an RC building may be induced if one of its ground-story columns is destroyed and the load-bearing capacity of the structure is less than the weight of the structure. This study intends to investigate the influence of some structural parameters on the load-bearing capacity of RC building frames under column loss. According to the seismic design code in Taiwan, twenty-seven earthquake-resistance RC buildings frames were designed with varied number of stories, span length and seismic coefficients. Nonlinear static pushover analyses were conducted to examine the seismic performance of the RC buildings frames. Nonlinear static pushdown analyses were conducted to those frames under three column-loss scenarios. Ratios of column-loss to seismic resistance were used to evaluate the progressive collapse potential. Analysis results indicated that span length may be the most critical factor for collapse potential of seismically designed buildings frames. The resistance ratio increased with decreased span length and number of stories. However, it was insensitive to the seismic coefficient. Both the yield and ultimate flexural strengths could have approximate predictions for collapse potential. However, the former could have more conservative results than the latter. Therefore, it can be used to make conservative evaluation for the progressive collapse potential of seismically designed RC building frames.

Reinforced concrete structures are usually vulnerable to collapse in areas where the earthquakes are frequent. Although plenty of research has been carried out in that regard the problem is still in place. Furthermore, there are buildings that did not collapse with the first and second earthquake but with the third one. That happens because many buildings are generally declared safe after being thoroughly inspected in the visible areas only, ignoring the extent of the damage in the column-to-foundation connections. The criterion of identifying the failure at the base of the columns of the ground floor is that after the earthquake there are no traces of failure. In other words, the cracks at the base of the columns have been healed and concealed the damage in the core of the columns.
thesis (PhDCivilEngineering)--University of South Australia, 2005.

Earthquakes are natural calamity which causes severe damage or collapse of buildings. Now a day’s many structures have irregular configurations both in plan and elevation. Damage due to earthquake are more severe at the point of discontinuity in the structure. Openings in the floors are common for many reasons like staircases, lighting, architectural and etc. these openings develop stresses at discontinuities. Discontinuous diaphragms are designed without stress calculations and are thought-about to be adequate ignoring any gap effects. In multi-storeyed framed building, damages from earthquake generally initiates at locations of structural weaknesses present in the lateral load resisting frames Diaphragms with abrupt discontinuities or variations in stiffness, which includes those having cut-out or open areas greater than 50 percent of the gross enclosed diaphragm area, or changes in effective diaphragm stiffness of more than 50 percent from one storey to the next. In structural engineering, a diaphragm is a structural system used to transfer lateral loads to shear walls or frames primarily through in-plane shear stress. Lateral loads are usually wind and earthquake loads. This paper focuses the general effects of diaphragm discontinuity on seismic response of multi-storeyed building on various structural parameters.

碩士
國立臺灣大學
土木工程學研究所
107
The objective of this work is to evaluate the seismic performance of retrofitted structural members of high-rise buildings in Banqiao, New Taipei City. This work presents test results of “Steel Double K-Braced Frame” conducted at the National Center for Research on Earthquake Engineering (NCREE) from 2016~2017. In general, test results showed acceptable seismic performance of retrofitted structural members based on the design requirement and ACI 374.2R (2013). The performances of KBF is presented in this study, focusing on the investigations of the overall structure and local members. For this purpose, in the beginning this study discusses the setup and the key experimental results of the specimen, such as the peak inter-story drifts and buckling of braces. Test results show that the brace members take about 80~85% actuator force at inter-story drifts under 0.02 radians,but gradually decrease to 67% actuator force when brace compression force decrease to 0.1Pcr(3% drift ratio). ABAQUS was used to simulate the responses of the single brace. The analytical results confirm that the magnitude of the severe out-of-plane buckling of the braces and buckling force can be accurately simulated. American Institute of Steel Construction (AISC Specification 360-16 (2016)) is conservative in predicting the buckling force of braces,but Wolchuk (1963) can give good accuracy result.

The dynamic soil-structure interaction effects for RC framed buildings with or without shear wall on raft foundation is evaluated by explicit consideration of structural nonlinearity and soilstructure interaction as per Indian and Ethiopian seismic codes. In the current study, the finite element model (Elastic continuum approach) employed for soil-foundation-structure model. Hence, four and eight number of stories with or without shear wall on raft foundation found on rock, dense, stiff and soft soils are designed and modeled using SAP 2000 v 21. The building studied with or without incorporation of SSI effect. The analysis is carried out in 3 stages: (1) response spectrum analysis, (2) soil-structure interaction analysis, and (3) nonlinear structural analysis (pushover analysis). The response spectrum analysis is used to design the section sizes of the members and a comparison is made according to IS 456: 2000 and ES EN-2. The nonlinear static pushover analysis is used to observe proper structural behavior for defined push displacement. The resulting pushover curves are studied through performance-based design (PBD). Finally, a comparison is made between the behavior of each building in the fixed base condition and SSI condition. This work demonstrates ES ES-2 moments exceed that of the IS 456: 2000 by an average of about 15.58% for beam area of tension reinforcement for span and 15.4% for support. So, Indian code provides a more economical design than Ethiopian code ES EN-2. Moreover, the nonlinear response of buildings was determined and compared between two cases: fixed-base and SSI conditions. Response quantities such as SSI effects on the target displacement, SSI effects on the story drifts, SSI effects on the plastic hinge mechanisms and rotations obtained from pushover analysis of superstructure. The numerical findings indicate that incorporating the soil-structure interaction generally increases the top displacement and plastic hinge rotation, reduces the base shear. Hence, it is very important point is that soil-structure increases the plastic deformation.

Il lavoro in questa tesi riguarda l’estensione, il miglioramento e la validazione della metodologia Simple Lateral Mechanism Analysis (SLaMA) per la valutazione sismica di strutture in CA. Raccomandato nelle linee guida neozelandesi del 2017 relative alla valutazione sismica, NZSEE (2017), SLaMA é un metodo di analisi non-lineare che permette di avere una stima della capacitá di strutture esistenti ed é valido per telai, pareti o sistemi misti telaio/parete. L’idea di base é procedere “dal locale al globale”, partendo dal comportamento di componenti singoli, estendendolo a specifici sottoschemi ed infine giungendo al comportamento globale dell’edificio. É anche possibile considerare gli effetti torsionali in campo non-lineare. Dato che il metodo si basa su ipotesi semplificate, non é necessario ricorrere a modelli numerici e i calcoli possono essere fatti “a mano (i.e. utilizzando un foglio elettronico). La prima parte di questo lavoro di ricerca riguarda i sistemi a telaio nudo, identificando aree di miglioramento della procedura SLaMA esistente e proponendo una procedura estesa e migliorata. Essa é stata validata attraverso la sua applicazione a 40 casi studio ideali e il confronto con i risultati di analisi numeriche raffinate (FEM Pushover). I risultati indicano che la procedura SLaMA modificata permette di identificare accuratamente il meccanismo plastico del telaio, considerando l’effettiva gerarchia delle resistenze dei suoi componenti, e di calcolarne la curva di capacitá con errori accettabili per i suoi parametri più significativi. La parte successiva del lavoro riguarda lo sviluppo di una nuova procedura SLaMA, non presente in NZSEE (2017), per sistemi a telaio tamponato, che rappresentano una cospicua parte del patrimonio edilizio, soprattutto in Europa. La nuova metodologia si basa su una procedura meccanica, proposta in questo lavoro, per disaccoppiare i contributi al taglio alla base relativi al telaio e alle tamponature, per un qualunque valore dello spostamento globale. La procedura di disaggregazione é applicabile a prescindere dalla distribuzione delle tamponature e della curva caratteristica dei puntoni equivalenti. Puó essere inoltre applicata per la post-processione dei risultati di analisi Pushover o Time History di telai tamponati. In analogia a quanto fatto per i telai nudi la procedura SLaMA é stata validata tramite confronto con i risultati di analisi Pushover per 72 casi studio. Sono stati inoltre considerati i sistemi resistenti misti telaio/parete con l’obiettivo di proporre una nuova procedura SLaMA che considerasse esplicitamente l’interazione tra la parte a telaio con quella a parete, includendo il calcolo delle forze da essi scambiate e le eventuali coppie concentrate dovute alla presenza di travi di collegamento. Con la nuova procedura SLaMA é possibile stimare il comportamento dei sistemi duali con grande accuratezza, come dimostrato da una vasta analisi parametrica (SLaMA vs Pushover) che coinvolge 24 casi studio. L’ultima parte del lavoro riguarda la valutazione sismica di un edificio realmente esistito e che ha subito notevoli danni durante la sequenza sismica di Christchurch (Nuova Zelanda) tra il 2010 e il 2011. Lo “score sismico” (capacitá fratto domanda) é stato indipendentemente valutato con diversi metodi di analisi: Lineare Statica, Lineare Dinamica, Non-Lineare Statica (Pushover e SLaMA), Non-Lineare Dinamica. In primis questo confronto incrociato dimostra l’affidabilitá del metodo SLaMA nella valutazione di casi reali complessi. Questo studio dimostra inoltre come le informazioni ottenute utilizzando SLaMA possano essere efficacemente usate per calibrare i parametri fondamentali necessari per gli altri metodi di analisi, o interpretarne i risultati. Sebbene alcuni passi della procedura possono essere calibrati in maniera piú raffinata grazie a sviluppi futuri si puó sicuramente affermare che SLaMA sia un metodo di analisi robusto. Esso é in grado di fornire al tecnico valutatore gli strumenti per comprendere i dettagli del comportamento di un edificio usando esclusivamente calcoli fatti a mano (eventualmente implementati in un semplice foglio elettronico).
This dissertation is focused on the extension, refinement and validation of the Simple Lateral Mechanism Analysis (SLaMA) method for the seismic assessment of RC buildings. Suggested in the 2017 New Zealand guidelines for seismic assessment, NZSEE (2017), SLaMA is an analytical non-linear analysis technique that provides a first estimation of the global capacity curve of the primary lateral-resisting systems in RC buildings, including bare frames, cantilever walls and dual wall/frame systems. The basic idea is to progress “from local to global”, extending the local behaviour of the structural members to selected sub-schemes, and finally to the global non-linear response of the building. Inelastic torsional effects are also included. Since simplified assumptions are made, no numerical computer model is needed and hence all the calculations can be performed “by hand” (i.e. implemented in an electronic spreadsheet). The first part of this investigation is related to bare frame Lateral Resisting Systems, with the identification of potential areas of improvement for the existing SLaMA procedure and the proposal of an extended/refined one. The refined procedure for bare frames is validated through the application to a set of 40 ideal case studies and the comparison with refined numerical analyses (FEM Pushover). The results show that the refined SLaMA procedure allows to accurately identify the expected plastic mechanism of the frame, also considering the actual hierarchy of strength of its members, and to properly estimate its non-linear capacity curve with acceptable errors on the most meaningful parameters. The subsequent part of the investigation involves the development of a novel SLaMA method to evaluate the capacity curve of masonry-infilled frames systems, which represent a large portion of the building portfolio, especially in Europe. The incorporation of the contribution of the infills is completely absent in the NZSEE (2017) SLaMA framework. The methodology is based on a proposed mechanically-based procedure to decouple the frame and infills contributions to the overturning moment (and hence base shear) capacity for any value of the global displacement. The decoupling procedure is applicable regardless of the distribution of the infills and of the non-linear Axial load-Axial strain of the equivalent struts. It can be applied to post-process the results of Pushover or Time History analyses of different types of infilled frames (material-wise). Similarly to what done for bare frames, an extensive SLaMA vs numerical Pushover comparison, for a set of 72 ideal case studies, is used to validate the proposed SLaMA procedure. Part of the investigation is dedicated to dual wall/frame system structures, proposing a novel SLaMA procedure in which the coupled behaviour of the frame and wall(s) components is expressly considered, including the calculation of the exchanged forces and the concentrated moment couples due to the possible presence of link beams. By using the new SLaMA procedure it is possible to capture the non-linear behaviour of the dual system with extreme accuracy, as demonstrated with an extensive SLaMA vs numerical Pushover parametric analysis comprising 24 ideal case studies. The last step of the work is the seismic assessment of a real case study building, severely damage in the Christchurch (New Zealand) sequence of earthquakes in 2010-2011. Different analysis techniques are used to independently derive the “seismic score” of the building (capacity over demand), including: Linear Static, Linear Dynamic, Non-Linear Static (numerical Pushover and SLaMA) and Non-Linear Dynamic analyses. Firstly, this demonstrates the reliability of the SLaMA method in assessing real, complex cases by means of a cross-validation. Moreover, and perhaps more importantly, it is deemed that this comparative study demonstrates how the insights gained by using SLaMA can be used to calibrate important parameters needed when adopting other analysis techniques, or interpreting their results. Additional investigations might help in fine-tuning some of its steps but, overall, it is deemed that SLaMA constitutes a robust analysis technique that allows the assessor to really understand the behaviour of an RC building only using hand calculations, possibly implemented in a simple spreadsheet.

碩士
國立屏東科技大學
土木工程系所
103
Abstract Student ID：N9733004 Total Pages：64 Title of Thesis：Evaluation of the progressive collapse potential of an RC building frame subjected to different column-loss scenarios by using the demand-capacity ratio (DCR) Name of Institute：National Pingtung University of Science and Technology Name of Department：Department of Civil Engineering Date of Graduation：May, 2015 Degree Conferred：Master Adviser： Tsai, Meng-Hao Lu, Jun-Kai Name of Studennt：Lee, Chih-Peng The Contents of Abstract in this Thesis： Linear static analyses were conducted in this study to evaluate the progressive collapse potential of a ten-story RC building frame. The analysis procedure recommended in the UFC 4-023-03 design guidelines was adopted. The demand-to-capacity ratio (DCR) of beam-end moment was used to evaluate the collapse potential of the building frame. Three difference column-loss locations at each of the first, second, sixth, and top stories were considered in linear static analyses. The analysis results indicated that removal of the peripheral and penultimate column in the longitudinal direction led to highest progressive collapse potential for the RC building frame. Also, larger DCR ratios were obtained for the removal of a higher-story column, which indicated that higher stories were more vulnerable to partial collapse under column-loss conditions. Even though, the collapse risk of the building frame was low according to the acceptance criterion suggested in the UFC guidelines. This implied a seismically designed RC building frame may have superior collapse resistance against column loss. Keywords:Linear static analysis, demand-to-capacity ratio, progressive collapse

Il problema della verifica di vulnerabilità sismica di edifici esistenti in calcestruzzo armato è stato oggetto negli ultimi anni di studi approfonditi, che hanno favorito lo sviluppo di un quadro di riferimento internazionale sul tema molto ampio, sia dal punto di vista della ricerca scientifica che da quello delle normative tecniche vigenti. Tuttavia, sono ancora molte le questioni irrisolte a riguardo di temi come la modellazione numerica e i metodi di analisi sismica, fasi fortemente influenzate da continue fonti di incertezza (conoscenza dei dettagli geometrici e strutturali, proprietà dei materiali, input sismico, accuratezza e affidabilità di modelli di capacità e strategie di discretizzazione). Ai fini di una valutazione affidabile delle prestazioni sismiche, tali problematiche richiedono lo sviluppo di strategie di modellazione e analisi innovative ed efficaci, soprattutto da un punto di vista di una accurata valutazione probabilistica e con uno sguardo attento alla pratica progettuale, dove la facilità di implementazione e i tempi di calcolo assumono un’importanza prioritaria. Dopo un’estesa ricerca bibliografica degli approcci proposti e utilizzati per effettuare verifiche di vulnerabilità sismica di edifici esistenti in calcestruzzo armato, proposti dalla letteratura scientifica e dalle normative tecniche vigenti, nella tesi sono stati discussi inizialmente alcuni aspetti critici di modellazione, relativi alle consuete ipotesi semplificative adottate. Nella fattispecie, l’influenza dell’ipotesi di piano rigido, con riferimento agli elementi strutturali secondari come il solaio, è stata analizzata, con l’obiettivo di proporre un’idonea strategia efficiente di modellazione per una pratica applicazione, rivolta a ricercatori e professionisti. Ciò stante, un’analisi iniziale di sensibilità è stata condotta, investigando quali parametri influenzano significativamente la risposta sismica globale della tipologia di edifici in oggetto. Sulla base dei risultati ottenuti, una nuova procedura numerica di modellazione dell’impalcato è stata proposta, atta a definire una piastra ortotropa equivalente capace di simulare la reale rigidezza nel piano, per azioni orizzontali. La metodologia adottata, nonostante incrementi lo sforzo computazionale dell’analisi, ha il vantaggio di evitare le assunzioni aprioristiche sulla rigidezza dell’impalcato. Al fine di validare quanto proposto, il metodo è stato applicato ad un edificio esistente in calcestruzzo armato, valutando i risultati e comparandoli con altre metodologie proposte dalla letteratura scientifica per considerare il comportamento nel piano dell’impalcato, come quella a puntoni equivalenti. Infine, è stata valutata la possibilità di applicare la procedura nei casi in cui si considera l’influenza delle tamponature esterne e successivamente, in una prospettiva di miglioramento o adeguamento sismico dell’edificio. In quest’ultimi casi, la prestazione dell’edificio alle azioni orizzontali è stata migliorata, mediante l’uso di tamponature rinforzate e mediante l’inserimento di pareti in calcestruzzo armato sul perimetro dell’edificio. Per quanto riguarda la fase di analisi sismica, stabilire quale sia la metodologia più efficace per identificare la risposta strutturale in campo elastico e inelastico assume una grande importanza, considerando soprattutto la vasta casistica di procedure proposte dalla letteratura scientifica e dalle normative tecniche vigenti. A valle di un’estesa valutazione di quest’ultime, con particolare attenzione ai metodi di analisi non lineari, sia statici che dinamici, la dissertazione presenta alcune applicazioni di analisi statiche non lineari, metodo che rappresenta la prima scelta da parte dei professionisti. Inizialmente, un’applicazione di analisi statica non lineare convenzionale è stata condotta su un campione di edifici esistenti ideali in calcestruzzo armato, con l’obiettivo di verificare il ruolo del nodo di controllo. Tuttavia, come già evidenziato dalle normative tecniche vigenti (Normativa Tecnica Italiana e Eurocodice 8), le procedure di analisi statica non lineare non possono essere sempre applicate, a causa di alcune limitazioni dovute alle caratteristiche dell’edificio analizzato, come le irregolarità e la forte influenza dei modi superiori. Con l’obiettivo di proporre una strategia che possa colmare i limiti sopraelencati, una possibile soluzione è rappresentata dai metodi non convenzionali come le analisi statiche non lineari multimodali o adattive. A questo proposito, una procedura semplificata di analisi statica non lineare multimodale è stata proposta. La peculiarità di tale metodologia è dovuta ad un algoritmo capace di fornire un singolo profilo di carico, facilmente implementabile nelle stesse modalità di un’analisi convenzionale. Al fine di verificare l’efficienza del metodo, quest’ultimo è stato applicato ad un edificio esistente in calcestruzzo armato, caratterizzato da irregolarità dinamiche e da elevata inomogeneità dei materiali in situ. Nella parte finale della tesi, è stata analizzata la possibilità di implementare i concetti alla base del Performance Based Earthquake Engineering (PBEE), metodo di elevata rilevanza scientifica, per applicazioni pratiche nella verifica di vulnerabilità sismica di edifici in calcestruzzo armato. Generalmente, l’applicazione del PBEE richiede conoscenze specifiche circa le teorie della probabilità e competenze specialistiche nel campo della modellazione e analisi non lineare, qualità non sempre comuni tra i professionisti. Con l’obiettivo di ridurre i sopramenzionati ostacoli, una metodologia di analisi dinamica non lineare è stata proposta, consistente in un’applicazione del metodo “multi stripe analysis” su modelli numerici redatti con programmi di calcolo commerciali. Nella fattispecie, la nuova procedura, chiamata “Few Stripe Analysis” (FSA) è stata applicata e testata su un campione di 15 edifici scolastici esistenti in calcestruzzo armato (nella provincia di Foggia, Sud Italia) e i risultati ottenuti, in termini di stato di danno e curve di fragilità, sono stati confrontati con quelli ottenuti utilizzando il programma di calcolo SPO2FRAG. Quest’ultimo consente di calcolare curve di fragilità, partendo da curve di capacità ottenute da analisi statiche non lineari. Infine, una nuova procedura di modellazione per valutare la risposta sismica globale di edifici in calcestruzzo armato è stata proposta. In particolare, la metodologia consente di produrre modelli 3D ad ordine ridotto (caratterizzati da pochi gradi di libertà), partendo dalle caratteristiche geometriche e meccaniche di un edificio esistente. Il vantaggio principale del presente approccio è quello di cogliere molti degli effetti predicibili con un MDoF, ma con bassi tempi di calcolo e analisi e elevata capacità di convergenza, caratteristiche tipiche dei modelli SDoF. L’efficienza di questi modelli semplificati è stata testata sul campione di edifici esistenti sopramenzionato e i risultati, in termini di risposta strutturale, stato di danno e livello di confidenza, sono stati confrontati con quelli ottenuti precedentemente dall’applicazione della metodologia FSA. La rilevanza e l’impatto futuro del lavoro di ricerca presentato può essere valutato in una prospettiva più ampia e relativa ad un’analisi di vulnerabilità del patrimonio costruito a scala territoriale, che risulta essere attualmente un aspetto critico sia per la comunità scientifica che per le autorità governative. Infatti quest’ultime hanno il difficile compito di proporre strategie di mitigazione del rischio sismico per un ampio e disomogeneo patrimonio strutturale, ma con risorse economiche spesso molto limitate. Pertanto, lo sviluppo di metodologie per la stima della vulnerabilità basata su dati limitati è un tema soggetto ad intense attività di ricerca. Le proposte presentate nella tesi possono fornire un potenziale strumento di analisi di grande utilità, in quanto potrebbero consentire, attraverso l’uso dei modelli 3D ad ordine ridotto combinati con la metodologia FSA, di superare le ben note limitazioni mostrate dagli approcci empirici, a favore di metodi meccanici, utilizzati in un quadro completo di analisi probabilistica.
The issue of seismic assessment of existing RC buildings has been extensively studied in the last few years and the international reference framework, both with regard to the scientific research and the development of technical codes, is very wide. Nevertheless, there are still a lot of challenging questions about the definition of reliable numerical models and methods of analysis, which are strongly affected by many uncertainty sources (knowledge of structural details, material properties, seismic input; accuracy and reliability of capacity models and discretization strategies). The management of these issues, especially in view of practice-oriented applications, requires the availability of effective strategies, so to allow a probabilistic assessment approach that can be relatively accessible in terms of implementation hurdle the computational time. After an extensive background about the approaches to vulnerability assessment proposed by recent scientific literature and technical codes, the dissertation discusses the critical aspects related to some assumptions commonly adopted in the seismic modelling of existing RC buildings, with the aim of proposing proper sanitization strategies, which can be particularly useful in view of practical applications. As a first issue, the influence on the global response of alternative modelling assumptions for secondary structural elements such as slabs is investigated. The usual hypothesis of rigid floor is assessed by performing a sensitivity analysis based on several parameters, which are particularly significant for the structural response evaluation. Then, based on the results of the analyses, a numerical procedure for modelling the floor system is proposed, defining an orthotropic equivalent shell element capable to simulate the in-plan stiffness of the floor. The methodology actually increases the computational efforts, but has the significant advantage of avoiding aprioristic assumptions about the floor stiffness. An application of the method to the numerical modelling of existing RC buildings is then proposed, by appraising the variation of results in comparison with alternative models for considering in-plan stiffness (namely, equivalent strut models). Lastly, the application possibilities of the proposed procedure are appraised, by presenting a number of examples. As an additional effect, the presence of infill panels is considered, in the perspective of retrofit solutions. More specifically, the possibility of increasing the capacity to horizontal actions by reinforcing the infilled frames or by introducing additional RC shear walls on the building perimeter is appraised. The second issue addressed in the dissertation is the definition of the most effective methodology to be used for identifying the structural response both in the elastic and inelastic field. After a review of the nonlinear methods of analysis provided by the scientific literature, both static and dynamic, the dissertation presents some applications of the pushover method, which is by far the most popular choice of practitioners. Firstly, an application of conventional pushover analysis is performed on a set of ideal buildings, with the aim of appraising the role of the control node position. Anyway, as highlighted by current technical laws (Italian building code and Eurocode 8), nonlinear static procedure cannot be always applied in its conventional formulation. In particular, some limitations arise in the presence of structural irregularities or in the cases where higher modes have a strong influence. With the aim to bridge these gaps, a solution can be represented by non-conventional methods as multimodal or adaptive pushover analysis. With regard to this question, a simplified multimodal pushover procedure is proposed in the dissertation. The main advantage of the proposal is represented by the easiness of application, thanks to the adoption of a single load profile in the computation, which is moreover an approach very familiar to practitioners. For assessing the reliability of the procedure, it is tested on a real case study characterized by relevant dynamic irregularity and a consistent inhomogeneity of in-situ materials. The final part of the dissertation is devoted to the possibility of extensively bringing the concepts at the base of Performance Based Earthquake Engineering (PBEE) to a wider audience of users, considering that this method has a high scientific relevance for the assessment of existing RC buildings. Generally, the application of PBEE needs a specialist knowledge about probability theories and about nonlinear modelling and analysis, which are skills not always common among practitioners. With the aim of reducing these obstacles, a methodology of nonlinear dynamic analysis is proposed, which consists in an application of the multi-stripe analysis on numerical models implemented through a commercial software. In particular, the new procedure, called Few Stripe Analysis (FSA), is applied on a sample of 15 existing RC school buildings (located in the province of Foggia, Southern Italy) and the results, in terms of damage states, are compared with the ones obtained from SPO2FRAG software, an userfriendly tool able to compute the fragility curves starting from pushover curves. Finally, a new simplified modelling procedure for estimating the global response of existing RC buildings is presented. It is able to produce 3D reduced-order models (characterized by very few degrees of freedom) starting from the geometrical and mechanical features of the case study. The main advantage of the present approach is to account for the effects predictable with MDoF models, but with low analysis time and computational efforts, with elevate convergence capacity, typical of the SDoF models. The performance of this simplified numerical modelling procedure has been tested by the application on the previously mentioned sample of school buildings and comparing the results, in terms of structural response, damage states and confidence levels, with the ones previously obtained from the application of FSA. The relevance and perspective impact of the research work here presented should be seen in the wider field of the vulnerability analysis of the building stock at the regional scale, which is a crucial issue for the scientific community and for the civil society. Governments and administrations are invested with the difficult task of providing mitigation strategies for the seismic risk for a very wide and inhomogeneous portfolio of buildings and the economic resources are often very limited. Therefore, the development of methods for estimating the vulnerability with limited data has been a subject of intense research activity. The framework that is depicted in the dissertation can provide a tool potentially very impactful, since it could allow, by the exploitation of the 3D Reduced Order Models combined with FSA, to overcome the well-known limitations of empirical vulnerability approaches in favor of mechanical based methods managed in a full probabilistic framework.

Tese de doutoramento em Civil Engineering
This PhD thesis presents a research work aiming at the development of a sustainable and multifunctional composite sandwich panel for the rehabilitation of reinforced concrete (RC) buildings from the 1960s to the mid-1980s. The sandwich panel retrofit solution developed in the thesis comprises four main components: (i) thin outer layers of Recycled Steel Fibre Reinforced micro Concrete (RSFRC); (ii) a lightweight core made of polystyrene; (iii) internally distributed glass fibre reinforced polymer (GFRP) connectors; and (iv) steel anchors for fixing the panel to the existing structure. The first part of this work’s experimental program encompassed pushout and pullout tests, carried out on reduced-scale specimens representative of the sandwich panel solution; these tests aimed at assessing the overall composite behaviour of the sandwich panel and analysing the influence of the type of core insulation layer, and of the anchoring conditions and diameter of the GFRP connectors. The tests showed that the adopted structural GFRP connectors are able to adequately ensure shear load transfer between RSFRC layers. The second part of the experimental program involved testing intermediate-scale RC frame specimens, representative of the target building typology, under in-plane cyclic loading conditions. The cyclic tests were performed on different variations of the referred RC frames: (i) a bare RC frame; (ii) an RC frame with a masonry infill wall; and (iii) an RC frame with the incorporation of the sandwich panel prototype developed in the scope of this research work. The results of the tests show that, in comparison with the traditional masonry infill wall solution, the proposed rehabilitation solution enabled a significant improvement of the RC frame’s cyclic performance, providing higher levels of load carrying capacity and energy dissipation. The numerical part of this study included numerical simulations conducted to assist the sandwich panel design process and, more specifically, the modelling of the failure mechanisms observed at the interface between the RSFRC layers and the polystyrene core; good agreement was obtained between experimental and numerical results, with important conclusions being drawn regarding the cohesion and friction angle between these components of the sandwich panel.
Esta tese apresenta um trabalho de investigação relativo ao desenvolvimento de um painel sanduíche compósito sustentável e multifuncional concebido para a reabilitação de edifícios porticados de betão armado (BA) construídos entre 1960 e meados da década de 1980. Este painel é composto essencialmente por quatro componentes principais: (i) finas camadas exteriores em microbetão reforçado com fibras de aço recicladas (BRFR); (ii) núcleo em poliestireno; (iii) conetores poliméricos reforçados com fibras de vidro (GFRP); e (iv) ancoragens metálicas para ligação do painel à estrutura a reabilitar. A primeira parte do programa experimental do presente trabalho envolveu a realização de ensaios de corte e ensaios de arrancamento em provetes de escala reduzida, representativos do painel em desenvolvimento; com estes ensaios, pretendeu-se avaliar o funcionamento compósito do painel através da análise da influência do tipo de camada de isolamento e do comprimento de ancoragem e diâmetro dos conetores em GFRP. Os resultados obtidos revelaram que os conectores em GFRP de cariz estrutural são eficazes na transmissão de esforços de corte entre as camadas de BRFR. A segunda parte do programa experimental consistiu na realização de ensaios cíclicos em pórticos de BA de escala intermédia, representativos da tipologia de edifícios a reabilitar. Os ensaios foram realizados utilizando três variantes dos referidos pórticos: (i) pórtico de BA isolado; (ii) pórtico de BA com parede de enchimento em alvenaria; e (iii) pórtico de BA reforçado com um protótipo do painel sanduíche desenvolvido no âmbito deste trabalho. Os resultados mostraram que, em comparação com a solução tradicional com enchimento em alvenaria, a solução de reabilitação proposta produziu uma melhoria significativa no comportamento cíclico do pórtico em termos de capacidade de carga e energia dissipada. A parte numérica do presente estudo incluiu a realização de simulações de apoio ao processo de dimensionamento do painel e, mais especificamente, no auxílio à interpretação do mecanismo de rotura observado na interface entre as lâminas de BRFR e o núcleo em poliestireno. Registou-se uma boa concordância entre as respostas numérica e experimental, o que permitiu obter conclusões importantes relativamente aos valores de coesão e ângulo de atrito que caraterizam a interface entre estes componentes do painel sanduíche.
Fundação para a Ciência e a Tecnologia (FCT)