Dissertations / Theses on the topic 'Dissipative brace'

Fast heat dissipation from brake discs is sought in current vehicles, where high power braking duties demand harmonic combination of strength, (undamped) disc mass and cooling abilities for a wide speed range. This work analyses the convective heat dissipation from ventilated brake discs and proposes means for its optimisation. The focus of research is the ventilation geometry of a standard brake disc with an outer diameter of 434mm and radial channels of 101mm in length. After analysing in detail data calculated with CFD simulations and from experimental work for various ventilation patterns, a parameter relating the local channel-averaged convective heat transfer coefficient to channel circumferential width, and radial location was derived. This new numerical parameter termed Flow Index, depicts graphically the link between channel geometry (width and position) to the heat transfer coefficient level attained. The FI was not only used as a tool to analyse the convective performance of conventional and new ventilation geometries, but it also allowed clear identification of changes necessary in the channel width in order to improve its convective heat transfer coefficients. New, optimised for convective heat transfer, ventilation geometries designed with the FI were achieved in this Thesis. Industrial (patenting) and academic applications are foreseen from the results of this Thesis and its future activities. Also, the work developed in this Thesis gives path and supporting frame for future research in the field of brake disc convective heat dissipation.

Despite many research pieces on brake systems, there is still research to be done on brake pad geometry and the dissipation of heat during brake engagements using the finite element analysis method. Brake application is a process in which the kinetic energy of the vehicle is mostly converted into thermal energy and then dissipated in the form of heat. Based on dynamometer test results it was seen that brake pad temperatures could reach up to 600° C [23]. Preliminary research using computer modeling software has shown that heat dissipation in brake pads with wavy geometries and air channels from the top to bottom is much better compared to pads that do not have those specific features. Brake pads that dissipate heat faster are prone to brake fade and other braking issues that may arise due to overheating [15]. For this research, two readily available brake pads and two designs of brake pads with new geometry were modeled using CAE software. Finite element analysis was then performed to test how well each brake pad dissipated heat after reaching brake fade temperatures. The readily available brake pads were from Power Stop and Wagner [26]. ANSYS Space Claim [25] was used to design and model the brake pads, ANSYS 18.2 [24] was used to perform the finite element analysis on the pads. After performing the analysis, results indicate that a brake pad with a design that had zones for turbulent air at ambient conditions and convection slots from the top to the bottom decreased in temperature by about 90° C more in the same time compared to the conventional design. By studying the changing values of the convection heat transfer coefficient with velocity, the placing of the turbulence zones can be more precise in order attain greater airflow to remove heat from the brake pad quicker.

L'elaborato di tesi tratta lo studio di un collegamento trave-pilastro di tipo semirigido dissipativo. L’idea progettuale alla base di tale studio è quella di posizionare nel nodo trave-pilastro di un telaio in acciaio una coppia di dispositivi metallici che durante il sisma si snervino prima dei pilastri. In tal caso infatti si concentrerebbe parte della dissipazione energetica in tali dispositivi ritardando la formazione delle cerniere plastiche alla base dei pilastri e preservando quindi questi ultimi dalla plasticizzazione. Lo studio è stato effettuato considerando come dispositivi metallici i Crescent Shaped Braces (CSB), dispositivi isteretici che, grazie alla loro configurazione geometrica, sono caratterizzati da un legame costituivo elastico-incrudente trilineare. A partire proprio da tale legame costitutivo (noto una volta ipotizzate le dimensioni e la sezione dei CSB) e dalla configurazione geometrica del nodo trave-pilastro, si è studiato il comportamento del collegamento fino alla determinazione del legame Momento-Rotazione: per ogni rotazione della trave rispetto al pilastro si ha infatti una reazione dei CSB che generano sulla trave un momento contrario alla rotazione stessa. Si è poi passati ad un particolare caso di studio, andando ad analizzare il beneficio in ambito sismico derivante dall’inserimento dei Crescent Shaped Brace nei nodi trave-pilastro di un telaio monopiano a singola campata in acciaio. Per verificare tale beneficio si sono eseguite delle analisi non lineari (statiche e dinamiche) su telai con e senza CSB e se ne sono confrontati i risultati.

In questa tesi si propone il miglioramento sismico di un capannone in calcestruzzo armato prefabbricato a due piani a pilastri isostatici mediante l'inserimento di controventi dissipativi in acciaio con forma speciale (Crescent-Shaped-Braces). PREMESSA In primo luogo si dimostra come la struttura studiata soddisfi già i requisiti del DM 2008, sia allo SLD (spostamenti d’ interpiano) che allo SLV (elementi strutturali verificati). OBIETTIVO Migliorare le caratteristiche prestazionali di un edificio in calcestruzzo armato prefabbricato a due piani, sottoposto ad azione sismica. STRATEGIA Inserimento di dispositivi dissipativi di tipo Crescent Shaped Brace in alcune specchiature del capannone prefabbricato, in entrambe le direzioni. PROGETTAZIONE DELLA STRUTTURA RINFORZATA 1) Identificazione delle caratteristiche (rigidezza e resistenza) dei dispositivi CSB, sulla base di obiettivi scalati al livello superiore (deformabilità allo SLV e resistenza allo SLC) per il sistema «struttura + dispositivi», attraverso lo sviluppo di una procedura specifica per capannoni prefabbricati a 2 piani. 2) Progettazione dei dispositivi CSB (scelta della geometria e della sezione) 3) Verifica delle effettive prestazioni ottenute mediante simulazioni numeriche time-history

Les instabilités vibratoires, telles que le crissement de frein, sont souvent étudiées par des analyses aux valeurs propres complexes sur des modèles éléments finis (EF). L'objectif de cette thèse est d'enrichir ces modèles en prenant en compte la viscoélasticité dont les effets sont l'amortissement et la rigidification des matériaux en fonction de la fréquence. Pour cela un viscoanalyseur a été développé. Il permet de caractériser en cisaillement les matériaux entre 100 et 3500Hz, sans utiliser les équivalences temps-température. Ce viscoanalyseur permet d'alimenter en paramètres le modèle rhéologique de Maxwell généralisé par le biais d'une nouvelle méthode d'identification particulièrement robuste. Le modèle de Maxwell généralisé est ensuite introduit dans les modèles EF grâce à un modèle d'état projeté sur un sous-espace adéquat. Ces modèles améliorés prédisent moins d'instabilités du fait de l'amortissement, mais ils montrent également que la viscoélasticité peut avoir des effets de déstabilisation du fait de la rigidification.

Elastoplastic energy dissipators are used in earthquake-resistant design in order to dissipate a substantial part of the seismic energy acting on a building. They are elements that are not part of the load-bearing structure and, therefore, are easily replaceable in case of damage. Their behaviour is usually stable and their degree of degradation difficult to appreciate visually. To assess their degree of degradation, damage indices are used which estimate their remaining dissipative capacity through the combination of a number of variables such as, for example, the number of cycles sustained and their amplitude, the energy dissipated, accumulated deformation and maximum deformation. In the first part of this doctoral thesis, the current state-of-the-art in terms of existing damage models is reviewed. The second part of this thesis brings together a wide experimental foundation based on data obtained in previous research works complemented with new tests carried out within the present thesis. In its third part, the validity of various fatigue models is assessed through the experimental foundation brought together in the second part of this thesis. In its fourth and final part, the validity of some of the best-known hysteretic models has been analyzed in order to reproduce the experimental response of the dissipators tested. Notable as the most important contribution of this thesis is the attainment of two models of mixed fatigue and dimensionless variables, which demonstrate excellent validity considering, in the same fatigue curve, dissipators of different types and geometry based on low carbon steel and uniform plastification in uniaxial states of stress
Els dissipadors d’energia elastoplàstics s’utilitzen en el disseny sísmic per dissipar una part substancial de l’energia sísmica introduïda en una construcció. Són uns elements que no formen part de l’estructura portant i, per tant, fàcilment reemplaçables en cas de quedar danyats. El seu comportament sol ser estable i el seu grau de degradació difícilment apreciable de forma visual. Per avaluar el seu grau de degradació es recorre als índex de dany, que estimen la capacitat dissipativa romanent a partir de la combinació de variables diverses com són, per exemple, el nombre de cicles suportats i la seva amplitud, l’energia dissipada, la deformació acumulada i deformació màxima. A la primera part d’aquesta tesi doctoral es revisa l’estat de l’art relatiu a models de dany existents. La segona part d’aquesta tesi recull una àmplia base experimental basada en dades obtingudes en treballs previs de recerca, complementats amb nous assajos realitzats a la present tesi. En una tercera part es valora la bondat de diversos models de fatiga mitjançant la base experimental recollida a la segona part. En la seva quarta i última part s’ha analitzat la bondat d’alguns dels models histerètics més coneguts per a reproduir la resposta experimental dels dissipadors assajats. La conclusió més important que s’extreu de la tesi és l’obtenció de dos models de fatiga mixtes i variables adimensionals, els quals demostren una excel·lent bondat considerant, en una mateixa corba de fatiga, dissipadors de diferent tipologia i geometria, basats en acers de baix contingut en carboni i plastificació uniforme en estat uniaxial de tensions
Programa de Doctorat en Tecnologia

碩士
國立交通大學
土木工程系所
107
Installation of displacement-dependent structural dampers will increase the stiffness of the entire structure, change its fundamental period and, as a consequence, affect the seismic design load. In light of the fact that design of seismic dampers cannot be independent of the structures, this study develops a damper design procedure that takes into account the structural system as a whole to serve as reference hopefully for practical application. This thesis proposes a two-stage damper design procedure including the preliminary design and detail design. Firstly, the ultimate displacement of the damper is defined in terms of the story-drift ratio of the structure. The yielding displacement of the damper is then calculated by dividing the ultimate displacement with the ductility estimated empirically. Since the maximum story shear occurs always in the first story where the damper tends to yield and be damaged first, damper for the first story are chosen as the design object in this study. The design target is set to be the concurrence of the ultimate displacement of the damper and the story-drift under the seismic design load required by the code. As the seismic design load is related to the fundamental period of structure which in turn is affected by the interaction between the structure and dampers, the initial stiffness of the damper in the preliminary design stage cannot be determined directly. An iterative process therefore is required by first wild guessing an initial stiffness of the damper and updating it iteratively until convergence of the ultimate displacement of the damper to the story-drift of the structure. The corresponding initial stiffness of the damper so determined will be the basis for the detail design of the damper at the next stage. The detail design then is based on the process developed earlier for the in-plane oval damper by the NCTU research team. Moreover, application of the proposed methodology for damper design has been illustrated using a five-story steel modal structure as the object while a series of shake table tests has been conducted accordingly. This thesis explores the seismic performance of the dampers corresponding to different ultimate displacements under El Centro, Chi-Chi and Kobe Earthquakes of various seismic intensities. Simulation results indicate that the seismic performance of the damper is earthquake-dependent that the optimal damper design may vary from one earthquake to another. Upon overall considerations, the ultimate displacement of the damper corresponding to 1% story-drift ratio is selected as the control device for the shaking table tests. The dampers are connected to the structure via H-beam in form of energy-dissipative braces. Results of shaking table tests indicate that, with dampers implemented, significant reductions in acceleration responses for all floors of the structure have been achieved. The control efficiency increases with the intensity of the input excitation as larger responses extend the yielded area of the steel plates and therefore enhance the control effect. The control effect is even more pronounced in terms of the root-mean-square responses (RMS) as the RMS acceleration is proportional to the vibrating energy which is accumulated over the entire earthquake process and reflects better the performance of overall response decay. Simulation analysis is well correlated with the test results, including the proposed damper design methodology is reasonable and the ETABS is reliable as a tool for structural assessment.

Earthquake-prone regions of the world are usually characterized by a high number of Reinforced Concrete (RC) buildings designed before seismic building codes were enforced. As a result, the amount of existing RC buildings requiring seismic assessment and likely retrofitting is large. The use of innovative techniques for the seismic amelioration of existing RC buildings has been attracting the attention of both academic and technical communities since the second half of the previous century. Among these techniques there is the employment of passive energy dissipating devices that are mounted in series to metallic braces installed within the existing RC frames. Such energy dissipating devices can be 1) fluid-viscous, 2) viscoelastic, 3) elasto-plastic, 4) frictional or 5) based on shape-memory alloys. The large number of devices available on the market is not accompanied yet, at least within the Italian Building Code, by a mature and detailed description of the design procedure, so that the practicing engineer who would like to adopt this technique is often referred to scientific publications. With the aim to contribute to fill this gap, an energy-based methodology is proposed and applied and compared with some of the most innovative design procedures available in the scientific literature to date. The validity of each procedure is appraised on the basis of non-linear static and non-linear dynamic analysis results.

碩士
國立臺灣大學
土木工程學研究所
100
Self-Centering Energy Dissipative Brace is a kind of brace which uses tendons to constrain compression elements of the brace and provide self-centering properties under tension and compression force (restore to zero residual deformation). Traditional self-centering energy dissipative brace’s deformation capacity relies on the elastic deformation capacity of the tendons used inside the brace, and results in limitation of the braces’ deformability. Traditional SCED brace has a maximum strain of 1.3% when the tendons reach 1.9% strain and the frame reaches 2% inter-story drift. Tendons required to have large elastic strain mainly uses composite material. However, tendons having over 2% elastic strain material properties are rare and seldom used or researched. This research develops a new kind of SCED brace by adding a second core element and another group of tension elements which doubles the deformation capacity compared to traditional SCED brace while using tension elements comprised of the same material properties (or largely reduce the elastic strain demand of the tendon elements to 1% under the same brace deformation when compared to traditional SCED brace). This research designed four specimens to validate the double core SCED brace which uses different materials for its tendons. Four specimens’ tendon uses D16 steel strand, D22 glass fiber, D29 glass fiber and D13 carbon fiber respectively. The results show that the mechanism of double core SCED brace is consistent with prediction. The test results and prediction of tendon strain is close which is 0.8%, 1.05%, 0.9% and 1.09% for specimen 1 to 4 respectively while the brace has a 1.2% strain corresponding to 2% inter-story drift. The result shows that double core SCED brace can significantly reduce the demand for tendon elastic strain. Except specimen 1 due to loss of pre-tension force has poor behavior in self-centering, specimen 2 to 4 have good behavior in self-centering with no pre-tension loss. This research also uses the finite element software ABAQUS to analyze double core SCED brace behavior and compare with the testing results which is proved similar. The parametric study of double core SCED brace we choose different pre-tension force, different friction force, and different tendons to observe the difference in brace behavior. Results indicate that the lager the friction force is the larger the energy dissipation there will be, yet in order to have full self-centering behavior, the pre-tension force should be larger than friction force. However the larger the pre-tension force is the smaller the deformation capacity there is left. Unlike pre-tension force and friction force, the difference of tendons only effect the post-stiffness of the response and limits the deformation capacity due to its limitation in elastic strain.

碩士
國立臺灣大學
土木工程學研究所
89
In recent years, a number of researches have revealed that the buckling restrained braced frame (BRBF) is an effective system for server seismic application. Buckling restrained bracing (BRB) members can be conveniently made from various kinds of structural steel shapes encased in steel tube and confined by infill concrete. When the brace is subjected to compressions, an unbonding material placed between the core bracing and the concrete infill is required in order to reduce the friction while restrain the bracing from buckling. 　In this research, a combined experimental and analytical research program has been conducted in order to investigate the effectiveness of various kinds of unbonding material, the brace-to-gusset connection details, and the design procedures for the BRBFs. A total of sixteen BRB specimens were fabricated and tested in National Taiwan University. Test results of ten single cross-shaped BRB specimens indicate that the 2mm thick silicon rubber sheets are most effective in minimizing the difference between the peak compressive and tensile strengths of the BRB members. Test results of six additional specimens suggest that the proposed BRB member employing steel double-T and twin steel tubes can stably sustain severe cyclic axial load reversals. Moreover, the proposed BRB members can be conveniently connected to the gusset plate in the same manner as that in the traditional double-T brace to gusset plate connections. 　These cyclic load test results have also made the implementation of a nonlinear brace element a success in a separate study on the development of a general purpose nonlinear structural analysis computer program. In this research, design examples are given for a six-story concentrically braced frame considering various stiffness ratios between the BRB member and the frame. Analytical results demonstrate that the BRB members can effectively dissipate seismic energy and reduce the nonlinear demands imposed on the beams and columns. This research concludes with the procedures and recommendation for the seismic resistant design of BRBFs.

碩士
國立臺灣大學
土木工程學研究所
106
Earthquake-resisting frame systems that are designed based on current seismic provisions provide life safety performance in a large earthquake, but may have significant structural damage or residual drift due to large energy dissipation in designated structural members. The damage leads to difficult or expensive to repair after a large earthquake. Therefore, the development of a structural system that has both energy dissipation and self-centering properties in earthquakes is needed to improve the seismic performances of buildings. This new invention in presents a viable solution that was validated by multiple cyclic tests of an innovative brace, called a self-centering brace with energy-dissipating bars (SCB+EDB). The proposed brace combines the self-centering property of a dual-core self-centering brace (DC-SCB) and the energy dissipation of a steel bar confined with a buckling-restrained tube. The difference in the SCB+EDB and the DC-SCB is that a friction-resistant device in the DC-SCB is substituted by an energy-dissipating bar with a buckling-restrained tube. The advantage of the SCB+EDB compared to the DC-SCB is easy to assemble and repair. A 6500 mm-long SCB+EDB, which uses ASTM A572 Gr. 50 steel as bracing members, ASTM A416 Grade 270 steel tendons as tensioning elements and CNS SD420 steel bars as energy-dissipative bars, was cyclically tested to validate its kinematics and cyclic performance. The test program demonstrated that the proposed novel SCB+EDB provides stable hysteretic response with appreciable energy dissipation, self-centering behavior and large deformation capacity before failure.

碩士
國立交通大學
土木工程系所
96
Buckling is usually conceived as an unstable structural behavior leading to lateral instability of axially loaded members if not properly supported. However, if a buckled strut is deformed in a guided direction and range, geometrical large lateral deformation of the steel struts in buckling will lead to inelastic behavior of the material and dissipate energy as a consequence. The purpose of this study is to develop a new type of seismic damper, named ductile braces, based on the concept of the geometrical deformation and the inelastic behavior of the material of the buckled strut. The energy-dissipative characteristics of buckled struts are investigated via full-scale component tests under cyclic loads. Experimental results indicate that, the force-displacement relationship of buckled struts exhibits mechanical characteristics of displacement-dependent dampers and the nature non-symmetric behavior of buckled strut is in non-symmetric layout. Numerical prediction of the component test result is further conducted using ANSYS with a non-linear model of the buckled strut. It is observed that the actual boundary condition of the tested buckled strut is in between those of the fixed and hinged conditions. The connection of buckled strut by bolts is not perfectly clamped as ideally, and the yielding behavior of the material is not as significant as expected. However, excellent control performance of the ductile braces in present design has been confirmed via a series of seismic performance tests. In practical application, energy-dissipative capacity of the buckled strut may be improved if the end connection could be welded in addition to bolting to make it closer to a clamped condition.

The self-centering energy dissipative (SCED) brace is an innovative cross-bracing system that eliminates residual building deformations after seismic events and prevents the progressive drifting that other inelastic systems are prone to experience under long-duration ground motions. This research improves upon the design and use of SCED braces through three large-scale experimental studies and an associated numerical building model study. The first experimental study increased the strength capacity of SCED braces and refined the design procedure through the design and testing of a new high-capacity full-scale SCED brace. This brace exhibited full self-centering behaviour and did not show significant degradation of response after multiple earthquake loadings. The second experimental study extended the elongation capacity of SCED braces through the design and testing of a new telescoping SCED (T-SCED) brace that provided self-centering behaviour over a deformation range that was two times the range that was achieved by the original SCED bracing system. It exhibited full self-centering in a single storey full-scale frame that was laterally deformed to 4% of its storey height. The third experimental study confirmed the dynamic behaviour of a multi-storey SCED-frame in different seismic environments and confirmed the ability of computer models of differing complexity to accurately predict the seismic response. To achieve these goals, a three-storey SCED-braced frame was designed, constructed, and tested on a shake table. Lastly, a numerical six-storey SCED-braced building model was constructed. This model used realistic brace properties that were determined using a new software tool that simulates the full detailed mechanics of SCED and T-SCED braces. The building model showed that initial SCED brace stiffness does not have a significant effect on SCED frame behaviour, that T-SCEDs generally perform better than traditional SCEDs, and that the addition of viscous dampers in parallel with SCED braces can significantly reduce drifts and accelerations while only causing a small increase in the base shear.

Concentrically braced frames, CBFs, are the most popular systems used in seismic areas in Canada, due to their large stiffness. However, after braces buckle in compression, their stiffness is significantly reduced and their hysteresis response, displayed in terms of force-displacement, shows an asymmetric behavior. To overcome this drawback, researchers proposed to add fuses that were conceived to be installed either in braces or brace-to-frame connections. The purpose of these fusses is to dissipate the earthquake input energy, while preserving braces to respond in elastic range. In this thesis, a new type of fuse, designed to be installed in brace-to-frame connections, is proposed. This device is labeled dissipative pin connection. Depending on the level of axial tension/ compression force that has to be transferred from the brace to the connection, this device can be manufactured in single-pin, double-pin and multi-pin configurations. The objective of this thesis was two-fold: i) to develop design rules for double-pin connections displayed in-line and in-parallel and ii) to study the seismic response of a 4-storey CBF building with and without dissipative connections, located in Victoria, BC. In this thesis, the computations were carried out by means of OpenSees (open system for earthquake engineering simulation). The numerical model developed for single-pin connection was calibrated based on experimental tests carried out at the Technical University of Lisbon. Similarly, the double-pin connection was calibrated using the same approach. Based on experimental test results conducted on single pin connections, design rules were proposed. It was concluded that by doubling the pin member and employing the parallel configuration, the load-carrying capacity of the dissipative connection increases two times, while the deflection is similar to that experienced by an equivalent single-pin device. The second part of this thesis emphasizes comparative results, in terms of seismic response of a 4-storey CBF building with and without dissipative connections. Building design was conducted according to S16-2009 and NBCC 2010 provisions. The seismic response was studied under two sets of ground motions that are representative for Victoria, BC: crustal and subduction events. The results have shown that forces generated in structural members were reduced due to an increase in building period and system ductility. Thus, by lowering the axial force developed in the CBF columns, a reduction of foundation size can be achieved which implies reduction in the overall building cost. The effect of earthquake type on the building response is also discussed. However, to prove the efficiency of double-pin connections displayed in-line and in-parallel, further experimental tests are required.

碩士
國立中央大學
土木工程學系
107
This study focused on the performance evaluation and FEM analysis of steel knee braced frames with curved dampers. The purpose of this study is to prevent the formation of plastic hinges on the beam of traditional knee braced frames. Hence, a new design was proposed. In order to validate the effectiveness of the proposed knee braced frames, a series of cyclic loading tests with various damper dimensions were conducted. According to the experimental results, this design could maintain the main structures in elastic stage. Also, the results showed that significant improvement could be achieved by adding steel curved dampers to the knee braced frames. To be more specific, the strength and stiffness of the proposed design were effectively enhanced. Therefore, the applicability of this design was verified through experimental and numerical studies of the test frames.