Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 121-130). Also available via the Internet.

Although the knowledge and technology of seismic analysis and seismic risk assessment tools have rapidly advanced in the past several decades, current seismic design codes and damage estimation methods ignore the effect of successive earthquakes on structures. In light of recent strong seismic events, mainshock-damaged structures are shown to be more vulnerable to severe damage and collapse during subsequent events. The increase in vulnerability during aftershocks results in the likelihood of increased damage and loss-of-life and property. After a major earthquake, structural engineers must assess whether mainshock-damaged buildings can be re-occupied or not, with due consideration to the threat of aftershocks. The outcome of this post-earthquake inspection is utilized to quantifiably judge the current status of structures (so-called building tagging). This tagging criterion is closely related to the evaluation of the residual capacity of damaged buildings as well as the computation of the probability of being in a damage state after an aftershock (aftershock fragility). The increased vulnerability estimation associated with the additional damage plays a significant role in assessing potential losses to facilitate crucial decision making such as emergency response mobilization, inspection priority, recovery strategy, and re-occupancy decision. The main objective of this research is to develop a probabilistic framework for accounting for these increased vulnerabilities in terms of the extent of damage associated with mainshock ground motions. Aftershock fragility curves are developed accounting for both the uncertainty from the seismic hazard and the uncertainty from the structural capacity. This proposed approach also allows for the inherent variability, such as modeling characteristics associated with the design codes, present in non-ductile and ductile reinforced concrete frames found in California.

The recent earthquakes in Turkey have shown the poor seismic performance of reinforced concrete. This led to widespread utilization of several strengthening methods, each of which is convenient in different aspects. However, what is required to apply any of these methods is to evacuate the building in question since the interruptions are mostly within the building and to the structural members. This study proposes a method for external strengthening of typical five storey reinforced concrete buildings that represent the majority of the built environment in Turkey. The method suggests addition of shear walls, which are connected to each other by means of diaphragms on two floor levels, to the existing external columns at four corners of the building. The positive effect of shear walls in seismic performance is already known / however / basically, the aim of this study is to discuss the feasibility of the proposed method in terms of architectural viewpoint since the method unavoidably covers great modifications on the architectural form of the building. Hence, the research mostly explores whether it is possible to give the reinforced concrete residential buildings, which constitute the majority of the built environment especially after 1950s due to the unhealthy urbanization period in Turkey, a common characteristic appearance by means of external structural members. As a whole, proposing an external strengthening method that provides not to evacuate the space, the study searches to obtain a typical fa&ccedil / ade resemblance by means of additional structural members.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (M.E.)--University of Canterbury, 2005. / Typescript (photocopy). Includes bibliographical references (leaves 222-228). Also available via the World Wide Web.

No description available.

Interação solo-estrutura é o objeto de estudo deste trabalho. O principal objetivo é verificar a verdadeira importância desse fenômeno na análise estrutural de edifícios usuais em concreto armado sobre fundações diretas. Inicialmente apresenta-se um estudo sobre o comportamento do solo. Logo após são descritos os processos de dimensionamento de fundações superficiais, com base na NBR 6122 (1996). Descrevem-se em seguida os elementos barra e sapata rígida, utilizados na modelagem do sistema superestrutura-subestrutura-maciço de solos. Discute-se a modificação do elemento sapata rígida, que representa fundação e solo, para a consideração de uma camada indeslocável no interior do solo. De acordo com a teoria apresentada, dois exemplos são submetidos a duas análises, com ou sem a consideração da interação sol-estrutura, para que os resultados sejam comparados. Aplicam-se separadamente as ações verticais e horizontais. A influência duma camada indeslocável no interior do solo e os efeitos da seqüência construtiva dos edifícios também são analisados. / Soil-structure interaction is the subject of this work. The foremost aim is to verify the real importance of that phenomenon on the structural analysis of usual reinforced concrete buildings on shallow foundations. At first, it is presented a study of soil behaviour. Design procedures of shallow foundations based on NBR 6122 (1996) are described afterwards. Then, the beam and rigid footing elements, used for modelling the superstructure-infrastructure-foundation soil system, are described. It is discussed the modification of the rigid footing element, which represents foundation and soil, to consider a rigid layer within soil. According to the theory above presented, two examples are subjected to two analysis, with or without the consideration of soil-structure interaction, in order to compare the results. Vertical and horizontal loads are separately applied. The influence of a rigid layer within soil and the effects of the sequence of buildings construction are also analysed.

Structural fire design represents one important aspect of the design of reinforced concrete buildings. The work presented in this thesis seeks to elucidate the structural behaviour of reinforced concrete slabs during exposure to heating from below, as would occur in the case of a building fire, with a particular focus on structural fire modelling using finite element analysis. The focus in on validating finite element models against experimental results and quantifying the sensitivity of model outputs to relevant thermal and mechanical input parameters. A primary goal of the work is to provide recommendations to structural fire engineering analysts and designers considering the performance-based design of reinforced concrete slabs for structural fire resistance using available finite element software. A critical review of the available knowledge of the structural fire response of reinforced concrete structures in general and concrete slabs in particular is presented, along with an awareness as to the importance of understanding structural response of concrete structures exposed to fires. Current techniques for structural fire design of concrete structures are reviewed, and shortcomings highlighted. Available experimental data are presented, and various finite element models of these slabs are developed and interrogated to identify important aspects for understanding, as well as for future improvement of similar studies (both experimental and numerical) with the intention of supporting future progress in structural fire engineering, in particular as regards performance based structural fire design of concrete slabs. A range of thermal and mechanical parameters that are potentially important and influential in the structural fire design of reinforced concrete slabs is then studied, including: fire scenario, thermal properties of materials (thermal conductivity and specific heat), heat transfer parameters (coefficient of convection and emissivity) and assumptions, restraint conditions at the supports, variations of span-to-depth ratio, reinforcement detailing, as well as plan aspect ratio are all investigated; their influence on the structural fire response of reinforced concrete slabs is studied and discussed. A key issue in validating finite element models against experimental results lies in defining the temperature inputs to the structural finite element models correctly. Variation of available thermal and mechanical input parameters, as recommended in Eurocodes, influences the predictive performance of thermal and structural finite element models, however these are not the main contributing factors in obtaining a credible prediction of response from the finite element models. The most challenging aspect in performing heat transfer analysis for fire furnace tested reinforced concrete slabs lies in defining the correct thermal boundary condition. For simply supported one-way spanning and two-way spanning slabs, increasing slab's thickness (lowering span-depth ratio) does not improve fire resistance rating for the slabs when both limiting deflection criteria and limiting tensile plastic strain are set as acceptance criteria. Two-way slabs with higher span-depth ratio have better fire resistance ratings, judging from the overall trends and magnitudes of mid-span deflections. The formation of plastic hinges is likely to occur for one-way spanning slabs modelled with finite rotational spring stiffness at supports, but not for two-way spanning slabs. A yield line mechanism in two-way slabs means that the behaviour is more complex as compared to the simple flexural mechanism for one-way slabs. In one-way slabs, plastic hinges potentially occur at the location where top reinforcement is curtailed, highlighting the importance of properly understanding the nuances in response of concrete slabs in fire. Investigation of the influence of aspect ratio in two-way spanning slabs confirms that slabs with lower aspect ratios have better structural fire resistance than slabs with higher aspect ratios when both limiting deflection criteria and limiting tensile strain in reinforcing steel were used as the performance indicators. A combination of both limiting mid-span deflection criteria as well as limiting tensile plastic strain is recommended for specifying acceptance criteria for both one-way and two-way slabs, since it gives more accurate and comprehensive assessment on the structural response of the slabs under exposure to severe heating from below.

Interação solo-estrutura é o objeto de estudo deste trabalho. O principal objetivo é verificar a verdadeira importância desse fenômeno na análise estrutural de edifícios usuais em concreto armado sobre fundações diretas. Inicialmente apresenta-se um estudo sobre o comportamento do solo. Logo após são descritos os processos de dimensionamento de fundações superficiais, com base na NBR 6122 (1996). Descrevem-se em seguida os elementos barra e sapata rígida, utilizados na modelagem do sistema superestrutura-subestrutura-maciço de solos. Discute-se a modificação do elemento sapata rígida, que representa fundação e solo, para a consideração de uma camada indeslocável no interior do solo. De acordo com a teoria apresentada, dois exemplos são submetidos a duas análises, com ou sem a consideração da interação sol-estrutura, para que os resultados sejam comparados. Aplicam-se separadamente as ações verticais e horizontais. A influência duma camada indeslocável no interior do solo e os efeitos da seqüência construtiva dos edifícios também são analisados. / Soil-structure interaction is the subject of this work. The foremost aim is to verify the real importance of that phenomenon on the structural analysis of usual reinforced concrete buildings on shallow foundations. At first, it is presented a study of soil behaviour. Design procedures of shallow foundations based on NBR 6122 (1996) are described afterwards. Then, the beam and rigid footing elements, used for modelling the superstructure-infrastructure-foundation soil system, are described. It is discussed the modification of the rigid footing element, which represents foundation and soil, to consider a rigid layer within soil. According to the theory above presented, two examples are subjected to two analysis, with or without the consideration of soil-structure interaction, in order to compare the results. Vertical and horizontal loads are separately applied. The influence of a rigid layer within soil and the effects of the sequence of buildings construction are also analysed.

<p>Past earthquake damage assessments have shown the seismic vulnerability of older non-ductile reinforced concrete buildings. The life safety-risk these buildings pose has motivated researchers to study, develop, and improve modeling techniques to better simulate their behavior with the aim to prioritize retrofits.</p><p><br></p> <p>This study focuses on the lap splice detailing at the base of the building in columns, shorter than those recommended by modern codes which consider seismic effects. Current modeling efforts in non-ductile reinforced concrete frame structures have considered the connection at the foundation fixed. This study models the influence of the performance of short lap splices on the simulation of response of an instrumented perimeter-frame-non-ductile building located in Van Nuys, California, and to compare results with those of previous studies of the same building.</p><p><br></p> <p>The methodology consisted of evaluating the response of a non-ductile concrete building subjected to a suite of ground motions through the comparison of three base connections: fixed, pinned, and a rotational spring modeling the short lap splice. Comparison and performance evaluation are done on the basis of drift as the main performance metric. In the building response evaluation flexure and shear forces in frame elements were also compared using the different base conditions. </p><p><br></p> <p>The models consist of two-dimensional frames in orthogonal direction, including interior and exterior frames, totaling into 4 frames. The dynamic analysis was performed using SAP2000 analysis software. The proposed rotational spring at the base was defined using the Harajli & Mabsout (2002) bond stress – slip relationship and moment – curvature sectional analysis, applied to 24d_b and 36d_b lap splices. Deformation considered flexure and slip. Adequacy of shear strength was checked prior to the analysis to verify that shear failure did not occur prior to either reaching first yield of the column reinforcement or splice capacity. </p><p><br></p> In this study, the response of the frames using the proposed rotational spring model was found to be between the fixed and pinned base conditions with regard to roof displacement and interstory drift ratio, also termed as story drift ratio. The behavior of the frames changed depending on the yielding of the longitudinal reinforcement, as depicted by the interstory drift ratio and displacement. The performance of the building frames also depended on the ground motion. The N-S and E-W direction frame computational models considered three and four earthquakes, respectively, totaling to 14 computational models per base condition. Three computational models out of the 14 with the proposed rotational spring base condition simulated recorded roof displacement results with accuracy. In the frame simulations where yielding of most of the column longitudinal bars was not calculated, the maximum interstory drift occurred in the upper stories, matching column damage observations during the event. The findings of the study showed that short lap splice increases the drift and displacement compared to the fixed base supporting its effect, i.e. the behavior of a non-ductile reinforced concrete case study building to an earthquake.