Seismic rehabilitation of structural systems is an effective approach for reducing potential seismic losses such as social and economic losses. However, little or no effort has been made to develop a framework for making decisions on seismic rehabilitation of structural systems that systematically incorporates conflicting multiple criteria and uncertainties inherent in the seismic hazard and in the systems themselves. This study develops a decision support framework for seismic rehabilitation of structural systems incorporating uncertainties inherent in both the system and the seismic hazard, and demonstrates its application with detailed examples. The decision support framework developed utilizes the HAZUS method for a quick and extensive estimation of seismic losses associated with structural systems. The decision support framework allows consideration of multiple decision attributes associated with seismic losses, and multiple alternative seismic rehabilitation schemes represented by the objective performance level. Three multi-criteria decision models (MCDM) that are known to be effective for decision problems under uncertainty are employed and their applicability for decision analyses in seismic rehabilitation is investigated. These models are Equivalent Cost Analysis (ECA), Multi-Attribute Utility Theory (MAUT), and Joint Probability Decision Making (JPDM). Guidelines for selection of a MCDM that is appropriate for a given decision problem are provided to establish a flexible decision support system. The resulting decision support framework is applied to a test bed system that consists of six hospitals located in the Memphis, Tennessee, area to demonstrate its capabilities.

Unreinforced masonry (URM) construction, which has been widely used in the United States, presents a large threat to life safety and regional economic development because of its poor seismic resistance. In this research, the nonlinear seismic properties of URM structures were investigated via a quasi-static test of a full-scale two-story URM building and associated analytical and numerical studies. The tests of the 24ft. by 24ft. in plan 22ft. high URM building revealed that the damage was characterized by (1) the formation of large discrete cracks in the masonry walls and (2) the rocking and sliding of URM piers. Both of these results were consistent with the predictions based on individual component properties obtained in previous research. However, the tests also revealed significant global behavior phenomena, including flange effects, overturning moment effects, and the formation of different effective piers in a perforated wall. This global behavior greatly affected the response of the URM building tested. In order to understand the nonlinear behavior of the test structure, a series of analytical studies were conducted. First, at the material level, a mechanical key model was proposed to describe the failure of URM assemblages under a biaxial state of stress. Second, at the component level, an effective pier model was developed to illustrate the mixed failure modes of a URM pier and its nonlinear force-deformation relationship. Third, at the structure level, a nonlinear pushover model was built using the mechanical models at the material and component levels to describe the nonlinear properties of a URM building. This nonlinear pushover model and a three-dimensional finite element model were employed to analyze the test structure. Both gave results in good agreement with the test data. Improvements to current provisions for the evaluation of existing masonry structures were proposed.

Earthquake ground motion can induce out-of-phase vibrations between adjacent structures due to differences in dynamic characteristics, which can result in impact or pounding of the structures if the at-rest separation is insufficient to accommodate the relative displacements. In bridges, seismic pounding between adjacent decks or between deck and abutment can result in localized deck damage, bearing failure, damage to shear keys and abutments, and even contribute to the collapse of bridge spans. This study investigates pounding in bridges from an analytical perspective. A simplified nonlinear model of a multiple-frame bridge is developed in MATLAB incorporating the effects of inelastic frame action, nonlinear hinge behavior and abutments. The equations of motion of the bridge response to longitudinal ground excitation are assembled and solved using the fourth-order Runge-Kutta method. Pounding is simulated using contact force-based models such as the linear spring, Kelvin and Hertz models, as well as the momentum-based stereomechanical method. In addition, a Hertz contact model with nonlinear damping (Hertzdamp model) is also introduced to model impact. The primary factors controlling the pounding response are identified as the frame period ratio, ground motion effective period ratio, restrainer stiffness ratio and frame ductility ratio. Pounding is most critical for highly out-of-phase frames. Impact models without energy dissipation overestimate the stiff system displacements by 15%-25% for highly out-of-phase, elastic systems experiencing moderate to strong ground excitation. The Hertzdamp model is found to be the most effective in representing impact. Traditional column hysteresis models such as the elasto-plastic and bilinear models underestimate the stiff system amplification and overestimate the flexible system amplification due to impact, when compared with stiffness and strength degrading models. Strength degradation and pounding are critical on the stiff system response to near field ground motions, for highly out-of-phase systems. Current design procedures are adequate in capturing the nonlinear hinge response when the bridge columns are elastic, but require revisions such as the introduction of time dependent reduction factors, and a frame design period to work for inelastic situations. Finally, a bilinear truss element with a gap is proposed for implementing energy dissipating impact models in commercial structural software.

Shape memory alloys are a class of alloys that display the unique ability to undergo large plastic deformations and return to their original shape either through the application of heat (shape memory effect) or by relieving the stress causing the deformation (superelastic effect). This research takes advantage of the unique characteristics of shape memory alloys in order to provide a moment resisting connection with recentering capabilities. In this study, superelastic Nitinol, a nickel-titanium form of shape memory alloy that exhibits a flag-shaped stress versus strain curve, is used as the moment transfer elements within a partially restrained steel beam-column connection. Experimental testing consists of a one-half scale interior connection where the loading is applied at the column tip. A pseudo-static cyclic loading history is used which is intended to simulate earthquake loadings. The energy dissipation characteristics, moment-rotation characteristics, and deformation capacity of the connection are quantified. Results are then compared to tests where A36 steel tendons are used as the moment transfer elements. The superelastic Nitinol tendon connection showed superior performance to the A36 steel tendon connection, including the ability to recenter without residual deformation.

This thesis investigates the performance of concentrically braced zipper frames through complementary experimental and numerical simulation approaches and proposes a design methodology for an innovative bracing scheme labeled as the suspended zipper frame. The suspended zipper frame intends to ensure that the top-story hat truss remains elastic, resulting in very ductile behavior of the structure. In the first part of the work, a three-story prototype frame was designed based on a preliminary design method. Three tests were conducted on one-third scale models of this prototype to verify the design procedure and assess the system performance under very different load histories. Comparisons of the results between analyses and experiments validated the partial-height zipper mechanism envisioned, and led to refinements of the design procedure and establishment of appropriate design details for these frames. The design and performance of this structural system are illustrated with three-, nine-, and twenty-story buildings designed for the same masses as those used in the SAC studies for the Los Angeles area. The proposed design strategy results in suspended zipper frames having more ductile behavior and higher strength than typical zipper frames. In addition, the suspended zipper frames also appear to reduce the tendency of chevron-braced frames to form soft stories and to improve seismic performance without having to use overly stiff beams. Finally, an explanation of the design philosophy as well as code language format of the design procedure is given.

In Turkey, most of the existing buildings are vulnerable to earthquakes due to their poor material quality and inaccurate design. Besides, so many destructive earthquakes occurred in the past, because Turkey is located on a seismically active region. Therefore, existing buildings should be assessed and necessary precautions should be taken before a probable earthquake. To assess seismic performance of the existing buildings, the 2007 Turkish Earthquake Code offers two methods which are linear and nonlinear. For linear assessment, members are controlled by comparing the force demands and capacities where for nonlinear assessment, strains corresponding to the plastic rotations of the members are compared with the limits given in the code. In this study, the building, which stands in Bakirk&ouml / y district of istanbul, was assessed according the linear elastic and nonlinear static procedures given in the 2007 Turkish Earthquake Code. In addition, it was retrofitted by adding shear walls to the structural system and same assessment procedures were performed. In the last case study, building is re-designed according to the code and re-assessed. Comparative results and conclusions were summarized in the last chapter.

Today the vast majority of urban population in Turkey is living in multi-story apartment blocks constructed of reinforced concrete due to the fact that in the late 19th century concrete and steel took the place of traditional materials such as masonry. However, it cannot be denied that masonry is still a crucial material for load bearing walls, internal walls and cladding of buildings. In addition to this masonry construction system has many advantages. From the architectural point of view, it provides flexibility in plan, spatial composition, wide variety of colours and textures and an impressive appearance for external walls. From the construction point of view, masonry system eliminates the cost of the frame because the structure is also the enclosing wall. In spite of these advantages, until recently, masonry was not considered to be a convenient material for building construction in seismic zones of Turkey. Thus, in 1950&rsquo / s for the residential building reinforced concrete started to be used as a construction material in every region of Turkey. This building material first became popular and was widely used but after a short while it was also used in smaller cities. Before the construction of reinforced concrete residential buildings each of these small-scale cities had their own local characteristics but after a rapid urbanization period all of these cities became similar to each other. Therefore, in this study firstly residential building typologies in some small-scale cities (Bolu, D&uuml / zce, &Ccedil / ankiri, &Ccedil / orum, Kastamonu, Kirikkale) are investigated and for these cities 4-storey masonry residential buildings is proposed instead of multi-story reinforced concrete apartment blocks. Here, it is aimed to enliven the use of masonry again in these regions. To achieve this aim it is necessary to verify the fact that it is possible to construct a four-story residential building with masonry bearing walls instead of reinforced concrete beam and column skeleton system keeping the existing plan scheme in other words without changing its architectural characteristics. In order to do this, 3D models are created to compare the behaviours of the masonry building and reinforced concrete building. The behavioural investigation of the two models is performed in the finite element platform with the help of SAP 2000. Finally it is certified that this proposal is successfully efficient.

Although there exist some consensus regarding seismic soil liquefaction assessment of free field soil sites, estimating the liquefaction triggering potential beneath building foundations still stays as a controversial and difficult issue. Assessing liquefaction triggering potential under building foundations requires the estimation of cyclic and static stress state of the soil medium. For the purpose of assessing the effects of the presence of a structure three-dimensional, finite difference-based total stress analyses were performed for generic soil, structure and earthquake combinations. A simplified procedure was proposed which would produce unbiased estimates of the representative and maximum soil-structure-earthquake-induced iv cyclic stress ratio (CSRSSEI) values, eliminating the need to perform 3-D dynamic response assessment of soil and structure systems for conventional projects. Consistent with the available literature, the descriptive (input) parameters of the proposed model were selected as soil-to-structure stiffness ratio, spectral acceleration ratio (SA/PGA) and aspect ratio of the building. The model coefficients were estimated through maximum likelihood methodology which was used to produce an unbiased match with the predictions of 3-D analyses and proposed simplified procedure. Although a satisfactory fit was achieved among the CSR estimations by numerical seismic response analysis results and the proposed simplified procedure, validation of the proposed simplified procedure further with available laboratory shaking table and centrifuge tests and well-documented field case histories was preferred. The proposed simplified procedure was shown to capture almost all of the behavioral trends and most of the amplitudes. As the concluding remark, contrary to general conclusions of Rollins and Seed (1990), and partially consistent with the observations of Finn and Yodengrakumar (1987), Liu and Dobry (1997) and Mylonakis and Gazetas, (2000), it is proven that soil-structure interaction does not always beneficially affect the liquefaction triggering potential of foundation soils and the proposed simplified model conveniently captures when it is critical.

Cities in Turkey are great risk pools. Underqualified building stocks are the major components of such risk pools. For the mitigation of risks, &#039 / engineering approach offers retrofitting of individual buildings as an ultimate method. However, this proposition has economic and legal difficulties. Instead, it is essential to develop new policies to focus on areas of high earthquake risk as comprehensive urban regeneration activities. This new policy requires new tools to monitor urban regeneration processes. It is obligatory to make comprehensive plans for high risk areas and to take low income groups into consideration in mitigation action plans. Comprehensive regeneration in existing districts could provide means and standards of safety not necessarily maintained by the retrofitting of individual buildings. Potentials of regeneration processes are readily observed and practiced in Turkey as means of regulating urban regeneration processes, even if for purposes other than safety. Analysis of a set of regeneration projects selected from world experience indicates that current regeneration practice in Turkey is far from a comprehensive approach. Municipalities are fully empowered to designate regeneration areas and carry out redevelopment activities often providing increased dentsities on compensate for the costs. This has been reinstated in the new draft law. Rather than a separate law, general regulation of regeneration could be accommodated in the Development Law 3194. A special Law concerning regeneration could instead focus only on risk reduction issues in cities throughout Turkey. The identification of priorities for such regeneration processes could be made by the Ministry of Public Works and Settlement as the central authority, clarifying the scale and timing of each project. The implementation tools of urban regeneration and issues like authorization, responsibility, funding, and auditing could be determined in this special law. A new approach for urban regeneration is needed to describe organizational, participatory, financial framework.

An analytical study was performed to evaluate the effect of shear wall ratio on the dynamic behavior of mid-rise reinforced concrete structures. The primary aim of this study is to examine the influence of shear wall area to floor area ratio on the dynamic performance of a building. Besides, the effect of shear wall configuration and area of existing columns on the seismic performance of the buildings were also investigated. For this purpose, twenty four mid-rise building models that have five and eight stories and shear wall ratios ranging between 0.51 and 2.17 percent in both directions were generated. These building models were examined by carrying out nonlinear time-history analyses using PERFORM 3D. The analytical model used in this study was verified by comparing the analytical results with the experimental results of a full-scale seven-story reinforced concrete shear wall building that was tested for U.S.-Japan Cooperative Research Program in 1981. In the analyses, seven different ground motion time histories were used and obtained data was averaged and utilized in the evaluation of the seismic performance. Main parameters affecting the overall performance were taken as roof and interstory drifts, their distribution throughout the structure and the base shear characteristics. The analytical results indicated that at least 1.0 percent shear wall ratio should be provided in the design of mid-rise buildings, in order to control observed drift. In addition / when the shear wall ratio increased beyond 1.5 percent, it was observed that the improvement of the seismic performance is not as significant.