A numerical study has been undertaken to evaluate the response of dual systems which consist of steel plate shear walls and moment resisting frames. The primary objective of the study was to investigate the influence of elastic base shear distribution between the wall and the frame on the global system response. A total of 10 walls and 30 wall-frame systems, ranging from 3 to 15 stories, were selected for numerical assessment. These systems represent cases in which the elastic base shear resisted by the frame has a share of 10%, 25%, or 50% of the total base shear resisted by the dual system. The numerical study consisted of 1600 time history analyses employing three-dimensional finite elements. All 40 structures were separately analyzed for elastic and inelastic response by subjecting to the selected suite of earthquake records. Interstory drifts, top story drift, base shears resisted by the wall and the frame were collected during each analysis. Based on the analysis results, important response quantities such as the response modification, the overstrength, the displacement amplification and ductility reduction factors are evaluated herein. Results are presented in terms of several measures such as the interstory drift ratio and the top story drift ratio. A discussion related to the influence of load share on the response factors is given.

Structural analysis of highway bridges using complicated 3-D FEMs to determine live load effects in bridge components is possible due to the readily available computational tools in design offices. However, building such complicated 3-D FEMs is tedious and time consuming. Accordingly, most design engineers prefer using simplified 2-D structural models of the bridge and live load distribution equations (LLDEs) available in current bridge design codes to determine live load effects in bridge components. Basically, the live load effect obtained from a 2-D model is multiplied by a factor obtained from the LLDE to calculate the actual live load effect in a 3-D structure. The LLDE available in current bridge design codes for jointed bridges were also used for the design of straight and skewed integral bridges by bridge engineers. As a result, these bridges are either designed conservatively leading to additional construction cost or unconservatively leading to unsafe bridge designs. Recently, LLDEs for integral bridges (IBs) with no skew are developed. To use these equations for skewed integral bridges (SIBs) a correction factor is needed to multiply these equations to include the effect of skew. Consequently, in this research study, skew correction factors for SIBs are developed. For this purpose, finite element models of 231 different three dimensional and corresponding two dimensional structural models of SIBs are built and analyzed under live load. The analyses results reveal that the effect of skew on the distribution of live load moment and shear is significant. It is also observed that skew generally tends to decrease live load effects in girders and substructure components of SIBs. Using the analyses results, analytical equations are developed via nonlinear regression techniques to include skew effects in the LLDEs developed for straight IBs. The developed skew correction factors are compared with FEAs results. This comparison revealed that the developed skew correction factors yield a reasonably good estimate of the reduction in live load effects due to the effect of skew.

Seismic resistance of many buildings in Turkey is insufficient. Strengthening using R/C infills requires huge construction work. Feasible, easy strengthening techniques are being studied in Structural Mechanics Laboratory of METU. In this project, it was aimed to develop an economical strengthening method. This method is based on addition of steel fibers and/or PP fibers in mortar and application of mortar on masonry wall. Project was sponsored by the Scientific and Technical Research Council of Turkey (T&Uuml / BiTAK). Physical properties of cement, aggregate, and mortar used in tests were determined by material tests. After performing flexural strength and compressive strength tests, optimum mortar was obtained. R/C frames strengthened by applying the mortar to brick infilled walls were tested under reversed cyclic loads. Before the frame tests, two series of panel tests were performed to correctly model strengthened infill walls and to gather information about behavior of walls under load. Totally 10 frame tests were done. 4 tests were done as reference tests, and other 6 were done as strengthened frame tests. In the analytical part of study, the plastered hollow brick infill wall strengthened by FRM was modeled as two separate compression struts. First strut was used to model the plastered hollow brick infill wall. Second strut was used to model the FRM. This technique is effective in improving seismic behavior by increasing strength, initial stiffness, energy dissipation, and ductility. Moreover, the method provides strengthening of the buildings without evacuating the structure.

Chevron braced steel frames require large beams to redistribute the unbalanced vertical forces exerted on the beams after brace buckling. A new frame configuration similar to chevron brace was proposed in literature, where zipper columns were attached between mid-spans of the beams from second to top story. During severe ground motion, the unbalanced vertical forces caused by buckling of lower story braces are in this case redistributed to the upper story braces by these zipper columns. Consequently, all story braces buckle successively from first to top story brace instead of concentration of inelastic action in one story. This system has been improved recently by adding an elastic hat truss between the top two stories to prevent formation of a full zipper mechanism and to prevent collapse. Two-phase numerical study is undertaken in this study to evaluate the response of chevron and suspended zipper braced frames, where the objective of the first phase is to observe the change in the performance of the configurations for different sets of initial imperfection and rotational spring stiffness values. Rotational springs are added at the end nodes of the braces to represent the effects of gusset plates and initial imperfection is assigned to the mid-length of the braces to achieve proper buckling behavior. The objective of the second phase is to compare the response of chevron and suspended zipper brace frames. For this purpose, three, nine and twenty-story buildings are designed for both brace configurations. The designed buildings are analyzed under static and dynamic loadings.

There is a large building stock in seismic regions of Turkey that require seismic upgrades. In order to minimize the disturbance to occupants and not to intervene with the functioning of the building, external strengthening methods can be preferred among different alternatives. This study reports the experimental findings on the upgrading of deficient reinforced concrete frames with external installed structural components. Specimens strengthened with an externally reinforced concrete shear wall, external steel frames, steel plate shear wall and one as-built reference 1/3-scale portal frame specimens were tested under constant gravity load and increasing cyclic displacement excursions. The RC frames had deficiencies those mimic the existing deficient building stock in Turkey. The test results showed that the external upgrading can increase both the lateral stiffness and strength of deficient RC frames considerably. Finite element analyses were conducted to specimen models to investigate the behaviors numerically. Furthermore, corresponding single degree of freedom (SDOF) models of specimens were generated to perform dynamic analysis. Results show the importance of hysteretic response and enhancement of energy dissipation capability with drift control.

Guyed masts are special type of structures that are widely used in the telecommunication industry. In the past, there was no guideline for seismic design of these types of structures in the corresponding design codes. On the other hand, in the latest &ldquo / G&rdquo / revision of the ANSI/TIA-EIA code there is a comprehensive design criterion for the seismic design of the guyed masts. However, during the design process of these structures the most common approach is to ignore the effect of seismic loading and use only the internal forces developed from the wind load and ice load analysis. In this study firstly the efficiency and accuracy of the commercial SAP2000 and PLS-TOWER software were investigated, then finite element models of three guyed masts that had been designed in Turkey with the heights 30m, 60m and 100m in the SAP2000 and PLS-TOWER software were analyzed under the effect of earthquake, wind and ice loadings. The most common design code recognized all over the world used for the design of the guyed masts is ANSI/TIA-EIA 222-G &ldquo / Structural Standards for Steel Antenna Towers and Supporting Structures&rdquo / . Thus, the corresponding sections of this code were followed during the study. The main objective of this research is to check the correctness of commercial SAP2000 and PLS-TOWER software and to investigate the effect of seismic actions on the guyed masts and also to gain a better understanding of the behavior of guyed masts under the effects of the wind, ice and earthquake loadings.

Double-layer grid systems are three-dimensional pin-jointed structures, which are generally used for covering roofs having large spans. In this study, evolution strategies method is used to optimize space trusses. Evolution strategies method is a type of evolutionary algorithms, which simulate biological evolution and natural selection phenomenon to find the best solution for an optimization problem. In this method, an initial population is formed by various solutions of design problem. Then this initial population starts to evolve by using recombination, mutation, and selection operators, which are adopted for optimization of space trusses by modifying some parameters. Optimization routine continues for a certain number of generations, and best design obtained in this process is accepted as optimum solution. OFES, a design and optimization software developed for optimum design of steel frames, is modified in this study to handle space truss systems. By using this v software, six design examples taken from real-life industrial applications with element numbers changing between 792 and 4412 are studied. The structural systems defined in examples are optimized for minimum weight in accordance with design provisions imposed by Turkish Specification, TS648. The optimization is performed based on selecting member sizes and/or determining the elevation of the structure and/or setting the support conditions of the system. The results obtained are compared with those of FrameCAD, a software which is predominantly used for design of such systems in national current design practice.

Reinforced concrete frame buildings are the most common type of constructions in Turkey which are exposed to various types of forces during their lifetime. Seismic performance of reinforced concrete frame buildings is dominated by columns which can be classified as primary members of these structures. When current codes are considered, all of them contain several provisions in order to implement reliable seismic performances of reinforced concrete columns. In order to evaluate the accuracy of these provisions, analytical and parametric studies are carried out for flexure critical reinforced concrete columns. In these studies, total numbers of 30 flexure critical columns are extracted from PEER database (2005) and analytically investigated. Once the seismic responses obtained from analytical investigations are close enough to experimental seismic responses, performance based displacement limits are pointed out according to TEC (2007), FEMA 356 (2000), Eurocode 8 (2003), and ASCE/SEI 41 Update (2009). In addition to this, total numbers of 144 flexure critical columns are generated in parametric studies to present the effects of various parameters such as column geometry, concrete strength, axial load ratio, transverse reinforcement ratio, and yielding strength of longitudinal reinforcement on performance based displacement limits. Performance based displacement limits proposed by TEC (2007), FEMA 356 (2000), Eurocode 8 (2003), and ASCE/SEI 41 Update (2009) are found very conservative compared to limits obtained from both experimental and analytical behavior. On the other hand, performance based displacement limits given in Eurocode 8 (2003) and ASCE/SEI 41 Update (2009) predict the experimental behavior more accurate than TEC (2007) and FEMA 356 (2000). Improvements on these limits are proposed.

The aim of this study is to produce maghemite nanoparticles by using different production methods. To achieve this purpose Sol-Gel Processing and Microwave Synthesis methods were employed. Suitable characterization techniques like XRD, TEM, BET, and VSM were performed to control the properties of the synthesized particles whether they are suitable for certain applications. In the sol-gel part of the study two different routes were employed to obtain maghemite nanoparticles. In the first route TEOS (tetraethoxysilane) was used as the precursor. Approximate particle sizes of these samples lie between 12.0-23.4 nm. From the magnetization measurements saturation magnetization (Ms) values are obtained between 4-12 emu/g. In the second route of the sol-gel method ethylene glycol and diethylene glycol were used as starting materials. Ms value was found as 28 emu/g for the ethylene glycol sample as the highest magnetization value due to having the highest amount of maghemite phase. The superparamagnetic behavior observed in these samples was tried to explain by curve fitting. Langevin and tangent hyperbolic functions were used to fit the magnetization curves. From the XRD study particle sizes of these samples lie in the 4.0-48.5 nm range and these results are consistent with the size distributions obtained from the TEM study. In the last part of the study microwave method was used to produce maghemite nanoparticles. Most of the samples contain maghemite and hematite phases together and particle sizes were between 3-30 nm. Ms values of these microwave samples were lower than that of the sol-gel samples with a value about 3.0 emu/g. Keywords: Maghemite, nanoparticle, superparamagnetism, sol-gel, microwave

The experimental research presented in this dissertation aims to develop a new rubber&ndash / based seismic isolator type on the basis of the idea that the damping of a conventional annular elastomeric bearing (EB) can be increased by filling its central core with small diameter steel balls, which dissipate energy via friction inside the confined hole of the bearing during their movements under horizontal loads. The proposed bearing type is called &ldquo / Ball Rubber Bearing (BRB)&rdquo / . A large set of BRBs with different geometrical and material properties are manufactured and tested under reversed cyclic horizontal loading at different vertical compressive load levels. Effect of supplementary confinement in the central hole of the bearing to performance of BRB is studied by performing some additional tests. Test results are used to develop design equations for BRB. A detailed non-linear finite element model is developed to verify the test results. The proposed analytical model is determined to simulate the structural hysteretic behaviour of the bearings. In design of BRBs, the proposed design guideline can be used in conjunction with the proposed non-linear finite element analysis. Extensive test results indicate that steel balls do not only increase the energy dissipation capacity of the elastomeric bearing (EB) but also increase its horizontal and vertical stiffness. It is also observed that the energy dissipation capacity of a BRB does not degrade as the number of loading cycles increases, which indicates remarkably reliable seismic performance.