Reinforced concrete (RC) columns are the primary type of vertical support used in building structures that sustain vertical loads. However, their strength may be insufficient due to fire, earthquake or volatile environments. The load demand may be increased due to new functional usages of the structure. The deformability of concrete columns can be greatly reduced under high axial load conditions. In response, a novel steel encasement that distinguishes from the traditional steel jacketing that is assembled by welding or bolt is developed. This novel strengthening method features easy installation and quick strengthening because direct fastening is used to connect the four steel plates surrounding the column. This new connection method is usually used to quickly and stably connect two steel components by driving high strength fastener into the steel components. The connections together with the steel plates behave like transverse reinforcement, which can provide passive confinement to the concrete. The confined column along with the steel plates resist the axial load. By this way, the axial load capacity and deformability of the column can be enhanced. Eight columns are tested to examine the reliability and effectiveness of the proposed method. The effects of the vertical spacing between adjacent connections, thickness of the steel plate and number of fasteners in each connection are studied to identify the critical parameters which affect the load bearing performance and deformation behavior. Lastly, a theoretical model is proposed for predicting the axial load capacity of the strengthened RC columns.

The seismic analysis of structures without applying the effects of soil can undermine functional objectives of structure so that it can affect all the desired purposes at the design and control stages of the structure. In this research, employing OpenSees and MATLAB software simultaneously and developing a definite three-dimensional finite element model of a high-rise concrete structure, designed using performance-based plastic design approach, the performance of Tuned Mass Damper (TMD) and Active Mass Damper (AMD) is both examined and compared. Moreover some less noted aspects such as nonlinear interaction of soil and structure, uplift, nonlinear behavior of structure and structural torsion have received more attention. For this purpose, the analysis of time history on the structural model has been performed under 22 far-field accelerogram records. Examining a full range of all structural seismic responses, including lateral displacement, acceleration, inter-story drift, lost plastic energy, number of plastic hinges, story shear force and uplift. The results indicate that TMD performs better than AMD except for lateral displacement and inter-story drift to control other structural responses. Because on the one hand, nonlinear structural parameters and soil-structure interaction have been added and on the other hand, the restriction on the control force applied that leads up to saturation phenomenon in the active control system affect the performance of AMD. Moreover, the control force applied by structural control system has created undesirable acceleration and shear force in the structure.

In recent years, the use of new materials and technologies with the aim of developing high-performing and cost-effective structures has greatly increased. Application of high-strength concrete (HSC) has been found effective in reducing the dimensions of frame members; nonetheless, such reduction in dimensions of structural elements in the most cases may result in the lack of accountability in the tolerable drift capacity. On this basis, strengthening of frame members using fiber reinforced polymers (FRPs) may be deemed as an appropriate remedy to address this issue, which albeit requires comprehensive and systematic investigations. In this paper, the performance of properly-designed, two-dimensional frames made of high-strength concrete and strengthened with Carbon Fiber Reinforced Polymers (CFRPs) is investigated through detailed numerical simulation. To this end, nonlinear dynamic time history analyses have been performed using the Seismosoft software through application of five scaled earthquake ground motion records. Unstrengthened (bare) and strengthened frames have been analyzed under seismic loading for performance assessment and comparison purposes. The results and findings of this study show that use of CFRP can be quite effective in seismic response improvement of high-strength-concrete structures.

Concrete filled double skin tubular members (CFDST) consist of double concentric circular or square steel tubes with concrete filled between the two steel tubes. The CFDST members, having a hollow section inside the internal tube, are generally lighter than ordinary concrete filled steel tubular members (CFT) which have a solid cross-section. Therefore, when the CFDST members are applied to bridge piers, reduction of seismic action can be expected. The present study aims to investigate, experimentally, the behavior of CFDST stub columns with double concentric square steel tubes filled with concrete (SS-CFDST) when working under centric compression. Two test parameters, namely, inner-to-outer width ratio and outer square steel tube's width-to-thickness were selected and outer steel tube's width-to-thickness ratio ranging from 70 to 160 were considered. In the results, shear failure of the concrete fill and local buckling of the double skin tubes having largest inner-to-outer width ratio were observed. A method to predict axial loading capacity of SS-CFDST is also proposed. In addition, the load capacity in the axial direction of stub column test on SS-CFDST is compared with that of double circular CFDST. Finally, the biaxial stress behavior of both steel tubes under plane stress is discussed.

Feasibility studies of a reinforced concrete (RC) deep pile foundation system with the compressed air energy storage (CAES) technology were conducted in previous studies. However, those studies showed some technical limitations in its serviceability and durability performances. To overcome such drawbacks of the conventional RC energy pile system, various steel-concrete composite pile foundations are addressed in this study to be utilized as a dual functional system for an energy storage medium and load-resistant foundation. This study conducts finite element analyses to examine the applicability of various composite energy pile foundation systems considering the combined effects of structural loading, soil boundary forces, and internal air pressures induced by the thermos-dynamic cycle of compressed air. On this basis, it was clearly confirmed that the role of inner and outer tubes is essential in terms of reliable storage tank and better constructability of pile, respectively, and the steel tubes in the composite pile foundation can also ensure improved serviceability and durability performances compared to the conventional RC pile system.

Recently, the plate bending analysis has been interpreted in terms of the tensor's components of curvatures and bending moments by presenting the conceptual perspectives of the Hydrostatic Method of Analysis (HM) and theoretical formulations that combine the continuum mechanics with the graphical statics analysis, the theory of thin orthotropic and isotropic plates, and the elasticity theory. In pursuance of uncovering a genuine formulation of the plate's flexural differential equations, that possess the general-covariance and coordinates-independency. This study had then, tackled various natural and structural problems in both solid and fluid branches of the continuum mechanics in a description of such theoretical and conceptual attainment in uncovering the dimensional independent diffeomorphism covariant partial differential laws.

In the recent decades, various optimization algorithms have been considered for the optimization of structures. In this research, a new enhanced algorithm is used for the size and topology optimization of truss structures. This algorithm, which is obtained from the combination of Crow Search Algorithm (CSA) and the Cellular Automata (CA) method, is called CA-CSA method. In the first iteration of the CA-CSA method, some of the best designs of the crow's memory are first selected and then located in the cells of CA. Then, a random cell is selected from CA, and the best design is chosen from the selected cell and its neighborhood; it is considered as a "local superior design" (LSD). In the optimization process, the LSD design is used to modify the CSA method. Numerical examples show that the CA-CSA method is more effective than CSA in the size and topology optimization of the truss structures.

A new simple solution for critical buckling of FG sandwich plates under axial and biaxial loads is presented using new modified power-law formulations. Both even and uneven distributions of porosity are taken into account in this study. Material properties of the sandwich plate faces are assumed to be graded in the thickness direction according to a modified power-law distribution in terms of the volume fractions of the constituents. Equilibrium and stability equations of FG sandwich plate with various boundary conditions are derived using the higher-order shear deformation plate theory. The results reveal that the distribution shape of the porosity, the gradient index, loading type and functionally graded layers thickness have significant influence on the buckling response of functionally graded sandwich plates.

In this study, the dynamic behavior of a three-span hybrid continuous arch bridge under vehicle loading is investigated. The natural vibration characteristics of the bridge were analyzed through pulsation test. In the dynamic loading test, the vibrations of the bridge under different truck speeds and different pavement conditions were tested, and time histories of deflection and acceleration of the bridge were measured. Based on the dynamic loading test, the impact coefficient was analyzed. The results indicate that the pavement smoothness had more impacts on the vibration of the bridge than the truck's speed. The vertical damping of the bridge under the excitation of the trucks is larger than the transverse damping. Resonance occurs at the side span of the bridge under a truck at 10 km/h.

To evaluate the performance of concrete load bearing walls in a structure under horizontal loads after being exposed to real fire, two steps were followed. In the first step, an experimental study was performed on the thermo-mechanical properties of concrete after heating to temperatures of 200-1000℃ with the purpose of determining the residual mechanical properties after cooling. The temperature was increased in line with natural fire curve in an electric furnace. The peak temperature was maintained for a period of 1.5 hour and then allowed to cool gradually in air at room temperature. All specimens were made from calcareous aggregate to be used for determining the residual properties: compressive strength, static and dynamic elasticity modulus by means of UPV test, including the mass loss. The concrete residual compressive strength and elastic modulus values were compared with those calculated from Eurocode and other analytical models from other studies, and were found to be satisfactory. In the second step, experimental analysis results were then implemented into structural numerical analysis to predict the post-fire load-bearing capacity response of the walls under vertical and horizontal loads. The parameters considered in this analysis were the effective height, the thickness of the wall, various support conditions and the residual strength of concrete. The results indicate that fire damage does not significantly affect the lateral capacity and stiffness of reinforced walls for temperature fires up to 400℃.