نشریه سازه و فولاد
سال دهم شماره 19 (بهار و تابستان 1395)

Steel plate shear walls with openings are highly interested because of their architectural aspects. A particular type of these systems is the steel plate shear wall with door-shaped opening; the opening is continued from the base to top beam and surrounded by boundary elements relatively weaker to main columns. Assuming the pure shear behaviour for this system, each of the side panels can be considered a steel plate shear wall with unequal VBEs (vertical boundary elements). Behaviour of this type of steel shear walls cannot be predicted by the common relations of steel shear walls; therefore, it has not been covered in technical literatures until now. In this study the behaviour of steel plate shear wall with one strong and one weak column is theoretically and numerically investigated. Theoretical relations to define the load-displacement curve were proposed. In order to study the theoretical relations comprehensively, 12 numerical models with various overall dimensions and column cross sections were investigated by finite element method; the probable errors of the results were also analysed. The obtained results show good agreement between theoretical relations and real behaviour of steel plate shear walls with unequal columns and persists the applicability of the relations in design of these systems.

Due to uncertainties manufacture of flange connections and complexity of their semi-rigid behavior, the behavior of such joints in the structure and the behavior of them when they are studied separately is different. In the present study, the behavior of a flanged joint system in real condition in a three story steel frame, three dimensional inverse problem solving method has been determined. To simulate the behavior of such a joint (beam elements and two plates with small gap from each other), a three story steel frame was modeled using finite element method. Frequencies vibration modes of structure for different modulus of elasticities were obtained using modal analysis. For the updating process for the three story steel frame, three dimensional finite element model by reducing the differences between experimental and analytical natural frequencies, the element beam flange connection system was replaced with specified Young’s modulus. Updated model, while providing a good approximation of natural frequencies in three story steel frame, a flexible behavior in different degrees of freedom could be attained to demonstrate the semi-rigid behavior in the structure.

Making inexpensive and efficient is one of the main requirements in the structural design process. In recent decades, the optimization algorithms have been developed for use in the engineering sciences. Optimization algorithms based on the natural phenomena are most useful criteria in structural design. In engineering, truss is commonly used in steel structures. In this paper, Teaching-Learning-Based Optimization (TLBO) algorithm has been used to optimize the steel truss. TLBO can calculate accurate and optimum value of a functions, using only the common controlling parameters such as the mean value in each iteration. Four steel trusses have been analyzed to investigate how TLBO improves designing process of the steel trusses. The results shown that TLBO algorithm has satisfactory performance with less calculation than other optimization algorithms.

To reduce or eliminate residual deformations in the main members of the structures after an earthquake, researchers presented the idea of using self-centering systems. Several types of self-centering systems have been proposed. One of the strategies for created self-centering in structures, using post-tensioned (PT) steel moment connections. Until now several types of PT steel connections is provided. In this paper, results of numerical analysis using finite element method in ABAQUS software for five full-scale model of interior PT steel connections with bolted top and seat angles has been studied. The results of numerical analysis in this research demonstrate the beams and columns remain essentially elastic while inelastic deformation of the top and seat angles provided energy dissipation and also using post-tensioning method, increase loading capacity significantly without residual deformation in main members of the connection. In a PT connection, maximum stresses in beam created at the flange of beam and using longer reinforcing plate, cause decrease stresses created in beam and reduce various damage index and risk of brittle fracture in tension angles. Cyclic behavior of numerical model of PT connection with combined axial load and drift demand shows that the axial load reduces bearing capacity of connection.

Extensive damages in welded unreinforced flange connections (WUF) in the Northridge 1994 earthquake led to the development of reduced beam section (RBS) moment connections to prevent premature brittle failure modes in welded connections. This paper investigates the seismic performance of recently developed drilled flange (DF) moment resisting connections as a simple and efficient alternative to RBS connections in seismic regions. DF connections are established by a series of holes made by drilling on the top and the bottom flanges of the beam (along the main axis) to create an intentional weak point, which can prevent stress concentrations at the connection edges. In this study, a series of analytical studies based on previous experimental researches were carried out to evaluate cyclic behaviour of DF,WUF and RBS beam to column connections. Different drilled flange hole configurations and panel zone shear strength ratios were used to obtain an optimum design and prevent premature failure modes in complete joint penetration groove welds. Results show optimum configuration of drilled flange holes in DF connections reduce the rapture index and equivalent plastic strains of critical points on welded joints and comparing with WUF and RBS connections provide an appropriate seismic performance. The diameter of holes increase by distance from column face for the optimum configuration of DF connections.

By gradual change in structural design methods from strength based to performance based methods, typical existing frames could not satisfy the criteria of latter methods and if structures are designed by applying all related criteria, it will be an uneconomical design. Main problem in typical frames is imbalance between stiffness and ductility. To prevent large drifts, structures should have sufficient lateral stiffness and in order to absorb earthquake energy they must have high ductility. The goal of this research is to study the seismic performance of rigid and semi-rigid steel frames and the effects of adding friction dampers to such structures. In this paper, semi-rigid connections are supposed to yield and dissipate energy like dampers. For this purpose, 5-story building frames are designed in four cases including bare moment frame, moment frame with friction damper, bare semi-rigid frame and semi-rigid frame with friction damper. Dynamic time-history analyses are carried out applying three earthquake records. By observing the results of numerical analyses of structures, one can find out that semi-rigid frame with friction damper have the best performance among studied frames. Obtained results show that using friction damper in the moment frame with semirigid connections compared to the case with rigid connections, maximum first story displacement and base shear decrease respectively 7 and 20%.

This research aims to investigate the effects of clamping force on the behavior of steel gusset plates with slip-critical connection. Six specimens with two different materials are tested which three specimens are bolted with bearing-type connection and three specimens are bolted with slip-critical connection. The effects of number of bolts and material properties are investigated as the variable parameters of study. The results show that in the slip-critical bolted connections, the clamping force can increase the stiffness of connection in the small deformation zone. Also, this force increases the ultimate resistance of the tensile and shear areas that cause more resistant connection.