نشریه سازه و فولاد
سال پنجم شماره 9 (پاییز و زمستان 1390)

One of the novel resistant systems to lateral loads is the use of composite shear wall, which is made up of a thin steel plate, with concrete cover on one or both sides. The utilization of this kind of wall is increasing due to its stiffness, high resistance, and also appropriate ductility. Research indicates that the existence of a gap between the steel frame and the concrete panel has deep impacts on the amelioration of wall behavior and its ductility. In this paper the influence of the gap between the concrete panel and the frame, on the behavior of the composite shear wall has been investigated. For this purpose, a nonlinear static analysis for various models of composite shear walls, with the span of 3, 4.5, and 6m, and different gaps have been done, and relationship between behavior of wall with different width and the number of stories has been studied. The results indicate that gap width of 50-80 mm between the concrete panel and the steel frame, has improved the ductility, ultimate strength of composite shear wall.

The seismic behavior of cable stayed bridge with 1255 meter span has been studied in this paper. A Finite Element model (FEM) has generated and the behavior of the bridge under ground motion has investigated, considering large deformation. The torsion can be occurred in the deck and other components of the bridge due to collision of seismic waves in direction expect of orthogonal directions of the bridge. Thus in this study, the effect of collision of seismic waves to the piers and abutment with different angle, has studied using the explicit dynamic analysis. Due to long distance of towers from each other seismic waves in from of uniform and nonuniform ground motion of the supports, have applied to the model. Moreover, local post-buckling behavior of the deck for different seismic loads has studied on the basis of geometric nonlinearity,. The results show that the top and bottom steel plates of the box girder, experience the post-buckling behavior and different responses can be obtained due to different strike angle with uniform and non-uniform support excitations. It shown that the study of long-span cable-stayed bridges under different strike angle of earthquake waves has necessity, and more economic sketch can be obtained with use of post buckling capacity.

This study is intended to present a method for the localization and evaluation of damage in structures based on changes in natural frequencies and mode shapes of the damaged structures using an optimization approach. The proposed method localizes and evaluates the damage (or damages) of structures using optimization of a objectivefunction (damage function) by colonial competitive algorithm. The performance of the proposed method has been verified using a numerical example, namely a two span steel bridge with and without noise in the modal data and containing one or several damages. The obtained results clearly reveal that the proposed method can be viewed as a powerful and robust method for structural damage detection in structures.

The application of seismic isolation system in developing countries was generally associated with important and special structures, but nowadays it seems necessary the relevance of this technology in residential homes, schools and hospitals where the replacement cost due to earthquake damage can be very significant. It is more imperative in developing countries such as Iran, which are located in areas prone to earthquakes. In this regard, seismic isolation system by rubbersoil mixture has been proposed in 2008 year for developing countries as a new method with distinctive advantages such as low cost. In this paper, the efficiency of this new seismic isolation system has been evaluated in nearfault area with or without forward directivity effect. Based on the results of this paper, performance of RSM depends on nearfault earthquake characteristics in addition to properties of RSM layer and super structure. Consequently, in design process of these systems, significant effect of characteristics of nearfault ground motions on seismic demand reduction should be assessed carefully.

Progressive collapse refers to a phenomenon in which a local damage of a primary structural element due to abnormal loads, leads to the failure of partial or whole structural system. Abnormal loads are those loads which are not considered in normal analysis of structures but if applied to the structure, the final damage is not proportional to initial damage. Although most researches in this field are based on deterministic analysis and by using median or nominal values of analysis parameters, for more realistic results, it would be better to consider uncertainty in material specifications and loads. In this regard sensitivity of the response to analysis parameters and loads should be specified. In this paper sensitivity analysis is performed to investigate the uncertainty effects of live load, dead load, modulus of elasticity and steel yield stress on the column removed point displacement. For sensitivity analysis, three methods, Monte Carlo simulation, tornado diagrams and First Order Second Moment (FOSM) method, are used. According to the results, the displacement of the structure is more sensitive to variation of dead load and steel yield stress.

Chapter ten of Iranian National Building Code recognizes a certain type of connection between I beam and double section built up column to be used in ordinary and intermediate MR frames. The behavior of this type of connection and its panel zone are studied by testing three full scale specimens under cyclic loading and finite element modeling. The first specimen is tested under cyclic lateral loading and the other two are tested under axial loading in addition to cyclic lateral loading. All specimens have sufficient strength and stiffness and are categorized as rigid connection. They also show sufficient ductility for being used in intermediate MR frames. The panel zoe behavior in this type of connection is different from that of an ordinary connection of I beam to H column, mainly because the webs of beam and column are not in the same plane. The results of this research demonstrate that the behavour of the connection is mainly affected by the I section comprising of column cover plates and vertical continuity plates. Due to high stress concentrations produced in full penetration and fillet welds, if fracture in welds occurs early, full plastic hinge may not form in beams as desired. Hence provision of criteria for design of column cover plates in connection region is a prerequisite for satisfactory performance of the connection for seismic application.

Many countries have their own specific code for seismic resistant design of structures. In all these codes, it is important to know site characteristics, site seismicity, building importance, type of structural resistant system and situation of building. corresponding, coefficients in different codes are varied. Defining the base shear and its distribution at floor levels are based on elastic analysis, which cannot simulate the actual behavior of structure under severe ground motions. This is mostly contributed to the formation of plastic hinges along the height of the structure which are not accounted for in elastic analyses. Therefore, new method referred to as "performance based plastic design" (PBPD) has been used to simulate the actual behavior of structures under severe ground motions. In this paper, the seismic performance of eccentrically braced steel frames with symmetric horizontal links (H-EBF) that are designed based on Iranian 2800 standard code (3rd edition), IBC 2009 and PBPD are compared. In PPBD method, the plastic hinge, story displacement and plastic rotation of links are uniformly distributed along the height and nonlinear behavior of the structure is accounted for.

Extensive damages in steel structures connections after 1994 Northridge earthquake, clearly showed main deficiencies of methods of designing and fabricating steel moment frames. Brittle fractures in steel structures welded connections revealed that damages in moment frames were associated with connection performance and that all these brittle fractures occurred in beam-column connection point. Present study analyzes rib restrained beam to box column connection. In this connection design, a strengthening plate is used to reinforce the connection, which connects to the column by full penetration weld and has a definite geometry. The rib plate is designed in such a way that induces the plastic hinge away from the column. Results show their effectiveness on transferring beam's plastic hinge away from column and improvement in ductility.