STRUCTURE AND STEEL
Year:2011 | Volume:7 | Issue:9|Papers Count:9

This paper provides an overview of reliability of the member stability criteria in the 2008 Iranian Structural Steel Specification. Steel building structures in the Iran have been designed from many years ago, but this is the first time that the LRFD methods have been developed and presented in this code. Development of LRFD design methodology involves consideration of safety factors to account uncertainty in loading, geometrical properties, modeling, analysis, material characteristics, etc. Management and control of risk due to uncertainties through proper design is a major engineering goal. The design codes and standards address uncertainties through safety factors that may be defined either implicitly such as those used for the allowable strength design (ASD) format or explicitly such as those used for the Load and Resistance Factor Design (LRFD) format. The purpose of this paper is to review the national reliability indices of the Iranian specification, using new information about material properties, and new evaluation of the relevant experiments. The paper will examine the reliability of beam, girders and column in some different load combination.

This paper presents improving analyses and designs method of end plate bolted simple connections, which is an exact way for designing this type of connections with load and resistance factor design (LRFD) and allowed stress design (ASD) method. Besides, finite element models of end plate bolted simple connections in various geometry is made and compared with experimental results. Prying action effect in these models is regarded and failure models are used to computation stiffness. Also, deformation and distribution of surface press which result from prying action phenomena is used. With using the result from parametric analyses, an improved method is presented to computation prying action. Then, an improved method is proposed to design bolted simple connections in regard with prying action effect. Accuracy assessment of proposed method, will display efficiency and favor accuracy in designing bolted connections.

The effect of semi-rigid connections on the behavior of structural systems always drowns the attention of many researchers to itself. In this article, the simultaneous effects of rigid and semi-rigid connections in dual systems such as braced frames are examined with nonlinear dynamic analysis. Each of the beam, column and the connections has been modeled in a three linear manner. The observed parameters in this research consist of energy dissipate of each story, ultimate base shear and hysteretic loops of semi-rigid connections. The parameters are observed under different earthquakes, and the effect of height of structure, as well as number of bays is considered. It can be seen from the energy dissipate diagram that in dual systems, the maximum observed energy between the two stories, occurred with a sudden and significant fluctuation which shows the viability of the structure in stories with the most energy absorption. The hysteretic diagram shows that the maximum energy absorption of the connection is occurred in special moment resisting frames. However the distribution of the energy between the neighboring bays of the semi rigid connection node is more fluent in dual braced systems, which prevents the energy concentration on the braced bay.

Dynamic characteristics of steel structures including flexural frame system with semi-rigid connections are investigated in this study. With this regard, four frames have been modeled including two-span two-story, three span four-story, three-span six-story and four-span eight-story frames. The frames are analyzed and evaluated for variation of the connections stiffness from semi-rigid to rigid and for both cases of push over static analysis and nonlinear dynamic analysis under earthquake acceleration. After that, plastic hinge formation in the frame, frame failure, energy dissipation in members and connections, maximum displacement of stories and frame, base shear force, behavior coefficient, coefficient of design load increased strength have been investigated.The results showed that stiffness increase of connections in the frame, increases the base shear force and coefficient of increased strength, and reduces the period, maximum and relative displacement (drift) and coefficient of frame behavior.

Progressive collapse refers to a phenomenon in which a local damage of a primary structural element leads to the failure of partial or whole structural system. To investigate the progressive collapse of structures, three analysis procedures: linear static, nonlinear static and nonlinear dynamic procedures can be used. For static analysis, the gravity force applied on the column removed bay should multiply by a constant factor 2. Using a constant Dynamic Increase Factor (DIF) is appropriate only for elastic systems. According to optimal design of structures, assuming elastic behavior after column removal scenario is conservative. Thus, it is necessary to establish expression for DIF that consider inelastic response. In this paper, using load-displacement and capacity curve of a clamped-clamped steel beam, an explicit expression for DIF is established for elastic-perfectly plastic and elastic-plastic with catenary action behavior.

Steel composite shear wall system is consisted of steel plates, I shape beams and columns, and composite columns with infill concrete, fc¢. In order to evaluate and improve the behavior of this innovated system, it is necessary to investigate the effect of these parameters on reversed cyclic response. In this paper, a tested steel composite shear wall subjected to cyclic load was modeled. The model was verified using nonlinear dynamic analysis. Several models, in which the effective parameters were varied, have been nonlinear analyzed under dynamic reversed cyclic loads. Results show that by varying these parameters, the general shape of hysteresis loops remained unchanged and the shear behavior with large capability of energy dissipation, were noted. The dissipated energy and dynamic strength increased 10 % to 31% and 20%, respectively, as these parameters changed, where the maximum increase was related to increase of steel plate thickness. Increase of concrete strength to more than 20MPa did not significant effect on ductility, thus using concrete with compressive strength more than 20MPa is not recommended. Based on the results, the ductility ratio of m=7 is determined and recommended.

In this paper, which is aimed to study the behavior of saddle like connections under cyclic loading, results of experiments on six different specimens are utilized. Initially details of each specimen and its setup and loading protocol are presented. Then observations during the tests consisting of position and situation of initial crack and final fracture are discussed and the moment-rotation curves are presented. Subsequently backbone curve of each specimen is provided and the performance levels are determined. Finally the results of finite element analysis consisting of moment-rotation curves, initial stiffness and ultimate strength are compared with those obtained from tests. Baesd on the tests conducted in this research, the main reason for reduction in moment capacity of the saddle like connections is fracture in the welds that connect top angle to column or beam. Therefore if the load bearing capacity of the connection for gravity loads is maintained, the connection behaves as a scissor like and moment carrying behavior of it can be considered as deformation control one.

Iran, among the world most earthquake-prone countries, has been exposed to the devastating earthquake in the past years and it is inevitable to find strategy for confronting with this phenomenon. In this regard, eccentrically diagonal bracing as a lateral system has been of less interest to the researchers and design engineers. To promote use of the system, in this study the cyclic behavior of steel frames with eccentrically diagonal bracing in two cases of simple and rigid beam to column connections are compared and the advantage of rigid connection in better drift control due to too much flexibility in simple connection has been investigated in two cases with high and low eccentricities. Close results (difference between link beam shear force and also axial forces in braces and columns of about 20%) of two cases in small eccentricity make it possible for engineers to get rid of the problems in rigidity achievement in Iran with full penetration welds. Moreover by increasing eccentricity, the behavior of the link beam would change from shear to moment link, reducing energy dissipation in the system.However, using rigid connection can increase energy dissipation up to 50%. The use of rigid connections in such frames with larger eccentricities decrease compressive stress about 12% and prevent buckling of braces compared to the case with simple connection.