STRUCTURE AND STEEL
Year:2008 | Volume:4 | Issue:2|Papers Count:14

The importance of welded connections on the behavior of steel moment resisting frames was the reason of researchers focus on welding details. In this paper result on 32 pilot tests indicate moment connection behavior are presented. In this experimental research, in order to connection strength evaluation, complete joint penetration (cjp) weld strength with different welding procedure, double side fillet weld out of plane strength, one side fillet weld out of plane strength and amperage intensity effect on welding quality, have been studied. Also in order to connection rehabilitation, rib stiffener effect on connection strength, T-stiffener effect on connection strength, electrode toughness effect on welding quality and grinding and rewarding effect on welding quality have been studied. Maximum strength of cjp weld is observed in welding with backing. Out of plane strength of double side and on side fillet weld have been determined. Connection strength increase amount with stiffener strengthening of connection have been proposed. It has also been proposed constructional recommendations about electrode toughness, rewelding and amperage intensity.

In this paper a new exact solution procedure, using energy method, is formulated for the buckling analysis of simply supported tapered rectangular plates subjected to uniform compressive load. At first, plates having uniform thickness are considered and their post-buckling paths and relative reductions in the membrane stiffness are calculated. Then, the buckling analyses of plates with linearly varying thicknesses are studied and the change in the buckling stress factors based on the reduction of the thickness is presented. Further, the buckling analyses of plates having thicknesses that vary non-linearly are studied. Finally, the post-buckling analysis of tapered plates is discussed.

In this paper, regarding to importance of reduction factor; various different studies have been performed for its calculation and some methods were developed. Lack of this factor for dual frame-panel and panel systems, which used as in filled, in Iranian code, is the major reason for this paper. In this study, seismic behavior of 3, 5 and 10 stories frames with different ratio of in filled panel are investigated subjected to EIcentro, Tabas and Naghan records. Records were selected in the manner that excites all effective natural frequencies of frames. Nonlinearity and energy dissipation due to hysteresis behavior of seismic excitation are fully established. Moreover, structural damping and over-strength and its relevant ductility are investigated. Finally, results obtained by nonlinear static and dynamic analysis show that reduction factor of dual frame-panel are approximately measured between 3 to 6 units.

In this research are investigated the behavior of EBF frames subject to far-fault and near-fault earthquakes. For this purpose two dimensional models of EBF frames with 3,6 and 12 stories and considering 3 different eccentricity/length ratio of (0.5,0.7,0.9) for each frame are modeled. Nonlinear dynamic behavior of EBF frames are investigated Under 4 pairs of far and near-fault records. Relative displacement, story displacement, coefficient Rm, base shear and ductility-demand are calculated and compared for near and far fault earthquakes. The research findings are: Ductility-demands and displacement-demands are larger for near-fault than those of far-fault. Recommended magnification factor for base shear in the 3, 6, and 12 story frames are 1.65, 1.64 and 1.89 respectively. Magnification factor of base shear is increased with an increase in structure's period. Hysteresis graphs show that more energy is applied in the near-fault earthquake with respect to far-fault earthquake.

Braces are used as effective seismic elements in seismic regions. They are widely used in low to high-rise buildings. However under an earthquake loading, Conventional braces are directed to the buckling rapidly. Repeated buckling and yielding of the braces cause a stiffuess and strength degradation which may reduce the overall frame stability. To solve the above problem, a number of studies have been introduced on the use of new Ductile brace using in Concentrically Braced Frames (DCBF), in which buckling has been restrained. This new brace is yielded in tension as well as in compression in which dissipate seismic energy in both direction of loading. This paper describes the main characteristics of the inelastic seismic response of the such Ductile Braces (DCB).In order to study the seismic behavior of the new developed DCBs with the new proposed cover and encasing material achieving a series of new effective and economical DCB, several large-scale braces have been tested. In this study, first the new four types of DCBs that have been developed at BEES are introduced, designed and tested, and then the hysteretic characteristics and energy dissipation of the DCBs under cyclic loading are investigated.

According to performance based design philosophy, utilization of damage indices defined as the inter story drifts of a frame is an effective method to estimate structural damage due to earthquake.The damage indices are not yet available for satchel frames. This is the incentive behind this research work in which two different performance levels are defined firstly as life safety and collapse prevention. Based on this definition and using the nonlinear static analysis (pushover), some performance criteria are described for 4, 6 and 8-story steel frames, on the basis of relative displacements (drifts). The substructures method is used here to model the frame elements including latticed columns, double beams, concentric cross braces and satchel joints. The results show that a drift of 1.5% at the roof level is a suitable measure for the collapse prevention level of satchel frames. Also, systematic procedures are presented to retrofit these structures to enhance their seismic behavior varying the related parameters.

In Knee-Braced Frames, KBF, one end of diagonal brace is connected to knee element rather than the beam column joint. In fact, knee element as a hysteretic damper is designed and detailed to behave like a structural fuse such that by sustaining controlled inelastic deformations and dissipating seismic energy, other members and connections would remain elastic. In this paper, the impact of different structural parameters on the behavior of KBF and also the situation of using DKBF (Double Knee Braced Frames) are studied using nonlinear finite element analysis. The results of this research show efficiency of using KBF in simple framing structures and some drawback of using DKBF compared to KBF.