نشریه سازه و فولاد
سال یازدهم شماره 22 (پاییز و زمستان 1396)

Local buckling of steel plates, buckling of hollow columns and lateral-torsional buckling of I-shaped beams are some of the vulnerabilities of steel members against buckling. In this study, the effect of GFRP plates on improvement of stability behavior of steel plates and sections was evaluated using ABAQUS finite element software. The results indicate that using GFRP plates for strengthening steel plates leads to an enhancement in their buckling capacity, particularly for plates with higher slenderness ratio. Also, strengthening columns with GFRP plates leads to enhancement in their load carrying capacity and for retrofitting of I-shaped beams by increasing critical buckling load can be effective to delay lateral-torsional buckling, specially when the flange and web have a higher width-to-thickness ratio.

Base isolation can improve the seismic performance of structures by reducing the seismic demands instead of increasing the capacity. Many of existing and new structures are asymmetric, thus the effect of asymmetry on the behavior of isolated structures should be studied. In asymmetric structures the horizontal distance between center of mass and center of rigidity, induce inherent torsional moment which can generate extra forces and deformations in the members. In the present research work the seismic behavior of asymmetric isolated concentric braced structures is investigated by nonlinear dynamic analyses using SAP2000 software. The behavior of fixed base and isolated asymmetric structures for different values of mass and stiffness eccentricities are studied and compared to each other. Based on the analysis results, base isolation has reduced story rotations and torsional amplifications in asymmetric structures in mass eccentric and stiffness eccentric structures. Also smaller torsional amplifications can be expected in stiffness eccentric structures than mass eccentric structures. Furthermore a new method for designing isolators in asymmetric structures is proposed which can reduce story rotations and torsional moments in such structures.

Buckling Restrained Braced Frame (BRBF) is one of the earthquake resisting systems. In this system braces yield in tension and compression without buckling. One of the drawbacks of conventional BRBF with steel core is residual displacement in frames that are equipped with BRB at the end of earthquakes. For solution of this problem, in this paper BRB is used in the frames with Shape Memory Alloy (SMA) core because of stess-strian diagram of SMA shows small residual stain during cyclic loading. For evaluation of BRB with SMA core, 4 and 8 story 2D frames are selected and equipped with BRB that has steel core and BRB that has SMA core. Frames have been analyzed under Nonlinear Time History with three Earthquake Records. Assessment of results reveal that residual drifts of BRB frames with SMA core are decrease respect to BRB frames with steel core. Evaluation of the rest parameters like maximum lateral story displacement, maximum story drift ratio and maximum story shear shows that BRB frames with steel core have better responses respect to BRB frames with SMA core in most cases.

The aim of this paper is to investigate a new energy dissipating system in steel moment resisting frames using finite element method, namely, slitted moment resisting frame system. Moment resisting frames are considered as one the most favorable novel lateral force resisting system. However, the minimum requirement of the beam span to depth ratio, to form the plastic hinges at the two ends of the beam to satisfy. By placing a sheer fuse in the middle of the beam, the flexural plastic hinges are transferred to the middle of the beam through nonlinear shear behavior. Therefore, shear fuse yielding precedes flexural yielding at the two ends of the beam and consequently the proposed system satisfies the code limitations. The fuse is a part of the beam, which, by entering into the nonlinear behavior, prevents other part of the beam from entering into the nonlinear behavior. Numerical models of the proposed system are developed in ABAQUS and are compared against the experimental results.

Practically there is a risk of explosion, and different structure's behavior should be examined against the effects of blast loadings. Sandwich panels are used for making some industrial and military structures. These panels are made of two sheets and an intermediate core. The core has a significant role in reducing the deflection and enhancing energy absorb of structure. In this study, sandwich panel's behaviors, which are made of aluminum and steel, are examined against the blast loadings. In the process of analysis, three kinds of profiles, which are: rectangular, trapezoidal and triangular, are considered as panel cores. The results show that the panels with steel core, absorb less energy and damp by their core. Those panels which are completely made of aluminum or the panels with steel core can sustain more strain energy by their back sheets. all the panels that are completely made of aluminum have more damped energy than others. Those panels which have only aluminum sheets or aluminum core are placed next to whole aluminum panels in order to damped energy level. Most of the deflections in panels that are whole aluminum made and steel core panels were belong to panel core with triangular profiles and the least deflection were for rectangular shaped profiles. In panels that only have steel sheets, unlike the other panels, the most deflection was for rectangular profiles and the least deflection was for triangular ones.

After Northridge earthquake reduced beam sections were suggested to improve connections performance. A new detail has been evaluated for reduced beam sections that includes a combination of two previously investigated models; reduced web section and accordion web section. According to comparison with other models through finite element analysis, it was found that the stresses and plastic strains have been more effectively reduced in the beam to column connection region of the combined detail and up to 9%. Increase in plastic rotation capacity may be achieved without a noticeable loss in strength. According to performed nonlinear static analyses results for well-designed 5, 10 and 15 story steel buildings with special moment resistant frame system, the amount of plastic drift capacity using the reduced beam sections slightly increases and this increase is more in connections with accordion web and accordion web together with reduced web sections respectively. Pushover curves indicate that the reduced beam sections has little effect on the linear part of the curves but increasing drifts, added strength is reduced. The rate of decrease for two connections with accordion web sections and accordion web with reduced web is more. Average rates of behavior factors 11.38 and 11.73 and 11.88 have respectively been obtained for moment resistant frames with reduced beam section and accordion web sections and accordion web with reduced web sections. It can be said that the average rates of behavior factor for frames that are designed based on the behavior factor of 8 has been considerably increased.

Good quality of fittings in steel structures and structural systems is integration key factor. In an intense earthquake connection problems designated as the destruction factor of many steel buildings. A poor connection can lead to series of successive and fundamental deterioration in the structural steel. With appropriate beam-to-column connections can be helped to improve the quality of construction. In this study, first, design a beam-to-column end plate connection according to American institute of steel construction. Then, to achieve purposes of this study, and according to this, in box columns welding fourth dimension continuity plate according to the implementation of these columns will not do well. As a result continuity plate will be deleted from connection of beam-to-column end plate designed. Study on the connection will do without continuity plate. In this study, we will survey the behavior of the two connections with bolt and rod bolt under push. There the additive load will applied on connections mentioned into two pushover and cyclic load. Moment-rotation charts for pushover to each of the two connections drawn and according to the comparison charts, information about ductility, resistance and ultimate loading was obtained. Then, by placing the cyclic load on the samples achieve to intended hysteresis charts for each of the two connections. By comparing these two charts we will find that in resistance and ultimate load, rod-bolt connections are superior than bolt connections.