نشریه سازه و فولاد
سال چهارم شماره 7 (پاییز و زمستان 1389)

Steel plate Shear walls are resistible systems against horizontal loading. They are used without stiffeners and with stiffeners types. It is necessary that the plate stress distribution is studied for determining the shear force and yield displacement of plate and the plate stress interaction effects on frame. In this paper، the plate stress distribution is studied by using two experimental steel plate shear walls without stiffeners and with stiffeners. The results show that، the plate third principal stress in post buckling field should be equal the plate shear stress buckling for determining the shear and yield displacement of plate and should be equal the half of plate shear stress buckling for determining the plate stress interaction effects on frame.

For investigating of structure، performance according to Instruction of seismic rehabilitation is suggested using of linear and nonlinear static and dynamic analysis. Moreover، for accurate evaluation of structure and to specify damage quantity، using of damage indexes that practiced them in some recent decades can be suitable approach. Advance of application of damage indexes is this that in addition to damage quantity specifies state of structure. In this paper، A steel structure investigated according to Instruction of seismic rehabilitation of existing buildings (publication No. 360) and with using of two damage indexes of «Ghobara» and «Krawinkler and Zohrei» that are respectively based on stiffness and cumulative deformation were determined، the damage and state of structure then with using of concentric and eccentric braces and shear wall، the structure was rehabilitated and for specifying effect of approach rehabilitation on structure performance determined state and damage index again. Results shown that the eccentric braces had better seismic performance.

In this paper، the two methods of genetic algorithm and neural networks have been combined to achieve the optimum design (minimum weight) of single-layer-lattice domes subjected to uniform gravitational loading. Herein، 378 models with six topologies، spans between 10 and 50 m and different span-to-height ratio from 1/8 to 1/2 have been analyzed and designed for the optimum weight and configuration using genetic algorithm. Furthermore، the results were being used to train the artificial neural networks to predict the optimum weight of the space domes. Thus، for a circular site plan with a specific diameter، an optimum single-layer-lattice dome with specific configuration could be proposed by using the neuro-genetic system.

In the present paper, dynamic characteristics of castellated beams are investigated and compared with the plain-webbed ones. Firstly, using the FEM-based software package ANSYS, modal analyses are performed on plain-webbed and castellated simply supported beams. The mode shapes are extracted and discussed. Afterwards, during a frequency-domain analysis, a white noise dynamic load with an appropriate frequency range is applied to both plain-webbed and castellated beams and their dynamic behaviors are studied through extracting the power spectral densities (PSDs) of various structural responses. The effect of full and local lateral bracing of the beams is considered in the present study. It can be concluded that the loading pattern is a critical factor in investigating the dynamic properties of simply supported castellated beams. For example, when a uniformly distributed load having white noise characteristics is applied to the whole length of the beam, some mode shapes can not be detected. However, when the same load is exerted on the half of the beam length, all mode shapes appear in the PSD of the acceleration response.

Viscous dampers are parts of energy dissipation devices which have received considerable attention in modern seismic design approaches. One of the most important challenges of them is fluid seals which needs maintenance. Considering technologies in Iran and idea of removing seals and so the need of maintenance، a dashpot using some parts of expansion joints was designed. The manufactured dashpot is a practical one، which has appropriate stroke، 65 mm، and efficient capacity، 224 kN، and also displays nonlinear damping behavior. Constitutive law characteristics of the dashpot using Kelvin Model is determined، and also Equivalent Linear Damping is calculated.

In this paper، the hybrid friction-yielding damper in the center of X-braced steel frame for dissipating seismic energy and its design methodology are introduced. Due to their relative simplicity and easy application with no need for any special material or technology، this high performance system have gained more attention compared to other means of energy dissipation devises. The advantage of failure localization at circular damper cause this system can be used for rehabilitation of existing building whose slender braces designed based on tension forces only. Possibility of Prompt installation of new ones after strong earthquake is another advantage of this simple system.

Kani method is a simple and robust tactic for analysis of building frames، which was proposed on 1950s and has been progressed substantially، so far. In contrast to the moment distribution approach، this technique can take into account the lateral transitions as well as nodal rotations of frames simultaneously. Based on this ability، Kani method is a suitable and cheap strategy for analysis of frame structure with the lateral shift. In this paper، Kani technique is extended to analyze braced frames to withstand lateral forces. The proposed formulation is utilized to solve some numerical problems. For the sake of the comparison، the results are also checked by matrix structural analysis method.

A lot of attempts and investigations have been done in recent years to improve the structural seismic design. The main approach governs on these attempts has been the control of structural performance during earthquake. During the large earthquakes, most of the structures reveal nonlinear behaviour. So to estimate the seismic performance of a structure, it is necessary to develop new methods which are based on nonlinear analysis. It seems that the nonlinear dynamic analysis is the most appropriate method, though it suffers from complexity. Therefore, the modern concept of "performance based seismic engineering” was developed, in which; we mostly use simple nonlinear static analysis to determine the nonlinear response of the structures. However, this method has also some weak points. One of these weaknesses is that only the first mode controls the whole response. And the other is that this mode remains unchanged after the structure under goes to inelastic range. Both of these assumptions are approximate, especially in tall buildings. It seems that the invariant lateral loads used in this method cannot consider these effects. In this paper, the accuracy of the invariant lateral load pattern in FEMA and modal pattern used in nonlinear static method and MPA method are considered in comparison with nonlinear response history analysis. This paper focused on drift and displacement as results of structure. These considerations were applied to three Steel moment EBF frames: 3, 9 and 15 stories and their detailed analysis were reported.