نشریه سازه و فولاد
سال هفتم شماره 12 (پاییز و زمستان 1392)

In this paper، the structural performance of steel rigid frame with pall friction damper is compared with a braced moment resisting frame as existing structure. The existing structure is a 5-story steel frame which is designed based on the 2nd edition of the No. 2800 standard and the performance evaluation is based on seismic retrofit guideline. It is observed that when the slip force reaches to 20 tons، about 100 percent of the total dissipated energy in the structure is dissipated by damper devices، which makes 20 tons be the optimum slip force. Also، under the design basic earthquake، the acceptance criteria for immediate occupancy performance level are satisfied in both frames. Investigating the demand to capacity ratio، DCR، in deformation - controlled actions reveals that in the existing frame about 20 percent of the elements reached nonlinear region and the acceptance criteria for force – controlled actions are hardly satisfied، while all members of the frame with damper remained in elastic behavior and the acceptance criteria for these actions are satisfied with 16 percent safety margin. Similar desirable results are obtained under an earthquake stronger than the basic design earthquake.

Since the application of structural control systems on nonlinear structures has been limited hence، in this paper designing active mass damper (AMD) for improving the seismic response of nonlinear frames has been studied. To this end، an eight-story steel frame with bilinear hysteretic behavior has been subjected to white noise excitation and AMD system has been designed by using the nonlinear instantaneous optimal control algorithm. For optimization of control system to minimize the maximum drift of structure، consequently the internal forces of the structural elements when a limited capacity has been considered for actuator،distributed genetic algorithm (DGA) has been applied. Also some practical limitations such as actuator capacity and AMD stroke length have been considered in design processes. The results of numerical simulations show the effectiveness of the proposed method in designing optimal AMDs for nonlinear frames. Also comparing the performane of AMD sysyem with that of passive mass damper (TMD) and active tendon control (ATC) shows that the AMD has been more effective in reducing the seismic response of nonlinear frames.

Optimal structural design is obtained by efficiently using material and members'' orientation. In this process، thin structures are designed. These kinds of structures are disabled against buckling. In other words، buckling phenomena causes system inefficiency، in spite of having the ability in the most parts of structure. Therefore، finding buckling load is very important. Generally، in order to study stability and calculating critical load، nonlinear structural analysis should be performed. At first، stability features are briefly discussed in this paper. Following this، some of the geometric nonlinear analysis techniques and stability analysis are reviewed. Finally، some of the interpolation functions are utilized and new methods for stability analysis are proposed.

Gate bracing system is a form of concentric bracing systems which is similar to chevron (inverted V) bracing. To provide enough space for openings، the members are not direct and joined together with different slope in one point. Bracing is joined to connection joint of beam and column in its other end. In this paper، overstrength factor، ductility factor and response modification factor of steel frames with gate bracing are evaluated. To do it، buildings with different story numbers on soil type II are considered. Static push over analysis، linear dynamic analysis and nonlinear incremental dynamic analysis are performed using Opensees software. To consider the uncertainties associated with earthquakes and to perform Incremental dynamic analysis procedure، 10 records of sever earthquakes ever happened including records of Bam and Tabas earthquakes are selected. Finally ductility factor، overstrength factor and response modification factor for gate bracing system are calculated and values of 3. 5 and 5 has been suggested for ultimate limit state and allowable stress design method.

Automatic inspection of steel surfaces is one of the basic processes in steel production. Most of steel producers have replaced the traditional human-based inspection methods with these new automatic and machine-based Methods. In this paper، a new approach has been proposed for detection and categorization of cold-rolled surface defects. The proposed algorithm is mainly based on artificial MLP neural networks and uncomplicated computational indicators. Experimental results show that the proposed method could detect up to 93. 3% of prevalent defects. In addition، this method is appropriate for real-time implementation because of its satisfactory execution time on a modern computer.

Knowing space structure behaviors for design of structures in seismic response is important. To guarantee better performance of space domes against strong earthquake from low weight index، safe geometry and high remain resistance. Seismic behavior and natural period of single layer Schewedler and Ribbed domes is studied in this paper. Six domes of both with different spans and the same number of nodes and elements as well as loading conditions are modeled by finite element method. Nonlinear static analysis is carried out. The force-displacement results are used to derive a formula for predicting the fundamental natural period. Using this equation، the behavior factor of domes is obtained in the form of a linear equation. Finally، behavior factor and natural period both of demes are compared.

In this paper، the Gravitational Search Algorithm (GSA) is employed for discrete optimization of truss structures using some steel profiles. GSA is compared to other heuristic methods including Genetic Algorithm، Ant colony optimization، Particle swarms optimizer، Harmony Search and some other methods. The performance of the GSA is evaluated through some numerical examples. The results demonstrate the efficiency of the presented method in structural optimization.