جستجوی مقالات مرتبط با کلیدواژه « nonlinear incremental dynamic analysis » در نشریات گروه « عمران »

Steel moment frames are among the conventional structural systems for bearing gravity and lateral loads, which are especially common in high-rise structures due to their lower weight. Since the most important member in the system of steel moment frames is the connections and degree of plasticity is decisive in the performance of moment frames. Therefore, detailed research and investigation regarding the performance of these connections in steel structures is of particular importance. Due to the fact that steel moment connection with side stiffener plate has been widely considered in the last three decades due to the ease of implementation and improvement of seismic behavior, many studies have been conducted to improve the performance of steel moment connection with side stiffener plate.In this article, due to the fact that fragility curves are a suitable tool for estimating the probability of vulnerability, it has been determined and used to check the adequacy of the connection behavior and compare it with the pre-approved WUF-W connection. In order to determine the fragility curves, incremental dynamic analysis and finite element analysis have been performed.According to the results of analyzes and examination of structural failure parameters in different earthquake intensities, it was shown that the probability of structural failure using steel moment connection with sidestiffener plate is lower than the pre-approved WUF-W connection. Therefore, the steel moment connection with side stiffeners has higher reliability and due to its higher rigidity and ductility, it is able to withstand more kneading cycles at higher spectral accelerations.

Although Buckling-Restrained Braces (BRBs) can dissipate a large amount of the seismic input energy. However, they need to be repaired or replaced due to large permanent deformation after a severe earthquake. To overcome this issue, the use of Shape Memory Alloys (SMAs) in the braces has recently received attention. These alloys are able to return to their original state after loading. The present study aims to analyze the fragility curves and to investigate the sidesway collapse of the BRB frames equipped with SMA during near-field earthquakes in comparison with those given for the case without SMA. For the purposes, two 5 and 15-story BRB and BRB-SMA frames subjected to 7-pair of near-fault earthquake records are studied. Nonlinear Incremental Dynamic Analyses (IDAs) are carried out using OpenSees software. On average, the simulation results showed that collapse capacity and collapse duration of the BRB-SMA frames are about 30% and 35% more than those given for the BRB frames, respectively. For an instance, a collapse probability of 38% for the 5-story BRB-SMA frame and a collapse probability of 60% for the BRB frame is given for 3g spectral acceleration. Furthermore, at the performance level of 50% for the 15-story frame, the collapse duration of the BRB-SMA frame is obtained 25.6 seconds, while it is given about 10 seconds for the BRB frame. In addition, the use of a memory alloy for spectral accelerations of 1 to 4 g resulted in a reduction of 50% to reach the collapse performance level of the frames.

Fluid storage tanks are one of the most important components of vital arteries that play a key role in various water and industry networks, including oil, petrochemical, and water transmission systems. A study of seismic damage reports of tanks in previous earthquakes shows that one of the major damages in reinforcement concrete tanks that are commonly used to store water is cracking and liquid leakage. Therefore, in the present paper, the analysis and evaluation of ground concrete tanks are investigated to develop the fragility curve for these tanks. For this purpose, nonlinear numerical analyzes have been performed for three types of concrete cylindrical tanks with variable height to diameter ratio, taking into account the cracking of concrete. Then, the fragility curves of the tanks for the critical crack width are extracted according to the recommendation of Journal 123. These curves are compared with the results of previous research conducted in a linear manner without considering the cracks in the reservoir body, and the effects of applying crack widths in the analyses are discussed. The results indicate the need to apply tank cracking conditions in increasing dynamic analysis and extraction of fragility curves.

Composite steel shear wall is a newest seismic resistant system that has a high stiffness, strength and ductility. The main advantages of this structural system are lower thickness and weight, don’t need to reinforcement and its easy implementation procedure with compared to concrete reinforced shear walls. Recently, the behavior of various types of this seismic resistant system has been investigated through numerical or experimental studies. Response modification factor, over-strength factor and deflection amplification factor are the most important parameters for analysis and design of any seismic resistant system. The response modification factor of concrete filled double steel plate shear wall (CFDSPSW) is determined in this paper. For this purpose, an eight-story building with two ratios of wall length to wall heights (1.5 and 2) are designed with CFDSPSW system. To investigation the effect of the concrete core thickness, three different thickness (50, 125, 200mm) is considered. The finite-element model of all cases is developed using ABAQUS software and the combination of nonlinear static pushover; nonlinear incremental dynamic and linear dynamic analyses are used for calculation of the response modification factor. The results are shown that the enhancement in the concrete core thickness lead to increasing ductility and decreasing force reduction factor. The over-strength factor and response modification factor are obtained respectively 1.76 and 6.47 for this seismic resistant structural system.

Structural redundancy is a non-independent concept in structural engineering and has inherent dependence on structural parameters such as overstrength and ductility، so that both of overstrength and ductility capacities should change corresponding to any variation in structural redundancy. Nevertheless، most of researchers notified that taking any increase in structural redundancy should be a desirable property to deal with more effectively against earthquake loading. Furthermore، this issue can reduce structural sensitivity to abnormal loads. In this research to clarify the pure role of redundancy in earthquake resistant design and to distinguish the role of redundancy from total overstrength capacity، a number of 3D reinforced concrete special moment resistant frames (RC-SMRF) with equal ultimate base shear coefficient were designed. The dynamic behavior parameters of the designed structures under natural strong ground motion were evaluated، especially with regards to configuration of nonlinear deformations. The analytical outputs obtained from analyzed structures are illustrated ensembles of maximum acceleration، maximum velocity and maximum drift of each story. Furthermore، adequacy and accuracy of response modification factor which should be assigned as general indicator of quality of total seismic behavior has been studied conceptually. The results of this research indicate that: (i) Assigning an increase in structural redundancy would not always lead to efficient improvement in structural seismic behavior. Furthermore، notification to process of increased redundancy should not be consider as a criterion for any basic improvement in structural performance. This issue means that it is better to consider the effects of redundancy on important seismic parameters such as both the structural member ductility and the overstrength capacity. (ii) The calculated response modification factors as mentioned in this research، can consider as an index of quality of structural dynamic performance which is corresponding to a certain level of redundancy. Accordingly، the above statement should be notified in general cases of those earthquake loadings which would cause a certain level of story drift. This certain level of story drift would denote the structural behavior typically follows the calculated response modification factor. Oppositely، if an earthquake loading causes more story drift from that assigned certain level، structural behavior typically does not follow the calculated response modification factor. (iii) The codified procedure of calculation of response modification factor which were discussed and assessed in this study، cannot be realized subjected to those input strong ground motions that able to display high amplitude and long period pulse or pulses in their velocity time history. It is important to know that strong near-fault ground motions often have an impulsive feature and impose large amounts of sudden intense kinematic energy which must be dissipated by structural system during a short period of time. This issue causes amplified deformation demands in structures which are associated with very few cycles of cumulative plastic deformations. Hence، the earthquake damages due to these seismic load cases are effectively related to maximum deformation as well as maximum ductility. Yet، structures cannot accomplish based on the calculated response modification factor in the mentioned cases.