benyamin mohebi

Post-Earthquake Fire (PEF) is an incident that can lead to a crisis and can be more critical than the earthquake itself due to the problems of passing vehicles and providing aid and assistance to the residents after the earthquake, and it can cause a lot of human and financial losses. Despite the large history of post-earthquake fires, the design regulations do not take into consideration the simultaneous effect of fire load and earthquake. On the other hand, in design based on the performance of structures, structural members should be designed for a specific level of performance that depends on the importance of the structure, which in the event of a post-earthquake fire, the performance level of the structure can change .Structures that are designed according to the regulations for the level of life safety performance may deviate from the desired level in the event of a fire after an earthquake. In this research, Post-Earthquake Fire was modeled in a moment steel frame. In this modeling, various levels of ground motion intensity and several time intervals were considered to extinguish the fire in the event of a post-earthquake fire. Three-story moment steel frame structures were modeled using OpenSEES software and studied to the performance level of life safety. Considering 44 different accelerograms, first, a scale of these accelerograms was applied to the structure. Then, assuming 60 seconds of free vibration to damping of the structure, the thermal load was applied to the members exposed to heat under the nine-point heat gradient, taking into account the ISO834 standard fire curve. Considering the maximum relative displacement between floors of 2.5% for the safety performance level, the quasi-acceleration spectrum component in the period of the first mode of the structure (Sa(T1)) was determined for this maximum relative displacement between floors under earthquake alone. Then, for different durations of post-earthquake fires, the maximum relative displacement between the floors under post-earthquake fires was determined and  Sa(T1) of a scale of the accelerogram applied was determined so that the structure under earthquake alone can have a maximum relative displacement between floors equal to the maximum displacement between floors under post-earthquake fire, and finally with this ratio Sa(T1) to Sa(T1) of the accelerogram scale, which had produced a maximum relative displacement of 2.5% between floors in the structure, a coefficient was obtained to modify the base shear to provide the performance level of life safety for various durations of post-earthquake fire.

One of the most important components of water supply systems is the liquid storage tanks. During an earthquake, the interaction of fluid and structure in the liquid storage tanks and the sloshing phenomenon has a significant effect on the response values of the structure. Regarding the importance of the effects of near-fault earthquakes and their effect on seismic behavior and structures loads, in this study, the sloshing height and vibration of 2D concrete rectangular tanks under near- and far-field earthquakes was investigated using numerical methods. The effect of tank's dimensions, depth of water and ground motion characteristics on the maximum sloshing height was taken into account. Therefore, 9 tank models and 10 near- and far-field ground motion records were considered. The results indicated that the median values of maximum sloshing height in the near-field records are significantly higher than those related to far-field records. The average of increase of sloshing heights in tanks with lengths 20, 40 and 60 meters is 65, 77 and 100 percentage respectively. Also, with increase of fluid depth and tank width, the median of the maximum sloshing height increases and decreases respectively. In tanks, subjected to far- and near-field earthquakes, sloshing height had the highest correlation with Arias Intensity and PGV respectively. According to the results of this research, correction coefficients for the relations presented in the codes can be proposed to consider the effects of near-field earthquakes in calculating the maximum sloshing height.

A parameter that quantitatively represents the strength of a ground motion is called Intensity Measure (IM). The value of an IM for a given hazard level is the output parameter of Probabilistic Seismic Hazard Analysis (PSHA) which is used in structural seismic analysis. In other words, an intensity measure is a link between PSHA and structural seismic analysis. The main desirable features of an appropriate IM are efficiency and sufficiency. The importance of using an appropriate IM is that the seismic performance assessment of structures can be performed more realistically. In this study, the performance of different scalar IMs to predict the collapse capacity of low to mid-rise steel Special Moment Resisting Frames (SMRFs) was evaluated. For this purpose, 3, 6 and 9-story steel SMRFs designed for the SAC project were simulated by OpenSees and the collapse capacity of these structures were determined by using incremental dynamic analyses under 67 far-field ground motion records. After calculating the collapse capacity values by using scalar IMs existing in the technical literature which are classified into structure and non-structure specific IMs, the performance of IMs including efficiency and sufficiency with respect to magnitude, source-to-site distance, and average shear-wave velocity at the upper 30 m was compared.

In this paper the damage location in beam like-structure is determined using static and dynamic data obtained using finite volume method. The change of static and dynamic displacement due to damage is used to establish an indicator for determining the damage location. In order to assess the robustness of the proposed method for structural damage detection, three test examples including a static analysis, free vibration analysis and buckling analysis for a simply supported beam having a number of damage scenarios are considered. The acquired results demonstrate that the method can accurately locate the single and multiple structural damages when considering the measurement noise. Finite volume method results provided in this study for finding the damage location is compared with the same indicator derived via finite element method in order to evaluate the efficiency of FVM. The acquired results are showed a good match between both Finite Volume method and Finite Element method and there are reasonable correlations between ones.

Damage detection has been focused by researchers because of its importance in engineering practices. Therefore, different approaches have been presented to detect damage location in structures. However, the higher the accuracy of methods is required the more complex deliberations. Based on the conventional studies, it was observed that the damage locations and its size are associated with dynamic parameters of the structures. The main objective of this research is to present a sophisticated approach to detect the damage location using multi-objective genetic algorithm (MOGA) along with modified multi-objective genetic algorithm (MMOGA). In this approach natural frequencies are considered as the main dynamic parameters to detect the damage. The finite element method (FEM) is utilized to validate the accuracy of the results extracted from the natural frequencies analysis with consideration of the beams with different support conditions. Accordingly the results emphasize the high accuracy of the proposed method with the maximum error of 5%.

One of the important effects of earthquake is impact of adjacent buildings. To eliminate or reduce the damage and destruction caused by the impact of adjacent buildings to each other, they should be separated by a gap or should be constructed with a minimum distance from the border. In this issue, the properties of near field records of earthquakes, with close distance to the source of the wave propagation makes them different from other records. Seismic Code 2800 Iran has made no mention of near-field earthquake response spectrum and seismic design spectrum in 2800 code is for far field earthquakes. Furthermore, a new method to reduce the effects of earthquakes on structures is using base isolators. In this study, the effects of base isolators in prediction of the behavior of concrete moment frames (medium ductility) located near the source of earthquake have been investigated and two-dimensional frames with same bays and different number of floors (2 4, 6, 8, 10 and 15 story frames) which represent the short, medium and high rises buildings have been considered. Results indicate that the required gap for isolated buildings located near faults is more than the predicted amount in Iranian Seismic Code (2800 standard). All the models are intermediate reinforced concrete frames which are separated from regular structures. One of the modern techniques for designing seismic resisting structures is using base isolations. There are several types of isolators which can be used practically in the structures. The damping of the isolators depends on the type of them and there are wide ranges of damping amounts based on isolators’ types. The main idea in this regard is to reduce the strength demand in the structures and also reduce the nonstructural damages even during severe earthquakes. Also it is possible to reduce non-structural damages by using base isolators. Base isolators with high damping, absorb earthquake energy using displacement. Although it is very good idea to use base isolators in seismic areas, but the gap should be produced between adjacent buildings to prevent buildings contact. This is very dangerous especially when the story levels are not same in the two buildings. In this case a concentrated load will induce to middle of column of another building. In this research it is tried to find the suitable amount of gap for base isolated structures. Also for considering near-fault effects, some of records with near-fault behavior have been selected and used. The structures considered to be retrofitted by base isolators. For calculating displacement demand of the structures under earthquakes the nonlinear time history analyses have been used. All the analyses performed using opensees software and scaled records. The results shows that the amount of Gap in Iranian Seismic Code (2800 standard) is suitable for structures which are not in near-fault regions. Of course there are some differences between the code and the results achieved in this research. But for structures in near-fault regions the proposed amount in the code is less than required amount of gap from the results of this research.

Provision of ductility has always been of concern in seismic design of structures. However, large variability in connection performance is observed during the recent earthquakes, due to brittle fracture of steel moment frame connections. In this study, Distribution of early fracturing pre-Northridge connections is optimized by genetic algorithm tool to quantify the sensitivity of seismic response of the structures to spatial variation of early fracturing connections for two hazard levels. Also, a non degrading ductile connection is modeled to compare the seismic performance of the structures. Probability assessment is carried out by implementation of incremental dynamic analysis to find the reliability of structures under this condition. Results show that configuration of fracturing connections in beams, in contrast to columns, can significantly affect the collapse capacity of structures.