Progressive collapse studies generally assess the performance of the structure under gravity and blast loads, while earthquakes may also lead to the progressive collapse of a damaged structure. In this study, the progressive collapse response of concentrically braced dual systems with steel moment-resisting frames was assessed under seismic loads through pushover analysis using triangular and uniform lateral load patterns. Two different bracing types (X and inverted V braces) were considered, and their performances were compared under different lateral load patterns using the nonlinear static alternate path method recommended in the Unified Facilities Criteria (UFC) guideline. Eventually, the seismic progressive collapse resistance of models was compared to their progressive collapse response under gravity loads. These studies showed that models under the seismic progressive collapse loads satisfied UFC acceptance criteria and limited rehabilitation objective. The structures had better performance under seismic progressive collapse than models under gravity loads because of more resistance, ductility, suitable load redistribution, and more structural elements that participated in load redistribution. Furthermore, despite studies on progressive collapse under gravity loads, the dual system with X braces showed better progressive collapse performance (more resistance, residual reserve strength ratio and ductility) under seismic loads than the model with inverted V braces.

seismic performance is an important issue in the design of buildings located in seismic areas. One of the most important parameters in the design of structures is ductility (ductility; ductility plays the role of a fuse in the structure. Damage to a strong member (such as walls) that is expected to be able to maintain its stability in the structure in any case. The presence of a malleable member in the structure gives the occupants of the building the opportunity to leave the building during an earthquake. This is the same seismic expectation that comes from the structure, meaning that the structure does not act without warning and does not collapse once. In masonry buildings, the parameter of strength, especially shear strength, is very important. In this study, in order to know more engineers, to present the seismic weaknesses of masonry buildings during earthquakes and methods Fixing it during design and execution (before the structure is damaged and causes casualties and needs to be repaired) and also The wit of the damaged structure is addressed after the earthquake.

Structural control mechanisms are used as a reliable and efficient methods to enhance seismic performance and stability of structures. Ensuring the integrity and stability of civil infrastructures such as marine structures, especially oil platforms exposed to difficult environmental conditions, poses challenges that engineers strive to overcome. Introducing innovative methods and improving existing system performance can significantly aid in addressing these challenges. The objective of the present research is to investigate the effect of different levels of pre-stressing on shape memory alloy wires in a passive damper based on shape memory alloy and its impact on reducing the seismic re-sponse of marine structures. For this purpose, a simplified marine structure is modeled, and a struc-tural control system with a passive damper using shape memory alloy is incorporated. The results of different scenarios after applying seven sets of scaled ground motions from far field earthquakes and time history analyses have been evaluated. The obtained results indicate that increasing the cross-sectional area of the wires and increasing their pre-stress level reduces the maximum displacement of the structure and improves the overall performance of the structural control system. Furthermore, considering three different scenarios for the frame, the influence of frame stiffness on the results has been assessed.

Isolating the earth structures such as retaining walls, bridge abutments and buried pipes using the compressible materials is a novel solution to reduce the lateral earth pressure. In this technique, a layer of the compressible material with relatively small stiffness and limited thickness is implemented between the retaining wall and the backfill. This material acts as a seismic buffer due to its high compressibility, which absorbs the excess dynamic earth pressure significantly and attenuates the transmitted force to the retaining structure. Choosing the appropriate materials for construction of seismic buffers is based on their physical and mechanical properties as well as cost-effective considerations. Most of the previous studies were focused on some specific materials such as expanded polystyrene (EPS) foam blocks and tire chips. This paper investigated the performance of polymeric seismic buffers made from Polyurethane (PU) foam on seismic response of non-yielding retaining walls. PU foam has appropriate properties and eliminates some of limitations on materials used in previous studies. The purpose of current study was to evaluate the applicability of PU foam as a new option for construction of seismic buffers with regard to its benefits. Hence, the behavior of non-yielding retaining walls was investigated in two conditions of with and without presence of the seismic buffers by conducting of a series of 1g shaking table tests. seismic buffers included PU foam blocks, which were prepared by injecting foam into the cubic molds and spraying a certain amount of water on the specimens. A total of 13 tests were carried out on two models (retaining wall with and without seismic buffer) with changing the input base acceleration from 0. 07g to 0. 46g. The input motion was a horizontal sinusoidal excitation with a constant frequency of 3. 6 Hz, which was applied for 10 seconds to the longitude direction of the model. The model responses including wall force and backfill soil displacement were measured during the excitation in each test. The results showed that the implementing seismic buffers made from PU foam reduce the total and dynamic horizontal wall forces on average of 30% and 45%, respectively. The force attenuation and backfill soil displacement have an inverse relationship to each other. For an equal Normalized compressible inclusion stiffness, this type of foam has a better performance in comparison with similar materials such as expanded polystyrene foam (EPS). Moreover, it is identifying that the force attenuation is not uniform along the height and the maximum attenuation occurs at the top of the retaining wall. The force distribution is triangular for static conditions. As the peak base acceleration is increased and the contribution of dynamic loads on upper elevations is increased, the force distribution becomes nonlinear. Therefore, at earthquakes with moderate to high intensity, the point of application of total horizontal force is transferred to the upper elevations of the retaining wall. Moreover, it is revealed that the efficiency of this technique increases for moderate to high-intensity earthquakes (acceleration amplitude more than 0. 24g).

The idea that a building can be uncoupled from the damaging effects of the ground movement produced by a strong earthquake has appealed to inventors and engineers for more than a century. seismic isolation is effective in reducing seismic demand for buildings and decreasing seismic damage costs. Today the concept has matured into a practical reality and is taking its place as a viable alternate to conventional (fixed base) seismic resistan t construction. This study, three bracing frame and three spacial moment frame were modeled and analyzed and the capacity curve wase plotted. The finaly, response modification Factors for steel frames equipped with base isolation were compiled as a table. Finally, based on the results of the analysis, it was observed that the structures equipped with the surface separator have a more obtuse curve than the non-separating state.

Use of passive control systems causes reduction in seismic demand and prevents damage to the main components of the structure. Yielding dampers are among the common tools used for dissipation of earthquake energy entering the structure. The main goal of the present research is introduction of a novel pseudo elliptical yielding damper for improvement of the seismic performance of the existing steel structures. Considering the impact of geometric parameters of the pseudo elliptical damper on its stiffness and strength, a precise numerical study was performed on the ratio of diameter to thickness and other dimensions of the damper in this research.  For evaluating the impact of proposed damper on the seismic performance of existing steel buildings, use was made of three benchmark structures with 3, 9 and 12 stories which were retrofitted by this type of dampers. Also, the nonlinear time history analysis has been performed using the near field and far filed accelerometers to evaluate the analyses results at different seismic states. The results of numerical analyses indicated the good performance of propose pseudo elliptical yielding damper in terms of dissipating the earthquake energy entering the structure and reduction in the seismic responses of retrofitted benchmark buildings by this type of dampers. It was found that on average, the maximum inter-story drift in the 3, 9 and 20 story benchmark buildings were reduced by 66, 69 and 67%, respectively.

In the present study, seismic analysis of concrete gravity dams strengthened by asphalt buttressing is presented for improving the seismic behavior of the Koyna dam in India subjected to Koyna ground motion. Fluid-Structure interaction is modeled including water compressibility and reservoir bottom absorption. The foundation is considered as rigid. A three-dimensional fixed smeared crack model is used to consider the nonlinear behavior of mass concrete. The analysis is carried out in the time domain by Newmark time integration scheme. Linear and nonlinear behavior of dam models subjected to horizontal and vertical components of selected record have been analysed. In order to investigate the effects of asphalt buttressing on the interface of dam and asphalt, the contact surface is defined using joint elements with a thickness of zero. The results of the analyzes confirm that the asphalt buttressing can improve the stability of the dam due to the pressure applied to the dam in counteracting the hydrostatic and hydrodynamic forces, Also the significant effect of asphalt Buttressing on the optimal distribution of stresses in the entire body of the dam as well as the prevention of stress concentration and reduction of fracture in the upper body near the dam crest show so that the crack at the lower section of the dam and at the interface of the dam and foundation is partially developed with a slower rate, and the cracking at the upper part near the crown of the dam does not spread to the upstream body of the dam and does not cause a total failure. Overall, it can be said that asphalt buttressing can improve the seismic stability of gravity dams by exerting pressure on the dam in opposition to hydrostatic and hydrodynamic loads.

In this paper a new ribbed bracing system (RBS) is proposed capable of performing as a variable stiffness system that can be used for controlling structural deformations and frequency shifting to compensate seismic energy. RBS has two important advantages. Because of ribbed system, the compressive member is rigidly moved like a piston and a cylinder and therefore it is a buckling prevented system. Also it is possible to use this system as a semi-active system by considering the story drifts and global structural damage and control the system if it is necessary to be open or closed based on the operational criteria assigned in the system. RBS has no need to any actuator and large power supply, but just a battery-size power supply to switch the ribbed mechanism to be on or off. RBS is composed of a ribbed supplemental part and a normal wind-bracing on each floor. Considering an appropriate criterion based on the storey drift, minimum number of bracing systems will be active on the height of structure during earthquake. In contrast with completely closed RBS (CC-RBS) by on-off bracing system arranged along the height of the building cause period shifting of the structure to the larger value. Three stages are considered in the numerical studies: conventional bracing frame (CBF), CC-RBS and semi-active RBS (SA-RBS). Damage indices and Fourier transforms are calculated in order to discuss on the efficiency of the proposed system. Nonlinear dynamic analysis of system has been carried out and structural behaviour has been investigated.Numerical results show the efficiency of CC-RBS in reducing structural damage and improving seismic energy. Also base shear is reduced when SA-RBS is used and structural damage is more uniform in this case.