In recent years, some authors have investigated the problem of SEISMIC bearing capacity by limit state procedures. In these studies, the inertia FORCES developed within the soil volume which were ignored in previous studies were considered.In this paper, the effect of the soil mass underneath a footing on its bearing capacity is studied using upper bound limit analysis method and considering rigid blocks. It is shown that the consideration of inertia FORCES within the soil is responsible for a decrease in the bearing capacity and its effects decreases as the internal friction of the soil increases.

Although segmental tunnel linings are often used for SEISMIC areas, the influence of segment joints on the segmental lining behavior under SEISMIC loading has not been thoroughly considered in the literature. This paper presents the results of a numerical study investigating the effects of the rotational, axial, and radial joint stiffness of the longitudinal joints on the structural FORCES in segmental tunnel lining under SEISMIC loading. A 3D finite element method is adapted to establish elaborate numerical models of the segments. The validity of the numerical model was tested by comparing the results obtained with the well-known analytical methods presented by Wang and Penzien. The results demonstrate that by increasing the rotational stiffness of the segmental joint, the bending moment increases. When the rotational stiffness ratio is less than 0. 5, the positive and negative bending moment variations are more. The numerical modeling results show the variations in the bending moment and the difference between the positive and negative bending moment values increased by increasing the acceleration of SEISMIC loading. Moreover, it is significant for the values. By increasing the rotational stiffness ratio of the segmental joint, the axial force ratio decreases. By increasing the axial and shear stiffness ratio of segmental joint, the variations in the bending moment and axial force in segmental lining is not significant and is ignorable in designing segmental lining.

During an earthquake, the better performance of segmental tunnel lining, compared to the continuous in-cast concrete lining, is generally related to the joints between segments. In order to better understand the influence of the segment joints, their effect on the internal FORCES induced in tunnel lining simultaneously with the effects of the other influential parameters should be considered. In this work, the segmental joints were simulated by the representative stiffnesses and effects of these characteristics in relation to the other parameters such as the soil-liner interface behavior, number of segments in each ring and thickness of segments on the internal FORCES induced in structure were investigated. For this purpose, 2D numerical analyses were performed and the results obtained were discussed. Results showed that under the SEISMIC condition, the components that had the most significant role on the internal axial FORCES induced in the segmental lining were rotational stiffness and axial stiffness of joints. Also the bending moments were more affected by the rotational stiffness. Generally, the radial joint stiffness had a less effect on the induced internal FORCES. With increase in the number of segments and their thickness, the effect of joint stiffness on the internal FORCES increases and the design of joints should be given more attention; however, the effects of joint stiffness and frictional behavior at the soil-liner interface on the maximum induced FORCES are almost independent from each other. Also in a specified joint behavior, by variation in each one of the other parameters including the soil-liner interface condition, number of segments and their thickness, the absolute magnitude of the maximum induced internal FORCES sometimes change significantly.

Energy dissipation systems have been broadly used in structures during the recent decades in order to reduce earthquake and wind FORCES as well as reduction of structural lateral drifts within the code limits. Viscous damper is considered as one of the energy dissipation systems which are classified as velocity-dependent dampers among passive control systems and have been paid attention and their further detailed properties taken into account by many researchers. Viscous damper consists of a piston with some orifices inside the cylinder which contains highly viscous fluid. Energy dissipation of this damper is through pushing viscous fluid out of the orifices.These are two types of these dampers: linear and nonlinear from which linear type with velocity power of one is more practical. The structural damping force is usually set according to the procedure described in FEMA273 and are optimized by three controlled modes of displacement, velocity and acceleration.This study examines the effect of adding viscous dampers on SEISMIC behavior of steel moment frames. For this purpose, three steel moment frames of 1, 3 and 6-story all in 3 bays, with viscous dampers having power factor of 1, 0.8 and 0.6 are selected. These sample structures are subjected to the nonlinear time history analysis under the El Centro, Kobe and Northridge earthquakes, and their response including displacement, acceleration and base shear is compared in two cases of with and without viscous dampers.Finally, regarding nonlinear time history analysis results based on the structural behavior in three modes controlled by displacement, velocity and acceleration, proper damping FORCES are specified as 94.7, 240.1 and 557.1 kN respectively for one, three and six story structures based on maximum acceleration and base share obtained from FEMA273.

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.

The base isolation system is a method developed to protect structures against earthquake excitations, which is designed and implemented based on SEISMIC codes. The aim of this study is the development of a procedure in Iran for the SEISMIC design of buildings using an isolation system. For this purpose, the Japanese Code for the design of base isolated buildings is considered the basis of the proposed procedure. The Building Standard Law of Japan and related Enforcement Order and Notifications have been substantially revised since the year 2000 to introduce a performance-based regulatory and deregulation system for building control systems. The verification procedures of SEISMIC performance in the new code are, in essence, a blend of the equivalent single-degree-offreedom modeling of a building and the site-dependent response spectrum concepts, which make possible prediction of maximum structural response against earthquake motions without using time history analysis. Simplified design procedures, based on the equivalent linear method for SEISMICally isolated buildings, have been issued from the Ministry of Construction. To develop the procedure, we compared the Japanese and Iranian (Standard 2800) codes from different points of view. For example, parameters of soil type, SEISMIC zone, design spectrum, fundamental period and distribution of SEISMIC load in height are compared. By considering both codes, the procedure for SEISMIC design of buildings with an isolation system in Iran is developed. Then, for evaluation of the procedure, several structural models were considered, and results are compared with results of nonlinear time history analyses. Based on analyses results, the responses of the structure models at near field were higher than far field excitations, by two times. In both far and near field records, base displacement responses (at the level of base isolation) were higher than base shear responses. In all models, the response of structures based on the proposed procedure was reliable. Also, it is necessary to consider factors for near field effects in the Iranian SEISMIC code.