In this paper, brick walls as seismic load carrying elements in masonry buildings have been studied. An experimented un-reinforced brick wall (UBW) has been chosen from ref. (1) to prove the ability of analytical modeling used in this paper by which a reinforced (RBW) and a confined brick wall (CBW), designed according to Iranian Earthquake Standards, have been modeled and nonlinearly analyzed. This analysis shows that UBW practically is not able to resist horizontal loads. According to the type and direction of cracks in UBW constructed by conventional methods, it is clear that these walls do not have sufficient shear strength, and the study of hysteresis curves of brick walls shows that the confinement in CBW and reinforcement in RBW increases the rigidity and capability to displacement of walls.

1. IntroductionSpace structures are mostly interested for their lightness. One of the recent branches of space structures are called tensegrity structures. These structures are composed of compression bars and prestressed cables. There are not sufficient works about dynamic characteristics and behavior of these structures. Sultan et al carried out some research on nonlinear dynamic behavior of these structures [1]. Ben Kahla and Moussa studied the dynamic effects of rupture of a cable in an expanded tetrahedron [2]. Ben Kahla also has carried out a numerical analysis study of seismic behavior of a tensegrity frame [3]. Following these studies, in this research a set of tensegrity barrel vaults are considered and their seismic behavior is studied.

In general, shear wall design is based on flexural ductility. In this design approach, behavior of the shear walls is more similar to a cantilever beam with significant bending moment at its base. In such systems, the main input energy dissipation during seismic events happens at the base of the shear wall. In this paper, in order to improve the behavior of these important lateral resisting mechanism in structural systems, the possibility of dual type behavior (flexural and shear) were investigated. At first, the potential of this approach in improving the behavior of shear walls has been examined in a simplified structural model. Later, three types of shear walls including slit walls, shear walls with opening and frame-wall systems have been studied. The results show the capability of dual ductility modes of behavior in all three systems. Energy dissipation dispersion in these systems is better than the ordinary shear walls. Among the dual ductility systems, the frame-wall system has shown a superior performance compared with that of the two other systems.

seismic behavior of reinforced concrete braced frames is investigated in this paper. Study includes the modeling of some two Dimensional Reinforced Concrete braced frames using nonlinear static and dynamic analysis. The results of braced frame analysis such as stiffness, strength, ductility and energy dissipation are compared with those of Reinforced Concrete frames and Reinforced Concrete frames with shear wall. This comparison concludes that Reinforced concrete braced frames have better seismic performance.

Moment-resisting steel frames (MRSFs) have high ductility, however, suffer from low lateral stiffness and large lateral drifts. Recently, a new LFRS called knee-braced moment frame (KBMF) has been introduced in the literature in which the seismic behavior of an ordinary moment frame is improved using some knee elements as structural ductile fuses in the vicinity of beam-to-column moment connections. In this research, seismic behavior of some 3, 6 and 10 stories KBMFs with different span numbers are studied using nonlinear static and dynamic time-history analyses. The results show that the overstrength factor as well as behavior factor of KBMFs are considerably larger than the corresponding factors for MRSFs. Furthermore, it was observed that the column axial demands in KBMFs – except for the top stories-are smaller than those proposed in the seismic Provisions for MRSFs.

Accelerated construction methods are extensively used worldwide to reduce the negative impacts of bridge construction on urban traffic. These methods usually require prefabricating parts of the bridge off-site, which reduces on-site construction time and improves the quality and safety of construction. While the use of precast elements for bridge decks is relatively common, using precast elements for bridge piers is a recent development, especially in high-seismicity regions. Prefabrication of bridge piers can further expedite the construction of bridges. Moreover, the use of precast elements can be combined with a self-centering capability, through which the earthquake-induced damage and cost of post-earthquake repairs are greatly reduced. Despite a number of previous numerical and experimental studies on the behavior of precast, self-centering bridge piers, limited information is available on the selection of design parameters for such piers, and important decisions such as the prestressing force needed to achieve suitable seismic behavior remains to a large extent uncertain. This study aims to investigate the seismic behavior of concrete bridges consisting of precast self-centering piers, in which unbonded, post-tensioned tendons are used for self-centering and reinforcing steel is used to dissipate earthquake energy. A two-dimensional numerical model was developed in OpenSees to simulate the behavior of concrete bridges consisting of precast self-centering piers. The model consisted of fiber elements to model concrete and mild steel, as well as truss elements to model unbonded post-tensioning steel. The model also involved the use of zero-length sections to model the bond-slip behavior of mild steel bars. The modeling approach was validated based on experimental results available in the literature on cyclic loading of four bridge piers. To evaluate the effects of various design parameters on the behavior of precast segmental bridge piers, 9 segmental piers with different percentages of prestressing force and reinforcing steel were designed according to 2017 AASHTO LRFD Bridge Design Specifications. All piers were designed to possess similar nominal flexural capacities. The piers were then subjected to monotonic, cyclic, and dynamic time history analyses. The results showed the positive effects of prestressing in delaying cracking and reducing the residual drifts of precast bridge piers. Increasing the prestressing force ratio up to 10 percent of compressive strength of the pier cross section was observed to improve the overall seismic behavior of the structure, above which a further increase in the prestressing level may result in a diminished performance. The optimal value for the prestressing force ratio, which resulted in the most desirable behavior for cyclic and dynamic loadings was therefore found between 0.1 and 0.15. In piers with a prestressing ratio above 0.15, a decrease was observed in the area of hysteresis loops, which was accompanied by negative stiffness of the base shear versus drift curve. Moreover, the residual drift of the pier increased when prestressing ratios greater than 0.15 were used. The maximum drift of the structure was found to be insensitive to the prestressing force ratio. The results of this study are of great value for optimal design of precast, self-centering bridge piers in high-seismicity regions.

Elevated tanks are very important structures and consist of various types. Water supply is vital to control fires during earthquakes. Also they are utilized to store different products, like petroleum supplies in cities and industrial zones. Damage to these structures during strong ground motions may lead to fire or other hazardous events. Elevated tanks should stay functional after and before earthquakes.However their dynamic behavior differs greatly in comparison with other structures. In this research, a sample of reinforced concrete elevated water tank, with 900 cubic meters capacity, exposed to three pair of earthquake records have been studied and analyzed in time history using mechanical and finite-element modeling technique. The liquid mass of tank is modeled as lumped masses known as sloshing mass, or impulsive mass. The corresponding stiffness constants associated with these lumped masses have been worked out depending upon the properties of the tank wall and liquid mass. Tank responses including base shear, overturning moment, tank displacement, and sloshing displacement have been calculated. Results reveal that the system responses are highly influenced by the structural parameters and the earthquake characteristics such as frequency content.

Elevated tanks are important structures in storing vital products, such as petroleum products for cities and industrial facilities, as well as water storage. These structures have various types and are constructed in a way that a greater portion of their weight is concentrated at an elevation much about the base. Damage to these structures during strong ground motions may lead to fire or other hazardous events. In this research, a reinforced concrete elevated water tank, with 900 cubic meters capacity, exposed to three pairs of earthquake records was analyzed in time history using mechanical and finite-element modeling techniques. The liquid mass of the tank was modeled as lumped mass known as sloshing mass, or impulsive mass. The corresponding stiffness constants associated with the lumped mass were determined depending upon the properties of the tank wall and liquid mass. Tank responses including base shear, overturning moment, tank displacement, and sloshing displacement were also calculated. Obtained results revealed that the system responses are highly influenced by the structural parameters and the earthquake characteristics such as frequency content.