Shape memory alloy braces and buckling restrained braces have been shown to exhibit favorable energy dissipating characteristics in steel structures. However, buckling restrained braces are unable to recover their original shape after unloading and consequently experience large residual inter-story drifts after the earthquake, which leads to large permanent deformations in the structure. On the other hand, shape memory braces possess the recentering feature which enables them to recover their original shape. Nevertheless, compared to buckling restrained braced frames, the shape memory bracing frame usually experiences larger maximum inter-story drifts during the earthquake. This paper presents the results of a numerical study conducted to investigate the benefit of using the combination of buckling restrained braces and shape memory braces (dual bracing) in one structure, for the new design as well as retrofitting purposes. The superelastic model of shape memory alloy and plasticity model of steel are incorporated into the nonlinear finite element program particularly developed for this research. Results revealed that, with the proper configuration, both aims, namely minimizing both residual and maximum inter-story drifts, can be attained.

Buckling-restrained braces are able to provide significant energy dissipation along with large ductile capacity through their excellent hysteretic behavior. However, due to their lack of recentering capability, buckling-restrained braced frames experience large residual drifts following a strong earthquake, leading to enormous repair costs. To overcome this shortcoming, super-elastic shape memory alloy braces with excellent recentering capacity have been introduced as a viable alternative to steel braces. Nevertheless, their energy dissipation capacity is usually low for seismic applications. This article proposes a robust self-centering energy-dissipative brace to be used in structural frames. The brace is capable of providing adequate energy dissipation capacity in the structure while simultaneously bringing the structure to its original configuration after the earthquake.

Abstract. The majority of connections in moment resisting frames are considered as being fully-rigid. Consequently, the real behavior of the connection, which has some level of flexibility, is ignored. This may result in inaccurate predictions of structural response. This study investigates the influence of flexibility of the extended end-plate connections in the steel moment frames. This is done at two levels. First, the actual microbehavior of extended end-plate moment connections is explored with respect to joint flexibility. Then, the macro-behavior of frames with end-plate moment connections is investigated using modal, nonlinear static pushover and incremental dynamic analyses. In all models, the P-Delta effects along with material and geometrical nonlinearities were included in the analyses. Results revealed considerable difference between the behavior of the structural frame with connections modeled as fully-rigid and those when flexibility was incorporated regarding to natural periods, strength and maximum inter-story drift angle.

As one of the most widely used materials in different structures, concrete is a material evaluated and categorized based on compressive strength criterion. In addition, national and international codes (INBC- part 9) and standards determine the tensile strength of concrete based on its compressive strength. The purpose of this research is to determine the relationship between compressive strength and tensile strength of C20, C30 and C40 grades. In this laboratory research, a total of 42 cubic specimens of 150 × 150 × 150 mm and 42 cylindrical specimens of 300 × 150 mm were assessed under compressive and tensile tests, respectively. Based on the results of this study, the relationships presented in Ninth Article of Iranian National Building Codes, ACI-318 and Euro Code 2 have been evaluated.

Abstract-This study presents the utilization of shape memory alloys in steel structures for retrofitting purposes in order to bring them to the state of the current specifications. Shape memory alloys with the super-elastic behavior can be exploited in order to operate as a suitable passive seismic control device in structural systems. This article presents the results of a numerical study in which the seismic behavior of a damaged steel moment resisting frame is improved using shape memory alloy braces. Super-elastic model of shape memory alloy and plasticity model of steel are incorporated into the nonlinear finite element program particularly developed for this research. Also, to compare the behavior of the proposed energy dissipative system, the behavior of the steel frame with shape memory alloy braces is compared with the behavior of the buckling restrained bracing system which is to date considered to possess the best performance among the existing concentrically braced frames. Results proved that using shape memory alloy braces for the retrofitting purposes is preferred to buckling restrained braces; particularly in high levels of seismic damage.