The maximum displacement responses under the seismic motions are usually considered as an indicator for damage evaluation. It is obvious that appropriate selection of drifts corresponding to various damage levels plays an important role in safety and economy of a design project. Despite the extensive use of the box-type structural system in mass construction and housing industry, there is no special design requirement for this structural system. Due to three-dimensional behavior and interaction of intersecting walls and slabs, it is expected that this system presents different seismic performance in comparison to the conventional shear wall buildings. This study evaluates the overall and story failure mechanism as well as global and local damage indices in this structural system. Maximum allowable drift ratios of 0.45%, 0.65%, and 0.8% are suggested for the immediate occupancy, life safety, and collapse prevention levels, respectively. Moreover, a damage index based on the maximum relative inter-story drifts is proposed to assess the failure in the height domain. According to the assessments, the story and global failure occurring due to considerable damages in main load bearing elements reveals high importance of local damage indices in box-type structural system. Based on the results, it is concluded that the proposed maximum values for drifts in different standards and codes are not reliable. Considering the shear-control behavior and depending on the expected performance levels, the proposed local damage indices are considered as accurate control indicators for box-type structural system.

In reinforced concrete structures comprising box-type (tunnel form) structural systems, although the link beams (LBs) experience heavy damage before the shear walls, dimensional and cross-sectional limitations make it challenging to design LBs as seismic fuses. In this study, replaceable steel coupling beams were considered as an alternative to concrete LBs and the seismic performance, seismic reliability and multi-level response modification factor of this new system was examined. The results showed that the steel LBs had considerable effects on the lateral stiffness and load-bearing capacity of the box-type structural system. Under design and maximum credible earthquakes, the steel LBs had less influence on the performance level of the structural walls, which are the main elements of the lateral-load-bearing system. Consequently, they will slightly reduce the seismic reliability of the system while achieving predetermined performance levels. The use of steel LBs is suggested due to their replaceability and high energy-absorbing capacity.

Performance analysis of reinforced concrete (RC) buildings during past earthquakes has shown that irregular distribution of mass, stiffness, and strength may cause severe damage in structural elements. Accidental torsion, one of the most common reasons of damage and failure under the strong ground motions, is a complex phenomenon in which several variables are involved. The box-type structural system is considerably sensitive to torsion due to shear wall arrangement and that the torsional mode which governs structural response. Thus, understanding and evaluating accidental torsion is a fundamental step in seismic reliability evaluation of this structural system in comparison with other common structures. Therefore, in this study, seismic sensitivity of the box-type structural system is evaluated for various configurations of mass, stiffness, and strength centers. Several analyses, such as eigen-value, push-over, nonlinear time history, and seismic reliability analysis are performed using artificial records to predict structural characteristics and probabilities of failure. The results show that the mass eccentricity has a greater effect on the seismic response in comparison with the strength and stiffness eccentricities. The most critical condition occurs when the mass and stiffness centers are shifted in the same direction, so the story drift under the design and maximum credible earthquakes are 2.45 and 2.26 times the symmetrical model drift, respectively. Furthermore, it is shown that this box-type structural system demonstrates acceptable seismic reliability under the accidental torsion since the main elements of lateral bearing system remain in an immediate occupancy performance level under the design earthquake.