Evaluation of slab–wall connections in tunnel form concrete structures: A multi-level approach based on seismic demand and capacity

Abstract

The seismic performance of an integrated tunnel-form concrete system relies heavily on the performance of walls, considering the safe design of slabs and the substantial length of in-place connections. However, despite ensuring suitable seismic behavior for slabs and walls, the lateral load resistance of the system depends on the capacity of connections between them, which has not received adequate attention in the existing technical literature and prescriptive codes. To address this gap, the present study focuses on the comprehensive evaluation of slab–wall connections in tunnel-form concrete systems. By analyzing 5-story and 10-story models, it was consistently observed that connections at lower levels are more vulnerable. Using the demand approach and considering the design basis earthquake (with a maximum acceleration of 0.35 g and a return period of 475 years) as the input excitation, the system exhibited a reliable immediate occupancy performance level with an estimated reliability of 100%. However, in taller structures, connections were predicted to experience cracking with a maximum demand to capacity ratio of 1.1. Applying the capacity approach and considering the earthquake corresponding to the immediate occupancy performance level in the system as the input excitation, the system achieved a reliable life-safety performance level with an estimated reliability exceeding 79%. However, in more than half of the building height, connections were predicted to experience cracking with a maximum demand to capacity ratio of 2. The results demonstrate that the existing shear-friction capacity adequately meets the demand of cracked connections in both approaches. Nevertheless, an evaluation of the shear-friction capacity demand ratio reveals that connections are undeniably one of the primary weaknesses of the tunnel-form concrete system, especially as the structure’s height, torsional effects, earthquake intensity, or allowable damage level increases. Therefore, special detailing is necessary to address this vulnerability.