Shake-Table Tests of a Pile-Supported Low-Rise Reinforced Concrete Building Designed to Japanese Building Standards

Abstract

In Japanese engineering practice, pile foundations are designed to lower base shear demands below that considered in the superstructure’s design. In recent earthquakes, such buildings incurred significant pile damage even in cases where the superstructure only had minor damage. This study looks to replicate this failure mechanism via large-scale shake-table tests of a pile-supported building designed following Japanese practice, compare its performance against a fixed-base case, and identify issues with such buildings. The specimen was a 40%-scaled 3-story reinforced concrete frame building supported on weak piles buried in soil. After completing shake-table testing of the pile-supported specimen, the specimen’s foundation was fixed directly to the soil tank to mimic a fixed-base condition, and further excitations were applied. For the pile-supported case, the piles underwent drift ratio demands of up to 14% and suffered local collapse failure at 1.0–1.5 times the design shaking intensity, whereas the superstructure only had a drift ratio of 0.17% and minor damage. These observations were consistent with postearthquake damage assessments, demonstrating that the shake-table tests were able to replicate realistic failure mechanisms. For the fixed-base case, the superstructure was able to withstand demands equivalent to 1.7–2.5 times the Japanese design spectra before reaching 2.0% drift and did not exhibit any strength degradation. Based on these results, buildings with weak piles will likely suffer significant failure at smaller intensity events than that which the superstructure would have been able to withstand. Furthermore, the lack of superstructure damage for such cases may lead to significant pile failure being unidentified during postearthquake inspections, resulting in unsafe buildings being occupied.