Bond–Slip Mechanism of Rammed Earth–Timber Joints in Chinese Hakka Tulou Buildings

Abstract

Hakka Tulou, a traditional form of Chinese building made of rammed earth and a timber frame, is characterized by its remarkable geometries, excellent thermal comfort, sustainability, and cultural value. The joints between rammed-earth walls and timber floor beams are critical structural elements and require an in-depth understanding of the load-bearing capacity for Hakka Tulou. To the best knowledge of the authors, this is the first study that investigates the bond–slip mechanism between timber beams and rammed earth. Eight pull-out tests were conducted on rammed earth–timber (RET) joints, in which the influence of compressive load, embedment length, and surface roughness was systematically studied. RET joints were analyzed based on the elastic solid-to-solid and pile-to-soil behaviors. The experimental results show that the bond–slip behavior could mainly be attributed to the friction, which depended on the normal stress and matric suction of unsaturated compacted earth. The test results were satisfactorily explained by geotechnical theories. Given the initial strength resulting from compaction and mobilized friction due to compression, a bond–slip model for rammed-earth structures was proposed. The parameters for the elastic zone were suggested for use in structural design. Rammed-earth buildings should be analyzed based on the principles of unsaturated soil mechanics, rather than elastic solid mechanics, even though rammed earth and underground soil are under fundamentally different conditions. The proposed design method for earth–timber joints could be applied to analyze Hakka Tulou or other similar earth buildings.