Seismic Performance of Post-tensioned Precast Concrete Joints Improved with Curved Steel Braces

Abstract

ABSTRACT The moment frames that consisted of prefabricated concrete beams and columns, which were linked by the unbonded post-tensioning, have been proposed for multi-story buildings. However, their lower structural strength and stiffness limited the applicability of their systems in the earthquake-prone areas. Curved steel braces were proposed in this study to improve the structural performance of the post-tensioned precast reinforced concrete (RC) beam-column joints, along with four joint specimens consisting of braces with different cross section height and eccentricity were tested under the reversed cyclic loads while the parametric analysis was also carried out using the finite element analysis (FEA) model. Also, the failure mode, strength, stiffness, and energy dissipation were analyzed. Based on the results, the whole joints have a stable mechanical behavior with an inter-story displacement angle of 5%, concrete crushing at the end of the beam, and a bending yield of curved braces form the failure mode. The curved steel braces could provide good strength, stiffness, and energy dissipation for the precast joints and these features of the joints could gradually increase with the expansion of the brace section height and the reduction of the brace eccentricity. The equivalent viscous damping coefficient at 4% inter-story displacement angle ranged from 0.12 to 0.2, which was two to three times higher than the general post-tensioned precast RC joints. When the eccentricity of the curved steel brace was less than 0.3, the joint strength was greatly impacted by the eccentricity and changed a bit when it was greater than 0.3. The results showed the practical feasibility of the post-tensioned frames with curved steel braces.