Seismic Analysis of Precast and Post-Tensioned Column-to-Footing Connections with Steel–GFRP Bars and GFRP Spirals

Abstract

A numerical model simulating the seismic behavior of precast concrete columns confined with a glass fiber–reinforced polymer (GFRP) spiral reinforced with longitudinal steel or a combination of steel and GFRP bars was developed. Four column specimens confined with GFRP spirals longitudinally reinforced with either only steel longitudinal bars (all-steel) or a combination of steel and GFRP longitudinal bars (hybrid) were tested under cyclic loads. Two columns, one hybrid and one all-steel, were post-tensioned using high-strength steel bars. For the post-tensioned columns, carbon fiber–reinforced polymer (CFRP) jackets were applied externally at the column end. The columns were connected to the footings using grouted duct connections. A computational model using OpenSees is presented to analyze the cyclic response of the precast reinforced/post-tensioned concrete columns with grouted ducts reinforced with a hybrid arrangement of steel and GFRP bars. The numerical model incorporates plastic hinge length, buckling, bond slip, and low cycle fatigue of intentionally debonded steel reinforcing bars. Material models for confined concrete by two layers of GFRP internal spirals and CFRP external jackets, reinforcing steel bars, GFRP bars, and post-tensioned high strength steel bars proved their effectiveness in simulating the experiments. Satisfactory agreement between the model and experiments was observed. The numerical model predicted bar fracture during the same drift ratio as the experiments. The cumulative hysteretic energy of the numerical models deviated from the experiments by <6.0%. The difference in peak post-tensioning force between the numerical model and the experiments was <5.0%.