The influence of the connection characteristics on the seismic performance of precast concrete structures

Abstract

Objective of the thesis is the study of the influence of the connection characteristics on the seismic performance of precast concrete structures. To that end a six storey high building with moment resisting frame was analyzed and designed. The precast concrete building consists of 3x6m span frames at 7.8m centre-to-centre in the transverse direction and 7x7.8m span frames in the longitudinal direction. A 350mm floor spans in the longitudinal direction. The capacity design method is applied in all the solutions; the concrete structure is verified according to EC8. The principle of weak beam strong column connection is applied. The bending moment in the column beam connections is calculated through the analysis model considering the stiffness of the connected members. The distribution of the seismic loading on the columns is influenced by the connected beams strength. Capacity design accounts for the connected members strength and its interaction influence during seismic loading. The required seismic design strength in the columns is verified against the action of the connected beams due to seismic loading in a direction and its reversal action. It is a function of the connected members bending moment strength with an overstrength factor and the seismic bending moment proportion to its bending moment resistance, which accounts for a seismic magnification factor. In the design with monolithic and HFC connections the strength reduction and the over strength factors are applied in the design of the shear in the beams and the columns and the flexural design of the columns, while in the design with DDC and the posttension assemblage, the capacity design principles are applied considering those factors within the design criterias. In the design of the connections the main aspects as yield locations, drift, ductility and degradation is considered with a specific solution for each type of connection. The emulated R/C connection is composed of cast in place elements on the column top. Hybrid-fibre concrete connection composed of precast elements connected on the column top and connected with interior precast concrete B55 beams The two connection types provides continuity in the stiffness, stresses, and shear. The yielding is relocated from the column faces in the beams where the ductility is provided. The required high shear resistance at the column faces is designed with conventional diagonal shear. In the design with HFC additional reinforcement in the connection core is applied in order to get a stiff and strong connection while the reduction in the reinforcement at the yield locations is used to get use of its high ductility. The Ductile Dywidag connection and the hybrid posttension connection are attached to the columns with ductile bars passing inside the column core and with posttension tendons passing inside PVC through the column. By posttension assemblage mild reinforcing provides energy dissipation during a seismic event is placed at the top and bottom of the beam through the joint and is grouted in place. The design with monolithic connections is verified using the non-linear analysis program Ruaumoko using two records scaled to the design shear force of Ag = 0.24g. Both design results are verified for degradation, using Takeda degrading and plastic hinges at the column bases. The design results in available ductility in the beams greater than the ductility resulting from the non-linear analysis. The design with the modified stiffness resulted in improved moment curvature hysteresis behaviour in the column beam connection.