Shutt 1997
In this paper, the application of a hybrid precast moment resisting frame is explained. Mild steel and PT strands that can absorb energy and provide self-centering were used in the connections of precast members. Firstly, the mechanism of connections and installation steps were explained, and then the advantage and the applications of this structure were mentioned.
System Concept
This system is composed of a precast concrete moment frame and PT strands at the connections. This frame is intended to absorb seismic energy independent from the structural members. The post elastic performance of the system is reliant on the connection rather than structural members. Hybrid frame classification is dependent on the connections between the precast columns and the beams. Standard reinforcing and high strength post tensioning steel cables are used in the beams. This combination provided two separate functions to the system: energy absorption and strength. Inelastic behavior from the movement of the joints enables energy absorption. High-strength post tensioned steel gives the joints the strength to resist applied dead, live and seismic loads. Moreover, mild steel at the connections serve as energy dissipaters. Strength and energy absorption are thusly separated from one another.
The elasticity of the joint allows it to open and close to accommodate seismic ground motion. By keeping the initial post tensioning force low relative to the strand’s ultimate strength, the high strength steel does not yield. This provides large reserve capacity for deformation.
Installation of the System
The columns are erected first and equipped with temporary steel corbels. Then the beams were set on the corbels and the reinforcing bars are placed in the trough. Next, the bars are passed through the ducts in the solid ends of the beam. Ducts from beams and columns line up with each other. The gaps between beams and the columns are then filled with a fiber-reinforced grout.
Results and Discussion
The hybrid precast moment resisting frame offers several advantages over other seismic systems. Some of them are lifecycle costs, simplicity, speed and safety. This system could be constructed economically with higher performance. Moreover, its drift capacity could exceed six percent. When used in this experiment, negligible cracks were observed only at upper stories, and they closed when loads were removed.
Reference
Shutt, C.A. (1997). “Hybrid Precast Frame Meets Seismic Challenges,” ASCENT, Spring 1997, pp. 14-19.