Rapid Construction of Bridge Piers with Improved Seismic Performance

Practical methods which permit efficient construction of bridge systems in locations of high density are needed. However, these systems must meet also the strict engineering performance requirements present in high seismic zones. Previous research indicates that concrete-filled tube construction can meet the performance and constructability requirements. Concrete-filled tubes (CFT) offer high strength, stiffness, and deformability and do not require separate column reinforcement and formwork. This improve constructability, decreases the cost and labor which will minimize traffic delays and construction costs. However, previous research has focused on the use of CFT elements for building construction and therefore little information is available regarding the design and performance of CFT connections (e.g. cap-beam-to-column, pile-cap-to-column) for bridge construction. The proposed research study will develop and validate appropriate connections for CFT bridge construction. The researchers have a long history of developing design methods for seismic design and performance-based design provisions for practicing engineers.

The research team will employ six tasks to conduct the study. In the initial phase, connection designs and construction methods will be proposed and studied analytically in conjunction with members of the advisory panel (consisting of engineers, contractors and practicing engineers). The research team will use experimental methods to develop and validate the proposed connections. Concrete-filled tube columns have large axial capacities and therefore a specialized reaction frame will be used in conjunction with a high-capacity testing machine to apply the axial load. The research team has successfully used this apparatus for testing of large-scale (20-in. diameter, 72-in. tall) column-to-footing connections and it can readily be adapted for this testing program. Finally, practical design methods and analytical tools will be developed in conjunction with the advisory panel.

The research will be conducted to provide design and construction recommendations for CFT bridge pier construction including: (a) reliable, thoroughly evaluated CFT piers and their connections for CFT bridge pier construction for seismic and fatigue demands, (b) design equations for predicting the stiffness and resistance of CFT bridge piers as a function of the yield stress of the steel, diameter and thickness of the steel tube, and the concrete strength, (c) analytical methods to predict the cyclic force-deformation response of CFT bridge piers using current CALTRANS technologies (e.g. moment-curvature analyses and lumped plasticity/plastic hinge length models), (d) design details and methods for connections of the steel tube to a reinforced concrete footing, reinforced concrete pile caps, reinforced concrete pier cap, and precast concrete pier cap, (e) guidance on selecting the steel type, the diameter and thickness of the tube, the weld types, environmental protection, and long-term maintenance and inspection of the CFT elements.

The proposed system provides a win-win solution to the challenges facing CALTRANS today. CFT pier bridge construction offers an opportunity for CALTRANS to simultaneously improve the engineering performance and provide rapid construction at reduced cost for their bridges. Without these efficiencies, bridges will continue to be costly and vulnerable to seismic demands and other types of extreme loadings.