Date of this Version
Abo El-Khier, Mostafa. 2021."Ultra-High Performance Concrete (UHPC) Deck-To-Girder Connection For Accelerated Bridge Construction." PhD Dissertation, College of Engineering, University of Nebraska-Lincoln.
Precast concrete deck systems have been successfully used for Accelerated Bridge Construction. In most systems, special deck-to-girder connections are designed to achieve structurally composite sections. These connections require tight production/erection tolerances that complicate deck and girder fabrication and compromise the economics of these systems. This study presents a new precast concrete deck-to-girder connection that takes advantage of the excellent mechanical, workability, and durability properties of ultra-high performance concrete (UHPC) to simplify precast concrete deck and girder fabrication and erection. Typical girder shear reinforcement is terminated below the soffit of deck panels to eliminate any conflicts with deck reinforcement and relax production and erection tolerances. Shear pockets with loose bars are filled with UHPC to provide shear transfer mechanism between concrete deck panels and girders.
To evaluate the performance of the new connection, a non-proprietary UHPC mix was developed using local materials at approximately one-third the cost of commercial mixes. Two interface shear planes were identified in the proposed connection: in the monolithic UHPC shear pocket at deck soffit; and between fresh UHPC and hardened conventional concrete (CC-UHPC) at the top of the precast concrete girder. Current code provisions do not provide guidance on either of the two planes. Therefore, experimental investigation was conducted to evaluate these interface planes using slant shear, direct shear, L-shape push-off, and double shear testing. Then, finite element analysis was conducted to perform a parametric study on the shear pocket diameter and reinforcement size. Full-scale push-off tests were conducted to evaluate the constructability and structural performance of the new connection.
Test and analysis results indicated that the interface shear resistance of CC-UHPC with surface roughening of 1/4 in. can be predicted using cohesion and friction factors of 0.63 ksi and 1.23 respectively. Interface shear resistance of monolithic UHPC can be predicted using cohesion and friction factors of 0.49√f’UHPC (ksi) and 0.85√f’UHPC, respectively. The UHPC mix stability was found to significantly affect the structural performance of the new connection. Cost analysis indicated that the proposed connection is 21% more cost effective than existing connections.
Advisor: George Morcous