Optimal three-dimensional strut-and-tie models for anchorage diaphragms in externally prestressed bridges

As a typical D-region in externally prestressed bridges, an anchorage diaphragm is usually severed as the end anchorage of external tendons. In this paper, an optimal three-dimensional strut-and-tie model for the anchorage diaphragm is proposed, and direct equations to facilitate the design are also developed. Both the topology optimization technique and the principle of minimum strain energy are incorporated to find out the optimal configuration of the strut-and-tie model, which makes the model rational based. A design procedure for dimensioning and detailing the model is then given according to ACI 318-08 provisions. The proposed model is further evaluated using three test results, and the comparisons show that the model predictions are consistent and conservative. Moreover, a design example is presented to demonstrate the effectiveness and convenience of the proposed method.