Study On The Suitability Of Strut-and-tie Model For Btidge Piers And Its Application Range

Reinforced concrete deep beam has drawn increasing attention from the bridge community due to its superior availability and bearing capability. The Bernoulli assumption(i.e., plane remains plane) is not suitable to deep beams.Due to the unclear mechanical mechanism of deep beams, the current design methods or standards are largely based on the regression analysis results from a large number of design experiments considering bearing and serviceability limit states. Although this kind of design methods can ensure the safety of a structural component, they are generally more costly as more reinforcing steel would be required. The finite element analysis may be performed to account for the nonlinearity involving in deep beams. But, it is time consuming and expensively,plus not every engineer is familiar with its use. Alternatively, the strut-and-tie model may be used, which is a practical method permitted by all design codes Currently, there is no specific design procedure pertaining to this practicalapproach available in the nation. In this paper, the basic theory of strut- and-tie model, its suitability, and the range of its applications as related to bridge pier systems are discussed, followed by the research discoveries.First, the basic theory and current design method of deep beams are described, where differences on the subject between China and USA are pointed out. The basics of strut and tie model, and the procedure of applying the model to bridge pier systems are highlighted in this paper. All the parameters used in the US design formula are adjusted to satisfy the Chinese standard safety factors and material requirements.Second, based on the actual bridge information made available, the strut-and-tie models are established for single-, double-, and four-column pier cap systems. ABAOUS software is utilized to verify the strut-and-tie models.The obtained stress contours are used as the basis to create these practical models, considering loads and boundary conditions. The distribution range of tensile and compressive stresses is ascertained to generate the ideal strut-and-tie models.Third, the required reinforcing steel amounts of the strut-and-tie models representing respectively the single-, double-, and four-column pier cap systems are determined based on both Chinese and American design standards, and are compared against to each other.Fourth, a reinforcement cage is introduced and embedded into the concrete cap beams to study if the enclosed reinforcing steel would be distorted with thevarious bridge pier systems, using ABAQUS software. As a result, the proposed strut-and-tie model is applicable to a wide range of applications including single-, double-, and four-column pier cap systems.In conclusion, the strut-and-tie model is theoretically sound, easier for use,and resulting in more economic designs。...