Modelling single span and continuous deep beams using Strut-and-Tie Method

In this study, a direct Strut-and-Tie Model (STM) modified from previous work (Tan et al. 2001, 2003) is proposed. By adopting an interactive stress-based failure criterion, i.e. Mohr's theory, to tensioncompression nodal zones of the deep beam, no pre-set empirical stress limit is needed for determining the ultimate strength of deep beams and the softening effect of concrete compressive strength due to transverse tensile strain can be taken into consideration. Several improvements have been made to the original model (Tan et al. 2001, 2003). The influence of stress distribution factor k on the model prediction is studied and it is shown and explained that the k value is not a critical factor in the model. The softening coefficient in the STM is explicitly derived and shown to be similar to Modified Compression Field Theory (Vecchio and Collins 1986, 1993), and Belarbi and Hsu's equations (1995). The modified model for simply supported deep beams (SSDBs) is then verified against 233 test results collected from the literature. The predictions are better than the original model in both accuracy and consistency. Based on the modified model, the strut-and-tie method is further extended to calculate the shear strengths of concrete continuous deep beams (CDBs). It is once again shown that the model predictions are in good agreement with the test results.