Strut and tie model for concrete beams
Date of Issue2009
School of Civil and Environmental Engineering
The strut-and-tie model was developed in 1899 and was first used in the calculations of the concrete members experiencing both shear and torsion. As the strut-and-tie model design became more frequently used, the strut-and-tie model was further applied for the calculations of complicated loading situations. The strut-and-tie model proposed various modelling methods for calculations of the discontinuity region, where it is more susceptible to shear stresses and deformations. These methods simplified the calculation process of complex truss models, hence became widely used. The main objective of the study is to predict the ultimate shear strength of reinforced concrete deep beams using a proposed analytical strut-and-tie model, based on the design codes in ACI 318-05. The adequacy of the shear strength calculations based on the strut-and-tie model from the ACI 318-05 Appendix A will be evaluated with experimental shear strength results from the tests of 69 reinforced concrete deep beams. The beams have concrete strengths, f’c, of the beams range between 22Mpa to 73.6Mpa; high strength concrete beams have strength above 41Mpa. The entire beam may be taken as a discontinuity region to simplify calculations. Experimental beams are mainly subjected to one concentrated load and are simply supported. The calculated capacities by ACI 318-05 are sufficiently adequate and conservative for majority of the beams. However, another strut-and-tie model may need to be introduced to the beams from Oh and Shin for a more accurate calculation of shear strength at failure. This will be further explained in chapter 4 of the report. The ACI 318-05 strut-and-tie model approach produces conservative but scattered results. Thereofore, considerations of limiting or introducing some design variables such as (a) the effective depth of the top strut and tie, (b) the area reduction factors for high-strength concrete deep beams and (c) the amount of horizontal web reinforcements and vertical web reinforcements suitable for the use of ACI-318-05 strut strength factors βs are recommended to improve the adequacy of the strut-and-tie model.
DRNTU::Engineering::Civil engineering::Structures and design
Final Year Project (FYP)
Nanyang Technological University