Refined strength prediction of concrete 2D bottle-shaped struts

Abstract

For better strength prediction using strut-and-tie models (STM), it is essential to use reliable strengthparameters of the model components; e.g., struts, ties, and nodes. Among all the elements of the STM, thestrength of the bottle-shaped struts is not well quantified. The purpose of this study is to develop moreaccurate formulas for the calculation of the effectiveness factors for 2D bottle-shaped struts, that areunreinforced, reinforced with minimum reinforcement, and reinforced with sufficient transversereinforcement. The nonlinear finite element analysis, with the aid of the software ABAQUS, has been utilizedin this study, which has been verified against experimental tests. The study has been carried out for gradesof concrete varying from 20 to 100MPa, and for bearing plate to width ratio varying from 0.1 to 0.9. Theobtained formulas for the effectiveness factors of bottle-shaped struts are functions of the concrete strength,which is not the case with the ACI 318-19 provisions. These formulas have been verified againstexperimental tests and have been compared with the ACI 318-19 provisions. The predictions based on theseformulas are more accurate than those based on the ACI 318-19 provisions. Also, the results from theseformulas are always on the safe side. On the other hand, the ACI 318-19 provisions lead to unsafe results inthe case of high-strength concrete and very conservative results for the case of unreinforced struts fromnormal-strength concrete