Date of Award
Master of Science (MS)
Civil and Environmental Engineering
Riyad S. Aboutaha
Construction defects, Finite element modeling, Low strength concrete, Nonlinear analysis, Reinforced concrete
In reinforced concrete (RC) beams, localized low concrete strength may occur under certain conditions, e.g., poor construction practice that results in concrete honeycombing. The performance of beams with localized poor zones has received considerable attention in civil engineering research. This report presents the response of beams with various localized poor zones along the length of simply supported flexural members. A finite element model approach is developed and calibrated against two experimental beam test data, conducted by others. Solid 65 elements for modeling the concrete and Link180 elements for modeling the steel reinforcing bars are combined together with spring elements between reinforcing steel and concrete. The modified Hognestad Model is adopted for describing the concrete properties, and the properties of steel followed a perfect elasto-plastic model. To model the bond between concrete and reinforcing steel bars, nonlinear spring element Combin39 is used to connect the concrete nodes and steel nodes. For the bond spring elements, the bond stress and slip curves are in accordance with the recent researches by CEB-FIP.
To simulate concrete degradation effect, the concrete strength at different locations is reduced. In this paper, the beam is divided into three major regions, one is sensitive to bending moment, one is sensitive to shear, and the third region is sensitive to bond slip. The variables investigated under this study also included four types of concrete strength and three different rebar sizes. A total of 30 FEM beams are investigated. The results of this research suggest that the most critical region to have
low concrete strength, along the beam length, is the bond slip zone near the supports, as reflected on the ductility of the load-deflection curves. A new generalized empirical model is developed with the objective to predict the load reduction effect of the localized concrete problem.
Xie, Feng, "The Effect of localized low concrete strength on flexural strength of RC beams" (2014). Theses - ALL. 43.