A NEW MODEL FOR PREDICTION THE EFFECTIVE STRENGTH IN CONCRETE BOTTLE-SHAPED STRUTS

Strut-and-Tie Model (STM) can be used to model the flow of compression within a concrete strut. Concrete struts are formed in various shapes such as prismatic or bottle-shaped. In order to study the behavior of concrete struts, a series of simple tests were performed. Eighteen reinforced concrete isolated struts with compressive strength of 65 MPa were tested to failure under point loading in the plane of specimens. The tested specimens were reinforced by various reinforcement layouts. The behavior of tested beams was investigated. Observations were made on transverse displacement, primary cracking and ultimate failure load and distribution of strain on the face of tested panels. Based on those observations, the geometry of the concrete struts was examined. At least a new model to analysis of concrete struts was proposed based on modified compression field theory (MCFT). A database of 44 tested specimens was compiled to evaluate the proposed model. The results indicate that using the ACI and CSA expressions regarding the amount of minimum required reinforcement in a strut produces conservative but erratic results when compared with the test data. Conversely, the new proposed model presents a more accurate prediction for the strength of 44 tested struts.