Simplified models to control plastic hinges in reinforced concrete frame structures

Researchers using structural analysis software (design software) like SAP2000® state that the plastic hinge length (L p) can be calculated based on analytical formulae, and is considered constant during the loading procedure. However, this datum varies and depends on several parameters. A first study is carried out using (SAP2000®.V14) to assess the influence of L p on the hinges response. The results show that the influence is not negligible, and the results are not unique, because they depend on L p. This code calculates the plastic rotation by multiplying L p by the plastic curvature for the hinges behavior assessment. In this connection, a better approach to control these plastic hinges has been developed using CASTEM2000, to calculate the plastic rotations, based on an integral calculus of curvature field along the length of the plasticized zone. Numerical investigations are carried out to control the plastic hinge appearance and positioning, as well as to get the corresponding L p. This study aims at proposing a new simplified finite-element model able to consider the nonlinear behavior of reinforced concrete frames. The predicted load–displacement results are confronted and validated by experimental ones. The assessed L p at failure were in good agreement with those predicted using the analytical formulae.