3D analysis of RC frames using effective-stiffness models

In the present study, a computer program has been developed using rigid diaphragm model for the three dimensional analysis of reinforced-concrete frames with cracked beam and column elements. ACI, CEB and probability-based effective stiffness models are used for the effective moment of inertia of the cracked members. In the analysis, shear deformations which can be large following crack development are taken into account and the variation of the shear stiffness due to cracking is considered by reducing the shear stiffness through appropriate models. The computer program is based on an iterative procedure which is subsequently experimentally verified by fitting the results of a test on a two-story R/C frame. A parametric study is also carried out on a four-story, three-dimensional reinforced-concrete frame. The iterative analytical procedure can provide an accurate and efficient prediction of deflections in R/C structures due to cracking under service loads. The most significant feature of the proposed procedure is that the variations in the flexural stiffness of beams and columns can be directly evaluated.