Fall 2001

Nonlinear Seismic Analysis of R.C.C. Buildings

Zebun Nessa Shoma

Reinforced Cement Concrete (commonly known as Reinforced Concrete and referred to as R.C.C., RCC or RC) is a complex composite material that provides a unique coupling of two materials (concrete and steel). When subjected to high stresses, it behaves like an elasto-plastic material. This behavior is particularly observed when the structure is subjected to dynamic loads. Considering the nonlinear behavior of R.C.C., parametric studies are performed in this thesis to investigate some important details of the behavior of R.C.C. Simple two-dimensional frames are taken for static structural analysis under increasing vertical load and nonlinear dynamic analysis under combined vertical load and seismic vibrations. Three known earthquake data (El Centro, Kobe and Northridge) are applied in the long and short directions of a number of buildings (2, 5, 10 storied) to study their responses. Various aspects of the nonlinear response of R.C.C. are studied. These include the effect of axial force on the Moment-Curvature (M-f) relationship, the mode of failure and the importance of increasing shear strength. From the analysis it is found that the failure of all the structures are due to excessive shear force in beam or column. In case of Kobe earthquake all the buildings taken into consideration failed (both long and short direction) and no failure occurred in the short direction due to El Centro earthquake. For Northridge earthquake low rise (2 storied) building frames failed due to excessive shear in the columns. But results of 5 and 10 storied frames showed that shear failure of beams occurs rather than the columns. Finally a study is carried out which include increasing the shear strength of beam, column and footing (1.7, 2 and 2.5 times) in order to improve the shear capacity of the structure.