Dynamic Analysis of Infilled R.C. Plane Frames with Openings in the in Fills
Dynamic analysis of an 8-story reinforced concrete building frame including raft foundation and infill panels is carried out. The wall panels are composed of building stones backed by plain concrete . Door and window openings are included within the wall panels. The dynamic loading used is the well-known El Centro N-S earthquake excitation of 1949 . The raft foundation is divided into a number of finite elements and the soil below is assumed homogeneous and extending below the raft foundation. Its stiffness matrix is obtained by inverting its flexibility matrix. Wall panels with openings are represented by plane stress plate finite elements. An opening in the panel is realized as an element of very small modulus of elasticity for its material or a very small thickness or both of them. Different opening configurations and sizes were utilized. The stiffness matrix of the structure components are assembled into the overall structure stiffness matrix. A computer program in FORTRAN was written to handle the described calculations.
The structure dynamic equation is written as:
M d2y / dt2 + C dy / dt + K y = Feff(t)
Feff(t) = -M d2yg / dt2
M is the mass matrix of the structure,
C is the damping matrix of the structure
K is the stiffness matrix of the structure
y is displacement of the structure joints, and its derivatives re[present velocity and acceleration of the structure joints.
F(t) represent the vector of forces applied to the structure.
d2yg / dt2 is the ground acceleration
The described frame is analyzed under gravity loads and El-Centro excitation. The first 10 periods of vibration are obtained for different configurations of wall panels with different sizes of openings. The first five modal shapes of the building frames are obtained. The horizontal displacements at the story levels were recorded. The effects of wall panels and openings on the structure behavior under the described loading is presented.
Keywords - Dynamic; infill; opening; mode shape; period; seismic