ELASTIC SHEAR STIFFNESS OF COLUMNS WITH WING WALLS AND BEAMS WITH SPANDREL WALLS

Abstract

 Wing walls and spandrel walls had been separated from columns or beams before the revision of AIJ Standard in 2010. After the revision of AIJ Standard in 2010, wing walls and spandrel walls are recommended to be cast monolithically so as to resist seismic load. However, elastic shear stiffness, which is necessary for constructing a model of structural members, of columns with wing walls and beams with spandrel walls had been investigated only limited conditions such as a column with same length wing walls on both sides. In this research, elastic shear stiffness of columns with wing walls and beams with spandrel walls is theoretically investigated based on the equilibrium of external work and internal work.

 As a result, the coefficient for shear deformation, which is 1.2 for a rectangular section as widely known, is obtained. In this research, the coefficient is defined to total cross sectional area of a structural member. The coefficient become more than 2 in the case of columns with thin wing walls and beams with thin spandrel walls. In the case of wall thickness larger than 0.4 times of column width or beam width, the coefficient is between 1.2 and 1.4.

 In this paper, a simple approximation method to estimate the coefficient is also proposed and it is similar to the method used in AIJ Standard for shear walls with boundary elements on both sides of wall panel. In this method, effective cross section is defined as the product of wall thickness and total depth of the column with wing walls or the beam with spandrel walls. The estimated value by this method is appropriate if the total depth of a member is 5 times larger than the depth of the column or the beam. It means that elastic shear stiffness of columns with short wing walls and beams with short spandrel walls cannot be obtained by using this method.

 Theoretical value of elastic shear stiffness is verified by using three series of experimental results. The specimens used in the experiments are the columns with thin wing walls on both sides of the column, the beams with different length of spandrel walls on the sides and the columns with a long wing wall on one side. The elastic stiffness obtained from these experiments are from 64 % to 137 % of the calculated value, and the validity of the calculation in this paper was shown.