Abstract
The purposes of this paper are to investigate the influences of the span ratios of flanges a/l_x and the thickness of flange for effective widths in elastic and plastic ranges, ultimate strengths and failing behaviour of reinforced concrete T-beams, and to discuss the application of elastic theory and the Code Requirements to effective widths of T-beams and the application of plastic bending theory to the ultimate strengths of T-beams. For these purpose, six simply supported reinforced concrete T-beams classifled by two kinds of a/l_x and three kinds of flange thickness were tested under a concentrated load, and effective widths and flexural rigidity in elastic range, effective widths for ultimate strength in plastic range and the shear cracks due to membrane shear stress at the joints of flange and web were analyzed and discussed. 1) Effective overhanging flange widths λ on either side of the web obtained from the experiments in elastic range decreased from the supports to the center of span and the distribution of λ along the span agreed with the curve calculated by two dimentional elastic theory. 2) Average values of λ along the span obtained from the experiments in elastic range agreed with the values of the Eq. (5) proposed by HIGASHI as average λ of members for the calculation of the flexural rigidities of T-beams. λ=(0.5-0.3a/l_x)a, [when a<l_x]……(5) Average values of-λ along the span obtained from the experiments for three kinds of flange thickness t/D=0.067, 0.133, 0.200 were approximately same and the influence of flange thickness for λ was not observed. 3) Ultimate strengths calculated by using full flange width as the effective flange width agreed with the values obtained from experiments in both positive and negative moments. It would be considered as the results of enough anchorage for longitudinal reinforcements and enough transverse reinforcements in flanges. 4) The shear cracks due to membrane shear stress were observed on the top surface at the joints of flange and web in plastic range. However, after such cracks occured the load did not decrease, because enough transverse reinforcements were placed at the joints. Tensile principal stress on the top surface at the joints when such cracks occured (which were calculated with the experimental results) were 1/12〜1/20 of the compressive strength of concrete F_c.
