Concrete was ordered from a ready mix plant with nominal com-
pressive strengths of 15.5 and 27.5 MPa, slump of 100 mm, and
maximum aggregate size of 10 mm. Twenty 753150 mm cylin-
ders were made at the time of castings and were kept with the
girders during curing. They were tested under uniaxial compres-
sion right before the beam tests. The compressive strength and
modulus of elasticity of concrete were 16.6 and 29.1 MPa and
13.8 and 19.3 GPa, respectively. Typical stress-strain plots of the
concrete with two different compressive strengths under uniaxial
compression test are shown in Fig. 1~b!.