A 16 x 20 in. column is made of the same concrete and reinforced with the same six No.9 (No. 29) bars as the column in Examples 3.1 and 3.2,

except that a steel with yield strength f, = 40 ksi is used. The stress-strain diagram of this reinforcing steel is shown in Fig. 2.19 for f, = 40 ksi. For this column determine (a) the axial load that will stress the concrete to 1200 psi; (b) the load at which the steel starts yielding; (c) the maximum load; and (d) the share of the total load carried by the reinforcement at these three stages of loading. Compare results with those calculated in the examples forf, = 60 ksi,keeping in mind, in regard to relative economy, that the price per pound for reinforcing steels with 40 and 60 ksi yield points is about the same.|3|