Some investigations of the effects of core size and steel and concrete quality in short reinforced concrete columns

Abstract

Summary: The work described is a continuation of earlier work on short concrete columns, which had as its object the determination of the effect of lateral reinforcement on column strength. It was clear from this earlier work that relative core size would be likely to have a significant effect on strength, and the present investigations were initiated primarily to examine this. On the assumption that the currently accepted formula for helically bound columns had some justification for taking as one of its terms “"core area by concrete strength,” it was believed that high quality concrete would demonstrate the effect of core size better than a more ordinary concrete and a series of tests (Group I) was carried out in this way. As the tests failed to indicate any marked effect, columns (Group II) were made with normal concrete and high quality steel. To round off the work a third group was made of normal quality steel and concrete. In the main, binders were of a normal square type and of a materially constant strength, but a few were of modified shapes. As a result of the tests it has been possible to formulate general conclusions concerning the effect of core size, cover thickness, concrete and main steel strength, and core shape, to confirm the general conclusions of earlier work that binder contribution to strength was proportional to 1/pitch2 and to indicate that there is material advantage in using high quality steel as main reinforcement. Actual test loads are compared in the tables with loads calculated by a formula derived from the earlier tests, where core area was a constant proportion of the column area (51 per cent.), where concrete strength was sensibly constant, and where main steel consisted of various sizes of normal black bar. The significance of the various changes is thus revealed more clearly.