STRESSES IN HELICOIDAL STAIR CASES

Abstract

The present study briefly reviews the theories for analys. Ing helicoidal stair cases, gives the details of the most accurate of those theories and presents the actual design details of a helicoidal stair half size model worked o xt on the basis of this theory. To verify the behaviour in practice a heitcoidal stair model 6 ft. high, 1.75 ft centeritno radius, 1.5 ft. width. 2.5 inch, slab thickness and 2400 horizontal . an .e was constructed. Firstly it was loaded uniformly by placing load over its entire surface aid. deflection observations taken. Finally a con- cantrated load was applied at its center till collapse occured. It was found that the model took nearly seven times the uniform designed load without shoving cracks any there. Under the concentrated load It cracked at a load of 4 Tons (about 6 times the total uniform design load) and collapsed at a concentrated load of 5.75 Tons, thus giving an additional factor of safety of 1.44 over the first cracking load. The deflection and twisting pattern was according to the theory but the measured values were very much less than theoretical. values.