In construction works, bolts used for connecting structural components are often subjected to severe conditions. These bolts are not always made of high toughness materials. Therefore, collapses of the components are sometimes caused by failure of the bolts.
In this study, to evaluate the strength of these bolts, tensile and fatigue tests were carried out on two kinds of bolts employed to build up caisson shafts. One of them was a group of the bolts which had been actually used in caisson works and the other was the unused one. Then by assuming a simplified model for a caisson shaft, stress in the bolt needed to connect blocks of the shaft was estimated by calculation and the results were compared with the experimental data.
A large amount of scatter was found in both tensile and fatigue strengths for the used bolts, as compared with those of the unused ones. It was also found that the maximum stress obtained by calculation reached almost to the yield strength of the tested bolts and the calculated stress amplitude was greater than their endurance limit.
From these results, the followings are recommended to prevent failure of the bolts for caisson construction: (1) to employ the bolts with higher strength than those which are generally accepted at present and (2) not to use the bolts which have been used once.
