Abstract
Previously, the authors carried out the static and the fatigue tests on various welded joints of the mild steel and the high tensile strength steel tentatively manufactured by the JSTM, and made a proposal on the allowable stress in the designs of welded steel bridges.
In this experimental research, (1) the authors carrid out the fatigue tests on butt welded joints connecting the thick plates of high tensile strength structural steel, under the repeated stresses of completely reversed type -σmax-+σmax, partly reversed type -6kg/mm2-+σmax. and pulsating type 0-+σmax., +6kg/mm2-+σmax., +12kg/mm2-+σmax., +20kg/mm2-+σmax..
The results of the present tests were compared with those of previous tests.
(2) Moreover, the authors studied the effect of the treatment of the welded part on the fatigue strengths.
The results obtained are as follows.
(a) In these tests the relation between fatigue strength σmax and σmin was found to be expressed by the linear equation at pulsating stress area on one hand, but by the non linear equation at reversed stress area on the other hand. For simplicity the same linear equation was adopted for the latter as it is in safety side.
(b) The fatigue strengths obtained from test (1) above were slightly lower than those obtained from the previous tests of the high tensile strength structural steel (t=12mm) trially manufactured by the JSTM.
The fatigue strength, however, can be raised up by finishing the welded part.
Judging from these test results, the general equation for the allowable stress of the welded steel bridges proposed by the authors previously, can also be applied to that of the welded bridges of the thick plate of high tensile strength structural steel.
(c) The fatigue failures of all specimens at as-welded condition and of those with peening on reinforcement occured at the side of the butt welds, which might be due to the stress concentration at that points.
(d) It was recognized that the fatigue strength of the as-welded specimen could be raised up greatly by the treatment of peening on reinforcement, and the specimens grinding finished after reinforcement was chipped off show the highest fatigue strengths.
