Fatigue behavior of welded diaphragm-to-beam connections
Abstract
The purpose of this research study was to evaluate the fatigue strength of welded diaphragm-to-beam connections. Experimental tests were performed in order to determine the fatigue resistance of the detail, examine failure modes, and to evaluate repair methods. Two diaphragm configurations were studied: one with diaphragms positioned back-to-back and one with staggered diaphragms. The experimental results indicate that the back-to-back diaphragms distribute load laterally more than the staggered diaphragms. The back-to-back configuration provides stiffness to the beam web and acts as a continuous transverse member. Because of the stiffness, many of the web and flange welds connecting the diaphragm to the beam fractured for the non-staggered diaphragms that resulted in decreased load transfer. Horizontal cracking also developed in the beam webs but did not affect the fatigue strength of the beam. The staggered diaphragms do not stiffen the beam web, but pull the beam web out-of-plane causing high out-of-plane bending stresses to develop. In the staggered diaphragm tests, cracks perpendicular to the stress field developed in the beam webs at the toe of a bottom flange weld. However, the beams did not fracture immediately. The repair methods investigated were removing the diaphragm and drilling holes at the beam crack tips, removing the diaphragm and peening the bottom flange weld toes, and leaving the diaphragm in place and peening the bottom flange weld toes. Peening the bottom flange weld toes before fatigue cracks developed did prevent cracks from forming for both diaphragm configurations. When a crack was present in the beam web, drilling holes at the crack tips arrested the crack growth. Finite element models of the welded diaphragm-to-beam connection were developed in order to determine the stresses near the welds. The stresses were then used in a crack propagation model that predicts the fatigue life of cracked beam members that have the welded diaphragm connection. Based upon the experimental and analytical results, it has been shown that beam members that develop cracks have a long fatigue life. Also, repair methods are effective in extending the fatigue life of a beam member once cracks develop and before the onset of cracks.
Degree
Ph.D.
Advisors
Bowman, Purdue University.
Subject Area
Civil engineering|Mechanical engineering|Mechanics
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