Fatigue of Joints with Staggered Holes

It is customary in contemporary design for fatigue resistance of bolted connections to use slip-critical joints. However, many existing bridges are more likely to have bearing-type joints that use either rivets or high-strength bolts. Moreover, in many of these cases, hole patterns are staggered. Fatigue fracture of tension members with bearing-type joints that use staggered holes is observed to take place on a plane perpendicular to the axis of the member. The $s^2/\mathrm{4g}$ rule, commonly used for static strength design of bolted tension members, is not applicable for this case, and current design rules do not make it clear just what net section is to be used to calculate the stress range. The fatigue resistance of bearing-type shear splices was investigated to assess the effect of bolt-hole stagger and gauge distance on fatigue resistance. Thirty-one symmetrical bearing-type shear splices were tested at different stress ranges. Staggers varying from zero to $75\mathrm{mm}$ were investigated on four sets of three specimens, and two gauge dimensions were investigated at two stress range levels. The test results indicated that neither the stagger nor the gauge dimension significantly influenced the fatigue life. An analysis of the test results indicated that none of the commonly used cross-sectional area definitions is adequate for stress range calculations. An approach that accounts for stress concentration in the calculation of the effective stress range is proposed. This approach multiplies the gross cross-section stress range by a correction factor determined using finite-element analysis. Design recommendations include a fatigue resistance curve with a slope of 7.0 and stress correction factors for the most common flat plate geometries. The proposed approach was validated using test results of other researchers on flat plates and built-up sections.