Effects of Flange Holes on Flexural Behavior of Steel Beams

Abstract

When fastener holes are made in structural beams, the Canadian Steel Design Code CAN/CSA-S16.01 -Clause 14.1 (CSA, 2003) states that no deduction in flexural strength is needed for holes up to 15% of the gross flange area. This clause was established many years ago, however, over the years the mechanical characteristics of structural steel have changed. This research study focused on the effects of flange holes on the flexural behavior of steel I-beams made of ASTM A992 steel. This study was conducted primarily based on an experimental investigation involving 25 beam specimens. Holes of various diameters, ranging from 0% to 48% of the gross flange area were laid by drilling holes (a) in the midspan of the tension flange and (b) in the midspan of both the tension and compression flanges. Additionally, beams having holes with fasteners (snug tight) were performed. Based on the test results, this study recommended a design approach, which is analogous to an axial tension member provision as per the current CAN/CSA-S16.01 (CSA, 2003) standard. Accordingly, the effects of holes on the flexural strength can be ignored if the gross-section plastic moment is greater than a modified net-section fracture moment hence, beam members shall be designed to carry the gross-section plastic moment. Otherwise, the beam members shall be designed to carry the modified net-section fracture moment. The comparison of the recommended procedure with the 15% exemption rule as per current steel standard S16.01 (CSA, 2003) demonstrated that the current code provision is unnecessarily conservative for steel grades such as A992 steel. On the other hand, the current provision may be more conservative for high strength steels such as HSLA 80 steel, ASTM A913 Grade 60 and HPS-485W having a minimum yield-to-ultimate strength ration value of more than 0.85. The analytical portion of the research study involved the application of nonlinear finite element method to verify and comprehend the experimental results. The analytical study was conducted using ADINA FE program. The test beams were modeled using 4-node shell element that includes both geometric and material nonlinearities. The material model utilized in the FE analysis was developed based on the experimental-numerical simulation of standard tensile coupons.