Shear strength of tapered I-shaped steel members

Steel plate girders with long or unstiffened web panels are often tapered to produce optimized members in buildings and bridges. Web shear strength is a critical limit state for these members because they usually have slender webs. Historically, shear has been apportioned to the web using two methods. The most common method is to assign the entire shear to the web. Alternatively, the Modified Shear Method considers the vertical component of each flange force resulting in web shear force not equal to the total shear. The first objective of this research was to experimentally determine the accuracy of these methods. It was found that the Modified Shear Method accurately predicted the shear resisted by the web at all 18 instrumented cross-sections in ten tested specimens. Several methods for predicting shear strength of unstiffened and long prismatic web panels are available in the literature. The second major objective of this research was to determine if one or more of these methods accurately predicts tapered member shear strength. Measured ultimate shear strengths were compared to predictions. Methods based on Basler's method provided inaccurate predictions. Methods based on Höglund's method and the method by Lee and colleagues provided accurate predictions.