Investigation of Through-Thickness Properties of Rolled Wide Flange Shapes

This thesis examines methods for measuring through-thickness tensile properties of a sample of steel taken from the flange of a W14x426 rolled wide flange shape made of A572 Gr. 50 Steel. This study was motivated by the widespread failure of welded moment connections in the Northridge Earthquake. These failures have raised concerns about possible deficient through-thickness properties of column flanges. Through-thickness tension tests are not routinely performed on rolled shapes in current construction practice, and test methods are not well developed or documented.

The primary objective of this thesis was to compare two different methods of preparing through-thickness tension coupons, and to determine if reliable measurements of strength and ductility are possible with these coupon types. One coupon type was a sub-length coupon, machined directly from the 3 inch thick column flange, and tested without the use of welded prolongations. The second coupon type was prepared by welding high strength prolongations onto the column flange material. For each coupon type, samples were prepared and tested in both the rolling direction and through-thickness direction to provide a more thorough evaluation of the influence of coupon design on the measured mechanical properties.

The test results indicate that reliable and repeatable measurements of ultimate stress and reduction of area were possible with both coupon types. Measurements of yield stress, however, were not consistent between the two types of coupons. The welded coupons in the through-thickness direction gave significantly higher yield stress measurements than the sub-length coupons.

For the sample of steel tested in this research program, the ultimate stress in the through-thickness and rolling directions were nearly identical. The ductility, as measured by reduction of area, was significantly lower in the through-thickness direction as compared with the rolling direction.