The performance of structural I-beams and box beams is highly dependent on the shear properties of the web materials. Some wood-base panel materials such as hardboard possess shear properties that indicate a good potential for such applications. Reports of the performance of hardboard-webbed I-beams are encouraging, although specific information necessary for design and for predicting their behavior is scarce. Also, the effects of two important factors, long-term loading and loading environment, have not been fully determined. This research expanded previous work conducted at the Forest Products Laboratory by including the effect of other important factors, such as mode of failure (as affected by span length) and type of web material, and by providing additional data. In addition, data will serve as a base for judging the effects of long-term loading and loading environment on similar I-beams made from the same lot of material. Results indicate that the behavior of hardboard-webbed I-beams subjected to short-term loading can be predicted reasonably well using fundamental engineering theory together with the properties determined from small specimen evaluations. (Author).