Experimental Investigation of Performance of Wooden Formwork Shores

Abstract

This paper presents the results of a laboratory evaluation of the performance of 104 used adjustable-length wooden formwork shores. The shore samples were randomly collected from eight different construction sites in Chicago, Milwaukee, and Minneapolis-St. Paul. The shores tested are known as Ellis shores. Ellis shores are very popular for shoring and reshoring elevated slabs in multistory concrete construction. An Ellis shore is made of two pieces of 100 mm × 100 mm (4 in. × 4 in.) nominal-size solid lumber attached together with two metal clamps. The collected shore samples were loaded to failure at four different lengths ranging from 2.4 to 4 m (8 to 13 ft). The observed modes of failure included bending failure, crushing of the wood under clamps, clamp failure, and crushing or splitting of the shore ends. The observed load-deformation behaviors and ultimate capacities are presented. Shore ultimate capacities are modeled with appropriate probability distributions.