ABSTRACT
The practice of filling Hollow Structural Section (HSS) columns with concrete is now commonplace, and most national or international design specifications give specific recommendations for determining the resistance of such elements. In addition, tubular members have been filled with concrete or grout at critical locations as a means of connection reinforcement, rather than externally plating the main hollow section member.
Initially, the advantages and disadvantages of concrete (or grout)-filling are reviewed, including the issues of self-weight, cost, connection strength, truss stiffness, fire resistance and truss strength. Concrete-filling affects truss performance by enabling strut or compression members to behave as composite HSS beam-columns, as well as transforming the truss into a rigid-jointed structure. In order to examine the structural implications of concrete-filling, two roof trusses are designed for typical Canadian roof loads in square hollow sections -a 36.6m medium span Warren truss, and a 70m long span Pratt truss. Each truss is designed as unfilled, to the 1994 Canadian (CSA) structural steel specification and filled. Furthermore, the design for the grout-filled trusses is also performed to the 1995 CIDECT Design Guide for Concrete-Filled Hollow Section Columns (which generally conforms with Eurocode 4). Overall, the paper shows that modest benefits are produced by concrete (or grout)-filling, with regard to increased fire resistance, reduced steel weights, and increased truss stiffness.
