Effect of utilizing simple mechanical truss joints on the performance of hybrid truss-concrete beams subjected to bending

Abstract

Changing the shape of concrete beam reinforcement to traditional hybrid rebar trussed skeletons enhances the structural integrity of concrete beams. However, eccentricities occur within the system joints due to misalignment between the diagonal axes and the top and bottom chord axes, causing complex stresses and potential buckling. Problems with cold bending and welding of the diagonals may also result in fractures in the bending zone at the upper chord joints and at the welding points in the lower chord joints. To address these challenges, this study introduces two new truss systems with simplified mechanical joints. Eight large-scale specimens were fabricated and tested in bending under four-point loads. Two of these specimens were regular hybrid trusses with welded joints: one was tested in phase I, without concrete, and the other was tested in phase II as a composite beam. The remaining six specimens were fabricated to test the hybrid truss systems with two innovative mechanical joints. Two specimens were tested in phase I and four in phase II. Factors such as beam depth, span-to-depth ratio, and the laminar truss angles in the lateral direction were studied and compared with the traditional system with welding joints. Results show that replacing welded joints with mechanical joints enhanced the beam system performance in both stages I and II in terms of load capacities, distributed stresses more evenly, and reduced the likelihood of joint failure and premature collapse in Phase I. In addition, the implementation of the proposed mechanical joints led to an increase in the maximum load-to-yield load ratio by as much as 14 %. This enables more energy to be absorbed before failure and acts as a visible warning sign before total collapse occurs, which is an essential aspect in phase I.