The last decade saw the emergence of a new type of space truss built with continuous chord members. Earlier studies on these trusses confirmed that besides the cost savings resulting from their simple jointing methods, their behaviour is sound and ductile. The present study investigates the possibility of using either a concrete slab or top timber boards acting compositely with the top chord, to improve the behaviour of these trusses. New techniques are developed to allow the easy and inexpensive attachment of both types of top continuum. With these techniques, a high level of shear interaction can be developed, leading to significant improvements in behaviour. The paper also introduces an analytical study based on the finite element method for the analysis of space trusses with continuous chords, both in the composite and non-composite states.
Externally post-tensioned tendons can cause an initial compressive stress in steel-concrete composite sections at the hogging moment region, and then a part of the tensile stress in the concrete flange can be relieved. This study presents a detailed finite element analysis of the nonlinear flexural response of continuous steel-concrete composite beams strengthened with externally post-tensioned tendons. The initial post-tensioning force is introduced as an initial strain in the truss element that used to simulate the external tendons. The accuracy of the finite element model is validated using existing experimental works. The effects of tendon eccentricity, longitudinal steel rebar ratio, and initial post-tensioning force on the beam behavior are explored. Furthermore, deterministic and stochastic shrinkage effects are carried out to obtain the long-term random responses of the strengthened beams as well as unstrengthened beams. However, the ultimate capacity of the strengthened beam increases only by 8%, the cracked moment redoubles, and an affirmative behavior over the unstrengthened beams is obtained. Also, a rapid decay in the long-term deformation of continuous steelconcrete composite beams is obtained at the early age while a linear decrease in the remaining part of the age occurs.
Strengthening of composite beams is highly needed to upgrade the capacities of existing beams. The strengthening methods can be classified as active or passive techniques. Therefore, the main purpose of this study is to provide detailed FE simulations for strengthened and unstrengthened steel–concrete composite beams at the sagging and hogging moment regions with and without profiled steel sheeting. The developed models were verified against experimental results from the literature. The verified models were used to present comparisons between the effect of using external post-tensioning and CFRP laminates as strengthening techniques. Applying external post-tensioning at the sagging moment regions is more effective because of the exhibited larger eccentricity. In the form of an initial camber and compressive stresses in the bottom flange prior to loading, this reasonable eccentricity induces reverse loading on the reinforced beams, reducing the net tensile stress induced during loading. Using CFRP laminates on the concrete slab for continuous composite beams is more effective in enhancing the beam capacity in comparison with using the external post-tension. However, reductions in the beam ductility were obtained.
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