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This study presents a detailed finite element (FE) analysis of the nonlinear flexural response of continuous steel-concrete composite beams strengthened with externally post-tensioned tendons. The initial post-tensioning (PT) force is introduced as an initial strain in the truss element that used to simulate the external tendons. The accuracy of the FE model is validated using existing experimental works. The effects of tendon eccentricity, longitudinal steel rebars ratio, and initial PT 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 plain beams. However, the ultimate capacity of the strengthened beam increases only by 8%, the cracked moment redoubles and an affirmative behavior over the un-strengthened beams is obtained. Also, using prestressed concrete flange deters the propagation of cracks and improves the composite action between the steel beam and the concrete flange. As the longitudinal steel rebars ratio increases, the contribution of the externally posttensioned tendons to enhance the beam capacity is diminished.

Applying pre-stressed Carbon Fiber Reinforced Polymers (CFRP) plate to steelconcrete composite beams is considered an active strengthening technique that can create permanent internal stresses in the beam opposite to the internal straining actions due to the service loads. This study presents a numerical analysis of steelconcrete composite beams stiffened with pre-stressed CFRP plates. The pre-stressing effect on CFRP plate is enforced in the finite element (FE) model as an initial stress on the solid element that used to simulate the strengthening plate and the epoxy is considered as a thin layer between CFRP plate and the steel flange. The deterministic and stochastic analysis is performed to obtain the long-term random responses of the strengthened beams as well as plain beams due to the effect of shrinkage. In addition, the effect of CFRP plate rigidity and strengthening schemes are investigated. By using CFRP plates, strengthening can be achieved up to 25% for the system explored. During the post-elastic range, stiffness is improved when adding pre-stressed CFRP plates and deflection of strengthened beams is reduced by 20% in comparison to the reference beam at the ultimate capacity. Also, a slight drop in ductility occurs with the addition of CFRP plates.

The improvement in the flexural behavior of continuous steel-concrete composite beams is evaluated after adding carbon-fiber-reinforced polymers (CFRP) laminates to the concrete surface at the hogging moment regions. In this paper, an experimental program consists of three specimens tested in an inverted position under four-point loading is carried out to simulate a part of continuous steel-concrete composite beams at the hogging moment region. The experimental findings are used to develop and validate a reliable finite element (FE) model to simulate the nonlinear flexural performance of strengthened beams as well as plain beams. However, CFRP laminates enhance the beam capacity, a reduction in the beam ductility occurs and causes a limitation in the moment redistribution at the hogging moment regions Moreover, adding more layers of CFRP laminates leads to higher values of the beam stiffness and capacity but more reductions in ductility will occur. As the longitudinal steel rebars ratio increases, the contribution of CFRP laminates to enhance the beam capacity is diminished. Also, applying CFRP laminates through the full length of the hogging moment region helps to reduce the creation of fatigue cracks in the steel rebars.