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.
In this research, analytical fragility curves for three existing structures are presented. Structures are 2-story, 6-story and 10-story residential reinforced concrete structures designed under dead ,live and seismic loads of zone 3 according to Egyptian code (2008). The design acceleration is 0.15g. The fragility curves are developed based on nonlinear incremental dynamic analysis of three dimensional structural models using SeismoStruct under twelve historic ground motions. Four performance levels are considered; fully operational, operational, life safe and near collapse.
Composite steel-concrete beams are used widely in bridge and building construction as the main structural elements in flexure. These structures have a design life and this may be reduced if loads are increased or environmental degradation occurs. Strength of such structure members and thus replacement or retrofitting may need to be considered. One method of retrofitting (stiffening and strengthening) a composite steel-concrete beam is to externally post-tension the beam. The present study focuses on evaluating the effect of adding the external post-tension as a strengthening technique on the simple composite beams. The study was conducted using the finite element program "ANSYS". Nonlinear material models for the components of the composite beam were used in the finite element model. The outcomes got from finite element analysis were confirmed against available experimental results. A broad parametric study was conducted to explore the effect of tendons profiles on flexural behaviour. This covers: load deflection behaviour, converting the simple beam into partially continuous beam, verifying an external post-tensioned simple beam.
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