The use of external posttensioning technique for strengthening reinforced concrete girders has been considerably studied by many\nresearchers worldwide. However, no available data are seen regarding strengthening full-scale composite prestressed concrete\ngirders with external posttensioned technique under static and repeated loading. In this research, four full-scale composite\nprestressed I-shape girders of 16m span were fabricated and tested under static and repeated loading up to failure. Accordingly,\ntwo girders were externally strengthened with posttensioned strands, while the other two girders were left without strengthening.\nThe experimental tests include deflection, cracking load, ultimate strength and strains at midspan, and loading stages. Test results\nwere compared with the design expressions mentioned in AASHTO LRFD specifications and ACI 318-2014 code. Also,\na nonlinear analysis was conducted using the finite element method (FEM). The presented analysis models were verified by\ncomparing the model results with test results. The general theme abstracted from both experimental tests and numerical analysis\nreflects that the performance and procedure of strengthening with external prestressing of girders were found to be effective in\nincreasing the load carrying capacity of the strengthened girders.
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