Retrofit Strengthening of a Seismically Inadequate Reinforced Concrete Frame Using Pre-Stressed Cable Bracing Systems and Beam Alteration
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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The primary objective of this thesis is to study analytically the effectiveness of prestressed cable bracing systems in conjunction with alteration of structural beams as a viable retrofit strengthening scheme for seismically inadequate reinforced concrete structures. Prototype buildings studied featured strong beams weak columns lateral force resisting frames. The failure mechanism is non-ductile and dominated by shear failure of the reinforced concrete short columns. The analytical study is carried out using DRAIN-2D, a computer program for dynamic or static incremental structural analysis of inelastic plane frame structures. The effectiveness of prestressed cable bracing on the response of a single story subassemblage of the prototype frame is re-examined. A parametric study is conducted to examine how systematically weakening the spandrel beams affects the frames failure mechanism. The response of unstrengthened, braced-unaltered and braced-altered subassemblages are studied under both monotonic and cyclic loads for incremental displacements. Retrofitting schemes are evaluated with respect to their adequacy for meeting current building code seismic strength requirements. It was concluded analytically that prestressed cable bracing and beam alteration used in combination can be an effective retrofitting strengthening scheme. For the prototype frame studied significant improvements in strength, ductility, and failure mechanism were achieved.
- Structural Engineering and Building Technology