Abstract
Experimental and numerical studies are presented evaluating the efficacy of a recycling technique applied to a 1:3 reduced scale damaged RC frame. The crumbled concrete at the beam-column connections was replaced with new high-strength concrete. Epoxy mortar was applied at the interface to secure bonding between the old and new concrete. Additionally, the connections were provisioned with steel haunches, applied below and above the beams. The retrofitted frame was tested under quasi-static cyclic loads. The lateral resistance-displacement hysteretic response of the tested frame was obtained to quantify hysteretic damping, derive the lateral resistance-displacement capacity curve, and develop performance levels. The technique improved the response of the frame; exhibiting an increase in the lateral stiffness, resistance and post-yield stiffness of the frame in comparison to the undamaged original frame. This good behaviour is attributed to the steel haunches installed at connections. A representative numerical model was calibrated in the finite element program SeismoStruct. A set of spectrum compatible ground motions were input to the numerical model for response history analysis. The story drift demands were computed for both the design basis and maximum considered earthquakes. Moreover, the technique was extended to a five-story frame, which was evaluated through nonlinear static pushover and response history analyses. Overstrength factor WR = 4.0 is proposed to facilitate analysis and preliminary design of steel haunches and anchors for retrofitting the low-/mid-rise RC frames.
Highlights
The recent damaging earthquakes have raised concerns among designers regarding the critically damaged RC frames
Average hysteretic damping of 9.50 % was obtained for the strengthened RC frame, which increased up to 11 % at the roof drift demand equal to 2.50 %
The strengthened RC frame resisted a maximum lateral force of 290 kN which is 52.63% higher than the later force equal to 190 kN resisted by the original frame
Summary
The recent damaging earthquakes have raised concerns among designers regarding the critically damaged RC frames. Considering a 5% elastic damping, the tested frame gives total viscous damping equal to 16% for the design level deformation capacity (i.e. 2.50% roof drift) As it is unlikely for structures responding inelastically during ground motions to develop symmetric force-displacement hysteretic response similar to the response obtained through quasi-static cyclic tests, Priestley et al [27] recommended correction factors to the hysteretic curve area-based equivalent viscus damping. The experimental model exhibited closing/opening of existing distributed cracks in beam/members outside the plastic hinge region under later load This adds flexibility to the member and results in pinching in the lateral resistance-displacement hysteretic response of the frame (Figure 9).
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