RC Frames Infilled into RC Walls for Seismic Retrofitting: Design, Experimental Behaviour and Modelling

TitleRC Frames Infilled into RC Walls for Seismic Retrofitting: Design, Experimental Behaviour and Modelling
Publication TypeReport
Year of Publication2012
Strepelias E, Fardis MN, Bousias S, Palios X, Biskinis D
Series TitleSEE Reports series
Date PublishedJanuary 2012
InstitutionUniversity of Patras
CityPatras, Greece
ISBN Number978-960-89691-7-9
Report NumberReport no. SEE 2012-02

This report addresses the conversion of bays of nonductile reinforced concrete (RC) frames into earthquake-resistant flexure-dominated RC walls, not thicker than the frame members and having behaviour and properties as close as possible to a monolithic RC wall. First, a thorough overview of past monotonic or cyclic test results of such composite walls and of companion monolithic specimens is undertaken; the yield resistance of these specimens (as controlled by flexure or shear), their pre-yield stiffness and their deformation capacity (as governed by flexure or shear) are compared to the values expected for monolithic of the same geometry and materials, to draw conclusions concerning the effectiveness of the connection between the new web and the surrounding frame members. Unfortunately almost all past tests are on relatively squat specimens, with large effect of shear on the behaviour and failure mode. Next, design procedures are proposed for the new web and its design shear force - as controlled by yielding of the composite wall at the base or by uplifting of the wall footing from the ground. It is proposed to connect the new web to the surrounding frame members through dowels, which are also lap-spliced (be it unconventionally) with the small-diameter two-way web bars to anchor them into the frame. Design procedure are proposed for this connection, as well as for the more costly and labour-intensive orthodox solution where the small-diameter web bars are anchored into the frame through dedicated same-diameter starter bars epoxy-grouted into the frame members. Pseudo-dynamic tests on three 3:4 scale, 4-storey frames converted into slender walls are used to study the effectiveness of both the costly orthodox and the cost-effective unconventional connection, and to derive/validate simple procedures for the estimation of the effective storey stiffness, strength and deformation capacity of the composite wall. Simple, albeit general, rules are derived for the determination of these properties. They are confirmed through numerical simulations of the nonlinear response of the three wall specimens modelled in this way and comparisons with the experimental measurements.

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