Selective Upgrade of Beam-column Joints with Composites

Many RC frames built without seismic provisions between the ’50’s and ’70’s need structural upgrade in order to match the minimum requirements of new building codes. Generally, the critical region of the strengthening design is represented by the beam-column connection. The strength hierarchy governs the upgrade requiring to protect the column and the panel so that the formation of a plastic hinge during a seismic event is in the beam. Composite materials such as fiber reinforced polymer (FRP) laminates and bars offer new opportunities for the strengthening of such joints. This paper presents a technique based on FRP laminate and bar external installation for the seismic upgrade of RC beam-column joints that was checked with an experimental program on 11 under-designed interior-type connections. The selective upgrade is obtained choosing different combinations and location of sheets and bars in order to obtain different structural performances of joints. Selected results are herein summarized in order to underline how different parameters (i.e., type and location of the strengthening, and axial load level in the columns) influenced the behavior of the joint in terms of strength and/or ductility.