Seismic retrofitting of R/C frames with deficient lap splices

Abstract

Many of the existing reinforced concrete frame buildings in use today may not have adequate seismic resistance due to detailing deficiencies including inadequate anchorage of longitudinal reinforcement, inadequate lap splices in the columns, lack of confinement in potential plastic hinge regions, inadequate joint shear strength, and absence of the strong column–weak beam condition. A significant amount of research has been devoted to the study of various strengthening techniques to enhance the seismic performance of such frame systems with detailing deficiencies. An alternative strengthening method consists of using externally applied carbon fiber reinforced polymers (CFRP), the effect of which has been investigated in this study on frames with inadequate lap splices. Within the scope of this work, 2/3-scale one-bay, one-story frames (portal frames) were constructed and tested under lateral loads for investigating the effect of inadequate lap splices on the frame response, as well as to propose a novel strengthening methodology to mitigate the negative effects. One specimen was constructed with continuous longitudinal reinforcement and according to detailing provisions specified by the latest seismic code, whereas two other specimens were constructed with inadequate lap splices on the column longitudinal reinforcement just above the footing, as well as insufficient transverse reinforcement in the lap splice regions. An original strengthening technique, using a combination of CFRP materials and steel anchorage rods, was developed and applied on one of the lap splice specimens for improving its lateral load behavior. In this technique, the CFRP sheets were installed both in the longitudinal direction of the columns for increasing their flexural capacity, as well as the in transverse direction to induce confinement effects. The test results showed a significant improvement in the lateral load capacity of the strengthened specimen, with no negative influence on its ductility.