Seismic Retrofit of R/C Columns Using Steel Jackets
Riyad S. AboutahaI
Appears on pages(s):
anchor bolts; columns (supports); ductility; hysteresis; earthquake-resistant structures; lap connections; reinforced concrete; shear strength; Construction
Inadequate shear strength and inadequate lap splices in the longitudinal reinforcement are two major deficiencies in non-ductile reinforced concrete columns. Such deficiencies limit the lateral strength and ductility of older reinforced concrete moment-resisting frames. Provisions of older codes led to columns with shear strength less than required to develop the member's flexural capacity. Consequently, non-ductile shear response may dominate the behavior of older short columns. In addition, lap splices in older concrete columns were primarily designed as compression splices, but may actually experience large tensile forces during earthquakes. As a result, lap splices in older concrete columns are often inadequate to develop the yielding strength of the spliced bars in tension. This paper presents results of an experimental investigation on the use of rectangular steel jackets for seismic retrofit of rectangular reinforced concrete columns with inadequate shear strength or inadequate lap splices. Three large scale columns with inadequate lap splices and four large scale columns with inadequate shear strength were tested under lateral cyclic loading. The basic unretrofitted columns showed early dramatic non-ductile failures. However, the retrofitted columns with steel jackets exhibited excellent response, higher strength, and much higher ductility and energy dissipation. Test results suggest that rectangular steel jackets can considerably improve the performance of columns with inadequate shear strength. Also, the steel jackets can significantly enhance the response of wide columns with inadequate lap splices, when stiffened with adhesive anchor bolts.