Emirates Journal for Engineering Research, 9 (2), 65-69 (2004) (Regular Paper) 65 DESIGN OF FRP JACKETS FOR SEISMIC RETROFIT OF CIRCULAR CONCRETE COLUMNS G. ELNABELSY and M. SAATCIOGLU Department of Civil Engineering, University of Ottawa P.O.Box 450, Ottawa, Ontario, K1N 6N5, Canada ﺘﻡ ﺇﺠﺭﺍﺀ ﺒﺤﺙ ﺘﺤﻠﻴﻠﻲ ﻭﻤﻌﻤﻠﻲ ﻟﺘﻁﻭﻴﺭ ﻨﻅﺎﻡ ﺘﺼﻤﻴﻡ ﻟﺘ ﺩﻋﻴﻡ ﺍﻷﻋﻤﺩﺓ ﺍﻟﺨﺭﺴﺎﻨﻴﺔ ﺍﻟﺩﺍﺌﺭﻴﺔ ﺍﻟﻘﺎﺌﻤﺔ ﻟﻤﻘﺎﻭﻤﺔ ﺍﻟـﺯﻻﺯل ﺒﺎﺴﺘﺨﺩﺍﻡ ﻗﻤﺼﺎﻥ ﻤﻥ ﺍﻟﺒﻭﻟﻴﻤﻴﺭ ﺍﻟﻤﻘﻭﻯ ﺒﺄﻟﻴﺎﻑ ﺍﻟﻜﺭﺒﻭﻥ. ﹰ ﻟﺒﺤﺙ ﺴﺎﺒﻕ ﺤﻭل ﺘﻁـﻭﻴﺭ ﻭﻴﻌﺩ ﺍﻟﺒﺤﺙ ﺍﻟﺘﺤﻠﻴﻠﻲ ﺍﻤﺘﺩﺍﺩﺍ ﻨﻅﺎﻡ ﺘﺼﻤﻴﻤﻲ ﻟﺘﺤﺯﻴﻡ ﺍﻷﻋﻤﺩﺓ ﻴﻌﺘﻤﺩ ﻋﻠﻰ ﺍﻹﺯﺍﺤﺔ. ﻭﺘﺘﻀﻤﻥ ﺍﻟﺩﺭﺍﺴﺔ ﺍﻟﻤﻌﻤﻠﻴﺔ ﺍﺴﺘﺨﺩﺍﻡ ﺃﻋﻤـﺩﺓ ﺃﺤـﺩ ﺍﻟﺠـﺴﻭﺭ ﺒﺤﺠﻤﻬ ﺎ ﺍﻟﻜﺎﻤل ﺘﻡ ﺍﺨﺘﺒﺎﺭﻫﺎ ﺘﺤﺕ ﺤﻤل ﺯﻟﺯﺍﻟﻲ ﻤﺼﻁﻨﻊ ﻴﺘﺄﻟﻑ ﻤﻥ ﻀﻐﻁ ﻤﺤﻭﺭﻱ ﺜﺎﺒﺕ ﻤﻊ ﺯﻴـﺎﺩﺓ ﺍﻹﺯﺍﺤـﺎﺕ ﺍﻟﻌﺭﻀﻴﺔ ﻋﻠﻰ ﻤﺭﺍﺤل ﻓﻲ ﺍﺘﺠﺎﻫﻴﻥ. ﻭﻜﺎﻨﺕ ﺍﻟﻌﻴﻨﺎﺕ ﻤﻤﺜﻠﺔ ﻷﻋﻤﺩﺓ ﻨﻤﻁﻴﺔ ﻷﺤﺩ ﺍﻟﺠﺴﻭﺭ ﺒﻴﻥ ﺍﻟﻘﻭﺍﻋﺩ ﻭﻨﻘﻁﺔ ﻋﺯﻭﻡ ﺍﻻﻨﺤﻨﺎﺀ ﺍﻟﺼﻔﺭﻴﺔ. ﻭﻴﻤﺜل ﺃﺤﺩ ﺍﻷﻋﻤﺩﺓ ﺍﻟﺫﻱ ﺘﻡ ﺍﺨﺘﺒﺎﺭﻫﺎ ﻅﺭﻭﻑ ﺍﻹﻨﺸﺎﺀ ﻓﻲ ﺍﻟﻁﺒﻴ ﻌﺔ ﻤﻊ ﺘﻘﻭﻴﺔ ﻁﻭﻟﻴـﺔ ﻤﺭﻜﺒـﺔ ﹰ ﺒﺎﻟﻘﺭﺏ ﻤﻥ ﺍﻟﻘﺎﻋﺩﺓ، ﻤﻤﺎ ﻴﺘﻴﺢ ﺘﻘﻴﻴﻤﺎ ﻟﻘﺎﺒﻠﻴﺔ ﺍ ﻟﺘﺸﻭﻩ ﻟ ﻸﻋﻤﺩﺓ ﺍﻟﻤﻭﺠﻭﺩﺓ. ﻭﺘﺸﻴﺭ ﻨﺘﺎﺌﺞ ﺍﻻﺨﺘﺒﺎﺭ ﺇﻟﻰ ﺃﻥ ﺍﻟﺘﺸﻭﻩ ﻓﻲ ﻫﺫﺍ ﹰ ﺒﻨﺴﺒﺔ ﺍﻨﺤﺭﺍﻑ ﺠﺎﻨﺒﻲ ﺍﻟﻌﺎﻤﻭﺩ ﻜﺎﻥ ﻤﺤﺩﻭﺩﺍ1 .% ﻭﺘﻭﻀﺢ ﺍﻷﻋﻤﺩﺓ ﺍﻟﻤﺸﺎﺒﻬﺔ ﺫﺍﺕ ﺍﻟﻤﻭﺍﺼﻔﺎﺕ ﺍﻟﻤﺘﻁﺎﺒﻘﺔ ﻭﻗﻤﺼﺎﻥ ﺍﻟﺒﻭﻟﻴﻤﺭ ﺍﻟﻤﻘﻭﻯ ﺒﺄﻟﻴﺎﻑ ﺍ ﻟﻜﺭﺒﻭﻥ ﺃﻨﻪ ﻴﻤﻜﻥ ﺘﺤﺴﻴﻥ ﺍﻷﺩﺍﺀ ﺒﺸﻜل ﺠﻴﺩ ﻤﻥ ﺨﻼل ﺍﻟﻘﻤﺼﺎﻥ. ﺇﻥ ﻗﻤـﺼﺎﻥ ﺍﻟﺒـﻭﻟﻴﻤﺭ ﺎﻟﺔ ﻓﻲ ﺘﺤﺴﻴﻥ ﺍﻟﺘﺭﺍﺒﻁ ﺒﻴﻥ ﺍﻟﺘﺴﻠﻴﺢ ﻭﺍﻟﺨﺭﺴﺎﻨﺔ ﻓﻲ ﻤﺩﻯ ﺍﻟﻤﻘﻭﻯ ﺒﺄﻟﻴﺎﻑ ﺍﻟﻜﺭﺒﻭﻥ ﻟﻸﻋﻤﺩﺓ ﺍﻟﻤﺴﺘﺩﻴﺭﺓ ﺘﻌﺩ ﻁﺭﻴﻘﺔ ﻓﻌ ﹰ ﺍﻟﺴﻠﻭﻙ ﺍﻟﻠﺩﻥ ﻓﻲ ﺤﻴﻥ ﻴﺘﻡ ﺃﻴﻀﺎ ﺘ ﺤﺯ ﻴﻡ ﻭﺍﺤﺘﻭﺍﺀ ﺍﻟﺨﺭﺴﺎﻨﺔ ﺍﻟﻤﻀﻐﻭﻁﺔ. ﻭﻗﺩ ﺃﻅﻬﺭﺕ ﺍﻷﻋﻤﺩﺓ ﹰ ﻓـﻲ ﺍﻟﻤﺩﻋﻤﺔ ﺘﺤﺴﻨﺎ ﻨﺴﺒﺔ ﺍﻹﺯﺍﺤﺔ ﺍﻟﺠﺎﻨﺒﻴﺔ ﺍﻟﺘﻰ ﻓﺎﻗﺕ5 .% ﹰ ﻟﻠﻨﻅﺎﻡ ﺍﻟﻤﻘﺘﺭﺡ ﺃﻅﻬﺭﺕ ﻭﺃﻭﻀﺤﺕ ﺍﻟﺩﺭﺍﺴﺔ ﺃﻥ ﺍﻷﻋﻤﺩﺓ ﺍﻟﺘﻲ ﺼﻤﻤﺕ ﻁﺒﻘﺎ ﺴﻠﻭﻙ ﺍﻟﻜﺴﺭ ﺍﻟﻤﻁﻭﻉ ﻤﻤﺎ ﻴﺘﻔﻕ ﻤﻊ ﺍﻟﺴﻠﻭﻙ ﺍﻟﻤﻔﺘﺭﺽ ﻓﻲ ﺍﻟﺘﺼﻤﻴﻡ. Analytical and experimental research was conducted to develop a design procedure for seismic retrofit of existing circular concrete columns using carbon fiber reinforced polymer (CFRP) jackets. The analytical research is an extension of earlier work on the development of a displacement based design procedure for column confinement. The experimental work involves full-size bridge columns tested under simulated seismic loading, consisting of constant axial compression and incrementally increasing lateral deformation reversals. The specimens are representatives of typical bridge columns between the footing and the point of inflection. One of the columns tested represents as-built conditions in practice with longitudinal reinforcement spliced near the base, providing an assessment of the deformability of existing columns. The test results indicate that the deformability of this column is limited to 1% lateral drift ratio. Companion columns with identical properties and CFRP jackets show that the deformability can be improved significantly through jacketing. CFRP jacketing of circular columns is effective in improving bond between reinforcement and concrete within the plastic hinge region while also confining the compression concrete. The lateral deformability of retrofitted columns shows improvements beyond 5% drift ratio. It is shown that columns satisfying the proposed design expressions develop ductile behavior, meeting the performance criterion adopted in design. INTRODUCTION Performance of bridges during previous earthquakes has demonstrated that many structural failures could be attributed to inadequate seismic design of existing bridge columns. Lack of transverse reinforcement and the splicing of longitudinal reinforcement in potential hinge regions constitute the primary reasons for poor performance. While it is not possible to re-build the entire bridge inventory of seismically critical columns, it is possible to retrofit them with fiber reinforced polymer (FRP) jackets. FRP jackets provide additional shear capacity, confinement of compression concrete and improved bond between the steel and concrete, enhancing column performance in all three areas of design deficiency. Combined experimental and analytical research is underway at the Structures Laboratory of the University of Ottawa to investigate the effectiveness of CFRP jackets on seismic performance of bridge columns. Some of the results on circular columns and seismic retrofit methodology involving a displacement based design approach are summarized in this paper. DESIGN APPROACH A displacement based design approach was developed for column confinement by Saatcioglu and Razvi 1 with lateral drift as the performance criterion. The design approach is based on computed drift capacities of columns with different levels of confinement and axial compression. The computation of drift was done using a computer program for static inelastic loading (push- over analysis) 2 that incorporated analytical models for