Theoretical Study of Self-Balancing Pretensioned CFRP Cable Braces for Seismic Resistance of Buildings

Abstract

Earthquakes cause nonstructural, if not structural, damage to buildings. This damage is proportional to interstory drift (ISD). Concentric braced frames (CBFs) are one of the most effective measures to limit the ISD in steel buildings. When compressed, conventional concentric hot-rolled (HR) steel braces tend to buckle when slender and are aesthetically unpleasant if stocky. This limitation of conventional concentric hot-rolled steel braces motivates the present work to use pretensioned carbon-fiber-reinforced polymer (CFRP) cables as braces in CBFs. The theoretically proposed self-balancing pretensioned CFRP cable braces (SPCCBs) in CBFs eliminate buckling in braces and provide a comparable elastic strain energy reserve for earthquake resistance design. Being slender, SPCCBs will add to the aesthetic beauty of buildings. The performance of the SPCCB system was evaluated by comparing it with conventional CBFs using stocky HR. CFRP cables with two different tensile strengths were used as braces in the SPCCB system, i.e., CFRP cable with tensile strength of 4,700 MPa (CB4700) and 3,600 MPa (CB3600). Fifty-seven models (19 each for HR, CB4700, and CB3600) were prepared using a commercially available code and were designed using Indian standards, keeping the compressive capacity of the braces similar for all three systems. The performance of all of the aforementioned systems was evaluated on the basis of energy dissipation (through total strain energy capacity of braces), fundamental time period, base shear attracted, ISD, and size of braces. This study showed that the SPCCB system has not only improved the strain energy capacity but also reduced the base shear compared to conventional hot-rolled steel brace CBFs. The overall performance of the building with CB4700 braces was found to be the best, followed by CB3600 and HR braces. Finally, a design guideline for the SPCCB system was proposed by following the Indian standards.