Non-compression X-bracing system using CF anchors for seismic strengthening of RC structures

Abstract

Cross-bracing (X-bracing) is one of the most popular methods of seismic retrofitting. Research results indicate that X-bracing significantly increases structural stiffness and enhances the strength of the structures. However, researchers have also noted that conventional steel X-bracing methods can involve brittle failure at the connection between the brace and the building, as well as buckling failure of the braces. The current research thus investigated the structural properties of a new type of non-compression carbon fibre (CF) X-bracing system with the goal of overcoming the brittle and buckling failures that can occur with conventional steel X-bracing methods. The proposed non-compression X-bracing system uses CF bracing and anchors to replace the conventional steel bracing and bolt connection. This paper reports on the seismic resistance of a reinforced concrete frame strengthened using CF X-bracing. Cyclic loading tests were carried out, and the structural stiffness and ductility were investigated along with the hysteresis of the lateral load-drift relations. CF is less rigid than the conventional materials used for seismic retrofitting, resulting in some significant advantages: the strength of the structure increased markedly with the use of CF X-bracing and no buckling failure of the bracing was observed. NotationD depth of column f c concrete compressive strength h o clear height of column K secant stiffness between yield and zero points (V y /ä y ) M u ultimate flexural strength N axial force R strength ratio, defined as V max /V y V max maximum shear strength V mu shear force at point of ultimate flexural failure V su ultimate shear strength V u ultimate lateral load-carrying capacity V y yield shear strength ä max displacement at the maximum point ä y displacement at the yield point ì ductility ratio, defined as the maximum displacement divided by yield displacement (ä max /ä y ) r f tensile reinforcement ratio (%) r s shear reinforcement ratio (%)

Existing prefab R/C industrial buildings: Seismic assessment and supplemental damping-based retrofit

“…as well as buckling-restrained [22,32] and other innovative layouts of steel braces [33][34][35][36][37]. The retrofit hypothesis developed here is based on the adoption of a dissipative bracing system incorporating pressurized fluid viscous (FV) spring-dampers, originally conceived and implemented by the authors for installation in frame buildings [38][39][40].…”

Specific seismic retrofitting of a compact reinforced concrete building with X-bracings and steel jackets. Application to a primary school in Huelva

“…Others have analysed the materiality of the braces because conventional steel braces have a buckling failure in some cases. For instance, in [34] the non-compression carbon fibre X-bracing system was analysed. They concluded that this system increases the strength and it has no buckling failure, but this system must be improved, especially in connection with the original structure.…”

Thirty Years Researches on Development for Sustainable Concrete Technology

“…. CF X bracing strengthening system for seismic [17] The externally bonded reinforcement (EBR) is typical strengthening method using FRP as shown in Figure 5. There are a number of researches about externally strengthening of reinforced concrete structures using FRP for flexural and shear, punching shear, extension of fatigue life, strengthening design methodology [14][15][16].…”

“…There are a number of researches about externally strengthening of reinforced concrete structures using FRP for flexural and shear, punching shear, extension of fatigue life, strengthening design methodology [14][15][16]. Recently, carbon fiber X-bracing strengthening system for seismic as shown in Figure 6 was developed and the structural efficiency was experimentally proved under the earthquake loading condition [17]. Above tremendous experimental results were contributed to establish the design and construction specification using FRP in Korea.…”