Experimental Study Of Externally Prestressed Concrete Beams With CFRP And Steel Tendons

With the development of high-strength concrete and new prestressed materials, externally prestressed structures are more and more used in new-constructed bridge and strengthing project.This paper is based on the experimental study of four externally prestressed concrete simply supported beams and three externally prestressed concrete continuous beams. Among the test specimens, CFRP tendons are used for externally prestressed tendons of three simply supported beams, while 7-wire steel strands are used for externally prestressed tendons of other beams. Through analyzing the experimental date, variation of strain of concrete, stress of non-prestressed tendons and prestressed tendons, deflection of beams and moment redistribution of continuous beams from the beginning of imposing load to the failure of the test specimens is discussed, and development of crack in the beams is discribed.The experiment indicates mid-span moment-deflection curve of simply supported beams and continuous beams always experience three stages which are respectively symbolized by crack of concrete in tensile area, yield of non-prestressed tendons and concrete crushing in condition that reinforcement index is moderate and anchorages are effective. No matter in simply supported beams and in continuous beams, stress increment of externally prestressed tendons and midspan deflection are completely or approximately in linear relation.After comparing calculated values with experimental values of ultimate stress of externally prestressed tendons, it is found that taking Pannell's deformation-based method to predict the ultimate stress in CFRP and steel tendons of externally prestressed concrete simply supported beams and continuous beams is feasible. The values of mid-bearing moment calculated by equations of American structural design code ACI 318-95, CEB-FIP MC 90 and Code for Design of Concrete Structures (GB50010- 2002) are close to the experimental values, while values calculated by other equations and experimental values has obvious difference. Most of the equations suggested by national codes, international codes and some researchers have considered that the main influence factor on mement redistribution are the relative height of equivalent compression zone.