Fatigue bond-slip properties of steel reinforcing bars embedded in UHPFRC: Extraction and development of an accumulated damage law

The occurrence of cyclic loads in RC structures is known to deteriorate the bond between the reinforcing bars and concrete by reducing both the bond strength and stiffness, eventually leading to debonding through large increases in slip. There is much research to quantify this bond deterioration for normal strength concrete but little research has considered UHPFRC, which is the subject of this paper. This research develops a testing approach and analysis procedure to quantify the deterioration in bond as a result of high-cycle fatigue. The procedure has been developed through 18 tests of steel reinforcing bars embedded in UHPFRC with steel micro fibres. A test rig has been developed to directly measure the bond-slip under monotonic and cyclic loads. Procedures are then developed for quantifying the bond stiffness and the incremental set, that is, the increase in slip per cycle, by using the known interaction between the monotonic and cyclic bond-slip already identified by other researchers. It is shown how these procedures can be used to quantify the bond degradation under combinations of fatigue loads and how simply measuring the crack width in a structure can give a very good indication of both the residual fatigue life and bond strength.Barbara Daniela Giorgini Sepulveda, Phillip Visintin, Deric John Oehler

Quantifying the fatigue material properties of UHPFRC with steel microfibers at cracks

Abstract not available.Barbara D.G. Sepulveda, Phillip Visintin and Deric J. Oehler

Experimental and theoretical analysis of cracking and tension stiffening in UHPFRC under high-cycle fatigue

OnlinePublTension-stiffening controls the serviceability behavior of concrete structures as it is responsible for crack formation and, consequently, the deflection of beams. In fiber reinforced concrete, such as ultra-high performance fiber reinforced concrete (UHPFRC), fibers bridge cracks and thereby transfer tensile stresses across the cracked region, allowing for tensile stresses to be carried by the concrete within the cracked region. Due to structures being designed for longer design lives, the consideration of long-term effects such as fatigue is required. Much research has examined tension-stiffening under fatigue when subjected to low cyclic loading, but very little has considered the effects of high-cycle fatigue, especially for UHPFRC. This paper presents the results of nine UHPFRC tension-stiffening tests under high-cycle fatigue in which the crack formation and development under varying cyclic ranges were studied. Specimens were subjected to as many as 5.7 million cycles, and crack readings were taken during each test. The experimental results demonstrate the random nature of cracking on UHPFRC as well as the increase in the crack width under cyclic loads. Finally, this research described the extension of an existing partial-interaction mechanics model to allow for the stress in the fibers and the increase in crack width due to high cycle fatigue.B. D. G. Sepulveda, P. Visintin, A. B. Sturm, D. J. Oehler