Universal Journal of Fracture Mechanics 2 (2014), 39-51 www.papersciences.com Application of the Peak - Load Method to CT and WS Tests for Determining Nonlinear Fracture Parameters of Concrete Ragip Ince Firat University, Engineering Faculty, Civil Engineering Department, 23279 Elazig, Turkey rince@firat.edu.tr Abstract To analyze a concrete structure using fracture mechanics, its fracture parameters need to be determined. Many nonlinear fracture models have been proposed in design codes and by investigators for use in determining fracture parameters of concrete. The two-parameter fracture model (TPM) requires two fracture parameters to describe fracture-dominated failure of concrete structures: the critical stress intensity factor, , and the critical crack tip opening displacement, CTOD c . In this model, the fracture parameters are obtained from one of two experimental methods: the compliance method and the peak-load method of which the theoretical basis is to solve four simultaneous nonlinear equations. However, eccentric compression prisms, beams and notched split-tension specimens, namely, cubes, cylinders, diagonal cubes, holed cylinders have been used in the peak-load method based on the two-parameter fracture model. In this study, the peak-load method was initially applied to compact-tension (CT) and wedge-splitting (WS) data from six series of experimental studies described in the literature. The results of the peak-load method appear to be viable and very promising. s Ic K Key Word and Phrases Concrete, Compact-tension test, Wedge-splitting test, Two-parameter model, Peak-load method, Double-K model. 1. Introduction Applications of linear elastic fracture mechanics (LEFM) to concrete were initiated by Kaplan [1] in 1961 and continued by Kesler et al. [2] in 1972, who concluded that LEFM was not valid for cement based composite materials. This inapplicability of LEFM is due to the existence of an inelastic zone in front of the crack tip in concrete with large-scale and full cracks. This so-called fracture process zone (FPZ) is ignored by LEFM. For this reason, several investigators have developed nonlinear fracture mechanics approaches to characterize the FPZ. These approaches primarily involve the fictitious crack model (FCM) of Hillerborg et al. [3], the crack band model of Bazant and Oh [4], the two-parameter model (TPM) of Jenq and Shah [5], the effective crack model of Nallathambi and Karihaloo [6], the size effect model of Bazant and Kazemi [7], the double-K model of Xu and Reinhardt [8], and the double-G model of Xu and Zhang [9]. In contrast to LEFM, in which a single fracture parameter such as the critical stress intensity factor is used, these models need at least two experimentally determined fracture parameters to characterize the failure of concrete structures. Accordingly, they require either multiple tests (at least three) or a closed-loop testing system. Analysis of an existing structure using fracture mechanics is impossible using many of the approaches mentioned above, and even for those approaches for which it is possible, specimens cored from structures must be tested after being processed to a specific geometry. However, in the peak-load method based on nonlinear analysis, the use of the cylindrical specimens, which can also be taken from existing structures by core drilling, lead to great advantage for estimating fracture properties of existing structures based on nonlinear fracture mechanics. Concrete splitting specimens have been commonly used in concrete fracture testing because they have certain advantages, such as compactness and lightness, compared to beams. Additionally, cubical and cylindrical test specimens have the following advantages [10, 11]. 1) These specimens are easy to handle, and there is no risk of breaking them during handling. 2) The same molds can be used to cast specimens for both fracture and strength tests. 39