Evaluation of Existing Fracture Models in Concrete


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Title: Evaluation of Existing Fracture Models in Concrete

Author(s): Sawarng Ratanalert Ratanalert and MethiI Wecharatana

Publication: Special Publication

Volume: 118


Appears on pages(s): 113-146

Keywords: concretes; displacement; evaluation; fracture properties; models; mortars (material); notch tests; stresses; tension; Structural Research

Date: 1/1/1990

Many fracture mechanics models have been proposed in recent years to account for the nonlinear behavior of concrete around the crack tip region. These well-known models are the fictitious crack model (FCM) by Hillerborg, the crack band model (CBM) by Bazant, and the two-parameter fracture model (TPFM) by Jenq and Shah, etc. To model the fracture process zone or microcracked zone, these models often assumed the linear or bilinear stress-displacement relationship to simplify the analysis since actual relationships were not available due to difficulties in conducting direct tension tests. To avoid tedious numerical computation and the need of stress-displacement relationship, TPFM was proposed based on the simple LEFM concept. The model was quite accurate when applied to the notched beam test. All these models presented some degree of satisfaction when comparing with some experimental data. Since more direct tension tests with complete postpeak stress-displacement relationships have been successfully conducted in recent years, the need of assuming the stress-displacement relationship or using the indirect notched beam test is no longer necessary. An evaluation of the FCM using the observed stress-displacement relationships versus the assumed one seems to be an interesting task to verify the validity of the model. For TPFM, the proposed two unique fracture parameters should be verified for specimen size independence. A series of experiments were conducted on two types of test specimens (notched beam and compact tension) with different geometries. The results indicate that the parameters recommended in TPFM seem to be unique only for the notched beam specimen. The same two parameters were found to be tenfold larger for the compact tension specimen. For FCM, the predicted load-CMOD and load-deflection curves using the observed stress-displacement relationship are in better agreement with experimental data than those determined from the assumed linear relationship. Although theoretically both predicted load-CMOD and load-deflection curves should have the same order of accuracy, in this study, they were found to be substantially different.