International Concrete Abstracts Portal

The limitations of known fracture mechanics (FM) models are noted, and to overcome them, a specific FM model was proposed based on modeling the stress distribution only along the crack fracture process zone (FPZ), with elastic concrete behavior out of the FPZ. This peculiar stress distribution was called physically verisimilar stress (PVS), and it was accepted as the basis of the proposed PVS model, which used three material parameters: maximum stress, intrastructural linear size a, and dimensionless value n, taking into account the plastic properties of the material. The relationships for determining the PVS model parameters were suggested for concrete. Strength problems were solved by the modified method of sections, in which the PVS was applied along the FPZ. The FM model based on PVS and the modified method of sections led to an acceptable in-practice method of strength design, which was considerably simpler than the known phase-field method. The proposed PVS model and design method allow for the prediction of the cracks development, considering their stable growth up to the critical (ultimate) values of the crack length and load. The unstable cracks propagation is considered also. The paper provides examples of designs and shows sufficient theoretical strength relative to the experimental one.

Steel reinforcing bars conforming to ASTM A1035 have enhanced corrosion resistance and significantly higher tensile strength compared to conventional reinforcing steel grades. However, the impact of the unique stress-strain characteristics of this steel on the failure modes and strength prediction models is not yet fully understood. This paper reports on the laboratory testing to failure of eight large-scale specimens having small shear span to effective depth ratios and containing or omitting web reinforcement. All specimens were longitudinally reinforced with deformed A1035 steel bars with measured stresses at the peak load from 695 to 988 MPa (100 to 143 ksi)—significantly higher than the design stress limits defined in current codes of practice. Members without web reinforcement failed in a brittle manner after the formation of diagonal cracks joining the loads and supports. For members containing web reinforcement, the shear span to effective depth ratio and the longitudinal reinforcement ratio were both found to influence the failure mode and post-peak ductility. It was possible to develop designs that could exploit the high reinforcement strength while exhibiting acceptable serviceability characteristics and adequate ductility at failure. The safety of capacity predictions using ACI ITG-6R-10 provisions is presented.

Unacceptable diagonal cracks frequently occur at service load in the vicinity of the re-entrant corners in structures such as the dapped ends of bridge girders and the ledges of inverted T bent caps. Such diagonal cracks are not only visually intimidating but also impose a potential danger of corrosion of reinforcing bars. Controlling such cracking is difficult due to the lack of a rational theory for crack prediction. In this paper, a compatibility-aided strut-and-tie model (CASTM) is proposed for predicting the diagonal crack widths at re-entrant corners. The validity of this model is supported by tests of seven full-scale specimens.

The goal of this research is to study the relationship between cracking and water permeability of normal-strength concrete under load and to compare the experimental results with theoretical models. A feedback-controlled wedge splitting test was used to generate width-controlled cracks. Speckle interferometry was used to record the cracking history. Water permeability of the loaded specimens was evaluated by a low-pressure water permeability test at the designed crack mouth opening displacements (CMODs). Water permeability results are compared with those previously obtained for unloaded specimens for which cracks were induced by a feedback-controlled splitting tension test. The experimental results indicate that water permeability of cracked material significantly increases with increasing crack width. The flow for the same cracking level is repeatable regardless of the procedure used for inducing the cracks. No direct relationship between water flow and crack length was observed, whereas clear relationships exist between CMOD or crack area and flow characteristics. Experimentally measured flow is compared to theoretical models of flow through cracked rocks with parallel walls and a correction factor accounting for the tortuosity of the crack is determined. Calculated flow through cracks induced by wedge-splitting test provides an acceptable approximation of the measured flow.

A methodology for predicting crack spacings and widths of reinforced concrete members in uniaxial tension at any given loading stage is presented. The method includes the proposal of a new expression for predicting the average gross strain of a member after the initiation of the first crack and accounting for the concrete contribution in the post-cracking range.The proposed method is based on an extensive experimental program which involved testing 34 specimens to study the cracking behavior of reinforced concrete members subjected to membrane tensile stresses in the presence of transverse reinforcement. Major variables included ratio of reinforcement, concrete cover, concrete thickness, and spacing between transverse reinforcements. Based on the test results, the paper introduces a range within which the theoretical prediction of crack spacing and width is acceptable. Using the proposed methodology, the prediction of the number of cracks was found to be within I crack for most measurements of crack number. The ratio of the predicted crack width based on the proposed method to the measured crack widths is found to be 1.17, which indicates a high degree of predictive accuracy.