International Concrete Abstracts Portal

This paper presents an inverse analysis approach to obtain material properties of fiber reinforced concrete in terms of Young’s modulus, Poisson’s ratio and tensile stress crack width parameters from the load deflection response of a round panel test. The properties were then used in a nonlinear finite element model to simulate the test of a full scale elevated slab subjected to a point load at mid span of the central slab. The simulation reasonably agreed with the experimental test data measured in the field; the predicted load capacity was higher than the test result by 15.5% and the ascending response was also stiffer than the measurement in the field. An alternative simpler yield line analysis was also used to calculate the material strength from the round panel test and then used to predict the load capacity of the full scale test. The load capacity predicted by the yield line theory was in between the finite element simulation and the experimental result.

Steel fiber-reinforced self-compacting concrete (SFRSCC) was developed and applied on the manufacture of structural façade panels composed of a grid ribbed system covered by a layer of 30 mm thickness. Panel prototypes of this structural system were tested using loading configurations that promote the flexural and the punching failure modes in order to assess the benefits of fiber reinforcement to the flexural and shear resistance of thin SFRSCC structural systems. A smeared multi-fixed crack model, implemented into a FEM-based computer program, was used to simulate the deformational behavior of the tested panel prototypes up to their failure. The fracture parameters characterizing the SFRSCC post-cracking behavior were obtained from inverse analysis, using the data derived from three point notched beam tests. The punching failure mode was well captured by adopting a softening diagram for both out-of-plane shear components.

This CD-ROM is a collection of papers organized for a session held at the ACI 2007 Fall Convention in Puerto Rico. Papers relate to material behavior and the structural implications of using fiber-reinforced concrete (FRC), and focus on the benefits of using fibers to enhance stiffness and reduce deflection of FRC members both with and without reinforcement. Used in combination with conventional reinforcement, FRC can increase stiffness and reduce deflection of cracked members as well as decrease the stress in the reinforcement. This is particularly important in thin sections and cement-based products where the geometry and profile play an important role in controlling deflection. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-248CD

Effect of open- or closed-loop deflection control on the measured flexural toughness of fiber reinforced concrete (FRC) was investigated. Third-point loading tests were performed as per ASTM C1609M on several high strength concrete mixtures containing low volume fractions of single, double and triple-fiber blends. A 3-stage loading sequence was adopted for the closed-loop deflection control tests to fully capture the load vs. deflection response immediately after the peak-load. The results indicate that the open-loop tests produce high instability in the load deflection curves after the peak-load. However, contrary to general belief, the open-loop tests also overestimated the flexural toughness compared to the closed-loop deflection control tests. Manually removing the instability from the open-loop curves helped bring the open-loop toughness values closer to the closed-loop toughness values.

This paper is part of an on ongoing research project involving testing of small and large-scale beams to investigate shear behavior of reinforced concrete beams with synthetic macro fibers. Six full-scale tests were completed on longitudinally reinforced concrete beams without stirrups. The size of the beam was 280 mm x 460 mm x 3200 mm and tested with a shear span to depth (a/d) ratio of 3.5. Synthetic macro-fibers were added at two volume fractions of 0.5 % and 0.75 %, which is equivalent to 4.6 and 6.9 kg /m3. Strains and deflection were measured under monotonic loading of the beams and cracking was also monitored. The test results show that the synthetic macro-fibers improved the first diagonal shear cracking strength and ultimate shear capacity of the beams. Ultimate shear capacity of the reinforced concrete beams was increased by 12 to 25 % depending on the dosage of synthetic macro-fibers used. Embedded strain gauges in the concrete beams indicated the fibers effectively distributed the load, improved tensile strain capacity and thus increased the shear capacity of the concrete beams. Load-deflection measurements show that synthetic macro-fibers improve the post-diagonal cracking stiffness and toughness of the concrete beams and reduce the brittleness of the shear failure.