Chote Soranakom

Flexural design of fiber-reinforced concrete

The authors present a set of closed form equations for fiber-reinforced concrete flexural design. Based on simplified tensile and compressive constitutive response, these equations may be used in a serviceability-based criterion or limit state approach that limits the effective capacity of tensile strain. Flexural moment-curvature response generation is allowed by the equations in regard to a rectangular beam section for use in calculating structural analysis, in addition to strain softening fiber-reinforced concrete design charts. Equations are also proposed for minimum post-crack tensile strength to prevent sudden post flexural cracking failure and control crack width. The average crack width of structural members is limited by the analytical tensile strain equations proposed for serviceability. Additionally short-term deflections of structural members are determined through use of the bilinear moment-curvature model in conjunction with the geometrical relationship between deflection and curvature. The calculation steps are demonstrated through an example of a one-way slab.

Effect of Material Non-Linearity on the Flexural Response of Fiber Reinforced Concrete

Abstract This paper demonstrates the use of a closed-form derivation of moment-curvature diagram and crack localization rules in simulating the flexural response of textile reinforced cement composites. Effect of non-linear material response obtained fiom uniaxial tension tests on the simulation of the flexural beam test results were studied in order to establish a rational approach to balance the discrepancy between experimental data. The study reveals that the material nonlinearity can be adequately addressed by modifying two intrinsic material parameters: the first cracking strain and initial tensile modulus. The direct use of uniaxial tension response to simulate flexural behavior underpredicted the response of textile cement composites. Modifications to the first cracking strain in the original tension model are recommended to yield better fit to the flexural experimental data.

Mechanical Properties of Alkali Resistant Glass Fabric Composites for Retrofitting Unreinforced Masonry Walls

Mechanical properties of a cement-based matrix – grid (CMG) system developed for masonry rehabilitation are discussed. CMG system is a composite consisting of a sequence of layers of cement-based matrix and alkali resistant (AR)-glass coated reinforcing grid. The experimental program included tension and flexural tests of composites with special consideration to long term durability. Variables studied include effect of composite thickness, fabric orientation, and effect of accelerated aging on the tensile and flexural responses. Results indicate that samples in the cross machine direction (XMD) showed the best combination of high tensile strength and Ultimate strain value (2.36%) as compared to the machine direction (MD). After 28 days of accelerated aging, tensile strengths reduced for the MD and XMD directions respectively, representing average reductions of 23% and 17%. In the flexural samples, cross machine samples (XMD) show a combination of high flexural strength and Maximum deflection as compared to the MD samples. Higher stiffness of fabrics in the cross machine direction due to the manufacturing process was the source of such differences in behavior. The first crack strain in flexure is as much as the ultimate tensile strength in tension for many composites. A discussion of comparison of tensile and flexural stress measures is presented.

Flexural Analysis and Design of Strain Softening Fiber-Reinforced Concrete

This paper describes how parameterized material models for strain softening fiber-reinforced concrete are used to express closed-form solutions of moment-curvature response of rectangular cross sections. By utilizing crack localization rules, engineers can predict flexural response of a beam. A parametric study of post crack tensile strength in the strain softening model is conducted to demonstrate general behavior of deflection softening and deflection hardening materials. Uniaxial and flexural test results of several polymeric fiber-reinforced concrete mixtures are used to demonstrate the applicability of the algorithm to predict load-deflection responses. The data are compared with the ASTM International test Method C1599, which represents the residual strength of the sample after cracking has taken place. The simulations reveal that uniaxial tensile stress-strain relationship is under-predicted using the flexural response test results.