Soranakom, C., Yekani-Fard, M., and Mobasher, B. “Development of Design Guidelines For Strain Softening Fiber Reinforced Concrete,” 7 th international Symposium of Fiber Reinforced Concrete: Design and Applications BEFIB 2008, Editor: R. Gettu, Sept. 2008, pp 513-523. 513 DEVELOPMENT OF DESIGN GUIDELINES FOR STRAIN SOFTENING FIBER REINFORCED CONCRETE Chote Soranakom (1) , Masoud Yekani-Fard (1) , and Barzin Mobasher (1) (1) Department of Civil and Environmental Engineering, Arizona State University, USA Abstract This paper summarizes flexural modeling and design procedures for strain softening fiber reinforced concrete. Closed form solutions for calculating neutral axis, moment and curvature are presented and used to study the effect of post crack tensile strength and compressive to tensile strength ratio. With simplification to the closed form solutions, a single equation to predict moment capacity of a flexural member is obtained. To avoid sudden failure in flexural loading and to control crack width caused by shrinkage and temperature, the minimum post crack tensile strength for each case is proposed. A design example of slab on grade is employed to illustrate the calculation steps. Once the design part is finished, the specified post crack tensile strength for the slab must be verified by material testing. 1. INTRODUCTION Fiber reinforced concrete (FRC) is a composite material consisting of cementitious matrix and discrete fibers such as steel, glass, or other synthetic materials. The fibers that are randomly distributed in the matrix act as crack arrestors. The deboning and pulling of fibers at crack surface requires energy dissipation, leading to a substantial increase in toughness and resistance to cyclic and dynamic load [1]. Since the introduction of fibers to the concrete market in late 1960’s, the demand for FRC has been steadily increased. The main areas of applications are slab on grade, tunnel lining, precast, and prestressed concrete products. Flat slabs made solely of SFRC has been successfully practiced in France and other European countries, however their applications in the United States have been limited [2,3]. It is expected that more FRC applications in new structural areas are forthcoming. In addition to the commonly used SFRC, a wide range of fiber reinforced concrete systems have been developed including glass fiber reinforced concrete (GFRC) [4], engineered cementitious composite (ECC) [5,6], steel infiltrated mat concrete (SIMCON) [7,8], DUCTAL ® [9], CARDIFRC ® [10], and other synthetic fiber systems. To standardize materials, Naaman and Reinhardt [11] defined the classifications of “strain hardening” and “strain-softening” materials based on hardening and softening tensile responses observed in tension tests. Within the last category, additional terms of “deflection-hardening” and “deflection-softening” are defined according to the hardening and softening deflection responses observed in bending tests. This