A computer based iterative algorithm for one-way GFRP concrete members is developed to the member thickness required to produce a computer deflection that satisfies maximum permissible deflections over a range of design conditions. The algorithm accounts for effects of cracking and long-term deflection due to creep and shrinkage. The calculated are compared with minimum thickness values based on ACI 318-05 allowable span-depth ratios based on the deterministic model. Recommendation are made for modify the current ACI 440.1R-01 provisions for minimum thickness.