Development length equation for high-strength materials

The goal of this study was to revise the development length equation of ACI 318- 05 and to better reflect test results for high-strength concrete. The revision of the equation was accomplished using test results tabulated in the Database 10-2001maintained by ACI committee 408. Equations for development length in ACI 318-05 and ACI 408.3 examined to understand the issues to be considered for revision on the variability of test data. The development length equation in ACI 318-05 was very conservative for [compressive strength of concrete][less than or equal to]14,000 psi based on the experimental data in Database 10-2001 of ACI Committee 408. On the contrary, the ACI 318-05 may be less conservative for high-strength concrete, [compressive strength of concrete] [greater than or equal to]14,000 psi . Thus, modified design equations were proposed to provide realistic values for normal strength concrete and conservatively for high-strength concrete. The ACI 318-05 equation was modified for 1) compressive strength of concrete and 2) confinement as expressed by the term [minimum side cover, cover over the bar or wire, or one-half the center-to-center spacing of the bars or wires] + [contribution of confining reinforcement across potential splitting planes] / [normal diameter of bar] in ACI 318-05. The basic assumption is that bar stress is a linear function of development length, and development length is the length required for bar stresses to reach the yield.