THE STRENGTH OF ANCHOR BARS: A REEVALUATION OF TEST DATA ON DEVELOPMENT LENGTH AND SPLICES

An equation has been developed for calculating lengths of lap splices of deformed bars from a nonlinear regression analysis of test results of beams with lap splices. It reflects the effect of length, cover, spacing, bar diameter, concrete strength, transvers reinforcement, and moment gradient on the strength of lap splices. The equation is also applicable in determining basic development lengths. Based on the equation developed, design recommendations are proposed for development lengths and lap splices and compared with AASHTO Interim Specifications for Bridges, 1974. The comparison shows that for the most unfavorable splice conditions (a clear cover of 1-1/2 in. on sides or bottom, splices with no transverse reinforcement, all bars spliced in a region of maximum moment, and bar spacing less than 6 in. on centers) AASHTO provisions overestimate lap lengths by 11 percent for #6, 16 percent for #8, and 25 percent for #11 bars. If cover is increased to 3 in. or transverse reinforcement is added, the splice length of large bars may be reduced by as much as 60 percent over that required by present AASHTO provisions. Furthermore, the equations governing development length are essentially the same as those for splice length. /FHWA/