Performance of Tension Lap Splices with MMFX High Strength Reinforcing Bars

The specialized microstructure and chemical composition of MMFX reinforcement results in a material that possesses both corrosion resistance and high tensile strength. MMFX Steel Corporation of America guarantees for its reinforcement a minimum ultimate tensile capacity of 150 ksi and a minimum yield strength of 100 ksi when measured using the 0.2% elongation method. To safely utilize the high strength of MMFX steel in design, proper anchorage of the reinforcement must be provided.

Development length equations included in the ACI 318-05 building design code and the 4th edition of the AASHTO LRFD bridge design code are based on data obtained from splice tests failing primarily at bar stresses less than their respective maximum allowable design yield strengths for tensile reinforcement of 80 ksi and 75 ksi. Limited data exists for splices failing at bar stresses greater than 75-80 ksi, and no data exists for splices failing at bar stresses greater than 120 ksi — a stress attainable by MMFX reinforcement.

To determine the adequacy of the development length equations in the ACI 318 and AASHTO LRFD design codes and a development length equation proposed by ACI Committee 408 at high bar stresses, the University of Texas, the University of Kansas, and North Carolina State University are each testing 22 beam-splice specimens designed to fail at bar stresses between 80 ksi and 140 ksi. Test variables include bar size, concrete compressive strength, splice length, concrete cover, and amount of transverse reinforcement (confinement). The results of 45 tests completed by the researchers are reported in this thesis. Splice design recommendations are presented for bars spliced at high stress, and general design considerations are outlined for flexural members reinforced with high strength reinforcing bars.