Performance of large size reinforced concrete beams containing a lap splice subjected to fatigue loads
Zacaruk, James A.
Extensive research has been conducted into the areas of low cycle high stress loading (seismic loading) and static loading of reinforced concrete beams containing lap splices. The knowledge acquired from this research has led to recommendations for changes in how seismic and static loading of lap splices are handled. For splices subjected to high cycle low stress load patterns (fatigue loading) current design of lap splices is very similar to that used for statically loaded splices, even though little research information is available on performance of lap splices under high cycle fatigue, particularly for larger size bars and members. With this in mind a testing programme was initiated to determine the effects of fatigue on the performance of lap splices proportioned and confined with transverse reinforcing steel according to the ACI Committee 408 recommendations for tensile static loading. In the test programme described in this report, only short lap lengths with heavy transverse confinement were investigated. Specimens used in this study were 7 m long with a 330 mm x 508 mm cross-section. Equal loading is applied at two points symmetrically placed two meters apart on the simply supported beam. Reinforcement consists of 2 - No. 30 Grade 400 tension reinforcement with either 2 - No. 30 or 3 - No. 25 Grade 400 compression reinforcement. Both tension bars contain 900 mm lap splices confined with 7 - No. 10 Grade 300 stirrups. The splices are located at mid-span in the constant moment, zero-shear region. Shear reinforcement consists of No. 10 Grade 300 stirrups placed at 150 mm on centre. Eight specimens were constructed and subjected to either cyclic loads or monotonically increasing loads (static loads) until failure. Cyclic loads were applied to seven specimens with a monotonically increasing load applied to the eighth. Different load ranges were used in the fatigue testing, but stress reversal was not applied. Six of seven cyclically loaded specimens failed when one or both of the main tension bars ruptured, while the seventh specimen failed when the compression zone crushed after the cyclic test was terminated at 3 million cycles and a monotonically increasing load was applied. The one beam subjected to a static load until failure exhibited a bond failure in the splice region. The tests showed that heavily confined splices proportioned according to the guidelines set out in ACI Committee 408 recommendations for static loading are adequate for cyclic fatigue loading, and the splice does not appear to influence the fatigue life of the specimen.