High cycle (fatigue) resistance of reinforced concrete beams with lap splices
Date
1993-08-01
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Degree Level
Masters
Abstract
The development of current design standards for reinforced concrete beams containing
lap splices has been mainly aimed at preventing failures due to static (monotonic) loading,
or low cycle, high intensity (seismic) loading. However, little consideration has been
given in these standards or in previous research to the performance of lap splices when
subjected to high cycle, low intensity (fatigue) loading. Also, recently proposed design
equations for lap splices under static loading will permit shorter lap lengths. For these
reasons, a study was initiated to investigate the fatigue resistance of reinforced concrete
beams with lap splices. A principal variable in this research program was the degree of
transverse reinforcement (stirrups) which was provided along the lap splice.
The specimens used in this experimental program were seven meters in length, with a
cross section 330 mm wide and 508 mm deep, and were reinforced with two No. 30
Grade 400 bars, top and bottom. A lap splice was provided in the bottom tension bars
situated in a constant moment region created by a symmetrical two point loading system.
The lap splice length and confinement were designed according to ACI Committee 408
recommendations for static loading.
Two different lap splice configurations were provided for the test specimens. The first
used the maximum number of stirrups that were deemed to be effective for static loading,
permitting a shorter lap length. In the second configuration nominal stirrups were
provided to the splice at a spacing of one half the effective beam depth, requiring a longer
lap length. Failure of the specimens with the heavier stirrups occurred from fatigue of the
tensile reinforcing steel and showed similar fatigue resistance to beams containing
continuous reinforcement. The specimens with nominal stirrups usually resulted in a
splice failure after fewer load cycles, after splitting and delamination of the concrete
confining the lap had occurred.
Both beams had a similar static bond resistance; however, the beams with the heavier
stirrup confinement (shorter lap length) displayed a greater fatigue resistance than the
beams with lighter stirrups (longer lap length). These results are in agreement with
conclusions reached for seismic loading conditions, which found that splice confinement
provided by a high degree of transverse reinforcement is required under cyclic loading to
offset the rapid deterioration of the concrete cover confinement.
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Degree
Master of Science (M.Sc.)
Department
Civil Engineering
Program
Civil Engineering