Hi everyone,
We know that AASHTO LRFD bridge design specification for stud design is based on the push-out tests performed by Slutter and Fisher. They proposed an equation showing the relation between stress range amplitude and number of cycles to failure for a shear stud as follows,
Δτ = 1020 n −0.186
where Δτ = stress amplitude and n = number of cycles
Could anybody please tell me whether this relationship is accepted by AASHTO LRFD to calculate number of cycles to failure when stress amplitude is known. If not, then how it can be determined.
The AASHTO LRFD Bridge Design Specifications (AASHTO 2007) bases most of its design on the research done by Slutter and Fisher (1966) at Lehigh University. They chose to develop equations that used the range of live load shear force (Zr) rather than the stress range as other codes have done. The following equation is used to determine the live load shear force (Zr):
Zr = αd2≥ 2.75d2 where α= 34.5-4.28 logN
Where N represents the number of cycles on the x-axis.
AASHTO (2007) provides a constant amplitude fatigue limit (CAFL) of 3.5 ksi, a stress range below which no propagation of fatigue cracks is expected. AASHTO (2007) also has some geometry requirements that give limitations on dimensions and spacing of studs.
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