Lap Splice Fatigue Capacity

[Quade999]

Hi Everyone,

Is the fatigue resistance of a contact lap splice the same as that of a continuous bar? I've only seen any differences for a splice fatigue resistance with respect to welded or mechanical splices, which leads me to believe it is the same, but am not 100% sure about the contact lap splice.

Thanks

 

[r13]

I wonder what is the motive/reason of this question. Can you provide an example that the splice is in a structural element that is subjected to repetitive/cyclic load with a great deal of stress fluctuation? Attach a calculated example with reinforcing layout will be appreciated. Also, please kindly provide the fatigue studies referred in your query. Thanks.

 

[dhengr]

Quade999:
What is a contact lap splice? They will all have different fatigue life characteristics because their make-up is so different as relates to the factors which cause fatigue problems. Each has a very different load path for the stress field, and each has different mechanisms which exacerbate the fatigue problem. The plane bar will be the standard or starting point, and various basic materials and material grades will act differently too. The plane bar has a straight path for the stress field/stress flow, an ideal condition, assuming there are no nicks in the bar surface or edges, which are stress raisers in themselves.

The lap splice causes the stress field to have to take a severe jog from the plane of one plate to the plane of the other plate. In the case of the welded lap jnt. you have residual stresses from the welding, likely perpendicular to the stress field; and you have the tensile stress field curving across (and perpendicular to) the weld root, a real serious fatigue issue. In the case of the bolted joint, you have the stress field moving from pl. to pl. and around a bunch of imperfect holes in the pls., again, significant stress raisers. Then, you have the bearing stresses of the bolts on the holes in the pls., the shear in the bolts and the compression btwn. the two pls. caused by the bolt tension, a very complex combined stress situation.

You really should dig out some basic textbooks on fatigue and fatigue design, and do some reading and self study. That study will tend to stick with you better. One of the most important things about designing for fatigue is good clean detailing, for good smooth stress flow, and then good clean fabrication and welding detailing.

 

[r13]

IMO, this is a theoretical question that can be, and shall be, avoided in real practice - do not splice in the high stress regions. Uses weld or mechanical coupler if there is absolute necessity.