chris456s
Structural
- Feb 2, 2017
- 50
Regarding bolt calcs in EN 1993-1-8
Is the bolt tensile load F_t,Ed equal to total tensile load including preload or is it only applied load external to preload?
The question arises for the following reasons:
1. Notice the tensile resistance check F_t,Ed <= F_t,Rd. Where resistance is K_2*F_ub*A_s/gamma. If Preload is as suggested 0.7F_ub*A_s and K_2 = 0.63 and F_t includes pretension, then the check will always fail under preload alone since 0.63/gamma is less than 0.7.
2. Also notice that the cat C combined slip resistance has a factor equal to preload (F_p,C) minus 0.8F_t,Ed. This make sense if F_t,Ed does not include preload since larger seperating load descreases contact force on the friction plane. But if F_t,Ed includes preload, this factor is double dipping
3. From the first to observations, I would assume that F_t,Ed does not include preload and is exclusively external load. However, that would mean that the tensile checks are not conservative as overly preloading a bolt may exceed tensile capcity which should be checked but isn't explictly. Also F_t,Ed not including preload would mean that the punch shear restistance check F_t,Ed <= B_p,Rd would not be conservative as the total punch shear load would not be accounted for.
Overall there seems to be a contradiction. I see this contradiction resolved if F_t,Ed = max(preload ; external load) and the largest allowable preload was reduced for countersunk bolts. However, that is an assumption with no justification other than it resolves the contradiction (which I could be wrong about) and is not stated in the code.
Is the bolt tensile load F_t,Ed equal to total tensile load including preload or is it only applied load external to preload?
The question arises for the following reasons:
1. Notice the tensile resistance check F_t,Ed <= F_t,Rd. Where resistance is K_2*F_ub*A_s/gamma. If Preload is as suggested 0.7F_ub*A_s and K_2 = 0.63 and F_t includes pretension, then the check will always fail under preload alone since 0.63/gamma is less than 0.7.
2. Also notice that the cat C combined slip resistance has a factor equal to preload (F_p,C) minus 0.8F_t,Ed. This make sense if F_t,Ed does not include preload since larger seperating load descreases contact force on the friction plane. But if F_t,Ed includes preload, this factor is double dipping
3. From the first to observations, I would assume that F_t,Ed does not include preload and is exclusively external load. However, that would mean that the tensile checks are not conservative as overly preloading a bolt may exceed tensile capcity which should be checked but isn't explictly. Also F_t,Ed not including preload would mean that the punch shear restistance check F_t,Ed <= B_p,Rd would not be conservative as the total punch shear load would not be accounted for.
Overall there seems to be a contradiction. I see this contradiction resolved if F_t,Ed = max(preload ; external load) and the largest allowable preload was reduced for countersunk bolts. However, that is an assumption with no justification other than it resolves the contradiction (which I could be wrong about) and is not stated in the code.
