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Converting LRFD values to service level

thread507-121600

Converting LRFD values to service level

Converting LRFD values to service level

(OP)
LRFD uses load factors and resistance factors applied to service loads and nominal strengths, respectively.  Do you think it is appropriate to find a maximum service load by multiplying the nominal strength R by the resistance factor phi and dividing that product by the load factor gamma?

sum (gamma*Q) = phi*R

Q=phi*R/gamma where Q is the service level load effect.

As an example say we calculate the strength of an anchor rod with CCD in the ACI 318-02 Appendix D.  This is a strength level calculation.  Can we convert that to a service load strength by the method described above?  Is there a better way to do it?

RE: Converting LRFD values to service level

I think you can look at it that way. The only thing I see a bit tricky is with the gammas, since they vary with load type. So the "service load strength" would vary with the ratio of the type of loads applied (dead, live, wind, seismic).

RE: Converting LRFD values to service level

gets even hairier with the load combination factor which is essentail for drift calculations and P-delta a seviceability calc., better to get a good accounting method going of all.  In my opoinion there is no simple way unless it is a 'simple' beam.

RE: Converting LRFD values to service level

(OP)
I agree that there isn't a straight forward method for all applications.  The only one that I'm interested in right now is using the ACI Appendix D method of anchor rod design but at a service load level.  If I assume the worst case load factor of 1.6 for wind I believe I would be safe.  Another method I've heard of is calculating the nominal strength, phi = 1, and dividing by a safety factor.  Both seem logical.  I was wondering if there is an established norm for this.  The allowable load tables in the IBC in chapter 19 are too conservative for headed bolts imho.  

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