OVERSTRENGTH FACTOR SECT 12.4.3.2

[MRberkeng]

In the new code (ASCE 7-05), when there is a discontinous load from a shearwall at a second story we are supposed to use Section 12.4.3.2 How is this applied? In the 97 UBC we would multiply the seismic uplift load by 2.8 onto a beam or post below that shearwall if it would not have a shearwall below. However, this code has Section 12.4.3.2 has a load combination that I need a little help understanding

Thanks

 

[JAE]

Can you elaborate your question a bit more?

What exactly do you not follow in the two special load combinations?

 

[RVSWA]

A bit more information will help but I can share some of the moments I had as we dug through this just to give you something to chew on and come back with...

A big change from UBC to IBC is that you no longer neglect the vertical component of the event when using ASD. You are using the 0.2*Sds*D to exaggerate the behavior of the dead load in the most unfavorable load combination.

Also gone is a rather confusing UBC provision that allowed you to basically ignore any over-strength force that couldn't be transfered by the connections. We called it the Run Home to Momma Clause. Why would one ignore the force at the connection when connections are of such concern. In fact with all the beams we design for the over-strength load case, it is generally the hangers or caps and bases that are impacted and less often the member itself. (Bear in mind I mostly design in wood)

The shear transfer connections must be designed for an additional 25% in those area's of plan irregularity.

Perhaps you have a specific problem that you can present...