Live Load (LL) reduction
Live Load (LL) reduction
(OP)
Hello,
I was reviewing a geotechnical report for a 40 story tower. One of the sections included settlement analysis.
The engineer, stated in one specific paragraph that for settlement analysis purposes, he considered 100% of the dead load and "a reduced live load (LL"). He did not go into more details about how much was the LL reduced and why.
Anyone one has any idea about this Live load reduction factor for settlement analysis purposes? and why?. TO my knowledge, it would make more sense to consider the full LL as we need to design for the worst case scenario.
I was reviewing a geotechnical report for a 40 story tower. One of the sections included settlement analysis.
The engineer, stated in one specific paragraph that for settlement analysis purposes, he considered 100% of the dead load and "a reduced live load (LL"). He did not go into more details about how much was the LL reduced and why.
Anyone one has any idea about this Live load reduction factor for settlement analysis purposes? and why?. TO my knowledge, it would make more sense to consider the full LL as we need to design for the worst case scenario.





RE: Live Load (LL) reduction
Perhaps some "real" geotechs here could chime in as well.
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RE: Live Load (LL) reduction
RE: Live Load (LL) reduction
RE: Live Load (LL) reduction
However, for a two or three story structure, the difference is minimal.
Usually, the live load on the roof structure is not reduced, only the floors.
Mike McCann, PE, SE (WA)
RE: Live Load (LL) reduction
DL + 0.4 LL is typical for calculating long term settlements.
RE: Live Load (LL) reduction
Mike McCann, PE, SE (WA)
RE: Live Load (LL) reduction
I do agree with a reduction in FS from 3 to 2 for transient loads, but not live loads. Most of the time structural engineers don't even split the loads out for us. We are usually just provided with a maximum column load - most time we have to make assumptions about column loads based on rough rules of thumb for the building type.
RE: Live Load (LL) reduction
RE: Live Load (LL) reduction
Just on another note about live loads, if you are designing the structure assuming apartment building, you would be looking at 40 psf design live load or at least in my location. Building are designed with full live load not to occur very often which is also one of the assumption why fatigue isn't fully designed for most cases. I would say an apartment including furniture and that a family is there at least half a day everyday, would hardly ever reach its full design load other than parties and such.