Temporary Loading Increase for Structural Steel
Temporary Loading Increase for Structural Steel
(OP)
I am designing a temporary soil retaining structure to be used during construction. The structure will only be in place for a day or two till it is removed.
Is there any code or provision I can use to justify increasing my allowable strength to yield? In order words designing the steel with a factor of safety closer to 1.0 then the standard allowable safety factors per AISC 13th ed?
Is there any code or provision I can use to justify increasing my allowable strength to yield? In order words designing the steel with a factor of safety closer to 1.0 then the standard allowable safety factors per AISC 13th ed?






RE: Temporary Loading Increase for Structural Steel
RE: Temporary Loading Increase for Structural Steel
www.PeirceEngineering.com
RE: Temporary Loading Increase for Structural Steel
I have seen this happen in larger projects, and the shoring system just sits there for years.
Consequently, I don't trust "temporary".
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Temporary Loading Increase for Structural Steel
Otherwise the factors are there for a reason, and that reason is independent of the time the structure is in place. The factor that reduces steel strength deals with variability of the steel material, not with the time the loads are in place.
RE: Temporary Loading Increase for Structural Steel
This is currently what i am doing full time so I have recently put some thought and research into this.
I would not recommend reducing the factor of safety as this allows for both steel variables and for variations in the soil from those that have been estimated.
The stress reduction mentioned by PEinc is a valid reduction which is mentioned in UK excavation literature (particularly TRADA - timber for excavations). In this book they talk of reductions of 25 to 50% in the flexural members due to arching of the soil between the much more rigid prop points. But as this is due to arching then the full load still needs to be allowed for at the props.
RE: Temporary Loading Increase for Structural Steel
Terzaghi & Peck's earth pressure envelopes for braced sheeting walls were intended to calculate the maximum anticipated bracing loads - not the load on every brace. Therefore, the envelope is generally conservative. That's why you can usually reduce the pressure to design the sheet piling or soldier beams.
For a few thousand temporary projects, I usually used the full earth pressure envelope for calculating the tieback and brace loads but then allow a 20% temporary overstress for the temporary sheet piling, soldier beams, and wales. It is almost always approved without question. Sometimes, a railroad will allow only a 10% overstress.
www.PeirceEngineering.com
RE: Temporary Loading Increase for Structural Steel
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RE: Temporary Loading Increase for Structural Steel
Safety factor is 1.6 for "transient" or persistent loads (no temporary anywhere). It can go up to 1.8 if the level of control of concrete is low.
RE: Temporary Loading Increase for Structural Steel