Lateral force caused by gravity load

[engr567]

Is there any reference to indicate how much percentage lateral force does gravity load cause? For example, if there is a freestanding deck to be designed for gravity load, we also have to design it for lateral movement/ load caused by gravity load. How do we calculate the lateral load in this case? Wind load and seismic is not important in this case. I would appreciate your inputs.

 

[suqlainUK]

The various UK building codes (replaced by Eurocodes in April 2011) suggested 0.5% of vertical load as the "notional horizontal force" for building structures, or actual wind loads...whichever was greater;

The new Eurocodes combine both the wind load and 0.5% Equivalent Horizontal Force (EHF). This will result in higher loading on lateral stability bracing members;

For free standing platform structures and mezzanines inside a building (i.e. where wind loads are low) 2.5% of the gravity loads has been historically used as the Notional Horizontal Force; and is one I would suggest in this case.... in additional to other design load cases and local code requirements etc.

 

[engr567]

Thanks for the response. However, this project is located in US. I am looking for a reference in IBC or any US referenced design codes.

 

[frv]

The minimum lateral force on any structure is 1% of the dead load (this is assuming Seismic Design Category A and no wind loading). See ASCE 7-05 Sec. 11.7.2 or ASCE 7-10 Sec. 1.4.3.

 

[ishvaaag]

This is the issue dealt with out of plumb initial imperfections, and so it is there where the answer lies. In more than that, in-member initial imperfections and geometrical and material nonlinearities will intervene in the sizing/checking of the structure.

ASCE 7-10

1.4.3 Lateral Forces
Each structure shall be analyzed for the effects of static lateral forces applied independently in each of two orthogonal directions. In each direction, the static lateral forces at all levels shall be applied simultaneously. For purposes of analysis, the force at each level shall be determined using Eq. 1.4-1 as follows:
Fx = 0.01 Wx (1.4-1)

where
Fx = the design lateral force applied at story x and
Wx = the portion of the total dead load of the structure,
D, located or assigned to level x.
Structures explicitly designed for stability, including second-order effects, shall be deemed to comply with the requirements of this section.

 

[ishvaaag]

... as frv said.

 

[firai]

It is very rare that neither wind nor earthquake would affect the anchorage or the design in some way. There are several minimum loads that apply:

1. For purely gravity loads, it depends on the out-of-plumbness (and out-of-straightness), which depends on the tolerance of the trade you're dealing with. For example, steel constructed according to the AISC Code of Standard Practice is held to L/500, so the maximum out-of-plumbness force is 0.2%. Note that this value is used when designing steel by the direct analysis method. Values can also be approximated for concrete and other trades.

2. For wind, most jurisdictions have adopted some form of IBC, which requires a 20psf net pressure laterally.

3. Earthquake requirements have been explained thoroughly above.

Hope that helps.

Structural Design Engineer
New York, NY

 

[frv]

firai is correct in that the 1% of dead load (almost) never controls. However, I believe he is mistaken in the 20 psf as minimum wind load.

There is an absolute minimum, and I don't have the code in front of me, but I believe ASCE 7 prescribes 10 psf as an absolute minimum. Again, the minimum rarely applies.

 

[firai]

Good catch; I stand corrected. ASCE 7 specifies 10psf as the minimum for most jurisdictions; 20psf is the minimum for the NYC code.

Structural Design Engineer
New York, NY