Wall with momentary lateral force 6

[BigBakwas77]

I have come across a project where I have to design a wall for a maximum lateral force of 1.25 kPa which is going to last a second and two. (Due to fire suppression system) Does anyone has any idea if I have to design it like any other case of sustained lateral pressure or I can reduce this design load. I practice in Canada. Any link to design code / material will be greatly appreciated.

 

[BridgeSmith]

I would be skeptical of reducing the load based on a duration of loading that is over a second, unless the mass of the wall (and therefore its inertia) was large. given that you're trying to reduce what is already a fairly small load (if I've done my conversions correctly, 1.25 kPa = 26.1 psf, less than a typical exterior wind pressure), I'm guessing the wall is not massive. That said, some materials (wood, for instance) allow an increase in the design material strength for short-duration loads.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[r13]

The linked paper below might help you to some extend.

Link

 

[MIStructE_IRE]

I’m not aware of any guidance for time dependent loading. My gut however has always questioned this, particularly with regard to 3 second wind gusts... I just don’t believe that a static analysis is truly comparable..

That said, I’ve never done this in a real world design - its just a hunch!! Nothing more. But it could make an interesting thesis for somebody!

 

[BigBakwas77]

Thank you all, for your valuable input! Much appreciated!

 

[struct_eeyore]

Well, not sure if Canada has something similar, but when designing wood in US, you get load duration factors. For a several second load, you are allowed to increase your material properties by a factors of 1.6.

 

[GeorgeTheCivilEngineer]

Eurocodes may treat this an an accidental action and reduce partial factors (action and material) to 1.0.

 

[BigBakwas77]

@GeorgeTheCivilEngineer
I was hoping for similar provisions in Canadian codes.

 

[jayrod12]

What kind of wall do you have that can't support 1.25 kPa. It's not like that's out of the realm of normal pressures.

 

[wannabeSE]

ASCE 7 has load combinations for extraordinary events in section 2.5. This doesn't provide any relief on the demand. But, it provides guidance for load combinations to use to combine forces on a bearing wall. For ASD design of wood, the load duration factor for 10 minutes (wind and seismic) is 1.6; for impact it is 2.0. In the 2018 NDS appendix B, there is a graph for the factor at various load durations that can be used for intermediate times.