Live Load vs Roof Live Load 2

[hamidun]

Hi all,

As per ASCE 7, Chapter 4, there are two definitions of live load, 1. Live Load 2. Roof Live Load.

Regarding to the definitions according to ASCE, can anyone tell me what is the difference between them? How we choose to apply them in calculation? Is there any specific factor needs to be added, when we apply those loads?

Please help! Thanks!!

 

[JStephen]

Live load is typically for floors inside, etc., roof live load is on the roof. See the definitions at the start of Chapter 4 and the specific loads given in the tables. Also see the load combinations specified in Chapter 2. There may be a regular building code involved with separate loads specified in it.
I think I've seen some other posts on putting solar panels on existing roofs, etc., and more information may get a better response in a case like that.

 

[TehMightyEngineer]

Here is my interpretation, the commentary for chapter 4 in ASCE 7 sheds some light on this. Roof live load is a construction loading and has it's own special live load reduction equations. Live load is an occupancy loading and varies depending on the occupancy, so if your roof has a dance floor then I would not consider that occupancy load as a roof live load for the load combinations and would not use the roof live load reduction equations.

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[JAE]

I'm not sure that roof live loads are considered as "construction" loads in the sense that they only occur during the initial construction.

In warmer climates where snow doesn't occur, or is of low intensity, the roof live load provides a level of competency in a roof that would typically be loaded only by maintenance workers, equipment and other materials through its life. This is suggested in the ASCE 7-10 section C4.3.3.



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[TehMightyEngineer]

JAE: Didn't mean to imply it was only initial construction. Roof maintenance, staging of re-roofing materials, installation of RTUs, etc. all would fall under "roof live load" in my understanding.

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[JAE]

Yep - agree.

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[MrHershey]

Any thoughts on considering it a different type of loading for different combinations?

Taking the roof dance floor example. I would think it probably a good idea to include it as a regular live load for earthquake combos since roof live loads aren't even included. Don't know that taking the full 1.0L during the wind event is necessary though. Wouldn't imagine you'd have a roof dance party during a 700 year storm. Same goes for the snow combinations.

 

[TehMightyEngineer]

Hershey: I agree, I've made rationals based on the load type to have reducing loading during wind and snow events. For example a rooftop garden may still see the full live load during wind and snow events but a rooftop dance floor is likely only going to have partial or no loading during a code level wind and snow event.

In the dance floor example I'd probably use (LRFD) 1.2D + 1.0W + 1.0L + 0.5L(roof dance) for the wind combo, (LRFD) 1.2D + 1.6(S or R) + (1.0L or 0.5W) (no roof dance live), and (LRFD) 1.2D + 1.0E + 1.0L + 1.0L(roof dance). Seems to meet the intent of the load combos and is rational for typical real world loading situations.

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[Contraflexure74]

Live load is live load be it on the roof or on internal floors. Consider various combinations of dead, wind and live. Construction load should be considered depending on the construction type, ie composite deck type construction.

 

[Hokie93]

IBC provides a different definition for live load and roof live load in Chapter 16 compared to that given in ASCE 7 Chapter 4. IBC 2012 defines live load (L) as "roof live load greater than 20 psf and floor live load". Roof live load (L_r) is defined as "roof live load of 20 psf or less". So with the roof dance floor example, per IBC, the live load would not be roof live load, but live load, assuming the live load magnitude exceeded 20 psf.

 

[cal91]

I think of it this way: Code level roof life loads will not occur concurrent with code level snow or rain loads. So I'll see what governs, including the "dance roof" live load as a regular live load and ignoring snow and rain, or not including the "dance roof" live load as a regular live load while considering snow and rain.