Horizontal Applied Load for Raised Freestanding Timber Deck

[BillyMates]

Please could anyone help to point me in the right direction of guidance for applied loadings to raised freestanding timber decks? The deck I have is 28ft out from the house and so should be classed as freestanding. There are intermediate beam strip limiting spans of joists etc, so no concerns on that front. I want to check the bracing and connection forces etc but cannot seem to find any definitive guidance for lateral loading.

As a light and open sided structure, Horizontal wind action is nominal (Obviously uplift will be considered). I believe the applied live loads may govern the bracing design and have read several quoted figures of applied Notional Horizontal forces ranging anywhere between 5 and 20% of the applied vertical loads. As a back up I would consider the Seismic approach to dynamic actions, but wondered if there are other reliable guidance texts available???

Another good analogy was a mezzanine floor inside a factory. Wind loads would not usually govern, but you could expect relatively high vertical imposed loading. What would the guidance be? I suspect it will be a similar answer but would love some firm confirmation if possible.

Many thanks for your assistance in advance.

Kind Regards,

Mark

 

[XR250]

I typically use 20% of the live load...

 

[focuseng]

There is no real conclusive item here. ASCE-7 makes reference to bleacher loading of 24plf of seating for lateral loads. Beyond that, some limited testing and research by Washington State University suggests using 8-10 psf due to occupant movement. If you got into a nice party dance, rhythmic situation you might see 3-25% of person body weight occupying the deck contribute to lateral forces so 10psf seems reasonable. Depending on the use category that might vary. Using Excel's # .2x40psf = 8 so that works nicely. Heavy assemble occupancy might want to think this over more. I believe occupancy lateral forces will control over seismic and or wind in general.

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MAP

 

[asixth]

I think that as long as it is braced to resist any incidental loads it should be okay. Timber decks are generally light, the code minimum requirements in my area are 2.5% of the working load applied horizontally. I would feel comfortable with 10% of the building weight applied horizontally or 0.5kPa applied over the elevation.

 

[a2mfk]

I had to deal with this a long time ago when designing some decks and pedestrian bridges for parks. I believe I used some loading criteria from AASTHO for pedestrian bridges. Focuseng's suggestion of bleacher lateral loads makes good sense to me. The only type of lateral loading (other than wind or seismic) scenario I can think of for a residential deck would be if a large group were to rush to one side of the deck all at once and then stop, the stopping force would impart a lateral load, which is an odd scenario IMO but possible. But what number would that equate to? Couldn't be that much.

I always found making the handrails/guardrails work were a big problem, and I have seen way too many loose and poorly designed and built handrails in residences. Now it is pretty easy to imagine a scenario that would cause a handrail failure, like that large group from above all leaning against it at the same time.

 

[focuseng]

I don't find the impact loading scenario unusual. Didn't you go to college? Ahhh... good times.

The testing done by Washington State did just this in fact (impact loading scenarios that is, not the college bit, as they ARE a college).
For cyclic loading they loaded up the deck to 30 and 40 psf with people and made them get into a groove.
For impulse loading that had 10 psf loading and make the people rush the deck. Imagine 3 300# college football players rushing the deck to catch a ball thrown by one of their buddies on the ground. How much is that? They were able to get an equivalent lateral load response of 9.4psf in a sideways direction and about 3psf in an outward (perpendicular to the building) direction.

The load response of the deck at the ledger was different depending on the decking direction (horizontal vs diagonal) and for cyclic vs impact loading.

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MAP