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forklift load on structural floor
i am designing a concrete slab supported by steel beams for live load and a forklift. is it acceptable to reduce the live load on a beam when looking at the forklift load? also, should the forklift load be increased for impact? i am trying to design the steel beams by asd. aisc asd manual a4.2 says live load should be increased to account for impact, but only crane systems are mentioned. my thinking on reducing the live load is that the full live load can't be applied if there is an aisle for the forklift. anyone have any thoughts, or a design guide reference?
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design for the worse of (a) dead load plus full live load without forklift load (b) dead load plus worst case forklift load without live load.
third option may be, (c) dead load plus forklift at midspan of member plus full live load minus live load at forklift footprint (like you mentioned).
i am not aware of any "code" that has specific requirements.
also, consider how many forklift may potentially load up a single member (it is not always one, depends on the
it may be possible for two fork trucks to be passing in an aisleway over the top of the beam.
agree with whyun and jike -
also - no impact for forklifts. - they don't go fast enough to "hit" the bumps and cause a surge in ll.
be sure to look out for the deflections in your beams relative to each other as one is loaded with the forklift and the other is not - the slab will have to allow for the resulting flex and you could end up with a huge crack problem....this from my own experience on a loading dock slab supported by composite beams and a fairly thin concrete slab.
with full ll on one beam compared to no ll on the adjacent beams, you get some very odd stress flows depending on where the forklift is located along the span...this initiates cracks in all sorts of directions.
we have tried to drastically limit the deflections and even added a custom combination of poly and steel fibers in the mix to control cracking.
so keep an eye on your tension stresses compared with the cracking stress.
the proper design of reinforcing steel in one way structural slabs for concentrated loads (such as fork trucks) is very important.
bottom main steel one needs to look at the truck positioned both parallel and perpendicular to the span and the additional moment caused by overlapping stresses from the adjacent wheel loads.
bottom distribution steel (at right angles to the main steel). this is significantly larger than the normal temperature steel.
top steel the most critical location is when the wheel load is right next to a support beam. you must also design for the condition when a truck at mid-span causes negative flexure in the adjacent spans.
if the building is designed for a 50 year life, the owner may also want to design for a larger truck than he currently uses so the building floor slab does not limit his future operation.
one thing you do have to consider is the momentum load from the loaded forktruck starting up and stopping quickly. that horizontal load can get the structure supporting the floor moving horizontally a lot more than you might think! take a good look at lateral bracing.
another thing to re
as an "aside", this is a classic example of where not to design to "r=1.03, say ok".
as whyun suggested, increase your estimated load liberally.
check whether solid rubber tires or pneumatic. have had considerable trouble with the small solid rubber tires because of the smaller footprint.
best, tincan
something that has not been mentioned but is quite important....
it is not advisable to count on composite metal deck for bottom reinforcing with forktruck traffic. it is my understanding that the deck will eventually loose its bond with the concrete due to fatigue. also, the slab thickness would most likely be inadequate for lateral distribution.
we typically use minimum slab thickness of 6" for lighter trucks and possibly 7 or 8" for heavier trucks. metal form deck may be used for forming but this would be added to the required thicknes. we always provide 2 layers of reinforcing steel.
thanks, everyone, for your very useful advice and feedback. i am proceeding with confidence. jike, thanks for the idea to consider two forklifts passing each other. i had not thought of that one. i agree with you that the slab must have serious reinforcing.

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