Fire Truck Loading

[abusementpark]

Has anyone come across a good design uniform live load for the apparatus bay of a fire station?

I know you could look at the loading of individual trucks and different wheel locations. I'm just wondering if anyone has determined an equivalent uniform live load that would simplify the design.

Any help is greatly appreciated.

 

[SkiisAndBikes]

We typically use a 250 psf specified load for fire trucks as a minimum and 54kN (12,000 lb) minimum concentrated load, however, they seem to be building bigger fire trucks these days so the above loads should be treated as a minimum.

 

[abusementpark]

SkiisAndBikes,

Did you get that 250psf number from a technical reference? or is that your own rule of thumb?

 

[rscassar]

I wouldn't idealize any traffic load with an equivalent uniform load. Depending on where the point load is positioned will affect the design actions. If it were shear or bearing critical, the design needs to account for all the action occurring in a concentrated location.

I just did a google search of fire trucks and the GVM of one vehicle is 29,000lbm with dimensions of 26' x 8'.

 

[SteelPE]

Probably not really what you are looking for.

Sometime ago when I had to design a large suspended exterior floor I asked a similar question. The only type of code reference that I was able to locate for firetrucks was the for the Denver CO amendments to the building code. Maybe this will help you. Look at page 88 of 271 of the following link:

http://www.denvergov.org/Portals/646/documents/DBC-2008.pdf

 

[SkiisAndBikes]

Code reference is the National Building Code of Canada, Part 4 - Structural Design. The design criteria is listed under 'loaded buses and trucks and all other trucking spaces'. The point load is for vehicles exceeding 9,000kg (20,000lbs) gross weight. Fire truck loading is considered a live load and factored as such. In my experience, supended slabs surrounding apartment buildings, commercial buildings, office towers, entranceways, etc... where fire trucks may access are designed to the 250 psf criteria (minimum) and 54kN point load (minimum). Up until about 7 or 8 years ago, this loading was considered fine for fire trucks. In a few of the larger cities, these load criteria have been bumped up a bit for the larger trucks, but not by much.

 

[larsacious]

I designed a fire station that had the truck and maintenance bays supported by precast. I specified that the precaster design the bay for the worst case of (2) load cases:

1) Uniform LL of 250 psf

2) Fire truck load with (2) front and (2) rear outiggers. The outriggers had an 8" x 8" bearing surface and the front and rear outriggers were spaced 16'-8" apart and the outrigger width was 7'-10". The front outriggers had a reaction of 12 kips each (24 kip axle)and the rear outriggers had a reaction of 29 kips each (58 kip axle).

The fire truck load in case (2) was provided to me from the fire department maintenance supervisor who had specification sheets from the fire truck manufacturer. I suggest you contact the fire department to get this information and any possible future trucks they may be purchasing(it is kind of like looking into a crystal ball).

Also, be sure to check for punching shear from the outriggers.

Hope this helps!

-Ryan

 

[beton1]

Agree with SkiisAndBikes and larsacious. 250 is the norm. But as you state,for 'apparatus bay'; it may warrant some research. Trucks/equipment are evolving and getting heavier as well.

 

[JAE]

The 250 psf goes way back in time. In many US downtowns, the basements of the high rise office buildings extended out to the street curb (i.e. under the sidewalk) and sometimes even further. To deal with the potential of traffic and fire truck wheel/outrigger loads the 250 psf was derived - again - way back in time somewhere.

I would agree that with todays larger firetrucks, the outrigger loads might be a controlling factor. Especially for individual slab areas.

 

[RHTPE]

I find it unlikely that the outriggers would ever be deployed inside an apparatus bay. I would expect the wheel loads to govern.


Ralph
Structures Consulting
Northeast USA

 

[larsacious]

Ralph,

You are absolutely wrong. The mechanics regularly deploy the outriggers in the aparatus bay. This is how they typically service the tires.

I saw them doing this during one of my visits...

 

[msquared48]

I recently ran into a situation with a new ladder truck, GVW 78,000 pounds with an outrigger load of 45,000 pounds. Over the 5.6 square foot area of the pad, that generates over 8000 psf, a ridiculous design amount.

In that this is probably figured with the ladder extended and at it's max reach and load, it would not be applicable to the firestation slab. However, it would raise H*(( with any PT slab or detention vault grate design.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[RHTPE]

larsacious - I stand corrected. I had an image in my mind of outriggers similar to those on my backhoe which simply pivot down from an upright position and I couldn't see how they could clear an adjacent wall or vehicle. I did not envision the outrigger style similar to that used on a hydraulic crane which slide out and have a hydraulic cylinder that extends the pad to the ground. I can see how that would be an easy way to jack up the truck for tire/wheel service.

This is why I love this forum - we all can learn from each other's experiences.

My humble apologies.


Ralph
Structures Consulting
Northeast USA

 

[larsacious]

No problem Ralph. I actually thought the same as you until I saw it myself.

 

[TXStructural]

I found this elsewhere:
"NFPA 1911, Inspection, Maintenance, Testing, and Retirement of In-Service Automotive Fire Apparatus, 2007 Edition, requires that all frontline and reserve fire apparatus, regardless of their year of manufacture, must be weighed once a year. It defines how the apparatus is to be loaded and requires that each axle be weighed separately and then the entire apparatus be weighed as a whole. If the weight on any axle, or on the vehicle as a whole, exceeds the corresponding GAWR or GVWR/GCWR, then equipment must be removed or re-arranged until the weights are below the rated values. If that cannot be done, the vehicle must be taken out of service immediately."

You should be able to get actual weight from the relevant agency.

This is from a California DOT fire apparatus weight exemption NPRM (via the Fire Apparatus Manufacturers Association website):

"CCR section 1411.7 will specify maximum axle weights allowed on fire apparatus vehicles. The Department proposes the following maximum weights:

single steering axle: 24,000 pounds
single drive axle: 31,000 pounds
tandem axles: 58,000 pounds
tandem rear drive steer axles: 48,000 pounds
tridem axles: 59,000 pounds"