Bleacher Design 5

[USFEngineer]

I am currently working on a project for a local university. The project includes the design of an aluminum bleacher/grandstands. My question is for those who have designed bleachers, what typically is the design dead load?
Other than the main beams and stringers (structural steel) all other components are aluminum. Are there any guidelines? I did not find anything in ASCE, IBC or ICC 300.

The bleacher manufacturer has used 100 psf as a reference for dead load in the past. That seems rather high!

Any info would be appreciated.

 

[JStructsteel]

The dead load is what it is. The live load I would use is 100, people jam pack bleachers sometimes, and standing, sitting, they are tight.

 

[USFEngineer]

That's what I figured. It is what it is! Just didn't know if there was a standard of sorts.

Thanks

 

[JAE]

Per ASCE 7 - bleacher live load = 100 psf

I once interviewed with a bleacher manufacturer for a position. They had no engineers on staff and wanted to get an engineer in to do full blown analyses, finite elements, etc. to fine tune their bleacher designs.

I asked the guy how they came up with the design they currently used and he stated that they built prototypes, loaded them up with sand bags until the bleacher collapsed, then added up the weight to see how well it did.

I didn't take the job and always after that felt a little uneasy sitting on high school bleachers.

 

[boo1]

Design Loads.
1. Live load: 100 psf gross horizontal projection.
2. Lateral sway load: 24 plf seat planks.
3. Perpendicular sway load: 10 plf seat planks.
4. Live load, seat and tread planks: 120 plf.
5. Guard Rail load:
a. Vertical load: 100 plf.
b. Horizontal load: 50 plf.
c. Point load: 200 pounds.
6. Wind load: Per local building code (if outside)


For capacity use 18" per person


International Building Code (IBC) of the International Code Council (ICC) lists requirements for
Guardrails:
Guardrails are required on open sides which are more than 30 inches above the floor or grade below. Guards must be at least 42 inches high, measured vertically above the leading edge of the tread, adjacent walking surface, or adjacent seatboard.
Open guards shall have balusters or ornamental patterns such that a 4-inch diameter sphere cannot pass through any opening up to a height of 34 inches. From a height of 34 inches to 42 inches above the adjacent walking surfaces, a
sphere of 8 inches in diameter shall not pass.

Openings:
Where footboards are more than 30 inches above grade, openings between the seat and footboards shall not allow the passage of a sphere greater than 4 inches.
When projected on a horizontal plane, horizontal gaps shall not exceed 0.25 inch between footboards and seatboards. At aisles, horizontal gaps shall not exceed 0.25 inch between footboards.

 

[JAE]

boo1...nice.

 

[USFEngineer]

Thanks...

It's actually pretty scary. The company that I am checking these bleachers out for pretty much told me that all of there bleachers in the past are built from "industry standard". All of the main beams, stringers, columns, braces and even footings are just copied and pasted into each project without any review. I hope whomever set the "industry standard" was conservative with his designs?

Just until recentlly I have reviewed a few of there more "complicated" projects.

I was familiar with the live loads and horizontal loads per ASCE and ICC 300. The contractor asked me if there was a "typical" dead load for bleachers. But thanks for the replies.

 

[MiketheEngineer]

Boo1 is quite correct.

However - if this going to Europe - I would double the numbers.

Those soccer(football) fans are just plain nuts....

 

[boo1]

Would Finite Element Analysis (FEA) Techniques can be apropriate to model the modes of vibration or natural frequencies of structure? Is ADA access required?

 

[USFEngineer]

Thanks for the replies.

One other question. The wind load design. What category if any would this fit under in ASCE 7? It is not an Open building or a Solid Freestanding Wall or Solid Sign? The only other category is other structures. However, when calculating the value of Cf it does not fit into any of the figures 6-12 thru 6-23. Any insight?

 

[youngstructural]

I have been involved in the design of two major grandstands here in New Zealand, as well as several smaller stands such as the one you are currently building. These are absolute monsters; They are prone to fatigue (specific checks must be undertaken), prone to horrendous vibration problems (again, specific checks required), prone to collapse (very common in the smaller stands), and prone to exposure problems. They're one of the few structures I can think of that you can actually have full loads on one side, with everyone jumping up and down, and an empty stand on the other side.

Regarding wind design most codes would deem this to be a special or unique structure requiring advanced computer modeling or scale model wind tunnels. Obviously that's not going to work for your small project, so I would just advise being as caution and conservative as possible. The local joint standard (AS/NZS 1170) actually does a pretty good job with grandstands... Might be worth getting a copy for your project. It is an excellent code with a detailed commentary.

I cannot recall off the top of my head whether it deals specifically with grandstand wind loading, however I know that it does the cantilevering roofs above in Wind.

If you can't get anyone to assist with your own code, I'd be happy to dig up some notes and post something for you.

Cheers,

YS



B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[USFEngineer]

YS,

Thanks for the info. I have found out the hard way that there is more than meets the eye when it comes to bleacher/grandstand design. Only after becoming partially involved in the the design did I realize the complexity of the design. I am curently working on a submittal to be reviewed by another structural firm so I want to make absolutely sure all the bases are covered.

Any information that you can provided would be appreciated.

 

[SteveGregory]

RE: Wind Loads
I investigated some aluminum grandstands (12 rows of seats??) for a high school soccer field that flipped over. The contractor did not want to anchor the stands down to a concrete pad foundation. He was given the option of using helical screw anchors similar to the ones used for mobile homes.

We found a box with the helical section of the anchor rods sawed off. I guess they had a hard time "driving" the rods in with those funny plates welded to them. It wasn't funny seeing the stands upside down in the middle of the field.

For wind loading, consider them to be like a lightweight sail.

 

[steve1]

Many years ago I worked for a firm that designed and manufactured bleacher systems. There are many unique problems associated with this type of structure. If you're not familiar with their design parameters then perhaps you are working outside of your area of expertise.

 

[youngstructural]

Re: Working outside one's area of expertise

If we didn't work outside of our field of expertise, we couldn't learn to expand our abilities. The question is how we go about doing this, and I certainly wouldn't be expecting to make a profit on the first of a unique type of stucture which I was designing.

I really don't think this is too much of a stretch if you've worked on bridges or forensic reporting. Grand stands are challenging, but not unsurmountable. If you need specific advice beyond that which this forum can provide, find someone local to assist in the design.

Oh, and as for my notes, I realised yesterday that they are on their way to Canada. One of the major disadvantages to moving across the world. If you can wait a couple of months, I'd be happy to help! *smiles*

If you want to post anything for review, I'd be happy to take a look for you. Steve Gregory has a good bit of advice for the wind loads, but I'll try to expand for you from memory:

1. Consider the benches under a partial live load and reversing wind load. This is to account for a windy day where only the die-hards come out. It has resulted in problems in the past; Adds to your overturning problem, depending on the design of the stand. I've applied serviceability wind, full strength across 3/4 of the stand and full live load across the final quarter, in both directions (looking out from stand and looking into stand).

2. Look at the stand as a wing if air can get underneath. I've been told that I'd be surprised how much lift these can gain, though have no personal experience with a project suffering this mode of loading/failure.

3. Get the ATC vibration guide if you are doing anything with concrete for a grand stand. Dr. Allen (And I believe Murray might have had a hand in the ATC vibration guide, but I'm not sure) have done quite a good job with that one.

4. Be very careful to consider the effects of any structural continuity. Because the structures are so light, simple span assumptions versus fixed end can result in significant live load moments at joints, without much dead load moment to counter balance.

5. Be entirely certain that you have correctly designed all of the joints. These structures, like many others, are particularly prone to connection failures.

I'll keep an eye on the thread and post if I think of anything else...

Good luck,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...