Steel access grate design

[civiboy]

Hi, just having a bit of trouble getting a grate-design off the ground.

I've been asked to determine the cheapest/thinnest design we can get away with when making a grate, that will withstand the predicted loads as specified in the Australian Standard AS3996 - 2006.

If I, for instance, wanted to design the grate to withstand Class D loadings, how would i go about this? Class D [Heavy Duty Commercial Vehicles] (as taken from the standard), has a Nominal Wheel Loading of 8,000kg (78.5 kN?), a Serviceability design load of 140kN and an Ultimate limit state design load of 210kN.

Not sure if I use the single wheel load of 8000kg (or 78.5kN?), as that is what would be rolling over the grate at a single point in time. Or do I use the Ultimate load of 210kN for safety purposes and divide it by number of wheels? or just the 210kN itself? Would the calculation involve a single point load in the middle of the grate of either 78.5kN or 210kN, or a UDL along the grate?

Am I looking into this too much? Not enough? If you can't tell, structures was a weakness of mine I'll shut up now!

Any help appreciated

 

[msquared48]

Grate manufacturers provide load/span tables for you to use. You just have to design their supports, whatever that is.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[civiboy]

thanks for the response.

I do have a few of these tables, but was wondering how I would go about it if I were to design it from scratch (ie: Bar Spacings, cheapest/most efficient width/depths of bars, strengths etc.)

I think this problem is a hell of a lot more structurally detailed than I am imagining, if I were to design and make it on site, that is.

 

[civiboy]

I will also add that I have the MBG 534-94 Metal Bar Grating Eng. Design Manual. Though kinda helpful, it doesn't conform to Aus standards, and our standards book is not as detailed as one would hope! If there were an Australian version of this design book (I've searched, nothing found), I would be in business haha.

 

[MiketheEngineer]

DO as M^2 says - pick up the that damn heavy phone and call a mfg.

They are usually more than helpful - if not call another one!!

 

[TLHS]

Yeah, you don't want to design your grating from scratch and field fabricate it. There are lots of welds that are really easy to automate but would take effort in the field.

Grating isn't a thing you bother to custom design unless you're way off of standard grating designs. You should be specifying and buying it. It's made by manufacturers significantly more cheaply than you're ever going to be able to do it.

 

[civiboy]

Thoughts and comments taken on board.

Thanks you all.

 

[civiboy]

*Thank.

Sorry, don't know how to edit that post