AS 5100 Live Load Distribution

[cooperDBM]

I'm a Canadian bridge engineer with no experience of AS 5100. Out of curiosity I was looking through a copy of AS 5100-2004 and noticed that it doesn't seem to provide a method (non-refined) for determining the distribution of live load to bridge girders or strips. If I didn't miss it, how do Australian engineers determine the live loading on say the exterior girder of a straight constant-width slab-on-girder bridge. Is it covered in a different document like a bridge manual? Is a statically-determinate rigid moment arm analysis done (hope not) or is a refined analysis required, like perhaps a grillage analysis as a minimum?

Thanks

 

[IDS]

A grillage analysis as a minimum has been pretty standard practice for bridge deck design in the UK and Australia ever since I started work on bridge design 40 years ago.

There are no standard load distribution provisions in AS 5100. The Part 5 (Concrete) section says:

7.2.1 Application
Linear elastic analysis shall be used for the purpose of determining the action effects in a
structure for strength and serviceability design.
For a structure that can be represented as a framework of line members, the analysis shall
comply with Clauses 7.2.2 to 7.2.11. For other structures, the analysis shall comply with the
general principles of Clauses 7.2.2 to 7.2.11, as appropriate.

7.2.2 General
The framework shall be analysed in its entirety, making due allowance for the effects of
shear lag. In the absence of more accurate methods, allowance for shear lag shall be made
in determining the properties of the beams for the analysis in accordance with Clause 8.8.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Shz713]

That is the weakness of this part, which is currently under investigation for improvement in Brisbane.

Shoot for the Moon, even if U miss, U still land among Stars!

 

[IDS]

That is the weakness of this part, which is currently under investigation for improvement in Brisbane

Could you expand on that a bit?

What is the weakness, what is being done to fix it, and who is doing it?

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Shz713]

Well, this is part of my PhD research.

It is about improvement of Tier 1 assessment approach in evaluating the existing bridges. Common practice here in AUS is grillage analogy (with SPACE GASS mostly). There is no doubt in goodness of grillage, but it involves many uncertainty in structural behaviour and in comparison to full 3D model, grillage results are more masked by uncertainties and yields conservative results which hidden the true in-service capacity of structural elements. This is an ongoing project and so far we have found promising results, which indeed will amend the current best practice.

Shoot for the Moon, even if U miss, U still land among Stars!

 

[IDS]

Sounds interesting.

You might like a look at a paper I did a few years ago:
BRIDGE DECK BEHAVIOUR REVISITED


Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Shz713]

I made a reference to this paper for my conference paper in upcoming ASEC 2016 Link

It is very informative paper. I posted a new thread Linkregarding obtaining the bridge component capacities for the purpose of assessment. Based on AS 5100.7, load effects on critical members must be checked against their design capacity. This design capacity is using design drawings? I need an example about this aspect because I noticed that in design office or engineering consultancy they use spreadsheet to quickly get let's say ultimate capacity of headstock and then compare it with vehicular loading (reference and accompanying vehicle). Code approach you know is always blurry and nothing like an illustrative example could grasp the idea. I searched every where to find an example design/assessing bridge component as per AS but so far no luck

Shoot for the Moon, even if U miss, U still land among Stars!

 

[CRQUT]

Just a thought Shz713 but have you tried approaching TMR directly and asking for a copy of some bridge design calculations? If you ran it through your thesis supervisor, they might have a contact. Alternatively, if you have a set of drawings detailing size and span of the members and reinforcement details you could work out the design capacity of the element eg girder

 

[Shz713]

Dear CRQUT

I did try to get some sample calculations but no success. Do you have any bridge design/assessment as per AS? I really couldn't find anything in any reference material. For doing assessment as per TMR or Main Road Western Australia, the live load effects are checked against the bridge component capacity e.g. girders. In my case, I do not have capacities only very limited hand-drawing of bridge dating back to 60's.
I just want to know how to get the ultimate capacity of let's say deck slab or headstock. Then I can figure out the ratios for various vehicular loading since I already have other load effects which are reference vehicle, DL, SDL and accompanying vehicle with corresponding factors.

Cheers,

Shoot for the Moon, even if U miss, U still land among Stars!

 

[rapt]

You would be expected to calculated the capacity for any specific member or component according to AS5100 design rules! No one is going to be able to do it for you.

 

[Shz713]

Well I asked about some guidance NOT someone else do it for me! If I had clue about it I wouldn't post it here.
Not everyone is as experienced as you might be

Shoot for the Moon, even if U miss, U still land among Stars!

 

[rapt]

Your comment was

"I just want to know how to get the ultimate capacity of let's say deck slab or headstock."

You do not seem to know how to calculate the capacity as suggested by CRQUT so I have told you where to look. I doubt that you will find published calculated capacities anywhere as each bridge is different.

 

[Shz713]

That's it, I have no reference for assessment as per AS. You know that design and assessment are entirely different philosophy. I have checked in details ""AASHTO Manual for bridge evaluation" but cannot extrapolate it to AS. When I have any assessment check for any part of bridge using AS then I can work out the rest.
Another issue I have is that for assessment usually good set of design drawings are needed, for which in my case I have partially drawings!
Anyhow, thanks for your feedback, I am aware that I have to do it it's part of my research; but if someone in case seen this thread and had a bridge assessment then I'd appreciate if s/he share it.

Cheers,

Shoot for the Moon, even if U miss, U still land among Stars!

 

[rapt]

I assume you are basing it all on

http://www.tmr.qld.gov.au/business-...ns/Bridge-design-and-assessment-criteria.aspx

I am not sure what other sort of "reference for assessment" that you want! This document refers you to AS5100 to calculate the capacity and the loadings.

 

[Shz713]

You're correct about that, but I am new to AS specifications and would like to have an exemplary work (any bridge work assessed as per AS).

Shoot for the Moon, even if U miss, U still land among Stars!