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GWright
#1 Posted : 07 April 2014 16:52:40(UTC)
GWright

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Hello,

I was wondering if you could clarify how to calculate the cost of including cables/hangers in the bridge. I'm not really sure what it means by "per kN of breaking load".

On the Tata Steel website, there is a Maximum and Minimum Breaking Force, but it is not clear how these are calculated. (http://www.tatasteelconstruction.com/en/design_guidance/steel_bridges/bridge_products/rods/)

Many thanks,

Gillian
David Brown
#2 Posted : 08 April 2014 08:37:57(UTC)
David Brown


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Hi Gillian

Lets say that the ultimate force in one cable is 900 kN and its 36 m long

The cost of that cable would be 900 x 5 x 36/100 = £1620

You would also need two ends, so that is 2 x 1 x 900 = £1800

Hope that example helps.

David
GWright
#3 Posted : 08 April 2014 09:59:00(UTC)
GWright

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Good morning,

Thanks for getting back to me so quickly.

It was actually the breaking force I'm not totally clear on how to calculate. I know we have been given a strength of 1600N/mm^2, but can we just use stress=force/area, or do we need to account for the fact that it is not a solid member?

Many thanks,

Gillian
David Brown
#4 Posted : 08 April 2014 11:00:17(UTC)
David Brown


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Morning!

I am sure that the ultimate force in the cable will have come from some analysis you have completed. This will be what you use to calculate the cost, as my earlier post.

The 1600 N/mm2 would allow you to estimate the size of the cables you need by force / 1600 = area. That would be the total area of the strand, so probably you could look on the web and find that a certain area of strand is delivered by cables of a certain numbers of individual wires, and conclude that the cable would therefore be a certain diameter.

Does that help?

David
GWright
#5 Posted : 08 April 2014 11:11:33(UTC)
GWright

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Thanks David, we were just not sure whether the force we should be using to calculate the cost should be the applied force (found from our analysis), or the force that our chosen cable is capable of resisting.

Thanks for your help,

Gillian
David Brown
#6 Posted : 08 April 2014 11:17:06(UTC)
David Brown


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No, I was not sure about that either. It seems rather unfortunate wording!

But for this competition, lets assume that you apply the cost calculations to the ultimate force from the analysis. As I am a judge, and we take these answers as correct, then you will be OK to follow my advice.

David
GWright
#7 Posted : 08 April 2014 11:25:04(UTC)
GWright

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That's great, thanks!

While I'm here, could I please check the duration of the railway possessions? Table 1 gives the cost as £250,000 per closure, but how long does this closure last?

Many thanks,

Gillian
David Brown
#8 Posted : 08 April 2014 12:51:28(UTC)
David Brown


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Well, that's for you to think about, but certainly the idea would be to minimise the closures of the main lines. That was emphasised in section 1.3c of the brief. You will know from your own experience that weekend closures are possible - typically from midnight on Friday night to 06:00 say on Monday morning. Sunday only closures are even more common, starting at say midnight on Saturday night. Anything more than a weekend would really be a hugely significant event, so perhaps over a Christmas break.

The judges will be looking to see how the design has developed to minimise the number of closures of the main lines. In real life, the challenges of construction during line closures often dominate the design.

David
GWright
#9 Posted : 08 April 2014 12:55:24(UTC)
GWright

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Hi David,

Thanks for your help. We were just wanting to check if a full-weekend closure would be priced differently from a Sunday only closure, even though both could be described as one single closure.

Gillian
David Brown
#10 Posted : 08 April 2014 13:01:51(UTC)
David Brown


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Same price, but the judges will look closely at the construction process to see if its reasonable and appropriate in terms of the closures you propose.

The closures will not be the most important part of the submission however, and I have to say that price is not either. Of much more importance is the development of the design and the preliminary calculations, and the presentation of the design on the drawings.

David
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