Structural Mechanics (bridges) anyone?

[cqueen]

Hi All

I have a favor to ask.

As part of my college work I have to provide the structural calculations for this bridge, to see if it is strong enough. Unfortunatly, structural mechanics was last year, I've forgotten the small amount that I understood!

Could anyone point me in the right direction? at least where I should start with this?

Pics of drawings provided, I have info on materials etc if required.

Many thanks

[URL=http://img193.imageshack.us/i/04042010267.jpg/][/URL]

[URL=http://img29.imageshack.us/i/04042010268.jpg/][/URL]

[URL=http://img144.imageshack.us/i/04042010269.jpg/][/URL]

[Oldandslow]

Well for a start you'll need the loading. How many people on the bridge, distributed as kg/m, then there's the weight of the structure itself, the main tubes and handrails. Assuming all the weight is carried by the tubes you'll need to calculate the max shear and bending forces the bridge will see and compare these to the max that the tube will support including a suitable safety factor. Check also for buckling stability. The strength of the tube may be available from tables assuming it's standard size and material or you may have to calculate that yourself.

If you're getting really into it you can look at side loads from wind and resonant frequencies.

[Mars]

No idea, but I used to live this:

http://www.bridgebuilder-game.com/

[jeff m]

I haven't waited for the pics to load.
But you need to use Young's Modulus with a safety factor.
You calculate the load on each member and work down. It was sometime ago I did this

Maybe you should wait for someone younger.

[a boardman]

the staircase with out any props under the half landing are going to add a decent load and moment to one side of the bridge beam, and dont forgot the reaction and twist from the handrails.

[mudster]

Don't forget the British Standards have been superseded by Eurocodes now. That's about the limit of my knowledge! Sorry. :-)

[james_tigerwoods]

I'm so sorry for posting this

Well, only a little

[pacman1]

james_tigerwoods said:

I'm so sorry for posting this

Well, only a little

Ha! That's just the sort of reply my old man would give me when I were a kid!
Unfortunately he's given me the same sense of humour and I get my own back now and again.
Recently, I start mouthing something to him, he thinks his hearing aid volume is not high enough so I wait for him to turn it up, and then I say " I SAID..."

[Steameh]

doogz said:

mudster said:

Don't forget the British Standards have been superseded by Eurocodes now. That's about the limit of my knowledge! Sorry. :-)

Have they? I'm actually a Mechanical Engineer, currently doing Naval structures, but never really done any civil type stuff, except my own barn roof!

OP, how you getting on with it?

I believe after april this year they are now in full effect. Not as clear as the British Standards I've been told, but since I'm only learning in Eurocodes I have no frame of reference.

[Tom_C76]

cqueen said:

Hi All

I have a favor to ask.

As part of my college work I have to provide the structural calculations for this bridge, to see if it is strong enough. Unfortunatly, structural mechanics was last year, I've forgotten the small amount that I understood!

Could anyone point me in the right direction? at least where I should start with this?

Pics of drawings provided, I have info on materials etc if required.

Many thanks

You should work out loadings to BS6399 and BS5400, with design to either BS5400 or BS 5950, assuming the bridge is steel. There's quite a lot to design there, if you really can't see where to start you're in the brown stuff at this point...

[Tom_C76]

Steameh said:

doogz said:

mudster said:

Don't forget the British Standards have been superseded by Eurocodes now. That's about the limit of my knowledge! Sorry. :-)

Have they? I'm actually a Mechanical Engineer, currently doing Naval structures, but never really done any civil type stuff, except my own barn roof!

OP, how you getting on with it?

I believe after april this year they are now in full effect. Not as clear as the British Standards I've been told, but since I'm only learning in Eurocodes I have no frame of reference.

Design to BS is still acceptable for most things, but publicly funded work has to be to Eurocodes

[a boardman]

depending on the section size it looks like a 330 CHS assuming this had a 10mm wall thickness,
if you take the ramp length of 36m and with only 1kn/m run on it,
the chs would deflect approx 877mm

[Size Nine Elm]

You could ask this guy... http://en.wikipedia.org/wiki/Thomas_Bouch

[SystemParanoia]

why not just cast the bridge out of solid steel, then cut out arch ways for the road/footpath/canal passing under it.

you can put it up in a few hours then, and spend the rest of the time in the pub

[a boardman]

if the bridge had a live load of 4 kn/m² then the 36m beam would deflect approx (assuming mild steel)
5 * (36*4*1.2*10^3) * 36000^3 / 384 * 205000 * 283.3*10^6 = 1800mm

[a boardman]

doogz said:

I thought you were using a line load on your first attempt. 4kN/m^2 seems a little high to me, where did you get that from?

my first attempt was only showing that only 1 kn whould produce a deflection that would be high. 4 kn/m² was taken from BS 6399.

[cqueen]

Hey all, thanks for the replies, sorry I've not kept up - busy busy boy.

So far I've managed to calculate that the max allowence for live load pedestrians is 972knm. The 36m ramp section equates to 1014knm, so will need an additional support midspan.

With this midspan support added, I calculate the live load now on 18m(36m/2)spans is 254kn/m and thus below 972knm.

So now I need to calculate the dead load for the bridge... Any advice on how I find out what the acceptbale value is?

Thanks

[Tom_C76]

cqueen said:

Hey all, thanks for the replies, sorry I've not kept up - busy busy boy.

So far I've managed to calculate that the max allowence for live load pedestrians is 972knm. The 36m ramp section equates to 1014knm, so will need an additional support midspan.

With this midspan support added, I calculate the live load now on 18m(36m/2)spans is 254kn/m and thus below 972knm.

So now I need to calculate the dead load for the bridge... Any advice on how I find out what the acceptbale value is?

Thanks

What's it made of? Guess a rough cross-sectional area, multiply by the relevant density. For example, concrete weighs 24kN/ cu m, steel weighs 78.5kN/ cu m.

ed to add your 2.7m x 20mm deck weighs 4.24kN/m plus the weight of the tubes and handrails. Not sure I understand what you wrote above though, you seem to have a mix of moment and udl.

Edited by Tom_C76 on Thursday 29th April 15:08

[Flying Toilet]

Do you have any bigger pictures? I am struggling to read some of the writing?

[a boardman]

dont forgot to factor up your loads.