New bridge,work in progress

[Steevo]

Great looking bridge @ColinV6 should do the job easily. I'm a structural engineer in Australia (Tasmania), so different standards and practices then your bridges but similar enough to make a few comments. I have never designed an all steel bridge, simply not used anywhere that I know of in Tassie, certainly not new ones any way. All my design experience is on reinforced concrete bridges and the occasional steel beams with a concrete deck, so no expert on steel bridges. The office i work out of is 15 minutes from the three largest pre-cast bridge builders in the state, so you might say we do a lot of work with concrete bridges. I will cover a couple of things mention back in the thread.

The cost from the big firm is likely due the standards/codes they have to design the bridge to and hence the liability of the design engineer/company if they go outside of this. I know that when a farmer (I know this as a farmer and engineer) comes to us and says "I want a bridge to carry X load, I will never need any more" he/she will undoubtedly at some point try and drive something heavier across it resulting in damage or failure, farmer measurements "if its good for 20 tonne, 30 won't hurt". We basically say we design it to Australia standard loads or we can design for one specific vehicle (weight, axle spacing, speed), you drive anything else across it and you are on your own.

I have never seen a bridge bolted to the abutments whether it be timber, concrete or steel. The epoxy should be stronger than the concrete or the bolts, it would be a race to see if the concrete cracked first or the bolts failed due to fatigue. Generally most bridges sit on a bearing pad of some type - steel on steel with grease, special rubber compounds, small bridges can just be steel to concrete. Thermal expansion would be an issue for the bolts as well as vehicles driving over the bridge causing deflection that would translate into forces into the bolts or movement in the bridge if it wasn't bolted down. The reason bridges aren't generally bolted to abutment is the it means the bridge beams are simple supported, which means that the abutments are isolated from the bridge beams. Simple supports only transfer load in the vertical direction, which means that your bridge (without the bolts) would try to crush the concrete abutment but that is ok as concrete is very strong in compression. By bolting it down you change how the load is transferred to the abutments, the bolt furthest from the abutment is in compression but the rear bolt is now in tension which the concrete is not as good at resisting. I would (at a guess) think that the thread on the rear bolt would fail before any major damage would be done as they don't look like terribly large bolts. Slotted holes would be alright at this stage, as has been mentioned before.

Some extra protection around the abutments is always good. Riprap is the term used in our design guides, just don't fill up the river with it. Had a job once to do scour repair on a rail bridge near Kimberley, asked a guy in one of our mainland offices to size up the riprap to place around the piers as he had done the hydraulic design on the bridge before. Came back with a with a design that would effectively Dam the Mersey River at Kimberley, absolute joke a design.

Lots of if, buts, and maybe with all that without knowing everything about the bridge as no two are the same. The loads I'm used to designing for are 60 tonne B-doubles with 9 axles going at 100km/h so i think the loads on your bridge will be a little bit under that so the risks are also lower. Sorry if that a bit over the top but I like knowing these things so thought someone else might like it.

Thanks for that - made an interesting read!!

Hope to see you in the "Today at work" thread with a few pictures of bridges!

 

[Lincsman]

Great looking bridge @ColinV6 should do the job easily. I'm a structural engineer in Australia (Tasmania), so different standards and practices then your bridges but similar enough to make a few comments. I have never designed an all steel bridge, simply not used anywhere that I know of in Tassie, certainly not new ones any way. All my design experience is on reinforced concrete bridges and the occasional steel beams with a concrete deck, so no expert on steel bridges. The office i work out of is 15 minutes from the three largest pre-cast bridge builders in the state, so you might say we do a lot of work with concrete bridges. I will cover a couple of things mention back in the thread.

The cost from the big firm is likely due the standards/codes they have to design the bridge to and hence the liability of the design engineer/company if they go outside of this. I know that when a farmer (I know this as a farmer and engineer) comes to us and says "I want a bridge to carry X load, I will never need any more" he/she will undoubtedly at some point try and drive something heavier across it resulting in damage or failure, farmer measurements "if its good for 20 tonne, 30 won't hurt". We basically say we design it to Australia standard loads or we can design for one specific vehicle (weight, axle spacing, speed), you drive anything else across it and you are on your own.

I have never seen a bridge bolted to the abutments whether it be timber, concrete or steel. The epoxy should be stronger than the concrete or the bolts, it would be a race to see if the concrete cracked first or the bolts failed due to fatigue. Generally most bridges sit on a bearing pad of some type - steel on steel with grease, special rubber compounds, small bridges can just be steel to concrete. Thermal expansion would be an issue for the bolts as well as vehicles driving over the bridge causing deflection that would translate into forces into the bolts or movement in the bridge if it wasn't bolted down. The reason bridges aren't generally bolted to abutment is the it means the bridge beams are simple supported, which means that the abutments are isolated from the bridge beams. Simple supports only transfer load in the vertical direction, which means that your bridge (without the bolts) would try to crush the concrete abutment but that is ok as concrete is very strong in compression. By bolting it down you change how the load is transferred to the abutments, the bolt furthest from the abutment is in compression but the rear bolt is now in tension which the concrete is not as good at resisting. I would (at a guess) think that the thread on the rear bolt would fail before any major damage would be done as they don't look like terribly large bolts. Slotted holes would be alright at this stage, as has been mentioned before.

Some extra protection around the abutments is always good. Riprap is the term used in our design guides, just don't fill up the river with it. Had a job once to do scour repair on a rail bridge near Kimberley, asked a guy in one of our mainland offices to size up the riprap to place around the piers as he had done the hydraulic design on the bridge before. Came back with a with a design that would effectively Dam the Mersey River at Kimberley, absolute joke a design.

Lots of if, buts, and maybe with all that without knowing everything about the bridge as no two are the same. The loads I'm used to designing for are 60 tonne B-doubles with 9 axles going at 100km/h so i think the loads on your bridge will be a little bit under that so the risks are also lower. Sorry if that a bit over the top but I like knowing these things so thought someone else might like it.

So in summary, the op should jack it up, cut the bolts off and put a sheet of greased steel plate under it? and possibly bolt a lump of metal at the downstream side of the deck to stop it being pushed off by a flood?

 

[JX1100U]

So in summary, the op should jack it up, cut the bolts off and put a sheet of greased steel plate under it? and possibly bolt a lump of metal at the downstream side of the deck to stop it being pushed off by a flood?

Yes, wouldn't hurt, slotted holes would be a good idea at least. Bolts could stay if the holes on the bridge were slotted, they can still provide some resistance to it washing away. Lots of bridges have locating bolts/pins/dowels just as long as its not trying to completely stop the bridge from moving.

 

[ColinV6]

Great looking bridge @ColinV6 should do the job easily. I'm a structural engineer in Australia (Tasmania), so different standards and practices then your bridges but similar enough to make a few comments. I have never designed an all steel bridge, simply not used anywhere that I know of in Tassie, certainly not new ones any way. All my design experience is on reinforced concrete bridges and the occasional steel beams with a concrete deck, so no expert on steel bridges. The office i work out of is 15 minutes from the three largest pre-cast bridge builders in the state, so you might say we do a lot of work with concrete bridges. I will cover a couple of things mention back in the thread.

The cost from the big firm is likely due the standards/codes they have to design the bridge to and hence the liability of the design engineer/company if they go outside of this. I know that when a farmer (I know this as a farmer and engineer) comes to us and says "I want a bridge to carry X load, I will never need any more" he/she will undoubtedly at some point try and drive something heavier across it resulting in damage or failure, farmer measurements "if its good for 20 tonne, 30 won't hurt". We basically say we design it to Australia standard loads or we can design for one specific vehicle (weight, axle spacing, speed), you drive anything else across it and you are on your own.

I have never seen a bridge bolted to the abutments whether it be timber, concrete or steel. The epoxy should be stronger than the concrete or the bolts, it would be a race to see if the concrete cracked first or the bolts failed due to fatigue. Generally most bridges sit on a bearing pad of some type - steel on steel with grease, special rubber compounds, small bridges can just be steel to concrete. Thermal expansion would be an issue for the bolts as well as vehicles driving over the bridge causing deflection that would translate into forces into the bolts or movement in the bridge if it wasn't bolted down. The reason bridges aren't generally bolted to abutment is the it means the bridge beams are simple supported, which means that the abutments are isolated from the bridge beams. Simple supports only transfer load in the vertical direction, which means that your bridge (without the bolts) would try to crush the concrete abutment but that is ok as concrete is very strong in compression. By bolting it down you change how the load is transferred to the abutments, the bolt furthest from the abutment is in compression but the rear bolt is now in tension which the concrete is not as good at resisting. I would (at a guess) think that the thread on the rear bolt would fail before any major damage would be done as they don't look like terribly large bolts. Slotted holes would be alright at this stage, as has been mentioned before.

Some extra protection around the abutments is always good. Riprap is the term used in our design guides, just don't fill up the river with it. Had a job once to do scour repair on a rail bridge near Kimberley, asked a guy in one of our mainland offices to size up the riprap to place around the piers as he had done the hydraulic design on the bridge before. Came back with a with a design that would effectively Dam the Mersey River at Kimberley, absolute joke a design.

Lots of if, buts, and maybe with all that without knowing everything about the bridge as no two are the same. The loads I'm used to designing for are 60 tonne B-doubles with 9 axles going at 100km/h so i think the loads on your bridge will be a little bit under that so the risks are also lower. Sorry if that a bit over the top but I like knowing these things so thought someone else might like it.

Wow very good read. Thanks for the reply. We have around 3/4 inch gap at either end Between the bridge and the concrete now and will definately be putting some rock armour on the abutments for protection.

 

[ColinV6]

 

[Wombat]

Looks great

 

[Steevo]

View attachment 878410

Wow!!!

Have you got any more do to?! Grant Shapps has pledged £2bn for road funding so I reckon you'd be able to put in a claim to that pot!!!

Either that or tender as main contractor for a contract on the motorways!!!

 

[ColinV6]

Wow!!!

Have you got any more do to?! Grant Shapps has pledged £2bn for road funding so I reckon you'd be able to put in a claim to that pot!!!

Either that or tender as main contractor for a contract on the motorways!!!

Basically done now Steevo, finish off the gateways to the fields either side of the bridge which due to the ramps will need altered a bit.

Hoping to make the debut crossing on Monday/Tuesday!! Will have to stop for a pic half way over and check for sagging

 

[Steevo]

Basically done now Steevo, finish off the gateways to the fields either side of the bridge which due to the ramps will need altered a bit.

Hoping to make the debut crossing on Monday/Tuesday!! Will have to stop for a pic half way over and check for sagging

If it was me I'd be leaving the concrete longer than that.....but all depends what you need to get done.

Don't forget the ribbon cutting ceremony!!!

 

[ColinV6]

If it was me I'd be leaving the concrete longer than that.....but all depends what you need to get done.

Don't forget the ribbon cutting ceremony!!!

It went down Wednesday morning so it’ll be getting on for a week... I will make a point of cutting a ribbon!!

 

[Lincsman]

It went down Wednesday morning so it’ll be getting on for a week... I will make a point of cutting a ribbon!!

Dont want to spoil your fun but concrete needs 28 days to keep the warranty.

 

[ColinV6]

Dont want to spoil your fun but concrete needs 28 days to keep the warranty.

28 days?! We’ve never left anything as long as that? Unfortunately the silage needs to come off

 

[JX1100U]

28 days?! We’ve never left anything as long as that? Unfortunately the silage needs to come off

28 Days is the theoretical time its take for concrete to reach its full design strength. Depends a lot on the concrete mix and what it needs to do. You should achieve at least 50%, if not 60-70%, of the full strength in 7 days. Most of the concrete I see is for precast bridge elements is design to reach 20-25mpa within 24 hours so they can take it out of the moulds and lift it but then take a longer amount of time to reach its full strength 40-50mpa. Then there's always the argument about how strong is the actually concrete we have had test sample of pours for 40mpa mixes that have come back as an actual tested strength of closer to 70-80mpa. So if the design strength was supposed to 40mpa the beam could have been in place and used within 7 days at 50% strength, of course no on actual does this because no one wants to get sued into oblivion if some thing did go wrong. I wouldn't be to concerned, just tell the drivers to take it easily over the bridge for the day.

 

[Lincsman]

28 days?! We’ve never left anything as long as that? Unfortunately the silage needs to come off

Its not a problem, just dont complain in 15 years its breaking up, if you want to run on it in 5 days, buy the mix that will allow it... a bit like if you want it very runny... order it runny.

 

[A1an]

I never realised this place was so awash with structural engineers.

 

[Lazy Sod]

I know nothing about the different coctete mixes available and what their different capabilities are. I rarely used readymix and all that we mixed ourselves was 1-2-4. Perhaps the OP could tell us what mix he used and the experts can tell us what that would be capable of.
@ColinV6, what have you finanlly done about the expansion question?

 

[ColinV6]

I know nothing about the different coctete mixes available and what their different capabilities are. I rarely used readymix and all that we mixed ourselves was 1-2-4. Perhaps the OP could tell us what mix he used and the experts can tell us what that would be capable of.
@ColinV6, what have you finanlly done about the expansion question?

I have literally no idea what they’ve used lol, they ordered it and dealt with it. All I know is it looks like concrete

Have left 3/4 inch joins at either end for expansion. Will be keeping a close assesment on the rest. There is thankfully access to the end bolts from underneath, wont take long to elongate them.

 

[ColinV6]

 

[Doing it for the kids]

View attachment 878740

would it be a good idea to fill that with sealant to keep weeds from growing out of it? if the bridge expands it pops the sealing out

 

[renewablejohn]

Hope you didnt get the hard frost we did the other night. Would not do the concrete much good.