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Author Topic: Steel vs concrete beams  (Read 2693 times)


Big John

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Re: Steel vs concrete beams
« Reply #1 on: May 25, 2021, 10:37:48 PM »

Steel makes for more flexible design in several aspects.

Concrete doesn't rust except for the rebar/tendons at the ends
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Duke87

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Re: Steel vs concrete beams
« Reply #2 on: May 26, 2021, 01:07:05 AM »

The only correct answer is "it depends".
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tolbs17

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Re: Steel vs concrete beams
« Reply #3 on: May 26, 2021, 07:49:36 AM »

The only correct answer is "it depends".
Like the cost?
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Duke87

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Re: Steel vs concrete beams
« Reply #4 on: May 26, 2021, 08:03:17 PM »

The only correct answer is "it depends".
Like the cost?

That is one thing on which it may depend, yes.
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Tom958

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Re: Steel vs concrete beams
« Reply #5 on: May 28, 2021, 06:15:49 AM »

It doesn't come into play that often, but concrete AASHTO beams are fabricated to standards designs and made of materials that can be obtained and/or fabricated easily and quickly, i.e. ready-mix concrete and standard-sized rebar, which is easy to cut and bend as needed. they can essentially be ordered out of a catalog. Had the collapsed I-85 viaduct in Atlanta been made of steel or cast-in-place concrete, it would've taken a great deal longer to replace. Georgia DOT had already swung decisively toward AASHTO beams for new bridges, but that catastrophic event will surely increase their resolve to stick with AASHTO beams for the rebuilt system interchanges and miles of elevated express lanes proposed for I-285. 
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tolbs17

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Re: Steel vs concrete beams
« Reply #6 on: June 07, 2021, 08:26:55 PM »

The new Southwest bypass in Greenville, NC is all concrete beams. The one at Bell Rd is steel. I guess it's just random.
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jeffandnicole

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Re: Steel vs concrete beams
« Reply #7 on: June 08, 2021, 06:50:15 PM »

The new Southwest bypass in Greenville, NC is all concrete beams. The one at Bell Rd is steel. I guess it's just random.

More or less, yes it is.  There's a lot of engineering factors that go into their decision, but from a layman's perspective like you or me, it appears fairly random what is used.
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tolbs17

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Re: Steel vs concrete beams
« Reply #8 on: July 06, 2021, 03:57:29 PM »

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spooky

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Re: Steel vs concrete beams
« Reply #9 on: July 07, 2021, 09:04:45 AM »

Fun fact: for Boston's Big Dig, designers had the flexibility to use steel or concrete beams for the structures that carry I-93 over surface roads. Since the job was separated into smaller contracts with different joint venture teams of consultants, this led to different treatments on adjoining sections.

This can be seen here: https://www.google.com/maps/@42.3421764,-71.0622163,3a,75y,23.74h,88.6t/data=!3m6!1e1!3m4!1s5z6kTyYXmnaE_TLMtorMtQ!2e0!7i16384!8i8192

This is Frontage Road NB approaching West Fourth Street, under I-93.
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Big John

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Re: Steel vs concrete beams
« Reply #11 on: July 11, 2021, 11:39:45 PM »

^^ The tubes are scuppers and is used for drainage to help keep the water off the bridge.
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tolbs17

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Bitmapped

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Re: Steel vs concrete beams
« Reply #13 on: July 13, 2021, 10:20:25 AM »

Which girder looks nicer? For me, I like the ones that are painted gray.

https://www.google.com/maps/@34.7687229,-77.3960272,3a,75y,221.35h,94.13t/data=!3m6!1e1!3m4!1sz8eocvKX44o39MPXaBtCbQ!2e0!7i13312!8i6656

The one that is painted gray is painted and requires ongoing upkeep. The brown one is weathering steel, which forms a petina of protective rust and doesn't need to be painted, so it has lower future maintenance costs.
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jeffandnicole

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Re: Steel vs concrete beams
« Reply #14 on: July 13, 2021, 03:16:35 PM »

https://www.state.nj.us/transportation/commuter/roads/rte72manahawkinbaybridges/photos.shtm

These bridges use both!



Here's the description why they did what they did:

Quote
This picture shows the completed new EB Bay Bridge (left) with a prestressed concrete girder superstructure sitting on new piers side by side with its twin, the reconstruction of the WB Bay Bridge (right) with a steel superstructure sitting on existing piers. Steel beams were used on the WB bridge to avoid overloading the existing piers, since steel is lighter than concrete beams. Measures were taken during design to develop similar features, while upgrading to the current standards for new construction. Pier geometry is similar for the two structures, and the new painted steel girders for the WB Bay Bridge were colored to match the concrete beams for the EB Bay Bridge.
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wxfree

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Re: Steel vs concrete beams
« Reply #15 on: July 17, 2021, 11:25:34 PM »

I remember reading about the construction of the Chisholm Trail Parkway.  Concrete beams are preferred, presumably for the cost.  Steel beams are used where the spans are long.  As I remember, concrete beams made in a factory and then driven to the site can be up to about 150 or 160 feet.  If they're too long, it becomes too difficult to haul them around.  They can't be assembled at the site.  Steel beams can be put together with rivets or duct tape or whatever they use, so shorter pieces can be hauled in and assembled at the site.  Some of the ones over CTP are curved.  I imagine a curved beam would be a bitch to drive around, so the maximum length would be even less.

I've never seen cast-in-place beams used in new construction.  A local street bridge rebuilt about 15 years ago has pre-cast concrete beams, and the spans are about 35 to 55 feet, which seems a little over-built.
« Last Edit: July 17, 2021, 11:36:20 PM by wxfree »
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tolbs17

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Re: Steel vs concrete beams
« Reply #16 on: July 25, 2021, 05:46:25 PM »

This steel is already starting to rust. Do you think these beams can be painted?
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Big John

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Re: Steel vs concrete beams
« Reply #17 on: July 25, 2021, 05:55:50 PM »

This steel is already starting to rust. Do you think these beams can be painted?
That looks like Cor ten (weathering) steel.  It is pre-rusted with the theory it won't rust any further.  It is not meant to be painted.
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tolbs17

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Re: Steel vs concrete beams
« Reply #18 on: October 06, 2021, 10:42:18 PM »

This flyover bridge is interesting because it uses BOTH steel and concrete on the same platform. I wonder why that is and yet steel is meant for curvy bridges. I'm surprised that this one uses both.

Here as well. Also using both. https://www.google.com/maps/@36.1372729,-79.8631596,3a,25.2y,352.76h,91t/data=!3m6!1e1!3m4!1s1ud55Zzn9O7T9WnRYa1ybQ!2e0!7i13312!8i6656
« Last Edit: October 06, 2021, 10:53:18 PM by tolbs17 »
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