News:

Thanks to everyone for the feedback on what errors you encountered at https://www.aaroads.com/forum/index.php?topic=33904.0
Corrected several already and appreciate your patience as we work through the rest.

Main Menu

Steel vs concrete beams

Started by tolbs17, May 25, 2021, 09:54:22 PM

Previous topic - Next topic


Big John

Steel makes for more flexible design in several aspects.

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

Duke87

The only correct answer is "it depends".
If you always take the same road, you will never see anything new.

tolbs17


Duke87

Quote from: tolbs17 on May 26, 2021, 07:49:36 AM
Quote from: Duke87 on May 26, 2021, 01:07:05 AM
The only correct answer is "it depends".
Like the cost?

That is one thing on which it may depend, yes.
If you always take the same road, you will never see anything new.

Tom958

#5
It doesn't come into play that often, but concrete AASHTO beams are fabricated to standard 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. 

tolbs17

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

jeffandnicole

Quote from: tolbs17 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.

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.

tolbs17


spooky

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.


Big John

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

tolbs17


Bitmapped

Quote from: tolbs17 on July 06, 2021, 03:57:29 PM
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.

jeffandnicole

Quote from: tolbs17 on July 12, 2021, 03:02:37 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:

QuoteThis 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.

wxfree

#15
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.
I'd like to buy a vowel, Alex.  What is E?

tolbs17

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

Big John

Quote from: tolbs17 on July 25, 2021, 05:46:25 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.

tolbs17

#18
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

tolbs17

As well as the I-40 and I-77 interchange in Statesville. Also is using concrete beams.

https://www.google.com/maps/@35.8093098,-80.8639123,3a,90y,94.44h,107.21t/data=!3m7!1e1!3m5!1soq3sRIUxIUpi5e_q9wUvdg!2e0!5s20210801T000000!7i16384!8i8192

But they are straight and not bendy like the steel ones are. So I assume this is new technology? :hmmm:

Dirt Roads

Quote from: tolbs17 on October 24, 2021, 11:53:35 PM
As well as the I-40 and I-77 interchange in Statesville. Also is using concrete beams.

https://www.google.com/maps/@35.8093098,-80.8639123,3a,90y,94.44h,107.21t/data=!3m7!1e1!3m5!1soq3sRIUxIUpi5e_q9wUvdg!2e0!5s20210801T000000!7i16384!8i8192

But they are straight and not bendy like the steel ones are. So I assume this is new technology? :hmmm:

You can construct a slight curve overtop of "stringers" (straight beams) as long as the curve radius is great enough.  Each of the stringers beneath the deck of curved roadway also need to be mounted at slightly different elevations to facilitate superelevation and rainwater drainage.  The design and construction of the deck gets more complex as compared to the smooth deck that can be used with curved steel stringers.  Even when low cost AASHTO-standard concrete stringers can be utilized, there is still a "grey area" whether they will be less expensive when compared to curved steel stringers.

We utilized AASHTO standards for bridges and guideways in the automated guideway transit (AGT) industry, even when steel-wheel/steel-rail applications were applicable.  But since the "deck" was often a proprietary design associated with the vehicle technology, we required the substructure design/contract to avoid the complicated deck interface you see here.  Even then, there was a tendency to utilize AASHTO-standard concrete stringers in curves whenever possible.  I'm assuming that a specialty bearing was placed atop each stringer to allow a smooth "deck" to rest on top.  (In some cases, we didn't get a full deck but rather two sets of plinths that run underneath each tire track).


jeffandnicole

Quote from: tolbs17 on January 02, 2022, 04:26:16 PM
I'm guessing that "steel" is the older type and "concrete" is more modern and heavier in design but I wonder how they will fix these rusted steel beams on these bridges. Since the 1980s, I don't really see these type of "green" bridges anymore although I have seen many have been painted white when refurbished.

https://www.google.com/maps/@35.7629247,-78.0040132,3a,73.3y,352.38h,91.76t/data=!3m6!1e1!3m4!1sxe7BHJ0MHVA26sOMQ_C1Ag!2e0!7i16384!8i8192

https://www.google.com/maps/@35.9951681,-77.8727061,3a,15y,169.8h,94.48t/data=!3m7!1e1!3m5!1sgfuo1uKZQas6iBNAYD7d6g!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fpanoid%3Dgfuo1uKZQas6iBNAYD7d6g%26cb_client%3Dmaps_sv.tactile.gps%26w%3D203%26h%3D100%26yaw%3D269.55658%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192

https://www.google.com/maps/@36.013525,-77.862932,3a,27.8y,5.3h,95.89t/data=!3m6!1e1!3m4!1s9X89oh1tFbpMUGk3WfDGMw!2e0!7i16384!8i8192

Different states have different methods, but very simply, generally the old paint and rust will be sandblasted off the beams, repairs made, then repainted. If there's a chance these bridges may be replaced, maybe they'll letting them go until they're removed.

Dirt Roads

Quote from: tolbs17 on January 02, 2022, 04:26:16 PM
I'm guessing that "steel" is the older type and "concrete" is more modern and heavier in design but I wonder how they will fix these rusted steel beams on these bridges. Since the 1980s, I don't really see these type of "green" bridges anymore although I have seen many have been painted white when refurbished.

Quote from: jeffandnicole on January 02, 2022, 09:38:08 PM
Different states have different methods, but very simply, generally the old paint and rust will be sandblasted off the beams, repairs made, then repainted. If there's a chance these bridges may be replaced, maybe they'll letting them go until they're removed.

The stringers (beams) don't need to be fixed, as it is unlikely that the rust will outpace the bridge.  On the other hand, rust from the stringers will speed up the corrosion process on the bearings.  When the bearings start to get too rusty, it's time to sandblast and paint everything.

tolbs17

Quote from: jeffandnicole on January 02, 2022, 09:38:08 PM
Quote from: tolbs17 on January 02, 2022, 04:26:16 PM
I'm guessing that "steel" is the older type and "concrete" is more modern and heavier in design but I wonder how they will fix these rusted steel beams on these bridges. Since the 1980s, I don't really see these type of "green" bridges anymore although I have seen many have been painted white when refurbished.

https://www.google.com/maps/@35.7629247,-78.0040132,3a,73.3y,352.38h,91.76t/data=!3m6!1e1!3m4!1sxe7BHJ0MHVA26sOMQ_C1Ag!2e0!7i16384!8i8192

https://www.google.com/maps/@35.9951681,-77.8727061,3a,15y,169.8h,94.48t/data=!3m7!1e1!3m5!1sgfuo1uKZQas6iBNAYD7d6g!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fpanoid%3Dgfuo1uKZQas6iBNAYD7d6g%26cb_client%3Dmaps_sv.tactile.gps%26w%3D203%26h%3D100%26yaw%3D269.55658%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192

https://www.google.com/maps/@36.013525,-77.862932,3a,27.8y,5.3h,95.89t/data=!3m6!1e1!3m4!1s9X89oh1tFbpMUGk3WfDGMw!2e0!7i16384!8i8192

Different states have different methods, but very simply, generally the old paint and rust will be sandblasted off the beams, repairs made, then repainted. If there's a chance these bridges may be replaced, maybe they'll letting them go until they're removed.
They won't be replaced for a LONG time that's just for a fact. They are not even 50 years old and they barely carry and traffic.



Opinions expressed here on belong solely to the poster and do not represent or reflect the opinions or beliefs of AARoads, its creators and/or associates.