×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Rigid Frame Bridges
3

Rigid Frame Bridges

Rigid Frame Bridges

(OP)
Hello
I am looking for guidelines/example calculations of Rigid Frame Bridges. So far I have found only two ancient books (Hayden, PCA). If anyone can name textbooks, or provide links to online resources, I will highly appreciate it.

RE: Rigid Frame Bridges

You might try looking for "integral abutments", "full retaining abutments" or "integral leg superstructures". "Rigid frame" is not a term typically used for bridges, because they are rarely, if ever, designed that way.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Rigid Frame Bridges

(OP)
Thank you very much for the suggestion.
By Rigid frame bridge, I mean to describe a slab bridge (typically having a parabolic soffit) constructed monolithically to high walls.
An example is in this photo:
https://distributedmuseum.illinois.edu/exhibit/rig...
On the contrary, if I search for Integral Abutments, I get information for girder bridges that are integrally connected to short abutments resting on flexible piles. This is not what I am looking for.

RE: Rigid Frame Bridges

Ah, what you you describe is what's generally referred to as a 3-sided box culvert or a bottomless box culvert. They're not generally used for spans over 20'; there's probably a reason for that.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Rigid Frame Bridges

(OP)
Well, they can have a much longer span.
This one in Canada is 108 feet.
https://historicbridges.org/bridges/browser/?bridg...

They are not culverts but real, full-scale bridges of single or multiple span. Unlike culverts overs water, they are mostly found at grade separation of intersecting roadways.

This one for example is two-span (each span 69 feet)
https://historicbridges.org/bridges/browser/?bridg...

Anyway, I am surprised that there isn't any significant resources to be found regarding design of these bridge. I am interested if books or design examples are available anywhere.

RE: Rigid Frame Bridges

Long span integral full retaining abutment bridges never were very common, and are even more rare now. The closest we've come to something like that is a long span concrete arch (commonly referred to as a Bebo arch structure). I would guess that finding a design example is going to be difficult. A basic moment frame analysis would suffice for the preliminary design, but a more efficient final design would probably require an FEA. I like a good challenge, but I'm not sure I'd want to tackle one of those.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Rigid Frame Bridges

That style of bridge was common in this area, I know exactly where the first one linked is. Up until recently, practically every bridge over a motorway with 6 lanes or less in Ontario was that style. Lately, with widening of main highways, the only thing they have been doing with those is ripping them out. I doubt if many bridges of that style have been built since the 1970s. Historical records?

RE: Rigid Frame Bridges

There are 100's of rigid frames in the NYC area but they've lost popularity because of cost and difficulty in building one over an existing roadway. I haven't seen any books on rigid frames other than Hayden or the PCA manual, which is still valid.

RE: Rigid Frame Bridges

They never caught on out in the western US, so I guess I didn't realize there were so many back east. Anyway, if you have design guides from when they were popular to build, that may be all the help you get. If you're designing a new one, it'll probably be cost-effective to create a detailed FEM for it. You'll probably need to consider how to mitigate the temperature differential associated with "mass concrete" placement.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Rigid Frame Bridges

(OP)
BrianPetersen,
Interestingly, the opposite is also true - Ontario is replacing girder bridges with precast rigid-frame bridges!
https://abc-utc.fiu.edu/mc-events/ontarios-rapid-i...
bridgebuster,
Found PCA manual online. Will look into it, thanks.
BridgeSmith,
I am evaluating an existing one, not designing any new one. But I thought to understand this type of bridge better, design examples would help. In particular, the earth pressure and temperature effects are certainly different from girder bridges sitting on bearings on top of abutments.

RE: Rigid Frame Bridges

Quote:

In particular, the earth pressure and temperature effects are certainly different...

For sure. For most bridges, we can ignore the effects of earth pressure, and only consider the effects of temperature in evaluation of the bearings and expansion joints. For a rigid frame, it might take some thought to figure out where those effects should be considered and at what level, if they reduce the stresses in some areas.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Rigid Frame Bridges

I have load rated a few older ones (all conventionally reinforced slabs) but never designed what the OP showed in the video. Are these being PT'd in Canada? There are a few older ones around our city but not a lot. Essentially you have a pinned base and moment continuity at the top between the superstructure and walls. Like BridgeSmith said, a 3 sided culvert but longer span. A skewed condition certainly will complicate things.

Rod, interestingly enough, BRASS-GIRDER does accomodate these. It's under the Control Option for Structure (B).

RE: Rigid Frame Bridges

Yes, STrctPono BRASS-Girder will do the analysis of the frame, and it's fairly straightforward. The more difficult aspect of the design is in applying the loads and resistances of the soil. The conservative approach would be to apply no passive resistance to counteract the loads on the span, but then apply full soil pressure with the minimum dead load on the span. How conservative that approach is, is difficult to say.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Rigid Frame Bridges

Working in Washington DC, they have a lot of longer span older rigid frame structures that I have load rated. Easy to analyze but there isn't any software that can perform a load rating so it's all done with spreadsheets to calc out the capacity of the variable depth span.



RE: Rigid Frame Bridges

Quote:

there isn't any software that can perform a load rating...


If you properly account for the soil loading/resistance, or ignore it, BRASS-Girder will provide load ratings.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Rigid Frame Bridges

(OP)

Quote (MIKE 311)

it's all done with spreadsheets to calc out the capacity of the variable depth span
Do you only check capacity of the deck ? or the vertical wall too ?
I have a situation where the mid-span capacity exceeds positive moment demand (that's good)
End-span capacity exceeds the negative moment demand (that's good)
But the negative moment demand on top of vertical wall exceeds its capacity there. What do we do in this case ? Any suggestion ?

RE: Rigid Frame Bridges

Quote (tmalik3156)

Do you only check capacity of the deck ? or the vertical wall too ?

You are supposed to check the walls also.

A few thoughts....

1. How are you calculating your effective section strip width? This is one category where I have implemented different strategies that I feel are reasonable and do not blindly follow the provisions of AASHTO for slab bridges.
2. What kind of boundary conditions or earth pressures are you applying in the model that you have shown above?
3. Are you utilizing the effects of the axial force on the walls? This will actually provide you a small additional amount of capacity. Think of the interaction diagram for a column with bending and a small amount of axial load.
4. I'm all for trying to tweak the model and play with the numbers to try and get a load rating to come out (within reason) but how old is this structure? Sometimes a load rating factor less than 1.0 can be warranted. However, if the structure is in great shape and is showing no signs of distress then I would be suspect about giving it a deficient rating. The fee on the job is also going to heavily influence how much tweaking I would be willing to do.

RE: Rigid Frame Bridges

(OP)
STrctPono

1. I am taking 1 m width in analysis. So my Finite Element (SAP2000) frame model is 1 m wide perpendicular to the page.
2. Triangular earth pressure with Ko = 0.5 (coefficient of earth pressure at rest)
3. I did not check P-M interaction.
4. The rural bridge (over 60 years old) was inspected, and no significant sign of distress on the wall was found.

RE: Rigid Frame Bridges

@tmalik3156 - I have a load rating calculation for a 54' concrete rigid frame bridge - was done in the 90's using AASHTO Standard Specs - that I could post if you think it would be of use.

RE: Rigid Frame Bridges

I would like to see that bridgebuster if you dont mind! Quite curious.

RE: Rigid Frame Bridges

(OP)
@bridgebuster, sure that would be awesome.

RE: Rigid Frame Bridges

Here's another one I found in my files. Unfortunately the copy isn't very clear making the calculations difficult to follow. I remember the gentleman who did the rating used a slide rule, trig tables, and the PCA manual from the 30's "Analysis of Rigid Frame Bridges (Without Higher Mathematics)". That's how I was able to get a Xerox of the manual. bigsmile

RE: Rigid Frame Bridges

Many thanks bridgebuster!

RE: Rigid Frame Bridges

Enable, you're welcome; glad I could be of help.

RE: Rigid Frame Bridges

Quote (tmalik3156)

Do you only check capacity of the deck ? or the vertical wall too ?
I have a situation where the mid-span capacity exceeds positive moment demand (that's good)
End-span capacity exceeds the negative moment demand (that's good)
But the negative moment demand on top of vertical wall exceeds its capacity there. What do we do in this case ? Any suggestion ?

We check every member, horizontal and vertical, AAHSTO will allow simplification (eg. ignore axial loads) if the axial loads are below 10% or 20%.

For your last point, if the structure isn't showing distress, we have made the assumption that a plastic hinge can form and you end up with a simple span. so if the positive moment rating is adequate (assuming pinned ends), you are good.


RE: Rigid Frame Bridges

(OP)

Quote (MIKE 311)

if the structure isn't showing distress, we have made the assumption that a plastic hinge can form and you end up with a simple span. so if the positive moment rating is adequate (assuming pinned ends), you are good.

That's a very good point. For a simply-supported condition, my positive moment capacity is only slightly below the positive moment demand. I can make it work.

@ bridgebuster

I was reading through your calculations for LIE over Cemetery Rd. I was able to follow it easily until I came to this part. Do you remember how axial load was calculated ? Where did these highlighted numbers come from?

RE: Rigid Frame Bridges

tmalik/mike,

I agree with the belief in the simply supported span but technically speaking AASHTO only allows you to redistribute a percentage of your moments up to a maximum amount.

RE: Rigid Frame Bridges

Evaluating it as a simple span on walls, is the simple approach, but in order to get there will likely mean cracked concrete at the rear faces of the abutment walls. That would typically not be acceptable, as it would shorten the service life.

If I was doing it, I would limit the capacity of the bridge to the load where the yield capacity of the wall is reached, assuming the maximum reasonable soil resistance, which would probably be something greater than the at-rest pressure, but less than full passive. Where it falls in that range will depend on the backfill material and the expected flexural movement of the wall. My guess is that you'd be just barely above the at-rest pressure, given the small deflections typical for a structure as stiff as I would anticipate it to be, and the relatively large movement required to mobilize full passive pressure for most backfill materials.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Rigid Frame Bridges

You'll get alot of help from the spreading of the load. The maximum moment will be generated with the truck wheel loads near midspan. You'll engage a much wider portion of the superstructure at the abutments due to lateral spreading of the load from the point of application. Once you include the lateral spreading, I think you'll find the critical loading will be with the maximum number of lanes loaded, and the full width of the wall resisting.

Per AASHTO Std. spec, Article 3.12.1, if you have 3 or more lanes loaded there's a 10% reduction in the live load. In LRFD, the improbability of coincident multiple design vehicles is accounted for by the multiple presence factor (MPF).

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Rigid Frame Bridges

@tmalik3156, I didn’t work on the calculations but I looked at the STAAD output for the influence lines. Joint 15 controls, which is Load Case 9. I found two of the coefficients for Member 6 but I need to another look about the third coefficient; I think I know what they did.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close