Screed Elevation Diagram

[OSUCivlEng]

I have been asked to develop a "Screed Elevation Diagram", which I have never seen or done before. The best that I can tell from a quick Google search is that this diagram shows finished grade elevations of the deck over each beam line at tenth points. It appears that this elevation needs to be adjusted by adding the deflection due to the deck and parapet/rail. The Ohio and Utah DOT say to use the deflection due to the deck and parapet, while Virginia says just to use the deflection due to the parapet. It seems to me that you would need to add the deflection from the deck and parapet to the finished grade elevation to determine the actual elevation that the screed would need to be at.

Is this a common diagram required by many DOTs? I am curious if anyone else does these on a regular basis and if I am understanding this properly.

I can't see how this is really that useful, because who has time to check all these elevations. In my experience you just run the finishing machine out and measure down with a tape measure to ensure that you have the proper deck thickness and cover. It seems even less useful considering that the top of beam elevations have been surveyed at tenth points and the haunch calculations have been done to ensure proper haunch thickness.

 

[BridgeEI]

Contractors in my area have been adding gps to the finishing machine so I can see how the elevations would be useful. They are starting to get where they want the alignment files for it also.

When I think of the screed elevation, my first thought is of the elevation of the rail itself and not necessarily the finished grade elevation. Caltrans has a manual that talks about it but I'd have to dig it up at the office.

Where I'm at, the DOT people in the design division get the information and decipher it so us lowly consultants never come across this.

 

[pikku14]

We often provide deck screed diagrams in Australia. It's just a simple diagram showing the deflection (typically at 1/4span intervals) to allow the contractor to adjust the levels allowing for deflection due to the deck slab pour/(s).
Not sure if that's exactly what you're after

 

[OSUCivlEng]

BridgeEI I hear you about the DOT keeping all the information for themselves and not letting it out to the consultants.

I did some more digging on this and my initial understanding is correct. The elevations on the screed diagram are the finished grade elevations of the deck above each beam line at 10th points along the beam PLUS the deflection due to the deck, haunch and traffic rail/parapet.

We always provide a deflection diagram with values at the 10th points along the beam. It is split into two rows, one for the weight of the beam and diaphragms/cross frames, and the second is for the deck, haunch and parapet. This information is used by the fabricator to create the camber diagram and the contractor to calculate the haunch elevations and thicknesses.

Sometimes a haunch elevation table is also shown, which is simply the elevation of the bottom of the deck above each beam at 10th points. These elevations take into account the deflection due to deck, haunch and parapet. The screed diagram is providing the same elevation, just at the top of the deck, not the bottom.

I guess if you had a GPS controlled deck finishing machine you could have greater precision with the finished grade. The problem is if the top of beam elevations are off, then all the elevations on the screed diagram would have to be adjusted accordingly.

 

[RHTPE]

What I typically see in my region is a table providing calculated deflections due to the deck concrete placement, the self-weight beam (including diaphragms) deflections, the desired finish grades, and a blank line for the field-shot grades for the beams. It is then up to the contractor to use this to establish the necessary elevations for the screed rail. This table is usually developed by the design consultant or the DOT.

Depending on the state involved, the desired finished elevations may need to be determined by the contractor based upon the roadway profile and cross pitch.


Ralph
Structures Consulting
Northeast USA

 

[3Fan]

Being a consultant in Ohio, ODOT requires us to provide and diagram and elevations at 1/4 span point or increments no greater than 25' for:

Final Deck Surface Elevations
Top of Haunch Elevations
Screed Elevations

A topping diagram is provided for prestressed superstructures.

We also have to provide a camber and blocking diagram for steel superstructures.

 

[OSUCivlEng]

The Screed Elevations could get tricky with a continuous plate girder. You have to account for deflections based on the order of the deck placement. Simple spans would be well quite simple.

BridgeEI are you in California? Where can I find more information about machine controlled deck finishing machines? I went to the website of several screed manufacturers and they didn't have any information on it.

 

[BridgeEI]

I'm out in oklahoma. Try this link, i don't think its the one I was looking for but I will look when I'm back in the office. I meant to track it down earlier but have been swamped at work...I'll make a reminder for Monday.

http://www.dot.ca.gov/hq/esc/constr...pleteManuals/BridgeDeckConstructionManual.pdf

 

[OSUCivlEng]

That's interesting, I work in Oklahoma. Do you do much work in OK?

 

[BridgeEI]

Most of the DOT work I do is in Oklahoma. We have the occasional bridge project out of state. I also do a lot of other smaller projects in different states but haven't done anything in California for a while.

 

[BridgeEI]

It appears I've lost the publication I was looking for in my reference material but I believe the link I sent was what I was referring to.