Stone Arch Bridges

[CoreyR]

Hi, I'm new to the group and a junior structural engineer in Providence Rhode Island. I've been given the task of rating an old stone arch bridge for vehicular traffic and was wondering if anyone could suggest some good references to help me out. Never having done one before I'm at a bit of a loss for methods. Thanks in advance.

Corey R.

 

[wiktor]

CoeryR:
Download the software from

http://www.shef.ac.uk/ring/.

This program could be used to calculate the forces within the arch. This one is for the circular arches, so if your arch is of different curvature, use any of the structural programs, and by modeling the arch as a series of beam elements (or better by FEM) establish the influence lines. Latter load the arch, find forces and compare to the capacity.

 

[jheidt2543]

How about looking in your engineering library for an old structures text or a text on masorny arch design? One such would be "Reinforced Concrete and Masonry Structures" by Hool and Kinne, McGraw-Hill Co., 1944.

Then use the method the original designers used, that is the graphical solution of the arch forces. You will learn more about the actual forces, workings of the arch and the design method than just plugging number into the computer. Nothing against computers, but the object is to learn about structures.

In one of the nearby communities we have a five span masonry arch railroad bridge that was designed in the 1860's and reinforced for heavier locomotives in the 1930's. The railroad gave me a copy of their graphical solution used during the 1930's renovation. It is really a quite elegant one page solution. New methods might be quicker and more precise, but not necessarily better.

 

[StephenEd]

It seems to me that the easy part might be the analysis and the hard part deciding what your allowables will be.

Anything with "Hool" in the title is a good place to start!

 

[djon]

Hi CoreyR, you should first do a careful inspection of the bridge to check its condition and note the following:

1. Type of material used in construction
2. Condition of mortar and degree of loss if any
3. Note any cracks and see what repairs are needed
4. Conduct careful survey of whole structure to determine its span, rise (shape of arch), depth of masonry ring and see whether either of its supports have rotated slightly or subsided. It may be necessary to take a core to check the depth of ring otherwise measure the voussoirs. From the latter you can determine the depth of fill over, having first taken road levels over the whole span length.
5. Once you have an accurate picture of what is going on it would probably be easiest to do a plane frame analysis of the arch giving it pinned supports. You will probably find the worst effects will be when the load is approximately a third of the way across the span. Take the wheel load distribution through the fill at a 2:1 slope. Don't forget to deduct the amount of mortar loss from the ring thickness when determining section properties.

Good luck,

Djon

 

[cyak]

Although the bridge is probably tappered, determine some appropriate centerline and break the arch in segments of equal width and varying depth approximating the shape of the arch. Try with dead loads over the whole span and some equivalent distributed load for 2/3 of the span.

Reduce the bending moments you get at the center of each segment to axial load acting at the appropriate eccentricity from the centerline. If this eccentricity is within the kern area of the section, no tension will appear in the section so you are 'OK'. You can then check against crushing stress in the section...

 

[plasgears]

The US Army Corps of Engrs had a bridge rating card for combat engrs. It might give you a quick method for rating the bridge. But, don't stop there. Use other methods as well. Try: Commandant, Engr School, Fort Belvoir, VA.