Fix-fix Arch Approximate Static Analysis

In summary, the conversation discusses the challenges of analyzing an arch bridge for approximate stresses, particularly in regards to finding an easy approximation formula for fix-fix conditions and estimating moments within the arch itself. The experts suggest using MEXE and ARCHIE, two computer implementations designed for assessing arch bridges for load carrying capacity.
  • #1
henie84
3
0
Hey there,

i´m dealing with a problem when I´m trying to analyze an arch bridge for approximate stresses in the arch. The normal force is quite easy to get for such structure.

The problem I´m running into is the fix-end moment for the arch under both dead load and live load (live load is approximated as one-half span length uniform load). Obviously, the stiffness plays an key issue. Is there an easy approximation formula that would get me the moment assuming fix-fix condition.

The following one for half-sided uniform load

MLL= - w L 2/ 64

doesn´t really do the trick, since it grossly underestimates the moment at the opposite side support, thus underestimates the total stress in the arch.

And I don´t even have a formula for dead load moments.


Back to the topic of moment, assuming pin-pin condition only normal force gets tranferred into abutments, however, significant moment can develop withing the arch itself @ approximately 5/16L ... any good formula for estimating such moment?

I´ve searched multiple books, papers, etc but I haven´t had much luck.
 
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  • #2
The moment (ha ha pun intended) you bring bending into it, you should be treating your structure as a curved beam, not an arch.

If you are trying to do more than MEXE or ARCHIE then you will need FE analysis.
 
  • #3
not sure what ARCHIE or MEXE is ... but the point is not to use FE analysis ... i can be doing 2D/3D FE models all day, not a problem, but I really need an approximate solution, because the FE packages are not available at locations where we are trying to implement this ...

worst case scenario i´ll have analyse 30-40 arch bridges and come out with span/height/load carrying capacity tables :-/ (here I run into the problem that I don't have that many as-builts)

not sure that I can treat an fix-fix arch 40m long, 10m high as a curved beam ...
 
  • #4
not sure that I can treat an fix-fix arch 40m long, 10m high as a curved beam ...

Sur you can. That is what it is if it carries bending.

not sure what ARCHIE or MEXE is ... but the point is not to use FE analysis ... i can be doing 2D/3D FE models all day, not a problem, but I really need an approximate solution, because the FE packages are not available at locations where we are trying to implement this ...

That is what MEXE and ARCHIE were developed for.

MEXE was originally developed in pre computer days as a quick field method for assessing arch bridges for load carrying capacity. It is very quick and easy. There are computer implementations these days. There is a UK Department of Transport on the subject. If I remember correctly, it is also discussed in Picard - The Masonry Arch.



ARCHIE is a PC implementation of theory developed bz Prof Harvey, during his tenure at the University of Strathclyde. It is available commercially for a small fee. It performs a similar function to MEXE.
 
  • #5
ok, i might have misunderstood what you meant by a curved beam, i was assuming a line element with small deflection angles :-)

Cool, I got to look up MEXE and ARCHIE then, especially MEXE sounds interesting to me. Thanks for the info.
 

1. What is "Fix-fix Arch Approximate Static Analysis"?

"Fix-fix Arch Approximate Static Analysis" is a method used in structural engineering to analyze the stability of an arch structure. It involves calculating the approximate load and displacement of an arch under various conditions, and making adjustments or "fixes" to improve its stability.

2. Why is "Fix-fix Arch Approximate Static Analysis" important?

This method is important because it allows engineers to quickly and accurately assess the stability of an arch structure before construction. It can also help identify potential problem areas and guide design modifications to ensure the safety and longevity of the structure.

3. How is "Fix-fix Arch Approximate Static Analysis" different from other methods of arch analysis?

Unlike other methods, such as numerical analysis or physical testing, fix-fix arch analysis is a simplified approach that uses basic equations and assumptions to estimate the behavior of an arch structure. This makes it a cost-effective and efficient option for initial design evaluations.

4. What factors are considered in "Fix-fix Arch Approximate Static Analysis"?

The method takes into account the geometry and material properties of the arch, as well as the applied loads and boundary conditions. It also considers the effects of self-weight, temperature changes, and creep on the structure.

5. What are the limitations of "Fix-fix Arch Approximate Static Analysis"?

While this method is useful for initial design evaluations, it is not as accurate as more advanced analysis techniques. It also assumes that the arch is symmetrical and does not account for dynamic effects. Therefore, it should not be used as the sole means of determining the stability of an arch structure.

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