need laminated neoprene bridge bearing info

[Randy2002]

Hello,

The 15th Ed. of the AASHTO Stnd. Road and Bridge Spec., sect. 14.4.1 had stress / strain curves for elastomeric bridge bearing pads as a function of shape factor. I would like to locate an electronic version of these curves. It could be just about any format, vector (CAD), graphic such as jpg or bmp, pdf, etc. I'd like to include it in my mathcad design file.

In particular I need the ranges similar to the ones in the AASHTO chart, below 1 ksi. I've found one chart on the web at the Nebraska Dept. of Roads site, but the curves do not show the low stress range in enough detail to be useful to me.

Thanks,
Randy Miner

 

[Qshake]

You can check out more state DOT websites from the FHWA website (which list all state DOT websites) and also check out these companies

D.S. Brown
Watson-Bowman

 

[Randy2002]

Thanks, I've checked out both of the companies web sites, no luck there. Even got an email from an engineer at D.S. Brown saying that they refer people to the AASHTO charts.

What I would really like to do is automate this part of the design. Anyone know of equations for the strain as a function of stress and shape factor? Otherwise I think I'd have to curve fit each shape factor curve in the chart, then interpolate between for a given shape factor. I'd rather not do that in mathcad if I can help it...

 

[Randy2002]

More on AASHTO Bearing Pad Design...

Well, there are some equations in the 15th ed. of the AASHTO standard specs that I think*should* result in the same compressive strain as the charts. Looking in the definitions for section 14 there is:

the effective compressive modulus Ec=3*G*(1+2*k*S^2) (psi)
Where k is an adjustment factor that depends on hardness, given in table 14.3.1
and S is the shape factor.

And then strain is P/(A*Ec)

This seems very straightforward, except that it does not give me the same strain as the graphs. So maybe I'm missing something here. I also have to take a look at the LRFD commentary tomorrow, as I think there may be some relevant info there.

Anyone familiar with this issue?

 

[justhumm]

A year or so ago, I met an engineer who had been working with elastomeric bearings for at least thirty years. He told me that those curves are not functions of any equations, but were purely plots of values recorded during experimentation...??? They may have been made by Dupont Rubber Company, several years ago?

As far as getting an electronic picture of the graphs, you might try a company called:

Amscot Structural Products Corp.

http://www.amscotnj.com

 

[chicopee]

If you have good data points on the curves that you have, why dont you do a regression analysis? Regression analysis of polynomials to the N th power can just about fit any of the curves that you have, I am sure.

 

[MichaelL]

I was just looking into doing the same thing. Did you have any success in automating this task?

 

[sam298]

Check this pdf for an equation to the stress strain curve.

http://www.steelbridge.org/scef/SCEF Manual 05.pdf

 

[chicopee]

I developed a basic program to do regression analysis for a of half dozen curves. Give me two dimensional data points ie x & y vaslues and I'll run them thru and get back to you in about two weeks as I am a little busy now and I'll publish the equation over this media for you.