Initial permanent deformation in Monorail 1

[HAR2011]

Hi,

A new monorail beam after load testing to rated service load got a 1/2" permamnent deformation at the center. It deflected overall 3/4" at the center and then after removal of the load went back 1/4". The span is 14 ft. The beam has got 1/2" thk. plates welded to the top & bottom flanges over the entire span. Assuming that the design of the beam is adequate for strength and deflection (span/450 limit) for the load specified, could there be any other reason for this initial deformation?

 

[ToadJones]

doesnt make much sense....bad measurements?

L/450 gives an allowable deflection of 3/8".
So, your 3/4" measurement leads me to beleive that the beam is under designed.

If it has a 1/2" permanent defection, --> it has yielded right?
This also implies bad design.

 

[MiketheEngineer]

Go back to the drawing board and check things out...

 

[Ron]

Explain how the test was done and what equipment was used. Did you use any bonded strain gages?

Was the measurement electronic or manual? Were the devices digital or analog?

What was the test load relative to the design load?

Was the support condition monitored for movement relative to the beam?

 

[HAR2011]

Hi Ron,

I have my suspicion on how the load test was carried out. It was done by a third party without much information provided. I am trying to find out how the measurements were taken. Thanks.

For the beam to go past it's elastic limit, the load will have to be almost twice the rated load. The test load was same as the rated load.

 

[MiketheEngineer]

Something is not right... Start from scratch and check out the procedures, calcs, etc.

 

[chicopee]

Take the beam and turn it upside down. It is already strain hardened.

 

[Ron]

HAR2011...then I suspect you have a testing anomaly. Any testing group that is not willing to lay out its procedures and results for review is suspect. I've done testing on construction materials, processes, and procedures for 35 years, including relatively high level and sophisticated destructive and nondestructive testing. The testing procedures should be transparent and there should be parametric testing to validate the process (e.g., testing the frame of reference for movement).

 

[paddingtongreen]

"A new monorail beam after load testing to rated service load"

Surely, if this was for certification, it was tested to twice the rated load? You may have thought you specified "test the actual rated load" but I'm not sure the test facility would understand unless it was really impressed on them with special language.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[hokie66]

I think Ron identified the problem. The supports moved...methinks.

 

[ToadJones]

As Paddington has alluded....test should have been done to more than rated capacity...usually 125%

 

[msquared48]

Or the beam was designed to be cambered up but installed upside down.

Mike McCann
MMC Engineering

 

[HAR2011]

Hi All,

Thanks for your inputs.
We actually went to site along with the load testing company and found out that there was zero deformation in the monorail beam and in fact it was cambered up by 1/8" in the center. The readings taken by the load testing company were faulty. We suspect that the new foundations supporting the monorail structure settled and this was neglected by the company. A re-load test will be carried out soon.