Load Vs deflection curve for simply supported beam under point load at centre

[Abrar_1512]

I have performed collapse analysis for a simply supported tubular beam by applying load at centre. And I am getting load Vs deflection curve at mid point as per attachment. Can anyone explain what is the reason for this type of behavior.

 

[BAretired]

Looks like you have elastic behavior from deflections of 0 to about 7cm. A plastic hinge starts to form under the load at a Load Factor (LF) of about 16. Strain hardening sets in at LF of about 24 but points adjacent to the load are reaching yield.

It is not clear why the curve continues to LF of about 90 and deflection of about 27cm. I would have expected the beam to collapse when the plastic hinge reached about 2*Fy if the beam was truly simply supported, i.e. pin and roller. With such large deflections, is it possible you were getting axial tension in the specimen? What was the span length?

BA

 

[Old Eng]

Hinges at both ends, no rollers?

 

[Abrar_1512]

Span 10m, Outer Dia 500mm, Thickness 5mm
Hinge support on both ends

 

[BAretired]

If you have a hinge support at each end, you will generate axial forces in the tube. To test a simple beam, you must have a roller support at one end.

If the point of load application prevents horizontal movement of the specimen, you must have a roller support at both ends.

BA

 

[rb1957]

please show a picture of the test.

at some stage i'd expect the load/displacement curve to "kick over" and give large displacements for small changes in load.

I assume the testpiece didn't fail in the test.

have you tried to FEA the test ? if both ends of the beam are pinned, so the beam cannot contract as it bends, then that'll induce tension in the beam.

another day in paradise, or is paradise one day closer ?

 

[prex]

Depending on how the point load is applied, you may have ovalization of the tube, reducing the moment of inertia. The same might happen at the supports. How much actual load corresponds to your 100% load factor?

prex
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[IDS]

The OP talks about an analysis. There is no mention of any test.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[klaus.]

well this behaviour is typical for nonlinear analysis and both end fixed.
As the load and deformation rises the beam will get tension force and then at some point 'change' to more cable like behavior
and the load can be raised up much more

This numerical test is good to test a program on nonlinear capabilities ....