Hi all.
Nice to meet you.
I have a model steel composite cable-stayed bridge with 6 span continuos by Rm Bridge V8, 2 side span have 150m, 4 main span is 300m. I don't known about allowed deflection of the bridge. I use AASHTO LRFD standard. If you known allowed deflection of type soft beam bridge, I hope you can tell me about it.
Thank you for reading and I hope your reply.
Best regards.
Hello Dang,
In general, the deflection limits for cable-stayed bridges preliminary design are the L/400 ratio for the spans total and L/800 for the live-load. It is code related and other criteria should also be considered, like fatigue and user comfort, considering structural factors like damping and the wind induced vibrations. This would require a structural dynamic analysis and then the limits would be the bridge natural frequency and maybe the Point Of Interest accelerations.
Best regards,
Marcos Beier
Senior Technical Support Engineer
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Hello Marcos Beier and Hi all.
Thank you for your reply, I am very happy.
In your reply, the deflection limits for cable-stayed bridges are L/800 for the live-load. But, if I use L/800 are the deflection limits for steel composite cable-stayed bridge because the beam of the bridge are soft beam with two steel beam height 3000mm composite with deck concrete height 260mm and the width of bridge is 35,6m with 8 lanes.
Therefore, if you know the deflection limits of the bridge which my mentioned above, I hope you tell me about it.
Hi Dang,
To use "soft beams" in bridges the longitudinal stiffness is certainly an issue that will require additional studies. Long span and slender bridges will need frequency and modal shape analysis and for any flexible Cable Stayed Bridge you will not find a fixed criteria, only instructions to the need of a deeper case-by-case model dynamic analysis. You might find papers and researches available, but with the conclusion that for displacements only the 1000, 800, 400 deflection limits criteria are safe.
Hi Marcos Beier.
Thank you, for your answer.
If L/400 deflection limits < deflection of Live load AASHTO LRFD 1998, Do you tell me how to adjusted my model?