Column bents - Response modification factor

[Nayan67]

I am currently designing a simply supported bridge that utilizes double bent columns, and I need to consider earthquake design. I have a question regarding the use of the response modification factor as recommended by the code. Should I apply the response modification factor for multiple bent columns only in the direction where framing action occurs (x-axis in the attached figure), or should I apply it in both directions (x-axis and y-axis)? I ask this because, in the direction where there is no framing action, the column behaves as a cantilever. In such cases, whether we should use the response modification factor recommended for the single column (R = 3, for operational cateogry other) rather than multiple column bents (R = 5, for operational cateogry other). I would greatly appreciate your suggestions and comments.

 

[HTURKAK]

This is basic knowledge for an experienced engineer.


Yes!! R= 5.0 shall only be applied at transversal direction ( X axis ) where the frame behavior occurs.



- In longitudinal direction ( along the bridge deck ) the bent columns behaves as a cantilevers and R=3.0


Probably , it would be better to ask services or consultancy of an experienced engineer ..










Don't underestimate a nail. A nail saves a horseshoe, a horseshoe saves a horse, a horse saves a commander, a commander saves an army, an army saves a whole country.. GENGHIS KHAN

 

[TLHS]

If you're using cantilever columns as a seismic resisting system, also check your code for other requirements. Because of the lack of redundancy and the stability concerns, the Canadian code has requirements like requiring Class 1 sections (compact), some other geometrical constraints, and capacity based connections for the restrained end. You have to ensure that the section stays stable if a hinge forms and that the connection can get you to that point without failing in a non-ductile way.

 

[Nayan67]

Hturkak and TLHS thank you so much for your response.