Pinned Boundary Condition for RC

[Wanna_be_SE]

Is there any guidance on assumptions for boundary conditions in reinf. concrete (articles, text books, etc.)?

I'd assume most, if not all end connections for concrete are fixed. Now when I say that, I'm not taking things down to the thousands or ten-thousands, but generally speaking if the end can not rotate then there's some degree of fixity and therefore some amount of moment developed in the connection. The only thing that comes to mind is for example a concrete beam where the end is NOT fixed would be bridge girders resting on a bearing assembly. Beyond that, if the reinforcement is hooked or embedded into the perpendicular concrete member its connecting to, how can you make the assumption the connection is pinned?

I understand we have to make assumptions to simplify things for analysis and design, but again for a concrete connection, it doesn't seem to make sense to ever design a RC connection for shear only, and neglect ANY moment developing in that connection.

Any thoughts or guidance would be greatly appreciated.

 

[phamENG]

Correct. If you ignore the moment developed by monolithic concrete and don't reinforce accordingly, it will crack. Then whatever shear capacity you were counting on may not be there anymore...

You still have analyze frames based on stiffness - you may develop the full moment capacity of a concrete beam at the connection, but the overall behavior will still be dependent on the stiffness of the columns and other beams framing into the joint.

 

[hokie66]

It is common practice to ANALYZE ends as simply supported, then DESIGN ends with some degree of fixity to control cracking.

 

[HTURKAK]

If the relative stiffness of the member say 10 times bigger than the perpendicular concrete member its connecting to, you may assume practically pinned for the stiff element etc..



I will suggest two books ;

1- Modern structural analysis , Modelling Process and Guidance ( by Iain Macleod )

2-Analytic modelling of structural systems ( by Iain Macleod )











I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[Wanna_be_SE]

phamENG (Structural),

You said "monolithic pour", what about retrofit jobs where we pour new conc onto exist conc....if you only design a connection of this type for shear, and don't account for any fixity or moment developing in that connection, you're essentially creating (or assuming) a pinned condition but in a general sense there's no rotation occurring so won't the concrete crack, or you'd at least need to check against Modulus of Rupture, right?

 

[phamENG]

True, a cold joint won't crack, but rotation can still happen and you can still get separation there. Unless it's a shear dominated deep beam, you will have some rotation at the ends if they are not restrained.