Saddle type connection around concrete beam

[Ipetu]

Please see attached file for a sketch. The steel saddle plate type base plate has been used due the limited 200 mm (8") width of the concrete grade beam. Due to the limited width we are unable to use a four-bolt anchoring pattern to fasten the column base plate to the concrete. A couple of thru bolts are used to attach the saddle plate to the concrete grade beam. What are the failure modes to be checked in the concrete grade beam? Block failure? etc. Please elaborate on how to evaluate each failure mode.

 

[hokie66]

You have to resist the 120 kN in bolt shear, bolt bearing on the concrete, tension in the vertical reinforcement, torsion in the beam between the piles, and development of the overturning into the pile. I suggest the beam will need continuous top and bottom bars and closed ties to resist the torsion. I would provide pairs of ties close to each bolt to resist the force directly.

 

[normm]

Ipetu

Other than what hokie has said, I will also add that the saddle and the concrete plinth may not be exactly same size tight fit in practice ie as there is no provision of grouting the gap, the stress calculations should not rely on full contact pressure developing between the saddle inner face and the vertical surface of the plinth. Also, is the threaded bar being cast in or drilled through after the concrete plinth is cast? If drilled through after, the stress calculations should allow for air gap between bolt and hole.

 

[Ipetu]

normm,

The threaded bar is being drilled through after the concrete plinth is cast.

 

[ishvaaag]

Maybe the solution lies in the inclusion of angled ties within the concrete able to take the capacity required of the shear in the bolts. That I remember, the 5th ed. of the PCI Handbook is full of such kind of "tie" details, with no much other worry than to ensure that the tie legs get properly anchored (or maybe sometimes, spliced). But the potential inaccuracies of drilling in hardened concrete makes such "solution" less attractive.