resistence of thrust in steel bents

[rittz]

I often debate with myself …. I have used two methods to resist thrust at the base of rigid frame steel buildings when using a foundation of cast-in-place-concrete piles and grade beams with grade supported slab: 1. Thrust rods under the slab (slab isolated from grade beam) and 2.Hairpin bars in the slab (slab doweled to grade beam). Battered piles are more appropriate for larger spans. The subject buildings are typically 100 x 200 x 18 + high ….wide open shops with perhaps an office area and/or an area of mezzanine.
What comments would anyone have? In some cases we are dealing with highly plastic clay. We would always use void form under the grade beam. But what about heave pressures on the slab? Does that make doweling slab-to-grade beam ill advised? Slip joints at partitions seem to be essential for one thing as heave anywhere from 1” to 4” is experienced in clay depending on plasticity of the clay sub soil. Replacing a meter or so of the soil beneath the slab and replacing with granular is an option

 

[ishvaaag]

All this amounts to use proven practices to get targeted behaviours. You in the name of the owner, or the owner itself will set the required specifications of allowed movement, be it heave or settlement and then everything must be geared to get such behaviour. Geotechs may help with sound recommendations, then reasonably complete models (even if of only some representative part) will laid the behaviour in front of your eyes; if not meeting targets something must be done.

On the specifics of the related questions, it will depend on the case. Sometimes tying things incorporates enough stregth as to prevent the undesirable behaviours; in other cases it may make appear some crack that wouldn't appear if the connection wouldn't exist. Hence only particularized study can show, I think.

 

[Teguci]

If you put structural loads into the slab on grade then you need to use ACI 318 to design the slab.

Heave is usually not acceptable in a slab whether it is structural or not.