3-point bearing

[LearningAlways]

Is multiple points of bearing for a spanning element achievable in reality?

Seems impossible to me, but maybe other industries or other systems outside of precast have more experience with multiple points of bearing.

With the variation in bearing heights, load distributions, shim stacks, etc. it seems almost impossible without a large investment in time and skill by the erector to achieve a true multi-point bearing.

 

[JAE]

Depends on the stiffness of the thing bearing on the supports. Also the stiffness of the supports.

It's easy to get full uniform bearing on mashed potatoes.

 

[BAretired]

Is multiple points of bearing for a spanning element achievable in reality?

Seems impossible to me, but maybe other industries or other systems outside of precast have more experience with multiple points of bearing.

With the variation in bearing heights, load distributions, shim stacks, etc. it seems almost impossible without a large investment in time and skill by the erector to achieve a true multi-point bearing.

A plate or slab bearing on three supports, one not aligned with the others is achievable in reality. With more than three supports it is a problem, like the four legged table which wobbles back and forth and spills the coffee if the floor is uneven.

A continuous beam can have multiple bearing points, so multi-point bearing is achievable, but the magnitude of individual reactions is dependent on beam stiffness and support settlement.

 

[Ron247]

Once you get contact at all points, it gets more uniform for additional loads, but prior to that, it is dependent on a lot of factors and most likely is not neatly distributed. Look at Table 3-23 page 3-225 of the 13th edition of the AISC manual. Set 42 is 4 spans that assumes perfect alignment, perfect loading and those reactions are not the same because of different span conditions.