Wats meant by spring supports in struct engg

Question

when lift ansalysis is performed using a software, it requires spring supports at edges - to impart stiffness in specified direction....but wats physical meaning of spring support...how does it affect global stiffness matrix assemblage... i get negative terms in diagonal of global K matrix when i dont use springs wen i tried lift of a box... pls clarify

Answer 1

Spring constants can be used in all 6 degrees of freedom (DOF).  It models a support in between a pinned support and a fully fixed support.  Spring constants have units of load/distance such as kips/in, lbs/ft, newtons/meter, etc.

When the model is loaded, these spring constants will deflect such that statics is maintained and deflections are consistent.  

When I model a slab on soil for example, I use spring supports at approximately 1 foot on center.  You can research how these are used in a geotechnical engineering text such as Bowles, etal.

Good Luck

Answer 2

The only time I have heard of spring support is in reference to soil. Soil is given a spring constant to approximate settlement but being a building engineer, that is only time I have heard of spring being used.