Can STAAD.Pro be used in designing a mat foundation?
The answer to the question is Yes. The following are the major steps involved in the modelling and design of mat foundations using STAAD.
1) The mat foundation has to be modelled using finite elements. If the length and width of the mat are at least 10 times larger than its thickness, plate elements can be used. If not, one may use 8 noded solid elements. The remainder of the structure involving the beams, columns and slabs also has to be modelled along with the mat. If beams share a common boundary with the mat and slabs, to ensure the proper transfer of load between the beams and the mat & slabs, the mat & slabs have to be divided into several elements, the beams have to be divided into several members, and the elements and members must share common nodes.
2) Generally, the supports for the mat are derived from the subgrade reaction of the soil. Using this attribute, and the influence area of each node of the mat, the spring constant for the supports may be derived. STAAD contains an automatic spring support generation facility for mat foundations. One may refer to Section TR.27.3 of the STAAD.Pro Technical Reference Manual for details onthis type of support generation.
3) Soil spring supports generally tend to be effective against resisting compressive forces only. They are ineffective in resisting uplift. This type of a unidirectional support requires those springs to be assigned an attribute call SPRING COMPRESSION.
4) The loads on the mat and the rest of the model have to be specified. Then, the structure has to be analyzed. This will generate the plate stresses and corner forces needed to design the mat.
5) You can then use the program's concrete design ability to design the individual elements which make up the mat. The only tedious aspect of this is that the program can presently design individual elements only. The task of taking the reinforcement values from each element and assembling the reinforcement picture of the overall mat has to be done by you manually.
We suggest you take a look at example problem number 27 in the STAAD.Pro examples manual for guidance on analyzing mat foundations. In that example, the aspects explained in steps 1,2, 3 and 4 above are illustrated. Example problems 9 and 10 discuss concrete design of individual plate elements.
Note : A better option is to use STAAD Foundation Advanced software for design of mat. Mat modeled and analyzed in STAAD.Pro can be imported into STAAD Foundation Advanced with all results data and it can be subsequently designed in STAAD Foundation Advanced. One can also model and design mats directly in STAAD Foundation Advanced.