subgrade need to be change as per area ?

Hi

in my model the subgrade reaction is calculated like follows,

** SBC 30T/M3 = 300 kN/m3
** ALLOWABLE DEFLECTION IS 15mm
*** SUBGRADE MODULUS = 20000 kN/m2

and the plate mesh i have created is 0.5mx0.5m. so in this case do i need to change the subgrade value to this 20000/(0.5*0.5) = 80000kN/m2  for internal plates

and for end plates 20000(0.5*0.25) = 160000

and for corner plates 320000 kN/m2 ????

can you clear this doubt? thanks in advance.

Parents Reply
  • For the ELASTIC MAT command, STAAD looks for spaces between nodes and assumes that those spaces are filled by actual physical objects like a concrete pad that can resist loads.

    The PLATE MAT command on the other hand is going to consider only the area with the individual elements to assemble the tributary area for the nodes.

    Your foundation is not a contiguous arrangement. It is 5 separate mats separated by gaps and connected by beams. Thus, a single ELASTIC MAT command isn't going to work for this arrangement. That is because, the tributary area calculated for the nodes at the edges of those gaps is going to include the contribution from the gaps, and thus will be different from the tributary areas in the PLATE MAT command.

    So the remedy is, replace that single ELASTIC MAT command with 5 separate commands as shown here

    1512 1518 1532 TO 1535 1930 TO 2097 -
    2098 ELASTIC MAT DIRECT Y SUBGRADE 19998 PRINT
    1513 1519 1528 TO 1531 1761 TO 1928 -
    1929 ELASTIC MAT DIRECT Y SUBGRADE 19999 PRINT
    1514 1515 1520 1521 1524 TO 1527 1544 TO 1759 -
    1760 ELASTIC MAT DIRECT Y SUBGRADE 20000 PRINT
    1516 1522 1536 TO 1539 2099 TO 2266 -
    2267 ELASTIC MAT DIRECT Y SUBGRADE 20001 PRINT
    1517 1523 1540 TO 1543 2268 TO 2335 -FOUNDATION Elastic-Revised.std
    2336 ELASTIC MAT DIRECT Y SUBGRADE 20002 PRINT


    This will exclude the gaps and consider just the area confined within the perimeter formed by the nodes of each command. It should be a good match with what you get with the PLATE MAT command.

    Corrected file is attached.



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