The document describes the steps to model and analyze a mat foundation in a structural analysis software: 1) A mat foundation with dimensions 9.5m x 10m and thickness of 0.45m is modeled using plate elements. 2) The plate elements are assigned a thickness property of 0.45m. 3) Subgrade reaction values of 750kN/m3, 1500kN/m3, and 3000kN/m3 are applied as support conditions. 4) Dead and live loads of -250kN and -150kN respectively are applied at the support nodes. 5) An analysis is run to determine support reactions and member forces/stresses. 6

1. MAT FOUNDATION FEM
DATA:
Width l : 9.50m
Length : 10.0m
(9.50m x 10.m)

2. STEP 1 (Creation of Geometry):
File  New Project  Select  space  File Name= mat foundation
Unit KNS Met.  Next   Add plate  Finish.
Type minimum Data on Data area.
Node X Y Z
1 0 0 0
2 0.50 0 0
3 0.0 0.0 0.50
4 0.50 0.0 0.50
Add 4 noded plates. Pick node 1,3,4,2.
1
21
43
XY
Z
(Note: Plate shall be preferably connected in anticlockwise direction.)
Select Plate 1 created. Click Translational Repeat icon.
Global direction X
Default spacing =0.50m
No. of steps =18 (9.50-0.50)/0.5 =18)
19 Plate elements created in X direction.

3. XY
Z
Select 19 Plates created.
Click Translational Repeat icon.
Global Direction Z
Default spacing =0.50m
No. of steps =19 (10.0-0.50)/0.5 =19)
XY
Z
STPE 2 (Member Property):
Main menu  Commands  Property  Thickness Plate 1 =0.45  Add.
Select all the plates using Plate cursor  Assign.

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Step 3 (Support condition):
Calculation of Sub grade reaction
SBC =120KN/m2
Elastic mat subgrade reaction value is KN/m2
/m
As per Bowels subgrade modulus =40 x FOS x SBC
(for 25mm settlement)
FOS =2.5 to 3
Sub grade modulus =40 x (2.5 to 3) x SBC
= 100 to 120 tomes SBC = X
For 50mm settlement =X/2
For 75mm settlement = X/3 (OR)
Subgrade reaction = SBC/ settlement of 25 mm
=100KN/m2
/0.025 =4000 KN/m2
/m.
Ks =subgrade reaction = 100 to 120 times SBC say 100 x 120
=100x120 =12,000KN/m2
Ka= area x ks
= (0.25x 0.25) x 12000
=0.0625 x 12000 = 750KN/m3
Kb= area x ks
= (0.5x 0.5/2) x 12000
=0.125 x 12000 = 1500KN/m3
Kc= area x ks
= (0.50x 0.50) x 12000
=0.25 x 12000 = 3000KN/m3

5. General  Support  create  click Fixed but
For ka  ky =750KN/m3
For kb  ky = 1500KN/m3
For kc  ky = 3000KN/m3
Select corner node ka  Ky=750KN/m3
 Assign.
Select intermediate end plates for kb  Ky =1500KN/m3
 assign.
Select all intermediate node kc for Ky=3000KN/m3
 Assign.
Step 4 (Loading):
Main menu  Commands  Loading  Primary load  Load case 1 =Dead
Load  Add.
Load case 2=Live Load  Add  close.
Select load case 1 (Dead Load) Add.
Self weight Factor =-1. Direction  Y.
Dead Load (from column reaction) Fy=-250KN  Add.
Select Fy =-250 KN  select all column support node  Assign.
Select Load case 2 (Live load)  Add .
Fy=-150KN  Add.
Select Fy =-150KN  Select all column support nodes  Assign.
Main menu Commands  Loading  Load comb  Load comb 3
Default =1.50  Add  Close.
Main menu Commands Loading Load list (selecting design load)
Ok Close.
Step 5 (Analysis Type):
Main menu Commands Analysis Perform Analysis  No Print  Ok.
Step 6 (Post Analysis print):
Main menuCommands Post analysis print Support reactions  Ok.
Step 7 (Design):
Main menu  Commands Design  Concrete Design  Current
code=IS456  Main menu  Tools  Set current input unit= length=mm;
Force =N OK. Select all plate elements  Define Parameters
Fc=25  Assign
Fymain=415  Assign
Fysec=415 Assign
Max Main=16  Assign
Min Main=10 Assign Close.
Commands  Design slab element all.
Step 8 (Analysis):
Main menu  Analysis Run Analysis Done.