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(OP)
Hello everybody.
I have posted the same question on bentley forus, but so far no luck.

I would like to model concrete cylinder in a tunnel - lets say to plug the tunnel.
So - idealised - the wedge is held in place by friction between the tunnel and itself.
How would i assign friction as a support - i was thinkging modeling it as a multilinear support that would allow every support to carry only maximum of say 10kn, and after that it would yield and extra load would be transfered to the next support...and so on, until everything is balanced.

Below you can find further explanation and a test model i made:
---------
I tried to accomplish this using multilinear springs...by making it that for every displacement, K is changed, so that product is

always 6kN (eg.1.6e-003*3.33e+003=6kN, 1.8e-003*3e+003=6kN ).

Currently - nothing is happening, as results are the same if whole multilinear part is deleted, and if i increse spring stiffeness, multilinear is also not doing anything :)

I tried plenty of load/stiffness combinations

Is this the right way for this problem? what am i doing wrong with multilinear here - it is a bit confusingly presented in technical reference.

START JOB INFORMATION
ENGINEER DATE 06-Nov-12
END JOB INFORMATION
INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
1 4 6 0; 2 4 5 0; 3 5 5 0; 4 5 6 0; 5 4 7 0; 6 5 7 0; 7 4 8 0; 8 5 8 0;
9 4 9 0; 10 5 9 0; 11 4 10 0; 12 5 10 0; 13 4 11 0; 14 5 11 0; 15 4 12 0;
16 5 12 0; 17 4 13 0; 18 5 13 0; 19 4 14 0; 20 5 14 0; 21 4 15 0; 22 5 15 0;
23 4 16 0; 24 5 16 0; 25 6 5 0; 26 6 6 0; 27 6 7 0; 28 6 8 0; 29 6 9 0;
30 6 10 0; 31 6 11 0; 32 6 12 0; 33 6 13 0; 34 6 14 0; 35 6 15 0; 36 6 16 0;
37 7 5 0; 38 7 6 0; 39 7 7 0; 40 7 8 0; 41 7 9 0; 42 7 10 0; 43 7 11 0;
44 7 12 0; 45 7 13 0; 46 7 14 0; 47 7 15 0; 48 7 16 0; 49 8 5 0; 50 8 6 0;
51 8 7 0; 52 8 8 0; 53 8 9 0; 54 8 10 0; 55 8 11 0; 56 8 12 0; 57 8 13 0;
58 8 14 0; 59 8 15 0; 60 8 16 0; 61 9 5 0; 62 9 6 0; 63 9 7 0; 64 9 8 0;
65 9 9 0; 66 9 10 0; 67 9 11 0; 68 9 12 0; 69 9 13 0; 70 9 14 0; 71 9 15 0;
72 9 16 0; 73 10 5 0; 74 10 6 0; 75 10 7 0; 76 10 8 0; 77 10 9 0; 78 10 10 0;
79 10 11 0; 80 10 12 0; 81 10 13 0; 82 10 14 0; 83 10 15 0; 84 10 16 0;
ELEMENT INCIDENCES SHELL
5 1 2 3 4; 6 5 1 4 6; 7 7 5 6 8; 8 9 7 8 10; 9 11 9 10 12; 10 13 11 12 14;
11 15 13 14 16; 12 17 15 16 18; 13 19 17 18 20; 14 21 19 20 22; 15 23 21 22 24;
16 4 3 25 26; 17 6 4 26 27; 18 8 6 27 28; 19 10 8 28 29; 20 12 10 29 30;
21 14 12 30 31; 22 16 14 31 32; 23 18 16 32 33; 24 20 18 33 34; 25 22 20 34 35;
26 24 22 35 36; 27 26 25 37 38; 28 27 26 38 39; 29 28 27 39 40; 30 29 28 40 41;
31 30 29 41 42; 32 31 30 42 43; 33 32 31 43 44; 34 33 32 44 45; 35 34 33 45 46;
36 35 34 46 47; 37 36 35 47 48; 38 38 37 49 50; 39 39 38 50 51; 40 40 39 51 52;
41 41 40 52 53; 42 42 41 53 54; 43 43 42 54 55; 44 44 43 55 56; 45 45 44 56 57;
46 46 45 57 58; 47 47 46 58 59; 48 48 47 59 60; 49 50 49 61 62; 50 51 50 62 63;
51 52 51 63 64; 52 53 52 64 65; 53 54 53 65 66; 54 55 54 66 67; 55 56 55 67 68;
56 57 56 68 69; 57 58 57 69 70; 58 59 58 70 71; 59 60 59 71 72; 60 62 61 73 74;
61 63 62 74 75; 62 64 63 75 76; 63 65 64 76 77; 64 66 65 77 78; 65 67 66 78 79;
66 68 67 79 80; 67 69 68 80 81; 68 70 69 81 82; 69 71 70 82 83; 70 72 71 83 84;
ELEMENT PROPERTY
5 TO 70 THICKNESS 0.2
DEFINE MATERIAL START
ISOTROPIC CONCRETE
E 2.17185e+007
POISSON 0.17
DENSITY 23.5616
ALPHA 1e-005
DAMP 0.05
TYPE CONCRETE
STRENGTH FCU 27579
END DEFINE MATERIAL
CONSTANTS
MATERIAL CONCRETE ALL
SUPPORTS
1 2 5 7 9 11 13 15 17 19 21 23 73 TO 84 FIXED BUT MX MY MZ KFY 5e+003
MULTILINEAR SPRINGS
1 2 5 7 9 11 13 15 17 19 21 23 73 TO 83 -
84 SPRINGS 0 5e+003 1.2e-003 4.3e+003 1.4e-003 3.75e+003 -
1.6e-003 3.33e+003 1.8e-003 3e+003 2e-003 3e+003 2.2e-003 2.5e+003 -
2.4e-003 2.3e+003 2.6e-003 2.14e+003 2.8e-003 30
48 FY 120
PERFORM ANALYSIS
FINISH

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