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Can someone upload the code required for recording the global stiffness matrix of the model? Now, I am trying to match the SAP2000 Model and OpenSees Model and I got into trouble for obtaining global stiffness matrix for OpenSees Model.

Because the zero - length elements exist in SAP2000 are defined in one node. In other words, there is no need for defining two nodes at the same coordinates in order to assign zero - length elements in SAP2000. Ans as you know, I have to constitute two nodes for zero - length element in OpenSees. How can I overcome this problem?

Hi Vesna,

Thank for your reply. I checked the properties determined by SAP2000 and those I define in OpenSees input. There is no difference between them, however, the OpenSees Model has 60 degree - of - freedom due to the assignment of zero - length elements and each node which the zero - length elements are assigned carries the half of mass of related 1 m pipe segment. Conversely, SAP2000 Model has 31 degree - of - freedom including the supports and each node carries whole mass beloging to related 1 m pipe segment. Is this the reason of incompatibility between OpenSees and SAP2000 in terms of modal analysis?

Hi,

I am trying to perform an modal analysis for my buried steel pipeline project. I use zero-length elements to model the soil surrounding the buried steel pipeline. The mesh size for this pipeline is assumed as 1 m and the mass of each 1 m pipe segment are assigned to the related nodes that are combined with each other by means of zero - length element. In order to assign the mass of 1 m pipe segment to the nodes, I divide the mass value by 2 and assign to related nodes having same coordinates so that I can simulate the model constituted in SAP 2000. However, the eigen value given by OpenSees is imcompatible with that given by SAP 2000. Here is my code;

" # OpenSees Model For Modal Analysis Of Buried Steel Pipeline

#Units: Length (m), Mass (Nsec^2/m), Time (Sec)

wipe; # Clear The All Objects, Recordes, Constraints etc. In The Domain Object
file mkdir Output; # Constitute The File Whose Name Output For Outputs

# Define The Model Builder

model basic -ndm 3 -ndf 6; # Three Dimensional System Which Has 6 - Degree - Of - Freedom

# Define The Node Coordinates

node 1 0.0 0.0 0.0;
node 2 1 0.0 0.0;
node 3 1 0.0 0.0;
node 4 2 0.0 0.0;
node 5 2 0.0 0.0;
node 6 3 0.0 0.0;
node 7 3 0.0 0.0;
node 8 4 0.0 0.0;
node 9 4 0.0 0.0;
node 10 5 0.0 0.0;
node 11 5 0.0 0.0;
node 12 6 0.0 0.0;
node 13 6 0.0 0.0;
node 14 7 0.0 0.0;
node 15 7 0.0 0.0;
node 16 8 0.0 0.0;
node 17 8 0.0 0.0;
node 18 9 0.0 0.0;
node 19 9 0.0 0.0;
node 20 10 0.0 0.0;
node 21 10 0.0 0.0;
node 22 11 0.0 0.0;
node 23 11 0.0 0.0;
node 24 12 0.0 0.0;
node 25 12 0.0 0.0;
node 26 13 0.0 0.0;
node 27 13 0.0 0.0;
node 28 14 0.0 0.0;
node 29 14 0.0 0.0;
node 30 15 0.0 0.0;
node 31 15 0.0 0.0;
node 32 16 0.0 0.0;
node 33 16 0.0 0.0;
node 34 17 0.0 0.0;
node 35 17 0.0 0.0;
node 36 18 0.0 0.0;
node 37 18 0.0 0.0;
node 38 19 0.0 0.0;
node 39 19 0.0 0.0;
node 40 20 0.0 0.0;
node 41 20 0.0 0.0;
node 42 21 0.0 0.0;
node 43 21 0.0 0.0;
node 44 22 0.0 0.0;
node 45 22 0.0 0.0;
node 46 23 0.0 0.0;
node 47 23 0.0 0.0;
node 48 24 0.0 0.0;
node 49 24 0.0 0.0;
node 50 25 0.0 0.0;
node 51 25 0.0 0.0;
node 52 26 0.0 0.0;
node 53 26 0.0 0.0;
node 54 27 0.0 0.0;
node 55 27 0.0 0.0;
node 56 28 0.0 0.0;
node 57 28 0.0 0.0;
node 58 29 0.0 0.0;
node 59 29 0.0 0.0;
node 60 30 0.0 0.0;

# Define The Fixities

fix 1 1 1 1 0 0 0;
fix 2 0 0 0 1 1 1;
fix 3 0 0 0 1 1 1;
fix 4 0 0 0 1 1 1;
fix 5 0 0 0 1 1 1;
fix 6 0 0 0 1 1 1;
fix 7 0 0 0 1 1 1;
fix 8 0 0 0 1 1 1;
fix 9 0 0 0 1 1 1;
fix 10 0 0 0 1 1 1;
fix 11 0 0 0 1 1 1;
fix 12 0 0 0 1 1 1;
fix 13 0 0 0 1 1 1;
fix 14 0 0 0 1 1 1;
fix 15 0 0 0 1 1 1;
fix 16 0 0 0 1 1 1;
fix 17 0 0 0 1 1 1;
fix 18 0 0 0 1 1 1;
fix 19 0 0 0 1 1 1;
fix 20 0 0 0 1 1 1;
fix 21 0 0 0 1 1 1;
fix 22 0 0 0 1 1 1;
fix 23 0 0 0 1 1 1;
fix 24 0 0 0 1 1 1;
fix 25 0 0 0 1 1 1;
fix 26 0 0 0 1 1 1;
fix 27 0 0 0 1 1 1;
fix 28 0 0 0 1 1 1;
fix 29 0 0 0 1 1 1;
fix 30 0 0 0 1 1 1;
fix 31 0 0 0 1 1 1;
fix 32 0 0 0 1 1 1;
fix 33 0 0 0 1 1 1;
fix 34 0 0 0 1 1 1;
fix 35 0 0 0 1 1 1;
fix 36 0 0 0 1 1 1;
fix 37 0 0 0 1 1 1;
fix 38 0 0 0 1 1 1;
fix 39 0 0 0 1 1 1;
fix 40 0 0 0 1 1 1;
fix 41 0 0 0 1 1 1;
fix 42 0 0 0 1 1 1;
fix 43 0 0 0 1 1 1;
fix 44 0 0 0 1 1 1;
fix 45 0 0 0 1 1 1;
fix 46 0 0 0 1 1 1;
fix 47 0 0 0 1 1 1;
fix 48 0 0 0 1 1 1;
fix 49 0 0 0 1 1 1;
fix 50 0 0 0 1 1 1;
fix 51 0 0 0 1 1 1;
fix 52 0 0 0 1 1 1;
fix 53 0 0 0 1 1 1;
fix 54 0 0 0 1 1 1;
fix 55 0 0 0 1 1 1;
fix 56 0 0 0 1 1 1;
fix 57 0 0 0 1 1 1;
fix 58 0 0 0 1 1 1;
fix 59 0 0 0 1 1 1;
fix 60 0 1 1 0 0 0;

# Define The Mass Values For Each Node

mass 2 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 3 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 4 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 5 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 6 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 7 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 8 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 9 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 10 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 11 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 12 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 13 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 14 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 15 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 16 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 17 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 18 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 19 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 20 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 21 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 22 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 23 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 24 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 25 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 26 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 27 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 28 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 29 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 30 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 31 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 32 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 33 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 34 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 35 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 36 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 37 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 38 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 39 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 40 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 41 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 42 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 43 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 44 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 45 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 46 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 47 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 48 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 49 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 50 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 51 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 52 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 53 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 54 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 55 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 56 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 57 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 58 5.907582 5.907582 5.907582 0.0 0.0 0.0;
mass 59 5.907582 5.907582 5.907582 0.0 0.0 0.0;

# Define The Force - Deformation Relationship For Soil Springs

uniaxialMaterial ElasticPP 1 472959.528571 0.003000 -0.003000 0.0; # Force - Deformation Relationship For Axial Soil Springs
uniaxialMaterial ElasticPP 2 984545.454545 0.003000 0.0 0.0; # Force - Deformation Relationship For Uplift Vertical Soil Springs
uniaxialMaterial ElasticPP 3 7244248.439845 0.0 -0.003000 0.0; # Force - Deformation Relationship For Vertical Downward Soil Springs
uniaxialMaterial ElasticPP 4 1132458.093238 0.008929 -0.008929 0.0; # Force - Deformation Relationship For Transverse Soil Springs
uniaxialMaterial Parallel 5 2 3; # Force - Deformation Relationship For Vertical Soil Springs

# Assign Transformation Function To The Buried Segmented Steel Pipe

geomTransf Linear 1 0.0 -1.0 0.0;
geomTransf Linear 2 0.0 -1.0 0.0;
geomTransf Linear 3 0.0 -1.0 0.0;
geomTransf Linear 4 0.0 -1.0 0.0;
geomTransf Linear 5 0.0 -1.0 0.0;
geomTransf Linear 6 0.0 -1.0 0.0;
geomTransf Linear 7 0.0 -1.0 0.0;
geomTransf Linear 8 0.0 -1.0 0.0;
geomTransf Linear 9 0.0 -1.0 0.0;
geomTransf Linear 10 0.0 -1.0 0.0;
geomTransf Linear 11 0.0 -1.0 0.0;
geomTransf Linear 12 0.0 -1.0 0.0;
geomTransf Linear 13 0.0 -1.0 0.0;
geomTransf Linear 14 0.0 -1.0 0.0;
geomTransf Linear 15 0.0 -1.0 0.0;
geomTransf Linear 16 0.0 -1.0 0.0;
geomTransf Linear 17 0.0 -1.0 0.0;
geomTransf Linear 18 0.0 -1.0 0.0;
geomTransf Linear 19 0.0 -1.0 0.0;
geomTransf Linear 20 0.0 -1.0 0.0;
geomTransf Linear 21 0.0 -1.0 0.0;
geomTransf Linear 22 0.0 -1.0 0.0;
geomTransf Linear 23 0.0 -1.0 0.0;
geomTransf Linear 24 0.0 -1.0 0.0;
geomTransf Linear 25 0.0 -1.0 0.0;
geomTransf Linear 26 0.0 -1.0 0.0;
geomTransf Linear 27 0.0 -1.0 0.0;
geomTransf Linear 28 0.0 -1.0 0.0;
geomTransf Linear 29 0.0 -1.0 0.0;
geomTransf Linear 30 0.0 -1.0 0.0;

# Assign The Buried Segmented Steel Pipe Materials

element elasticBeamColumn 1 1 2 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 1;
element elasticBeamColumn 2 3 4 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 2;
element elasticBeamColumn 3 5 6 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 3;
element elasticBeamColumn 4 7 8 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 4;
element elasticBeamColumn 5 9 10 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 5;
element elasticBeamColumn 6 11 12 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 6;
element elasticBeamColumn 7 13 14 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 7;
element elasticBeamColumn 8 15 16 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 8;
element elasticBeamColumn 9 17 18 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 9;
element elasticBeamColumn 10 19 20 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 10;
element elasticBeamColumn 11 21 22 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 11;
element elasticBeamColumn 12 23 24 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 12;
element elasticBeamColumn 13 25 26 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 13;
element elasticBeamColumn 14 27 28 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 14;
element elasticBeamColumn 15 29 30 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 15;
element elasticBeamColumn 16 31 32 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 16;
element elasticBeamColumn 17 33 34 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 17;
element elasticBeamColumn 18 35 36 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 18;
element elasticBeamColumn 19 37 38 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 19;
element elasticBeamColumn 20 39 40 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 20;
element elasticBeamColumn 21 41 42 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 21;
element elasticBeamColumn 22 43 44 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 22;
element elasticBeamColumn 23 45 46 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 23;
element elasticBeamColumn 24 47 48 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 24;
element elasticBeamColumn 25 49 50 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 25;
element elasticBeamColumn 26 51 52 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 26;
element elasticBeamColumn 27 53 54 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 27;
element elasticBeamColumn 28 55 56 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 28;
element elasticBeamColumn 29 57 58 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 29;
element elasticBeamColumn 30 59 60 0.001509 200000000000.000000 76923076923.076920 0.000005 0.000002 0.000002 30;

# Assign The Zero - Length Elements For Soil Springs
element zeroLength 31 2 3 -mat 1 4 5 -dir 1 2 3;
element zeroLength 32 4 5 -mat 1 4 5 -dir 1 2 3;
element zeroLength 33 6 7 -mat 1 4 5 -dir 1 2 3;
element zeroLength 34 8 9 -mat 1 4 5 -dir 1 2 3;
element zeroLength 35 10 11 -mat 1 4 5 -dir 1 2 3;
element zeroLength 36 12 13 -mat 1 4 5 -dir 1 2 3;
element zeroLength 37 14 15 -mat 1 4 5 -dir 1 2 3;
element zeroLength 38 16 17 -mat 1 4 5 -dir 1 2 3;
element zeroLength 39 18 19 -mat 1 4 5 -dir 1 2 3;
element zeroLength 40 20 21 -mat 1 4 5 -dir 1 2 3;
element zeroLength 41 22 23 -mat 1 4 5 -dir 1 2 3;
element zeroLength 42 24 25 -mat 1 4 5 -dir 1 2 3;
element zeroLength 43 26 27 -mat 1 4 5 -dir 1 2 3;
element zeroLength 44 28 29 -mat 1 4 5 -dir 1 2 3;
element zeroLength 45 30 31 -mat 1 4 5 -dir 1 2 3;
element zeroLength 46 32 33 -mat 1 4 5 -dir 1 2 3;
element zeroLength 47 34 35 -mat 1 4 5 -dir 1 2 3;
element zeroLength 48 36 37 -mat 1 4 5 -dir 1 2 3;
element zeroLength 49 38 39 -mat 1 4 5 -dir 1 2 3;
element zeroLength 50 40 41 -mat 1 4 5 -dir 1 2 3;
element zeroLength 51 42 43 -mat 1 4 5 -dir 1 2 3;
element zeroLength 52 44 45 -mat 1 4 5 -dir 1 2 3;
element zeroLength 53 46 47 -mat 1 4 5 -dir 1 2 3;
element zeroLength 54 48 49 -mat 1 4 5 -dir 1 2 3;
element zeroLength 55 50 51 -mat 1 4 5 -dir 1 2 3;
element zeroLength 56 52 53 -mat 1 4 5 -dir 1 2 3;
element zeroLength 57 54 55 -mat 1 4 5 -dir 1 2 3;
element zeroLength 58 56 57 -mat 1 4 5 -dir 1 2 3;
element zeroLength 59 58 59 -mat 1 4 5 -dir 1 2 3;

puts "eigen value: [eigen frequency 1]" "

How can I solve this problem?