# SurfaceLoad Element

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This command is used to construct a SurfaceLoad element object.

 element SurfaceLoad \$eleTag \$iNode \$jNode \$kNode \$lNode \$p

 \$eleTag unique integer tag identifying element object \$iNode \$jNode \$kNode \$lNode the four nodes defining the element, input in counterclockwise order (-ndm 3 -ndf 3) \$p applied pressure loading normal to the surface, outward is positive, inward is negative

The SurfaceLoad element is a four-node element which can be used to apply surface pressure loading to 3D brick elements. The SurfaceLoad element applies energetically-conjugate forces corresponding to the input scalar pressure to the nodes associated with the element. As these nodes are shared with a 3D brick element, the appropriate nodal loads are therefore applied to the brick.

NOTES:

1. There are no valid ElementalRecorder queries for the SurfaceLoad element. Its sole purpose is to apply nodal forces to the adjacent brick element.
2. The pressure loading from the SurfaceLoad element can be applied in a load pattern. See the analysis example below.

EXAMPLES:

SurfaceLoad element definition with element tag 1, nodes 1, 2, 3, and 4, and pressure of -10.0

```element SurfaceLoad 1  1 2 3 4  -10.0
```

Code Developed by: Chris McGann, Pedro Arduino, & Peter Mackenzie-Helnwein, at the University of Washington

EXAMPLE ANALYSIS:

The example input file below involves applying a compressive 0.1 kPa loading to a four-element mesh of brick elements. The applied loading is increased linearly over the first 0.1 seconds of pseudo-time, then held constant.

```wipe

model BasicBuilder -ndm 3 -ndf 3

# nodes
node  1  0.0 0.0 6.0
node  2  3.0 0.0 6.0
node  3  6.0 0.0 6.0
node  4  0.0 0.0 3.0
node  5  3.0 0.0 3.0
node  6  6.0 0.0 3.0
node  7  0.0 0.0 0.0
node  8  3.0 0.0 0.0
node  9  6.0 0.0 0.0
node 10  0.0 3.0 6.0
node 11  3.0 3.0 6.0
node 12  6.0 3.0 6.0
node 13  0.0 3.0 3.0
node 14  3.0 3.0 3.0
node 15  6.0 3.0 3.0
node 16  0.0 3.0 0.0
node 17  3.0 3.0 0.0
node 18  6.0 3.0 0.0

# boundary conditions
fix  1  1 1 1
fix  2  1 1 1
fix  3  1 1 1
fix  4  1 1 1
fix  5  1 1 1
fix  6  1 1 1
fix  7  1 1 1
fix  8  1 1 1
fix  9  1 1 1

# material
nDMaterial ElasticIsotropic 1 25000.0 0.0

# brick elements
element SSPbrick 1  1 2 5 4 10 11 14 13 1
element SSPbrick 2  2 3 6 5 11 12 15 14 1
element SSPbrick 3  4 5 8 7 13 14 17 16 1
element SSPbrick 4  5 6 9 8 14 15 18 17 1

# surface load elements
element SurfaceLoad 5  10 11 14 13  -0.1
element SurfaceLoad 6  11 12 15 14  -0.1
element SurfaceLoad 7  13 14 17 16  -0.1
element SurfaceLoad 8  14 15 18 17  -0.1

# recorders
recorder Node -file displacement.out -time -nodeRange 1 18 -dof 2 disp
recorder Node -file reactions.out    -time -nodeRange 1 18 -dof 2 reaction
recorder Element -file stress.out    -time -eleRange  1 4  stress

# load pattern
pattern Plain 1 {Series -time {0 0.1 10000} -values {0 1 1} -factor 1} {
eleLoad -ele 5 -type -surfaceLoad
eleLoad -ele 6 -type -surfaceLoad
eleLoad -ele 7 -type -surfaceLoad
eleLoad -ele 8 -type -surfaceLoad
}

# analysis
constraints Transformation
test        NormDispIncr 1e-5 50 1
algorithm   Newton
numberer    Plain
system      SparseSPD
integrator  LoadControl 0.01
analysis    Static

analyze    105

wipe
```