workshop 6 bridge truss - fsb online · bridge truss. ws6-2 nas120 ... zlearn to view the different...

WORKSHOP 6

BRIDGE TRUSS


Workshop ObjectivesLearn to mesh line geometry to generate CBAR elements

Become familiar with setting up the CBAR orientation vector and section properties

Learn to set up multiple load cases

Learn to view the different CBAR stress components in Patran


Problem DescriptionThe preliminary design of a steel truss bridge has just been finished. You are asked to evaluate the structural integrity ofthis bridge.The truss is made from steel with E = 30 x 106 psi and n = 0.3The truss members are I-beams with H = 18 in, W = 12 in, Tf = 0.5 in, and Tw = 0.5 in The bridge needs to be able to support a 23,000 lb truck traveling over it. The truck weight is supported by two planar trusses. Model one planar truss with half the truck weight applied to it.One end of the truss is pinned while the other end is free to slide horizontally.


11,500 lb

(Subcase 1)

x

y

11,500 lb

(Subcase 2)


Suggested Exercise Steps1. Create a new database. 2. Create a geometry model of the truss using the table on the previous

page. 3. Use Mesh Seeds to define the mesh density.4. Create a finite element mesh. 5. Define material properties. 6. Create Physical Properties using the beam library. 7. Create boundary conditions.8. Create loads.9. Set up load cases.10. Run the finite element analysis using MSC.Nastran.11. Review the Nastran input file.12. Plot displacements and stresses.13. Review the .f06 file.


b c

d

e

f

g

Step 1. Create New Database

Create a new database called bridge_truss.db

a. File / New.b. Enter bridge_truss as

the file name.c. Click OK.d. Choose Default

Tolerance.e. Select MSC.Nastran as

the Analysis Code.f. Select Structural as the

Analysis Type. g. Click OK.

a


Step 2. Create Geometry

Create the first pointa. Geometry: Create / Point /

XYZ.b. Enter [0 0 0] for the Point

Coordinate List.c. Click Apply.d. Turn Point size on.

a

b

c

d



Finish creating all 12 points.



Create curves to represent the truss members

a. Geometry: Create / Curve / Point.

b. Screen pick the bottom left point as shown.

c. Screen pick the top left point. A curve is automatically created because Auto Execute is checked.

a

b

c



Finish creating all 21 curves.


Step 3. Create Mesh Seeds

Create a uniform mesh seeda. Preferences/Picking… Set

rectangular/polygon picking to Enclose Centroid.

b. Elements: Create / Mesh Seed / Uniform.

c. Enter 6 for the Number of Elements.

d. Click in the Curve List box.e. Rectangular pick the

bottom of the truss.

b

c

d

e

a


Step 3. Create Mesh Seeds

Create another mesh seeda. Elements: Create / Mesh

Seed / Uniform.b. Enter 2 for the Number of

Elements.c. Click in the Curve List

box. d. Rectangular pick the rest

of the truss, as shown.

a

b

c

d


Step 4. Create Mesh

Create a finite element mesha. Elements: Create / Mesh /

Curve.b. Set Topology to Bar2.c. Click in the Curve List box.d. Rectangular pick all of the

curves as shown.e. Click Apply.

a

b

c

d

e


Step 4. Create Mesh

Equivalence the modela. Elements: Equivalence /

All / Tolerance Cube.b. Click Apply.

a

b


Step 5. Create Material Properties

Create an isotropic materiala. Materials: Create / Isotropic

/ Manual Input.b. Enter steel as the Material

Name.c. Click Input Properties.d. Enter 30e6 for the elastic

modulus and 0.3 for the Poisson Ratio.

e. Click OK. f. Click Apply.

d

e

a

b

c

f


Step 6. Create Physical Properties

Create element propertiesa. Properties: Create / 1D /

Beam.b. Enter i_beam as the

Property Set Name.c. Click Input Properties.d. Click on the Select

Material Icon.e. Select steel as the

material.f. Click on the Beam Library

button.

a

b

fc

d

e



Define the beam section a. Enter i_section for the

New Section Name.b. Enter the appropriate

values to define the beam’s dimensions .

c. Click Calculate/Displayto view the beam section and its section properties.

d. After verifying that the section is correct, Click OK.

a

b

c

d



Define the bar orientation a. Enter <1 2 0> for the

Bar Orientation.b. Click OK.

Note:Any vector in the XY plane that is not parallel to any truss member would work as well.

a

b



Select application regiona. Click in the Select

Members box.b. Rectangular pick the

entire truss as shown.c. Click Add.d. Click Apply.

b

a

c

d



Verify the beam sectiona. Display: Load/BC

/ Element Props.b. Set Beam Display

to 3D:FullSpan.c. Click Apply.d. Shade the model.e. Rotate the model

and zoom in to verify that the I-beams are oriented correctly.

f. Return to the front view.

g. Set Beam Display back to 1D:Line.

h. Click Apply.

a

d

e

f

b g

c h


d

e

Step 7. Create Boundary Conditions

Create a boundary conditiona. Loads/BCs: Create /

Displacement / Nodal.b. Enter left_side as the New

Set Name.c. Click Input Data.d. Enter <0 0 0> for

Translations and <0,0, > for Rotations.

e. Click OK.

a

b

c



Apply the boundary conditiona. Reset graphics.b. Click Select

Application Region.c. Select the bottom left

point as the application region.

d. Click Add.e. Click OK. f. Click Apply.

be

f

c d

a



Create another boundary condition

a. Loads/BCs: Create / Displacement / Nodal.

b. Enter right_side as the New Set Name.

c. Click Input Data.d. Enter < ,0,0> for

Translations and <0,0, > for Rotations.

e. Click OK.

d

e

a

b

c



Apply the boundary conditiona. Click Select

Application Region.b. Select the bottom

right point as the application region.

c. Click Add.d. Click OK. e. Click Apply.

b c

da

e


Step 8. Create Loads

Create the mid span loada. Loads/BCs: Create / Force /

Nodal.b. Enter mid_span_load as

the New Set Name.c. Click Input Data.d. Enter <0 –11500 0> for the

Force.e. Click OK.

d

ec

b

a


Apply the mid span loada. Click Select Application

Region.b. Set the geometry filter to

FEM.c. For the application region

select the node in the middle of the span to the right of the center, as shown.

d. Click Add.e. Click OK.f. Click Apply.


a

cd

e

f

b



Create the truss joint loada. Loads/BCs: Create / Force /

Nodal.b. Enter truss_joint_load as

the New Set Name.c. Click Input Data.d. Enter <0 –11500 0> for the

Force.e. Click OK.

d

e

a

b

c



Apply the loada. Click Select Application

Region.b. Set the geometry filter to

Geometry.c. For the application

region select the point at the center of the bridge, as shown.

d. Click Add.e. Click OK.f. Click Apply.

b

c d

e

f

a


Step 9. Set Up Load Cases

Create a load casea. Load Cases: Create.b. Enter mid_span as the

Load Case Name.c. Click Input Data…d. Click on Displ_left_side,

Displ_right_side, andForce_mid_span_load to add them to the Load Case.

e. Click OK.f. Click Apply.

d

e

a

b

c

f


Step 9. Set Up Load Cases

Create another load casea. Load Cases: Create.b. Enter truss_joint as the

Load Case Name.c. Click Input Data…d. Click on Displ_left_side,

Displ_right_side, andForce_truss_joint_load to add them to the Load Case.

e. Click OK.f. Click Apply.

d

e

a

b

c

f


Step 10. Run Linear Static Analysis

Choose the analysis typea. Analysis: Analyze / Entire

Model / Full Run.b. Click Solution Type.c. Choose Linear Static.d. Click OK.

d

c

a

b


Step 10. Run Linear Static Analysis

Analyze the modela. Analysis: Analyze / Entire

Model / Full Run.b. Click Subcase Select.c. Click Unselect All.d. Click on mid_span and

truss_joint to add them to the Subcases Selected list.

e. Click OK.f. Click Apply. c

d

e

a

b

f


Step 11. Review the Nastran Input File

Review the Nastran input file.a. Open the file

bridge_truss.bdfb. Review the two subcases.


Step 12. Plot Displacements and Stresses

Attach the results filea. Analysis: Access Results /

Attach XDB / Result Entities.

b. Click Select Results File.c. Choose the results file

bridge_truss.xdb.d. Click OK. e. Click Apply.

a

b

c

e

d



Create a deformation plot for the mid span result case

a. Results: Create / Deformation.

b. Select the Mid Span Result Case.

c. Select Displacements, Translational as the Deformation Result.

d. Check Animate.e. Click Apply.f. Click Stop Animation

and Refresh Results Tools.

Max Deformation =

____________

a

c

d

e

b



Create a Fringe Plot of X Component Axial Stress

a. Results: Create / Fringe.

b. Select the Mid Span Result Case.

c. Select Bar Stresses, Axial as the Fringe Result.

d. Select X Componentas the Fringe Result Quantity.

e. Click on the Plot Options icon.

f. Set the Averaging Definition Domain to None.

g. Click Apply.

b

c

d

a

e

f

g



View the resultsa. Record the maximum

and minimum X component axial stress.

Max X Axial Stress =

_________________

Min X Axial Stress =

__________________



Create Fringe Plots of maximum and minimum combined bar stresses

a. Results: Create / Fringe.b. Click on Select Results

icon.c. Select the Mid Span

Result Case.d. Select Bar Stresses,

Maximum Combined as the Fringe Result.

e. Click Apply.f. Record the Maximum

combined stress. Max Stress= _______

g. Repeat the procedure with Bar Stresses, Minimum Combined as the Fringe Result and record the Minimum Stress. Min Stress = _______

a

b

c

d

e



Create a deformation plot for the truss joint result case

a. Reset graphicsb. Results: Create /

Deformation.c. Select the Truss Joint

Result Case.d. Select Displacements,

Translational as the Deformation Result.

e. Check Animate.f. Click Apply.g. Click Stop Animation

and Refresh Results Tools.

Max Deformation =

____________

b

d

a

c

f

e



Create a Fringe Plot of X Component Axial Stress

a. Results: Create / Fringe.b. Select the Truss Joint

Result Case.c. Select Bar Stresses,

Axial as the Fringe Result.

d. Select X Component as the Fringe Result Quantity.

e. Click on the Plot Options icon.

f. Set the Averaging Definition Domain to None.

g. Click Apply.

b

c

d

a

e

f

g



View the resultsa. Record the maximum

and minimum X component axial stress.

Max X Axial Stress =

_________________

Min X Axial Stress =

__________________



Create Fringe Plots of maximum and minimum combined bar stresses

a. Results: Create / Fringe.

b. Click on Select Results icon.

c. Select the Truss Joint Result Case.

d. Select Bar Stresses, Maximum Combined as the Fringe Result.

e. Click Apply.f. Record the Maximum

combined stress. Max Stress= _______

g. Repeat the procedure with Bar Stresses, Minimum Combined as the Fringe Result and record the Minimum Stress.Min Stress = _______

a

b

c

d

e


Step 13. Examine the .f06 File

Examine the .f06 file

a. Open the directory in which your database is saved.

b. Find the file titled bridge_truss.f06 .

c. Open this file with any text editor.

d. Verify that the displacement and stress results agree with the graphical results shown in Patran.

workshop 6 bridge truss - fsb online · bridge truss. ws6-2 nas120 ... zlearn to view the different...

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