WS05 Bridge Truss

NAS120v, Workshop 5, November 2010Copyright 2010 MSC.Software Corporation WS5-1

BRIDGE TRUSS

WORKSHOP 5



● Workshop Objectives● Mesh curve geometry to generate CBAR elements ● Set up CBAR orientation vector and section properties● Set up multiple load cases● View CBAR stress components in Patran


● Problem Description● The preliminary design of a steel truss bridge has been completed.

You are asked to evaluate the structural integrity of this bridge.● The truss is made from steel with E = 30 x 106 psi and n = 0.3● The 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 named bridge_truss.db 2. Create the geometry of the truss using the table on the previous page3. Set Picking preference.4. Create a mesh seed of 6 elements per curve along the bottom of

truss (Y = 0) and of 2 elements per curve for the rest of the truss (Y > 0)

5. Create a finite element mesh of 2-noded bars and equivalence the model

6. Create a material property for steel: elastic modulus = 30e6 and Poisson’s ratio = 0.3

7. Create a 1D beam physical property● Apply the isotropic material to the model● Create an I-beam with dimensions as shown on page WS5-4 ● Orient the bars so the strong axis is vertical


● Suggested Exercise Steps (Cont.)8. Create boundary conditions

● Constrain all degrees of freedom except rotation about the z-axis at the left end of the truss

● Constrain all degrees of freedom except translation along the x-axis and rotation about the z-axis at the right end of the truss.

9. Create loads.● Create 11500 lb force in the negative Y direction on the node: X = 840, Y

= 0● Create another 11500 lb force in the negative Y direction, apply this load

to the midpoint of the truss. 10. Create two load cases.

● For first load case, select the displacement constraints and the load at X = 840.

● For the second load case, select the displacement constraints and the load at the mid-span.


● Suggested Exercise Steps (Cont.)11. Run a linear static analysis with two subcases using the load cases

created in the previous step.12. Create fringe and deformation plots for both subcases. Record

maximum and minimum axial stresses, combined stresses, and deformations.

13. Examine the .f06 file. Verify that the displacement and stress results agree with the graphical results shown in Patran.


Step 1. Create New Database

a

Create a new database called bridge_truss.db:

a. Under the Home tab click the New icon in the Defaults group.

b. Enter bridge_truss as the File name.

c. Click OK.d. Select Default for Tolerance.e. Select MD Nastran as the

Analysis Code.f. Select Structural as the

Analysis Type. g. Click OK.

d

f

g

e

b c


Step 2. Create Geometry

a

b

c

Create the first point:a. Under the Geometry Tab click

XYZ in the Points group.b. Enter [0 0 0] for the Point

Coordinate List.c. Click Apply.d. Under the Home tab, click the

Point Size icon in the Misc. group.

d


Finish creating all 12 points with the data from the table below

Step 2. Create Geometry (Cont.)


b

c


Create curves to represent the truss members:

a. Under the Geometry Tab click Point in the Curves group.

b. Screen pick the bottom left point as shown.

c. Screen pick the top left point. A curve will automatically be created, if Auto Execute is checked; else click Apply.

a



a. Finish creating all 21 curves.


b

Step 3. Set Picking Preferences

Set Picking Preference:a. Preferences / Pickingb. Select Enclose entire entity

under Rectangle/Polygon Picking.

c. Click Close.

a

c


Step 4. Create Mesh Seeds

Create mesh seeds:a. Under the Meshing Tab click

Uniform in the Mesh Seeds group.

b. Enter 6 for the Number of Elements.

c. Click in the Curve List box.d. Click and drag mouse to

rectangular select the bottom of the truss.

e. Click Apply, if Auto Execute is not selected.

c

e

d

a

b


c

e

d

f

Step 4. Create Mesh Seeds

Create another mesh seed:a. Reverse the setting made in

Step 3. Select Enclose any portion of entity under Rectangle/Polygon Picking, then click Close.

b. Under the Meshing Tab click Uniform in the Mesh Seeds group.

c. Enter 2 for the Number of Elements.

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

the truss, as shown. f. Click Apply

b

a


b

c

d

e

Step 5. Create Mesh

Create a finite element mesh:a. Under the Meshing Tab click

Curve in the Meshers group.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

Step 5. Create Mesh (Cont.)

Equivalence the model:a. Under the Meshing Tab click

Equivalence in the FEM Actions group.

b. Click Apply.

a


Step 6. Create Material Properties

Create an isotropic material:a. Under the Properties tab click

Isotropic in the Isotropic group.

b. Enter steel as the Material Name.

c. Click on Input Properties.d. Enter 30e6 for Elastic

Modulus and 0.3 for Poisson Ratio.

e. Click OK. f. Click Apply.

d

e

b

c

f

a


b

f

c

d

Create element properties:a. Click Beam in the 1D

Properties group.b. Enter i_beam as the Property

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

icon.e. Select steel as the material.f. Click on the Beam Library

button.

Step 7. Create Physical Properties

d

a

e

f


a

c

d

Step 7. Create Physical Properties (Cont.)

Define the beam section: a. Enter i_section for the New

Section Name.b. Enter the appropriate values

as shown to define the beam’s dimensions.

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

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

b


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

a

b


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

Orientation.b. Click OK.


a

b

d

e

c

f

Select application region:a. Click on Select Application

Region.b. Click in the Select Members

box.c. Rectangular pick the entire

truss, as shown.d. Click Add.e. Click OK.f. Click Apply.



b

e

g

ch


Verify the beam section:a. Display : Load/BC/Element

Props….b. Set Beam Display to 3D:Full-

Span.c. Click Apply.d. Right-click in the viewport

and select Viewport Display > Smooth Shaded from the context menu.

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

f. Right-click in the viewport and select Model Orientation > Orthographic > Front View from the context menu.

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

h. Click Apply again.

a

f

d


b

d

ec

Step 8. Create Boundary Conditions

Create a boundary condition:a. Under the Loads/BCs Tab

click Displacement Constraint in the Nodal group.

b. Enter left_side as the New Set Name.

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

Translations and <0, 0, > for Rotations.

e. Click OK.

a


e

c

d

Apply the boundary condition:a. Click on Select Application

Region….b. Select the bottom left point

as the application region.c. Click Add.d. Click OK. e. Click Apply.

Step 8. Create Boundary Conditions (Cont.)

a

b


b

c

d

e


a

Create another boundary condition:

a. Click Displacement Constraint in the Nodal group again.

b. Enter right_side as the New Set Name.

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

and <0,0, > for Rotations. e. Click OK.


a

b

c

Apply the boundary condition:a. Click on Select Application

Region.b. Select the bottom right point

as the application region.c. Click Add.d. Click OK. e. Click Apply.


d

e


c

b

d

e

Step 9. Create Loads

Create the mid span load:a. Click Force in the Nodal

group.b. Enter mid_span_load as the

New Set Name.c. Click on Input Data.d. Enter <0 -11500 0> for Force. e. Click OK.

a


a

d

e

f

b

Step 9. Create Loads (Cont.)

Apply the mid span load:a. Click on 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.

c


b

c


a

d

e

Create the truss joint load:a. Click Force in the Nodal

group again. b. Enter truss_joint_load as

the New Set Name.c. Click on Input Data.d. Enter <0 -11500 0> for Force. e. Click OK.


a

b

d

e

f

Apply the load:a. Click on Select Application

Region.b. Set the geometry filter to

Geometry.c. For Application Region,

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

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


c

c


b

c

d

e

f

Step 10. Set up Load Cases

Create a load case:a. Click Create Load Case

under Load Cases.b. Enter mid_span as the Load

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

Displ_right_side, and Force_mid_span_load to add them to the Load Case.

e. Click OK. f. Click Apply.

a


a

b

c

d

e

Step 10. Set up Load Cases (Cont.)

Create another load case:a. Enter truss_joint as the

Load Case Name.b. Click on Input Data.c. Click on Displ_left_side,

Displ_right_side, and Force_truss_joint_load to add them to the Load Case.(if mid_span_load is still an assigned load / BC, click, and remove selected row)

d. Click OK. e. Click Apply.


b

Step 11. Run Linear Static Analysis

Analyze the model:a. Under the Analysis tab click

Entire Model in the Analyze group.

b. Click on Solution Type.c. Select Linear Static as the

Solution Type. d. Click OK.

a

c

d


a

c

b

d

e

Step 11. Run Linear Static Analysis (Cont.)

Analyze the model:a. Click on Subcase Select.b. Select Unselect All to

deselect any existing Subcase.

c. Click on mid_span and truss_joint to add them to the Subcases Selected list.

d. Click OK.e. Click Apply.


Step 11. Run Linear Static Analysis (Cont.)

Review the Nastran input file.a. Open the file

bridge_truss.bdf b. Review the two subcases.


b

c

e

d

Step 12. Plot Displacements and Stresses

a

Attach the results file:a. Click XDB in the Access

Results group.b. Click on Select Results File.c. Select the results file,

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


d

e

b

c

Step 12. Plot Displacements and Stresses (Cont.)

Create a deformation plot for the mid span result case:

a. Under the Results tab, click Deformation in the Result Plots group.

b. Select the mid_span Result Case.

c. Select Displacements, Translational as the Deformation Result.

d. Check Animate. e. Click Apply.f. Record the maximum

deformation.g. Click Pause Animation and

Refresh Results Tools.Max Deformation = ____________

a


b

c

d

f

g


Create a Fringe Plot of X Component Axial Stress:

a. Click Fringe in the Result Plots group.


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.

a

e



View the results:a. Record the maximum and

minimum X component axial stress.

Max X Axial Stress = _________________Min X Axial Stress = __________________


b

c

d


a

Create Fringe Plots of maximum and minimum combined bar stresses:

a. Click on the Select Results Icon.


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

d. Click Apply.e. Record the Maximum

combined stress. Max Stress= _______

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


c

d

b

f


a

e

Create a deformation plot for the truss joint result case:

a. Click Deformation in the Result Plots group.

b. Select the truss_joint Result Case.

c. Select Displacements, Translational as the Deformation Result.

d. Check Animate.e. Right-click in the viewport

and select Reset Graphics from the context menu.

f. Click Apply.g. Record the maximum

deformation.h. Click Stop Animation and

Refresh Results Tools.Max Deformation = ____________



f

a

b

c

d

e

g

Create a Fringe Plot of X Component Axial Stress:

a. Click Fringe in the Result Plots group.

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.



View the results:a. Record the maximum and

minimum X component axial stress.

Max X Axial Stress = _________________Min X Axial Stress = __________________


a

b


Create Fringe Plots of maximum and minimum combined bar stresses:

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

b. Click Apply.c. Record the Maximum

combined stress.Max Stress= _______

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


Step 13. Examine the .f06 File

Examine the .f06 filea. 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.

This completes the workshop.


Documents

WS05 Bridge Truss