STEP-BY-STEP TUTORIAL

SNAPBoxBeam is a family member of SNAPBridge: Bridge Analysis and Design Suite, which is used for Steel Box Girder Bridge Analysis and Design.

SNAPBoxBeam is a family member of SNAPBridge: Bridge Analysis and Design Suite developed by SAS Suite, LLC. It is a functional module which requires the SNAPBridge Basic Configuration including SNAPManager, SNAPTxtEditor and SNAP2DFrame. SNAPManager is the executable used to manage the Project Workspace. SNAPTxtEditor is a text editor for the Suite. SNAP2DFrame is a functional module for two-dimensional frame analysis.

In order to use SNAPBoxBeam, users should run SNAPManager to create a Workspace first. Then you use the Steel Box Girder command in the Designer menu or the shortcut Button in the Toolbar to launch the SNAPBoxBeam.

When starting a new problem, SNAPBoxBeam will display General Information Definition dialog box which asks you to input the basic information for the bridge. A graphic structural model will be generated when you press OK button.

After that, users must define the material properties, girder section properties, typical roadway section dimensions, load information and details information. Use the Divide Element command to modify the model and use Assign Section command to assign Girder Section to elements. Users may need to change Settings using the Settings command to select the Code etc. Then users can run the analysis and design, and display the results to check the design. If the initial trial is not good, you may have to modify the Girder Sections, Details and re-run the analysis and design.

Refer to the COMMANDS and FUNCTIONS chapter (Chapter 3) for in-depth information on the features available with SNAPBoxBeam.

This example is a three-span 100-100-100ft continuous steel box girder bridge with 2 traffic lanes taking HS20-44. The bridge has two box girders spaced at 16ft with 3ft overhang. The design criteria is as follows:

Roadway: Curb-to-curb width: 27ft. Out-to-out Width 30ft.

Design Specification: AASHTO Standard Specifications for Highway Bridges.

Design Method: Load Factor Design

Loads: (1) HS20-44 with Alternate Military Loading

Materials: Structural Steel is ASTM Grade 50. Strength of Deck Concrete is 4000psi.

The spacing of cross frames is assumed to be 25ft.

To define material properties, click on Material Properties command in Input Menu or Shortcut Menu. The Material Property Definition dialog box will appear. There are default values for the required data. The default values are ASTM Grade 50 for steel, 4000psi for concrete. Therefore, we do not need to change the values. If any of the properties is not the same as the predefined, just input the value in the approproate textbox, then click OK button.

Select Girder Sections from the Input menu or the Shortcut menu. The Girder Section Definition dialog box will appear. Here we define 3 sections:

Section 1: Positive Moment Region in Span 1 and Span3

Section 2: Negative Moment Region Near Interior Supports

Section 3: Positive Moment Region in Span 2

The dimensions of the sections are as follows:

To define roadway section, select Typical Section command in Input menu. The Typical Section Definition dialog box will appear. In the dialog box, change the Edge Width to1.5, Curb-to-Curb Width to 27.0, Overhang Width to 3, Beam Spacing to 16, Slab Thickness to 8, Haunch Width to 18, Haunch Thicknes to 2, Number of Beams to 2.

Click on OK to close the dialog box.

Select Loads command from the Input menu or Shortcut menu to have the Load Definition dialog box appear.

To define Steel Girder and Deck Slab self-weight dead load, select 1. Dead Load: Selft-Weight: Stage 1 (Non-Composite) from the load case combo box. The Dead Load: Self-Weight Multiplifier text boxes will be enabled. In the Steel Multiplifier text box, input 1.15 that means we assume 15% as miscelleneous steel percentage. Keep concrete multiplifier as 1.0. Press Add button to add this load case into the list box.

Assume 15psf construction allowance as 3N-Composite superimposed dead load. This load is equivalent to 15x27/2/1000 = 0.202 klf for each girder. To define this load:

• Select 2. Distributed Superimposed Dead Load: Stage 2 (3N-Composite) from the load case combo box. The text boxes in Superimposed Dead Load group will be enabled.
• Input the starting coordinate of 0.0 into From text box.
• Input 300 into the To text box.
• Input 0.202 into the Intensity @ 1.
• Press Add button. The load case is added.

The future wearing surface load is assumed to be 1N-Composite superimposed dead load. This load is equivalent to 20x27/2/1000 = 0.27 klf for each girder. To define this load:

• Select 3. Distributed Superimposed Dead Load: Stage 3 (1N-Composite) from the load case combo box. The text boxes in Superimposed Dead Load group will be enabled.
• Input the starting coordinate of 0.0 into From text box.
• Input 300 into the To text box.
• Input 0.27 into the Intensity @ 1.
• Press Add button. The load case is added.

The barrier weight is a 3N-Composite superimposed dead load. This load is equivalent to 335x2/2/1000 = 0.336 klf for each girder. To define this load:

• Select 2. Distributed Superimposed Dead Load: Stage 2 (3N-Composite) from the load case combo box. The text boxes in Superimposed Dead Load group will be enabled.
• Input the starting coordinate of 0.0 into From text box.
• Input 300 into the To text box.
• Input 0.336 into the Intensity @ 1.
• Press Add button. The load case is added.

To define Highway Live Load HS20-44,

• select 7. Live Load Highway from the load case combo box. The Live Load combo box will be enabled.
• In Live Load combo box, select HSxx-44. The live load multiplifier text is enabled.
• In this text box, input 20 for HS20.
• Press Add button to add this load case.

Click on OK to close the dialog box.

Select the Details command from the Input menu to define the details information. After Deails Definition dialog box appears, define the Lateral Bracing information first.

To define Transverse Stiffener information, click the Transverse Stiffener button to open the Transverse Stiffener Definition dialog box.

• Input 0.0 in the From text box, 30.0 in the To text box, and Abut. A in the Label text box. 6 in the spacing text box. This defines the transverse stiffeners spaced at 6ft near Abut. A.
• Press Add button to add this case into the list box.
• Input 70.0 in the From text box, 130.0 in the To text box, and Pier 1 in the Label text box. 6 in the spacing text box. This defines the transverse stiffeners spaced at 6ft near Pier 1.
• Press Add button to add this case into the list box.
• Input 170.0 in the From text box, 230.0 in the to text box, and Pier 2 in the Label text box. 6 in the spacing text box. This defines the transverse stiffeners spaced at 6ft near Pier 2.
• Press Add button to add this case into the list box.
• Input 270.0 in the From text box, 300.0 in the to text box, and Abut.B in the Label text box. 6 in the spacing text box. This defines the transverse stiffeners spaced at 6ft near Abut.B.
• Press Add button to add this case into the list box.

Click on OK to close the dialog box.

 To define Shear Connector information, click Shear Connector button to open Shear Connector Definition dialog box. The default is Shear Stud of 7/8" in diameter. We keep the default values. Click OK to exit the dialog box.

Note that SNAPBoxBeam supports three types of shear connectors: Shear Stud, Channel and Other.

Click OK to exit the Details Definition dialog box.

To define longitudinal stiffener at bottom flange, assume one stiffener at center of bottom flange in negative moment area. Input from 60 to 140, and 160 to 240, 1 stiffener with Is = 200 and As = 6.

Every element should be assigned a Section, otherwise the stiffness of the element not assigned will be zero, which will induces singularity in structural stiffness matrix. To assign Section to elements, follow the steps below:

• Select the element or elements using Select, Select All, or Window Select command,
• Click Assign Section command from Edit menu or Shortcut menu to open the Assign Element dialog box,
• From the list box on the Assign Section dialog box, select the Section to be assigned.
• Click on OK to close the dialog box.

In this example, assign Section1 to Element 1 to 8 and 23 to 30. Assign Section 2 to Element 9 to 12 and 19 to 22. Section 3 to Element 23 to 28.

Click on Settings command to open the Setting dialog box. Change the design method option to Load Factor Design. Keep all other seetings.

Run analysis and design by clicking Run command. A Run Progress dialog box will appear. It shows where the program is running. When the analysis finishs, click on OK button to exit the dialog box. Then you can start to look at the result file or display the results graphically.

After running the analysis and design, you can look at the results by clicking the Display Result File command. SNAPTxtEditor will be invoked to display the file. You can also edit the file, search/replace strings in the file using the Find/Replace command of SNAPTxtEditor. For more information about SNAPTxtEditor, please read SNAPTxtEditor manual. But remember, when you re-run the analysis/design and you did not save the file edited, the program will overwrite it.

In addition to look at the result file, you can look at the analysis/design results graphically. To display the results in a graphical mode, select the commands from the Display menu.

SNAPBoxBeam provides the commands to display Deflection diagram, Camber diagram, Element Force diagram, Typical Roadway Section, Girder Elevation, Framing Plan etc.

To display Deflection diagram, click Deflection command in Display menu. A dialog box appears to ask you to specify which load case to show. The following picture shows the deflection diagram of this example for Steel+Concrete Deck load case.

To display Camber diagram, click Camber command in Display menu. A dialog box appears to ask you to specify which load case to show. The following picture shows the camber diagram of this example for Steel+Concrete Deck load case.

To display Element Force diagram, click Element Forces command in Display menu. A dialog box appears to ask you to specify whether Moment or Shear to show. After you select the option and click OK, the screen will show the force diagram. The first picture shows the Factored Moment diagram of this example, and the second shows the Factored Shear diagram.

You can check your input data graphically. In the stage of structural definition, you input the dimensions of typical roadway/bridge section. To display the typical section, click Typical Section command in Display menu.

To display the Framing Plan, click Framing Plan command in Display menu.

To look at the Girder Elevation, click Girder Elevation command in Display menu. A dialog box appears, which asks you to input a number. This number is a scale factor which is used to scale the depth of the girder.

In Display menu, there is a command Structural Model which is used to switch any of the graphic screen back to Undeformed Structural Model. For example, if the screen shows Framing Plan right now, the screen will witch to Undeformed Structural Model when you click the Structural Model command.

This example is a three-span 80-100-80ft continuous steel box girder bridge with 2 traffic lanes taking HL93. The bridge has four girders spaced at 8ft with 3ft overhang. The design criteria is as follows:

Roadway: Curb-to-curb width: 27ft. Out-to-out Width 30ft.

Design Specification: AASHTO LRFD Bridge Design Specifications.

Design Method: Load and Resistance Factor Design

Loads: (1) HL93 Loading

Materials: Structural Steel is ASTM Grade 50. Strength of Deck Concrete is 4000psi.

The spacing of cross frames is assumed to be 20ft.

1. Type in Project Name: SNAPBoxBeam Test Project across Test River
2. Type in Project Number: Example02-1-1
3. Type in Comments: Example of Steel Box Girder Design by LRFD
4. Select Type of Road from the Combo box: 1. Freeways …
5. Select ADTT from the Combo box: 2. More than 2500
6. Assign ADTT Single Lane as 2500 (Default).
7. Type in Number of Design Lanes: 2
8. Type in Span Length: 80 and press Add button, 100 and Add, and 80 and Add because the bridge consists of 80-100-80ft spans.
9. Click OK to exit the dialog box. The screen will display a three span model with only three elements.
10. Select File Menu-Save As command to save the data into a file: Example.bem. Users are recommended to save your file periodocally. You will see an entry under Steel Box Girder Files in the Project Workspace. It shows the location of your saved file.

To define material properties, click on Material Properties command in Input Menu or Shortcut Menu. The Material Property Definition dialog box will appear. There are default values for the required data. The default values are ASTM Grade 50 for steel, 4000psi for concrete. Therefore, we do not need to change the values. If any of the properties is not the same as the predined, just input the value in approproate textbox, then click OK button.

Select Girder Sections from the Input menu or the Shortcut menu. The Girder Section Definition dialog box will appear. Here we define 2 sections:

Section 1: Positive Moment Region in Span 1, Span 2 and Span3

Section 2: Negative Moment Region Near Interior Supports

The web inclination slope is 1:4, which corresponds to a web inclination ratio of 0.25.

The dimensions of the sections are as follows:

To define roadway section, select Typical Section command in Input menu. The Typical Section Definition dialog box will appear. In the dialog box, change the Edge Width to1.5, Curb-to-Curb Width to 27.0, Overhang Width to 3, Girder Spacing to 16, Slab Thickness to 8, Haunch Width to 18, Haunch Thicknes to 2, Number of Beams to 2.

Click on OK to close the dialog box.

Select Loads command from the Input menu or Shortcut menu to have the Load Definition dialog box appear.

To define Steel Girder and Deck Slab self-weight dead load, select 1. Dead Load: Selft-Weight: Stage 1 (Non-Composite) from the load case combo box. The Dead Load: Self-Weight Multiplifier text boxes will be enabled. In the Steel Multiplifier text box, input 1.15 that means we assume 15% as miscelleneous steel percentage. Keep concrete multiplifier as 1.0. Press Add button to add this load case into the list box.

Assume 15psf construction allowance as 3N-Composite superimposed dead. This load will be equivalent to 15x27/2/1000 = 0.202 klf for each girder. To define this load:

• Select 2. Distributed Superimposed Dead Load: Stage 2 (3N-Composite) from the load case combo box. The text boxes in Superimposed Dead Load group will be enabled.
• Input the starting coordinate of 0.0 into From text box.
• Input 260 into the To text box.
• Input 0.202 into the Intensity @ 1.
• Press Add button. The load case is added.

The future wearing surface load is assumed to be 1N-Composite superimposed dead load. This load will be equivalent to 20x27/2/1000 = 0.27 klf for each girder. To define this load:

• Select 3. Distributed Superimposed Dead Load: Stage 3 (1N-Composite) from the load case combo box. The text boxes in Superimposed Dead Load group will be enabled.
• Input the starting coordinate of 0.0 into From text box.
• Input 260 into the To text box.
• Input 0.27 into the Intensity @ 1.
• Press Add button. The load case is added.

The barrier weight is assumed to be 3N-Composite superimposed dead load. This load will be equivalent to 335x2/2/1000 = 0.336 klf for each girder. To define this load:

• Select 2. Distributed Superimposed Dead Load: Stage 2 (3N-Composite) from the load case combo box. The text boxes in Superimposed Dead Load group will be enabled.
• Input the starting coordinate of 0.0 into From text box.
• Input 260 into the To text box.
• Input 0.336 into the Intensity @ 1.
• Press Add button. The load case is added.

To define Highway Live Load HL93,

• select 7. Live Load Highway from the load case combo box. The Live Load combo box will be enabled.
• In Live Load combo box, select L93. The live load multiplifier text is enabled.
• In this text box, input 1.0 for HL93. (Actually it does not matter).
• Press Add button to add this load case.

Click on OK to close the dialog box.

Select the Details command from the Input menu to define the details information. After Deails Definition dialog box appears, define the Lateral Bracing information first.

• Input 0.0 in the From text box, 80.0 in the to text box, 4 in the Number of Brace Spacings, and Span 1 in the Bracing Label text box. This defines the cross frames spaced at 20ft in span 1.
• Press Add button to add this case into the list box.
• Input 80.0 in the From text box, 180.0 in the to text box, 5 in the Number of Brace Spacings, and Span 2 in the Bracing Label text box. This defines the cross frames spaced at 20ft in span 2.
• Press Add button to add this case into the list box.
• Input 180.0 in the From text box, 260.0 in the to text box, 4 in the Number of Brace Spacings, and Span 3 in the Bracing Label text box. This defines the cross frames spaced at 20ft in span 3.
• Press Add button to add this case into the list box.

No transverse stiffener for this beam.

To define Shear Connector information, click Shear Connector button to open Shear Connector Definition dialog box. We keep the default values. Click OK to exit the dialog box.

To define longitudinal stiffener in bottom flange, input from 50 to 110, and from 150 to 210 for one stiffener with Is=200 and As=6.

To assign Section to elements, follow the steps below:

• Select the element or element using Select, Select All, or Window Select command,
• Click Assign Section command from Edit menu or Shortcut menu to open the Assign Element dialog box,
• From the list box on the Assign Section dialog box, select the Section to be assigned to the selected element(s),
• Click on OK to close the dialog box.

In this example, assign Section1 to Element 1 to 8, 13 to 18 and 23 to 30. Assign Section 2 to Element 9 to 12 and 19 to 22.

Click on Settings command to open the Setting dialog box. Change the design method option to Load and Resistance Factor Design. Keep all other seetings.

Run analysis and design by clicking on Run command. A Run Progress dialog box appear. It displays where the program is running. When the analysis finishs, click on OK button to exit the dialog box. Then you can start to look at the result file or display the results graphically.

After running the analysis and design, you can look at the results by clicking the Display Result File command. SNAPTxtEditor will be invoked to display the file. You can also edit the file, search/replace strings in the file using the Find/Replace command of SNAPTxtEditor. For more information about SNAPTxtEditor, please read SNAPTxtEditor manual. But remember, when you re-run the analysis/design and you did not save the file edited, the program will overwrite it.

To display Deflection diagram, click Deflection command in Display menu. A dialog box appears to ask you to specify which load case to show. The following picture shows the deflection diagram of this example for Steel+Concrete Deck load case.

To display Camber diagram, click Camber command in Display menu. A dialog box appears to ask you to specify which load case to show. The following picture shows the camber diagram of this example for Steel+Concrete Deck load case.

To display Element Force diagram, click Element Forces command in Display menu. The picture shows the Factored Moment diagram of this example.

You can check your input data graphically. In the stage of structural definition, you input the dimensions of typical roadway/bridge section. To display the typical section, click Typical Section command in Display menu.

To display the Framing Plan, click Framing Plan command in Display menu.

To look at the Framing Plan, click Girder Elevation command in Display menu. A dialog box appears, which asks you to input a number. This number is a scale factor which is used to scale the depth of the girder.

In Display menu, there is a command Structural Model which is used to switch any of the graphic screen back to Undeformed Structural Model. For example, if the screen shows Framing Plan right now, the screen will witch to Undeformed Structural Model when you click the Structural Model command.

This chapter provides two examples to demonstrate the procedures to use SNAPBoxBeam for steel box girder design. Example 1 is a three-span continuous box girder bridge designed by Load Factor Method. Example 2 is a three-span box girder bridge designed by Load and Resistance Factor Method. This Step-by-Step tutorial delivers you the general information and procedures. Please refer to Chapter 3: Commands for details of each command. If you want to know the methodology of SNAPBoxBeam, please refer to Chapter 2: Technical Summary.