sap seminar - session 01 - modelling a truss

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SAP2000 SeminarSession 1Modelling a 3D Truss Structure

By Alden Paul Balili, MSCEDRBENGS, DLSU

SAP2000 Program

• Made by Computers and Structures, Inc. (CSI)• General FEM Program for different structures!• Great Program!

Congratulations! You chose the right program

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Why SAP2000?

• Quick Modeling of Structures• Quick Generation of Loads• Easy processing of output• Easy to learn!

Modeling is quick and easy with SAP2000!

Why SAP2000?

• Structure can be modelled as per actual geometry!

• Through right modelling practices, dummy/fictitious members are no longer necessary!

Modeling is quick and easy with SAP2000!

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SAP2000 Models Done - Highlights

• Arch Bridges

Waiwhakaiho Bridge in New Zealand


• Network Arch Bridges

Makira Arch in Solomon Islands

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• Signage


• Stadium

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• Multistory Building


• 3D Truss System

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• Segmental Bridges

Why Model Entire Structure?

• Easy export to BIM software• Errors from transfer of loads from one

component to the other minimized (ex: Roof to building frame)

• Could capture actual behaviour easily.

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Why Model Entire Structure?

• Easy to optimize. • In SAP2000, there are enough tools available to

model the entire structure

The SAP2000 Interface

Main Windows2 Windows are ok for large monitorsFor small ones, it is recommended just to close the other window

Top Buttons

Sid

e B

utt

ons

Menu

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The Sample StructureSteel PropertiesFy = 248 MpaE = 200000 MpaUnit Wt = 77 kN/m3

Loads NSCP2010/ASCE7-05 Wind Loads

The Sample Structure: Key Dimensions

7.5m

2.8m 4.0m 4.0m4.0m 4.0m 4.0m 4.0m4.0m 2.8m4.0m 7.5m

7.5m

7.5m

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The Sample Structure: Key Dimensions

0.3m

3m

20 panels Equally spaced

SAP2000:Starting• Before anything else, we must change the unit

shown on the bottom-right part of the interface.• For our example, our desired unit is kN, m.• This is necessary because SAP2000 (also

ETABS) has a bug of reverting to this “default” unit

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SAP2000:Creating a New Model• In the menu click File Menu > New Model.• There are many options for the template. For

our example click “Grid Only”

SAP2000:Creating Grids• The “Quick Grid lines” window will appear as

shown below. • This option only sets uniform spacing for all the

grids. This could be edited later.

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SAP2000:Creating Grids: Discussion• In SAP2000, utilizing grids properly would

make life easier for the user.• Always give a good thought on the gridlines at

the start of any model!

SAP2000:Creating Grids• For our example, it would be prudent to use the

grids shown below.

Nend

Mid

Send

Wend EendWapex Eapex1 2 3 4 5 6 7 8 9

Xgrids

Ygrids

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SAP2000:Creating Grids• For our example, it would be prudent to use the

grids shown below. For elevation

Bot

Top

1

SAP2000:Creating Grids• Input the number of grids in the window shown

below. Input the appropriate spacing. Spacingscould be adjusted later

Click ok when done!

Type “6/2” and see SAP2000 compute!

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SAP2000:Creating Grids• You will now see the grids on the Main Windows

ETABS:Extra: Axis Convention• Local axis direction determined by connectivity• SAP2000 Local Axis default shown below• Global Axis also shown. Time to adjust if you came

from the “Y”-up system program

1 axis = red

3 axis = Blue

2 axis = White(Gray for presentation purposes)

Local Axis

For Global, Z is up! Time to adjust if you want to use SAP2000

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SAP2000:Adjusting Grids• Now let us adjust the grids to match our

structure.• Go to Define Menu > Coordinate Systems/Grids• Choose Modify/Show System

SAP2000:Adjusting Grids• In the window that appears, the coordinates of

each gridline is shown.• Since, spacing of grids are usually shown in

plans, it is recommended to use “spacing” option

Click this and notice the change of values of the ordinates

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SAP2000:Adjusting Grids

Ok!

To be changed

Defining Grid Data

To be changed


Change the spacing for the X-grids as shown

Please note in the spacing methodology, the last grid is always zero

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Change the spacing for the Z-grids as shown

SAP2000:Adjusting Grids• Once the grids are set: Click ok to finalize them.• Click ok again in the original window you came

from. Warning: clicking cancel would nullify all the previous changes!

Click ok again!

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SAP2000:Grids• Now the grids are complete.• Next.. Let us navigate between these gridlines.

SAP2000:Navigation• In using SAP2000, it is recommended to have

two windows, one showing the 3d view and one showing the plan or elevation view.

Plan or Elevation 3d View

Let us use this convention for this training!

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SAP2000:Navigation• Now let us see the plan views!. Do the following:

1. Click the upper bar of the plan/elevation window

2. In the top buttons, click

1 2

SAP2000:Navigation• To navigate between different levels in the

structure. Click these buttons • The current plan view elevation being shown is

indicated in the 3D View window.

Up one levelDown one level

Highlight indicates where you are

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SAP2000:Navigation

• For the elevation views. Do the following:1. Click the upper bar of the plan/elevation

window2. In the top buttons, click

12

The XZ plane is highlighted

SAP2000:Navigation• For the elevation views. Do the following:

1. Click the upper bar of the plan/elevation window

2. In the top buttons, click

1 2

The YZ plane is highlighted

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SAP2000:Navigation• To navigate between different coordinates you

could also click these buttons

Up one levelDown one level

SAP2000:Defining Materials• To define the material properties go to Define

Menu > Materials• Click “Add New Material”

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SAP2000:Defining Materials• In the window appears, change the data as

shown below for A36 steel

Name and material type

Variables for Analysis

Variables for Design

Input “36*6895” to ensure it is correct conversion!

Click ok when done

SAP2000:Defining Materials• Alternatively, we could use the different

materials available in the SAP database.• To do this click “Add New Material Quick”

There are multiple options to choose from!

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SAP2000:Defining Materials• For our example, use the following

Material Type: SteelSpecification: ASTM A36

• Notice that the name “A36” is added to the materials list

Click ok when finishedClick ok when done!

SAP2000:Defining/Importing Sections• Now we have our materials, let us now import

the sections• First and foremost, the sections needed for this

project are shown below

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SAP2000:Defining/Importing Sections• Let us define these sections using the following

methodsImport from the SAP2000 databaseCreate a typical section with modified dimensionsUse the SAP2000 Section Builder

SAP2000:Defining/Importing Sections• The following are the designated sections for the

truss below

Double Angle Section (2L)

Single Angle Section (L)

Four Angle Section (4L)

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SAP2000:Defining/Importing Sections• Let us import all the double angles (2L) from the

SAP2000 database

SAP2000:Defining/Importing Sections• Importing Sections

Go to Define Menu > Section Properties > Frame SectionsClick “Import New Property”

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In the window that appears, click the “Double Angle” option.A window will prompt you to choose the source of the sections

Default directory is C:\Program Files\Computers and Structures\SAP2000 14

SAP2000:Extra: Notes on the Steel Databases• Old angular sections like the 2L1.5x1.5xthk

sections are contained in the AISC.pro file• Newer sections are contained in the AISC3.pro

file

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For our example, since we have the “old” sections. Let us choose AISC.pro. Click open when doneOn the window that opens, choose the appropriate material (A36), then choose the sections you will use

SAP2000:Extra: Notes on Selection in lists• Please note the following in selecting in a listboxHold Shift, then click where arrows are present

Hold Ctrl, then click where arrows are present

Just click where the arrows are present

1st

2nd

1st

2nd

1st

2nd

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We have the option of choosing the ones we needOr we can choose to import everything.In our example, select everything using the “press shift” method shown earlier

Remember to scroll down to the last option!

Click ok when finished


A window will appear showing a sample section from the list. Just click ok when this appears.The section list is now populated with all the 2L sections of the AISC.pro database

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SAP2000:Defining/Importing Sections• Defining Sections

Now let us define the single angle sectionsClick “Add new property” in the frame properties window. Click “Single Angle”, in the window that appears


Change the data in the window that appears as per below

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The just defined section is now added to the list


Do the same process for the following single angle sections

L-38x38x6L-63x63x6L-75x75x6

You can use the “Add Copy of Property” Button so that only a few parameters need to be changed

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SAP2000:Defining/Importing Sections• Defining Sections using Section Builder

Lastly let us define the 4L sections using the section builder. SAP2000 doesn’t have this section. Hence, we need to use the section builder

SAP2000:Defining/Importing Sections• To Defining Sections using Section Builder

Click “Add new property”Choose “Other” in “Add frame section property”Click Section Designer

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In the window that appears, change the data as per belowClick section designer when done.

By changing to this option, the steel section can be checked


The section designer has many features. Up to the user to further explore the features.For our example, we will create a 4L-90x90x6 sectionSince the we have 4 angles, let us first create a 2L 90x90x6.

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To create a double angle, click the icon shown belowThe arrow will change indicating you are in draw mode. Click where you want to put the section.

Click at the origin


After clicking, the default angle sections used are shownRight click the shape to change its properties. Edit properties as shown below

Click ok when done

Note that X and Y centeris at the midheightand midwidth of member

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The new section is now shown. Use the replicate command to mirror the section.Select first the section by clicking on it. (note the selection status on the bottom left)Go to Edit Menu > Replicate


On the window that appears click the Mirror tabChoose the X-axis option and click okWe now have a 4L 90x90x6 sectionClick done on the lower right when finishedClick ok again on the previous window to confirm

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The section is now added to the list!

SAP2000:Defining/Importing Sections• Once all the sections have been set. We can now

draw the sections!

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SAP2000:Defining/Importing Sections• First let us draw the truss indicated below.

SAP2000:Drawing Frame Members• Before we proceed, let us go to the elevation view

(Y-Z) of the grid shown below

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SAP2000:Drawing Frame Members• Let us draw the top and bottom chord

Go to Draw Menu > Draw Frame/Cable/TendonA small window will appear with different options. Let us explore them one by one in the next slideFor the top and bottom chord, choose the options shown below

SAP2000:Drawing/Modifying Frame Members• The cursor changes to indicate you are in draw

mode.• The cursor automatically snaps to gridpoint

intersections.• Let us draw the main members as shown on the

next slide by clicking on the key points

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SAP2000:Exiting Drawing Mode• When it is desired to quit the draw frame mode

mode, Press the esc button.• If this doesn’t work at first, this means that the

main window is “not active”.• Click the top bar of the main window and press esc

again. This will go back to “select mode”

Click and press escape

SAP2000:Drawing Frame Members

To draw the top chord, click the points in a sequence as indicated by the numbers below

1

2 4

5

3

Note that there will be difficulty in drawing members 1-2. It is recommended to use the zoom window command

Once in zoom mode, you can always use the pan button

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SAP2000:Extra: Zooming• Before proceeding, let us explore the navigation

capabilities of SAP2000.• In the top buttons, notice this portion.

• We will explore them one by one in the next slides.

SAP2000:Extra: Zooming• Rubber band zoom.

Zooms into one spot.Click the rubber band zoom icon, then click the upper left and drag to the lower right corners of the “zoom spot”

Lower Right Corner

Upper Left Corner

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SAP2000:Extra: Zooming• Restore Full view.

Zooms out so that whole structure is visible.Click this and the whole structure is now visible

SAP2000:Extra: Zooming• Zoom in and Zoom out.

Your standard zoom and zoom out buttons.

• Pan Button.Can be used if middle button in mouse not present.

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Member complete!


Do the same for the bottom chord

1 2

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Top and bottom chord now drawn!

SAP2000:Drawing/Modifying Frame Members• Now let us draw the vertical 4L section

Change the section, prior to clicking the nodes!

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SAP2000:Drawing/Modifying Frame Members• Now let us draw the web members (verticals and

diagonals). For this let us use L75x75x6For the frame drawing command, let us use the offset function.We know that each vertical is spaced at 7.5m/10 eq spaces = 0.75m

0.75m

SAP2000:Drawing/Modifying Frame Members• Using this let us draw the first vertical web

member1. Set section = L75x75x62. Set xy Plane Offset Normal = 0.753. Click from pt 1 to pt 2

0.75m

1

1

2

2

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SAP2000:Drawing/Modifying Frame Members• Now the first vertical is drawn. • But notice that it still should be trimmed

SAP2000:Drawing/Modifying Frame Members• To trim the following

must be done.1. Click the line to be

trimmed2. Click the point at the

end where the line is to be trimmed

3. Select the cutting line4. Go to Edit Menu >

Edit Lines > Trim/Extend Frames

5. Choose trim and select ok

1

2

3

4

5

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SAP2000:Drawing/Modifying Frame Members

• Now the first vertical has been trimmed!• The same methodology is applied for extending

frames


• For the other verticals, we will do the following.Replicate the first vertical member 8 times with dy= -0.75m.Trim all these verticals simultaneously.

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• For the other verticals, we will do the following.Replicate the first vertical member 8 times with dy = -0.75m.1. Select the first vertical2. Goto Edit Menu > Replicate3. Set the data as per below

and click ok

1

2


• For the other verticals, we will do the following.Trim all these verticals simultaneously.1. Select all the verticals indicated2. Click the ends where the verticals will be trimmed3. Click the cutting line4. Go to Edit Menu > Edit Lines > Trim/Extend

Frames. Choose Trim Frames and click ok

1

2

3

4

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• Now the verticals for one side is complete!


• Now let us draw the diagonal members first for one side before proceeding with doing the other side.

• Choose the options below for the frame and draw all diagonal members

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• Since the diagonal members are discontinuous, we must “cancel” the continuous line every time we draw one diagonal. Do the following:1. Draw a diagonal member2. Click the right click button on the mouse (Here

we will notice that the drawing command is still active but now the line is cut)

3. Draw the next member.

1 3


• Now the diagonals (for one side) are complete!

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• To complete the truss, let use “mirror” the members about the (X-Z) plane

X-Z Plane


• To complete the truss, let use “mirror” the members about the (X-Z) plane1. Select all the diagonal members2. Go to Edit Menu > Replicate3. Go to the mirror tab and input the data shown.

Click ok when done

12

3

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• The truss is now complete!

SAP2000:Extra: Shrinking Members

• To “shrink” the graphic of the members, go to View Menu > Set Display Options

• Check the shrink objects option

Click ok when Done!

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SAP2000:Extra: Shrinking Members

• “Shrunk” members shown below with the connectivity obvious.

SAP2000:Extra: Member Connectivity• Q: Are the members highlighted below

connected to each other, since the bottom chord is just one member)?

• A: In SAP, yes, it is connected by the frame auto mesh feature. Members will automatically divide at joints by default

• To see this, right click any member

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SAP2000:Extra: Member Connectivity• In Line Information window, you will notice in

the Assignments tab the followingAutomatic Mesh, Mesh Option = At intermediate joints

This option turned on by default

SAP2000:Extra: Member Connectivity• To turn off this feature you have to (FYI only, no

need to do this)Select a memberGo to Assign Menu > Frame > Automatic Frame MeshChoose “No Auto Meshing” in the new window

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SAP2000:Extra: Member Connectivity• However, it is more prudent to turn on this

feature (auto mesh) at all times because some members might not be divided properly!

SAP2000:Defining Support Conditions

• Now that the frames have been drawn, we can now assign supports.

• Let us assign the following supports for this truss

Pinned Pinned

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SAP2000:Defining Support Conditions• To assign supports do the following

Click the desired nodes where supports will be placedGo to Assign Menu > Joint > Restraints. A window will appear

Note the “x” mark indicating joint selection

Also check this to ensure correct selection

SAP2000:Defining Support Conditions• There are preset supports as indicated below• For our example, choose pinned (the 2nd button),

then click ok

Fixed Pinned RollerUnrestrainedJoint

Graphic showing support type shown

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SAP2000:Defining Load Patterns• To Define Load Patterns, go to Define Menu >

Load Patterns• By Default the Dead load is already defined. You

will notice that Self Weight Multiplier = 1, which means self weight will be computed

SAP2000:Defining Load Patterns• Let us define a wind load pattern called “L”

1. Load Pattern Name = “L”2. Type = “Live”3. Self Weight Mutiplier = 04. Click Add new load pattern5. It’s now in the list

2 34

1

5

It’s now in the list!

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SAP2000:Defining Load Patterns• If ever you make a mistake

1. Click the pattern to be corrected.2. Change the Necessary data at the top portion3. Click “Modify Load Pattern:

1

23

SAP2000:Extra: Load Pattern Types• Q: Why specify load pattern types?• A: It helps SAP2000 figure out if the lateral load

factor (specially for ASD design) for allowable stresses is to be applied

• A: SAP2000 would recognize that a combination has a lateral load and would automatically apply the increase in allowable stress (in AISC ASD = 4/3)

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SAP2000:Defining Load Combinations• Now let us define a single combination named

“D+L”Go to Define Menu > Load CombinationClick “Add new combo”

SAP2000:Defining Load Combinations• In the Load Combination Data Window

Load Combination Name = D+LLoad Combination Type = Linear AddAdd Dead with factor = 1Add L with factor = 1. Click ok when done

Click ok againDo not cancel!

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SAP2000:Extra: Different Combination Types• The different options for combination type are

as followsLinear Add – adds the loadsEnvelope – gets the envelope (the max and min values, useful for getting beam moments)Absolute Add – Absolute sum (disregards signs)SRSS – Square root of the sum of the squares ( usually for dynamics!)

SAP2000:Assigning Joint Loads• Now let us assign joint loads for Dead and Live

loads for the 2D truss • First compute the value of each joint load using

Tributary area concepts.• Let us assume the following area loads

D : 0.45 kPaL : 0.6 kPa

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SAP2000:Assigning Joint Loads• We are usually familiar with the term load cases,

specially for other software• In SAP2000, the equivalent of this term are

actually load patterns• Let us create some load patterns Dead (D) and

Live load (L)

SAP2000:Assigning Joint Loads• Dead Load joint force

Tributary area of one joint = 0.75 x 4 = 3m2.Joint load per middle node = 3 x 0.45 kPa = 1.35 kN

• Live Load Joint Force3 x 0.6 kPa = 1.8 kN

4m

0.75m

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SAP2000:Assigning Joint Loads• To assign the dead load joint forces dot the

following1. Select the nodes2. Go to Assign Menu > Joint Loads > Forces3. Input -1.35 kN for “Force Global Z” for Load

pattern “DEAD”

1

2

Click ok when done!

SAP2000:Assigning Joint Loads• The dead load is now assigned

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SAP2000:Assigning Joint Loads• Do the same steps for live load

1. Select the nodes2. Go to Assign Menu > Joint Loads > Forces3. Input -1.8 kN for “Force Global Z” for Load

pattern “L”

1

2

Click ok when done!

SAP2000:Assigning Joint Loads• The live load is now assigned

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SAP2000:Analysis• Now let us do a check of the model before

analysisMember PropertiesLoads

• Once everything has been checked we are ready to analyze!

• Set the view limits to “View All” if you haven’t before analysis

SAP2000:Analysis• To Analyze go to Analyze > Run Analysis• In the window that appears note that the case

“Modal” is present. This is usually activated by default

• You could set this to “Do Not Run” by clicking the case and clicking the “Run/Do Not Run” button

• Click Run Now!

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SAP2000:Analysis• After analysis a screen will appear as shown

below. Just close it so that it doesn’t block your view

SAP2000:Analysis• By default, the deflection diagram is first shown

after analysis• The deflection diagram helps you see if there are

errors in the model. Check each gridline to see if there are “funny” deflections

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SAP2000:Member Design Actions• Before proceeding to the member design let us

view the forces in the truss• To see the Axial force diagram of the members

go to Display Menu > Show Forces/Stresses > Frames/Cables

• Choose the desired case, action and click ok

SAP2000:Member Design Actions• The axial force diagram is now shown• To check out the details of any particular

member you can right click any member• You can choose the design action you

desire from any load case!

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SAP2000:Deflections• To see the deflections, go to Display > Show

Deformed Shape • Choose the appropriate load case and click ok!• Adjust the Scale factor if shape is not “exaggerated

enough!

SAP2000:Deflections• To get the actual deflection at a particular point,

just right click any node during “deflected shape” mode and the deflections will appear.

Load case shown

Always check units at lower right just in case you forgot!

Glo

bal Y

Glo

bal X

Glo

bal Z

Click to close

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SAP2000:Wind Loads Automated• Now let us define the wind parameters

1. Click the wind load case “WD”2. Click “Modify Lateral Load Pattern”3. A window will appear where we can edit the

parameters

1

1

SAP2000:Wind Loads Automated• In the window that appears input the constants

as shown below

Input 200/1.6 to convert kph to mph!

Click ok when done!

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SAP2000:Steel Design - ASD• After analysis, we can now design each member.• For our design we have the following parameters

Code: AISC ASD 89Steel Fy: 36 ksi = 248 Mpa

• Go to Design Menu > Steel Frame Design > View Revise Preferences to revise these parameters

SAP2000:Steel Design - ASD• Let us change the parameters to the following

Deflection limits useful for beams in buildings! Very convenient if you know how to use it

Click ok when done

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SAP2000:Steel Design - ASD• Now let us choose the load cases to be included in

design. Go to Design Menu > Steel Frame Design > Select Design Combos

• Click the D+L load case and click add• Uncheck “automatically generate code-based...”

then click ok

This is useful, but we already have load combinations

SAP2000:Steel Design - ASD• To Design go to Design Menu > Steel Frame Design

> Start Design/Check of Structure • Now each member will be checked for the code!• After design, colors will assigned indicating the

design results

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SAP2000:Steel Design - ASD• To see the design results, you can right click any

member. The critical load case is automatically highlighted. Right-Click the bottom chord

• It can be seen that the member fails. Click the details button for more information

Click this to see detailed design calculations

SAP2000:Steel Design - ASD• Detailed design calculations shown

Click to close

Notice that the Length used is 15m, but in reality the bottom chord might be braced at midspan

Failure notifications. A lot of provisions violated!

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SAP2000:Steel Design - ASD• Since the initial truss model is 2D, we can’t

incorporate bracing members.• Hence, to take these into account we must apply

design overwrites.

Say bottom chord is braced at ½ length by a 2L member

Say top chord has lateral restraint per node due to purlins

Note that braces are not in the model!For illustration purposes only

SAP2000:Steel Design - ASD• To apply design overwrites

1. Select the bottom chord2. Go to Design Menu > Steel Frame Design >

View/Revise Overwrites3. Since bottom chord is braced at the middle, set

Unbraced length Ratio (Minor,LTB) to 0.5

1

2

Click ok when done

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SAP2000:Steel Design - ASD• Design again the structure by going to Design

Menu > Steel Frame Design > Start Design/Check of Structure

• If we right click the bottom chord again, we could notice that it has now passed (as indicated by a ratio number < 1.0)

Click ok when done!

SAP2000:Steel Design - ASD• Now click both the top chords and apply an

unbraced length ratio (Minor, Ltb) = 1/10 = 0.1

Click ok when done

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SAP2000:Steel Design - ASD• Design again the structure by going to Design

Menu > Steel Frame Design > Start Design/Check of Structure

• Right click the members to see the design results

SAP2000:Steel Design - ASD• Click the details button and we can see that the

unbraced length is now modified Click this

Then this when done

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SAP2000:Steel Design – Using Auto-Select• In the previous slides, it could be noticed that the

ratios for ASD design where less than 1.• If we want to get the most economical sections, we

need to use auto-select feature of SAP2000.

SAP2000:Extra: Unlocking Models• However, before editing the model again, we need

to unlock the model.• As a precautionary measure, SAP locks the model

before analysis so that no changes can be made that could cause errors.

• To unlock the model, do the following.1. Click the lock icon. Then click ok when prompted.

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SAP2000:Steel Design – Using Auto-Select• Now let us create an auto-select section in SAP.

1. Go to Define Menu > Section Properties > Frame Sections

2. Click “Add New Property” Button3. Choose “Auto Select list”

1

Cont’d on next page

2

3

SAP2000:Steel Design – Using Auto-Select• Now let us create an auto-select section in SAP.

4. In the window that opens, name the section as “AUTO-2L”

5. Select all sections 2L sections (use selection techniques shown earlier) and click the Add button

Click ok when done

4

5 Now the section is in the list

Click ok again!

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SAP2000:Extra: Selection Tools• We will assign the “AUTO-2L” section to all the 2L

sections (namely the top and bottom chord).• We can click them one by one or use the selection

tools to make our life easier.

SAP2000:Extra: Selection Tools• To select all top and bottom chords using the

selection tools, do the following:1. Go to Select Menu > Select > Properties > Frame

Section2. Choose 2L4x4x1/4 then click ok

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SAP2000:Extra: Selection Tools• Now all top and bottom chords are selected, we can

now assign the frame section.• While the members are selected do the following

1. Go to Assign Menu > Frame > Frame Section2. Choose “AUTO-2L” then click ok

1

2

SAP2000:Steel Design – Using Auto-Select• Now, the auto select section has been assigned.• Notice that the member assignments are shown.• If we zoom in to the member, we could notice

initial section.• This section is the median section as seen in the

definition window of the auto-select section

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SAP2000:Steel Design – Using Auto-Select• This section is the one that will be used initially for

analysis.• Once SAP has designed the truss, it would assign a

new optimal section.• The structure should be analyzed again because the

design section is different from the analysis section

SAP2000:Steel Design – Using Auto-Select• Now let us analyze and design the structure.

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SAP2000:Steel Design – Using Auto-Select• After this, we can see that SAP has “selected” the

optimal section for the given forces for the top and bottom chord.

• If we right click the member, we could see that on the upper left corner, the analysis and design section are indicated

SAP2000:Steel Design – Using Auto-Select• It is recommended that analysis and design be

repeated until analysis and design section match.• Shown below are the results after the 2nd iteration

of the analysis and design cycle.

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SAP2000:Steel Design – Using Auto-Select• Final result after 5 iterations

They now match!

SAP2000:Steel Design – Using Auto-Select• We can also apply an auto-select L section for the

web members.• Results of using auto-select for the web members

are shown below.

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SAP2000:Steel Design – Using Design Groups• It could be noticed that in designing the web

members, multiple types of members were acquired.

• In construction, it is often desired to use similar sections to save on costs.

• For the auto-select sections, we can make a certain number of members to have similar sections by using design groups.

• Unlock the model first before proceeding!

SAP2000:Steel Design – Using Design Groups• Let us apply design groups

to the design of the top and bottom chord.1. Select all top and bottom

chord members.2. Go to Assign Menu >

Assign to group

2

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SAP2000:Steel Design – Using Design Groups• Let us apply design groups to the design of the

top and bottom chord.3. Click “Add New Group”4. Name the group “TopAndBotChord” in the

window that opens.

3 4


top and bottom chord.5. Going back to the previous window, click

“Replace Group” then click ok when done.

5Group has been assigned!

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top and bottom chord.6. To include the group in the design, go to Design

Menu > Steel Frame Design > Select Design Groups

7. Select the group “TopAndBotChord” and click “Add” Button

6

7

Click ok when done

SAP2000:Steel Design – Using Design Groups• Now let us redesign the structure. • Notice that all Top and Bottom chords have the

same sections.• For design groups, SAP adopts the biggest section

in the design results in a group.

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SAP2000:Steel Design – Using Design Groups• Let us also assign a design group for the web

members called “VerticalsAndDiagonals”• Results shown below when including the said

group in the design groups

SAP2000:Completing the 3D Model• Now we know most of the basic commands, let us

implement this in completing the 3D Structure!

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SAP2000:Completing the 3D Model• Since the truss structure is symmetric in one axis,

the best strategy is to do ½ of the structure and use replicate to complete the other half.

The first truss is currently here

Replicate this halfUse drawing and replicate tools

SAP2000:Completing the 3D Model• Complete the 3D Model

1. Replicate the trusses shown belowExisting Truss

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1. Replicate the trusses shown belowa. Select all members of the first trussb. Go to Edit Menu > Replicatec. In the window that opens, set dx = 4, number = 2.

Click ok when done

a

Check if selection is correct!

bc


1. Replicate the trusses shown belowd. The replicated members can now be seen when

using 3D

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SAP2000:Extra: Advanced Replicate Options• Before proceeding let us right click the members

from the original truss.• It could be noticed, that the group we assigned is

present as seen below.

SAP2000:Extra: Advanced Replicate Options• If we right click, the replicated members notice

that the group assignments were not copied.

What the?!?

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SAP2000:Extra: Advanced Replicate Options• For the replicate command to copy group

assignments, we need to use advanced replicate options.

• Before proceeding, let us delete the replicated trusses.

SAP2000:Extra: Advanced Replicate Options

1. Replicate again the trusses shown belowa. Select all members of the first trussb. Go to Edit Menu > Replicatec. In the window that opens, set dx = 4, number = 2. d. Click “Modify/Show Replicate Options”

a

Check if selection is correct!

bc d

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SAP2000:Extra: Advanced Replicate Options

1. Replicate again the trusses shown belowe. In the window that opens, we can see multiple

options. For our example, check first “Group Assigns”.

f. Click the select groups button

e

f

g. Choose both groups and click ok all the way to the parent window

SAP2000:Extra: Advanced Replicate Options• If we right click, the replicated members again,

the group assignments have now been copied!• Other features of the advanced replicate options

can be explored on your own time.

Click ok when done!

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1. Now let us complete the other trusses using replicate commands. Don’t forget the advanced replicate options for every replicate command!

4m2.8m 4m

Already present

Use 2 separate replicate commands

Replicate half of the adjacent truss

SAP2000:Extra: Reshape Command• It could be noticed that the bottom chord for the

half truss at the middle must be shortened. • An alternative to the trim command is the

reshape command

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SAP2000:Extra: Reshape Command• To implement reshape, do the following

1. Go to the gridline where the half truss is present.2. Go to Draw Menu > Set Reshape Element Mode3. Click anywhere on the member except the end

nodes.

1

2

3

SAP2000:Extra: Reshape Command• To implement reshape, do the following

4. The member would now look like as per below5. Drag the end of the member that needs to be

moved to the desired spot.6. The member has been edited!

4 5

Desired Spot

6

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SAP2000:Extra: Reshape Command• Why reshape (rather than delete then redraw)?

Important member assignments might be lost if we delete then redraw!

4 5

Desired Spot

6


1. Don’t forget to put a pin support on the currently unsupported end of the half-truss!

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1. Complete this truss using the XZ view in the plane shown on next slide.

7.5m


1. Use Auto-2L for the top and bottom chord and auto-L for the web members.

2. Also use 10 divisions for the panels for 8.5m long truss (replicate 9 times the nearest vertical member by dx = -0.75m. Assign sections then trim!)

3. Use commands learned earlier!

Nearest Vertical

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SAP2000:Completing the 3D Model• Half Truss now drawn!

7.5m

Don’t forget the pin support!

SAP2000:Completing the 3D Model• To draw the 45degree half-truss, we must draw in

3d mode!

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SAP2000:Completing the 3D Model• Do the following for the 45 degree truss

1. Go to 3d view2. Zoom window on the desired spot.3. Draw an “Auto-2L” member on the joints

indicated.

Desired spot2

Note that these are grid point intersections

3


4. When drawing in 3d mode, the user must always be cautious because the ends of any member may snap to an erroneous node.

5. The top and bottom chord members are now drawn!

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1. To do the web members without dividing the top and bottom chord, we must use the extrude points to line command.

SAP2000:Completing the 3D Model• Do the following for the 45 degree truss. For

drawing web member:1. Go the the yz view of the truss shown below.2. Select the nodes on the top chord on the side of

the 45 degree truss

Yz view of this truss

2

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drawing web member:3. Go to Edit Menu > Extrude > Extrude Points to

Frames.4. Choose any property and input dx = - 10, dy and

dz = 0 and number = 1.

3 We could now see the extruded lines!


drawing web member:5. Since the new lines intersect with the top chord of

the 45 degree truss, they could now be trimmed! 6. Select all generated lines and the end to be

trimmed and select the top chord of the 45 degree truss

7. Execute the trim command

6

7

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drawing web member:8. Now we have key points at the bottom chord. Use

the same extrude to frame command to draw the verticals!

9. Choose the top chord nodes of the 45 degree truss and Use dy = -4, dx and dz = 0 and number = 1

9


drawing web member:10. Now trim the verticals using the bottom chord!

Use the arrow keys to rotate the 3d view and get a good view. Don’t forget to assign section property Auto-L!

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drawing web member:12. Remove the guide members previously drawn to

remove the clutter13. Now we can draw diagonals using standard

drawing tools. Use Auto-L for the section. Always be careful when drawing in 3d mode!

12 13


drawing web member:12. Remove the guide members previously drawn to

remove the clutter13. Now we can draw diagonals using standard

drawing tools. Use Auto-L for the section. Always be careful when drawing in 3d mode!

12 13

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drawing web member:14. The same procedures can be used to draw to

smaller half-trusses

SAP2000:Completing the 3D Model• The trusses below can now be replicated using the

mirror command with respect to the x-z plane. Please note of the constants used below.

• Note that the selection of the 45 degree truss and the smaller half-trusses will be a challenge.

Click ok when done!

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SAP2000:Completing the 3D Model• And of course, don’t forget the pinned supports!

SAP2000:Completing the 3D Model• Now let us draw these remaining items.

1. The 2L-2x2x1/4 member bracing the bottom chord.

2. Purlins3. Roof area elements

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1. The 2L-2x2x1/4 member bracing the bottom chord.

1. Go to the x-z view of the middle grid2. Draw frames using 2L2x2x1/4 member

1

2


2. Purlins1. Define a 150x50x20x1.6 cold formed section as per

below

Click ok all the way when done

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2. Purlins2. Go to the y-z view of the middle bay and use extrude

points to frames by using the top chord points and using section = C150x50x20x1.6


2. Purlins3. Trim the purlins using the top chord of the 45

degree truss

3

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2. Purlins4. Do the same method for the other purlins. (You can

also use mirror command for the upper purlins)


3. Roof area elements1. The roof area elements are convenient for easy

application of area loads from dead, live and wind.2. The roof element may represent the stiffness

contribution of the roof but it is preferred that roof stiffness is neglected.

3. Hence we will create a roof area element which will be for loading purposes only without any stiffness contribution

Roof element

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3. Roof area elements4. Let us define an area roof element

a) Go to Define Menu > Section Properties > Area Sections

b) Click Add New Section

a

SAP2000:Completing the 3D Model

• Now let us draw these remaining items.3. Roof area elements

4. Let us define and draw an area roof element

c) Enter the options shown on the figure on the right

d) Click “set modifiers” and set the values as shown on the left. These values ensure that the element does not contribute stiffness and its own selfweight.

Click ok all the way when done!

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3. Roof area elements4. Let us define and draw an area roof element

e) Draw the first area element. Go to Draw Menu > Draw Poly Area

f) Click the 4 joints indicated below in a counterclockwise manner for our first poly area.

f1

f2f3

f4



e) Draw the first area element. Go to Draw Menu > Draw Poly Area

f) Click the 4 joints indicated below in a counterclockwise manner for our first poly area.

f1

f2f3

f4

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g) The area has now been drawn. We need to divide this area so that it is “connected” to the purlins. But before this let us rotate the local axis.

h) Select the area: To select it, click anywhere on its middle part without clicking any frame members.

h A dashed line indicates area selection



i) Turn on the local axis of the area by doing the following.

a) Go to View Menu > Set Display Options b) Check the “local Axes” option under “Areas” and click ok

a b

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c) Now we will see the local axis of the area we just drawn. Note that when we apply a one-way load, the load will go in the direction of the red arrow. Since the direction of the load must be towards the purlins, we need to rotate the axis of this area by 90 degrees!




c) To rotate the local axis, select the area then go to Assign Menu > Area > Local Axes

d) Input 90 and click ok! The area is now oriented in the right direction!

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j) Now we are ready to divide the area element. Select the element and the purlins that will divide it.

k) Go to Edit Menu > Edit Areas> Divide Areas



l) Choose the option shown below and click ok.

The area is now divided!

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l) Doing the same for all and the roof elements are complete

SAP2000:Assigning Area Loads• Now let us assign area loads for dead and live for

all areas.Select all areas by using the selection tools.

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all areas.Assign the area dead load one way by doing the following.

Input 0.45 for Dead then click okSelect the areas again and assign 0.6 kPa for the areas


all areas.Area loads have been assigned!

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SAP2000:Final Things to do• Replicate the half-structure to the other side

Check the Uniform to frame option in the “Loads and Design” tab in the replicate options.

SAP2000:Final Things to do• Remove all design

overwrites so that SAP could automatically generate it.

Select all members.Go to Design Menu > Steel Frame Design > Reset All Steel Overwrites

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SAP2000:Final Things to do• Remove all joint loads

1. Select all members2. Go to Assign Menu > Joint Loads > Forces3. Choose “Delete Existing Loads” For dead load

case and click ok.4. Do the same steps for Live load, L.

1

23

SAP2000:Final Things to do• Now we are ready to analyze and design the

structure!• Analyze the structure and check the results.

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SAP2000:Final Things to do• First let us check if the one-way distribution

worked for the purlins.• Activate the M33 diagram

1. Go to Display Menu > Show Forces/Stresses > Frames/Cables

2. Choose L Load Case and choose Moment 3-33. Click ok afterwards

2

3

1 The moment diagrams are now shown

SAP2000:Final Things to do• While the M33 diagram is active, right click one

of the middle purlins• It can be observed that there is a uniform load of

0.48 kN/m on the beam. This is near the correct answer because 0.6 kPa x 0.8 spa = 0.48 kN/m

• The slanted length was used for the computation.

0.75m

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SAP2000:Final Things to do• Designing the structure, we can check if SAP will

implement the automatic detection of unbracedlength. Note that we have removed all steel design overwrites.

SAP2000:Final Things to do• Right clicking on the bottom chord it is apparent

that the brace has been considered in the design

Bracing due to connectivity considered in L factor

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SAP2000:Final Things to do• It can be seen that analysis and design section

still don’t match.• Multiple cycles of analysis and design is needed

for analysis and design section to match.

SAP2000:The End?• Doing a structural model can be broken down into the

following steps:1. Create a New Model2. Define/Edit Grids and Floors3. Define Materials4. Define Sections5. Draw Members6. Assign Member Properties7. Generate Load Cases8. Assign Loads9. Define Combinations10. Pre-analysis Check11. Process the Output12. Design the Members

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SAP2000 SeminarSession 1Modelling a Truss Structure

The End. See you again for Session 2!

Not everything can be learned in a day (or 4 hours) in a classroom, you have to experience it to truly learn it!

sap seminar - session 01 - modelling a truss

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