Static Analysis and Design
of
2D Transmission Tower
Using SAP2000
(Metric Units)
ACECOMS, AIT
Static Analysis and Design
of
2D Transmission Tower
Table of Content
Objective ... 3 Problem ... 3 Step by Step... 51. Start Model with Template... 5
2. Modify Model ... 7
3. Define Material Properties ... 8
4. Import Angle Members and Define Auto Selection Member ... 9
5. Assign Frame Member ... 11
6. Define Load Case ... 12
7. Assign “WIND” Load Case ... 13
8. Assign Groups ... 14
9. Analysis the Model... 18
10. Design Steel Members ... 19
Objective
To demonstrate and practice step-by-step on the modeling, static analysis and design of 2D transmission tower.
Problem
Find the suitable steel angle members for 2D transmission tower by using AISC-LRFD93 design code with the following details
Material Properties (Steel)
Young Modulus of Steel (Ec) = 2,000,000 kg/cm2
Unit Weight of Steel = 7,800 kg/m3
Yield Stress of Steel (Fy) = 2,400 kg/cm2
Tensile Stress of Steel (Fu) = 4,000 kg/cm2
Load Case
Load Name Load Type Details
DEAD Dead Load Self Weight: Calculate automatically using Self Weight Multiplier in SAP2000
WIND Wind Load See in Elevation View
Load Combination for Pushover Analysis
Name Details
DSTL1 1.4 DEAD
DSTL2 1.2 DEAD +1.6 LIVE
DSTL3 1.2 DEAD + 0.5 LIVE + 1.3 WIND
DSTL4 1.2 DEAD - 0.5 LIVE + 1.3 WIND
DSTL5 0.9 DEAD + 1.3 WIND
DSTL6 0.9 DEAD - 1.3 WIND
Step by Step
1. Start Model with Template
Step 1-1: Select Working Unit and Start New Model with Template
Start up screen of SAP2000, select working unit to be “kg-m” at drop-down menu on the bottom-right of screen and click on to start new model with template
Step 1-2: Select Template Type
Step 1-3: Specify Geometry Properties
Specify two “Braced Frame” geometry properties as shown in above figure.
Step 1-4: Create Model
2 bays tower has been created from parameters that specified from previous steps. The left bay will be deleted in the next step. Close left window by clicking on .
2. Modify Model
All leg and horizontal members will be deleted in this step.
Step 2-1: Select Leg Members in Left Bay
Click on to change to selecting mode and draw rectangular selection to cover leg member in left bay as shown in above figure.
Step 2-2: Select Horizontal Members
Click on to change to “Select using Intersecting Line” and draw selecting line to pass all horizontal members in left bay as shown in above figure. Press “Delete” to delete all selecting members.
3. Define Material Properties
Step 3-1: Change Working Unit and Select Material
Change working unit to “kg, cm”, go to Define > Material, select “STEEL” and click on “Modify/ Show Material” button.
Step 3-2: Specify Steel Material Properties
4. Import Angle Members and Define Auto Selection Member
All angle member properties will be imported from built-in database first and define all imported L-Shaped member to the list of section (“AUTO1”) for auto member selection in design step.
Step 4-1: Import Angle
Go to Define > Frame/Cable Section, select “Import Angle” from first drop-down menu as shown in above figure and click on “Add New Property” button
Step 4-2: Specify Steel Member Database
Go to folder that SAP2000 has been installed (normally should be “C:\Program Files\Computers and Structures\SAP2000 8”) and select database name “AISC3.PRO”.
Step 4-3: Select All Angle Members
Select all angle members by clicking on first member and clicking on the last member by holding “shift” button and click on “Ok” button in “Angle Section” dialogue.
Step 4-4: Define Auto Selection Member
Back to “Frame Properties” dialogue, shows all angle members have been imported to the properties list at left column. Select “Add Auto Select” from second drop-down menu and click on “Add New Property” button.
Step 4-5: Select Section Properties for Auto Selection Member
Select all angle members (same method as previous step) and click on “Add->” button to move all angle members from list (left column) to auto selection list (right column).
5. Assign Frame Member
Step 5-1: Select all Members
Step 5-2: Assign Frame Selection
Go to Assign >> Frame/Cable >> Sections, select “AUTO1” and click “OK” button.
7. Assign “WIND” Load Case
Step 7-1: Select Nodes
Select 5 nodes from top by selecting and drawing rectangular line to cover desired nodes as shown in above figure.
Step 7-2: Assign “WIND” Load Case
Go to Assign >> Joint Load >> Forces, select load case and specify “Force GlobalX” as shown in above figure.
Step 7-3: Assign Windward Pressure Coefficients
Repeat step 7-1 and step 7-2 to assign nodal force to the remaining nodes
8. Assign Groups
3 member groups are required in this example (Leg, Horizontal and Brace) for steel design.
Step 8-2: Add New Group
Go to Assign >> Assign to Group and click on “Add New Group” button.
Step 8-3: Assign “LEG” Group
Step 8-4: Select Horizontal Members
Draw selection rectangular to cover all horizontal members one by one. To check all horizontal members are selected or not by selecting View >> Show Selection Only to view only selected members
Step 8-6: Select Bracing Members
To show all members, go to View >> Show All. Clicking on and draw selection line to pass all members as shows in figure. This selection will select all horizontal and bracing members.
Step 8-7: Deselect Horizontal Members
Go to Select >> Deselect >> Groups and select. Only bracing members are selected now. That can be checked from View >> View Selection Only.
Step 8-8: Assign “BRACING” Group
Go to Assign >> Assign to Group and repeat step 8-2 and 8-3 to assign “BRACING” group.
Step 9-2: Check Error Message
Check error message after analysis status show “ANALYSIS COMPLETE”.
10. Design Steel Members
Step 10-1: Select Design Code
Go to Options >> Preference >> Steel Frame Design and select “AISC-LRFD93” from design code
Step 10-2: Select Design Group
Go to Design >> Steel Frame Design >> Steel Design Group and select all 3 groups as shown in above figure by selecting and clicking “Add - >” button.
Step 10-4: Assign Effective Length Factor
Select all members by clicking on , go to Design >> Steel Frame Design >>
View/Revise Overwrites and change parameters as shown in above figure.
Step 10-5: Start Design
Go to Design >>Steel Frame Design >> Start Design/ Check of Structures and wait until SAP2000 show the design output.
Step 10-6: Check Analysis and Design Section
Go to Design >>Steel Frame Design >> Verify Analysis vs Design Sections, to see number of difference sections between analysis and design. Click on “OK” button.
Step 10-7: Reanalysis
Step 10-8: Redesign and Reanalysis
Repeat Step 10-5 to Step 10-7 until there is no difference between analysis and design member.
Step 10-9: View Design Member
Go to Design >> Steel Frame Design >> Display Design Info and select second drop-down menu and select “Design Sections” as shown in above figure.