Minimum needed version to run this example:
STAAD Foundation Advanced 2024 (24.00.00)
Unit System Used: Kip-in or Kip-ft (Imperial)
Problem statement:
In the attached STAAD.pro file there are two column members modelled of sections W36x853, each with a height of 10 feet. Each of the column members carry a dead vertical downward load of 90 kips and a dead moment of 62 kip about global X axis. Model foundations of 100 in x 100 in under both the columns along with the material and soil data using STAAD Foundation Advanced. Import the STAAD.Pro file into the application.
STAAD file: STAAD File for Example 1
SFA file: Example_1 Part-1
Considerations:
The steel column is supported on the top of the isolated pad footing through pedestals and the isolated footing is founded at 4 feet below the top of the soil level.
Material Data:
Characteristic compressive strength of concrete: 4000 psi
Strength of reinforcing steel: 60 ksi
Soil Data:
Assume medium dense sand with modulus of subgrade reaction as 350 kcf.
Use Bowles’ approximate conversion equation, ks = 12* SF * qa to calculate the bearing capacity. Assume the bearing capacity to be gross. Assume SF = 3.
Thus, qa can be considered as 9 ksf.
Assume same soil for overburden loads. Assume dry density as 90 lb/ft3 and wet density of the soil as 100 lb/ft3.
Finally assume friction coefficient of 0.4.
Water Table Data:
2 ft. below ground level.
Load Data (as defined in STAAD.Pro file)
LOAD 1 LOADTYPE Dead TITLE DEAD LOAD
JOINT LOAD
2 4 FY -90 MX -62
LOAD 2 LOADTYPE Live REDUCIBLE TITLE LIVE LOAD
JOINT LOAD
2 4 FY -23
LOAD COMB 3 1.2 DL + 1.4 LL
1 1.2 2 1.4
LOAD COMB 4 1.0 DL + 1.0 LL
1 1.0 2 1.0
Solution: Step by step process
Step 1: Make sure that the STAAD.Pro file is not open. SFA will not be able to import a STAAD.Pro file which is already open.
Step 2: Open the STAAD Foundation application and click on “Import STAAD.Pro File”. Please refer to Figure-1 below.
Figure - 1
Step 3: In the form that appears, please browse to the STAAD.Pro file in your computer by clicking the “Browse” button. As defined in the problem statement, the soil level is defined as 0 ft. We consider the datum at the same level as the top of the soil surface and hence, we specify it as 0 ft. as well. The water table is considered as 2 ft. below the ground level, and hence we specify it as -2. Now, press the “Create” button.
The following figure (Figure-2) shows the sequence of the steps to be followed.
Figure - 3
Step 4: The STAAD.Pro file is unanalyzed. Unless it is analyzed, SFA will not be able to find the reaction information which will be created as loads on the foundation. Hence, the application asks the user if he would like to run the STAAD.Pro analysis. Say “Yes”. Please refer to Figure-4 below.
Figure - 4
Step 5: Now the “Model Import” box appears. Press, the “Import” button, as shown in Figure-5 below.
Figure-5
Step 6: You will now see that the physical forms of the columns that you have defined in the STAAD.Pro files now appears on the SFA viewing area. Please refer to Figure-6.
Figure-6
Step 7: Now, create the first isolated footing under the left column. Click on Geometry > Isolated > Point. This is a way of creating the isolated footing using the point method. Please refer to Figure-7 below.
Figure-7
Step 8: The “Create Rectangular Footing” box appears. Please specify the modelling parameters as shown in Figure-8.
Figure-8
Note for the user: “Column Alignment” is set as “Top”, as it is assumed that the column transfers its load on the top of pedestal. We said “Yes” for pedestals below steel columns, which means that if there is a gap between the bottom of the column and the top of the foundation slab, that would be filled by the pedestals. In version 2024, the user does not have a way to model the pedestals. The plan coordinates of the center of the foundation is X=0 ft and Z = 0 ft. Since, the foundation is bottom fixed the Y is – 4 ft, which the level where the slab is founded.
Press the “Create” button.
Step 9: Now, our first foundation under the left column has been modelled. You will see that a representative base model has been created under the steel column and the remaining gap between bottom surface of the base plate and top surface of the foundation slab has been filled with pedestal.
You will also notice a bluish representation on the top of the foundation slab. This is representative of the water present in the soil up to the level of water specified, which is 2 ft. below the ground surface.
Step 10: Now, we want to create the second isolated foundation under the second column, which is on the right. However, we will use a different method in creating this foundation. So, the user clicks on Geometry > Isolated > Object. This is to create the foundation by clicking on the object or column under which it is to be created.
Figure 10
Step 11: The “Create Rectangular footing” box pops up. The user needs to take his mouse over the column in the viewing area and click on it. The user will see that the member number is now registered as “Selected Object” – please refer to the highlighted information in the “Create Rectangular Footing” dialog box. Press the “Create” button.
The foundation is now shown for both the columns (Figure 11).
Figure 11
Step 12: Now, we will go for material creation of concrete and rebar steel, as is specified in the problem statement. Go to Specification > Concrete > Select, as shown in Figure 12.
Figure 12
Step 13: The following box pops up on the screen. Select the check box besides 4000 psi to specify the concrete strength. Now, click on “Add to Model”.
Figure 13
Step 14: Now, select reinforcing steel grade by going to Specification > Rebar Steel > Select.
Figure 14
Step 15: In the box that pops up, select appropriate steel grade and select “Add to Model”.
Figure 15
Step 16: Now, let us finally specify the soil properties as has been instructed in the problem statement. Let us click on Specification > Create (Soil).
Figure 16
Step 17: In the “Create Soil” box, specify the following parameters. Once done, please press the “Create” button.
Figure 17
Step 18: Finally, click on Support > Assign (Soil). Refer to Figure 18.
Figure 18
Step 19: Now, follow the steps as shown in Fig 19 to assign the soil support and soil overburden.
Figure 19
Step 20: Once, you have clicked on the “Assign” button, two brownish layers appear beneath bottom and above the foundations to show that the soil support and soil overburden have been assigned to both the footings. Please refer to Figure 20.
Figure 20
Concluding Remarks: Now, this foundation has been modelled along with it’s associated material properties, soil support and overburden soil pressure. Now, this model is ready to be set for analysis and post-analysis.