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:

Further to Part-1, this part covers defining load case type, load combinations for design of Isolated footing. Procedure to add Permanent and Temporary surcharge load is explained. Creating Load combination based on the Soil and water level and creating analysis criteria are covered in this part.

 

STAAD File: STAAD File for Example 1.STD

 

SFA File: Example_1 Part-2

 

Solution: Step by step process

 

Step-1: Load case type

Users can click on the following option under the Loading tab to define load case type if it is not identified by program.

Figure-1

Program auto identify the type of load case if it is defined in STAAD.pro. refer below snap showing the load types available in STAAD.pro.

Figure-2

If the load cases available in the STAAD.pro file are assigned with loading types, program auto identifies the load type. However, option is provided to user to change the load type. If the load type is missing in STAAD.pro, option is available to define it in the program.

Figure-3

It is important to define the load case type on this screen to make sure that its effect should be considered on the design. Example: for earthquake and wind load combinations it is allowed to increase the permissible soil bearing capacity as per Indian design code. Based on type of load the strength reduction factors vary as per Euro design code.

 

Step-2: Adding Permanent and Temporary surcharge load on footing

Program allows users to add primary load cases other than defined in STAAD.pro. If you click on the tabs shown below, list of load type would be available to user.

A permanent and temporary surcharge can be created by adding a new primary load case.

Figure-4

Associate load case and load factor can be assigned to newly created load case. This load factor would be used to create a load combination. Refer below snap showing inputs to be provided for Associate load case and load factor.

Figure-5

If the Permanent Surcharge load case is associated with the dead load, the existing load cases are updated with addition of Permanent Surcharge load having load factor same as dead load.

 

After creating load cases, users can add load on the footing as follows,

Click on the Create button of Area load under Loading tab. User can provide the Name for the load and select the load case. As it is an area load, user can provide the pressure intensity. After providing the information click on the create button on left bottom side and add the load under load case.

Figure-6

After adding load for Load cases, the next step is to assign it to isolated footing. Click on the Assign button of Area load under loadings. There are various options available to assign load to isolated footing. Select one of them and select load case and load item. Select the isolated footing and click on the assign button on bottom left.

 

Figure-7

The load has been assigned to isolated footing.

Figure-8

 

Refer to snap below showing the original load combination from STAAD.pro are updated with new primary load cases added in program.LC 1013 and LC 1014 are added for Permanent and temporary surcharge load cases respectively.

Figure-9

S1:3 and S1:4 are the original load combination from STAAD.pro. ASL_S1:3 and ASL_S1:4 is the new load combination updated with newly added primary load cases in the program.

 

Step-3: Load combinations Type

To assign load combination type, the user must click on the following option under Loading tab.

Figure-10

Program auto identifies the load combination type whether it is service or ultimate based on the load factors. Facility is available to change the load combination type on this screen. At a time one LC type can be assigned to one load combination. Option is also provided to keep the load combination un-ticked in case it is not used for sizing and design.

Figure-11

Step-4: Define Analysis Criteria

Next step is to define analysis criteria. To create an analysis criterion, refer to the snapshot below,

Figure-12

Upon clicking on the Foundation button, the following inputs would be available to define analysis criteria.

Figure-13

Element Type: The foundation can be designed as a Mat or footing.

Analysis Type: For Mat, finite element analysis is available. For Isolated footing, Rigid and Finite element analysis are available. Users can select the analysis type for isolated footing as per design requirements.

In this example, we have created analysis criteria as AC1 (Rigid) for isolated footing IF3 and AC3 (Finite element) for IF6.

Load combinations: Based on the soil and water level, users can select the load combinations for design of isolated footing. By-default fully dry, fully saturated and Saturated and dry options are selected by the program. Users can select these options based on the project requirements. If users have un-ticked all the options, program always select the minimum fully dry options for the design. Users can select all the load combinations by selecting the tick button which is available along with the title of the load type. However, a facility is provided to select individual load combination for that load type.

Figure-14

 

Consider Thickness for Force Transfer:

If this option is ticked, the load from the pedestal/column would be transferred to the bottom of isolated footing. Or else load would be transferred to top of isolated footing.

 

 

Users can create more than one analysis criteria and assign to different isolated footings. One footing can be assigned with analysis criteria created using rigid design approach and another footing can be assigned with analysis criteria which is created for finite elements analysis type.

 

Concluding Remarks: Load cases, load combinations are defined to isolated footing and analysis criteria is created. Permanent and temporary surcharge loads are assigned along with overburden soil weight are assigned to footing. Next step is to assign criteria of Post analysis check and sizing of isolated footing.