Generation of Load Combinations per ASCE 7-2016

In the General and Toolkit modes of STAAD Foundation Advanced, load combinations can now be generated per the ASCE standard titled ASCE 7-16 - Minimum Design Loads and Associated Criteria for Buildings and Other Structures. In order to generate combinations using this code, the basic load cases need to be assigned one of the following types in STAAD Foundation Advanced.

1. Dead
2. Live
3. Wind Along X
4. Wind Along Z
5. Seismic Along X
6. Seismic Along Y
7. Seismic Along Z
8. Fluid Load
9. Snow Load
10. Dead Weight of Ice
11. Flood
12. Active Earth Pressure
13. Rain
14. Self Straining (Loads due to Temperature & Shrinkage are included in this type)
15. Wind on Ice Along X
16. Wind on Ice Along Z
17. Roof Live

The combination cases generated by STAAD Foundation Advanced are in accordance with Section 2.3 of the ASCE 7-16 document for Strength Design, and, Section 2.4 of that document for Allowable Stress Design. Recall that for foundation designs based on the ACI 318 code, the concrete design of foundations must be based on combination cases for strength design, while soil pressure and stability checks should be done using combination cases for allowable stress design. (Strength cases are also referred to by the name Ultimate cases in STAAD Foundation Advanced.)

In STAAD Foundation Advanced, a facility for generating these combinations is available in the General mode and in the Toolkit mode, with separate buttons for service and strength. Each mode of the program contains a table that comes populated with the factors for the respective load types. The following figure shows the facility that is available in the General mode.

Notice in the above figure that there is a check box in the second column, which if unchecked, instructs STAAD Foundation Advanced that the combination case defined by that row should not be generated.

Combined Footing Design

STAAD Foundation Advanced now supports the standards for foundation design for China GB 50007-2011 Code for design of building foundation for the analysis and design of combined footings.

This feature is available through the General mode of the program. In the Toolkit mode and Plant modes, the Chinese code is currently not available for these or other types of foundations.

How does one create a combined footing job?

In What’s New in CONNECT edition V9.1, the procedure used for creating an isolated footing job to the Chinese code was described. The same procedure can be used to create a combined footing job.

The rules for performing the concrete design of the footing are similar to those for other codes. Users are urged to go through the various sections of the Technical manual for information on this topic.

The sections of the GB 50007 code that are used in performing the various checks for combined footings are similar to those for isolated footing. See Isolated Footing Design per GB 50007-2011 for details.

Calculation report

If the design of the footing is successful, a calculation sheet is displayed containing the details for the checks mentioned above, and the governing load case for each check. For a failed design, the cause of the failure has to be interpreted by reading the messages displayed in the Output Pane, which is the panel below the drawing area.

The report can be obtained in either Chinese or English.

Drawings

Drawings of the foundation plan and layout are also produced.

Solved examples

Two solved examples that illustrate the procedure used for designing these footings is available in Chapter 10 of the verification manual of this program.

The STAAD Foundation Advanced models for these examples are available in the Examples folder.

Implementation of the ACI Metric Bar database

For all the foundation types in STAAD Foundation Advanced for which design can be performed per the metric editions of the ACI 318 code, the reinforcing bar database that is used henceforth is per the specifications of that edition. Most of these editions have an Appendix where the bar details are listed.

Metric bar size chart from ACI 218 2011 Appendix E

Implementation of the Australian Reinforcement Bar Database

For all the foundation types in STAAD Foundation Advanced for which design can be performed per the Australian code AS3600-2018, the reinforcing bar database per the Australian standards is now available. The source of this information is the Australian standard AS/NZS 4671:2001 with Amendment No.1.

Pilecap module – identifying the individual piles with a number

For the pilecap module, in the various places where the pile arrangement is available in pictorial form, each pile is now annotated with a number for quick identification. This enables easier correlation between the pile and the forces in the pile as reported in the tables for oneway shear, punching shear, etc., in the calc report.

Viewing the pile reactions for a mat foundation on piles

For mat foundations on piles, a table that shows the pile reactions for all the piles of the current mat job for the selected load case is now available for viewing from a table named "Pile Reactions" in the output pane. Please note that the selected load case should be part of the current mat job if its reactions are to be displayed. This is because, the reactions are calculated only for those load cases which are included in the job and analyzed. Hence, if the selected load case it is not included in the job, the table will be blank for that case.

Miscellaneous enhancements

1. For combined footings, a table of soil pressures for ultimate load cases is now provided in the calculation sheet. This is to assist users who are interested in validating the shear force and bending moment values used in the various concrete design checks.
   
2. The name of the code used in the load combination generation is now mentioned in the calculation report.
   
3. Octagonal footings can now be designed per the Australian code AS3600-2018.
   
4. For pilecap jobs, the loads applied at the top of the pilecap are now presented in separate tables - one for service cases, the other for strength cases. In past versions, this segregation was not available.
   
5. Pedestal design to various codes such as ACI, Australian, etc., is now available for many more foundation types.
   
6. For a mat foundation on piles, the pile reaction summary presented in the calculation sheet is now reported in two separate tables – one for service cases, the other for ultimate cases.
   
7. For pilecaps, the pile reactions are forcibly calculated as soon as the analysis is launched. This has been done because there are numerous ways in which data that affects the pile reactions can be altered. To avoid the possibility of an accidental omission in keeping track of those changes, as well as to avoid forcing the user to calculate the reactions manually each time such a change is made, the process of calculating the reactions has been automated so that the design of the pilecap reflects the most up-to-date changes in the input data.
8. For pedestal design per the various editions of the ACI 318 code, the value of Pn,max is now annotated on the P-M curve.
9. For a mat foundation job, if there are pedestals beneath the columns, the program was failing to consider the pedestal weight for the analysis of the mat. This has been rectified.
10. An error in the location of the column design load on the P-M curve for the Australian code has been corrected. This affects isolated footings and combined footings which have pedestals.
    
11. An error in the calculation of reinforcement bar spacing for isolated footings designed to the ACI 318 codes has been corrected.
12. The global setting for the value of the height of the pedestal for design for axial load + biaxial bending was not being honored for the Australian code. This has been corrected.
13. Miscellaneous improvements have been made in identifying errors in input. For example, for vessel foundations, if time period is specified as 0.0, the user is notified of this through a warning message. Identification of empty load cases is another – these are load cases which have only a title but contain no load items.
14. An error in calculating the bending moments in pilecaps under buoyant conditions has been corrected.
15. For pedestal design to the Australian code, in version 9.2.0.34 of STAAD Foundation Advanced, a check described in Clause 10.6.3 which says that columns can be designed to that clause only if their L/B ratio does not exceed 3.0, had been implemented, where L and B are the longer and shorter of the cross section dimensions of the column. However, the pedestal design implementation in STAAD Foundation Advanced is not based on this clause. Instead, it is based on Clause 10.6.4. Hence, the above check is not applicable, and has been removed.
16. For mat foundations designed to the ACI 318 codes, various numerical errors in the values shown in the plot of the moment capacity diagram and in the details presented in the calculation sheet for reinforcing zoning reports have been corrected. Also corrected was an error in the calculation of effective depth used in these computations.
17. In past versions, soil pressure diagrams were being displayed for mats supported only on piles (meaning, no soil supports are present). This has been corrected. These diagrams will henceforth appear only if soil supports are present.
18. An error in identifying corner piles for a vertical vessel on a square footing on piles has been corrected.
19. Minimum steel calculation per the Eurocode was based on the full depth of the footing. This has been changed to effective depth as required by section 9.2.1.1 of Eurocode 2.
20. An error that caused a failure to consider the column reaction loads for a mat foundation in some instances has been corrected.