Sample Spreadsheet Calculations for Portal Frame Shed

Example spreadsheet calculations for determination of wind loads on a building with  a doubly pitched roof to the criteria of AS1170.2. Once reference wind pressure been found, then pressure coefficients on the external surfaces are found for directions theta=0 (transverse wind load) and theta=90 (longitudinal wind load). The moments in an assumed single span doubly pitched portal frame (or gable frame), are then calculated using Kleinlogel rigid frame formula: the frame is assumed to have fixed bases (eg. moment connections). Then based solely on sectional strength a minimum size steel section is selected. This section may not be suitable if cannot provide adequate lateral torsional restraint, and pass the detailed member capacity checks.

These calculations can be carried out using the following spreadsheet:

schShedDesignerR01.xls

Additional structural calculations are required to design a full building, this is just the calculations for the action-effects of the primary frame, and the design actions on the building. Ignoring the rigid frame, the spreadsheet simply provides the wind actions for the surfaces of the building which can be used to assess/design other components. Other components would include the following:

1. Roof X-Bracing and struts
2. Wall X-Bracing and struts
3. Roof Purlins (cladding rails)
4. Wall Girts (cladding rails)
5. End Wall Mullions

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schShedDesignerR01 by Conrad Harrison

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Revisions:

[08/06/2014] : Original
[14/09/2015] : Added some notes.

Member Selection Charts for Portal Frame Sheds (cold-formed Steel)

MEMBER SELECTION CHARTS

FOR PORTAL FRAME SHEDS

10° Doubly Pitched Frames

FOR

WIND

REGION A1

TC3

(DRAFT ONLY)

26 Design Charts, basically iso-moment contours in a span versus height space. The iso-moment curves reflect the AS4600 section moment capacities of readily available cold-formed c-sections.

Depth/Thickness	10	12	15	19	24	30
50
75
100	X	X	X	X
150		X	X	X	X
200			X	X	X
250				X	X
300					X	X
350						X

Typical Sizes of C-Sections Available in Australia.

Each chart is for a different spacing of the portal frames, so once a spacing has been decided on, and the appropriate chart chosen, it is then possible to identify which c-section to use for a given height and span for AS1170 wind region A1 and Terrain Category 3.

Since the charts are based on a linear elastic analysis and are only iso-moment curves, it is possible to calculate magnification and/or reduction factors for different loading conditions, and so select the appropriate c-section for say TC2. Further more it is not necessary to restrict selection to c-sections, once the moment capacity of the c-section has been identified other structural sections with compatible structural capacities can be substituted.

It should be noted that the design basis behind the charts is purely bending moment and moment section capacity. The charts are therefore only suitable for estimating purposes and a Chartered Structural Engineer (CPEng. NPER(structural)) should be consulted to determine if the charts are suitable for a particular building project.

To put it another way use the charts for conceptual design to assess the viability of a building proposal, then obtain the services of a structural engineer to complete the detail design: number and location of fly bracing, connections, footing piers etc... . When costing allow for the possibility that the section size may have to be increased when the building is fully engineered.

If the charts say not feasible, then not feasible, if charts indicate is feasible, then detail design may require a larger section to accommodate performance issues not considered in the charts. Such as high gravity loads which may buckle the columns, or deflection constraints. The feasibility of forming a moment connection may also indicate the use of thicker material or a larger section. The charts therefore only consider one issue: the minimum strength frame for the ultimate strength live loading and wind loading to Australian loading code AS1170.

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MorfJV01001 by Conrad Harrison

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Revisions:

[08/06/2014] : Original
[14/09/2015] : Editing of Notes

Height Span Chart Cold-Formed Steel Sheds TC2

Chart9CTC2y04m06d14R2 by Conrad Harrison

Height Span Chart Cold-Formed Steel Sheds TC3

Chart9BTC3y04m06d14R2 by Conrad Harrison

Technical Function Library

This is a library of functions for calculations to various Australian structural standards including:

1. AS1170.2 Wind loading 
2. AS4100 Steel structures code 
3. AS4600 Cold-formed steel structures code 
4. AS1720 Timber structures code 

It also contains a lot of experimental litter. It is an absolute necessity for using all my other spreadsheets. Spreadsheets are useful, but I find vba code more reliable and easier to read when it come to conditional tests, branching, and looping. Spreadsheets are not very reliable when it comes to tabulated calculations nor efficient. In a database management system an equation is defined once for a group of records and then progressively executed on each record. In a spreadsheet the equations have to be defined for each and every record (row) of the spreadsheet and that leads to potential error. It is also easier to expend an array in vba than it is to add extra rows to tables and mesh several tables together. Even if using tables of calculations in a spreadsheet it is easier to call vba functions to achieve greater consistency for each cell calculated, and too hide lots of complex conditional tests behind the scenes. Each different audience and purpose for calculations requires a different presentation, having vba functions provides greater flexibility compared to merely replicating hand written calcs in a worksheet.

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Taken from the ExcelCalcs.com website.