How to Analyse a Portal Frame in ClearCalcs

Scope

Our portal frame sheets are designed to perform quick 2D analysis on level and gabled steel portal frames. Our steel section library is included to calculate all design actions on the structure according to the exact loads as applied by the engineer. These sheets do not apply load factors nor calculate strength capacities of structural members.

Types of Portal Frames in ClearCalcs and Key Inputs

Our portal frame calculators are available for single bay flat and gable roofs. They are designed to allow for quick FEA analysis of a 2D portal frame without needing to waste time modelling nodes and members in a full-fledged analysis software.

Diagrams are included with each calculation, but the below images summarise what the key geometry inputs relate to:

flatPortal.PNGgablePortal.PNG

General Notes

  • The main purpose of these sheets is to determine the shear, moment, and deflection of the portal frame.
  • Supports can be specified as pinned or fixed, and each member can be specified independently
  • The geometry of the portal frame is pre-specified to save the time otherwise spent specifying nodes and fixicities. Simply specify a height and width.
  • Loads are not factored, so any factoring must be performed by the engineer prior to entry if desired.
  • Loads are applied either from the left hand side or from the bottom of the selected member (i.e. how many mm from the left hand side of a horizontal member or from the bottom of the vertical member)
  • Axis selected refers to the direction of the load (visible on the diagram). Global Y refers to a force travelling straight up or down, Global X refers to a left-right load, while local will apply the load perpendicular to the selected member (i.e. on a 90 degree angle to the member, regardless of its given angle or location).

signConvention.PNG

  • Loading orientation refers to the orientation of the members individually with respect to the applied loads.
    • About major axis - the members are connected such that the loads are applied perpendicular to the major bending axis of each specified section. Typically, the major axis is characterised by a higher Ix value
    • About minor axis - the members are connected such that the loads are applied perpendicular to the minor bending axis of each specified section. Typically, the minor axis is characterised by a lower Ix value 

axisLoading.PNG

Design Example

The attached PDF covers the inputs required to follow achieve analysis for the below example. Note that whilst the portal frame analysis calculator doesn't automatically factor loads, we can achieve the 1.2G + 1.5Q case by typing a formula (just like you would in Excel) into the load entry/magnitude field (For example: =1.2*3+1.5*5). In this instance, that combination has resolved to 11.10 kN/m. Adding Self-Weight which is toggled on by default, the total downward load resolves at 11.64 kN/m.

Worked Example Portal Frame PDF Output

portalFrameExample.PNG

 

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