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Chapter 2.5 Framed Structures

Figure 2.5.11 Wind Moments

A fixed framework comprises structural beams and posts connected together with fixed connections transferring moments across the joists. Distribution of forces and deflected shape will depend largely on the degree of fixity of the supports (the extent to which moments are transferred). A recap of fixed end moments is followed by a review of moment distribution in a three member joint with varying support fixity. The principle off simple braced frames, wind frames and goal post frames is explored showing how simplifications can lead to fast and effective evaluation of frameworks.

Sometimes architectural demands are not easily met with cross bracing or strut bracing. A building may have a heavily glazed façade with no solid walls behind which the bracing may be hidden. Before the advent of personal computers engineers resorted to short cuts which were good approximations of real behaviour. Wind frame analysis was a commonly used method of designing frames up to three stories which used relatively few calculations.’
Figure 2.5.12 Base Column Deflection
The deflection for the bottom storey can be estimated by applying the rules of guided beam deflection, or cantilever with tip bending moment (deflection=mh²/2EI, where m=wh). Recapping, the frame will allow some rotation at the joists. The estimated deflection is likely to be greater by approximately 30%.

Demonstration Spreadsheets

The following figures are available to download in MS Excel format.