(5) The hinges in the mechanism are formed at the level of the underside of the haunch in the column and close to the apex.Įach chart requires a knowledge of the geometry of the frame and the design loading as input data in order to determine approximate sizes for the column and rafter member. (4) The ratio of span to eaves height is between 2 and 5. (3) The rafter slope lies between 10° and 20°. (2) The hunch length is approximately span /10 (1) The rafter depth is approximately span / 55 The application of the method relies on the following assumptions The simplicity of the charts depends on a series of three charts developed by Weller. Weller’s chart is usually used to quickly determine the plastic moments that can enable initial sizing of members.
In the plastic analysis of portal frames, preliminary analysis is usually carried out to determine member sizes before detailed checks are carried out to determine the adequacy of the selected sections.
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