CLEI: section classification
The methods currently available to classify cross-sections are simply not capable of addressing the problem of biaxial bending plus axial force stress state. Besides, the currently widely spread method to classify cross-section under mono-axial bending plus axial force (e.g.Owens GW and Knowles P.R., The Steel Designersí Manual, 5th ed., Steel Construction Institute) implicitly assumes to keep axial force constant when moving from applied stress-state to plastic locus (i.e. it keeps axial force fixed while computing a related plastic moment). That is not coherent with a linear increase of internal actions. In fact, they increase both.
The method presented in the previously cited paper, instead, not only is able to classify cross-sections under mixed internal actions, but it can also be generalized to generic cross-sections (L, T, box, et cetera). This method uses a planar map (in a plane named load-modes plane in the original paper) to plot generic S=(N, My, Mz) stress state. As the map is divided in regions where the cross-section classification is constant (class 1, 2, 3 or 4), the method has been called re-classes method, i.e. region-classes method.
The Author has developed this method in 1992 to implement Eurocode 3 automatic checks into the program Sargon. A stand alone simple application presenting this method has been bundled with a book published in Italy, and is now made available for international use in this web site. Its name is CLEI.
In the following of this page a simple user's guide is provided. The program is free and may be downloaded here.
Fig.1. Cross-section classification of a single stress state is here 2 (black dot, light blue region, reclass 2). HE 500A-S420. N=-1000N; M2=423000Nmm; M3=-56500Nmm.
The program first asks for a cross-section name and a material name (list boxes on the left). You can also enter material by entering the yield stress. The list of the cross-sections available includes IPE, HEA, HEB, HEM, HEAA. Cross-sections are listed in alphabetic order.
Then you have to specify one stress state by entering 3 numbers to set N, My (named M2 in the program) and Mz (named M3). Then you must press the button "Compute!".
Fig. 2. Cross-section classification to a vector of stress states read from file.
You may also specify a vector of stress-states (a cloud or strip of points as in Fig. 2), by reading a file into CLEI. The file must be .TXT and the format can be seen by considering the examples in the program folder.
For each stress state a black dot appears in the coloured map. The region where this/these point falls/fall into, specifies its/their class (cross-section classification according to Eurocode 3 may be 1, 2, 3, or 4). Regions (reclasses) may be filled and coloured or gray-scaled. Finally an image may copied into the clipboard and pasted into any bitmap-compatible file format, or directly printed.
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