BS5950 Part 1 : 1990
Web Buckling (4.5.2.1)
RAM Frame assumes that when calculating the slenderness of an unstiffened web of depth d, lambda is taken as 2.5d/t. This assumption implies that the column flange on which the load is applied is effectively restrained against rotation relative to the web, and lateral movement relative to the other flange. Where stiffeners are used to resist this load they will be designed according to 4.5.2.3. The stiffeners are also checked as bearing stiffeners per 4.5.3.2.
Web Bearing – Tension and Compression (4.5.3.1)
If stiffeners are required they are designed in accordance with 4.5.3.2. If the column does not have the capacity to carry the applied load, then the web bearing capacity is recalculated using the lower of the nominal yield strength of the column web and the stiffener.
Web Tensile Force (4.5.4, 6.7.6)
Where required, stiffeners are designed in accordance with 4.5.4. Per 6.7.6, the dimension rc (and zc) is assumed to equal the column k (dimension from outer column flange face to the root of the web-to-flange weld) less the thickness of the column flange (k-tf). For built up sections the engineer should provide the appropriate k value in the master steel table to obtain the correct zc value.
Web Shear (4.5.6)
RAM Frame will not design diagonal web stiffeners. However, the required force for diagonal stiffener design is provided in the output. The capacity of the column web is calculated using the design yield strength of the column. If this capacity is not sufficient, then the column web capacity is recalculated using the lower of the column web and stiffener plate yield strengths. The reported stiffener design force is the horizontal shear calculated as the difference between the applied force and the capacity of the web (calculated using the lower of the web and stiffener nominal yield strength’s).
Stiffener Design
Where stiffeners are required for web buckling (4.5.2.1) then they are designed in accordance with 4.5.2.3. Note that a 20 N/mm2 reduction is not taken on the design yield strength of the stiffeners. The stiffeners are designed using the lower of the web and stiffener yield strengths. Where stiffeners are checked for bearing per 4.5.3.2 the cope dimension is considered. The stiffeners are always designed in accordance with 4.5.2.3, 4.5.3.2 and 4.5.4 when applicable. Note that the stiffeners are not considered to be intermediate stiffeners per 4.5.5., i.e. they are not considered necessary to resist shear buckling. The engineer has significant control over the stiffener design dimensions. The criteria by which the stiffener dimensions are calculated can be modified in the dialog displayed by invoking the criteria-joints command. The width of the stiffener is calculated first. If the thickness is calculated per code then per specification 4.5.1.2 the outstand of the stiffener from the face of the column web will not exceed 13 ts Epsilon. The length of the stiffener (when not required to be full length) is calculated according to 4.5.10. The minimum length of stiffener that will be provided by RAM Frame is one-third of the depth of the column.
BS5950 Part 1 : 2000
The provisions of BS 5950-1:2000 for web bearing (4.5.2.1), web buckling (4.5.3.1) and local flange bending (6.7.5) have been implemented in RAM Frame. Note that for the beam flange that frames into the absolute top of a column, the ae and be values in 4.5.2.1 and 4.5.3.1 are conservatively taken as 0.0. Refer to the previous section on BS5950 Part 1:1990 for more information.