EN 1993 calculating Alpha_cr est for multi-storey buildings

[mohamed abdel aziz]

hello everyone,
in EN 1993-1-1 5.2.1 effects of deformed geometry on the structure it is stated that you can calculate alpha_cr as per expression 5.2 provided that axial compression in beams or rafters are not significant and it doesn't state how to calculate alpha_cr when axial compression is considered significant as per 5.3 expression of lamda_ however various resources online including SCI P399 refer to calculation of alpha_cr_est as per J. Lim and C. King I found this reference mainly concerning single storey portal frames the questions is do I have to calculate alpha_cr_est for multi-storey flat roof buildings too? in case there is high axial in rigid horizontal beams?

 

[HTURKAK]

My points ;

- BS EN 1993-1-1 Clause 5.2.1 (4) B ( Portal frames with shallow roof slopes and beam-and-column type plane frames in buildings may be checked for sway mode failure with first order analysis if the criterion (5.1) is satisfied for each storey. In
these structures αcr should be calculated using the following approximative formula, provided that
the axial compression in the beams or rafters is not significant ) and suggests the equation (5.2) .

- However, the second-order effects due to the rafter compression (P-Δ) , this check for αcr is un-conservative for portal frames. A better accurate formula has been developed by J. Lim and C. King details as shown on your post.

- Multi storey bldgs should be checked as per clause 5.2.1 Effects of deformed geometry of the structure.






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[mohamed abdel aziz]

Many thanks HTURKAK for taking the time to help with this I really appreciate it