Based on the lateral displacements of the story diaphragms, the interstory drifts and the elastic critical load factor, λ _cr , per BS 5950 can be calculated and displayed. RAM Frame offers two methods for specifying the locations at which λ _cr values are calculated: λ _cr values can be viewed for any point on a floor plan within the slab edges by selecting the Results – Lambda Critical – At a Point command or they can also be viewed for specific pre-defined points by selecting the Results – Lambda Critical – At Control Points command.

The Results - Lambda Critical - At A Point command allows the user to select the point for which λ _cr values are desired. This requires that the current view be a plan view. If the current view is not a plan view, the View - Plan command will automatically be invoked. With the view in plan the user uses the target cursor to select the point at which the λ _cr values are to be calculated and displayed. The point selected does not necessarily have to fall on a lateral member. The output will be displayed showing the deflection, interstory drift, and λ _cr values at that point for each of the appropriate load combinations for every level, not just the level currently on the screen. The values at any number of points may be viewed in this manner.

A printed output can be obtained by selecting the Print command or the Print icon while in the Lambda Critical Output view screen.

The Results - Lambda Critical - At Control Points command allows the user to predefine up to four points, called control points, for which λ _cr values are desired. The points defined do not necessarily have to fall on lateral members. The user first enters the coordinates of the Control Points. Control Point coordinates may be added, deleted, or changed at any time. The results can be displayed by selecting View Results. The λ _cr output will be displayed showing the deflection, inter-story drift, and λ _cr values at the control points for each of the appropriate load combinations for every level.

A printed output can be obtained by selecting the Print command or the Print icon while in the Lambda Critical Output view screen.

The lambda critical values are based on the notional loads. For the general case of a model with Dead, Live and Roof loads, the lambda critical results will be listed for 16 load combinations. Eight of these combinations correspond to the factors used for notional loads in the gravity load combinations. The other eight of these combinations correspond to the factors used on gravity loads in the lateral load combinations. In this way, the user can determine the lambda critical value associated with any load combination.

The output view screen is exited by selecting the lower control bar in the upper left hand corner of the screen.

If a level has no diaphragm or the selected point is outside a slab edge, the displacement of the point of interest at that story will be assumed to be zero. λ _cr is calculated by looking at the deflection of the next story below where the selected point is inside the slab edge.

Lambda Critical reports are not available for models for which the Diaphragm criteria in Criteria - Diaphragm are set to Flexible for all levels. Also, if model does not have any notional load case or there exists no notional load case analyzed, this report will not be available.