Initial Bow
The initial bow is used to determine the initial shape of the member for the analysis. Because of this when the initial bow is not equal to zero secondary moments will be generated even if the analysis type is not P-Delta. The total initial bow is the sum of the prestressing camber and the additional bow the user inputs (positive being towards the exterior).
Floor Tie
The floor tie is used in the analysis by staging the loads into two stages, pre and post floor tie. The analysis is run with the pre-floor tie loads, selected based on a user input, using all boundary conditions besides the floor tie. Then the analysis is run with the remaining loads, including self weight, using the deflected shape from the initial stage. These results are summed together for the final analysis results.
Structural Model
The method of analysis is the displacement or stiffness method. The structure is represented by a matrix consisting of member stiffnesses. These are derived for three possible movements at the ends of members: vertical, horizontal, and rotational. The following boundary conditions are then applied to the matrix:
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The sign conventions follow the right hand rule. Currently Eriksson Wall ignores local effects such as the concrete ‘columns’ on each side of a door or window. The analysis engine does, however, take the door or window into account in the stiffness matrix.
Second Order Effects
P-Delta Analysis
An elastic second order analysis is performed when second order effects are set to P-Delta. In this analysis, the deformed geometry of the wall panel is included in the equilibrium equations so that the additional moments due to the deflected shape are included. The program always captures these second order effects from the temperature gradient and the initial bow. Enabling P-Delta ensures we also capture these effects from the lateral loads on the panel.
Moment Magnification
Slenderness may be neglected if kl/r < 22, where
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Walls are designed using the factored axial load, Pu, and a magnified factored moment, Mc, defined by:
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Cracked Section
The iterative approach based on the work by Robert Mast is used to perform the cracked section analysis (this procedure is covered in detail in the PCI Design Handbook). This iterative procedure consists of assuming a depth to the neutral axis, computing the section properties of the net cracked section, checking stresses at the assumed neutral axis location, and then revising this location as necessary to make the concrete stress equal to zero at the assumed neutral axis location.