Initial Bow
Floor Tie
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:
No vertical or lateral displacement at the bottom restraint.
All other restraints are restrained against horizontal displacement but are on rollers vertically.
Through matrix manipulation, the true displacements at the ends of each member are computed for each given loading condition. Then the exact end moments and forces are determined using the computed displacements. If member properties are altered, its effect is reevaluated in the above manner.
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
K = 2.0, l = wall or column height, and r = 0.3 T / 12
Walls are designed using the factored axial load, Pu, and a magnified factored moment, Mc, defined by:
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.