After completing column calculations/design, the Governing case dialog, shown in the figure below, may be opened on the screen.
If the results of column calculations/design exist, the dialog may be opened in two ways:
- from the text menu by selecting the command: Results > Governing Case;
- from the toolbar by selecting the 'Column: Results' icon
.
The Governing case dialog presents the list of all load combinations taken into account during column design and indicates a position of the design cross-section (see also Column design procedure). For a selected combination the following elements are presented: column section with the neutral axis, compressive zone (yellow color) and tensile zone marked on it and appropriate safety factors. Once the calculations are performed (or once the verification is performed), the critical load combination (design combination) is selected in the dialog.
When the "Column: Results" dialog is opened, selection of load combinations in the dialog results in changing the section of the interaction surface displayed in the dialog (section in the plane of the selected load vector). The view may show the cross-section through the N-M or My-Mz interaction surface.
The right part of the dialog contains a table describing the list of load combinations. The table for basic and accidental combinations is presented separately. Each line shows parameters of one of the load combinations checked during column design. Next to components of a given combination there is an indication of the cross-section position: A - upper cross-section, B - lower cross-section and C - middle cross-section. A number of lines in the table corresponds to the three-fold number of load combinations. The next columns show the information as follows: axial force, bending moment around the Y axis, bending moment around the Z axis, as well as, if shear was considered, values of shear forces along the Y and Z axes.
For example, the combination saved as "1.35P1+1.5L1+1.05L2 (B)" was generated due to combining first dead load taken with the coefficient 1.35, first live load with the coefficient 1.5 and second live load with the coefficient 1.05; the action of forces resulting from this combination concerns the lower cross-section of the column.
The central bottom part of the dialog presents the drawing of the column real section in which the following elements are marked:
- longitudinal reinforcement,
- compressive zone (marked with yellow)
- tensile zone (marked with gray).
The Governing case dialog holds a table with safety factors which contains the following lines:
Rd/Sd
The Rd/Sd field shows the safety factor Rd/Sd for a combination selected on the list and the cross-section position, where:
Sd - load vector length
Rd - length of the load vector that corresponds to the ultimate limit state of the cross-section with the load acting on a given eccentricity.
MRd/MSd
The MRd/MSd field shows the safety factor MRd/MSd for a combination selected on the list and the cross-section position, where:
MSd - moment value (length of the projection of a load vector onto the MyMz plane)
MRd - value of the moment of the load vector that corresponds to the ultimate limit state of the cross-section with the load acting with a given axial force and with the effective moment in the direction determined by the components My, Mz.
NRd/NSd
The NRd/NSd field shows the safety factor NRd/NSd for a combination selected on the list and the cross-section position, where:
NSd - value of an axial force of the load vector
NRd - value of an axial force of the load vector that corresponds to the ultimate limit state of the cross-section with the load acting with a given moment.
The table columns present a comparison of the allowable value (on the left) with the value resulting from calculations for a given combination (on the right). If any of this conditions is not satisfied, the field will be marked in red.
ACI 318-14
The table with safety factors for the ACI 318-14 code contains the following lines:
ϕ*Sn/U
The ϕ*Sn/U field shows the safety factor ϕ*Sn/U for a combination selected on the list and the cross-section position, where:
ϕ - strength reduction factor
Sn - nominal moment, shear, axial, torsional, or bearing strength
U - strength of a member or cross section required to resist factored loads or related internal moments and forces in such combinations as stipulated in the code.
ϕ*Mn/Mu
The ϕ*Mn/Mu field shows the safety factor ϕ*Mn/Mu for a combination selected on the list and the cross-section position, where:
ϕ - strength reduction factor
Mn - nominal flexural strength at section, in.-lb
Mu - factored moment at section, in.-lb.
ϕ*Pn/Pu
The ϕ*Pn/Pu field shows the safety factor ϕ*Pn/Pu for a combination selected on the list and the cross-section position, where:
ϕ - strength reduction factor
Pn - nominal axial compressive strength of member, lb
Pu - factored axial force; to be taken as positive for compression and negative for tension, lb.
Additionally, for the ACI 318-14 code, the Governing case dialog holds a table with strength reduction factors which contains the following lines:
εt*1000
The εt*1000 field shows the factor, where:
εt - net tensile strain in extreme layer of longitudinal tension reinforcement at nominal strength, excluding strains due to effective prestress, creep, shrinkage, and temperature.
ϕ
The ϕ field shows the factor, where:
ϕ - strength reduction factor.