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The program now implements fire design procedures from NDS Chapter 16. The option of retaining the procedures from IBC 722.6.3 remains in the program.
Radio buttons in Beam and Column Input view allow you to choose between IBC 7.22.6.3 and NDS Chapter 16 procedures. Note that this can be saved as a default for new files via the “Save as Default” and “Restore factory” options, and can be applied to Concept mode via the button in the Load Input view that is used to apply settings input in Beam and Column mode to the open Concept mode file.
A line has been added to the CALCULATIONS section of the Additional Data section of the Design Check results giving the procedure used.
The input for fire design parameters has been moved from a dialog box invoked when the Fire Design button is pressed, to the main Beam Input and Column Input views and the fire design button has been removed.
The input for the default value for whether fire design is applied and the default fire rating have been moved from the Design Settings to the Default values settings page.
Fire design input for Concept mode is still located in the Beam and Column Groups dialog boxes.
The required duration of fire design has been changed in the Default Settings and in Beam and Column view from an input in minutes to a dropdown that allows you to choose between 1 hr, 1.5 hrs, and 2 hrs, with the “factory” default being 1.5 hours. The corresponding setting in Concept Mode remains in minutes.
The program allows you to select between 0, 3 and 4 sides exposed. This is the same functionality as when the input settings were in the dialog box.
A new input for fire protection is described below.
For both the NDS and IBC procedures, the program now takes into account the protection from fire afforded by materials covering the exposed surfaces of the affected members. This is not specified in either the NDS or the IBC; it comes from Fire Resistance of Wood Members with Directly Applied Protection (Robert H. White 2009)
You are limited to the choices of one- or two-ply 5-8” fire rated (Type X) gypsum wall board for as they were tested and results published for them in Fire Resistance of Wood Members with Directly Applied Protection .
The duration of fire used in the charring calculations is reduced from the required fire rating by the amount of time afforded by the Protection type selected. For one ply 5-8” fire rated (Type X ) gypsum wall board it is 30 minutes; for two ply of this material it is 60 minutes. Protection is assumed to be applied to all exposed surfaces
The fire protection material has been added to the line in the materials specification where it currently gives rating and no. of exposed sides.
The duration of fire protection has been added to the CALCULATIONS section of the Additional Data section of the Design Check results.
The IBC clause number has changed from IBC 7.21.6.3 to IBC 7.22.6.3. This is reflected in the input field and in the Design Check output.
Fire protection as described above has been added to this procedure as well as being implemented for the NDS procedure.
The program now implements NDS 2012 Chapter 16, which involves design for bending, axial design, and combined axial and bending of the member using residual cross section after charring, and the use of special modification factors. Note that this procedure first entered the NDS design standard in 2001, however this is the first time it has appeared in Sizer.
The same inputs are used for both procedures, that is Duration, No of Sides Exposed, and Protection, described above.
The effective char rates βeff calculated in 26.2-1 and shown in Table 16.2.1 are used, based on a nominal char rate βn of 1.5 in./hr. as recommended. A residual section size is calculated using this char rate multiplied by the input fire duration rating.
Only load combinations involving Dead, Live and Snow are evaluated at reduced cross section for fire design criteria (earthquake, wind, live roof, and impact are excluded).
The member is analysed using the stiffness EI of the full section. Since stiffness is constant over the length of the member, the resulting reactions and stresses are the same as for the reduced section.
The design criteria given in 16.2.2 are calculated using the residual cross section as the member breadth b and depth d values. These are
For beams and columns:
Bending – positive moment
Bending – negative moment
For columns only
Axial compression
Axial tension
Combined bending and axial tension
Combined bending and axial compression
These design criteria are equivalent to the main design criteria of shear, bending, deflection, and vibration. The member design is considered to have failed if one of them fails, and the program passes over a candidate section when designing for unknowns if it fails one of these criteria.
The adjustment factors shown in Table 16.2.2 are the only modification factors applied. The size factor CF , glulam volume factor Cv, and flat use factor Cfu are calculated using the full cross section of the member ; the stability factors CL and CP use the modified section.
A section at the end headed by Fire has been added, and a line for each fire design criterion giving stress, allowable stress, and design ratio.
Lines have been added for each fire design criterion giving the modification factors to. Modification factors not in Table 16.2.2 and which are irrelevant to fire design are shown with a dash.
The CALCULATIONS section of the Additional Data section of the Design Check results gives the size of the residual section, the char rate, and the Design Stress to Member Stress factor from Table 16.2.2 for each design criterion used. It also repeats that the CD factor = 1.0 for emphasis.