Canadian Design Parameters

Parameters controlling the steel design are entered on the Member Design Parameters spreadsheet. These parameters are entered on a per member basis, and control the code checking on a per member basis.

w1 - Interactive Bending Coefficient

w1 is the coefficient to determine equivalent uniform bending effect in beam-column, as described in Section 13.8.6 of CSA S16-99. If left blank, will calculate it. The w1 value is dependent on the member's end moments, which may change from one Load Combination to the next. Therefore it is a good idea to leave this entry blank and let the program calculate it.

w2 - Bending Coefficient

w2 is the coefficient to account for increased moment resistance of a laterally unsupported doubly symmetric beam segment when subject to a moment gradient, as described in Section 13.6.1 of CSA S16-19. If left blank, the value will be calculated by the program. The w2 value is dependent on the moment in the member, which may change from one Load Combination to the next. Therefore it is a good idea to leave this entry blank and let the program calculate it.

Canadian Limitations

It is assumed the transverse load on the member is occurring through the member's shear center. This means secondary torsional moments that may occur if the load is not applied through the shear center are not considered.

Pipes and Bars - For pipes and round bars for S16-14 and earlier, the code check is calculated based on an SRSS summation of the y and z-axis stresses calculated for the pipe or bar. For S16-19, the code check is calculated based on biaxial bending for both orthogonal axes in accordance with Clause 13.8.3.

S16-19, S16-14, S16-09

Tapered Wide Flanges - No code checking is done for "Tapered WF" members which have different "Start" and "End" Depths, or which have top and bottom flanges of different widths. In other words, the "Tapered WF" may only be used for prismatic, doubly symmetric sections.

Single Angles - For S16-09 and earlier, single angles in compression are not checked for Clause 13.3.2.2 or 13.3.2.3 because there is insufficient information regarding the connections and usage of the member. They are not checked for Clause 13.3.2 (Flexural-Torsional Buckling) either. Instead they are checked for Euler Buckling about their geometric or principal axes per Clause 13.3.1. The slenderness classification for single angles is based on the longer leg.

S16-09 recommends using a "rational analysis" to account for lateral-torsional buckling and shear checks on single angles, so RISA uses the AISC 360-10 (14th Edition) provisions for these checks.

For S16-14 and newer codes, the program takes into account 13.3.2.2 for the effective modified KL/r buckling method. In the properties panel, under design properties, there is a dropdown for Single Angle Conn. which sets the design method for axial compression. Users will not see this dropdown if a single angle is not the current shape type or the CSA S16-14/19 code is not selected. Below are behaviors for each of the items in the dropdown:

• Long Leg is selected: The program will follow clause 13.3.2.2 and use the modified KL/r method to determine design axial compression.

• Short Leg is selected: The program will follow 13.3.2.2 and modify the KL/r with the appropriate increase factors to determine design axial compression.

• Other is selected: The program will follow axial compression design calculations based on Clause 13.3.1.1 using an unmodified KL/r.

When the leg length ratio is greater than 1.7 the program will always follow clause 13.3.1.1 regardless of the method specified in the dropdown. For both the Long Leg and Short Leg provisions, the user will need to confirm that the limitations of this section are met. This includes, single angles connected through the same one leg, members attached by a minimum of two bolt connections and no intermediate transverse loadings along the length of the member. Currently the program does not check axial compression in accordance with clause 13.3.2.3 for box and space trusses.

For S16-19, the program calculates flexural bending properties for single angles about their principal axes, even when the member is fully laterally braced. While the S16-19 code introduced new provisions for bending about a single geometric axis, the software currently cannot distinguish this condition from biaxial bending. Due to this limitation, the program defaults to using principal section properties for all single angle bending cases, effectively maintaining the behavior used in S16-14 and earlier codes.

For older models that do not have this dropdown, the program will automatically assign the Other property to the member. This follows a similar method for previous axial compression design calculations. For any members that are drawn, the dropdown will always default to Long Leg.

Class 4 Members - Members with both Class 4 (slender) webs and Class 4 (slender) flanges are not designed. Per S16, Clause 13.5.c.i these members must be designed per S136. Where only the web or the flange is Class 4 (slender) the capacity is determined per the provisions of S16, Clause 13.5c.

The code is not clear on whether this applies to WT, Double Angle, and Single Angle members, since they do not have a "web". Therefore, for these member types, the program calculates an effective (reduced) yield stress for each leg/flange/stem and uses the smallest value for the entire section.

Axial compression design: Class 4 members in compression must be designed with consideration for a reduction in available capacity due to the possibility of elastic local buckling of slender elements. For CSA S16‑14 and earlier editions, the axial compression capacity is determined using the effective yield stress method per Clause 13.3.4b. For CSA S16‑19, all Class 4 members other than pipes and round HSS profiles are designed using the effective area method per Clause 13.3.4a.

Pipes and Round HSS - The code does not address how to determine the shear capacity of Class 3 or Class 4 (Noncompact, Slender) pipes. Therefore no design is done for those members. Class 1 and 2 member capacities are determined per the provisions of S16.

Shear Capacity - The code does not address how to determine the shear capacity of WTs, Double Angles, or Single Angles where shear buckling is a consideration (S16 Clause 13.4.3). Therefore no design is done for members where d/w or b_el/t exceeds 1014/(F_y)^1/2.

WTs - The lateral-torsional buckling moment capacity calculation (Clause 13.6e.i) in the code does not address how to calculate L_u when the stem of the WT is in compression. Therefore L_u is always taken as zero, which is conservative. For S16-14 and earlier, the code does not address how to calculate β_x when the stem is in compression. Therefore, I_yc is taken as zero, which results in a negative value of β_x, which is conservative. For S16-19 and later, the β_x given in the CISC Structural Section Tables will be used. For custom shapes, or shapes from other databases where β_x is not given, the value will be calculated using the general equation shown below from the CISC Handbook of Steel Construction (12th Edition).

Double Angles - The code does not address how to calculate lateral-torsional buckling moment capacity. RISA therefore uses the AISC 360-22 (16th Edition) provisions for these checks, as they are a widely accepted rational method. When this method is used, it is assumed that Cb = ω2. The slenderness classification for double angles is based on the longer leg.

Welded Reduced Flange (WRF) Members- Since these members are classified within RISA as "Tapered", there is currently no design done for them. This limitation will be removed in a future release.

Torsional Buckling and Flexural Torsional Buckling (S16-09 and earlier) - The limit states of torsional buckling and flexural torsional buckling are not considered for wide flange and channel members. This means that the value F_ez is not calculated for these members per Clause 13.3.2. The program takes the lesser of F_ex and F_exy for axial buckling capacity for the S16-09 and earlier codes. These limit states are fully considered for S16-14 and later because an L_torque input was added into the program for these later editions of the code.

Compressive Strength (S16-09 and earlier) - For the equations in section 13.3.1, the parameter "n” is assigned a value of 1.34 for all shapes for S16-09 and earlier codes. This is conservative for WWF shapes and HSS shapes that are stress-relieved. For S16-14 and later, members designated as type "Tapered WF" use n = 2.24 while members designated as type "WF" use n = 1.34.

Double Channels - Double channel design for Canadian code is only available for S16-14 and later. Connector spacing requirements are not checked for double channels.

S16.1-94, S16-01, S16-05

WT and LL Shapes - The criteria in the AISC LRFD 2nd Edition code is used to perform code checks on WT and LL shapes since the Canadian code does not explicitly specify how to calculate the flexural strength of WT and LL shapes.

The Canadian code does not address the rare case where Lateral Torsional (or Flexural Torsional) Buckling occurs for WT's and double angles bent about their weak axis.

Tapered Wide Flanges - The AISC LRFD 2nd code is used to perform code checks on Tapered WF shapes when the Canadian code is specified. The Canadian code CAN/CSA S16.1-94 does not address web-tapered members.

Single Angles - Code checking on single angle shapes is performed for tension only. Single angles will have the following message displayed on the Steel Code Check Spreadsheet to remind the user of the tension only code check: "Single Angle code check based on Axial Tension ONLY"

Please see Single Angle Stresses for more information on the calculation of single angle stresses.

Slender Shapes - Shapes with any slender elements are not supported for axial compression. Shapes with slender webs or flanges are not supported for flexure. These shapes use the criteria in the CAN/CSA S136 code, which is not supported at this time.

Canadian Special Messages

When a code check is not performed for a particular member a message explaining why a code check is not possible will be listed instead of the code check value. You can click the cell that contains the message and look to the status bar to view the full message. Following are the messages that may be listed specifically for the Canadian Code: