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Technical Wall Example

Technical Information

General - Presented in the load tables are maximum uniformly distributed specified loads.

Steel - Conforms to ASTM A653/A653M or A792/A792M. Grade 33/230; Yield stress 33 ksi/230 MPa and tensile stress 45 ksi/310 MPa. Grade 50 /345; Yield stress 50 ksi/345 MPa and tensile stress 65 ksi/450 MPa.

Finishes - A25/ZF75, G90/Z275 or AZ50/AZM150. For heavier metallic coatings, refer to ASTM A653/A653M or A792/A792M.

Load Tables - Significant changes have been made in the 2005 Edition of the National Building Code of Canada (NBCC) and are now contained in the 2010 Edition regarding the determination of the specified wind and snow loads. Importance factors have been introduced that are applied to both strength (ULS) and serviceability/deflection (SLS) limit state design considerations. A lower load factor for wind of 1.4, instead of 1.5 used for live and snow loads, has also been introduced. This lower load factor for wind somewhat offsets the higher wind loads (1 in 50 year return) that are now listed in the NBCC by geographic location. The importance category of the end use of the building/structure must also be recognized, such as Normal or Low.
All of these changes impact how the load tables are to be used. In an effort to help the design professional with the load tables, the information below was taken directly from Division B, Part 4 (Structural Design) of the NBCC.

Specified Wind Load

The importance factors, Iw and Is, have been incorporated in the load tables, as well as the importance category. The parameters in the boxed-in portion of Equations [1] and [2] must be determined by the design professional in accordance with the NBCC.

Strength - The maximum uniformly distributed specified load based on strength in the load table must be equal to or greater than the(specified live load).

Serviceability (Deflection) - The maximum uniformly distributed specified load based on deflection in the load table must be equal to or greater than the specified live load. The effective moment of inertia for deflection determination was calculated at an assumed specified live load stress of 0.6Fy.

EXAMPLE (Use of Load Table)

WF 324 Wall (Normal Importance Category)

Given: (Metric units)

(LLF = 1.4 and Iw = 0.75)
~ Deck thickness, t = 0.610 mm
~ Triple span continuous, L = 3.2 m each span
~ Bearing length, N = 50 mm
~ L/360 deflection limit
~ Wind live load, LL = 1.5 kPa

The live load is the value of the boxed-in portion of the specified wind load expression [1].

Solution:
Strength S

  1. Specified wind live load = 1.5 kPa
  2. Maximum specified load (from Load Table)
    Is 2.34 kPa
    Since 2.34 > 1.5 ∴OK
  3. Check web crippling (N = 50 mm)
    a) End reaction = 0.400(1.5)3.2 = 1.92 kN/m
    (from section property table)
    Pe = Pe1 + Pe2[N/t]½
    = 1.24 + 0.310[50/0.610]½ = 4.05 kN/m
    Since 4.05 > 1.92 ∴OK
    b) Interior reaction = 1.1(1.5)3.2 = 5.28 kN/m
    (from section property table)
    Pi = Pi1 + Pi2[N/t]½
    = 2.46 + 0.418[50/0.610]½ = 6.24 kN/m
    Since 6.24 > 5.28 ∴OK
Deflection D
From table L/240 = 3.42 kPa
For L/360, multiply 3.42 by 240/360 = 2.28 kPa
Since 2.28 > 1.5 ∴OK