CHAPTER 5: SECONDARY MEMBERS DESIGN
5.2. Secondary Structural Framing
5.2.1. Cold Formed Cross Sections Properties and Capacities 1. 200mm depth Z-sections
Table 5.19
General Data Allowable
Shear Force
Allowable Bending Moment
(**) Based on a reduction factor of 0.70 for continuous spans and an increase of 33% on allowable stress for wind load applications resulting in compression in the unrestraint flange while the other tension flange are fastened to sheeting.
(Applicable only if the span of the longest member is not more than 20% longer than the shortest span). For simple spans multiply Ma2 values by 0.5/0.7.
Notes :-
1. Dimensions are out to out of section thickness ‘t’.
2. All sections are designed in accordance with the Cold-Formed Steel Design Manual, AISI 1986 Edition.
3. Specific yield strength Fy of light gauge cold-formed steel = 34.50 kN/cm2
4. Coil width = 345mm
5. For the properties of Nested Purlins add the appropriate individual section properties except Rx, Ry and H/t.
6. Section are used for roof purlins & wall girts
20
5.2.1.2. 250mm depth Z-sections
Table 5.20 Section Properties
About X-X Axis About Y-Y Axis Others
General Data Allowable
Shear Force
Allowable Bending Moment
(**) Based on a reduction factor of 0.70 for continuous spans and an increase of 33% on allowable stress for wind load applications resulting in compression in the unrestraint flange while the other tension flange are fastened to sheeting.
(Applicable only if the span of the longest member is not more than 20% longer than the shortest span). For simple spans multiply Ma2 values by 0.5/0.7.
Notes :-
1. Dimensions are out to out of section thickness ‘t’.
2. All sections are designed in accordance with the Cold-Formed Steel Design Manual, AISI 1986 Edition.
3. Specific yield strength Fy of light gauge cold-formed steel = 34.50 kN/cm2
4. Coil width = 390mm
5. For the properties of Nested Purlins add the appropriate individual section properties except Rx, Ry and H/t.
6. Section is used for roof purlins & wall girts (Special loads or bay spacings.
5.2.1.3. Z-sections overlaps
Z-shaped purlins are adopted for pre-engineered buildings that can provide a great advantage of being lapped at support points and nested together in order to increase the stiffness. This capability provides additional strength and reduces deflections.
Type of Laps:
There are three types of Purlin laps used according to lap length:
1. Short Lap: These purlins are with a 130-mm total lap over supports (65 mm from either side), and distance between bolts being 80 mm. This lap is constant whether it occurs in end bays or in interior bays. This type of lap is normally used for short bays (< 6m) and light loads. The capacity of this lap connection is determined as follows:
Allowable shear per 12 mm A307 bolt = 7.8 kN.
Therefore allowable couple = 0.08 x 7.8 x 2 = 1.25 kN-m
2. Continuous Lap: For moderate bays (6m-9m) the lap is 385mm on either side of support making the total lap length of 770mm. It is termed ‘Continuous Lap’ since it provides a reasonable continuity of purlins over the supports.
3. Long Lap: For long bays (> 9m) the lap length is of 705 mm on either side of support. It is referred as `Long Lap'. This type of lap provides almost full continuity used for long bays and heavier loads.
Purlin Lap Details Note: All Bolts M12 - MB A307
• NOTE: For nested Z-purlins (full laterally restraint) bending moment and shear force capacities are the summations of capacities of the individual sections.
5.2.1.4. 120mm depth C-sections
Table 5.21 Section Properties
About X-X Axis About Y-Y Axis Others
Section Gross Ix 120C20 120.2 120.2 20.04 20.04 4.81 25.97 12.99 6.58 12.67 2.24 2.05 2.921 120C25 148.5 148.5 24.76 24.76 4.78 32.34 16.71 8.26 15.51 2.23 2.085 2.924 120C30 175.9 175.9 29.33 29.33 4.75 38.67 19.33 9.97 18.23 2.23 2.121 2.294
Section Capacities
(*) Based on a reduction factor of 0.40 for simple spans with one unbraced compression side and an increase of 33% on allowable stress for wind load application.
1. Dimensions are out to out of section thickness, t.
2. All sections are designed in accordance with the Cold-Formed Steel Design Manual, AISI 1986 Edition
3. Specific yield strength “Fy” of light gauge cold-formed steel = 34.50 kN/cm2
4. C.G. = Center of Gravity 5. S.C. = Shear Center 6. Coil width = 260 mm
7. Section are used for framed openings, Doors
5.2.1.5. 200mm depth C-sections
Table 5.22 Section Properties
About X-X Axis About Y-Y Axis Others
Section Gross Ix
General Data Allowable
Shear
(*) Based on a reduction factor of 0.40 for simple spans with one unbraced compression side and an increase of 33% on allowable stress for wind load application.
Notes :-
1. Dimensions are out to out of section thickness, t.
2. All sections are designed in accordance with the Cold-Formed Steel Design Manual, AISI 1986 Edition
3. Specific yield strength “Fy” of light gauge cold-formed steel = 34.50 kN/cm2
4. C.G. = Center of Gravity 5. S.C. = Shear Center 6. Coil width = 390 mm
7. Section are used for framed openings, wall girts & end wall posts and beams, mezzanine Joist.
d
5.2.1.6. 300mm depth C-sections
Table 5.23 Section Properties
About X-X Axis About Y-Y Axis Others 300C20 1308.5 1308.5 87.23 74.29 11.50 91.81 45.91 14.55 41.90 3.04 2.19 3.61
Section Capacities
Section
General Data Allowable
Shear Force Allowable Bending Moment (kN.m)
(*) Based on a reduction factor of 0.40 for simple spans with one unbraced compression side and an increase of 33% on allowable stress for wind load application.
Notes:
2. Dimensions are out to out of section thickness, t.
3. All sections are designed in accordance with the Cold-Formed Steel Design Manual, AISI 1986 Edition.
4. Specific yield strength “Fy” of light gauge cold-formed steel = 34.50 kN/cm2
5. C.G. = Center of Gravity 6. S.C. = Shear Center 7. Coil width = 495 mm
8. Section is used as end wall rafter and posts mezzanine Joist.
5.2.1.7. Double ‘C’ -sections
- Double ‘C’ section are C-sections connected back to back using stitch bolts forming assembled I-section used as end wall posts & rafters or as mezzanine joists.
- C-section of depths 200mm and 300mm are used for assembled I–sections.
- For Fully Lateral Braced sections the capacity of the double sections capacities are twice the single sections capacities (tables 5.22&5.23).
- For cases of sections laterally braced at intervals (gable posts & rafters) the section properties about axis Y-Y are calculated as I –section for the cases when the stitch bolts spacing satisfying the requirements of AISI 1986,1989 addendum clause (D1.1.) otherwise two ‘C’ section are considered acting independently.
- The section properties of the double ‘C’ satisfying the AISI requirements above are as follows
Table 5.24 – 200 Double ‘C’ -Section Properties
SECTION PROPERTIES
ABOUT X-X AXIS ABOUT Y-Y AXIS
SECTION Gross Ix cm4
Defl.
Ix.
cm4
Gross Sx.
cm3
Eff.
Sx.
cm3
Rx.
cm Iy
cm4 Iyc
Cm4 Sy
cm3 Ry
cm
200][20 982.0 963.66 98.34 82.90 7.86 240.8 120.4 28.33 3.90
200][25 1221.2 1219.8 132.12 107.42 7.91 302 151 35.53 3.94
300][20 2617 2617 174.46 148.58 11.50 278.6 139.4 32.77 3.75
d
Y
Y
X X
200 ][ 20
d=Depth SHAPE t = THICKNESS
85mm
C.G.
S.C.
L
85mm
5.2.1.8. Eave Strut-section
Table 5.25 Section Properties
GENERAL DATA ALLOW.
SHEAR
NOMINAL MOMENT
ALLOWABLE BENDING MOMENT (KN-M)
SECTION WEIGHT KG/M
1. Calculation dimensions are out to out of Section thickness, t.
2. All Sections are designed with reference to the Specifications of "Cold-Formed Steel Design Manual"
AISI 1986 Edition.
3. Specific yield strength of light gage Cold-Formed steel Fy
= 34.50 KN/cm2
4. (+) Based on reduction factor of 0.40 for simple span due to wind load uplift or suction - with 33% increase (with fully unbraced compression flange).
5. (*) Based on reduction factor of 0.60 for continuous span due to wind load uplift or suction - with 33%
increase (Applicable if the longest member span is not more than 20% of the shortest span).
6. CG = Center of Gravity.
7. SC = Shear Center 8. Used as eave strut