HƯỚNG DẪN SỬ DỤNG PHẦM MỀM TÍNH XÀ GỒ CFS
1. Material and Section:
1.1.
Material:
It can be applied as Carbon Steel or Stainless Steel. As design practice, it is usually chosen as
below:
-
Black purlin: A36
Fy= 245 MPa; Fu= 400 MPa.
- Galvenized Purlin: chọn A572, Grade 65
Fy= 450 MPa; Fu= 550 MPa
 What is the difference between Cold-form and Hot-rolled steel?
+ Hot-rolled: form at elevated temperature
-
-
Advantage:
Less processing.
Cheaper.
Wider range of Shape.
Disadvantage:
Not have thin thickness.
Usually low strength.
Shape effected by process, so not accuracy.
Rough surface.
+ Cold-formed: essentially hot-rolled, but form at low tenparature (Purlin Coil, Steel plate for
built-up section).
-
-
Advantage
Have thin thickness.
High strength.
Accuracy shape.
Good surface
Disadvantage:
More processing
Expensive
Limited of shape (only for Coil,…)
1.2.
Section:
C: apply for single-span beam
Z: apply for multi-span beam
-
Z150x62x68x20x(1.5, 1.75, 1.95, 2.4, 3.0)
Z200x62x68x20x(1.5, 1.75, 1.95, 2.4, 3.0)
Z250x62x68x20x(1.5, 1.75, 1.95, 2.4, 3.0)
Z250x73x79x20x(1.5, 1.75, 1.95, 2.4, 3.0)
Z300x73x79x20x(1.75, 1.95, 2.4, 3.0)
Z300x93x100x20x(1.75, 1.95, 2.4, 3.0)
Do not stick to highlight by green colour, due to safety reason:
+ Apply cold work of forming strength increase: only use strength of material in CO-CQ.
+ Apply inelastic reserve strength increase: it need to meet some requirements from AISI to use this
tip, but encourage to design only in elastic condition.
1.3.
How to get section properties from AutoCAD:
Command PL to form Shape.
Command REG to define region.
Move UCS to section Centroid.
Command MASSPROP to get section properties.
2. Design process:
2.1.
Choose section:
- From Library (available created).
- From AutoCAD
2.2.
Analysis Model (Analysis Wizard):
Choose type of Structure
 Note 1: Parameter of beam in Model
Lap length: Lap in 1 side
Lap detail in CFS
When tick to Fixed End Support, cannot use Cantilever length.
+ Cách chọn đoạn Lap trong CFS:
Dựa vào biểu đồ nội lực và chiều dài giới hạn để vận chuyển.
 Note 2: Bearing length and Fastening support:
+ Bearing length: see definition in AISI, and calculate for Web Crippling condition
- Case 1: Purlin directly connect to rafter flange: b= width of rafter flange
- Case 2: Purlin connect Rafter by connection plate, with no gap between purlin and rafter
b= width of rafter flange (as indicated in AISI Specification)
- Case 3: Purlin connect to Rafter by connection plate, with gap 10mm between purlin and rafter
(usually use this case): No need to check Web crippling connection, all force come to Machine bolt
(connect Purlin to Rafter).
+ Fastening support:
- Yes: Purlin connect to Rafter
- No: Purlin does not connect to Rafter.
 Note 3: Member bracing: distance of Purlin bracing:
L < 5m: 0 (None)
5 ≤ L < 8: 1 (Mid)
8 ≤ L < 9: 2 (Third)
9 ≤ L ≤ 12: 3 (Quarter)
12 L: fully brace
 Note 4: Brace flange:
Top and Bottom is braced (Top flange connected to Sheeting by Screw, Bottom flange connected to
Rafter to Bolt).
 Note 5: Reduction Factor: depend on type of beam structure:
If there is a braced flange, enter the moment reduction factor as defined in the AISI or ASCE
Specification for your situation. For example:
R=0.70 for continuous span Z sections
R=0.60 for continuous span C sections
R=0.70 for simple span C or Z section, depth £ 6.5"
R=0.65 for simple span C or Z section, 6.5" < depth £ 8.5"
R=0.50 for simple span Z section, 8.5" < depth £ 12"
R=0.40 for simple span C section, 8.5" < depth £ 12"
 Note 6: Stiffness and length Lm
+ Rotational Stiffness k:
“The rotational stiffness provided to the braced flange by connection to the bracing material (deck,
sheathing, etc.). This stiffness is incorporated in the distortional buckling calculations for the flange
which is braced (bottom, top, left, or right). The units for this input are moment/radian/unit length
(such as k-in/rad/in) which is then reduced to a force (such as k). Refer to the AISI Specification
and Commentary for more information on determining what value to use.”
Value k= 0.667 to 1.96; for condition purlin connect to sheeting in compression flange check-design
case.
For safety reason, encourage k= 0
+ Length Lm:
“The distance along the length of the member between discrete rigid restraints that restrict
distortional buckling. If there are no discrete restraints for distortional buckling, leave this as a large
value (such as the span length) and CFS will calculate the distortional buckling wavelength. If the
member is fully restricted against distortional buckling, use Lm = 0. If the shape does not have a
distortional buckling failure mode, the value of Lm has no effect.
In cases where rotational stiffness is provided to the braced flange by connection to bracing
material, Lm does not represent the spacing between fasteners. It is the distance between rigid
restraints against distortional buckling, if they exist.”
 Rigid renstraints against distorsional buckling is rarely exists, it is not purlin brace spacing, and
also not screw spacing. So use Lm is length of entire beam.
2.3. Loading information:
2.3.1. Load case:
- Tributary Width: purlin spacing
 Include beam self-weight:
+ Dead load is include weight of purlin and roof sheeting -> No stick
+ Weight of purlin is excluded from Dead load -> Stick
- Dead load (D): Self weight of (Purlin), Sheeting, Accessories.
- Live load (L): In usuage stage
- Product load (P): Collateral load (lighting, piping, HVAC,…)
- Roof live load (Lr): live load in erection stage in erection stage.
- Snow load (S): Snow load in roof.
- Wind Uplift (W): Wind load uplift
 Load angle: get 90o as define.
2.3.2. Load combination:
D: D
D+L: D+L+P
D+Lr : D+Lr
D+0.75(L+Lr): D+0.75(L+P+Lr)
D+0.75(L+S): D+0.75(L+P+S)
D+0.6W: D+0.6W
D+0.75(0.6W+L+Lr): D+0.45W+0.75(L+P+Lr)
D+0.75(0.6W+L+S): D+0.45W+0.75(L+P+S)
0.6D+0.6W: 0.6D+0.6W
* Conclusion: base on this definition in CFS, we define load as below:
-
Dead load (D): Self weight of (Purlin), Sheeting, Accessories.
Live load (L): In usuage stage
Product load (P): Collateral load (lighting, piping, HVAC,…)
Roof live load (Lr): live load in erection stage in erection stage => No data (0)
Snow load (S): Snow load in roof => No data (0)
Wind Uplift (W): Wind load uplift (From other spreadsheet source).
2.4. Analysis:
2.4.1. Destruction type:
In-elastic consition can be chosen in Material define, but it should not be used, except maximum
optimization.
2.4.2. Member check:
2.4.3. Web crippling (not check when Case 3 is controlled)
2.5.
Elastic Buckling Analysis of member:
This is another way to determine cold-form section strength: