Function
- Select the structural frame type (braced/unbraced) with respect to the global X- and Y-directions. Select the auto-calculation option for the effective buckling length factors for column members.
Call
From the Main Menu select [Design] tab > [Type : Steel Design] > [Design Input Data] group > [Design Parameters] > [Definition of Frame]
From the Main Menu select [Design] tab > [Type : RC Design] > [Design Input Data] group > [Design Parameters] > [Definition of Frame]
From the Main Menu select [Design] tab > [Type : SRC Design] > [Design Input Data] group > [Design Parameters] > [Definition of Frame]
From the Main Menu select [Design] tab > [Type : Cold Formed Steel Design] > [Design Input Data] > [Design Parameters] > [Definition of Frame]
Input
The following dialog box is used to enter the data:
Fig. Definition of Frame dialog box
Definition of Frame
Define the type of structural frame.
X-Direction of Frame
Select Unbraced | Sway or Braced | Non-sway frame in the global X-direction (Default = Unbraced | Sway).
Y-Direction Frame
Select Unbraced | Sway or Braced | Non-sway frame in the global Y-direction (Default = Unbraced | Sway).
Design Type
When members in a 3-D structure are designed, a Design Type is selected to account for only the forces in the selected plane to design the members as a 2-D frame.
3 - D : Design is carried out while accounting for all the member forces in the 3-D frame.
X - Z Plane : Design is carried out while accounting for only the member forces in the GCS X-Z plane as a 2-D frame.
Y - Z Plane : Design is carried out while accounting for only the member forces in the GCS Y-Z plane as a 2-D frame.
X - Y Plane : Design is carried out while accounting for only the member forces in the GCS X-Y plane as a 2-D frame.
Note
This option may become handy when a structure with continuity in one direction is to be designed as a 2-D frame.
Auto Calculate Effective Length Factors
Select if the effective buckling length factors are to be automatically calculated.
Note
Auto Calculation procedure for effective length factor
(1) Calculate the stiffness, S (=EI/L), of the members which are connected to the Member a as shown in the figure 1 below. If the joint of the flexural member is fixed or hinged as shown in the figure 2 below, the stiffness, S, is modified as below.
Fixed joint: S = (1/1.5)* EI/
Hinge: S= (1/2.0)* EI/L
Where,
E: Modulus of elasticity
I: Moment of inertia of section
L: Span length of flexural member measured from center to center of joints
(2) Calculate Ψ and Ψ. Ψ is the ratio of Σ(EI/lc) of compression members and Σ(EI/l) of flexural members in a plane at one end of a compression member. As shown in the figure 3 below, if the end of the compression member is fixed or hinged, Ψ is taken as 1 or 10 respectively. If the compression member is not connected to any flexural member, Ψ is taken as 1000.
(3) Calculate the solution, X, in the stability equation below.
Braced / Nonsway frames
For the transcendental Eq. 2, which can only be solved by numerical methods, the French Rules propose the following approximate solution:
Unbraced / Sway frames
Where, Ψ: Ratio of Σ(EI/lc) of compression members to Σ(EI/l) of flexural members in a plane at one end of a compression member.
Although simpler than Eq. 2, this equation cannot be solved in closed form either. The French Rules recommend the following approximate solution:
* [Reference: "Steel structures" (1982), Ballio and Mazzolani]
The OK Button : Enter the selection and close the dialog box.
The Close Button : Do not enter the selection and close the dialog box.