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 main menu, select [Design] tab > [Design Input Data] > [Design Parameters] > [Definition of Frame]
Input
The following dialog box is used to enter the data:
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).
Auto Calculate Effective Length Factors
Select if the effective buckling length factors are to be automatically calculated.
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/L
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
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.
(4) Calculate the effective length factor, K
Reference: "Steel structures" (1982), Ballio and Mazzolani
Design Type
3D : Calculate the forces for and design all the members.
X-Z Plane : Calculate the forces for and design all the members parallel with X-Z Plane.
Y-Z Plane : Calculate the forces for and design all the members parallel with Y-Z Plane.
X-Y Plane : Calculate the forces for and design all the members parallel with X-Y Plane.
: Enter the selection and close the dialog box.
: Do not enter the selection and close the dialog box.