Function
- Enter the Effective Length Factors for the unbraced lengths for bending about the strong (y-axis) and weak (z-axis) axes of the selected members.
Call
From the main menu, select [Rating] tab > [Type : Steel Bridge] > [Rating Input Data] group > [Rating Parameters] > [Effective Length Factor(K)]
Input
First, select the members in the model and enter the following
Effective Length Factor(K) dialog box
Factor
Enter the effective buckling length factors.
Ky : Effective buckling length factor for buckling about strong axis (Default = 1.0)
Kz : Effective buckling length factor for buckling about weak axis (Default = 1.0)
Apply : Apply the entered values to the selected members.
Close : Close the entry Dialog Bar.
Use one of the two following methods for entering data
Enter the values directly in the Ky and Kz fields.
<Method 2>
Click ... button and use the K-Factor Input dialog box shown below to enter the values.
Select the effective buckling length factor for the member's strong or weak axis in the K-Factor Input dialog box and click OK button.
K-Factor input dialog box
In the Enter effective buckling length coefficient dialog box, select the effective buckling length coefficient for the member axis or member axis that you want to enter, and click the OK button.
If the values for Ky and Kz have not been entered, the values Ky = 1.0 and Kz = 1.0 are applied.
The program's automatically calculated values can be used as the effective buckling length factors for column members. In order to automatically calculate the effective buckling length factors, select the Auto Calculate K-Factor option in Definition of Frame.
Follow the procedure below to access Definition of Frame.
From the main menu select [MODS] > [Design] > [Common Para.] > Definition of Frame
Reference > Automatic Calculation Algorithm of Effective Buckling Length Factor for Column Members
For the derivation of equilibrium equations, refer to "Steel Structure, 1980(Charls G.Salmon and John E.Johnson, Steel Structure : Design and Behavior, 2nd Edition, 1980, Harper & Row Publishers, New York, Page 848∼851)", which describes only the final equations applied to the program. f the effective buckling length coefficient is K and X =, the equilibrium equation for the transverse and non-transverse frames is as follows.
§ a transverse frame :
§ an unilateral frame:
In deriving the equilibrium equation, the following assumptions are premised.
1. All actions are within the elastic range.
2. The member maintains a cross section.
3. All columns are subject to buckling load simultaneously.
4. The structure consists of a symmetrical orthogonal frame.
5. At one node, the constraint moment by the girder is distributed to the pillar in proportion to the stiffness of each pillar.
6. The girder is elastically constrained by columns at both ends, and the size of rotational displacement at both ends of the girder is the same and the direction is opposite at the moment of buckling.
7. The girder does not bear the axial load.
The nonlinear equation solution is obtained by the Newton-Raphson method, and the equation for the repeated solution is as follows.
In the process of finding the solution of the equation and the tanX or tan(X/2) of the equation becomes infinite or 0, so Civil has taken proper consideration of this to ensure that a safe solution is always obtained.
The effective buckling length factors are calculated simultaneously with the execution of design functions. The calculated values are applied to the relevant column members (elements).
However, if the user specifies the values through the dialog bar, the user-specified values are applied.
The effective buckling length factors obtained by the auto-calculation of the program are produced and marked in the steel member strength verification and the RC column member design results.
If the auto-calculated effective buckling length factors do not represent the true configurations of the members and yield abnormally large values, it is recommended that appropriate design values be directly entered by the user.
If the effective buckling length factor is repeatedly entered for the same member, the following procedure is used to set the applicable value :
1. The effective buckling length factor last entered by the user
2. The effective buckling length factor obtained from the auto-calculation option
The entered effective buckling length factors can be reviewed in the data table arranged in the order of element numbers. The user may Modify/Add and Delete items in the data table.
Access the data table following the procedure below.
From the Main Menu select [MODS] > [Design] > [Common Para.] > Effective Length Factor(K)