在 RFEM 6 中计算截面时考虑抗剪刚度

本文将分别介绍考虑和不考虑剪切刚度的连续梁的内力和位移。

在 RFEM 6 中，程序会自动考虑杆件的抗剪刚度。 However, this consideration leads to different results than those you might obtain with a manual calculation. To show this, as well as to illustrate how to deactivate the shear stiffness for a cross-section calculation, a practical example will be provided. The model of interest is a timber beam with two spans of 4 m each, loaded with 1.5 kN/m, as shown in Image 1.

1 均布荷载作用下的连续梁

First, we can perform the manual calculation of internal forces and displacements for the continuous beam of interest. For this purpose, the available data can be entered into well-known beam design and deflection equations for a continuous beam with two equal spans and a uniformly distributed load. The distribution of internal forces is shown in Image 2, and the results obtained are as follows:

\frac{3 q L}{8} = \frac{3 * 1.5 * 4}{8} = 2.25 k N

剪力 V₁和 V₄

\frac{5 q L}{8} = \frac{5 * 1.5 * 4}{8} = 3.75 k N

剪力 V₂和 V₃

\frac{9 q L^{2}}{128} = \frac{9 * 1.5 * 4^{2}}{128} = 1.6875 k N m

弯矩 M₁

\frac{q L^{2}}{8} = \frac{1.5 * 4^{2}}{8} = 3 k N m

弯矩 M₂

Δ_{m a x} = \frac{q L^{4}}{185 E I} = \frac{1, 5 * 4^{4}}{185 * 2911.76} = 0.0007 m

最大挠度 Δ_max

2 内力分布

Next, you can perform the same calculation in RFEM 6 and look at the results obtained as shown in Image 3. As already mentioned, the difference with respect to the results of the manual calculation is due to the automatic consideration of the shear stiffness and the increased deformation.

3 考虑剪切刚度的结果

However, if you are interested in obtaining results for which the shear stiffness is not considered, this is also possible in RFEM 6 since you have the possibility to control the consideration of shear stiffnesses separately for each cross-section. To do so, you should open the associated "Edit Cross-Section" dialog box, as shown in Image 4. The influence of the shear depends on the cross-section areas A_y and A_z (Image 4).

These cross-section properties can be displayed in tables or cross-section entries and adjusted, if necessary. In addition, the shear stiffness can be deactivated (Image 5) and thus, not considered in the cross-section calculation. In this case, the results obtained in RFEM 6 (Image 6) will be identical to those calculated manually.