Rigid Columns in RF/JOINTS Steel  Column Base
Technical Article
A structural analysis does not only determine and design internal forces and deformations. It also ensures that the forces and moments in a structure are generated in a reliable way and applied to the foundation. Dlubal Software provides a wide range of products for structural analysis and design of steel and timber connections. The RF/JOINTS Steel  Column Base addon module allows you to design footings of hinged and restrained column bases. The design can be performed for both column base plates with or without stiffeners.
This article presents an example of crosssection designs of a column set in a concrete bucket foundation. This example is also described in [1].
System
The column is a crosssection HEB 280 made of steel S 235 JR.
Figure 01  System and Loading
According to [1]
Geometry parameters of the column
base are set in Window 1.4 of RF/JOINTS in compliance with [1]. The selected restraining
depth is 65 cm.
Figure 02  Window 1.4 Footing in RF/JOINTS
Base plate parameters are defined in Window 1.5.
Figure 03  Window 1.5 Column in RF/JOINTS
Internal Forces
The following design internal forces are available.
N_{Ed} = 396.0 kN
V_{Ed} = 21.5 kN
M_{Ed} = 118.0 kN
Design of Required Bucket Depth
The governing value is the minimum restraining depth based on the concrete strength.
Figure 04  Window 3.1 Design  Summary Including Details of Required Bucket Depth
The minimum restraining depth of 54.86 cm is required. This is provided by the selected depth of 65 cm.
Design of Column Section Resistance
The force and moment distribution in the column corresponds to the following distribution, according to [1].
Figure 05  Distribution of Forces and Moments in Column Base According to [1]
Normal stress from the maximum moment is calculated as follows:
$${\mathrm\sigma}_\mathrm{Ed}\;=\;\frac{\mathrm N}{\mathrm A}\;+\;\frac{\max\;{\mathrm M}_{\mathrm e,\mathrm d}}{{\mathrm W}_\mathrm y}\;=\;\frac{396.0}{131.0}\;+\;\frac{11,818.7}{1,380.0}\;=\;11.6\;\mathrm{kN}/\mathrm{cm}²$$
For the maximum shear stress, the following applies:
$${\mathrm\tau}_\mathrm{Ed}\;=\frac{\max\;{\mathrm V}_{\mathrm e,\mathrm d}\;\cdot\;{\mathrm S}_\mathrm y}{{\mathrm I}_\mathrm y\;\cdot\;\mathrm t}\;=\;\frac{310.18\;\cdot\;767.00}{19,270.00\;\cdot\;1.05}\;=\;11.76\;\mathrm{kN}/\mathrm{cm}²$$
The corresponding stresses and design details can also be found in the result table under Crosssection resistance.
Figure 06  Window 3.1 Design  Summary Including Details of Column Section Resistance
Design of Column Inside Bucket
Figure [5] shows the designrelevant locations. The section BB on the compression side is governing:
The normal stress in the Xdirection is calculated as follows:
$${\mathrm\sigma}_{\mathrm X,\mathrm d}\;=\;\frac{\mathrm N}{\mathrm A}\;\;\frac{{\mathrm M}_{\mathrm e,\mathrm b,\mathrm d}}{{\mathrm l}_\mathrm y}\;\cdot\;{\mathrm z}_1\;=\;\frac{396.0}{131.0}\;\;\frac{3,897.3}{19,720.0}\;\cdot\;9.8\;=\;5.0\;\mathrm{kN}/\mathrm{cm}²$$
The following normal stress acts in the Zdirection:
$${\mathrm\sigma}_{\mathrm Z,\mathrm d}\;=\;0.45\;\cdot\;\frac{{\mathrm p}_\mathrm{Rd}}{\mathrm t}\;\cdot\;{\mathrm\alpha}_\mathrm b\;=\;0.45\;\cdot\;\frac{12.34}{1.05}\;\cdot\;0.55\;=\;2.90\;\mathrm{kN}/\mathrm{cm}²$$
The maximum shear stress is:
$${\mathrm\tau}_\mathrm{Ed}\;=\;\frac{\max\;{\mathrm V}_{\mathrm e,\mathrm d}\;\cdot\;{\mathrm S}_{\mathrm y,1}}{{\mathrm I}_\mathrm y\;\cdot\;\mathrm t}\;=\;\frac{310.18\;\cdot\;716.58}{19,270.00\;\cdot\;1.05}\;=\;10.99\;\mathrm{kN}/\mathrm{cm}²$$
Design Details of Window 3.1 include the corresponding stresses and ratios:
Figure 07  Window 3.1 Design  Summary Including Details of Design of Column in Bucket
The program completes the design by analyzing the joint in compression and the welds. However, these are not explained in this article.
Summary
RF/JOINTS Steel  Column Base allows you to design footings of hinged and restrained column bases. In the case of a column set in a concrete bucket, the addon module analyzes the required depth of the bucket, the resistance of the column section, and the resistance of the column inside the footing with regard to the arising tension and compression stresses. The analysis is completed by the design of the concrete under the base plate in compression as well as the design of welds between the base plate and the column.
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Figure 01  System and Loading According to [1]

Figure 02  Window 1.4 Footing in RF/JOINTS

Figure 03  Window 1.5 Column in RF/JOINTS

Figure 04  Window 3.1 Design  Summary Including Details of Required Bucket Depth

Figure 05  Distribution of Forces and Moments in Column Base According to [1]

Figure 06  Window 3.1 Design  Summary Including Details of Column Section Resistance

Figure 07  Window 3.1 Design  Summary Including Details of Design of Column in Bucket