Did you know that you could use Consteel to calculate rotational stiffness for bolted column/beam moment bearing connections?

This capability is implemented through the Joint module, where connection behavior is evaluated in accordance with Eurocode EN 1993-1-8. The software does not treat joints as idealized (purely pinned or rigid), but allows the engineer to consider semi-rigid behavior by calculating the actual rotational stiffness based on connection components such as bolts, end plates, welds, and stiffeners.

In practical terms, the rotational stiffness is derived from the component method, where the stiffness contribution of each tension and compression component is taken into account. This enables a more realistic representation of the joint response, especially for moment-resisting beam-to-column connections where stiffness significantly influences global structural behavior.

Bolted connection

In this case, the connection exhibits relatively low rotational stiffness compared to a fully rigid joint. The flexibility is primarily governed by bolt deformation and end plate bending. Such connections are typically classified as semi-rigid and partial strength. They allow noticeable rotation under moment, which can be beneficial for redistribution of internal forces but must be considered in global analysis.

Bolted connection

This configuration shows a higher stiffness due to improved component arrangement, such as thicker end plates, larger bolt diameters, or additional stiffening. Although still semi-rigid, the connection provides significantly more resistance to rotation. This intermediate behavior often results in a more efficient structural system by balancing stiffness and material usage.

Welded connection

The welded joint behaves as a rigid connection with full strength. Rotational stiffness is high enough that joint deformation has negligible influence on the global structural response. In Consteel, this is reflected by a stiffness value approaching the rigid classification limit defined by the standard. Such connections are typically used where continuity and moment transfer must be ensured without significant rotation.

Using the Joint module, these behaviors can be modeled and evaluated through a structured workflow:

• Joint creation: Define the connection either manually or based on the global structural model using automatic recognition.
• Connection configuration: Assign geometry, cross-sections, bolt layouts, welds, and optional stiffeners.
• Loading definition: Apply either user-defined internal forces or import them directly from the global analysis.
• Analysis: The software evaluates moment resistance, shear resistance, and both initial and secant rotational stiffness using Eurocode-based procedures.
• Integration: The calculated stiffness can be applied back to the global model, enabling second-order effects and realistic force distribution.

Considering rotational stiffness leads to more accurate structural models. Instead of assuming ideal boundary conditions, the engineer can:

• Reduce conservatism in member design
• Capture redistribution effects in frames
• Optimize connection detailing
• Improve overall structural efficiency

This approach is particularly important in steel frames where joint flexibility can significantly affect deflections, internal forces, and stability.

Download the example model and try it!

If you haven’t tried Consteel yet, request a trial for free!

Did you know that you could use Consteel to consider connection stiffness for global analysis?

One of Consteel’s unique strengths is its ability to integrate joint modeling and calculation directly into the global analysis.

The Joint module performs all analyses in line with the standard procedures of Eurocode 3 Part 1-8, covering almost the entire scope of the code. This ensures results that are both reliable and fully compliant, across a wide range of connection types such as: Moment connections, Shear connections, Hollow section connections.

Modern structural design increasingly considers the mechanical interaction between the global model and its joints — whether rigid, semi-rigid, or pinned.

If you’d like to dive deeper into how semi-rigid joints influence structural behavior and stiffness classification, check out our detailed article: Semi-rigid joints in modeling of structures.

This integrated approach leads to results that are both more realistic and more economical, but it also requires more sophisticated modeling. Consteel makes this process straightforward:

• Joints can be created manually or automatically based on the model geometry.
• The create joint by model function examines member positions and cross-sections, then offers suitable joint types.
• Once defined, the joint can be placed into the global model, and its connection stiffness can be included in the global analysis.
• After placement, the joint is always rechecked against the latest analysis results.

In order to consider the connection stiffness of the placed joint, open the analysis parameters, tick the Include connection stiffness checkbox, and rerun the analysis.

Let’s explore how the behavior of a simple frame changes under different connection assumptions:

In the first case, where no actual connection stiffness was considered and the members were assumed to have continuous rigid ends, the results showed a bending moment (My) of 129.23 kNm at the column upper end and 115.25 kNm at the beam midspan. The corresponding deflection in the beam’s midspan (z-direction) was –17.4 mm.

In the second case, the connections were modeled with their actual semi-rigid stiffness of 29.8% and partial strength. Here, the bending moment at the column upper end decreased to 90.45 kNm, while the beam midspan moment increased to 154.03 kNm. The beam midspan deflection reached –26.5 mm, representing an increase of 52% compared to the rigid assumption.

In the third case, with a higher semi-rigid stiffness of 53.6% and partial strength, the results balanced between the two extremes: the column end moment was 104.37 kNm, the beam midspan moment was 140.11 kNm, and the midspan deflection was –23.2 mm. This corresponds to an increase of 33% in deflection compared to the rigid assumption.

These examples clearly demonstrate how connection stiffness significantly influences global structural behavior. Assuming rigid connections may underestimate beam deflections and distort moment distribution, while considering realistic semi-rigid stiffness, provides a more accurate representation of structural performance.

Download the example model and try it!

If you haven’t tried Consteel yet, request a trial for free!