Designing steel connections at the Connection Workshop in Belgium

Recently, in collaboration with InfoSteel, we organized a Connection Workshop in Belgium that focused on exactly this.

Divided into three teams, participants tackled two challenging design issues. Each team was assigned to design a steel connection with attention to strength and stiffness as well as practicability. The presence of junior and senior profiles allowed them to learn from each other and was also an excellent opportunity to meet and catch up with colleagues.

Experienced structural engineer Stijn Jespers was present to assess the designs and support the teams in their design choices. During the process, we were able to model the connections directly from IDEA StatiCa. This gave the engineers immediate insight into the 3D model and results, which we could then analyze and discuss together.

Curious about the teams' different design choices? We explain the results below, starting with task 1.

Case 1 - Moment resisting

In the first assignment, we look at a node where three HEA300 beams meet on a HEB300 column. The challenge was in the three HEA300 beams that all had to be connected as moment resisting. With significant shear forces and bending moments on the beams, this was a serious test for both the strength and stiffness of the connection.

A number of design considerations emerged during the discussions. First, there was the consideration of whether the column should be continuous or whether the beams M1 and M2 should be continuous. This difference can also be seen in the design of groups 1 and 2 compared to group 3.

Group 3 chose this solution in part to achieve three identical connections, which promotes production and reduces error proneness, especially when several such nodes occur in the project. The results of the CBFEM calculation are shown below. All three designs meet the code-checks. The dimensions of the plate thicknesses, welds and haunches can be further optimized.

During the design process, it was noted by an experienced engineer that the tolerances of the steel sections must be taken into account when choosing for a continuous beam. If the column is just slightly wider than the beam (or vice versa), a stagger occurs. As a result, the endplate cannot be assembled flush, or the welds cannot be laid correctly.

Another important consideration when extending the beam over the column is whether the bending moments at M1 and M2 always occur simultaneously. If they do not, a continuous column may be a structurally cleaner solution and help prevent unforeseen stresses in the node. A continuous beam over a column is optimal only if the forces (M1 and M2) are always present simultaneously.

Furthermore, it was a challenge to make the connections moment-resisting, especially for beam L, because it is connected in the weak direction of the column. A rigid connection in this situation requires a haunch. However, this also requires stiffeners in the column to ensure proper force transfer. These stiffeners affect the manufacturability of the connection. If a stiffener is used at both the top and bottom flange, it is impossible to install the bolts on site.

With IDEA StatiCa Connection, the engineer can analyze the stiffness of a connection. Such an analysis was performed for the Group 3 steel connection to verify that the connection can be classified as Rigid. The moment-rotation diagram was prepared for this column-beam connection and the results below show that the connection is classified as Rigid.

Case 2 - At an angle

In the second case, we consider a node in which four beams come together at an angle of 30 degrees. The HEB240 beams are loaded with axial compression, bending and shear, while the edge members, constructed in RHS120/80/8 or IPE120, transfer axial tensile or compressive forces.

The angle between the members creates a tight joint. At first glance, the designs of the three groups are very similar, but each takes just a different approach to efficiently transfer forces.

All groups selected an effective connection, joining the beams with an end plate and attaching the RHS members to the end plates using a fin plate connection. This avoids additional plate work and creates an orderly node that can be assembled on the construction site with relative ease.

Below are the results from IDEA StatiCa Connection. 100% of the load is transferred and all code checks are met.

Further design considerations that came up during the discussions are the placement of the bolts and the choice of whether the splice plate extends at the top or bottom. This often depends on available space. Constructively, an additional row of bolts at the top may be more effective because that is where tensile forces occur. However, if the bending moment in the HEB240 beam can also occur in the other direction, the effect of this bolt row is limited. This shows how many factors influence the design of a steel connection and that this is not easy to capture in one calculation example.

Groups 2 and 3 chose two identical but mirrored endplates. This is more economical for production, cutting and welding, as well as assembly. Furthermore, be aware that because the edge members are connected directly to the endplates, the shear force in the bolts may not fully match your initial hand calculation. In IDEA StatiCa we can see the direction of the shear forces in the bolts and find that they are influenced by the shear force in the HEB240 beams as well as the tensile force in the RHS members.

When designing such compact connections, 3D modeling is very useful because you can immediately check whether the bolts fit and can be assembled on site. This allows an immediate decision to be made whether a plate needs to be extended or a row of bolts needs to be shifted.

Final word

The design of steel connections depends on many factors: the continuity of beams or columns, the placement of bolts and plates, the choice of sections, and the efficient transfer of forces. Each decision affects both the manufacturability and the structural clarity of the connection. With IDEA StatiCa Connection, you can quickly evaluate all these aspects: calculate stiffness, perform code checks, and verify whether the design is practically feasible. This way, you obtain a connection that is technically sound and can be efficiently realized on site.