Analysis of Thick Extended Endplates and Multiple Bolts per Row with Steel Joints Addon for RFEM

Analytical Model

This study adopts the design criteria specified in EN 1993-1-8 for evaluating bolt resistance (shear and tension) and plate resistance (bearing and punching shear), utilizing the limit state formulations provided in Table 3.4.

The design resistance of the equivalent T-stub is evaluated independently for the endplate and the column flange components. For each component, the governing design resistance, F_T,Rd is defined as the minimum value derived from three potential failure mechanisms.

The individual resistance for each mode is calculated based on the plastic moment capacity of the flange (M_pl,1Rd and M_pl,2,Rd) and the tension resistance of the bolt group(∑F_t,Rd). These modes account for complete flange yielding (Mode 1), bolt failure coupled with flange yielding (Mode 2), and pure bolt fracture (Mode 3).

• Failure Modes:

• Plastic Resistance Moments:

Failure Modes of T-Stub Elements

Geometric details of beam to column connection

Consistent with standard construction practice, all beam and column members were fabricated from S235 steel, while the endplates utilized higher-strength S355 steel. The geometric configurations, including endplate and bolt group arrangements, are detailed in Figure 2, with the corresponding experimental test matrix and measured material properties provided in Tables 1, respectively.

As defined in the test matrix, Group A (specimens 1A–3A) utilized an HEA 300 column section (t_w = 8.5mm; t_f = 14mm), while Group B incorporated the heavier HEB 300 section (t_w = 11mm; t_f = 19mm). To evaluate the performance of a weak-column strong-beam hierarchy, a uniform HEB 300 beam section and 30 mm thick endplates were maintained across all specimens, ensuring the Group A configurations were column-critical.

• Table 1: Geometric Configuration of Tested Specimens

(a) Typical beam-column bolted connection and (b) component method representation.

Endplate/Bolt Configuration

Discussion

Steel Joints for RFEM Solution

Utilizing the FE-based Steel Joints add-on for RFEM 6, the connection design process was fully integrated into the primary structural model. This study presents an experimental and numerical investigation into the structural performance of six extended thick end-plate beam-to-column connections, with a specific emphasis on the influence of non-conventional bolting patterns involving multiple bolts per row. To isolate the inherent rotational stiffness of the nodal zone, all specimens were configured without supplemental column web stiffeners. The experimental matrix interrogated two distinct failure hierarchies: (1) a weak-column/strong-beam configuration (HEA300 column; HEB300 beam) and (2) a balanced-stiffness configuration (HEB300 column and beam).

These investigations were augmented by targeted T-stub characterization and high-fidelity finite element (FE) analysis. Upon validation against experimental data and verification via Eurocode 3 (EC3) frameworks, the FE models were employed to extract granular insights into localized deformation mechanics. Fig. 4&5 and Table 2&3 illustrate the comparison of moment resistance and stiffness-Experimental, ROFEM, Steel Joints in RFEM to EC-3. And Table-4 illustrates the failure modes.

Comparison of Moment Resistance – Experimental, ROFEM, Steel Joints in RFEM and EC-3

Comparison of Stiffness – Experimental, ROFEM, Steel Joints in RFEM and EC-3

• Table 2: Comparison of moment resistance, Stiffness - Experimental, ROFEM, Steel Joints in RFEM & EC-3-1-8.

• Table 3: Stiffness comparison.

• Table 4: Failure modes.

Equivalent Stresses and Plastic Strain of T1A Model

Equivalent Stresses and Plastic Strain of T2A Model

Equivalent Stresses and Plastic Strain of T3A Model

Equivalent Stresses and Plastic Strain of T1B Model

Equivalent Stresses and Plastic Strain of T2B Model

Equivalent Stresses and Plastic Strain of T3B Model

Design Ratio and Rotational Stiffness of T1A Model

Design Ratio and Rotational Stiffness of T2A Model

Design Ratio and Rotational Stiffness of T3A Model

Design Ratio and Rotational Stiffness of T1B Model

Design Ratio and Rotational Stiffness of T2B Model

Design Ratio and Rotational Stiffness of T3B Model

Conclusion

Preliminary experimental data were used to assess the applicability of EN 1993-1-8 provisions to Steel Joints. In line with findings reported for conventional carbon steel members, the Eurocode stiffness model was found to overestimate the initial rotational stiffness, with the analytical predictions demonstrating considerable scatter relative to the measured values.

The experimental results confirm that both moment resistance and initial stiffness increase with bolt number, with 12-bolt specimens (T1A, T1B) consistently outperforming 6 and 8 bolt counterparts. The EC3-1-8 component method generally underestimates moment capacity while overestimating initial stiffness most notably for T1B (41.83 vs. 22.31 MNm/rad) consistent with the overestimation trend observed under EN 1993-1-8.

The EC-3/RFEM ratios ranging from 0.59 to 0.94 indicate conservative moment resistance predictions from the Eurocode component method, with the low ratio for T3B (0.59) suggesting significant underestimation for certain connection geometries.

References

1. Eurocode 3. Design of steel structures part 1–8: design of joints. European Standard EN 1993-1-8. European committee for standardization, Brussels, Belgium; 1993.
2. Gary S. Prinz, Alain Nussbaumer, Luis Borges, Shyam Khadka, Experimental testing and simulation of bolted beam-column connections having thick extended endplates and multiple bolts per row, Engineering Structures, Volume 59,2014, Pages 434-447, ISSN 0141-0296, 10.1016/j.engstruct.2013.10.042