Abstract
Steel beam-to-column connections are fundamental to the structural integrity and safety of steel-framed buildings. A critical issue arises when gaps exist between stiffeners and connected elements, referred to as unfitted stiffeners, which introduce uncertainties in the load-bearing capacity and deformation behaviour of these vital connections. This problem potentially compromises structural safety and leads to inefficient designs, as the precise impact of these gaps on connection performance is not fully understood.The Study investigates the impact of stiffener-to-flange gaps on the structural integrity and performance of steel beam-to-column connections under various loading conditions, including concentrated and distributed forces and pure moments. By combining experimental methodologies with finite element simulations, the study assesses the mechanical responses of fully welded connections enhanced with stiffeners of varying gap sizes up to 3 mm in the experimental research and up to 5 mm in the numerical study.
Experimental tests were conducted on grade S275 steel, adhering to BS EN 10025-2 standards, to systematically evaluate the tensile and compressive strengths of the connections. The results reveal that connections with no gaps exhibit the highest load-bearing capacity and minimal deformation, confirming the critical importance of precise stiffener fit for optimal connection performance. As the gap size increases, a progressive decline in structural integrity is observed due to reduced effectiveness in load transfer and increased flexibility, leading to higher stress concentrations and deformation.
Finite element analyses extended these findings by investigating numerous study cases across multiple metrics, including stress distribution and deformation patterns. A key outcome of the numerical study is the estimation of an empirical coefficient β, which quantifies the reduction in stiffness and strength due to the presence of stiffener gaps. The value of the empirical coefficient β primarily depends on the size of the stiffener-to-flange gap. Additionally, it is influenced by the type of loading applied and the specific geometric configuration of the connection. Larger gaps generally result in a more significant reduction in stiffness and strength, leading to lower β values. Conversely, smaller gaps maintain higher structural integrity, reflected in higher β values. This coefficient is incorporated into a Gap Influence Factor (αg), which can be applied in design calculations according to Eurocode 3 to adjust for the effects of stiffener gaps.
Key results indicate that adding fitted stiffeners significantly enhances connection performance, reducing maximum stresses and improving load-bearing capacity. While stiffeners with gaps up to 3 mm maintain acceptable performance levels, their effectiveness diminishes with larger gaps, although they still offer improvements over unstiffened connections. The study underscores the critical role of stiffener fit and weld quality in enhancing the durability and safety of steel structures.
Concluding with recommendations for minimizing stiffener gaps and incorporating the Gap Influence Factor into design practices, the research contributes valuable insights into optimizing steel connection designs. The findings have significant implications for the revision of design codes, particularly Eurocode 3, and for improving fabrication and construction practices to ensure safer and more resilient steel structures.
| Date of Award | 3 Dec 2025 |
|---|---|
| Original language | English |
| Supervisor | Jiping Bai (Supervisor), David Moore (Supervisor) & Paul Davies (Supervisor) |