Comparison of Two Novel Heat-Treated Beam Section and Self-Centering Pinned Connection with Friction Damper Steel Beam–Column Connections ^†

Abstract

This study presents a comparative analysis of the structural performance of two innovative steel beam–column connections, namely a self-centering pinned connection with friction damper (SC-PC-FD) and a heat-treated beam section (HBS). The findings indicate that the SC-PC-FD connection exhibits stable, flag-shaped behavior, while the HBS connection can withstand applied loadings up to a rotation of 6% without any occurrence of lateral–torsional buckling. Upon comparison of these connections, it is evident that the SC-PC-FD connection can eliminate residual drifts and provide higher ductility up to a rotation of 7%, while maintaining the main members within the elastic range.

1. Introduction

In light of the experiences gained from the Northridge 1994 and Kobe 1995 earthquakes, two approaches have been employed to relocate plastic hinges away from column faces. The first approach involves strengthening the connection through the installation of haunches, brackets, and cover plates. The second approach entails weakening a beam in a zone far from the column face, such as the reduced beam section (RBS). However, it should be noted that while RBS connections offer certain advantages, they reduce the elastic stiffness of the beam and also exhibit decreased resistance against local buckling of the web and lateral–torsional buckling [1]. Research has shown that a decrease of 40% to 50% in the flange area of the RBS leads to an increase of 4.5% to 8% in drift [2]. Therefore, despite the significant improvements in the seismic performance of beam–column connections, it is crucial to introduce a new connection that offers enhanced ductility, eliminates residual deformations, and effectively dissipates seismic energy. This new connection should also maintain simple constructional details. In order to achieve these objectives, the seismic performances of two novel connections, namely SC-PC-FD [3] and HBS [4,5], are compared to each other.

2. Materials and Methods

To establish a connection with the HBS approach, it was necessary to subject the flanges and web of a steel I-shaped IPE140 section to heat treatment using the heating protocol proposed by Morrison et al. [5] (Figure 1a). The weakened heat-treated zone’s distance from the column face is indicated as a₁, while the length of the heat-treated zone highlighted in red is denoted as b₁. It was considered that a₁ = 0.6b_f and b₁ = 0.75d_b, where b_f represents the flange width and d_b represents the section height. It is important to note that only the strength of the steel material was reduced through the heat treatment process, while the other material characteristics remained constant. Based on the findings of the experimental study conducted by Akbari Hamed and Basim [4], it was assumed that the heat-treated steel strength was reduced to 68% of its initial value for the ST37 steel grade. Figure 1b shows a 4-strand SC-PC-FD connection using the same steel beam section. It is worth emphasizing that both models had a beam length of 1.7 m and a column length of 3 m. The column of the models was assigned a rectangular hollow structural section with the dimensions of 160 × 160 × 12. To compare the cyclic performance of these innovative beam–column connections, an incrementally quasi-static loading history was applied to the tip of the beams.

3. Results and Discussion

According to Figure 2a,b, it can be observed that the protected zone of the SC-PC-FD connection and strands remained within the elastic range. Consequently, the yield of the main members was prevented, and the induced energy was dissipated solely by the disposable friction dampers. In the HBS connection, only the weakened region experienced yielding, and at a rotation of 0.06 rad, the yielding extended towards the vicinity of the column. Furthermore, the numerical study revealed that the HBS connection exhibited maximum strength, ductility, and initial stiffness values of 21.10 kN.m, 4.03, and 2604.87 kN.m/rad, respectively. On the other hand, the corresponding values for the examined four-strand SC-PC-FD connection were 20.41 kN.m, 14.67, and 2585.89 kN.m/rad, respectively. Therefore, the ratio of strength, ductility, and initial stiffness parameters of the HBS connection compared to the SC-PC-FD connection were 1.03, 0.27, and 1.01, respectively. Based on these findings, it can be concluded that although the HBS connection exhibits slightly higher strength and initial stiffness compared to the SC-PC-FD connection, the latter demonstrates a significant increase in ductility along with its flag-shaped hysteretic curve (Figure 2c) and simple constructional details. Additionally, the SC-PC-FD connection ensures that the main members remain within the elastic behavior range.

4. Conclusions

The analysis of the obtained results led to the conclusion that the novel SC-PC-FD connection exhibits a substantial enhancement in ductility, thanks to its straightforward constructional details. Additionally, it effectively eliminates residual drifts through its stable, flag-shaped, self-centering performance. Consequently, structures equipped with SC-PC-FD connections can be considered a dependable substitute for conventional moment-resisting frames in regions prone to seismic activity.