The rapid growth of using the short links in steel buildings due to their high shear strength and rotational capacity attracts the attention of structural engineers to investigate the performance of short links. However, insignificant attention has been oriented to efficiently developing a comprehensive model to forecast the shear strength of short links, which is expected to enhance the steel structures’ constructability.
1. Introduction
Short links are
W−shape steel sections that are either constructed or rolled with link length ratio,
e/(
M/V), less than 1.6 (AISC, 2016)
[1]; where
e represents the link length,
M and
V represent the plastic moments, and shear capacity, respectively. Short links are widely employed in steel bridges, Eccentric Braced Frames (
EBFs) and coupled walls. The short links have several advantages, such as exceptional plastic rotational capacity and plastic shear capacity
[2]. However, several studies observed that the AISC formula underestimates the predicted short links’ shear strength
[3][4][5][6][7]. The AISC, 2016
[2] Equation (F3–2) estimates the plastic short links’ shear strength using
Vp=0.6×Fy (d − 2tf)×tw; where
Vp represents the plastic shear strength (N),
Fy represents the measured steel yield strength of the web (MPa),
d is the link depth (mm),
tf and
tw are the flange and web thicknesses (mm), respectively. Several investigations revealed the major factors that control the shear link strength, such as flange contribution
[3][5], cyclic hardening
[3], web slenderness
[4], and link length ratio
[4][6][7].
The testing program of McDaniel et al., 2003
[5], which included two full-scale built-up short links, revealed that in terms of degrading the shear strength of tested links, the cutting-edge factor is a brittle fracture on the linked web. As a result, the tested short links exhibited overstrength factors of 1.83 and 1.94. In addition, Dusicka et al., 2010
[8] investigated the effect of steel yield stress 100, 225, integrated steel strength of 100 and 440, 345, 485 MPa for five plate steel shear links. The obtained results illustrate that the steel links with a low grade attained a plastic rotation of 0.2 rad while the conventional links reached 0.12 rad, and the low-grade steel links achieved an overstrength factor considerably higher than conventional links. Moreover, the average overstrength factor for the tested 12 short links (length ratio ranges from 0.58 to 0.97) was 1.9, Ji et al., 2015
[3]. Furthermore, the very short links reached a plastic rotation of 0.14 rad greater than the 8% limit of AISC 341-10
[9][10]. In addition, Ji et al., 2016
[11] found that the average shear strength of four built-up short links reached 2.0.
Similarly, Liu et al., 2017
[4] noticed that the short links’ shear strength was significantly impacted by the web slenderness and link length ratio, and the overstrength ratio for the 12 built-up short links was between 1.35 to 1.5. The link length was critical in the steel links, Okazaki, T. 2004
[7]. The experimental program included 16 link-to-column connections with different link length ratios, where the overstrength ratio varied between 1.05 and 1.47. Bozkurt and Topkaya 2017
[12] discovered that plastic rotation and the overstrength ratio are negatively associated with the link length ratio. The test program included seven short links considering several features (i.e., loading protocol, the link length ratio and stiffeners spacing). In addition, an overstrength ratio of 1.87 to 2.3 was achieved in Bozkurt et al., 2019
[13], where six specimens with a link length of 600 to 800 mm were tested.
To explore the link’s ultimate rotational capacity, shear capacity, buckling of flanges, and web, the analysis of complex finite element of shear links was implemented
[3][14][15][16][17][18][19][20]. However, finite element simulation is considered time consuming, especially in the modeling process and validation of the performance of the predicting model. Moreover, FEA requires special experts in the mechanics of materials and computer aided-software engineering. Recently, the huge availability of databases in the wide range of engineering applications paved the way to extensively and successfully use the machine learning tools to help engineers save the cost, time, and efforts. A leaping use of machine learning has been witnessed in the various civil engineering fields over the last decade. While machine learning has been successfully utilized in the civil engineering applications
[21][22][23][24][25][26][27][28][29][30][31][32][33], limited studies used machine learning tools to address the shear strength of short links; where a few studies have employed actual experimental databases to validate
ML algorithms.
2. Analytical Models
The literature includes three analytical models to assess the shear strength of shear links (i.e., AISC 2016
[1], Corte et al., 2013
[15], and G. Almasabha 2022
[34]). The following discussion summarizes the available models.
2.1. AISC 2016
The AISC 2016
[1] adopted Equation (1) for the assessment of shear strength of links. It is worth mentioning that Equation (1) does not take into consideration the role of link length proportion, the contribution of flanges, and the slenderness ratio of web or flanges.
2.2. Corte et al., 2013
A finite element-based algorithm
[15] has been proposed to estimate the overstrength ratio (
V0.08/Vy) of wide flange shear links without axial restraint, where
Av=(d−tf)tw and
Vy=(Fy/√3)(d−tf)tw. It is worth mentioning that the authors derived Equation (2) for the hot rolled steel link. However, the experimental database of the current study includes both hot rolled and built-up steel links.
2.3. G. Almasabha 2022
This study used the gene expression model to build a mathematical equation for the shear link strength (
VGEP)
[34]. Various parameters were considered in this equation, such as
bf/tf,
d/tw,
Af/Aw,
Af fyflange,
Awfyweb, and
e/(M/V).
2.2. ML Models
Although innovative ML algorithms outperform traditional models in most research disciplines
[35][36], ML models are still humbly utilized to forecast the short links’ shear strength such as
[15][16][17][18][37][38][39], also limited variables with humble datasets have been applied in these studies. On the other hand, these studies’ executed ML models seem somewhat traditional. Therefore, the need to use sophisticated
ML models for shear strength prediction of short links to reduce prediction error with better accuracy is becoming required. The
XGBOOST technique was recently developed using a tree-based ensemble, a complex gradient boosting with higher processing abilities, and an excellent tool to deal with over-fitting concerns
[40]. The learning method uses a boosting framework-based decision tree called
LightGBM, released by Microsoft in 2017. It is quicker, uses less memory, and is more accurate than
XGBOOST [41].
LightGBM also provided decision rules for category features, which transform factors into one-time multidimensional functionality, saving time and memory
[42].