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CONTENTS
Volume 60, Number 4, August 25 2026
 

Abstract
Accurate assessment of in-service strength and failure behavior of large-scale wind turbine blades requires a comprehensive representation of extreme loads under the full set of Design Load Cases (DLCs). However, existing studies simplify the governing mechanisms to a 2D bending-moment-based perspective, neglecting the coupled effects of torsion, shear forces, and axial force, which may lead to misestimation of local strength margins and failure risk. To overcome this, an integrated blade structural analysis framework combining the load envelope, six-component load mapping, and 3D global failure assessment is developed and applied to a 5 MW wind turbine blade. The results indicate that the explicit inclusion of torsional moment, shear and axial forces provides a more complete characterization of extreme load states compared with conventional bending-based approaches. Comparative analyses reveal that the traditional 2D bending perspective method tends to underestimate fiber failure risk in the leading-edge and trailing edge regions, while overestimating it in other areas, with a maximum discrepancy of approximately 5% in the fiber failure index. Further analyses reveal that fiber failure dominates the skin response, with damage-prone regions mainly located between the blade root and the maximum chord section. Global failure assessment further reveals that extreme fiber failure indices mainly occur in DLC 1.3, DLC 5.1, DLC 6.1, and DLC 7.1, whereas matrix failure is primarily associated with DLC 6.1 and DLC 7.1.

Key Words
composite structure; finite element analysis; Puck failure criterion; structural analysis; wind turbine blade

Address
Fangyuan Sheng:1)Zhejiang University, Hangzhou 310058, China
2)Interdisciplinary Student Training Platform for Marine areas, Zhejiang University, Hangzhou 310027, China

Xu Liang: Zhejiang University, Hangzhou 310058, China

Baoxuan Wang:1)Zhejiang University, Hangzhou 310058, China
2)Interdisciplinary Student Training Platform for Marine areas, Zhejiang University, Hangzhou 310027, China

Xiaohan Li:Zhejiang University, Hangzhou 310058, China

Hang Zhang:Zhejiang University, Hangzhou 310058, China

Yang Liu: Zhejiang University, Hangzhou 310058, China

Fu Li:China Quality Certification Center, Beijing 100070, China

Zhenyu Wang:1)Zhejiang University, Hangzhou 310058, China
2)Interdisciplinary Student Training Platform for Marine areas, Zhejiang University, Hangzhou 310027, China

Abstract
Cold-formed steel (CFS) sections have become increasingly prevalent in structural engineering due to their lightweight nature, favorable strength-to-weight ratios, geometric versatility, and ease of transportation. Among CFS profiles, Sigma sections have demonstrated superior performance compared to conventional CEE and ZEE sections under flexural loading. However, their behavior under pure torsion remains insufficiently understood, as previous studies have primarily focused on bending or combined bending–torsion loading. This study extends the experimental program previously conducted by the authors by investigating the torsional behavior of Sigma sections through numerical simulations and parametric analyses. The ABAQUS finite element model was first calibrated and validated against the existing experimental results to ensure accurate representation of the tested beams. Following validation, an extensive parametric study was performed using both finite element and finite strip methods, considering 20 cross-sectional geometries, three span-to-depth ratios (L = 3D, 6D, and 10D), and two steel grades. Results indicate that existing code provisions significantly underestimate torsional capacity, by 24% for CEE sections and 77% for Sigma sections on average. Based on these findings, a design equation was developed to predict the torsional strength of Sigma sections, demonstrating a mean error of approximately 4% relative to numerical predictions and a coefficient of variation of 8.8%. The findings of this study address a key gap in literature and offer a practical and reliable approach for the design of sigma sections subjected to torsional loading.

Key Words
ABAQUS; bimoment; cold-formed steel; CUFSM; finite element analysis; sigma sections; warping

Address
Ahmed G. Elrakhawey:Structural Department, Ain Shams University, 1 El Sarayat St., ABBASSEYA, El Weili, Cairo, Egypt

Ali Hammad:Structural Department, Ain Shams University, 1 El Sarayat St., ABBASSEYA, El Weili, Cairo, Egypt

Sherif M. Ibrahim: Structural Department, Ain Shams University, 1 El Sarayat St., ABBASSEYA, El Weili, Cairo, Egypt

Abstract
This paper systematically investigates the structural behavior of tapered lightweight concrete-filled double skin stiffened steel tubular (LHRTL-CFDSST) members with large hollow ratios subjected to combined compression bending-shear loading. Initially, experimental studies were conducted to examine the effects of various parameters, including the shear-span ratio and the presence of longitudinal stiffeners. Subsequently, detailed finite element (FE) models were developed and validated against experimental results. These models were then used to analyze the distribution of contact stress, axial stress, and shear stress within the members. The results indicated that failure consistently occurred at the bottom cross-section, characterized by local buckling of steel tubes and concrete crushing. The addition of longitudinal stiffeners notably improved the members's load-bearing capacity and stiffness. It was observed that shear forces had minimal influence on the load-bearing capacity when the shear-span ratio exceeded 2. Finally, a calculation method for evaluating the compression-bending-shear load-bearing capacity was proposed based on parametric analyses and the established capacity relationships. Verification against experimental and numerical results demonstrated the accuracy and reliability of the proposed method, thus providing theoretical support for practical engineering design.

Key Words
calculation method; compression-bending-shear test; large hollow ratio; nonlinear numerical analysis; tapered concrete-filled double-skin steel tubular members

Address
Bofan Li:School of Civil Engineering, Xi'an University of Architecture & Technology, No. 13, Middle Yanta Road, Beilin District, Xi'an 710055, China

XianTie Wang:School of Civil Engineering, Xi'an University of Architecture & Technology, No. 13, Middle Yanta Road, Beilin District, Xi'an 710055, China

WangGeng Liang:School of Civil Engineering, Xi'an University of Architecture & Technology, No. 13, Middle Yanta Road, Beilin District, Xi'an 710055, China

WenLong Lu:School of Civil Engineering, Xi'an University of Architecture & Technology, No. 13, Middle Yanta Road, Beilin District, Xi'an 710055, China

JinZe Ge:School of Civil Engineering, Xi'an University of Architecture & Technology, No. 13, Middle Yanta Road, Beilin District, Xi'an 710055, China

Abstract
In timber concrete composite systems, the shear connector which ensures the connection between the concrete slab and the timber beam is a critical component influencing the overall behavior of the system. In previous studies, all designed shear connectors were fully embedded in concrete. Consequently, the damage occurred not only in the shear connector but also in the concrete slab and timber beam. In this study, a new perspective on shear connector design has been introduced. In the proposed design, the shear connector is partially isolated from the concrete, providing a space that allows it to bend freely within the slab. This configuration delays damage in the concrete slab and timber beam, leading to damage localization on the shear connector itself. Even at advanced damage levels, the structural integrity of the system can be maintained. As part of the experimental program, push out tests were conducted on nine full-scale asymmetric specimens, and bending tests were performed on three beams with a length of 450 cm. The load-carrying capacities, stiffness, energy dissipation capacities, and damage patterns of the specimens were determined and compared with those of conventional shear connectors.

Key Words
bending test; composite structures; concrete; push-out test; steel plate shear connectors; timber

Address
Fatih Cebir: Karadeniz Technical University, Department of Civil Engineering, 61080, Trabzon, Türkiye

Hussien A. Soalih:1)Department of Civil Engineering, School of Civil and Hydraulic Engineering, Institute
of Technology, University of Gondar, Gondar, Ethiopia
2)Graduate School of Natural and Applied Science, Karadeniz Technical University, 61080, Trabzon, Türkiye

Ayşegül Durmuş Demir:Karadeniz Technical University, Department of Civil Engineering, 61080, Trabzon,Türkiye

Serhat Demir:Karadeniz Technical University, Department of Civil Engineering, 61080, Trabzon, Türkiye

Abstract
The application of cold-formed steel (CFS) tubular X-joints in structural systems is growing due to their structural efficiency; however, their efficiency is frequently constrained by their tendency towards joint instability and localized deformations of the chord. The objective of this paper is to explore the axial behaviour of both the unreinforced and ring stiffened CFS tubular X-joints through experimental and numerical analysis as well as artificial intelligence algorithms (machine learning). To begin with, a detailed parametric non-linear finite element (FE) study was performed by changing geometric properties such as brace-to-chord diameter ratio (β = 0.25 ‒ 1.0), chord slenderness (dc/2tc = 12.67 ‒ 50), joint inclination angle (θ = 30° ‒ 90°), and the different stiffener configurations. The obtained experimental results are used for verification and calibration of the proposed FE models showing a good match of the results with relative errors less than 10%. Furthermore, a validated FE database was implemented to generate a predictive Artificial Neural Network (ANN) to quickly predict the ultimate axial load carrying capacity. The ANN model considers seven geometric input parameters as input and predicts the maximum force of the joint with very accurate prediction error as indicated by RMSE and MAE error values and R2 ≈ 0.99 coefficient of determination. Feature Importance and SHAP analyses reveal that the brace-to-chord diameter ratio (β) and chord slenderness govern the strength of the joint. On the other hand, stiffener thickness and location demonstrate threshold efficiencies, where further additions provide little contribution to the joint capacity. Optimized ring stiffeners increase axial capacity by up to 60% over un-stiffened specimens. The key innovation of this research is the development of a FE-ML model using experimental data to predict and interpret the governing factors that control axial joint capacity. The proposed FE-ML approach is useful for engineers designing joints and estimating axial capacities while optimizing stiffener configurations.

Key Words
Artificial Neural Network (ANN) modeling; axial load-carrying capacity; cold-formed steel tubular X-joints; nonlinear finite element analysis; ring stiffener reinforcement

Address
G.R. Iyappan:Department of Civil Engineering, SRM Valliammai Engineering College, SRM Nagar, Kattankulathur – 603 203

P. Sangeetha: Department of Civil Engineering, Sri Sivasubramaniya Nadar College of Engineering,
Chennai, Tamil Nadu 603 110, India

Abstract
For high-rise buildings with large structural height and significant vertical load, traditional reinforced concrete (RC) shear wall design inevitably leads to larger reinforcement quantities, diameters and denser spacing in the boundary elements, complicating onsite splicing of longitudinal rebars. This study proposes a novel composite shear wall in which spiral hoop confined concrete-filled tube (SHCFT) completely replace the longitudinal rebars and hoops in the boundary elements. Full-scale SHCFT shear wall and RC shear wall specimens were tested under quasi-static cyclic loading. The results show that, compared with the RC walls, the SHCFT shear walls exhibited an average increase of 9.03 % in load-bearing capacity, together with improved ductility and energy dissipation capacity. The spiral hoops provide substantial confinement to the core concrete and ensure composite action between the steel tube and the surrounding concrete. A finite-element modelling approach and load-bearing capacity formulas are also presented, both of which correlate well with the test results and can be used to predict the mechanical behavior of SHCFT shear walls.

Key Words
cft; composite shear wall; spiral hoops; seismic performance; quasi-static cyclic test; finite element

Address
Jia Qin: School of Civil Engineering and Architecture, Hainan University, 58 Renmin Avenue, Haikou, Hainan, China

Yun Chen: School of Civil Engineering and Architecture, Hainan University, 58 Renmin Avenue, Haikou, Hainan, China

Abstract
This article investigates the vibration behavior of cracked porous functionally graded plates resting on elastic foundations. The analysis considers a Winkler-Pasternak elastic foundation. The cracked plate is modeled and analyzed using an efficient method, namely the extended finite element approach. Higher-order shear deformation theory is utilized to derive the plate's kinematics, while enrichment functions are incorporated into the displacement field to represent the discontinuities arising from displacement jumps. The level set technique is enacted to identify the enriched nodes. The plate is assumed to be porous with uniform porosity distribution throughout the domain. The functionally graded material (FGM) is modeled using the power law. Porous materials possess a high strength-to weight ratio, which makes them well-suited for use in aerospace, automotive, and various other engineering fields. A comparative study for validating the developed MATLAB code is conducted, and the accuracy of the results is demonstrated. A comprehensive investigation of the FGM plate featuring edge and center cracks is conducted. The results are presented for different gradient indices, porosity indices, crack dimensions, and elastic foundation parameters.

Key Words
composite structures; crack; dynamic analysis; numerical analysis; plate; structural analysis; vibration analysis

Address
Ahmed Raza:Research Institute for Aerospace Engineering and Technology, Korea Aerospace University,
Goyang-si, Gyeonggi-do 10540, Republic of Korea

Mohammad Amir:Research Institute for Aerospace Engineering and Technology, Korea Aerospace University,
Goyang-si, Gyeonggi-do 10540, Republic of Korea

Sang-Woo Kim:1)Research Institute for Aerospace Engineering and Technology, Korea Aerospace University,
Goyang-si, Gyeonggi-do 10540, Republic of Korea
2)Department of Aeronautical and Astronautical Engineering, Korea Aerospace University,
Goyang-si, Gyeonggi-do 10540, Republic of Korea
3)Department of Aerospace and Mechanical Engineering, Korea Aerospace University,
Goyang-si, Gyeonggi-do 10540, Republic of Korea

Abstract
With the development of fuse connections sustaining large plastic deformation without significant degradation, a key question arises about whether a fuse connection should be replaced after an earthquake or if it can remain to resist future events during the building's lifespan. This study proposes an assessment framework aimed at improving the seismic resilience of steel special moment-resisting frames with Simpson Strong Tie™ Yield-Link® connections under successive earthquakes. The framework evaluates structural response after an initial earthquake and considers the influence of accumulated damage and residual deformation on the structural performance during a subsequent event. Successive earthquake scenarios are simulated by sequentially applying by sequentially applying two ground motions in nonlinear dynamic analyses. The second event is applied to the structure with the residual deformation and fatigue damage generated by the initial event. Fragility curves are then developed for selected limit states. Based on this framework, nonlinear dynamic analyses are conducted using 2- and 4-story models to evaluate seismic performance and examine the effectiveness of replacement strategies between events. Key findings indicate that multiple earthquakes can increase seismic fragility due to accumulated damage in fuse materials, leading to a deterioration in frame stiffness and load-resisting capacity. Replacement of damaged yield-link components, whether in part or throughout the structure, was highly effective in reducing seismic fragility in future events. Criteria based on residual interstory drift and rotation helped identify replacement locations and improve resilience. Since replacement plans depend on performance levels and repair costs, the framework can leverage replaceable fuse connections to provide practical, cost-effective approaches ensuring long-term functionality of steel moment-resisting frames.

Key Words
seismic performance; seismic resilience; steel special moment-resisting frames; structural fuses; successive earthquakes

Address
Sangwook Park:School of Architecture & Building Science, Chung-Ang University, Seoul 06974, Korea

Patricia Clayton:Department of Engineering, Wake Forest University, Winston-Salem, NC 27109, U.S.A.

Jin Woo Moon:School of Architecture & Building Science, Chung-Ang University, Seoul 06974, Korea

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