Steel Structures Research Articles

Characterization of the stress-state dependent ductile fracture behavior for Q960 ultra-high-strength structural steel

Ultra-high-strength structural steels are gaining popularity in civil engineering due to their exceptional strength-to-weight ratio. However, their inherent lower ductility compared to normal strength structural steel warrants particular attention and further investigation for safety assessment. In this study, a total of 24 specimens made of Q960 ultra-high-strength steel (UHSS), including 21 tensile specimens with various stress states and 3 three-point bending specimens, were tested to assess its mechanical behavior undergoing large deformation. Subsequently, the impact of stress state on plasticity, damage evolution and fracture initiation was analyzed and characterized. The Bai-Wierzbicki yield surface with a deviatoric associated flow rule was identified to characterize the complex plasticity behavior of Q960 UHSS. With respect to damage evolution, the stress-state dependent fracture energy Gf was proposed in this study to describe the damage softening behavior. The uncoupled Hosford-Coulomb locus with a non-linear weight function was utilized to predict the fracture initiation behavior. Finally, the utilized stress-state dependent constitutive models for Q960 UHSS, with the calibrated parameters and user-defined material subroutine VUMAT, were successfully verified through the three-point bending test with good agreement. Moreover, based on a parametric analysis of radius-to-thickness ratio, the bendability design regarding the minimum radius-to-thickness ratio of Q960 UHSS was proposed.

A Novel Method for Increasing the Concrete Resistance to Chloride Ions Erosion

Concrete structures generally play an important role in the infrastructure construction. The corrosion of reinforcing steels in concrete structures is one of the main causes of the degradation and reduction of their service life, especially when they are exposed to marine environment or de-icing salts. An understanding of the process of chloride transportation in concrete is of great importance for engineers to predict the service life of concrete structures. Therefore, we synthesized corrosion inhibitor for improving the chlorine resistance of concrete.

Research and Application Status of Soft Steel Dampers

Soft steel dampers have stable hysteresis characteristics and can effectively dissipate energy under repeated loads, providing good shock absorption effects for structures. It can be used for both seismic design of new buildings and seismic reinforcement of existing buildings. Suitable for various structural forms of buildings, including concrete structures, steel structures, and heavy-duty wooden structures. It is also applied in bridge structures, which can effectively reduce the vibration response of bridges under earthquake, wind vibration, etc., and improve the seismic performance and safety of bridges. Countries with rapid development in the application of structural control technology, such as the United States, Japan, Canada, New Zealand, and Mexico, are the main ones. Italy, France, Russia, Singapore, and other countries are also actively applying it in practical engineering. More than a hundred buildings abroad have adopted soft steel dampers.

Using Iterative Correction to Improve the Accuracy of the Blind-Hole Welding Residual Stress Test.

An iterative correction method for the stress release coefficient, leveraging numerical simulation, has been innovatively developed to address the significant error issues associated with the blind-hole method in high-stress residual stress testing of steel structures. This method effectively reduces measurement error in high residual stress regions through a discriminant iteration process. The finite element analysis technology was employed to accurately simulate the blind-hole method's test process, and additionally, Python was utilized for customizing the secondary development of ABAQUS software, thereby automating and optimizing the method. When compared with simulation and experimental data from the welding process, the efficiency, accuracy, and reliability of the correction method have been verified. The proposed method eliminates the need for tedious calibration experiments inherent in traditional methods, significantly enhancing the test's automation level and convergence speed, and ensuring measurement accuracy, which provides an innovative solution for the accurate evaluation of residual stress in steel structures.

Strain measurement of CFRP-Steel bonded joints using distributed optical fibre sensors

ABSTRACT Externally bonded carbon fibre reinforced polymer (CFRP) is widely employed for strengthening steel structures. The CFRP-steel bond behaviour is typically conducted using the single-lap joint (SLJ) and double-lap joint (DLJ) shear tests. This study utilizes advanced distributed optical fibre sensors (DOFS) to measure strains in CFRP-steel SLJs and DLJs, with a specific focus on examining the bending effect. An experimental investigation was conducted to verify the appropriate adhesive and fibre coating materials, achieving synergistic deformation between optical fibre sensors and adherends. The strain results reveal that PI-coated fibres bonded with epoxy resin enhance deformation compatibility. The CFRP strain distributions within the joints are accurately measured by DOFS, enabling the calculation of bending strain to assess joint bending effects. The observed strain aligns well with the finite element (FE) predictions. A more significant bending effect is observed in SLJs compared to DLJs, predominantly concentrated at the loaded end. It can be inferred that the SLJs are subjected to mixed-mode I/II loading in shear tests, and the DLJs appears to be mainly influenced by mode II loading. Additionally, the verified FE model demonstrates that the shear strain across the thickness of the adhesive layer exhibits significant variation at the bond ends.

Python-based numerical study on bolted joints between Fe-SMA and steel plates for structural reinforcements

In order to rehabilitate the performance of deteriorated steel structures, the active prestressed reinforcement employing new intelligent material, Iron-based shape memory alloy (Fe-SMA), has received extensive attentions. To reveal the mechanical properties of bolted joints between Fe-SMA and steel plates, a parametric method to establish finite element model via secondary development of ABAQUS based on Python scripts was proposed. It greatly reduces modelling costs and improves modeling efficiency. Besides, the proposed numerical models were verified against the experimental results by failure mode, final deformation, load-displacement characteristics, ultimate load-bearing capacity and initial stiffness. It is demonstrated that the numerical simulation results are in good agreement with the experimental results. What is more, a parametric study on thickness and geometry of steel plates, as well as the end distance, edge distance and thickness of Fe-SMA plate was conducted to verify the applicability of current leading specifications for steel structures. It is evident from the results that the thickness of Fe-SMA should be controlled to prevent failure of parent steel structures. Furthermore, similar to steel plates, the thickness of Fe-SMA plate can be considered linear and the failure of bolt can be avoided, as described in Chinese code GB 50017–2017 and Eurocode 3 Part 1–8. However, the minimum allowable edge distance in Chinese code GB 50017–2017 and the ultimate load-bearing capacity calculated by Eurocode 3 Part 1–8 is conservative for bolted joints between Fe-SMA and steel plates. Hence, it is urgent to formulate design specifications for this kind of bolted joints for the scientific and economical application of Fe-SMA in structural active reinforcements.

The Influence of the Hot-Rolling Temperature on the Microstructure and Mechanical Properties of Ti-Nb Microalloyed 21%Cr Ferritic Stainless Steel

Microalloying and heat treatment are essential processing techniques for ferritic stainless steel (FSS). Three different compositions of 21%Cr FSS with 0.28Ti, 0.21Ti + 0.05Nb, and 1.05Ti + 0.17Nb were prepared. The interaction effects of the Nb and Ti contents and hot-rolling annealing on the microstructure, mechanical properties, and precipitate phases of FSS were studied. The microstructure, crystal structure, and precipitation phase of steel at 930, 980, and 1030 °C with Ti-Nb microalloying were investigated using an optical microscope (OM), X-ray diffractometer (XRD), and scanning electron microscope (SEM). The room-temperature tensile properties, surface roughness, and hardness were tested separately. This study found that the composite addition of Ti and Nb had a dual effect of fine-grain strengthening and precipitation strengthening. The 1.05Ti + 0.17Nb steel specimen had a moderate grain size and the best uniformity after hot rolling at 980 °C. The tensile strength and elongation were 454 MPa and 34.2%, which achieved an optimal balance between strength and plasticity.

Air temperature characteristics of cable-girder pin joint node of suspension bridge under pool fire

Under the action of high temperature, the mechanical properties of steel structure will be reduced. Cable-girder pin joint nodes (referred to as the node) of suspension bridges are composed of steel structures. Before studying the fire resistance of structures, it is necessary to accurately predict the air temperature characteristics under fire. In this paper, the FDS calculation model of the node is established for the pool fire. The air temperature characteristics of the node are clarified by numerical simulation and theoretical analysis. The effects of main factors such as fire location, wind speed, leakage hole radius and space height are studied. The unfavorable fire scenario and air heating mathematical model are obtained. The main conclusions are as follows: (1) As the fire source distance increases, the peak value of air temperature at the node gradually decreases, while the heating time steadily increases and eventually reaches a stable state. (2) The air temperature at the node initially increases and then gradually decreases as the wind speed increases. (3) Increasing the leakage hole radius from 0.02 m to 0.06 m results in a decrease of approximately 60 % in the air heating time at the node. (4) Increasing the space height from 0.25 m to 1.7 m leads to a maximum decrease of 72 % in air temperature at the node. (6) In the unfavorable fire scenario, the peak air temperature at the node can reach approximately 1200 °C, and the heating time ranges from 67 s to 149 s (7) A mathematical model of the air temperature rise curve, considering the influence of space height, is developed. This model can serve as a theoretical foundation and reference for the study of fire resistance of the node exposed to pool fires.

Mechanical Characterisation of Gypsum-Based Passive Fire Protection Mortars with Micro and Nano Silica Particles

Steel structures are vulnerable to fire due to the degradation of their mechanical properties at high temperatures, making it necessary to protect them when exposed to high temperatures. This paper presents the results of an experimental research work to characterise the mechanical properties of gypsum-based fire-resistant mortars with and without nano and micro silica particles by destructive and non-destructive tests at ambient temperature. Five compositions were studied: one commercial composition was used as a reference and four were developed in the laboratory. Two were based on gypsum with perlite or vermiculite, and the other two included nano and micro silica particles. Twenty specimens underwent ultrasonic pulse velocity, flexural, and compression tests, while five specimens were tested by the impulse excitation of vibration. Young’s modulus, shear modulus, and Poisson’s ratio were assessed by non-destructive tests, and the flexural and compression strengths were assessed by destructive tests. Additional tests included density and porosity assessments, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy. Results indicated that adding nano and micro silica particles posed challenges to the mechanical and physical properties. Despite this, vermiculite compositions showcased superior or similar properties to the commercial composition, while perlite compositions exhibited slightly lower properties.

Short Immobilization in a Sling Does Not Lead to Increased Salivary Cortisol Levels in Pigs

The goal of the present study was to evaluate the potential stress developed in farm hybrid pigs and miniature laboratory pigs briefly restrained in a sling, by measuring salivary cortisol levels. The study was performed in 20 healthy pigs grouped into three groups: group HYB-F: hybrid female pigs (n = 12), housed at the CREBA facility (Lleida, Spain); group MIN-F: Specipig® miniature female pigs (n = 4), housed at the CREBA facility; group MIN-M: Specipig® miniature male pigs (n = 4), housed at the Almirall facility (Barcelona, Spain). Upon arrival, the animals were enrolled in a social habituation and training program, which included habituation to a restraint sling. The sling was a stainless steel structure with a canvas hammock which had four openings for placing the animal’s feet. The assessment of stress levels in the sling was carried out by measuring cortisol levels in saliva samples. Five saliva samples were collected from each animal over 4 days: Sample 1 (basal sample): taken after animals perceived the presence of the technicians in the pen; Sample 2: taken after animals saw the sling in the pen; Sample 3: taken when animals were in the sling; Sample 4: taken 1 min after the previous one; Sample 5: taken after animals were released back on the floor. In group HYB-F, five animals (5/12) showed strong resistance and could not be restrained in the sling on at least one day. All animals in the groups of miniature pigs could be restrained on all the days. Within each group, the manipulation phase did not affect salivary cortisol levels. Likewise, salivary cortisol levels did not change significantly across days in either group. In conclusion, salivary cortisol levels did not increase when pigs were lifted and briefly restrained in the sling, even though some of them (in particular, the hybrid pigs) showed apparent signs of stress. The lack of correlation between such apparent stress and salivary cortisol levels might be because the vocalizations and movements were not really signs of stress, but simply a way of releasing discomfort, learned in the process of socialization and habituation. In light of this unexpected conclusion, further studies are needed to collect other physiological and behavioral data to clarify what actually happens when pigs are restrained in a sling.

Silane functionalization of titania-graphene oxide nanocomposite for superior anticorrosion polyurethane coatings on steel

This research investigated the enhancement of anti-corrosion properties in polyurethane (PU) coatings on steel substrates through the Silane (N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane) functionalization of Graphene Oxide (GO) with Titania (TiO₂) nanoparticles. Comprehensive characterization techniques, including Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM), Thermogravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray diffraction analysis (XRD), Brunauer-Emmett-Teller (BET), and electrochemical analyses, confirmed the effective integration of TiO₂ within GO layers. The SEM and TEM analyses showed uniform dispersion of TiO₂ nanoparticles, while TGA indicated improved thermal stability of the functionalized GO-TiO2 (fGO). FTIR and XRD analyses verified the composite's successful chemical bonding and structural integrity. BET analysis revealed a specific surface area and pore volume reduction from 505.540 m²/g and 0.867 cc/g for GO to 211.622 m²/g and 0.708 cc/g for fGO, respectively. The enhancement in anti-corrosion properties can be attributed to the uniform dispersion of TiO₂ nanoparticles within the GO matrix, which increases the coating's barrier properties by filling pores and voids. This prevents electrolyte penetration and enhances adhesion to the steel substrate, inhibiting corrosion. Electrochemical analysis demonstrated excellent corrosion resistance of fGO-modified PU coatings, with a maximum observed resistance of 0.821 TΩ.cm2. Salt spray tests further validated these findings, showing delayed and reduced corrosion due to the protective layer formed by fGO. These results highlight the potential of fGO-modified PU coatings as advanced protective materials for steel structures in corrosive environments.

Analysis and Evaluation of Load-Carrying Capacity of CFRP-Reinforced Steel Structures.

Carbon Fiber Reinforced Polymer (CFRP) can be used to reinforce steel structures depending on its high strength and lightweight resistance. To analyze and evaluate the load-carrying capacity of CFRP-reinforced steel structures. This study uses the Finite Element Analysis (FEA) and the experimental tests combined to investigate the influence that the reinforcement patterns and the relevant parameters have on the load-carrying capacity. We made specimens with different reinforcement patterns. Take the steel beam specimen with full reinforcement as an example. Compared with the load-carrying capacity of the steel beam reinforced by two-layer CFRP cloth, that respectively increases by 5.16% and 11.1% when the number of the CFRP cloth increases to four and six, respectively. Based on a specimen set consisting of CFRP-reinforced steel structures under different reinforcement patterns, the random forest algorithm is used to develop an evaluation model for the load carrying. The performance test results show that the MAE (Mean Absolute Error) of the evaluation model can reach 0.12 and the RMSE (Root Mean Square Error) is 0.25, presenting a good prediction accuracy, which lays a solid foundation for the research on the CFRP-based reinforcement technology and process.

Simple Aseismic Reinforcement of Steel Structures Using Knee Braces with High-Hardness Vises

A novel technique for upgrading the seismic resistance of steel buildings by adding knee braces to existing structures using vises was proposed by researchers in 2022. A feature of this retrofitting method is the easy setup owing to its use of vises made from high-hardness metal. Tests were conducted to investigate two main failure modes: slipping failure at the connection and yielding and buckling failure of the knee brace. The retrofitting design is discussed based on a comparison between the slipping strengths obtained through tests and calculations. Furthermore, an analytical study, using the finite element method (FEM), was conducted to evaluate the test results of retrofitted frames that failed in terms of the yielding and buckling of the knee braces. The findings of the analyses are consistent with the test results. This study included a stress relaxation test to assess the long-term performance of the vises.

Study on the heating process, high temperature mechanical properties and fatigue properties of a low-carbon microalloyed steel

The dynamic continuous cooling transformation (CCT) experiments of a low-carbon microalloyed building structure steel were conducted on a Gleeble-3500 thermal simulation test machine, and the corresponding dynamic CCT curve was drawn. According to the dynamic CCT curves, different austenitization temperatures were designed to clarify the influence of austenitization temperature on the transformation and microstructure of the tested steel. The results showed that when the austenitization temperatures were set as 1050, 1150 and 1250 °C, respectively, the microstructure mainly consisted of ferrite and granular bainite. With the increase of austenitization temperature, the starting temperature of ferrite transformation gradually decreased, but the starting and ending temperatures of bainite transformation gradually increased, leading to the increase of the volume fraction of granular bainite. In addition, the tensile properties of the tested steel at different temperatures were determined. The tensile strength gradually decreased with the increase of the tensile temperature, and the highest tensile strength was 502 MPa for the room-temperature sample, while the elongation showed different trends. It was the largest elongation (57.8%) at the tensile temperature of 500 °C, while the smallest value of 19.2%–23.2% was obtained in the 200–300 °C tensile samples. Finally, the fatigue property of the experimental steel was detected by plotting the corresponding fatigue curves. The fatigue limit strength under 1 million cycles was about 376.2 MPa. Results provide a theoretical reference for the setting of heating process in the real industrial production and the application of the low-carbon microalloyed building structured steel.

Facile and effective construction of superhydrophobic, multi-functional and durable coatings on steel structure

Nowadays, steel is one of the most significant materials in industry and daily life. Unfortunately, the defects of steel structures such as collapse at high temperature, poor corrosion resistance, and bad surface functionality have severely restricted their further application. Applying functional coatings for steel structures is considered the effective strategy for settling theses disadvantages. Inspired by nature, eco-friendly, superhydrophobic, and multifunctional-integrated coatings were fabricated on steel via one-step spraying strategy in this paper. Along with silicon dioxide (SiO2) nanoparticles and epoxy resin/silicone resin (EP/SR), the coatings are jointly constituted by hydrophobic flame retardants (M-ALHP@ZIF-8) prepared via multi-stage modification. Due to the formation of micro/nano-scaled rough structure with low surface energy, the water contact angle (WCA) and water sliding angle (WSA) of as-prepared coatings can reach 162.4° ± 1.2° and 2.8° ± 0.4°. The water repellency with low water adhesion can endow the surface of steel with excellent self-cleaning, anti-fouling, and long-lasting anti-corrosion ability. Additionally, the superhydrophobic coatings have displayed good mechanical robustness, chemical stability and weather resistance, which can exhibit certain actual values. Accorded with Zn-catalyzed charring effect of flame retardants, as-prepared coatings have possessed outstanding fire protection capacity with the lowest backside temperature of 181 °C after 1 h fire impact tests. Consequently, this work has provided a facile and effective route for synchronously tackling the key challenges of poor fire protection and surface functionality for steel structures, which will be expected to pave the wide pathway for constructing multifunctional coatings in more fields.

Structural strain and crack monitoring based on the fluorescence response of graphene quantum dots

Graphene quantum dots (GQDs), a novel nanomaterial, offer new avenues for structural health monitoring owing to the remarkable fluorescence response. In this study, the GQDs-epoxy resin composites were fabricated and applied to structural surface. Tests including tension, compression, bending, and fatigue were conducted to explore the fluorescence response of composites to structural strain and cracks. Results show that composites exhibited a heightened fluorescence sensitivity to structural strain. During the tensile tests of coated steel specimens, the fluorescence intensity of composites exhibited positive and negative correlation responses with increasing strain. Whereas in the compression test of coated concrete specimens, solely increased fluorescence intensity with rising strain was observed. Composites demonstrated excellent crack characterization on concrete and steel structures, whether penetrating or developing cracks. The fluorescence response of composites to cracks was based on the fluorescence enhancement at the crack site, and fluorescence intensity was approximately inversely proportional to crack width.

Heat transfer mechanism of superabsorbent polymers phase change energy storage cold-formed steel wall under fire

The superabsorbent polymer phase change materials (SAP materials) exhibit exceptional water absorption and retention properties, offering substantial potential for fire protection in steel structures, thereby reducing the need for sheathing boards and fire-retardant coatings, while minimizing energy consumption. Understanding the heat-mass exchange theory of SAP materials is crucial for enhancing their application in the building industry. This study develops a comprehensive theoretical model for heat-mass exchange in cold-formed steel (CFS) walls incorporating SAP materials. An equilibrium phase change model and a simplified thermal radiation model were developed to capture the water loss and dynamic heat exchange processes in SAP materials. These models were integrated into a transient fluid-solid-thermal coupling model using Ansys Fluent and User Defined Functions. In the case study, the newly developed numerical models can accurately predict temperature field changes in CFS walls with SAP materials, demonstrating the heat transfer mechanisms of hot and cold flanges at different temperature rise stages. The developed numerical model was used to investigate the effects of factors such as the moisture content of the SAP material, web depth, and flange width on the fire resistance of the CFS wall. Results indicated that increasing the wall stud height improves fire resistance, while increasing flange width has little effect on hot flange temperature. These findings provide a theoretical foundation and practical guidelines for the application of SAP phase change insulation materials in the building industry, promoting energy reduction and supporting sustainable construction practices.

A probabilistic model to predict specimen geometry effects on fracture toughness in ferritic–pearlitic steels

This work describes a probabilistic framework for cleavage fracture of ferritic–pearlitic steels incorporating experimental measurements of microcrack distribution associated with the cracking of the pearlitic microstructure. A central objective of this study is to explore and further extend application of a probabilistic framework incorporating the statistics of microcracks to predict specimen geometry effects on the fracture toughness distribution for a typical ferritic–pearlitic structural steel. Fracture toughness values for an ASTM A572 Grade 50 structural steel derived from fracture tests using conventional SE(B) specimens with varying thickness and a/W-ratios provide the cleavage fracture resistance data needed to assess specimen geometry effects on the probability distribution of Jc-values. The present exploratory study successfully predicts the measured statistical distribution of cleavage fracture toughness in shallow crack specimens and provides further support of the proposed probabilistic model as a more advanced and effective engineering-level procedure in fracture assessment methodologies.

Study on the tensile properties of a novel modular splicing joint

The interconnection among module elements within a modular structure assumes a pivotal role in upholding structural integrity and stability. To address the challenges posed by existing inter-module connection joints, which necessitate operational space and may compromise the integrity of the module unit while impeding assembly efficiency, an innovative modular steel structure splicing joint is proposed. Through adjustments to the dimensions of the connection box and fastener components, four distinct spliced joints were established for axial tensile analysis. The subsequent evaluation included an examination of axial tensile capacity, strain distribution, and failure modes at critical points across various joints, providing insights into their tensile effectiveness. To comprehensively explore the influence of size parameters on tensile performance, a corresponding numerical model was developed for parametric analysis. Results indicate that tensile failure modes entail the extrication of the lower-end plate from the upper module column connection box and the cylindrical radius of the fastener. Notably, the protrusion radius of the fastener (R2), markedly influences the tensile bearing capacity of the spliced joints, with precedence over the lower end plate thickness (d0), cylinder radius (R1), sliding block thickness (d1), and limiting plate thickness (d2). The joint obviates the need for external operations to interlink module units, thereby augmenting the installation efficiency of the modular structure and mitigating complexities in design and the enigmatic transmission of forces within the self-locking joint.

Feasibility assessment of non-contact acoustic emission monitoring of corrosion-fatigue damage in submerged steel structures

Corrosion-fatigue is considered to be one of the main degradation mechanisms affecting the structural integrity of offshore support structures. This paper presents a feasibility assessment for the detection and monitoring of corrosion-fatigue damage using non-contact acoustic emission (AE). An accelerated corrosion-fatigue experiment was conducted on a S420NL dog-bone specimen. A corrosion-fatigue cell was designed and fabricated to simultaneously apply accelerated corrosion and cyclic loads on the specimen submerged in artificial seawater. A three-electrode electrochemical configuration under potentiostatic control was used to accelerate corrosion. The ultrasound signals were continuously measured using underwater AE transducers (in the frequency range of 50–450 kHz) placed at a fixed distance from the tested coupon. The results of the accelerated corrosion-fatigue experiment suggest that corrosion-fatigue-induced ultrasound signals can be detected with a satisfactory signal-to-noise ratio using non-contact AE sensors. The mean energy of the corrosion-fatigue-induced ultrasound signals was one order of magnitude higher than that of the corrosion-induced signals. The trends of the AE parameters extracted from the AE signals were analysed as functions of the load cycles. The results revealed high potential for the identification and monitoring of corrosion-fatigue damage using the non-contact AE technique.