Large-scale Steel Structures Research Articles

The Stability of Corroded Circular Steel Tubes Under Axial Compression Investigated Through Testing, Finite Element Analysis and Theoretical Approaches

Circular steel-tube members are extensively used in various large-scale steel structures. The detrimental effects of corrosion on the ultimate bearing capacities of these structures require urgent attention. This study designed six circular steel tube specimens to explore the degradation pattern of the ultimate bearing capacity of corroded circular steel tubes under axial compression; three were subjected to accelerated corrosion by electrification, and the other three were used as the control group. Following the accelerated corrosion test, both groups of specimens were subjected to material-property and axial-compression tests. These tests provided data on the bearing capacity and midspan displacement of the corroded circular steel tubes, allowing for the construction of load–displacement relationship curves. The test results demonstrate that corrosion significantly affects the bearing capacity of circular steel tubes. As the severity of the corrosion increased, the bearing capacity and stiffness of the corroded circular steel tubes progressively weakened. To simulate the behavior of circular steel tubes, a numerical model was established that provided the ultimate bearing capacity under axial compression and generated load–displacement curves. The simulation results closely aligned with the test results. This study introduced a novel approach for accurately computing the stability-bearing capacity of circular steel tubes subjected to corrosion and axial compression. Comparative analyzes with test results validated the superior performance of the proposed method in accurately predicting the ultimate bearing capacity.

Mechanics of structural size effect in impact brittle fracture of steels and consequent scaling laws for fracture

A large structural size effect on brittle fracture energy was observed in studies of impact fracture of steels by Stanton, Batson and Docherty, nearly 100 years ago. The size effect was seen in macroscopically brittle fractures of geometrically similar specimens tested over a large size range. These historical findings have great significance in designing large-scale steel structures such as ships and bridges. However, there has been no physical principle or theory yet to explain the size effects observed by Stanton, Batson and Docherty. In the present work, a new approach based on net-section mechanics is used to explain the size effect. It is shown that the change in net-section strain energy predicts well the size effect on fracture energy , under the constant condition of cleavage crack initiation stress at the notch root. The spectacular decrease in specific fracture energy with increased specimen size is explained by noting the three-dimensional nature of stored strain energy and the two-dimensional nature of fracture energy dissipated in the crack layer. By scaling both energies to a reference cubic specimen volume and equating, an expression that describes the inverse size dependence of specific fracture energy has been formulated. The mechanics of the size effect is illustrated by assessing the theory with extensive experimental data. Further, scaling laws for fracture energy have been developed. This work honours the pioneering studies of Stanton, Batson and Docherty, which have been instrumental for the development of the present theory and analysis.

Fatigue crack growth behavior of 42CrMo high-strength steel with tempered sorbite/bainite microstructures: Roles of grain and constituent in microstructures

Microstructural differences through the thickness have always been an attention focus for large-scale steel structures, since they could significantly influence fatigue crack propagation (FCP) characteristics. Here, the effects of microstructure in FCP behaviors of 42CrMo steel were analyzed with emphasis on two different tempered sorbite/bainite (TS/B) microstructures: (i) fine TS/B structures (M42); (ii) coarse TS/B structures (M52). The results show that the FCP rate is relatively slower for M52 than for M42 in the regime through the later stage of near-threshold (I-L) to the early stage of Paris-regime (Ⅱ-E) with low ΔK, but is fairly similar for the two cases in the other ΔK regimes. Under relatively low ΔK, the FCP path of M52 is more tortuous with numerous micro-cracks in B and larger-sized crack deflections at the carbides and boundaries compared to M42, especially in the I-L where fatigue micro-cracks can deflect at the single coarse carbide, thereby resulting in roughness-induced crack closure and crack retardation behavior. Theoretical analysis shows that FCP behaviors are closely related to the cyclic plastic region size (Δrp) at the crack-tip. In the early stage of near-threshold region, Δrp is restricted within a grain-size scale for both steels, thus leading to a similar FCP rate. However, from the I-L to the Ⅱ-E, coarse B/ferrite-grains in M52 are always larger than the Δrp of fatigue crack-tip, and thereby lead to numerous micro-cracks formation and crack deflections at the carbides and B boundaries, inducing crack closure. In the later stage of Paris region, B/ferrite-grains in the two cases are much smaller than Δrp, so that FCP behaviors depend on the microstructure group effects, or overall strength and fracture toughness of materials, which cause the close FCP rate.

Loosening Identification of Multi-Bolt Connections Based on Wavelet Transform and ResNet-50 Convolutional Neural Network.

A high-strength bolt connection is the key component of large-scale steel structures. Bolt loosening and preload loss during operation can reduce the load-carrying capacity, safety, and durability of the structures. In order to detect loosening damage in multi-bolt connections of large-scale civil engineering structures, we proposed a multi-bolt loosening identification method based on time-frequency diagrams and a convolutional neural network (CNN) using vi-bro-acoustic modulation (VAM) signals. Continuous wavelet transform was employed to obtain the time-frequency diagrams of VAM signals as the features. Afterward, the CNN model was trained to identify the multi-bolt loosening conditions from the raw time-frequency diagrams intelligently. It helps to get rid of the dependence on traditional manual selection of simplex and ineffective damage index and to eliminate the influence of operational noise of structures on the identification accuracy. A laboratory test was carried out on bolted connection specimens with four high-strength bolts of different degrees of loosening. The effects of different excitations, CNN models, and dataset sizes were investigated. We found that the ResNet-50 CNN model taking time-frequency diagrams of the hammer excited VAM signals, as the input had better performance in identifying the loosened bolts with various degrees of loosening at different positions. The results indicate that the proposed multi-bolt loosening identification method based on VAM and ResNet-50 CNN can identify bolt loosening with a reasonable accuracy, computational efficiency, and robustness.

S-version finite element strategy for accurately evaluating local stress in the vicinity of dynamically propagating crack front in 3D solid

Developing a numerical method to accurately simulate the brittle crack propagation phenomenon is crucial for ensuring the safety of large-scale steel structures. Although recent studies have demonstrated that using the local fracture stress criterion as the fracture condition is effective, the most critical issue is that the methods for evaluating local stress in the vicinity of the dynamically propagating crack front have not been established. To address this, this paper proposes a strategy for analysing a dynamically propagating crack in 3D solids on the basis of the s-version finite element method (s-method). In the proposed strategy, the local mesh is defined in the vicinity of the crack front as an ideal structured mesh aligned with both the crack front direction and crack propagation direction to accurately simulate the local stress field. The dynamically propagating crack front was modelled by a combination of the nodal force release method and local mesh update. The proposed strategy was verified by evaluating the accuracies of the local stress in stationary and dynamically propagating circular crack problems as well as those of the stress intensity factor. The results demonstrate that the proposed strategy provides unprecedented accuracy and efficiency of local stress evaluation in problems of dynamic crack propagation in a 3D solid without requiring any complicated remeshing procedures. Therefore, the proposed strategy has potential as the basis of a numeral framework for analysing dynamic brittle crack propagation problems dominated by the local fracture stress criterion.

Influence on mechanical behaviors considering construction hosting process of large-scale steel structure

In the design of large-scale steel structure, the design calculation of the structure is usually based on the service state. But in the process of steel structure construction, the displacement and stress produced in the construction process cannot be completely consistent with that in the design state. With the progress of construction process, the deformation and stress caused by self-weight and construction load gradually accumulate until the structure is formed, which will produce construction error relative to the design state. In this paper, FEM method was used to simulate the construction process of the steel grid roof of the theater in the Beijing Sub Center Theater project, and the influence of the accumulated deformation and stress on the mechanical properties of the structure during the construction process was analyzed. The results show that the cumulative deformation and stress in the construction process have a great influence on the final deformation and stress distribution of the structure. The maximum vertical displacement in the actual construction state is 599.6% of that in the design state, and the maximum stress is 119.7% of that in the design state. This will lead to the difference between the construction-completed structure and the design structure, which makes the design result dangerous. The measures to optimize the construction process were also given in this paper, which provides guidance for the construction process of large-scale steel structure.

Analysis and Research on Multi-layer Docking Error of Complex Interlayer Column Module Based on Point Cloud

Modular design of large offshore oil and gas module reduces the construction difficulty of the whole building, but increases the cumulative error between modules. For large-scale steel structure buildings, the error between the inter-story column modules will affect the overall building stability. It is a feasible method to use point cloud to monitor the errors in real time, so as to trim the columns in time. The goal of this paper is to put forward a set of error analysis method which is suitable for point cloud pre-matching of interlayer integral column. This method includes the calculation and analysis of the center line angle error of each butt joint and the position error of butt joint center of gravity after transformation based on interlayer optimal matching. In practical work, the column structure with large error can be trimmed according to the calculated data.

On the influence of the geometrical irregularities in the mechanical response of Wire-and-Arc Additively Manufactured planar elements

The use of Additive Manufacturing (AM) technologies in the construction industry is still at its pioneering stage. The first investigations indicate that, among actually available metal 3D-printing strategies, Wire-and-Arc Additive Manufacturing (WAAM) process appears to be the most suitable for realizing large-scale steel structures. Nonetheless, the limited knowledge of the mechanical response of WAAM-produced alloys requires further experimental work for a reliable evaluation of the structural behavior of WAAM structural members. One specific issue which still needs to be fully investigated is the peculiar geometrical irregularity resulting from WAAM process that could have non-negligible effects on the mechanical behavior, such as anisotropy and non-homogeneous stress-strain fields.The present work explores the influence of the inherent geometrical irregularities of planar 308LSi stainless steel WAAM specimens on the tensile response. For this purpose, detailed geometrical characterization of the external surface of WAAM specimens was carried out with 3D scanning techniques and random field theory. Different sets of specimens were subjected to tensile tests to evaluate the influence of surface finishing (machined vs. as-built), orientation (with respect to the printing layers) and cooling strategy on the key mechanical parameters. The whole strain field was then studied in detail through Digital Image Correlation (DIC) monitoring technique. Key findings are given in terms of geometrical characterization of surface roughness and thickness variability, as well as a quantitative assessment of the influence of geometrical irregularities on the main mechanical parameters. The material response reveals a significant anisotropy related to a marked crystallographic micro-texture. The geometrical irregularities negatively impact some of the mechanical parameters of the as-built material, suggesting further considerations for practical structural design applications.

Deformation detection of a double-clamped beam according to ultra-weak fiber Bragg grating.

Metal beam strain detection may offer valuable insight into health monitoring for large-scale steel structures. This research presents, to the best of our knowledge, the first implementation of ultra-weak fiber Bragg gratings for the deformation detection of a double-clamped beam because of their higher multiplexing and denser detection points compared to fiber Bragg gratings. The measured values are entirely consistent with those determined by strain gauges applied for reference and demonstrate that the strain of each sensing point increases linearly with the load at the middle of the beam. The errors of different loads at different load points between inversion maximum deflection and measured displacement are less than 9.59%.

The impact of corrosion-stress interactions on the topological features and ultimate strength of large-scale steel structures

Aged marine structural analysis often relies on simplified corrosion modelling. Empirical or statistical methods are used to predict a uniform thickness reduction over time. Although convenient, this approach cannot incorporate the corrosion evolution or the rough surfaces in the damaged area. This is fundamentally due to the lack of representation of the underlying corrosion mechanisms in service environments. To better understand how structural response changes based on corrosion under service loads, this paper presents a series of finite element analyses which consider the coupling relationship between the surface mechanical stresses and the resulting change of corrosion rate. The coupling provide complex corrosion-stress interaction depending on the experimental datasets. The quantification of this interaction is based on in situ experimental measurements of corrosion kinetics at different stress levels. The simulations show the stress effect results in the generation of more realistic corrosion patterns on the structural surface, based on a two-bay/two-span large-scale panel model subject to uniaxial compression. In addition, the incorporation of corrosion experiments allows the modelling of corrosion evolution based on physical observations instead of empirical assumptions. The irregular surface damage leads to a change in structural buckling mode, and up to 8% reduction in ultimate strength compared to models without considering the stress effect.

Prediction of Welding-Induced Distortion of Fixed Plate Edge Using Design of Experiment Approach

Abstract The paper presents the results of experimental studies on distortion of the fixed plate edge due to formation of a butt joint. This is a hidden form of weld distortion present in structural nodes and identified at the ship hull pre-fabrication stages. The investigations were performed according to a design of experiment (DoE) approach in laboratory conditions resembling those encountered in the shipbuilding industry. The presented analysis includes the technological–construction parameters influencing the evaluated distortion shape. The implemented method of experimental results evaluation allows the utilisation of the approximation dependence to predict the fixed plate edge distortion in large-scale steel structures.

Prevention of cold cracking by the welding process for reducing diffusible hydrogen in high-tensile thick plate welding

ABSTRACT Cold cracking sensibility is a severe problem in the welding fabrication of large-scale steel structures. It is well known that diffusible hydrogen content in the weld metal strongly influences this cracking. In recent years, a novel welding process using a special welding torch was researched and developed. By using this process, the amount of hydrogen content in the weld metal can be greatly reduced than the conventional process. In this study, the effect of cold cracking prevention and required preheating temperature reduction by new welding process were confirmed. The window type restraint weld cracking test was applied. Both base metal and welding material were 780 MPa class high-tensile steel. During the test, the preheat and interpass temperatures were controlled strictly. Moreover, the temperature level was changed from 50°C to 0°C. As a result, cold cracking (transverse crack) occurred with the conventional method in which the temperature was kept under 50°C. In contrast, there is no crack with the developed one under 50°C and 25°C. When the controlled temperature was lowered to 0°C, many cracks were observed with the developed process. From the above, the effect of cold cracking prevention by the novel welding process for reducing diffusible hydrogen was confirmed and about 50°C preheating temperature reduction effect was demonstrated. These test results confirmed the consistency with past research results. A very good agreement was obtained when comparing the test results and the past research results of cold cracking control indexes in terms of root cracking and multi-pass weld transverse cracking. Therefore, the validity of this study was demonstrated.

Fatigue Testing of Large-Scale Steel Structures in Resonance with Directional Loading Control

Offshore structures such as jacket and monopile foundations for wind towers and platforms for oil and gas are large steel structures that are subjected to severe fatigue loading conditions. When developing constructions using novel welding techniques, high-strength steel grades or specific bolted assemblies there is a need for validation testing of large-scale components. Conventionally, such fatigue tests are carried out on servo-hydraulic test which are time-consuming.Alternatively, fatigue tests can be performed in resonant bending by a cyclic excitation force with frequency close to the first eigenfrequency of the test specimen. In this paper a new test setup is presented suitable for testing large-scale steel components in resonance with control of the loading direction by two counter-rotating excentric masses.A wide range of loading conditions can be applied with a frequency from 20 to 40 Hz. The test specimen, that can weigh up to 25 ton, is supported in the nodes of its natural wave-form, so that no dynamic forces are transmitted to the setup.The working principles of the test setup are illustrated based on test results of a 711 mm diameter x 25.4 mm wall thickness steel pipe, a welded X-node representative for a welding detail of an offshore jacket foundation structure and a large-scale HE-beam. Crack initiation is detected using acoustic emission while crack growth is monitored by local strain gauge measurements as well as the global stiffness reduction of the test specimen. Finally, the beach marking method is used to visualize crack fronts for post-mortem analysis.

Thermal Stress FE Analysis of Large-scale Gas Holder Under Sunshine Temperature Field

The temperature field and thermal stress of Man type gas holder is simulated by using the theory of sunshine temperature field based on ASHRAE clear-sky model and the finite element method. The distribution of surface temperature and thermal stress of gas holder under the given sunshine condition is obtained. The results show that the thermal stress caused by sunshine can be identified as one of the important factors for the failure of local cracked oil leakage which happens on the sunny side before on the shady side. Therefore, it is of great importance to consider the sunshine thermal load in the stress analysis, design and operation of large-scale steel structures such as the gas holder.

Fracture analysis and assessment: From materials to large-scale steel structures

Fracture analysis and assessment: From materials to large-scale steel structures

Detection of back-surface crack based on temperature gap measurement

For large-scale steel structures such as orthotropic steel decks in highway bridges, nondestructive inspection of deteriorations and fatigue damages are indispensable for securing their safety and for estimating their remaining strength. As conventional NDT techniques for steel bridges, visual testing, magnetic-particle testing and ultrasonic testing have been commonly employed. However, these techniques are time- and labor- consuming inspections, because special equipment is required for inspection, such as scaffolding or a truck mount aerial work platform. The present authors developed a new thermography NDT technique for crack detection, which is based on temperature gap appeared on the surface of structural members due to thermal insulation effect of the crack. The practicability of the developed technique to through crack was demonstrated by the field experiments for highway steel bridges in service. In this paper, the applicability of the inspection technique based on temperature gap measurement to back-surface crack detection is investigated by the laboratory testing. The testing was conducted for several specimens. A fatigue crack was introduced in a back surface of each specimen by 4 point bending fatigue test. This investigation has revealed that back surface fatigue crack can be detected by the proposed technique.

A basic study for application of laser peening to large-scale steel structure

Laser peening can introduce compressive residual stress to the surface and therefore is effective in enhancing fatigue strength. In this study, we conducted laser peening in air with a water film formed by a nozzle and examined whether the distribution of residual stress along the thickness was different from that achieved by laser peening in water in our previous studies. We also assessed the resultant residual stress and fatigue life when the pulse energy was reduced for developing a simple method to conduct laser peening on large structures. Compressive residual stress equivalent to that observed after laser peening in water was obtained in nozzle-type laser peening in terms of magnitude and depth. With the reduction of pulse energy, it was observed that the depth of the compressive residual stress tended to decrease significantly and the fatigue life also tended to reduce. The results indicate that the depth of the compressive residual stress has a considerable effect on the fatigue life of welded structures as well as the magnitude of the surface residual stress.

Damage-based optimization of large-scale steel structures

A damage-based seismic design procedure for steel frame structures is formulated as an optimization problem, in which minimization of the initial construction cost is treated as the objective of the problem. The performance constraint of the design procedure is to achieve repairable damage state for earthquake demands that are less severe than the design ground motions. The Park-Ang damage index is selected as the seismic damage measure for the quantification of structural damage. The charged system search (CSS) algorithm is employed as the optimization algorithm to search the optimum solutions. To improve the time efficiency of the solution algorithm, two simplifying strategies are adopted: first, SDOF idealization of multi-story building structures capable of estimating the actual seismic response in a very short time; second, fitness approximation decreasing the number of fitness function evaluations. The results from a numerical application of the proposed framework for designing a twelve-story 3D steel frame structure demonstrate its efficiency in solving the present optimization problem.

Design and experimental verification of an intelligent wall-climbing welding robot system

Purpose – This paper aims to present a new intelligent wall-climbing welding robot system for large-scale steel structure manufacture, which is composed of robot body, control system and welding system. Design/methodology/approach – The authors design the robot system according to application requirements, validate the design through simulation and experiments and use the robot in actual production. Findings – Experimental results show that the robot system satisfies the demands of automatic welding of large-scale ferromagnetic structure, which contributes much to on-site manufacturing of such structures. Practical implications – The robot can work with better quality and efficiency compared with manual welding and other semi-automatic welding devices, which can much improve large-scale steel structure manufacturing. Originality/value – The robot system is a novel solution for large-scale steel structures welding. There are three major advantages: the robot body with reliable adsorption ability, large payload capability and good mobility which meet the requirements of welding; the control system with good welding seam tracking accuracy and intelligent automatic welding ability; and friendly human – computer interface which makes the robot easy to use.

Thiourea-Assisted Phosphate Conversion Coating on Mild Steel and Characterizations by Cathodic Polarization and Linear Polarization

Using highly acidic phosphating solutions that dissolve rust, brush-on phosphating for large-scale steel structures can reduce the cost of rust removal, without the need of a post-treatment rinse. In very low pH medium, the presence of thiourea helps the formation of high-quality conversion films. A hydrogen sulfide acceleration mechanism is proposed, based on cathodic polarization data and previous studies. The formed films are amorphous and contain high water content, therefore a rather long post-treatment desiccation period is required and supported by analyzing the linear polarization resistance values in a desiccation model.