Unfavorable Load Research Articles

An intelligent method for temperature load of arch dams

Temperature load significantly affects the deformation and stress of arch dams. Traditional methods for determining temperature loads may not adapt to complex environments, such as high-altitude regions with large temperature variations. This study proposes an intelligent method for temperature load of arch dams. Based on the measured data from existing dams, a physics-informed convolutional neural network is developed, enabling direct application to newly designed dams. The intelligent method delivers annual temperature boundaries on the dam surface, aiding the finite element model in predicting deformation and stress during operational phases. Validation demonstrates accurate results for dam body temperature and deformation, aligning closely with measured data, while also pinpointing critical stress areas within the dam. This method advances the AI-assisted design by predicting temperature loads during dam operation, providing strong support for determining the most unfavorable loading without measured data and ensuring the safety of the structure.

Mechanical Basis of Lumbar Intervertebral Disk Degeneration

Abstract The etiology of degenerative disk disease (DDD) is multifactorial. Among the various factors, mechanical processes contributing to endplate or discal injuries have been discussed as the initiating events in the degenerative cascade. DDD encompasses the multitudinous changes undergone by the different structures of the spinal segment, namely intervertebral disk (IVD), facet joints, vertebral end plate (VEP), adjoining marrow (Modic changes), and vertebral body. It has been etiologically linked to a complex interplay of diverse mechanisms. Mechanically, two different mechanisms have been proposed for intervertebral disk degeneration (IVDD): endplate-driven, especially in upper lumbar levels, and annulus-driven degeneration. VEP is the weakest link of the lumbar spine, and fatigue damage can be inflicted upon them under physiological loads, leading to the initiation of DDD. Disk calcification has been put forth as another initiator of inflammation, stiffening, and abnormal stresses across the IVD. The initial mechanical disruption leads to secondary IVDD through unfavorable loading of the nucleus pulposus and annulus fibrosis. The final degenerative cascade is then propagated through a combination of biological, inflammatory, autoimmune, or metabolic pathways (impaired transport of metabolites or nutrients). Abnormal spinopelvic alignment, especially pelvic incidence, also significantly impacts the degenerative process. Hence, the etiology of DDD is multifactorial. Mechanical pathways, including VEP injuries, increased disk stiffness, and abnormal spinopelvic alignment, play a significant role in the initiation of IVDD.

A Study on the Impact of Low-Frequency Random Loading and Unloading on Silo Structures

To investigate the development of cracks in the walls of reinforced concrete silos under feeding–discharge cycle loading, their causes, and their fatigue life during dynamic loading, a study was conducted using a combination of in situ monitoring and numerical simulation analysis. The following conclusions were drawn: during the loading and unloading process of the silo, the time of occurrence of the minimum pressure points follows a 4:3 ratio; extreme points are approximately 15 min apart; the minimum pressure increases during material addition and decreases during material subtraction; and the load in the non-discharge area is 1.43 times that of the load in the discharge area. That is, at the same elevation, the load borne by the silo wall is uneven, with fluctuations and rotational effects occurring. Under such uneven load conditions, the silo wall experiences significant bending and torsional moments, causing excessive local tension and leading to cracking. Our analysis showed that the most unfavorable load condition occurs when discharge ports 5 and 7 are operating simultaneously, which causes the maximum tensile damage to the silo wall. For the first time, a fatigue life prediction model for reinforced concrete silos was proposed, and the accuracy of this prediction method was verified based on actual conditions.

Load Identification in Steel Structural Systems Using Machine Learning Elements: Uniform Length Loads and Point Forces

Actual load identification is a most important task solved in the course of (1) engineering inspections of steel structures, (2) the design of systems rising or restoring the bearing capacity of damaged structural frames, and (3) structural health monitoring. Actual load values are used to determine the stress–strain state (SSS) of a structure and accomplish various engineering objectives. Load identification can involve some uncertainty and require soft computing techniques. Towards this end, the article presents an integrated method combining basic provisions of structural mechanics, machine learning, and artificial neural networks. This method involves decomposing structures into primitives, using machine learning data to make projections, and assembling structures to make final projections for steel frame structures subjected to elastic strain. Final projections serve to identify parameters of point forces and loads distributed along the length of rods. The process of identification means checking the difference between (1) weight coefficient matrices applied to unit loads and (2) actual loads standardized using maximum load values. Cases of neural network training and parameters identification are provided for simple beams. The aim of this research is to enhance the reliability and durability of steel structures by predicting consequences of unfavorable load, including emergency impacts. The novelty of this study lies in the co-use of artificial intelligence elements and structural mechanics methods to predict load parameters using actual displacement curves of structures. This novel approach will enable engineering inspection teams to predict unfavorable load peaks, prevent emergency situations, and identify actual causes of emergencies triggered by excessive loading.

Multiaxial Fatigue Damage Analysis of Steel–Concrete Composite Beam Based on the Smith–Watson–Topper Parameter

The fatigue performance of steel–concrete composite beams is crucial for ensuring structural safety. To account for the member’s multiaxial stress state, this study employed the critical surface method, using fatigue damage parameters as an evaluation index for assessing fatigue performance. Static and fatigue performance tests on steel–concrete beams were conducted to identify failure characteristics, which informed the development of a finite element model that incorporates concrete damage. Using the SWT model, the most unfavorable loading parameters were determined by analyzing critical paths on the test beams, providing a basis for predicting how initial defects impact fatigue performance. The impact of initial defects on the fatigue performance of the composite beam is assessed using this criterion. The results indicate that the discrepancy between the actual and predicted load capacities of the test beam is within 5%, and cyclic loading significantly affects the test beam’s mechanical properties, resulting in a 27% reduction in load capacity and a 48% increase in deflection after 2 million cycles. Finite element modeling reveals that components experience multiaxial stress, with test beam mechanical property changes aligning with predicted fatigue damage parameters, confirming the reliability of using these parameters as a criterion. As the strength of the composite beams diminished due to pore defects, the fatigue damage parameter escalated, increasing the likelihood of crack formation. However, once the concrete’s strength fell to a level where the pegs were insufficiently constrained, the structural damage pattern shifted, and the fatigue damage parameter subsequently decreased.

Characteristics and analysis of static strain response on typical asphalt pavement using fiber Bragg grating sensing technology

To study the real internal strain response of asphalt pavement and provide crucial data for optimizing pavement design. By burying the fiber grating sensors on site, the strain tests of four asphalt pavement structures under different working conditions were carried out, and the results showed that the static strain time curve is viscoelastic and conforms well to the Bugers model, and the fitting coefficient of determination is 0.98. The strain response of the asphalt surface courses of the four pavement structures under static load shows a double hump variation with the transverse position, with peaks occurring directly beneath the wheel load center. The transverse strain fluctuated between tension and compression, mirroring changes in the lateral position. While longitudinal strains, always tensile, were symmetrically aligned with the centerline of the longitudinal sensors, this pattern differed notably from that of the transverse sensors. In the base layers, the strain profile typically presented a single peak, located at the wheel gap, underscoring a critical area of stress concentration. Numerically, the peak strain of asphalt surface course is larger than that of base course. The most unfavorable loading position of the base course occurs at the wheel gap of the lower base course. The most adverse loading position of the surface course appears at the wheel load at the bottom of the upper or middle course. The research results can provide data support for improving the design method of asphalt pavement.

Assessment of maximum and minimum hanger forces in a triple-cable suspension bridge under live load: Analytical algorithm with manta ray foraging optimization

Triple-cable suspension bridges (TCSBs) are widely used in sea-crossing, island-linking projects with extra-long spans and ultra-wide decks. Their safe operation requires sufficient resistance of all bridge components (towers, cables, girders, and hangers) to static/dead and cyclic/live loads. Therefore, reliable assessment of maximum and minimum axial forces acting on each hanger is topical. This study proposes an analytical algorithm for assessing the internal forces and deformations of a TCSB. Specific steps and formulae for solving the coefficients are described by taking the estimation of girder response under random eccentric line loading as an example. Parameters of the suspension bridge under dead load are treated as known quantities. Actual engineering scenarios, including girder displacements along the bridge, are analyzed and discussed in detail. Basic unknown quantities are determined via governing equations under conditions of elevation differences’ closure and conservation of main cables’ unstressed lengths, yielding direct solutions for deformations of the main cables, girder, towers, and hangers. The proposed analytical model’s feasibility is verified via the finite element method. Optimal solutions to the above equations are derived by the manta ray foraging optimization (MRFO) algorithm to find the most unfavorable load distributions for all vehicle lanes of the bridge and the maximum and minimum axial forces of random hangers. Finally, the proposed method is successfully applied to a TCSB with a 1600 m main span under two operating conditions. The most unfavorable load distributions and the maximum and minimum axial forces of hangers at the mid-span and at the quarter-span point are estimated. The calculation results are compared against those obtained by the influence surface method, showing their good correlation and superiority of the proposed method in computation workload.

Life-cycle seismic performance of Q690 steel columns with H-section under various bi-directional cyclic loading paths

The ageing effect in the life-cycle assessment should be considered for the high-strength steel structures constructed in corrosive environments and high-seismicity zones. Additionally, the structures can suffer multi-dimensional seismic excitations because of the spatial effect of ground motions. Therefore, this study aims to investigate the impact of different loading protocols on the mechanical properties of Q690 steel columns with H-section during the whole life-cycle. Firstly, numerical methods considering time-varying corrosion process are used to simulate the ageing steel columns. After that, the nonlinear hysteretic behaviors of the ageing steel columns under different loading protocols are investigated. The factor of resistance degradation (the degree of degradation of ultimate resistance) is employed to quantify the effect of loading protocols on ageing steel columns. Finally, the biaxial ultimate interaction curve considering the ageing effect and a practical design process are proposed. The findings demonstrate that the steel columns exhibit different mechanical properties under various loading protocols, and the coupling direction of bi-directional displacement loads influences the degree of degradation of ultimate resistance. As service time increases, the factor of resistance degradation of steel columns gradually reduces by up to 40%. The proposed biaxial ultimate interaction curve has acceptable accuracy. These findings emphasize the importance of employing the unfavorable loading protocols in conducting the seismic design of the steel columns in different life-cycle stages.

Numerical Calculation of Static Strength Performance of Planar Gate Structures

As an important part of the ecological environment, rivers provide an important guarantee for the production and life in China. At present, domestic and foreign for the construction of the gate has been gradually shaped, hydraulic steel gate gradually developed as a hydroelectric power station high head, flood discharge flow of large gate type, the smooth opening and closing of the gate is related to the entire water conservancy hub and downstream of the safety of the residents' lives. For the safety of plane gate, this paper adopts Ansys software to establish a finite element model of plane gate, and calculates the most dangerous point stress of plane gate by considering its most unfavourable loading condition. At the same time, the service life of the allowable stress reduction was considered. The analysis results show that the planar gate meets the strength safety. The main beam is simplified into slender beam and thin-walled deep beam, and the calculation formula of slender beam in the mechanics of materials and thin-walled deep beam in the literature is used to calculate the positive bending stress in the mid-span cross-section of the main beam of the gate, and a comparative analysis is carried out with the results of Ansys, which shows that the positive bending stress in the mid-span cross-section of the main beam obtained by simplifying the main beam into a thin-walled deep beam is more close to the results of Ansys calculation. The results of this paper provide an important reference for the structural strength analysis of planar gates.

Rock anchor hanger effect on single-tower earth-anchored suspension bridge mechanical performance: An analytical model and multi-objective golden eagle optimization

The application of a composite saddle in single-tower earth-anchored suspension bridges (STEASBs) replaces the tower on the steep slope side, which is a cost-effective solution that improves bridge safety and provides environmental protection for the steep bank slope of the valley. However, this novel bridge design needs an appropriate model to evaluate the effect of rock anchor hangers on the structure in the non-girder area and adjust their parameters to optimize the mechanical response of the whole bridge structure. This study proposes an approach to quickly evaluate the most unfavorable load cases of the STEASB and further optimizes the structural parameters of rock anchor hangers to enhance structural safety. An analytical model for the STEASBs under the live load is proposed and verified by the finite element model (FEM), with the maximum relative error not exceeding 7.37%. Combined with the golden eagle optimizer (GEO), the most unfavorable load cases of the corresponding design indices are yielded. The Pareto optimal solutions for the spacing, cross-sectional area, and initial tension of the vertical rock anchor hangers are obtained through multi-objective optimization to improve the mechanical behavior of STEASBs. In addition, it is clarified that the main function of rock anchor hangers is to reduce the peak value of the stress amplitude of the hangers and girder-end rotation, providing a theoretical basis for the STEASB design.

Comparative study of CAD/CAM reconstruction and miniplates for patient-specific fixation in LCL-type mandibular reconstruction.

Miniplates offer superior clinical handling and facilitate postoperative removal after mandibular reconstruction but unfavorable load distribution under high stress has been shown. This study aimed to compare the clinical outcome of patient-specific 3D-printed (PS-3D) titanium miniplate with reconstruction plate fixation in three-segmental LCL-type reconstructions for the first time. Patients undergoing three-segmental LCL-type mandibular reconstruction after malignant tumor resection between April 2017 and July 2023 were analyzed in a retrospective single-center study. Inclusion criteria were primary reconstruction using a fibula free flap and PS-3D titanium mini- or reconstruction plate fixation. Complication rates were recorded and analyzed within 6 months after surgery using the N - 1 Chi2- and unequal variance t-test. 38 patients (10 females, 28 males; mean age 61.4 ± 7.6 years) met the inclusion criteria. In 14 patients (36.8%) miniplates were used in the anterior region. Rates of fixation failure, plate exposure, incomplete osseous union, wound infection, soft tissue, and overall complications did not differ significantly between the two plate systems. Complication rates did not differ significantly between PS-3D mini- and reconstruction plates in three-segmental LCL-type mandibular reconstructions. Given their advantages in clinical handling and postoperative removal, PS-3D miniplates can be a viable alternative also in larger mandibular reconstructions.

Experimental and numerical study of road-bridge link slabs in fully jointless bridges using rubberized engineered cementitious composites (R-ECC)

This paper presents a different way using crumb rubber and fine sand totally replaced for silica sand within ECC mixtures to make rubberized engineered cementitious composites (R-ECC) to solve the issues of high construction cost of the road-bridge link slab for fully jointless bridges (FJBs). The crumb rubber with a size of 80 CR was replaced with fine sand from a volume rate of 5–20% in multiples of 5% to prepare the R-ECC material. Five different R-ECC mixtures (CR0-CR20) with different mix designs were prepared and tested, then an optimum mix proportion for the R-ECC mixtures was found. An R-ECC road-bridge link slab made of the optimum mix proportion which replace with fine sand in a volume rate of 15% was constructed, and its absorptive deformation capacity, tensile performance, and crack distribution under the most unfavourable load (temperature drop load) were studied. It is found that the R-ECC slab has good absorptive deformation capacity, crack control capacity and better internal force distribution. Therefore, R-ECC mixtures can be utilized for road-bridge link slab construction. Then, a sensitivity finite element comparative analysis was carried out considering the content of crumb rubbers, the friction coefficient and the slab length. It is found that the design length has a greater influence on the tensile performance of the R-ECC slab than other factors. Finally, a preliminary design theory of road-bridge link slab for FJBs has been established.

Strength analysis of welded joints in support structures of heavy machinery subjected to changeable loading conditions

The durability of bearing units of large machines depends mainly on the condition of their welded joints. With this in mind, we developed numerical models of the analyzed bearing units, for which we performed FEM simulations of the stresses in welded joints in several basic load cases. In each of the respective variants the technical condition of the bearing nodes was different and it corresponded to the severity of the degradation processes. Different positions of the superstructure in relation to the undercarriage were also taken into account. The simulations used the hot-spot method dedicated to FEM analyses of complex welded structures. We discovered that the loads have a significant influence on the values and distribution of von Mises principal stresses and their axial components. Based on the carried out analyses, we identified the most unfavorable load cases that generate the highest stresses in the welded joints of the assessed nodes. We also demonstrated that the applied method effectively assesses the stresses of welded joints subjected to variable working loads.

Dynamic response and blast resistance mechanism of polyurea coating on RC slab during contact explosions

Polyurea (PU) coated reinforced concrete (RC) has been widely studied in structural strengthening under contact explosion, however, experimental investigations on dynamic response and failure mechanism of the coating during explosion remain scarce. In this paper, four contact explosion experiments are conducted on uncoated and rear side coated RC slabs. Dynamic strains and dynamic deformation of the coating are obtained by large-range strain gauges and a proposed measurement method based on a high-speed camera. Dynamic response characteristics of the coating are discussed and the blast resistance mechanism is further analyzed. Additionally, the effect of coating rebounding on the RC substrate and the effect of explosive placement on the coating are discussed. The results show that PU coating dissipates the blast energy through elastic deformation, plastic deformation, rupture and debonding. Glass transition at high strain rate may cause the rupture of the coating, and coating thickening significantly reduces the tensile strain rate under the same contact explosion conditions. With the development of breach and spalling of the RC substrate, PU coating on the rear side can be divided into four zones, and the blast resistance mechanism of the coating varies in different zones. Additionally, the elastic potential energy release of the coating may produce a secondary impact on the RC substrate. Coatings are more severely damaged when contact explosives are placed in locations that avoid rebars and should be considered as the most unfavorable load for the retrofitting of RC structures.

Mechanical Performance Prediction Model of Steel Bridge Deck Pavement System Based on XGBoost

Steel bridges are widely used in bridge engineering. In the structural design of steel bridge deck pavement systems, engineers focus on obtaining mechanical properties by calculating design parameters and are keen to establish a quick and accurate solution method. Because of the complex knowledge system involved in the numerical calculation method, it is difficult for the general engineering designer to master it. Researchers have started using artificial intelligence algorithms to solve problems in civil engineering. This study developed an XGBoost-based mechanical performance prediction model for steel bridge deck pavement systems. First, numerical simulation tests are conducted at unfavorable load locations using a finite element model to establish a dataset. Then, an XGBoost model is built using this dataset, and its parameters are optimized and compared with traditional machine learning models. Finally, an explanatory analysis of the model is performed using SHAP, an interpretable machine learning framework. The results indicate that the developed XGBoost model accurately predicts the mechanical properties of steel bridge deck pavement systems.

Optimizing the marketing of flexibility for a virtual battery in day-ahead and balancing markets: A rolling horizon case study

Industrial electricity consumers with flexible demand can profit from adjusting their load to short-term prices or by providing balancing services to the grid. Markets which support this kind of short-term position adjustment are the day-ahead market and balancing markets. We propose a formulation for a combined optimization model that computes an optimal distribution of flexibility between the balancing and day-ahead markets. The optimal solution also includes the specific bids for the day-ahead and balancing markets. Besides the expected profits of each market and their different rules for bidding, our model also takes their different roles in a continuous marketing of flexibility into account. To prevent overrating short-term profits we introduce a variable penalty term that adds a cost to unfavorable load schedules. We evaluate the optimization model in a rolling horizon case study based on the setting of a virtual battery at TRIMET Aluminum SE, which is derived from a flexible aluminum electrolysis process. For such a battery we compute a daily optimal split of flexibility and trading decisions based on data in the period 04/2021–03/2022. We show that the optimal split is more profitable than using only one market or a fixed split between the markets.

Flexural performances of steel–concrete composite section of self-anchored suspension bridge: Experimental and theoretical research

This paper aims to clarify the flexural performance and the cracking load, the ultimate bearing capacity calculation theories of the steel–concrete composite section of the self-anchored suspension bridge. A refined local finite-element (FE) model of the steel–concrete composite section was built to evaluate the mechanical performance of key parts under three unfavourable load conditions. A test model of the steel–concrete composite section with a length × width × height of 7 m × 1.833 m × 1.2 m was fabricated according to the scale of 1: 3, and a four-point negative bending test was carried out. The test results show that the test model is in the elastic stage, and the residual displacement ratio is 0.7 % under the design load condition. Under the overload condition (2.3 times the design load), the experimental model is in the elastic–plastic stage, and the residual displacement ratio is 19 %. At the same time, the stress of each component still meets the requirements. Under the two conditions, the deformation angle of the composite section is small, and the stiffness transition is stable. The relative slip between the top steel plate and the concrete in the composite section is small (no more than 0.25 mm). The stress of the top steel plate and bottom steel plate of the composite section gradually decreases during the transfer from the steel stiffening beam to the concrete side. The bearing plate is the main bearer of the force transmission of the steel–concrete composite section, accounting for about 51.24 %, while the top steel plate, bottom steel plate and shear connectors share the remaining load. The steel–concrete composite section of the test model has reasonable force, smooth force transmission and good deformation coordination performance. In addition, the calculation methods of cracking load and ultimate bearing capacity of the prestressed steel–concrete composite section were proposed. The theoretically calculated value of the ultimate bearing capacity of the steel–concrete composite section is in good agreement with the FEA value, and the difference does not exceed 10 %.

Hydrodynamic Response Analysis of a Fixed Aquaculture Platform with a Horizontal Cylindrical Cage in Combined Waves and Currents

Biofouling on net cages adversely affects structural safety and the growth of aquacultural fish. Therefore, a novel fixed aquaculture platform with a rotatable horizontal cylindrical cage is proposed in this study, which is convenient for the cleaning of biofouling. Based on ANSYS, the numerical model of the fixed aquaculture platform was established. The response results of the strain, acceleration, and displacement of the structure under the combined action of waves and currents at three typical attack angles were calculated. The effects of water depth and cage rotation on the hydrodynamic response of the structure are discussed. The results show that the strain, acceleration, and displacement of the cage increase with the increase in wave height; however, the change with the wave period is not obvious. The direction perpendicular to the long axis of the cage is the most unfavorable load direction. The acceleration of each position increases with the increase in water depth; however, the strain response has the opposite trend. When the rotation constraint of the horizontal cylindrical cage is released, the acceleration of the cage is larger than that when the cage is fixed. The rotation of the cage has a tiny effect on the structural strain and load acting on the structure.

Stability Analysis of a Simple-Supported Bridge with Steel Truss Structure Based on Abaqus Software

With the continuous development and improvement of modern bridge construction technology, the bridge based on steel structure materials has gradually become the mainstream. It is not difficult to find that steel structure has good comprehensive performance and significant advantages compared with other materials, so it can be widely used. In order to explore the stability of steel structure in different states, this paper selected steel truss bridge as the research object. At the same time, the structure of simply supported bridge is selected as the main analysis structure, by using Abaqus modeling software to establish a finite element model and to analyze the overall stability under the most unfavorable load. The analysis and integration of the finite element simulation results show that the stress of the truss under the most adverse load is concentrated in the upper chord. According to the horizontal displacement nebulae, the horizontal displacement of the lower chord is the most serious, and the node is also affected. This experiment can provide a certain reference for the actual design and construction of simply supported bridge with steel structure as the main, and can make a certain deal with the load situation mentioned in this paper.

Three-dimensional finite element analysis of stress distribution on short implants with different bone conditions and osseointegration rates

ObjectiveThis experiment aimed to investigate the effects of bone conditions and osseointegration rates on the stress distribution of short implants using finite element analysis and also to provide some reference for the application of short implants from a biomechanical prospect.Materials and methodsAnisotropic jaw bone models with three bone conditions and 4.1 × 6 mm implant models were created, and four osseointegration rates were simulated. Stress and strain for the implants and jaws were calculated during vertical or oblique loading.ResultsThe cortical bone area around the implant neck was most stressed. The maximum von Mises stress in cortical bone increased with bone deterioration and osseointegration rate, with maximum values of 144.32 MPa and 203.94 MPa for vertical and inclined loading, respectively. The osseointegration rate had the greatest effect on the maximum principal stress in cortical bone of type III bone, with its value increasing by 63.8% at a 100% osseointegration rate versus a 25% osseointegration rate. The maximum and minimum principal stresses under inclined load are 1.3 ~ 1.7 and 1.4 ~ 1.8 times, respectively, those under vertical load. The stress on the jaw bone did not exceed the threshold when the osseointegration rate was ≥ 50% for Type II and 100% for Type III. High strain zones are found in cancellous bone, and the maximum strain increases as the bone condition deteriorate and the rate of osseointegration decreases.ConclusionsThe maximum stress in the jaw bone increases as the bone condition deteriorates and the osseointegration rate increases. Increased osseointegration rate reduces cancellous bone strain and improves implant stability without exceeding the yield strength of the cortical bone. When the bone condition is good, and the osseointegration ratio is relatively high, 6 mm short implants can be used. In clinical practice, incline loading is an unfavorable loading condition, and axial loading should be used as much as possible.