Bearing Capacity Of Structure Research Articles

Prediction Model for Fracture Toughness of Waterborne Polyurethane Modified Concrete at Different Temperatures

In certain extreme environments, the bearing capacity of concrete structures diminishes significantly as temperatures soar, simultaneously exposing them to a heightened risk of brittle cracking. The paper aims to elucidate the fracture toughness of waterborne polyurethane modified concrete (WPMC) at different temperatures. Furthermore, a predictive model for the fracture toughness of WPMC, which incorporates both temperature and the waterborne polyurethane (WP) content, is proposed. The flexural strength and fracture toughness of WPMC were tested separately at 20℃, 40℃, 60℃, and 80℃. Utilizing digital image correlation (DIC) technology, the bottom longitudinal strain of WPMC under flexural loading was analyzed. The impact of temperature and WP content on the energy absorption capacity and deformation behavior of WPMC exposed to extreme environment was also investigated. By introducing the microstructural parameters C and Cw to characterize the elastic and plastic deformations of WPMC before and after cracking, a fitting model between the microstructural parameters and temperature, WP content was established. This model enables the prediction of the fracture toughness KIC of WPMC at different temperatures by measuring Fmax.

Assessment of the quality of full depth reclamation (FDR) using a dynamic cone penetrometer (DCP): a case study

The full-depth reclamation with no stabilization (FDR-NS) is widely used as a pavement rehabilitation technique. It is important to evaluate the on-site characteristics of FDR-NS materials to avoid short-term underperformance. The need for performance-based testing could then be supported by in-situ and non-destructive testing, such as dynamic cone penetrometer (DCP). DCP allows to estimate the bearing capacity of the pavement structure and to verify its homogeneity according to the depth. The objective of this research is to evaluate the applicability of using DCP to assess the quality of FDR-NS. Overall, DCP results showed a good reliability, allows to measure the effective depth of reclamation and to observe a significant reduction (average of 75 %), in terms of DCP values, between before and after the reclamation process. Thus, the potential of using DCP for FDR-NS rehabilitation was confirmed. The results from this research provide a rational basis for establishing specifications.

Wireless vibration testing and bridge deck damage identification using underneath maintenance walkway

Bridges will inevitably experience structural damage during long-term operation, which will decrease their structural load bearing capacity and durability. The vibration characteristics of bridge structures can be used as evaluation indicators for accurately diagnosing their deterioration. This study aimed at developing a vibration testing method for identifying bridge deck damage that does not affect traffic and is easy to implement. The vibration tests on the in-service bridge revealed it was mainly subjected to vertical vibrations, with the accelerations in the vertical direction about twice those in the horizontal direction. Based on fast Fourier transform analysis, the dominant vertical vibration frequencies were 2.34 Hz, 4.10 Hz, 10.30 Hz, 14.45 Hz and 18.75 Hz. A series of 0.1–0.3 Hz bandpass filters were used with those frequencies at the centers for modal analysis. The experimental results were then compared to the finite element analysis results. This study proposed a vibration-based damage identification method based on the differences between the bridge deck and both main steel girders. The study confirmed the convenience and effectiveness of using underneath maintenance walkways for wireless vibration testing.

Research on the failure mechanisms and preventive actions of tunnels under butterfly load in loess regions

The results of surrounding rock pressure measurements from numerous loess tunnels exhibit a butterfly distribution pattern, subsequently referred to as ’butterfly load’. This pattern significantly deviates from the load distribution and magnitude—referred to as ’specification load’—calculated by current Chinese tunnel design specifications. By means of model experimental and numerical simulation, the mechanical behavior, failure cause, failure mechanism and preventive actions of tunnel structure under different load distribution are studied. The experimental results indicate that the ultimate bearing capacity of the tunnel structure under the butterfly load is significantly lower than that under the specification load, with the ultimate bearing capacity decreasing as load unevenness increases. The butterfly load increases the unevenness of the axial force distribution throughout the annular structure and also causes the structure to produce reverse moments in the vault and arch shoulder. Similarly, the morphological characteristics of the cracks show that the butterfly load most significantly influences the tunnel vault and arch shoulder. Under the influence of the butterfly load, the lining structure is prone to developing cracks at the arch shoulder and arch foot positions, with tensile cracks located at the vault position. Aiming at the failure mechanism of tunnel structure under butterfly load, it is suggested to implement advanced small conduit grouting at the tunnel arch to suppress the dislocation of the formation and to lay root piles at the arch foot to improve the bearing capacity of the tunnel bottom. The prevention effect of this technology in different loess regions is sandy loess > general loess > clay loess.

Mechanical‐performance deterioration of RC segment of shield tunnel under high corrosion degree and the transformation of eccentric‐failure mode

AbstractReinforcement corrosion in shield tunnel segments has an important impact on the structure's bearing capacity and failure mode. Generally, a shield tunnel structure is under small eccentric compression, but if the reinforcement corrosion develops sufficiently, then a transition occurs from small to large eccentric load state, thereby lowering the structural bearing capacity and endangering the safety of tunnel operation. In the study reported here, based on the compressive bending load characteristics of the shield lining structure, corrosion test columns with small eccentric loading were designed to simulate the actual force state of the tunnel lining, and the whole evolution process of their mid‐span strain, ultimate bearing capacity, and cracks under different corrosion degrees was analyzed. With increasing corrosion, the bearing capacity, concrete strain, and depth of the compressive zone of a test column decrease more and more rapidly, and at the maximum corrosion degree of 68.32%, the maximum reduction of bearing capacity is 53.23%. The tests show that the failure mode of a test column with high corrosion degree (≥46.25%) is transformed from small to large eccentric failure. Based on theoretical analysis of the normal section bearing capacity of reinforced concrete flexural members, a theoretical method is proposed for calculating the critical corrosion degree for the tunnel lining structure to transform from small to large eccentric failure. The theoretical calculation method is verified against finite‐element calculations, and the present research results offer theoretical support for the durability design and safety evaluation of shield tunnel lining structures.

Study on the Effect of Hot and Humid Environmental Factors on the Mechanical Properties of Asphalt Concrete.

To investigate the effect of hot and humid environmental factors on the mechanical properties of asphalt mixtures research, in this paper, the dynamic modulus of asphalt mixtures under the effects of aging, dry-wet cycling, and coupled effects of aging and dry-wet cycling were measured by the simple performance tester (SPT) system, and the dynamic modulus principal curves were fitted based on the sigmoidal function. The results show that under the aging effect, the dynamic modulus of asphalt mixture increases with the aging degree; the dynamic modulus of short-term aged, medium-term aged, long-term aged, and ultra-long-term aged asphalt mixtures increased by 9.3%, 26.4%, 44.8%, and 57%, respectively, compared to unaged asphalt mixtures at 20 °C and 10 Hz; the high-temperature stability performance is enhanced, and the low temperature cracking resistance performance is enhanced; under the dry-wet cycle, the aging effect of asphalt water is more obvious in the early stage, and dynamic modulus of resilience of the mixture is slightly increased. In the long-term wet-dry cycle process, water on the asphalt and aggregate erosion increased, the structural bearing capacity attenuation, and the dynamic modulus of rebound greatly reduced at 20 °C and 10 Hz. For example, the dynamic modulus of asphalt mixtures with seven wet and dry cycles increased by 3% compared to asphalt mixtures without wet and dry cycles, and the dynamic modulus of asphalt mixtures with 14 cycles of wet and dry cycles and 21 cycles of wet and dry cycles decreased by 10.8% and 16.5%, respectively, compared to asphalt mixtures without wet and dry cycles. The main curve as a whole shifted downward; the high-temperature performance decreased significantly; in the aging wet-dry cycle coupling, the aging asphalt mixture is more susceptible to water erosion, and the first wet-dry cycle after the mix by the degree of water erosion is relatively small, along with the dynamic modulus of rebound. The dynamic modulus of resilience is relatively larger, and the high-temperature performance is relatively better, while the low-temperature performance is worse.

Research into multi-directional high stability techniques in the same plane for satellite static testing

In order to ensure the structural strength reliability of spacecraft base plate during launch and operation, it is necessary to perform the structural strength test of load synchronous loading on the base plate in the same plane to evaluate its structural bearing capacity under certain axial and shear loads. In order to meet the test requirements and simulate the real stress condition of the base plate, a reliable implementation scheme is proposed in this paper. Multi-directional uniform loading of a satellite base plate is completed by using the same plane multi-directional high stability test technology. The mechanical test of a satellite using this technology shows that the test strain is consistent with the theoretical simulation deformation. This technology effectively solves the problem of uniform loading in the same plane of the satellite base plate in mechanical testing.

Optimization design of composite cap-shape pillar structure based on gaussian process of combined kernel function

Abstract To quickly realize the optimal design of the cap-shaped structure, an optimization design method of composite cap-shaped pillar structure based on combined kernel function Gaussian process was proposed. First, the shortcomings of two kernel functions representing different linear characteristics of data in model construction were analyzed, on which a new combined kernel function was constructed. Based on the finite element numerical simulation results, a database with the web thickness, web height, fiber volume, and ultimate bearing capacity of the cap-shaped structure was constructed. Then, a Gaussian process model based on the combined kernel function was established and the model parameters were trained by the maximum likelihood method. Finally, taking the ultimate bearing capacity per unit volume as the optimization objective, the artificial fish swarm algorithm was used to quickly obtain the structure design parameters under the optimal objective function, and the simulation results were compared with the initial design parameters. The results showed that the method proposed in this paper can optimize the structure performance, improve the design efficiency, and meet the engineering design requirements.

Crack arrest characteristics and dynamic fracture parameters of moving cracks encountering double holes under impact loads

Brittle materials such as rock or concrete contain a large number of micro-cracks, voids, and other defects. Under external impacting loads, the interaction between fissures and holes affects the bearing capacity and stability of Engineering structures. To study the interaction mechanism between moving cracks and circular holes, A large-size semi-circular notched with a fissure and double circular hole (SNFDH) specimen was suggested in this research, and the dynamic fracture tests were carried out on the SNFDH specimens with different double circular hole spacing (35mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, and 70 mm) using a drop hammer impact test device. Crack propagation gauges were employed to track the time and velocity at which the crack propagated along its trajectory. Dynamic Drucker-Prager yield criterion and the cumulative damage failure criterion were used in the numerical simulation of SNFDH concrete materials. The program AUTODYN was employed to simulate the crack growth characteristics when a crack encounters the double hole. The program ABAQUS was applied to calculate the dynamic fracture parameter of cracks. The test results manifest that the crack propagating trajectory has three different characteristics according to the double hole spacing; the double circular hole has an arresting function for a moving crack; the size of the double hole spacing has a significant effect on the crack propagating velocity, crack propagating length, dynamic stress intensity factor and dynamic energy release rate; the configuration of the SNFDH specimen can be used to investigate the crack arrest mechanism when moving crack encountering double holes.

Study on the bending mechanical properties of composite tube and metal joint bonding structure

Abstract The study of the mechanical properties of composite adhesively bonded joints is a very important issue, which directly affects the safety and reliability of the structure. This article studies the bending performance of carbon fiber composite tubes and metal joint bonding structures, as well as obtains the structural bearing capacity, influencing factors, and structural failure modes. Through mechanical analysis and static bending load tests, it is shown that the failure model of composite tube adhesively bonded metal joints under bending load is manifested as the first layer peeling or interlayer failure of the composite material in the bonding area between the tube and the joint, leading to local crushing at the end of the tube. There is no gap between the tube and the joint, which has little effect on the bending bearing capacity. The thickness gradient treatment at the end of the joint does not help improve the bending bearing capacity. The adhesive layer is at a 90 ° angle, which makes it easy for the first layer to peel off; it should be avoided. Other angle layers have little impact on load-bearing capacity. The longer the bonding length is, the stronger the bending capacity is. The adhesive J133 or 420 has a similar load-bearing. Wrapping a carbon fiber unidirectional layer around the ends of tubes and joints is helpful in improving their bending load-bearing capacity.

Buckling-restrained behavior of woven steel strip shear walls: Experiment and numerical simulation

A novel woven Buckling-Restrained Steel Strip Shear Wall (WBR-SSSW) is proposed for low and medium-rise buildings in this study. The proposed shear wall, comprising inclined arrangements of steel strips with varying dimensions, is categorized into compression and tension steel strips under horizontal loads. By weaving the steel strips, the out-of-plane buckling deformation of the compression strips is significantly alleviated. Cyclic tests were carried out on two 1/3-scaled single-story single-span SSSW specimens to investigate the seismic behavior of woven and non-woven SSSW. Finite element models of two types of SSSW were established and validated by test results. The results showed that the WBR-SSSW exhibited a distinct stress transfer path and stable bearing capacity, with the tension steel strip bearing the majority of the shear load. Compared to specimen SSSW, the WBR-SSSW reduced out-of-plane displacement by over 35 % at each loading level. Parametric analysis of the thickness, number, and width-to-spacing ratios of the steel strips was conducted to optimize the woven-net size. Additionally, a simplified theoretical model for WBR-SSSW was developed, showing good accuracy compared to finite element results, which can be used to estimate the structural shear bearing capacity.

Hybrid Evaluation Method of Bridge Bearing Capacity

This study proposes a new method to assess the bearing capacity of similar bridges while avoiding the disadvantages of costly static loading tests. First, we present a detailed evaluation of the bearing capacity for a repaired pre-stressed concrete continuous-beam bridge following a ship collision. We have developed a finite element model, modified it, and combined with two other methods to evaluate its bearing capacity. The first method proposed is the bridge design code-based method, where the bearing capacity is assessed using specified design parameters. The second is the field test-based method, where the bearing capacity is evaluated using field tests combined with structural appearance observation. Considering the relative merits of these two methods, a new and improved method for bearing capacity evaluation is proposed and implemented by combining the design code, finite element model, and field loading tests. The innovation and contribution of this paper lie in obtaining modal parameters through a convenient dynamic load test to predict the static behaviour of the bridge structure based on the modified finite element model. Based on the dynamic test results, the static behaviour of the bridge, predicted by the modified finite element analysis, and the appearance test data of the bridge structure, the bearing capacity of the bridge structure is evaluated.

Hydrodynamic Characteristics of Preloading Spiral Case and Concrete in Turbine Mode with Emphasis on Preloading Clearance

A pump-turbine may generate high-amplitude hydraulic excitations during operation, wherein the flow-induced response of the spiral case and concrete is a key factor affecting the stable and safe operation of the unit. The preloading spiral case can enhance the combined bearing capacity of the entire structure, yet there is still limited research on the impact of the preloading pressure on the hydrodynamic response. In this study, the pressure fluctuation characteristics and dynamic behaviors of preloading a steel spiral case and concrete under different preloading pressures at rated operating conditions are analyzed based on fluid–structure interaction theory and contact model. The results show that the dominant frequency of pressure fluctuations in the spiral case is 15 fn, which is influenced by the rotor–stator interaction with a runner rotation of short and long blades. Under preloading pressures of 0.5, 0.7, and 1 times the maximum static head, higher preloading pressures reduce the contact regions, leading to uneven deformation and stress distributions with a near-positive linear correlation. The maximum deformation of the PSSC can reach 2.6 mm, and the stress is within the allowable range. The preloading pressure has little effect on the dominant frequency of the dynamic behaviors in the spiral case (15 fn), but both the maximum and amplitudes of deformation and stress increase with higher preloading pressure. The high-amplitude regions of deformation and stress along the axial direction are located near the nose vane, with maximum values of 0.003 mm and 0.082 MPa, respectively. The contact of concrete is at risk of stress concentrations and cracking under high preloading pressure. The results can provide references for optimizing the structural design and the selection of preloading pressure, which improves operation reliability.

Individual-portal support with a pre-tensioned canopy for a coal mine roadway junction

Abstract This paper presents an alternative model of individual-portal support structure with a pre-tensioned canopy for coal mine roadway junctions in the geological and mining conditions of underground mines in Vietnam. The aim of the research is to determine the bearing capacity of the individual-portal support structure with various configuration. For this purpose, an analysis of the rock mass behaviour around the three-way roadway junction was carried out using the difference element method-based programme (FLAC3D). Additionally, other analysis of the bearing capacity of the selected individual-portal support structure was also conducted using the finite element method-based programme (COSMOS/M). The geological and mining conditions of Vietnamese mines were taken into account during performing these analyses. Based on the results, the optimal individual-portal support structure was proposed for the roadway junctions driven in the geological and mining conditions of underground mines in Vietnam.

Failure Analysis of Ni-8YSZ Electrode under Reoxidation Based on the Real Microstructure.

During the operation of solid oxide fuel cells (SOFCs), the Ni-8YSZ anodes are subjected to thermal mismatch and reoxidation, accompanied by the risk of damage and failure. These damages and failures are generally induced by small defects at the microscopic level, leading to the degradation of the structural bearing capacity. Therefore, the distribution and quantification of the stresses in the real microstructure of Ni-8YSZ electrodes is essential. In this study, the real Ni-8YSZ microstructure was reconstructed based on nano-computed tomography, and the stress distribution of the real microstructure was analyzed based on the finite element method under reoxidation and different operating temperatures. The failure probability of 8YSZ at different degrees of reoxidation was evaluated according to the Weibull method, and the amount of damaged 8YSZ elements was statistically counted. The study results indicate a high level of stress in the thin necks and relatively sharp areas of the microstructure. The 8YSZ has a high failure probability at a reoxidation extent of 5-10%.

RESEARCH OF THE METHODS OF STRENGTHENING REINFORCED CONCRETE COLUMNS DURING THE RECONSTRUCTION OF INDUSTRIAL BUILDINGS

Over the past two years, Ukraine has noted significant losses of the state's residential and non-residential stock as destroyed or partially damaged. Damaged or destroyed buildings must be restored, reconstructed and dismantled and new ones erected in their place.Industrial facilities suffered significant destruction. In addition, the condition of the structures of many old enterprises is extremely unsatisfactory.Currently, only in Kyiv, about 30% of the city's territory is industrial territory.Depending on the level of reconstruction of the object, it is possible to perform certain structural and enclosing elements. Any intervention in the structural elements of buildings must be preceded by an examination of both the building as a whole and these structures themselves.Repair, dismantling or strengthening of frame structures are among the typical types of work during the reconstruction of industrial facilities. The vast majority of old industrial buildings in our country have a reinforced concrete frame, especially the buildings that were erected in the 60s of the 20th century and in later periods. These are those buildings whose structural condition still allows for reconstruction or repair in order to continue their intended use. Buildings of an earlier stage, as a rule, are subject to reconstruction (if they are monuments of culture and architecture) or dismantling.The article investigates various methods of reinforcing reinforced concrete columns, which are key structural elements of industrial buildings, during their reconstruction. The technological and organic features of reinforcement are presented. The destabilizing factors that affect the efficiency of work are systematized. Modern technologies are studied, including changing the structural scheme, increasing the cross section, injecting into the body of the structure and external gluing of metal reinforcing structures.The effectiveness of each method is analyzed, which allows to assess their advantages and disadvantages, costs and duration of the reconstruction process. In particular, attention is focused on methods that increase the bearing capacity and durability of structures without significant interference with the overall structural scheme of the building.The results of the study allow us to identify optimal solutions for different types of industrial buildings, which helps engineers and designers ensure the sustainability and safety of reconstructed facilities.

Multi-scale analysis of ultimate bearing capacity in composite hull joints: failure mechanism and numerical simulation

ABSTRACT Progressive failure analysis method is the main method to analyse the ultimate bearing capacity and failure mode of composite structures. Multi-scale method can effectively reduce the dependence of damage mode and stiffness degradation analysis on material parameters. Based on the multi-scale method, from micro-scale to mesoscale and then to macro-scale, the equivalent modulus and equivalent strength of fibre bundles, single-layer laminates and multi-directional laminates were predicted respectively, and the prediction method of ultimate bearing capacity of large-scale composite structures from material level to structure level was constructed. The mechanical properties of standard composite materials and the ultimate bearing capacity of full-scale composite joints were tested respectively, and the ultimate bearing capacity and failure mode of L-joints were predicted by numerical method. The results show that the numerical simulation method based on multi-scale can accurately predict the ultimate bearing capacity and failure mode of large-scale joints of the hull.

An interface-based microscopic model for the failure analysis of masonry structures reinforced with timber retrofit solutions

This paper presents a refined Finite Element (FE) modeling strategy for analyzing the failure behavior of regular masonry structures reinforced with timber-based retrofit solutions. The proposed model schematizes the masonry as brick units, modeled using two-dimensional linear elastic plane stress elements, mutually joined through zero-thickness cohesive interface elements. These interface elements serve to reproduce the nonlinear behavior of masonry because of the occurrence of failure mechanisms of the mortar joints. Reinforced timber frame elements are modeled using truss elements that exhibit elastic brittle fracture behavior. The interaction between the masonry sub-structure and the reinforced timber frame system is accounted for using special constraint conditions that simulate the mechanical behavior of anchorage connections. The reliability of the proposed model in reproducing the failure behavior of masonry is assessed through comparisons with experimental and numerical data available in the literature. Additionally, the efficacy of the retrofit technique based on timber frame structures is investigated in detail through pushover analyses on a two-story masonry wall representative of real-life masonry buildings. The results indicate that the proposed retrofitting strategy is an effective and eco-friendly retrofit solution to enhance the in-plane bearing capacity of masonry structures subjected to horizontal forces.

Meta-arch structure: Designed reinforcement cage to enhance vibration isolation performance

In this study, inspired by the mechanical metamaterials with bandgap properties, a new type of meta-arch structure (MAS) for the attenuation of elastic waves is proposed. In this metastructure, the reinforcement cage, typically employed to enhance the tensile properties of building materials, has been redesigned and transformed into a new structure containing circular tubes with embedded resonant microstructures. The vibration reduction performance of the MAS was illustrated by the frequency response analysis in the simulation calculation, and the generation mechanism of the vibration attenuation band was revealed. The specimens of the complex MAS consisting of gypsum, reinforced steel bars, and tubes were fabricated, and the vibration response experiments were carried out to determine the dynamic properties of the novel MAS. The results show that the designed arch structure exhibits a broad vibration attenuation band without sacrificing its structural bearing capacity. Additionally, the robustness of the band gap is demonstrated by analyzing how changes in the positions of excitation and response points influence the band gap. Moreover, the MAS can be customized for specific application scenarios of vibration reduction according to the parameter analysis. Finally, the experimental results closely align with the numerical estimations, confirming the feasibility of the design method for reducing vibrations. This work provides a new method for the development of building structures for vibration and noise control.

Mechanical Response and Anti-Reflective Crack Design in New Asphalt Overlays on Existing Asphalt Overlaying Composite Portland Cement Pavement

A detection and evaluation system containing a two-level index of structural integrity and bearing capacity was constructed based on ground-penetrating radar (GPR) and a falling weight deflector (FWD). This system was constructed to solve problems with the detection, evaluation, and structural and material design of asphalt rehabilitation for the prevention and control of asphalt reflection cracks in asphalt overlaying composite Portland cement pavement. Based on the detected data from the GPR and FWD, the reasonable and recommended thickness range of the stress-absorbing layer was determined by the finite element method, and the optimization design of an anti-reflective crack structure is proposed. Furthermore, a material design and engineering application of the stress-absorbing layer was carried out. The results show that an additional 10 cm layer of repaved asphalt can reduce temperature stress by 64.1%, reduce fatigue stress by 29.3% at the cement slab bottom, and extend the service life by 23.1 years. The reasonable thickness of the stress-absorbing layer ranges from 1.6 cm to 2.0 cm, and the recommended structural combination design is a 4 cm SMA-13 upper layer, a 4 cm AC-16 lower layer, and a 2 cm stress-absorbing layer overlaying existing asphalt overlay. The impact toughness of the designed stress-absorbing layer is 1.05 times and 1.44 times that of the other stress-absorbing layer and the AC-16 asphalt mixture, respectively, which have been successfully used for more than 5 years. The recommended design rehabilitation has good engineering application. The uniformity of the stress-absorbing layer can reach 63%, and an anti-reflective crack effect is expected. The results of this study provide design methodology and experience for composite pavement repaving.