Stress State Of Structure Research Articles

Effect of loading area on triaxial compression behavior of microcapsule-based self-healing concrete

Concrete is customarily subjected to a complex triaxial stress state in structures under service. True triaxial experiments using cubic specimens in laboratory settings often utilize shims marginally smaller than the specimen surface for loading purposes. However, the influence of shim dimensions on the triaxial mechanical characteristics of concrete remains obscure. Therefore, in this study, for urea-formaldehyde (UF)/epoxy microcapsule-based self-healing concrete, shims of varying sizes were designed to conduct true triaxial compression experiments, examining the effects of loading area size and microcapsule content on triaxial mechanical behavior. The crack damage morphology was observed using a scanning electron microscope (SEM), the rupture of microcapsules was analyzed through energy-dispersive X-ray spectroscopy (EDS), and the micropore structure was determined via nuclear magnetic resonance (NMR). The research findings reveal that reducing the loading area induces stress concentration near the shim edge, significantly decreasing the first peak strength with a maximum reduction of 37%; while also increasing the second peak strength, with a maximum increase of 52%. Notably, a “sleeve-like” delamination occurs when the loading area is below 95% of the specimen surface area. Incorporating microcapsules into concrete enhances ductility and porosity, achieving a maximum 1.9% increase in first peak strain and 1.98% in porosity. This study may offer valuable insights and data for the optimization of concrete materials and structural design, thereby contributing to the safety and durability of engineering structures.

Experimental study on bearing capacity of steel-pipe PBL shear connectors

In composite open-web sandwich plate structures, when the span is large, the restraining effect of the bottom chords on the top chords makes the stress state of the material interfaces tend to be complicated, which restricts the structural load-bearing capacity. Therefore, To improve the overall stress state of such structures and increase their load-bearing capacity, this study introduces an innovative design for Steel-pipe PBL shear connectors(Perfobond rib shear connectors). In this design, steel pipes are welded to the openings of conventional PBL shear connectors. By utilizing the circular cross-section of the steel pipe to resist the complex stresses at the material interfaces, the stiffness of the shear connectors and the load-bearing capacity of the structure are improved at the same time. This study evaluates the shear performance of the new PBL shear connectors by testing nine specimens with varying parameters: steel pipe diameter, length, wall thickness, perforated rebar diameter, and concrete strength. The results indicate that steel pipes modify the failure mode and bearing mechanism of conventional PBL shear connectors, significantly enhancing shear stiffness and ultimate bearing capacity. Among all parameters, the steel pipe diameter has the most substantial impact on the bearing capacity of Steel-pipe PBL shear connectors. Based on the experimental data, this article presents a calculation formula for assessing the ultimate bearing capacity of Steel-pipe PBL shear connectors.

Stress evolution in rocks around tunnel under uniaxial loading: Insights from PFC3D-GBM modelling and force chain analysis

In underground engineerings, the evolution of the stress state in the surrounding rocks can effectively reveal its fracture mechanism. To precisely describe this microscopic information, the present study utilizes the three-dimensional Grain-based model based on Particle Flow Code (PFC3D-GBM) to construct a square numerical specimen with a pre-existing hole representing a tunnel and subjected it to uniaxial loading. In this model, different types of mineral structures and internal force chain networks are distinguished at a three-dimensional scale. Furthermore, the evolution of force chain networks in the top, bottom, left and right regions around the tunnel is quantitatively characterized. The anti-fracture capability depending on stress state of various structures is calculated and then the fracture mechanism from the point of anti-fracture capability is discussed. The research results indicate that at at the beginning of loading, some red force chains with higher level have appeared on both sides of the tunnel. As the load goes on, red force chain network extending from both sides of the tunnel to the upper and lower ends of the specimen have emerged. The average value and sum value of all force chains show an increasing trend before the peak load and a decreasing trend after the peak load. The average value of force chains within a specific structure can accurately reflect the microscopic mechanical properties of that structure. The average values of force chains on the left and right sides of the tunnel are higher, both in terms of starting points and ascending rates, than those in the upper and lower regions of the tunnel. The orientation distribution of all force chains is relatively uniform, but force chains with higher level are generally align with the loading direction. The fundamental reason for the high degree of fragmentation on the left and right sides of the tunnel is that these regions bear more external load than the upper and lower regions, rather than being inherently more prone to fracture.

Dynamic Monitoring of Steel Beam Stress Based on PMN-PT Sensor

Steel beams are widely used load-bearing components in bridge construction. They are prone to internal stress concentration under low-frequency vibrations caused by natural disasters and adverse loads, leading to microcracks and fractures, thereby accelerating the instability of steel components. Therefore, dynamic stress monitoring of steel beams under low-frequency vibrations is crucial to ensure structural safety. This study proposed an external stress sensor based on PMN-PT material. The sensor has the advantages of high sensitivity, comprehensive frequency response, and fast response speed. To verify the accuracy and feasibility of the sensor in actual engineering, the LETRY universal testing machine and drop hammer impact system were used to carry out stress monitoring tests and finite element simulations on scaled I-shaped steel beams with PMN-PT sensors attached. The results show that: (1) The PMN-PT sensor has exceptionally high sensitivity, maintained at 1.716~1.726 V/MPa in the frequency range of 0~1000 Hz. The sensor performance is much higher than that of PVDF sensors with the same adhesive layer thickness. (2) Under low-frequency random vibration, the sensor’s time domain and frequency domain output voltages are always consistent with the waveform of the applied load, which can reflect the changes in the structural stress state in real time. (3) Under the impact of a drop hammer, the sensor signal response delay is only 0.001 s, and the sensitivity linear fitting degree is above 0.9. (4) The simulation and experimental results are highly consistent, confirming the superior performance of the PMN-PT sensor, which can be effectively used for stress monitoring of steel structures in low-frequency vibration environments.

Exploration of the behavior and evolution features of beam-column joints with T-stub using the structural strain energy method

Based on the structural strain energy method, the work behavior of four T-stub connection joints under cyclic loading is analyzed to visualize their working behavior and failure evolution. The experimental strain data are modeled as generalized strain energy density (GSED) to characterize the structural stress state and the corresponding characteristic parameters, and the Mann-Kendall (M-K) criterion is formulated to determine the performance characteristic points (P and Q) of the joint Mj-Ej curves and to derive the starting point of structural continuity damage. Then, by analyzing the parameters of the joint working state (strain, deformation, joint energy dissipation, connection stiffness, bolt force and pry force), the trends of the joint stressing state curves before and after the critical loading are reflected. Finally, the feature point data interpolation (EDI) method is introduced to effectively expand the joint test data, visualize the change process of the strain/stress field, and deeply reveal the mechanical response mechanism and evolutionary degradation law behind it. The contribution of the above work is to quantitatively identify the P and Q characteristic points in the changing trend of the joint working state, to reveal the mechanical mechanism and the failure degradation law from the perspective of energy evolution, and to visualize the mutation of the field data before and after the P/Q using the EDI method, which is a generalized method that can be applied to the other progressive failure structures.

Research on Double-Layer Support Control for Large Deformation of Weak Surrounding Rock in Xiejiapo Tunnel

Double-layer primary support is proposed to control the deformation of surrounding rock in tunnels within weak geological conditions, where engineering challenges such as large deformations, tunnel faces, and arch collapse are encountered. This approach is based on the principle of combined resistance and release. A combined approach of numerical modeling and on-site surveillance was utilized to analyze the displacement and stress state of the tunnel support structure at different construction stages of primary support for the second layer, using Xiejiapo Tunnel as an engineering case. The findings indicate that the implementation of two-layer primary support can mitigate the progression of large deformations effectively in weak surrounding rock; the sooner the primary support for the second layer is applied, the better the deformation control, and the later the application takes place, the more effectively the tension in the surrounding rock is diminished, whereby the self-supporting capacity of surrounding rock comes into its own. The force of the shotcrete is reduced. Considering the structural deformation and stress state, as well as combination of resistance and release, it is best to implement the primary support for the second layer 10 feet behind the primary support for the first layer.

Hyperspectral imaging features for structural stress state assessment: An experimental study

To explore the feasibility of hyperspectral machine vision for detecting stress states of underground structures, this study utilized a hyperspectral camera to acquire spectral datasets from the surfaces of concrete and sandstone specimens under different stress conditions. Machine learning models were established to predict stress states based on raw spectral data and data pre-processed using the Savitzky-Golay (S-G) method. The results indicated that satisfactory outcomes were obtained with no pre-processing and S-G pre-processing. In addition, the hyperspectral response characteristics of concrete and sandstone under different stress states were investigated. The hyperspectral dataset of sandstone was observed to yield higher predictive accuracy than that of concrete. Finally, a comprehensive analysis of the performances of the principal component regression, partial least squares regression, and least-squares support vector machine models was performed over various datasets in terms of computed model evaluation metrics.

Theoretical and numerical analysis of buckling stability of bi-directional corrugated sandwich panels

ABSTRACT Considering the biaxial stress state of underwater pressure-resistant structures, this paper proposed a bidirectional corrugated structure based on the cuttlefish bone's unidirectional corrugated wall structure. Building upon the calculation method for the equivalent stiffness of corrugated plates, formulas for the equivalent bending stiffnesses and equivalent torsional stiffness of bidirectional corrugated plates were derived. Kirchhoff's laminated plate theory was employed to derive the buckling critical loads for biaxial compression of bidirectional corrugated core panels with four simply supported edges. By comparing with finite element method results, the accuracy of various calculation methods in evaluating the equivalent stiffness of unidirectional and bidirectional corrugated plates is analyzed, and the proposed calculation method for the critical buckling load is validated. It is shown that the buckling resistance capacity of the bidirectional corrugated laminate structure can reach approximately 2.34 times that of an equivalent mass flat plate.

The stress state of a thick-walled shell with allowance for contact with a hydrogen-containing medium

Numerical and experimental methods are used to solve a multidisciplinary problem on determining the stress state of a steel shell of revolution under mechanical loading and thermal effect with allowance for its contact with a hydrogen-containing medium. The study uses a well-developed mathematical tool for solving heat conduction problems in order to solve the problem of hydrogen diffusion into metal. The effective stresses and their invariants are determined by solving the nonlinear boundary value problem of thermoplasticity of a thick-walled shell of revolution in a three-dimensional formulation. The study takes into account the experimentally found effect of changes in the mechanical properties of steel affected by hydrogen. The correctness of the proposed method and the performed calculations is quantitatively estimated by comparison with a well-known problem having an analytical solution. The paper shows that it is possible and necessary to take into account the change in mechanical properties when determining the stress state of steel structures operating in contact with a hydrogen-containing medium.

Energy-dependent correlation between micro/nano-morphology and stress state of femtosecond laser-induced modification in fused silica

Due to the importance of stress control in the laser processing of brittle transparent dielectrics such as glass and crystal, investigating the evolution of laser-induced stress state and its manipulation mechanism is highly desirable for ensuring high-performance crack-free laser micro/nanostructuring of dielectrics. Herein, the internal stress state of a femtosecond laser-modified fused silica glass sample at a broad range of pulse energy from 0.34 to 3.5 μJ was evaluated using a cantilever displacement method. Two obvious transition zones in the variation of microscale displacement were identified and analyzed by polarized optical microscopy, scanning electronic microscopy, and confocal micro-Raman spectroscopy. A strong energy-dependent correlation between the evolution of the micro/nano-scale morphology and stress state in laser-induced structures has been investigated and discussed. The analyzed result is beneficial for developing high-efficiency and high-quality manufacturing of 3D large-scale and high-precision glass microstructures.

Сomputational approach to thermal-stressed state modeling of tire based on the algorithm of its self-heating analysis. Part 2 – Practical results of applying the approach

Elastomers and their composites are widely used in modern innovative technology: for the production of aviation and automobile tires, anti-vibration elements (rubber, rubber-metal springs), dampers, elastomeric bearings. Also they are used in shaft suspensions, as spacers between structural parts, supporting parts and fasteners. Elastomeric elements of structures have a high dynamic load, in particular of a cyclic nature, which is accompanied by the formation of hysteresis loops and, as a result, the occurrence of the phenomenon of self-heating. An increase in temperature in the middle of materials causes significant changes in their mechanical properties, reduces strength characteristics, accelerates aging and degradation processes, and has a significant impact on fatigue processes. In addition, an increase in temperature causes an additional thermal stress state, capable of significantly changing the qualitative picture of the structure's deformation characteristics' distribution. Thus, the purpose of this study is development of approach to assessing the thermal stress state of structures made of elastomeric materials for the possibility of further analysis of its influence on the structure work as a whole. The appropriate approach was built on the basis of numerical modeling of thermal and deformation processes which takes place into the structure during operation. The proposed approach includes several related calculations by using FEM and is based on the fundamental approaches of the theories of elasticity and viscoelasticity, thermal conductivity and thermo-elasticity. Thus, the article presents an approach to the analysis of the thermal stress state of structural elements under operating conditions. This approach was applied to determine the thermo-strain-stress characteristics of a pneumatic tire and corresponding pictures of its distribution were obtained.

Multilayered elastic medium reinforced with interfacial thin film: A theoretical model for geogrid reinforced HIR asphalt pavement

Aiming at modeling the reinforcement behavior of geogrid reinforced HIR asphalt pavement structure accurately and efficiently, a mathematical formulation using the Generalized Kelvin Solution (GKS) based method for multi-layer three-dimensional elastic system with the consideration of elastic membrane without thickness is put forward in this thesis to simulate the geogrid reinforcement for HIR pavement. Solutions in transform and physical domain, solutions for z = 0, and specific solutions of surface displacements are determined. Four special cases including homogeneous half space with buried and surface thin film reinforcement, Boussinesq's solution, unreinforced multilayered half space are introduced to validate the solution. Moreover, the mechanical effect of geogrid on the deformation, stress state and fatigue life of the pavement structure is investigated using the proposed model and solution. The geogrid stiffness has significant effect on the vertical and radial strain. After the reinforcement, both the radial stress and hoop stress near the interface reduce to a very low level, the stress concentration is effectively alleviated. Meanwhile, geogrid reinforcement plays a positive role on enhancing the fatigue damage resistance of pavement stricture Our proposed method provides a novel way to model reinforcement mechanism of the geogrid on pavement structure, which is helpful to engineering practice.

Bearing stress detection and evaluation of hydraulic steel gate members

Based on the principle of mathematical statistics, we describe the theory and algorithm of establishing the stress characteristics of gate members by using the method of data regression analysis based on multiple levels of actual load detection data. Following, we demonstrate the test results of an arc gate of a spillway dam by regression analysis. Then, we calculate the structural stress state under the design condition by regression equation, and the finite element results are used to verify each other. Finally, according to the current standard, we give the safety evaluation of the structure stress calculation data under the design condition.

Rapid acquisition method for structural strength evaluation stresses of the ship digital twin model

The existing ship hull structure stress monitoring can only give the stress state of typical measuring points, but the monitoring point may not be the most dangerous location of the ship hull structure. To solve this problem, this paper carried out the research of ship strength digital twin. Concretely, to meet the real-time requirements for obtaining the structural stress state, this paper proposed a rapid acquisition method for structural strength evaluation stresses of the ship digital twin model, which realizes the rapid acquisition for structural yield strength evaluation stresses at the monitoring point and the non-monitoring point. To illustrate the specific application and application effect of the proposed method, the amidships three compartments section of a 21,000TEU ultra-large container ship was selected as the research object. And the case that this research object may suffer from the vertical wave bending moment and the horizontal wave bending moment simultaneously was considered. Related studies show that the proposed method can accurately recognize the load actually suffered by the ship monitoring structure. And the specific meaning of the ship monitoring structure referred to here is the ship hull structure that requires structural stress state monitoring. At the same time, related studies also show that the maximum error of the calculation results obtained by the proposed method does not exceed 0.0005% in obtaining the structural yield strength evaluation stress at the monitoring point, while the maximum calculation error does not exceed 0.032% in obtaining the structural yield strength evaluation stress at the non-monitoring point.

Ішкі бойлық жарықшақтың жоғарғы жағындағы рельс конструкцияларының кернеулі күйін зерттеу

The study of the stress state in the puncture zone will be incomplete without a detailed consideration and analysis of the picture of stresses arising at the ends of the VAC, because it was from them that the destruction of some rail ends began during testing. An assessment of the effect of various types of loading on the VP will help to understand more deeply the mechanism of the formation of gouges and gouges and explain why defects 11 and 21 do not occur in this section.One of the most important criteria for assessing the stress state of structures with cracks is the stress intensity coefficient (KIN) [98, 101]. It not only determines the stress state at the crack tip, but can also be used to predict the crack growth rate. Therefore, the purpose of this study is to determine the stress intensity coefficients at the points of the VAC front.

Flexural bond evaluation of deformed steel rebars in recycled aggregate concrete

An accurate quantification of the bond between embedded rebar and recycled aggregate concrete (RAC) is a prerequisite for confident use of RAC. However, there is a noticeable lack of experimental data that can faithfully represent the actual bond stress state in real RAC structures. To address this limitation, a total of 37 beam specimens were tested in strict conformity with the RILEM testing protocol. The strength grade of old concrete was among several control variables studied for their impact on the bond strength. The findings reveal that the incorporation of coarse or/and fine recycled aggregate (RA) does not alter the expected mode of bond failure for a beam; however, it significantly affects the beam’s bond strength in flexure. Using RA sourced from weaker parent concrete leads to much inferior interfacial bonding, but there exists an almost linear relationship between the bond strength of RAC relative to that of natural aggregate concrete (NAC) and their relative water absorption ratio. This relationship seems to hold true regardless of the strength of RA. Based on the probabilistic analyses conducted herein, the anchorage length specified in existing codes developed for NAC is found inadequate and unsafe for RAC. A modifier is therefore proposed to remedy this unconservatism.

Longitudinal deformation of Shield tunnel based on construction monitoring data

The rapid development of urbanization has changed the traffic and transportation in the central area. The change of the surrounding rock and structural stress state of the project under construction caused by the tunnel construction in the same period has caused great harm to its safe use and casualties. Shield construction technology can achieve safe excavation and lining, with high degree of automation. And it is a relatively common construction method at present. But its adaptability to section size and section environmental conditions is poor. In view of this, from the analysis of construction monitoring data, the study established a longitudinal model considering lateral effects from the perspective of lateral characteristics. It also achieved stress assessment and improvement through lateral deformation calculation, segment ring bolt calculation and formula correction. The experimental results showed that the opening at the circumferential seam of the right line of the test tunnel under this method is 8.9 mm. The radius of curvature is 758 mm, and the safety assessment level of longitudinal deformation is 3. This method can effectively guarantee the safety of shield tunnel construction and has good guiding value for tunnel management and maintenance.

Structural and stress state dependence of small-scale deformation in bulk metallic glass

Bulk Metallic Glasses (BMGs) are attractive for myriad structural applications at multiple length scales (nano-micro-macro) but show limited bulk plasticity due to the tendency for shear localization. However, there is limited understanding of the effect of structural state and stress state on the small-scale deformation behavior of BMGs. Here, the micro-scale deformation behavior of a model Ni-based BMG was studied in as-cast and corresponding relaxed state under multiaxial nano-indentation, uniaxial micro-pillar compression, and micro-cantilever beam bending. The relaxed BMG showed 6 % higher hardness, 22 % higher yield strength, and 26 % higher bending strength compared to its as-cast counterpart. The increase in hardness, yield strength, and bending strength for the relaxed alloy compared to its as-cast counterpart demonstrates the relation of intrinsic free volume present in a BMG to its resistance for initiation of plastic events at this scale. Both the as-cast and corresponding relaxed samples showed stable notch opening and blunting during micro-cantilever bending tests rather than unstable crack propagation. However, pronounced notch weakening was observed for both the structural states, with the bending strength lower by ∼ 25 % for the notched samples compared to the un-notched samples. This work may stimulate further investigations into the deformation behavior of BMGs in response to complex stress states pertinent to real-world structural applications at small scale.

Mechanical Analysis of the Stress State and Damage Risk of Asphalt Pavement Based on a Three-Dimensional Space Calculation Program

The existing research on pavement mechanics was rarely conducted from the perspective of the spatial stress state. In this research, by utilizing analytical solutions, a three-dimensional space calculation program for asphalt pavement was developed to study the spatial distributions of the stress state and damage risk of the pavement structure. First, this study selected various types of pavement structures to analyze the spatial distribution of the stress state. The results indicated that the important influence factors are the order and quantity of asphalt-bound material, chemically stabilized material, and granular material in the structure. In contrast, the thicknesses of these materials have a limited effect. Then, the stress states of the asphalt pavements in winter and summer were compared. The results demonstrated that the tensile region bulges upward at low temperatures, and the structure is more inclined to experience tension and compression simultaneously. In addition, the failure criterion suitable for asphalt mixture materials was applied, and a strength conversion coefficient between different temperatures was proposed to calculate the damage situations of asphalt mixture layers. Three-dimensional images were generated to display the differences in the dangerous positions and damage forms for different structural types and temperature conditions.

Parametric Study of Drilling Method Performed on One-Way Post-Tensioned Slabs

Abstract Determination of the stress state in concrete structures is a very important, but difficult task. In the case of new structures, it is possible to easily instal measurement instruments which can provide important data as a part of real-time monitoring. However, the evaluation of stresses in existing structures is much more challenging. Currently, stress relief methods are a well-established approach for the evaluation of the actual state of existing structures. The so-called Drilling method (also known as Stress-relief coring technique) is one of the possible techniques for such analysis. For practical use of this method, knowledge of pivotal factors which influence stress relief is crucial. Therefore, this paper presents a parametric study performed on a one-way post-tensioned slab which can help to understand the effect of the depth of the core and the distance from the edge of the hole (position of strain gauges) on the change in stress in the vicinity of the drilled core. Finally, based on the obtained data, the recommendations for the subsequent experimental program will be summarized. According to the study, it seems that the depth of drilled core does not significantly influence the stress relief and the main impact can be attributed to distance from the edge of the hole.