Load Bearing Capacity Of Structures Research Articles

Macroscopic and mesoscopic mechanism of hydration instability of the rock-grout coupled structure

In order to investigate the macroscopic and mesoscopic mechanism of hydration instability of rock-grout structure under the influence of moisture content, a direct shear test combined with particle flow code (PFC) simulation was conducted subject to various moisture content levels and normal stresses. The results show that a higher moisture content would compromise the load bearing capacity of soft rock anchorage structures by deteriorating the structural integrity of the surrounding rock and the bonding effect between the anchorage interfaces. The load bearing capacity of the surrounding rock is also rapidly reduced. The rock-grout structure has four main shear damage modes, which are influenced by both moisture content and normal stress. When the saturated moisture content is reached, the anchorage structure has lost its bearing capacity, and the rock is muddied and subsequently debonded from the bolt. The energy required to break the internal adhesion of the rock-grout structure under the effect of hydration is greatly reduced, resulting in easy decoupling and dispersion between the rock skeleton particles. In turn, the rock surface particles bonded by the anchor agent are separated from the deeper particles, resulting in the failure of the bonding surface and weakening the coupling effect between the anchor and the surrounding rock. According to the test results, the control measures for surrounding rock of muddy roadway are put forward.

Factores anatómicos y biomecánicos de la fractura vertebral osteoporótica y la aparición de las fracturas en cascada

Osteoporosis weakens the structural strength of bone to such an extent that normal daily activity may exceed the capacity of the vertebra to bear this load. Vertebral fracture and deformity is a hallmark of osteoporosis. The detriment of trabecular bone properties alone cannot explain the occurrence of osteoporotic vertebral fracture. The ability of the spine to bear and resist loads depends on the structural capacity of the vertebrae, but also on loading conditions arising from activities of daily living or low-energy trauma. This review describes the mechanical properties of the vertebral bone, the structural load-bearing capacity of the various elements forming the spine, the neuromuscular control of the trunk, as well as the biomechanics of the loads to which the spine is subjected in relation to the presence of osteoporosis and the risk of vertebral fracture. A better understanding of biomechanical factors may help to explain both the high incidence of osteoporotic vertebral fractures and their mechanism of production. Consideration of these issues may be important in the development of prevention and management strategies.

Experimental and Finite Element Analyses of Adjustable Foundation Bolts in Transmission Towers

Uneven settlement of transmission tower foundations can result in catastrophic events, such as tower collapse and line failures, disrupting power transmission operations. To address the challenging repairs caused by uneven foundation settlement of transmission towers, we propose an adjustable foundation bolt (AFB). This paper provides a detailed theoretical analysis of the AFB’s stability and load-bearing capacity, including critical buckling force formulas and maximum normal stress expressions. Finite element simulations confirm the precision of our theoretical formulations. Additionally, we introduce a method using baffles to enhance its load-bearing capacity, analyzing the impact of different numbers of baffles through numerical simulations. The experimental results validate the effectiveness of baffles in enhancing structural load-bearing capacity. The device brings convenience and efficiency to the maintenance of transmission towers.

Fabrication and mechanical properties of thermoplastic corrugated sandwich panel with enhanced face‐core interface

AbstractThermoplastic sandwich structures are widely utilized in engineering fields due to their high specific strength and stiffness, recyclability, and impact toughness. The face‐core interface strength is crucial to maximize the performance benefits of sandwich structures. Two sizes of corrugated sandwich panels with hot‐melt bonding and resistance welding connection methods were fabricated. The mechanical properties of sandwich panels were compared using a combination of experimental, numerical, and analytical investigation. Edgewise compression (EC) and 3‐point bending (3 PB) tests were conducted to obtain load–displacement curves and investigate different failure modes of sandwich panels. The peak edge compression and bending loads of the resistance welded structures were 42% and 92% higher, respectively, and the face‐core interface was always well‐connected compared to those of the hot‐melt bonding. The results indicate that the resistance welding method can be utilized as a core bonding technique for thermoplastic composite sandwich structures and has great potential for aerospace application.Highlights A method that includes hot‐melt bonding and resistance welding are develop to produce thermoplastic composite corrugated sandwich panels (TPC‐CSPs). The TPC‐CSPs fabricated by resistance welding exhibit superior interface connection performance compared to hot‐melt bonding and this method enhance the structural load bearing capacity. The numerical and analytical method were presented to investigate the failure model, which was consistent with the experimental results.

Geometric Complexity Control in Topology Optimization of 3D-Printed Fiber Composites for Performance Enhancement.

This paper investigates the impact of varying the part geometric complexity and 3D printing process setup on the resulting structural load bearing capacity of fiber composites. Three levels of geometric complexity are developed through 2.5D topology optimization, 3D topology optimization, and 3D topology optimization with directional material removal. The 3D topology optimization is performed with the SIMP method and accelerated by high-performance computing. The directional material removal is realized by incorporating the advection-diffusion partial differential equation-based filter to prevent interior void or undercut in certain directions. A set of 3D printing and mechanical performance tests are performed. It is interestingly found that, the printing direction affects significantly on the result performance and if subject to the uni direction, the load-bearing capacity increases from the 2.5D samples to the 3D samples with the increased complexity, but the load-bearing capacity further increases for the 3D simplified samples due to directional material removal. Hence, it is concluded that a restricted structural complexity is suitable for topology optimization of 3D-printed fiber composites, since large area cross-sections give more degrees of design freedom to the fiber path layout and also makes the inter-layer bond of the filaments firmer.

Experimental and numerical evaluation of geometrical imperfection effects on the load bearing capacity of small-scaled voussoir arches

The study of the behaviour of masonry arches represents a complex problem, which involves different aspects that can significantly affect the load bearing capacity of such structures. In this regard, geometrical imperfections, such as the irregular shape of the arch blocks, the initial position of the first and last voussoirs (boundary conditions), the alignment between the adjoining blocks and the rounded corners of each block, play an important role. An experimental campaign was conducted on a toy arch made by eleven irregular blocks, with the aim of evaluating the effect of such irregularities. A numerical model was developed basing on lower bound (LB) and upper bound (UB) limit analysis approaches (referred to as the static and the kinematic theorem, respectively). A linear programming (LP) solving algorithm was implemented in the software MATLAB and used to solve the minimization/maximization problems. The probability distribution of each considered nonlinearity was estimated, the results of the numerical analysis were correlated with the experimental outcomes and a Montecarlo simulation was carried out to validate the hypothesised probability distributions.

Optimization of geometrical factors for enhanced performance of carbon fiber reinforced polymer cores under transverse loading

The high strength-to-weight ratio and ease of manufacturing of composite materials make them widely used across a variety of industries. A commonly used method of improving composite structure load-bearing capacity is to employ carbon fiber-reinforced polymer (CFRP) cores. The mechanical properties of CFRP, however, vary in different directions due to its anisotropic behavior. Due to higher tensile strength along the fibers, anisotropy can lead to failure based on directions other than the fiber orientation. A thorough analysis of CFRP core failure modes has been conducted. Experimental analysis, finite element analysis, and micromechanical modeling techniques have been used in these studies. In this research, specific emphasis has been placed on understanding failure behavior under transverse loading conditions. Failure modes have been thoroughly examined in relation to geometric parameters such as interference, wedge angle, and friction coefficient. Modeling CFRP core failure and displacement behavior was carried out using FEA simulations to validate the research findings. A comparison of the obtained results with existing literature ensured that they were accurate and reliable. Additionally, response surface methodology was employed for optimization, aiming to minimize two critical factors: radial compressive stress and core displacement. By minimizing these factors, the performance and reliability of CFRP cores in applications related to grid capacity can be enhanced. The analysis of the research data revealed that the friction coefficient and interference play significant roles as interacting factors, albeit with opposite impacts on the stresses within the CFRP cores. The optimal values for interference and friction coefficient were found to be 0.0224 mm and 0.4, respectively, to minimize radial stress. Furthermore, the wedge angle exhibited a substantial influence on core displacement, with an optimal value of 3.5°.

Effects of adhesive layer thickness on the fracture properties of a concrete-epoxy resin interface

Adhesive layer thickness is a crucial factor that affects the performance of interfaces in cement-based composite structures. However, the influence of adhesive layer thickness on the fracture properties of concrete–epoxy resin remains unclear. In this study, a two-parameter fracture model of a concrete-epoxy resin interface from the perspective of fracture mechanics. Digital image correlation (DIC) technique was used to investigate the evolution of the fracture process zone (FPZ) of nine specimens with adhesive layer thicknesses of 2 mm, 5 mm, and 8 mm, respectively. The interfacial fracture toughness parameters of the concrete-epoxy resin interface were determined based on the four-point bending (FPB) tests. The test results indicated that increasing the adhesive layer thickness changed the failure mode of the interface from approximate-brittle to quasi-brittle. The load-carrying capacity and interfacial stiffness of the concrete-epoxy resin interface decreased by approximately 13.8 % and 61.1 % with an adhesive layer thickness from 2 mm to 8 mm, respectively. The deflection across the specimen increased by approximately 37.2 % with an increase in adhesive layer thickness due to the lower elastic modulus of epoxy resin compare to the concrete. Furthermore, the FPZ for the adhesive layer thickness of 5 mm was the longest; it was approximately 18.7 % longer than that for the test specimen with an adhesive layer thickness of 2 mm. In terms of structural load-bearing capacity and fracture toughness, the concrete-epoxy resin interface exhibited the best working performance when the thickness of the adhesive layer was 5 mm.

Physical informed neural network for thermo-hydral analysis of fire-loaded concrete

In the event of a fire within a tunnel, the rapid and substantial increase in temperature can prompt swift fractures within the concrete lining. This situation can severely compromise the structural load-bearing capacity and overall safety of the tunnel. The intricate interplay of factors within the tunnel, including temperature, humidity, and pore pressure, necessitates the adoption of a thermo-hydro coupled model for comprehensive analysis. However, these highly coupled models exhibit profoundly nonlinear characteristics that cannot be readily solved through analytical means. In this study, a Physics-informed neural network (PINN) is harnessed to address this intricate multi-field coupled issue. Neural networks possess a significant advantage in their capacity to autonomously differentiate and directly capture variations within the spatiotemporal domain. Through a comparison with experimental results, the proposed method’s reliability is effectively demonstrated. The research findings hold the potential to significantly aid engineering professionals in swiftly conducting fire resistance assessments and risk evaluations for tunnels, whether they are under construction or already in operation.

Experiment and Numerical Simulation on Damage Behavior of Honeycomb Sandwich Composites under Low-Energy Impact

It is well-established that the honeycomb sandwich composite structures are easily prone to damage under low-energy impact. Consequently, it would lead to a dramatic decrease in structural load-bearing capacity and a threat to overall safety. Both experimental and numerical simulations are carried out to investigate the impact damage behavior of honeycomb sandwich composite specimens. The damage mode, damage parameters, and contact force-time curves of three types of panel materials with T300, T700, and T800 are obtained under different impact energies of 10 J, 20 J, and 40 J by the drop-weight impact experiment. Moreover, digital image correlation (DIC) tests are used to measure the deformation and strain of the lower panel. The experimental results reveal that the degree of damage increases with increasing impact energy. Particularly, the T300 panel specimen exhibits visible fiber fracture when subjected to an impact energy of 40 J. The impact process involves matrix cracking, fiber fracture, and delamination of the upper panel occurring first, followed by immediate crush damage to the honeycomb core and, finally, slight fiber damage to the lower panel. Due to its higher strength, the T800 panel specimen exhibits the highest damage resistance compared to the T700 and T300 panel specimens. To consider the microscopic failure criteria and various types of contact during the impact process, a finite element model of honeycomb sandwich composites is established, and numerical simulation analysis of low-energy impact is performed to determine the damage mode, damage size, and contact-force curves. Comparative analysis demonstrates good agreement between the simulation and experimental results. The findings of this study provide valuable technical support for the widespread application of honeycomb sandwich composites in the aviation field.

From Reliability-Based Design to Resilience-Based Design

Abstract Reliability-based design has been a widely used methodology in the design of engineering structures. For example, the structural design standards in many countries have adopted the load and resistance factor design (LRFD) method. In recent years, the concept of resilience-based design has emerged, which additionally takes into account the posthazard functionality loss and recovery process of a structure. Under this context, the following questions naturally arise: can we establish a linkage between reliability-based design and resilience-based design? Does there exist a simple resilience-based design criterion that takes a similar form of LRFD? This paper addresses these questions, and the answer is “yes”. To this end, a new concept of structural resilience capacity is proposed, which is a generalization of structural load bearing capacity (resistance). The probabilistic characteristics (mean value, variance, probability distribution function) of resilience capacity are derived. Applying the concept of resilience capacity, this paper explicitly shows the relationship between the following four items: time-invariant reliability-, time-invariant resilience-, time-dependent reliability-, and time-dependent resilience-based design methods. Furthermore, an LRFD-like design criterion is proposed for structural resilience-based design, namely, load and resilience capacity factor design (LRCFD), whose applicability is demonstrated through an example. The LRCFD method can also be used, in conjunction with LRFD, to achieve reliability and resilience goals simultaneously of the designed structure.

Experimental study on real bridge before and after simple-supporting to continuous reinforced concrete hollow slab

This article studies a concrete hollow slab simply supported-continuous actual engineering project in a certain city. Before the reinforcement of the bridge, there were cracks and exposed rebars, etc. In order to ensure the safe operation of the bridge, a reinforcement method of simply supported-continuous was adopted, prestressed steel strands are used to convert the simple-supported structure into a continuous structure, thereby improving the structural load-bearing capacity and overall integrity. Through conducting comparative analysis of load tests on a bridge before and after reinforcement, this article studies the improvement effect of the simply-supported-to-continuous reinforcement method on the bearing capacity of the bridge. A finite element model of the bridge was established, and comparative analysis was carried out before and after the reinforcement of the bridge. The bearing capacity and work performance of the bridge structure were evaluated. The research shows that the simply supported-continuous reinforcement method has a good improvement effect on the load-bearing capacity of the concrete hollow slab and can be used to improve the insufficient load-bearing capacity of the concrete hollow slab bridge in the city.

Numerical analysis of the effects of fire with cooling phase on reinforced concrete members

Fire exposed structures may collapse during or after the fire decay phase, with risks for building occupants and firefighters; yet, understanding of the effects of the fire decay phase on structural loadbearing capacity remains limited. This paper describes a numerical investigation on the behavior of reinforced concrete columns, beams, and walls under natural fires including cooling down phases. Finite element models are benchmarked against experiments capturing the behavior during heating. The models are then used to simulate the structural response of the concrete members under fires with various cooling rates and load ratios. The analyses capture the irreversibility of material properties through tracing of the temperature history in the structure. The results show that temperatures and deformations continue increasing after the end of the fire heating phase. As a result, concrete columns, beams, and walls may fail during the cooling phase. Faster cooling rates reduce the likelihood of failure in cooling. For beams, failure can be inferred from the maximum reinforcement temperature reached throughout the fire, but for columns and walls a thermal–mechanical analysis of the member throughout the fire history is needed. A relationship is proposed to evaluate the burnout resistance from the fire resistance rating and cooling rate. The presented numerical method allows assessing the structural stability throughout a fire event, an important requirement for designing a fire resilient built environment.

Multi-objective optimization of loading path for sheet hydroforming of tank bottom

As a critical component of the propellant tank, the tank bottom is subjected to complex loads such as internal pressure and vibration and has high requirements for structural load-bearing capacity. Hydroforming deep drawing is one of the techniques for the integral forming of the tank bottom. As the tank bottom is a large-size thin-walled structure, defects such as cracks and wrinkles are prone to occur during the hydroforming deep drawing process. Aiming at reducing these defects, the hydraulic pressure loading path and blank holder force loading path of the hydroforming deep drawing process are studied, and a multi-objective optimization method is proposed to improve the surface accuracy and thickness distribution uniformity of the tank bottom. The complex loading path curve optimization problem is transformed into a functional relationship between hydraulic pressure and blank holder force with time. The hydraulic pressure and blank holder force at each time node are used as design variables, and the maximum wall thickness reduction rate, rupture trend factor, wrinkle height, and wrinkle trend factor are used as optimization targets. The radial basis function (RBF) neural network is used to establish the approximate model between the loading path and the optimization target, and the multi-objective particle swarm optimization (MOPSO) algorithm is used to optimize the solution. Taking the hemispherical tank bottom as an example, the optimal hydraulic pressure loading path and blank holder force loading path are obtained, and the quality of the formed part is improved.

Hierarchical multiscale analysis for 3D woven composite leaf spring landing gear

In this work, a hierarchical multiscale analysis method was used for 3D woven composite leaf spring landing gear. The structural finite element models at micro, meso and macro scales were established and discussed, respectively. The influence of weave patterns on the tensile properties of 3D woven composites were carried out by experiment and numerical simulation. Finally, the multiscale model was established to predict the mechanical properties of 3D woven composite leaf spring landing gear. The results showed that the maximum prediction error was 9.01% at the microscopic scale, 4.55% at the mesoscopic scale, and 5.61% at the macroscopic scale, thus verifying the effectiveness of the used hierarchical multiscale analysis strategy. The presence of stuffer yarn within the material and the yarn arrangement density were the key factors affecting the structural load-bearing capacity in the design of 3D woven composite leaf spring landing gear.

The influence of the fire temperature on the condition of steel roof structure

Contemporary process of structure designing takes into account the requirements for the structural load-bearing capacity, parameters in terms of serviceability, as well as safety and resistance in the case of fire occurrence. The fire protection required by law does not guarantee full resistance, but only the safety of the integrity of the structure subjected to fire over a certain period of time. Structures after a fire are assessed in terms of their further use. A special case is the partial damage to the structure of some load-bearing elements, including their separate elements. The research issue is the assessment of the structure both as a whole and as individual components. Usually some elements have to be replaced and some can be used directly or after strengthening. This issue has been discussed in the article.Fire in the sports hall building developed as a result of improper use of the ventilation system. The range and effects of fire affected some of the structural elements. An assessment of the fire consequences was carried out, numerical analyzes were performed and the results were compared with accurate measurements of the structure deformation. The obtained conclusions allowed to determine the impact of the fire on the structural elements and the procedure for the repair of the damaged facility. Some elements, mainly the roof covering, had to be replaced, and the main elements of the structure were strengthened to ensure the required level of safety.

Numerical Study on Flexible Pipe End Fitting Progressive Failure Behavior Based on Cohesive Zone Model

Flexible pipes are extensively used to connect seabed and floating production systems for the development of deep-water oil and gas. In the top connection area, end fitting (EF) is the connector between the flexible pipe and floating platform, as a critical component for structural failure. To address this issue, a combined numerical and experimental prediction method is proposed in this paper to investigate the failure behavior of flexible pipes EF considering tensile armor and epoxy resin debonding. In order to analyze the stress distribution of the tensile armor and the damage state of the bonding interface as the tensile load increases, a finite element model of the EF anchorage system is established based on the cohesive zone model (CZM). Additionally, the effects of the epoxy resin shear strength (ss) and the steel wire yield strength (ys) on the structural load-bearing capacity are discussed in detail. The results indicate that wire strength and interface bonding have a substantial effect on the anchorage system’s failure behavior, and the low-strength wire anchorage system has a three-stage failure behavior with wire yielding as the predominant failure mode, while the high-strength wire anchorage system has a two-stage failure behavior with interface debonding as the predominant failure mode.

Estimating the elastic modulus and bending stiffness of steel ruler with crack using three-point bending test

Cracks are the early signs of distress in structures and must be diagnosed accurately. They reduce the structural stiffness, strength, and may adversely affect the behavior of the structure. This study aims to estimate the elastic modulus and the bending stiffness of a steel ruler with varying crack lengths. A low cost and simple three-point bending test was used for the measurements. A pristine ruler and rulers with three different crack lengths were subjected to loads of up to 6 kg (roughly 13 lbs) and the displacement close to the load location was measured. The load and displacement at the center of the specimen, for loading and unloading, were measured at equal load steps. The effect of a crack on the elastic modulus and the bending stiffness was compared with that of the pristine ruler. Permanent deformation was observed on the 10 mm and 15 mm crack ruler. The presence of crack reduced the elastic modulus of the ruler by 14% and the bending stiffness by 26.5%. The structural load-bearing capacity depends on the presence of cracks. Anticipating the extent of reduction in elastic modulus and bending stiffness aids designers in minimizing the need for repeated design revisions. This investigation supports both structural designers in designing structures such as airplanes and bridges, as well as repair technologists in upgrading existing structures.

Effect of Surface Modification of Carbon Nanotubes on the Properties of High-Strength and High-Conductivity Copper Matrix Composites

The use of carbon nanotubes (CNTs) as the reinforcing phase to prepare copper-based composite materials can improve the strength and high conductivity of copper-based conductors. In order to analyze the effect of surface oxidation modification on the structural properties of carbon nanotubes and its strengthening effect on composite materials, this article combines heterogeneous copolymerization liquid phase mixing method and spark plasma sintering molding method; prepares the carbon nanotubes/copper composite materials using carbon nanotubes under different oxidation treatment conditions as the reinforcing phase (the volume fraction of carbon nanotubes is 3%); and characterizes the microstructure, mechanical properties, and electrical and thermal conductivity of the composite material. Studies have shown that the tensile strength and hardness of composite materials first increase with the increase of CNT oxidation treatment time and then decrease with the increase of oxidation treatment time. When the oxidation treatment time is 4 h, CNTs are uniformly dispersed in the matrix while maintaining good structural integrity and load-bearing capacity, and the composite material has the highest mechanical properties. The tensile strength of the composite material made of 80‐ nm CNTs reaches 452.4 MPa, which is 1.6 times that of pure copper, and the hardness reaches 127.4HV, which is twice that of pure copper. The electrical conductivity and thermal conductivity of the composite material first increase with the increase of the oxidation treatment time of carbon nanotubes and then decrease with the increase of the oxidation treatment time. The 80 nm CNT reinforced composite material has better CNT dispersion performance and higher conductivity than that of 15 nm CNT preparation. The electrical conductivity of the composite material reaches the maximum value of 92% IACS when the CNT oxidation treatment time is 4 hours, which is 95% of the pure copper sample, and the electrical conductivity is significantly better than that of the CNT/Cu composite material and copper alloy prepared by other methods. The thermal conductivity of composite materials is lower than that of pure copper. The thermal conductivity of carbon nanotubes with an oxidation treatment time of 2 h decreases most obviously, indicating that the thermal resistance generated by the interface and agglomeration phases in the composite material affects its thermal conductivity.

Experimental study on bearing capacity of a Tensairity arch

Based on the advantages of tension-string structures and inflatable membrane structures, this paper proposes a Tensairity arch and designs and builds a model for the structure. The mechanical response of the structure under a concentrated load is studied by carrying out static tests. From three aspects of the midspan deflection deformation, the strain of upper chord member and the tension of steel cable, this paper studies the influence of the internal inflation pressure, the tension of the lower chord steel cable, and the combinations of the steel cable on the bearing capacity of the structure. The results show that increasing the inflated air pressure to a certain extent can significantly improve structural stiffness, but compared with traditional spindle-shaped Tensairity, the prestress applied during the inflation process is not conducive to enhancing the structural load-bearing capacity. Changing the stress distribution of the upper chord member by tensioning the lower chord cable is beneficial to achieve a better material performance and weaken the adverse effects caused by the inflation of the airbag. The supplementary tension of the horizontal steel cable can improve the ultimate bearing capacity of the structure, thus contributing to the safety of the structure.