Bearing Capacity Of Structure Research Articles

Study of the flexural behavior of UHPC-HPC composite beams strengthened with BFRP sheet after chloride secondary erosion

To solve the issue of insufficient durability of reinforced concrete (RC) structures, a new structure of ultra-high performance concrete (UHPC)-high performance concrete (HPC) composite beam was designed, and the flexural performance of the composite beam strengthened with basalt fiber reinforced polymer (BFRP) after pre-damage was investigated. Results indicate that main cracks are formed and developed after the secondary erosion of chloride salt, leading to three forms of failure modes of the beams: BFRP sheet fracture and concrete crushing, BFRP sheet debonding and concrete crushing and BFRP sheet debonding. The test beam failure process can be classified into three stages: linear elasticity, crack development and yield. The maximum cracking and ultimate loads increased by 27.9 % and 35.8 %, respectively. The crack load growth rate of the beam decreased after 7 days (d) of secondary chloride salt erosion. The formula for calculating the peel strength of the UHPC-HPC composite beam was modified. The calculated bending capacity of the beam agrees well with the measured value. This study provides a reference for enhancing the lifespan and calculating the flexural bearing capacity of structures in corrosive environments.

Experimental Study of the Flexural Performance of GFRP-Reinforced Seawater Sea Sand Concrete Beams with Built-In GFRP Tubes.

The use of seawater sea sand concrete (SSSC) and fiber-reinforced polymer (FRP) has broad application prospect in island and coastal areas. However, the elastic modulus of FRP reinforcement is obviously lower than that of ordinary steel reinforcement, and the properties of SSSC are different from that of ordinary concrete, which results in a limit in the bearing capacity and stiffness of structures. In order to improve the flexural performance of FRP-reinforced SSSC beams, a novel SSSC beam with built-in glass FRP (GFRP) tubes was proposed in this study. Referring to many large-scale beam experiments, one specimen was used for one situation to illustrate the study considering costs and feasibility. Firstly, flexural performance tests of SSSC beams with GFRP tubes were conducted. Then, the effects of the GFRP tubes' height, the strength grades of concrete inside and outside the GFRP tubes, and the GFRP reinforcement ratio on the flexural behaviors of the beams were investigated. In addition, the concept of capacity reserve was proposed to assess the ductility of the beams, and the interaction between the concrete outside the GFRP tube, the GFRP tube and concrete inside the tube was discussed. Finally, the formulas for the normal section bearing capacity of beams with built-in GFRP tubes were derived and verified. Compared to the beam without GFRP tubes, under the same conditions, the ultimate bearing capacities of the SSSC beam with 80 mm, 100, and 200 mm height GFRP tubes were increased by 17.67 kN, 24.52 kN, and 144.42 kN, respectively.

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.

Study on Water Entry of a 3D Torpedo Based on the Improved Smoothed Particle Hydrodynamics Method

The water entry of a torpedo is a complex nonlinear problem, involving transient impact, free surface deformation, droplet splashing, and fluid–structure coupling, which poses severe challenges to traditional mesh methods. The meshless smoothed particle hydrodynamics (SPH) method shows unique advantages in capturing the complex features of the water entry of the torpedo at different entry angles. However, it still suffers from some inherent shortcomings, such as low surface discretization accuracy, poor discretization flexibility, and low calculation efficiency. In this study, an improved adaptive SPH algorithm is proposed to investigate the water entry of the torpedo accurately and efficiently. This method integrates meshless point generation and adaptive techniques simultaneously. The numerical results demonstrate that when the torpedo vertically enters the water at different velocities, the induced impact loads acting on the head of the torpedo fluctuate significantly with two peak values in the initial stage and thereafter stabilize in a later stage. The impact load acting on the torpedo, the entry depth of the torpedo, the splash height of the droplets, and the size of the cavity generated around the torpedo increase with the increment in the entry velocity. When the torpedo enters the water at different entry angles under the same initial entry velocity, both the vertical and the horizontal movements of the torpedo are observed, which results in more complex variations in parameters along the x- and y-axes. The findings and the corresponding numerical method in this study can provide a certain basis for the future designs of the entry trajectory and the structural bearing capacity of torpedoes.

Wind-Induced Response Analysis and Fatigue Life Prediction of a Hybrid Wind Turbine Tower Combining an Upper Steel Tube with a Lower Steel Truss

Based on the WindPACT-3MW wind turbine tower commonly used in wind power engineering, a finite element model (FEM) of a hybrid wind turbine tower combining an upper steel tube with a lower steel truss is designed and established. On this basis, a static optimization analysis, wind-induced vibration analysis, and fatigue life analysis of the hybrid tower structure are performed. The results show that under the same design parameters, the overall stiffness and static bearing capacity of the tower structure can be significantly improved by using subdivided truss webs, increasing the truss height as much as possible and increasing the width of the truss base appropriately. Under normal operation conditions, the response of the tower structure in the along-wind direction is significantly greater than the response in the crosswind direction, indicating that the aerodynamic thrust generated by the rotation of the blades is the main factor causing the wind-induced vibration of the tower structure. For the tower structure analyzed in this study, when considering the entire range of wind speeds from the cut-in wind speed to the cut-out wind speed, the fatigue life of the structure is 38.5 years.

Research on the anti-collapse performance of steel frame structures with infilled walls in the form of reduced beam sections connections

Steel has more deformation capacity and resistance to compression buckling than concrete materials, which providing steel frames a distinct edge in preventing collapse. This study examines the anti-collapse performance and mechanism of steel frame structures with infilled walls in the form of reduced beam section connections. It also examines the effects of wall thickness, frame aspect ratio, and connection control size on performance and addresses the applicability of current code formulas in the early deformation of the structure. The study discovered that steel frame structures with infilled walls in the form of reduced beam section connections can, during the failure stage, enhance the infilled wall's contribution to the collapse bearing capacity, thereby stimulating the structure's potential performance, in contrast to those with infilled walls in the form of non-reduced beam section connections. Due to the supporting effect of the double strut that forms inside the infilled wall during the failure stage, steel frame structures with infilled walls that have non-reduced beam section connections have higher deformation capacity than corresponding pure frames; however, this effect also decreases the deformation capacity of the structure with reduced beam section. Furthermore, the infilled walls cause the structure to collapse in a same way across a range of aspect ratios, yet their contribution to the structural bearing capacity differs across these same aspect ratios. It is noteworthy that altering the local connection control size can greatly enhance the structure anti-collapse performance, even in unfavorable aspect ratio scenarios. The study also discovered that the bearing capacity of the structure studied in this paper was overestimated by the FEMA356-2000 code and the MSJC code, which were used to predict the initial bearing capacity of infilled frames. The former's overestimation reaches a maximum of 39 %, while the latter's prediction is only accurate within a limited range of aspect ratios. Furthermore, the formula by Qian and Li, which has a maximum error of 9 % in bearing capacity prediction within the standard range of aspect ratios, is better appropriate for the failure mode of the structure described in this study.

Imperfections for the calculation of steel structures by the finite element method. Part 1

It is well known that imperfections are always present in structural elements. Imperfections can significantly affect the behavior and bearing capacity of steel structures, especially in the case of stability-related tasks. Therefore, inconsistencies must be taken into account in the loadbearing capacity model and their correct application (setting the shape and value) is a key point in the numerical analysis process. In recent decades, much attention has been paid in the domestic scientific space to updating imperfection models for use in numerical models, including taking into account modern more accurate manufacturing and installation technologies for steel structures. The purpose of this study is an analytical review and analysis of scientific research and technical literature, followed by synthesis and elaboration of recommendations on imperfections in relation to the calculation of steel structures using computer modeling technology, including the finite element method. The results of the study contain instructions on how to set the shapes and values of imperfections for different groups of imperfections. The article consists of two parts. The first part is devoted to the study of geometric imperfections, residual stresses and rules for the combination of imperfections, the second part of the article is devoted to equivalent imperfections.

Numerical simulation of local scour around an inclined monopile in steady current

Local scour around the underwater supports of constructions would reduce the embedment depth and bearing capacity of support structures, seriously threatening the safety of the structures. Most existing investigations focused on the local scour of a vertical pile. However, in practical engineering, inclined piles are widely applied in underwater foundation structures to withstand lateral loads. The pile inclination can result in flow field alteration around the pile, thereby affecting the development of local scour. Consequently, a threedimensional numerical model of local scour around an inclined pile under steady current is established using the open-source CFD package OpenFOAM, in which the hydrodynamics are solved based on the Reynolds-averaged Navier-Stokes (RANS) equations together with k – ω SST turbulence closure in this model. It is then coupled with both bed load and suspended load transport descriptions, which drive the resultant morphology of the bed. The numerical model is verified by comparing it with the existing laboratory experiment. Discussions are carried out on the effects of inclination angles on the flow field alteration and the local scour depth variation.

Study on bearing capacity and damage mode of carbon fiber composite J-type structures in oilfield completion tool connections

Carbon fiber composite structures have a broad application prospect in oilfield completion tool module connection. However, the material failure mechanism is still unclear. In this paper, the mechanical properties and failure mode of T700/7901 composite J-type structure are investigated from experimental and finite element perspectives. Firstly, the load-carrying and failure properties of the structure were analyzed through typical mechanical property experiments such as tensile, bending, and compression, and the fiber, matrix damage, and delamination damage are the main reasons for the failure of the mechanical properties of the material. Secondly, a numerical model of the progressive damage ontological relationship of the composite material was established, and the accuracy of the model was verified by combining the experimental results. Based on the above study, this paper proposes the failure mechanism and optimization of composite J-type, which provides useful guidance for the design of fiber composite structures for oilfield completion tool types in the future.

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 study and refined numerical simulation of ultimate pressure-bearing performance of rope-reinforced airship envelope structures

Stratospheric airships require a lightweight envelope to contain lighter-than-air buoyancy gas, making the lightweight design and pressure-bearing performance of the envelope structure a key research issue. The stress state at different cross-sectional positions of the airship envelope structure is different, resulting in a low utilization rate of the overall material performance of the envelope structure. This paper proposes a design scheme for reinforcing envelope structures with sliding reinforcing cable to improve the bearing capacity of the composite fabric structure while reducing its weight, ultimately achieving the optimal strength-to-weight ratio. Two types of composite fabric structures (A-airship and B-airship) were subjected to inflatable burst tests, and the strain changes in the envelope gores were analyzed by digital image correlation. Through re-assembly of the broken composite fabric pieces and analysis of their tear textures, crack origination positions, failure causes, and the stress behavior and state at the failure position were identified. An envelope structural model with consideration of the cutting pattern effect was established, allowing the stress distribution of the envelope to be analyzed and the damage positions to be more accurately predicted. Based on the analysis of the ultimate pressure-bearing performance of an airship envelope structure, a novel idea of incorporating coupled tensile-shear stress into the strength criterion was proposed. Through the data in the study and existing references, it is verified that the strength criterion can accurately predict the ultimate pressure-bearing performance of the envelope structure.

Numerical simulation on the load-bearing capacity of CFRP-strengthened concrete arches

To investigate the bearing capacity of concrete structures strengthened by carbon fiber reinforced composite (CFRP), this study conducted numerical simulation research on seven CFRP-strengthened concrete arch structures with five different strengthening schemes. The finite element model was established by HYPERMESH, the simulation results were compared with the experimental results to verify the accuracy of the model. Based on this, the interfacial bonding performance of concrete and CFRP under different strengthening schemes was analyzed, and the static damage mode of the reinforced concrete arch structure was revealed. The results indicate that the application of CFRP to the surface of a concrete arch will increase the linear segmental stiffness, cracking load, and ultimate load of the structure. The five strengthening schemes in this paper provide enhancements ranging from 2.9 % to 57.6 % for concrete arch cracking loads, from 3.3 % to 14.7 % for ultimate loads, and from 1.1 % to 17.6 % for stiffness. If both the inner and outer sides are strengthened with CFRP, the ultimate bearing capacity of the arch structure can be significantly enhanced. Circumferential wrapping of CFRP can delay the concrete cracking and further enhance the bearing capacity of the arch, and the strengthening effect can be maximized. This study can provide a valuable reference for the strengthening of old concrete arch structures and the construction of newly assembled arch tunnels.

Investigation of the Post-Fire Behavior of Different End-Plated Beam–Column Connections

Heat affects the mechanical properties of steel and the bearing capacity of steel structures, with joints being a crucial factor in determining their behavior. Steel can regain its mechanical properties that are lost owing to heat if the temperature remains below 600 °C, allowing for the possibility of reusing steel after cooling. In such cases, it becomes essential to assess the damage caused by heat exposure to decide whether to demolish the structure or continue using it. However, continuing its usage requires anticipating the potential negative effects of heat. To achieve this, it is necessary to determine the behavior of steel joining tools experimentally or numerically after exposure to heat. This study aims to ascertain the post-fire behavior of various end-plated beam and column connections, providing a cost-effective alternative to expensive fire experiments. Three different end-plated combination models were heated to a specified temperature, and steel frames were constructed after the elements cooled. Six three-point bending tests were conducted, and the experimental data obtained were validated using finite element models. The results indicate that the temperature causes a reduction in the bearing capacity of the joint, and the length of the end plate has a significant effect on the connection behavior. The finite element model validated by experiments is expected to facilitate numerical studies with different characteristics.

Free vibrations of variablesection beams taking rotational and frictional forces into account

Introduction. Beams are widely used in the construction industry as load-bearing structures of bridges, overpasses, coverings, slabs, stairs, equipment platforms, etc. In order to fully utilize the bearing capacity of such structures and to reduce the rate of material consumption, beams of variable cross-section along the length can be used. During operation, such structural elements are subjected to various types of vibrations, which determines the relevance of studying various aspects of vibrational motion.Aim. To apply numerical methods for studying the influence of rotational inertial forces in the presence of viscous frictional forces on free vibrations of variable-section beams. This area of research presents interest, since the calculations are directly related to the determination of frequencies and forms of natural vibrations of structures.Materials and methods. Free vibrations were described by a homogeneous partial differential equation of hyperbolic type. The methods of variable separation and finite differences were used. A discrete domain in the form of a set of uniform grid nodes and a homogeneous system of algebraic equations were introduced. The system of equations in the matrix-vector form was used.Results. The spectra of natural frequencies, damping coefficients, and eigenforms of beam vibrations are determined. It is shown that the coefficient matrix has a banded and pentadiagonal form. The matrix elements are functions of the characteristic index. The damping coefficient and the frequency of free vibrations are determined from a system of two nonlinear equations. The solution of the system of equations is found using the method of coordinate descent. An example of calculation of a welded I-beam is considered. Five elements of the spectra of damping coefficients and natural frequencies are calculated.Conclusions. State-of-the-art MATLAB solvers allows numerical and graphical methods to be combined. In the solved examples, the advantages of these methods were successfully applied to determine the eigenvalues of matrices and eigenfunctions. The high validity and accuracy of the results obtained confirm the simplicity and versatility of the methodology for determining the characteristics of free vibrations of beams of variable cross-section.

Model Test Study on the Vertical Uplift Bearing Characteristics of Soil Continuous Solidified Pile Group Foundations

To solve the problem of the high bearing capacity of structures in deep and weak soil layers, we invented a new type of pile group foundation in which the soil was continuously solidified between piles (hereinafter referred to as the SCS pile group foundation). Considering the two key factors of pile spacing and CSM depth, the antipulling load characteristics of SCS pile group foundations in dry sand were studied via indoor half-model tests and numerical simulations. The results showed that the ultimate uplift capacity of the SCS pile group foundation with a 2D–6D CSM depth was about 2–3 times that of the traditional pile group. When the stiffness of the CSM is so large that its effect can be ignored, the greater the pile spacing is, the greater the ultimate uplift capacity is. For the same pile spacing, the greater the depth of the CSM is, the greater the ultimate uplift bearing capacity is. When the CSM depth is greater than 10D, the uplift effect of the CSM can be effectively exerted, and the antipulling advantage of the SCS pile group foundation can be fully utilized. This study provided a reference for the antipulling design of SCS pile foundations.

Interfacial debonding detection for steel-concrete composite structures part I: Benchmark test and signal calibration of contact and non-contact measurement

Interfacial bonding state is one of the crucial factors affecting the bearing capacity and durability of steel-concrete composite structures (SCCS). To achieve efficient interfacial debonding detection for SCCS, contact and non-contact method-based novel non-destructive test (NDT) is performed in this study. In order to figure out the dominant frequency and vibration mode of steel plate above interfacial debonding defects in SCCS, systematic theoretical analysis and finite element simulation are carried out. Then, the contact NDT experimental study is carried out utilizing piezoelectric lead zirconate titanate (PZT) sensors and acceleration meters. Conventional and high-frequency microphones, as well as high-precision scanning laser Doppler vibrometer (SLDV), are introduced for non-contact measurement. According to benchmark test on steel plate-bonded reinforced concrete cube with preset interfacial debonding defects in different dimensions, the signal calibration with Pearson correlation coefficient is further performed to quantitatively assess the variation and difference between contact and non-contact measurements. Research findings indicate that the synthetic experimental testing platform integrating contact vibration measurement, non-contact SLDV, and acoustic vibration measurement established in this study is capable of performing non-destructive tests using impact-response method, impact-echo technique, impact-acoustic vibration approach, and modal test simultaneously. Moreover, SLDV can precisely obtain the vibration mode of steel plates above interfacial debondings. Aided by high-precision scanning laser-based vibration measurement, the accuracy and efficiency of in-situ non-contact tests can be improved. The research findings in this study can provide practical guidance on non-destructive evaluation of interfacial damages in SCCS.

Mechanical performance and design of aluminium alloy beam string structures

Aluminium alloys are widely used in spatial structures because of their lightweight, high-strength, and favourable corrosion resistance characteristics. However, the low elastic modulus of this material results in reduced structural stability compared to that of other construction materials. Therefore, this study proposes incorporating prestress into aluminium alloy structures to improve their structural performance. In this study, two types of aluminium alloy beam string structures (ABSS) are presented along with their corresponding joints. Through static tests conducted on various ABSS joint configurations, this study assesses the in-plane bearing capacity and failure modes of the structures, revealing the mechanism by which prestressing enhances the in-plane performance of aluminium alloy beams. Specifically, this study investigates the influence mechanisms of various factors, such as the rise-span ratio, sag-span ratio, and initial cable force, on the in-plane bearing performance of an ABSS through numerical simulations. Finally, a method calculating the ultimate bearing capacity of aluminium alloy beam string structures is derived by employing the Ritz method, accompanied by design recommendations. The results demonstrate that introducing a prestress can significantly increase the load-bearing capacity by 5–6 times, and the flange-connected joint is determined as more suitable for being implemented in ABSS.

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.

Working mechanism evaluations of full-scale joints with bolted-cover plate connection for modular steel buildings

The force-reliability of the modular structural joints is crucial for ensuring the structural integrity of modular steel buildings. However, the welds connecting the beam and column within the module are susceptible to tear during seismic events. This mode of failure greatly undermines the ability of these joints to withstand seismic forces. Four full-scale modular structural joints with bolted-cover plate connection were designed and conducted for seismic performance testing, emphasizing the significance of methods such as reinforcing diagonal braces and strengthening flanges on the protective effect of beam–column welds in the module. The simplified modular structural joint and frame finite element model were proposed based on experimental data, refined finite element modeling, and theoretical analysis. The findings suggest that the seismic behavior of the modular structural joint remains unaffected by variations in axial compression ratio within the designed range of parameters. The beam–column weld of the module in the reinforced joint exhibits almost no weld tearing, and both strengthening methods demonstrate exceptional capacity for energy dissipation. The proposed simplified modeling method facilitates the efficient determination of the modular structural joint bearing capacity and the lateral stiffness of the modular frame. The research findings presented in this paper can serve as a valuable reference point for the engineering design of modular steel structures.