Failure Phenomena Research Articles

Infective Endocarditis by Listeria Species—A Systematic Review

Infective endocarditis (IE) is a disease associated with significant morbidity and mortality. It is more commonly caused by Gram-positive cocci, but Gram-positive bacilli may seldom cause the disease. Listeria monocytogenes is an aerobic Gram-positive coccobacillus and a foodborne and opportunistic pathogen most commonly causing gastrointestinal infections, even though bacteremia, sepsis, meningitis, and fetal infections may also occur. Listeria IE has rarely been described, with most reports being case reports or case series. Thus, the characteristics of this disease remain largely unknown. This systematic review aimed to present all published Listeria IE studies and describe their characteristics. A search of PubMed, Scopus, and the Cochrane Library for studies providing information on epidemiology, clinical findings, treatment, and outcome of Listeria IE cases was performed. A total of 54 studies containing data from 62 patients were included. Among all patients, 64.5% were male; the median age was 69 years. Among all patients, 54.8% had a history of a prosthetic valve. The aortic valve was the most commonly affected, followed by the mitral. Fever, heart failure, and embolic phenomena were the most commonly encountered clinical findings. The only isolated species was L. monocytogenes. Antimicrobial resistance was relatively low for aminopenicillins and aminoglycosides, the most commonly used antimicrobials for treating L. monocytogenes IE. Surgery was performed in 27.4% of patients. Mortality was 37.1%. Patients who survived were more likely to have had a prosthetic valve, to have necessitated transesophageal echocardiography for the diagnosis, to have mitral valve IE, and to have had surgical management; however, no factor was identified in a multivariate logistic regression model as an independent factor for overall mortality.

Process optimization of wet etching for split gate trench MOSFET

Abstract In this paper, the influence of etching technology on the performance of Split Gate Trench (SGT) MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistor) is studied, and the significance and contribution of these improvements in the fields of mechatronics, robotics and control systems are discussed. Etching can be categorized into wet etching and dry etching, with wet etching being widely used for etching the gates of SGT MOSFETs. Due to the isotropic nature of wet etching, issues such as undercutting, trenching, and insufficient link-up region length can arise, leading to short circuits between the gate and the source. The improvement of this problem directly promotes the enhancement of mechatronics system efficiency, the improvement of robot dynamic performance and accuracy, and the realization of efficient control strategies in control systems. By optimizing the process flow to enhance the adhesion of photoresist, increase the density of the HDP (High Density Plasma) deposited oxide film, and adjust the etching rate and frequency of wet etching, it is possible to mitigate the issues of isotropy and insufficient precision in wet etching. These improvements address failure phenomena and enhance product yield.

Seismic behavior of exterior joint of CFDST column to steel beam with RC slab

To investigate the seismic performance of an exterior joint connecting concrete-filled double-skin steel tubular (CFDST) column to steel beam with reinforced concrete (RC) slab, four scaled-down joint specimens were designed at a ratio of 1:2. Quasi-static tests were conducted with different axial compression ratios were performed, and the failure mode, hysteresis curve, skeleton curve, bearing capacity, energy dissipation capacity, strength and stiffness degradation, and strain analysis of the composite joint were analyzed. A finite element method (FEM) model of the joint was constructed and validated against the obtained experimental results. Additionally, a parametric study was carried out to investigate the influence of various factors, including the hollow ratio of the CFDST column, the concrete strength of the slab, the thickness of the slab, and the width-to-thickness ratio of the outer steel tube on joint. Based on experimental studies and finite element analysis (FEA), a theoretical calculation method was proposed to evaluate the flexural capacity of the composite joints. The test results showed that the composite exterior joint specimens with RC slab failed at the beam end. Typical failure phenomena of fracture at the steel beam and horizontal end plate interfaces, steel beam flange buckling, and concrete crushing at the RC slab were observed in the experiments. While the interior joint specimen experienced significant plastic deformation and buckling at the column flange. The hysteresis curve of the specimen is elliptical and full without pinching. The presence of RC slab can effectively improve the ultimate bearing capacity, initial stiffness and energy dissipation capacity of the specimen. The FEA results show that the bearing capacity of the composite joints was improved significantly with the increase of the thickness of the slab and the width-thickness ratio of the outer steel tube. The theoretical calculation results of the flexural capacity of the joint are 86 %–112 % of the results of the finite element calculation. The stability and accuracy of the calculation method are excellent and can be effectively applied to calculate the flexural capacity in CFDST composite structural systems.

Large ventricular myxoma causing inflow and outflow obstruction of the right ventricle; A Case Report

BackgroundMyxomas are the most common primary benign heart tumors, typically found in the left atrium, with only 2–4% occurring in the right ventricle. Clinical presentations vary widely, including congestive heart failure and systemic embolic phenomena. This case report describes a rare right ventricular myxoma causing both inflow and outflow obstruction, presenting as progressive exertional dyspnea.Case PresentationA 23-year-old male presented with two weeks of worsening exertional dyspnea. He was stable but tachypneic with a systolic murmur over the tricuspid area. Elevated erythrocyte sedimentation rate (ESR) and C-Reactive protein (CRP) were noted, while other lab tests were normal. Imaging, including echocardiography and chest tomography scan (CT) revealed a 4 × 3.8 × 4.6 cm mass in the right ventricle extending to the pulmonary trunk. Surgical resection via right ventriculotomy was performed, and histopathology confirmed myxoma. The patient recovered uneventfully.ConclusionRight ventricular myxomas, though rare, can cause significant obstruction and present with diverse symptoms. Timely diagnosis using imaging techniques like echocardiography is crucial. Surgical resection remains the definitive treatment, offering excellent outcomes and low recurrence rates. Early intervention is vital to prevent serious complications and ensure favorable patient prognosis.

Research on the corrosion mechanism of Q345R steel under water-oil two-phase flow with the HCl and NH4Cl corrosive medium in low-temperature system of petrochemical plants

The serious corrosion failure phenomenon of HCl and NH4Cl in the water-oil two-phase flow are usually occurred in the low-temperature system of petroleum refinery facilities. In this paper, the corrosion mechanism of these corrosive medium in two-phase flow environment was investigated in detail by using corrosion weight loss, electrochemical measurement methods, surface analysis techniques, and numerical research methods. The results indicate that the corrosion rate of Q345R steel in an HCl-NH4Cl coupling medium falls between the rates observed with each medium alone. The stirring of the corrosive fluid creates an unstable oil-in-water emulsion. The formation of an oil film on the surface of Q345R steel slows down the corrosion process and alters the surface corrosion morphology when the oil phase was not originally present. Increasing the proportion of the water phase accelerates the corrosion rate, and the stronger wettability of the oil phase makes the loose γ-FeOOH products easier to cover the surface, which can effectively prevent the mass transfer and corrosion reaction process.

LITERATURE SURVEY OF WEB CRIPPLING EXPERIMENT ON CEE-SHAPED SPECIMENS WITHOUT PERFORATIONS

Cold-Formed Steel (CFS) products are widely used in the field of building construction due to their inherent characteristics such as high material strength and design versatility. Depending upon their application and loading configuration, these structures are prone to different types of failures. Web crippling is a type of localized failure mode observed in CFS beam structures due to concentrated loading over them. The web crippling behavior in CFS products are influences by various factors including geometric, material, loading and environmental properties, making it a complex failure phenomenon. This literature survey investigates ten research studies performed on Cee-shaped CFS specimen, focusing on various dimensions and loading configurations. By examining the experimental and analytical methodologies considered across various studies, the paper attempts to consolidate the key findings which could propose future researches. The survey offers an insight into discrepancies in the design practices for predicting the ultimate web crippling strength in Cee-shaped Cold-Formed Steel specimens.

An analytic traction-displacement model for a reinforcing ligament bridging a crack at an arbitrary angle, including elastic, frictional, snubbing, yielding, creep, and fatigue phenomena

A micromechanical model is developed that generates analytic expressions for the crack displacement vector u given an arbitrary far-field stress state σa for a crack that is bridged by an array of ligaments oriented at an arbitrary angle with respect to the crack plane. The model is applicable to various materials, e.g., fibrous ceramic composites, or polymer composites reinforced by stitches or z-pins or woven tows, and deals with interfacial friction, enhanced friction due to increased contact pressure (“snubbing”), and the possibility of ligament deflection enabled by yield or damage. The model also conveniently incorporates ligament failure and rate dependent phenomena (fatigue or creep). Adaptability of the model is enabled by the definition of a standard Reference Model, which generates analytic expressions for the crack displacement for given possible yield, ligament deflection, and friction and snubbing effects and is invariant for all geometrical and material choices. The switching on or off and the strengths of all phenomena are governed by assigning values to a handful of material parameters. The material parameters will generally be calibrated against data in a top-down strategy, the model thereby mapping material selection onto engineering fracture via the predicted bridging relationship u[σa]. The relationship u[σa] can depend strongly on bi-angular ligament orientation. Yield and deflection can change u[σa] qualitatively, e.g., by creating fracture surface contact even when σa includes substantial opening tension. Snubbing has significant effects, including possible stabilization of the pullout of a finite ligament. Since model output is computed via analytic expressions, its speed will support the model's use in large-scale material simulations or as constraining physical information in machine learning algorithms.

Characterization of Wormhole Growth and Propagation Dynamics during CHOPS Processes by Integrating Rate Transient Analysis and a Pressure-Gradient-Based Sand Failure Criterion in the Presence of Foamy Oil Behavior

Summary Characterization of wormhole growth and propagation dynamics has been made possible with the semi-analytical models developed in this work by integrating both rate transient analysis (RTA) and a pressure-gradient-based (PGB) sand failure criterion in the presence of foamy oil behavior. The nonlinearity caused by the foamy oil properties is linearized using pseudofunctions, while the source function and finite difference methods are applied to obtain the solutions for the linearized models in the matrix and wormhole subsystems, respectively. A sequential method is adopted to solve the coupling fluid-solid problem, where new wormhole segments can be generated once the PGB sand failure criterion has been achieved, while their updated petrophysical properties can be sent back to obtain the solutions for the fluid flow in the next time interval. Furthermore, the influence of sand failure/fluidizing and foamy oil properties on the dynamic wormhole network can be investigated with the generated type curves. Both wormhole growth and foamy oil flow dictate an upward fluid production at the early times, while the production-induced pressure depletion dominates the declining production at the late times. The fractal wormhole networks can be dynamically characterized by history matching the field fluid and sand production profiles. Both the sand failure degree and foamy oil properties dictate the effective wormhole coverage and intensity. Sand production is found to be influenced by both the breakdown pressure gradient and wormhole conductivities, while oil production rate can be dominated by the wormhole coverage and intensity. Foamy oil flow can increase the oil production rate and increase the wormhole coverage compared with the conventional oil. The newly developed method in this work has been validated and then applied at field scale to dynamically characterize the wormhole growth and propagation by considering both the sand failure phenomenon and foamy oil properties within a unified, consistent, and accurate framework. Compared to the conventional numerical simulations, the novelty of such a semi-analytical method can not only allow us to characterize the growth and propagation dynamics of the fractal-like wormholes without the need for grid refinement near the wormhole grids but also take the complex sand failure and foamy oil behavior into account. In addition, it can minimize the impact of grid orientation effects in numerical simulations, enabling the growth and propagation of the wormholes in arbitrary directions rather than orthogonal directions conditioned to the largest pressure gradient.

Quasi-static cyclic tests of FRP-confined steel-reinforced HPFRCC circular columns

This study presents a novel composite component comprising of steel-reinforced high-performance fiber reinforced cementitious composites (HPFRCC) circular columns confined by fiber-reinforced polymer (FRP), with the goal of improving the mechanical behavior of conventional reinforced concrete (RC) columns. Quasi-static cyclic loading tests were conducted to investigate various aspects of the column specimens, including failure phenomena, load-displacement response, sectional compression-bending performance, plastic hinge length, and lateral strain distributions in the FRP jacket, etc. A self-designed frictional force measurement device was employed to accurately measure the actual force borne by the specimen. The experiment results revealed that FRP confinement effectively improved the load-bearing capacity and deformation capacity of the specimens and delayed the deterioration of the sectional compression-bending performance. The superior tensile ductility of HPFRCC led to increased yielding displacement and peak load compared to FRP-confined concrete specimen, although this enhancement was limited. Furthermore, the peak load of the FRP-confined HPFRCC specimen increased with axial load, while the sectional compression-bending performance after the peak load remained relatively stable until approaching the collapse prevention (CP) limit state.

Analysis on failure test and evaluation about refueling receptacle of onboard hydrogen system

ABSTRACT As the key component of the onboard hydrogen system, the service life and failure problem of the refueling receptacle easily leads to the hydrogen leakage accident which give rise to the suffocation, the frostbite, the burns, and the impact injuries. The typical hydrogen leakage accidents include the accidental leakage, the ignition, the deflagration, and the explosion. Therefore, the failure test and evaluation problem about the refueling receptacle is focused on. In this paper, the failure test and evaluation about the refueling receptacle covering the vibration resistance performance, the temperature resistance performance, and the durability was studied. First, the failure mechanisms of the refueling receptacle involving the vibration, the temperature, and the durability based on the vehicle operating conditions were clarified. Second, according to the test experience and the vehicle operating condition, the test methods about the failure phenomenon of the refueling receptacle were established, respectively. Finally, the failure test results of the refueling receptacle were analyzed. The failure of the refueling receptacle may caused by the aging and failure of sealing element, the metal creep aging and material damage, the decline in the contact stress at the low-temperature connection, the loose connection, and the internal structural ectopia.

Analysis of Topological Properties and Robustness of Urban Public Transport Networks

With the acceleration of urbanization, public transport networks are an important part of urban transport systems, and their robustness is critical for city operation. The objective of this study is to analyze the topological properties and robustness of an urban public transport network (UPTN) with a view to enhancing the sustainability of urbanization. In order to present the topological structure of the UPTN, the L-Space complex network modeling method is used to construct a model. Topological characteristics of the network are calculated. Based on single evaluation indices of station significance, a comprehensive evaluation index is proposed as the basis for selecting critical stations. The UPTN cascading failure model is established. Using the proportion of the maximum connected subgraph as the evaluation index, the robustness of the UPTN is analyzed using different station significance indices and deliberate attack strategies. The public transport network of Xuzhou city is selected for instance analysis. The results show that the UPTN in Xuzhou city has small-world effects and scale-free characteristics. Although the network has poor connectivity, it is a convenient means to travel for residents with many independent communities. The network’s dynamic robustness is demonstrably inferior to its static robustness due to the prevalence of cascading failure phenomena. Specifically, the failure of important stations has a wider impact on the network performance. Improving their load capacity and distributing the routes via them will help bolster the network resistance against contingencies. This study provides a scientific basis and strategic recommendations for urban planners and public transport managers to achieve a more sustainable public transport system.

Frequency switching leads to distinctive fast–slow behaviors in Duffing system

The slowly forced Duffing system has been found to exhibit unique fast–slow behaviors in descending frequency switching scheme, the typical of which is the sliding bursting, which is instructive for understanding the dynamics of ubiquitous frequency switching systems in scientific research and practical engineering. This paper is devoted to further refining the fast–slow dynamics of the slowly forced Duffing system with another commonly encountered frequency switching scheme, i.e., the ascending frequency switching, characterized by switching the frequency synchronously according to the increase or decrease of state variable values. Taking the forcing amplitude as an example, this paper provides a theoretical way to fully summarize the fast–slow behaviors in frequency switching systems with the variation of parameter values based on the proposed superposition analysis of one- and two-parameter bifurcations of subsystems. As a result, two typical bifurcation structures and eight threshold windows with distinct switching vector fields therein are identified, inducing up to ten different bursting patterns. Among them, several novel fast–slow dynamics, such as multiple jumps hysteresis loop formed by boundary equilibrium bifurcations and the switching failure phenomena, are presented and investigated. In particular, the underlying mechanism of threshold modulation, i.e., the evolution of unconventional bifurcations, is also found. These findings contribute to complementing and contrasting the existing studies on the fast–slow dynamics of frequency switching systems.

Transverse failure prediction of unidirectional carbon fiber reinforced polymer composites subjected to uniaxial and biaxial loading by stress-triaxiality-dependent computational micromechanics

Accurate characterizing the mechanical behavior of the component materials is crucial for failure predicting of unidirectional carbon fiber reinforced polymer (UD CFRP) composites. A stress-triaxiality-dependent micromechanics model is developed for the transverse failure prediction of the composites in this study, in which the stress triaxiality is innovatively adopted to define the plastic hardening behavior of the matrix material. Therefore, diverse hardening behaviors generated by heterostructures, accurate confirmation of biaxial failure, as well as hardening behavior evolution caused by stress status changes during loading process can be considered. The accuracy performance of the micromechanics model is provided by comparing the predicted results (stress–strain curves, RVE profiles and failure points) with existing experimental data and failure envelopes of failure criterion. The comparison results show that the micromechanics model can accurately capture the failure phenomenon and failure evolution mechanism of the composite under uniaxial and biaxial loadings.

Effects of soldering temperature and preheating temperature on the properties of Sn–Zn solder alloys using wave soldering

Purpose This study aims to address the problem of low-temperature wave soldering in industry production with Sn-9Zn-2.5 Bi-1.5In alloys and develop qualified process parameters. Sn–Zn eutectic alloys are lead-free solders applied in consumer electronics due to their low melting point, high strength, and low cost. In the electronic assembly industry, Sn–Zn eutectic alloys have great potential for use. Design/methodology/approach This paper explored developing and implementing process parameters for low-temperature wave soldering of Sn–Zn alloys (SN-9ZN-2.5BI-1.5 In). A two-factor, three-level design of the experiments experiment was designed to simulate various conditions parameters encountered in Sn–Zn soldering, developed the nitrogen protection device of waving soldering and proposed the optimal process parameters to realize mass production of low-temperature wave soldering on Sn–Zn alloys. Findings The Sn-9Zn-2.5 Bi-1.5In alloy can overcome the Zn oxidation problem, achieve low-temperature wave soldering and meet IPC standards, but requires the development of nitrogen protection devices and the optimization of a series of process parameters. The design experiment reveals that preheating temperature, soldering temperature and flux affect failure phenomena. Finally, combined with the process test results, an effective method to support mass production. Research limitations/implications In term of overcome Zn’s oxidation characteristics, anti-oxidation wave welding device needs to be studied. Various process parameters need to be developed to achieve a welding process with lower temperature than that of lead solder(Sn–Pb) and lead-free SAC(Sn-0.3Ag-0.7Cu). The process window of Sn–Zn series alloy (Sn-9Zn-2.5 Bi-1.5In alloy) is narrow. A more stringent quality control chart is required to make mass production. Practical implications In this research, the soldering temperature of Sn-9Zn-2.5 Bi-1.5In is 5 °C and 25 °C lower than Sn–Pb and Sn-0.3Ag-0.7Cu(SAC0307). To the best of the authors’ knowledge, this work was the first time to apply Sn–Zn solder alloy under actual production conditions on wave soldering, which was of great significance for the study of wave soldering of the same kind of solder alloy. Social implications Low-temperature wave soldering can supported green manufacturing widely, offering a new path to achieve carbon emissions for many factories and also combat to international climate change. Originality/value There are many research papers on Sn–Zn alloys, but methods of achieving low-temperature wave soldering to meet IPC standards are infrequent. Especially the process control method that can be mass-produced is more challenging. In addition, the metal storage is very high and the cost is relatively low, which is of great help to provide enterprise competitiveness and can also support the development of green manufacturing, which has a good role in promoting the broader development of the Sn–Zn series.

ОЦЕНКА РЕЗУЛЬТАТОВ ПРИМЕНЕНИЯ АЛГОРИТМА ВЫБОРА ОПТИМАЛЬНОГО ХИРУРГИЧЕСКОГО ДОСТУПА К ЗАБРЮШИННОМУ ПРОСТРАНСТВУ У ПАЦИЕНТОВ С РАЗЛИЧНЫМИ ПАРАМЕТРАМИ КОНСТИТУЦИИ.

Relevance. Despite the rapid development and predominance of endovideosurgical techniques in the treatment of pathologies of organs and structures of the retroperitoneal space, the implementation of transperitoneal or retroperitoneal approaches for open surgical interventions remains a routine activity. Surgical treatment of various pathologies of retroperitoneal localization leads to the development of nonspecific life-threatening complications in 23.8% - 30% of clinical observations, and associated mortality - 7.2% - 11% of cases. Previously, our works presented the results of comparing the number of this type of complications when using laparotomy or retroperitoneal access, depending on the constitutional parameters of the patient. An assessment was made of the significance of the influence of constitutional parameters on the development of nonspecific life-threatening complications, on the basis of which an algorithm for choosing the optimal surgical access to the structures of the retroperitoneal space was developed [patent application No. 2024113445 dated May 17, 2024]. Purpose of the study. To evaluate the effectiveness of using an algorithm for selecting the optimal surgical approach in the surgical treatment of pathologies of organs and structures of retroperitoneal localization. Materials and methods. Comparative analysis of the results of surgical treatment of patients with various surgical pathologies of the retroperitoneal space. Group I (n = 167), where the choice of surgical approach was determined using the “optimal surgical approach selection algorithm.” Group II (n = 284), in which the choice of access to the structures of the retroperitoneal space was not unified and was chosen without taking into account the constitutional parameters of the patient. In the perioperative period, the duration of surgical intervention, the volume of intraoperative blood loss, the number of days of stay in the intensive care unit, the time of postoperative respiratory support, the duration of postoperative intestinal paresis and the number of postoperative bed days were assessed. Criteria assessed in the postoperative period: development of myocardial infarction, acute cardiovascular failure, ARDS with the development of respiratory failure, acute kidney injury; cases of development of ischemic colitis and small intestinal obstruction, requiring repeated interventions, as well as the phenomenon of multiple organ failure. Wound complications included failure of retroperitoneal and laparotomy wounds, including eventration. To calculate quantitative characteristics, the median (Me) and percentiles (Q0.25 - Q0.75) were determined. Calculation of statistical significance between groups was performed using the Mann-Whitney U test**, for comparison of qualitative indicators - the Chi-square test* in IBM SPSS Statistics 25 software. Results. In group I, compared with group II, there was a shorter surgical intervention time [140.8 vs 179.5] min, p = 0.031**, a smaller volume of intraoperative blood loss [280.4 vs 413.3] ml, p = 0.024* *; postoperative respiratory support [4.5 vs 8.5] hours, p = 0.041**; length of stay in the intensive care unit [1.8 vs 3.4] days, p = 0.021**; postoperative intestinal paresis [1.2 vs 4.8] days p = 0.024**; and duration of total postoperative hospital stay [9.1 vs 16.4] days p = 0.003**. The number of postoperative nonspecific life-threatening and wound complications in group I was 24 (14.4%), and in group II - 64 (22.5%) cases (p = 0.023*). The number of complications-related deaths in group I was 9 (5.4%); in group II - 32 (11.26%) cases (p = 0.037*). Conclusion. The use of an algorithm for selecting the optimal surgical approach for surgical treatment of pathologies of organs and structures of the retroperitoneal localization of the access leads to a reduction in the number of nonspecific life-threatening complications to 14.4%, and associated deaths to 5.4%.

Predictive factors of atrioventricular conduction disorders

Atrioventricular conduction disorders represent an alteration in the normal function of the heart’s electrical conduction system, a system that connects the atria and ventricles through the atrio-ventricular node and the His-Purkinje system. Consequently, bradycardia can develop and lead to the occurrence of symptoms (dizziness, loss of consciousness, tachyarrhythmias, heart failure phenomena). Identifying patients at risk of developing atrioventricular conduction disorders will allow early interventions on risk factors and improvements in prognosis. This narrative review explores the risk factors that determine the development and progression of atrioventricular conduction disorders. We will discuss traditional risk factors (age, sex, arterial hypertension, ischemic cardiac disease, diabetes, chronic kidney disease), but also risk factors that are currently being researched (genetic predisposition and inflammatory markers). Finally, we will discuss the limitations and challenges of predicting risk factors for atrioventricular conduction disorders.

Failure analysis and structural improvement of helicopter landing gear seals based on experiments and three-dimensional numerical simulation

The utilization of O-ring seal structures in landing gears has historically been associated with high rates of failure. Therefore, this study analyzes helicopter landing gear friction failures based on experimental and numerical simulations. The model is designed to replicate the failure phenomena including “seal extrusion”, “seal leakage”, “seal wear”, and “seal distortion”, and to further investigate causes of failure. Corresponding failure criteria are also presented. Addressing the deficiencies inherent in the original O-ring structure, three composite seal structures—namely, the VL seal, double triangle seal, and T-seal—are introduced to enhance the respective seal structure of the buffer pillar. The findings exhibit that, following the transition to the composite seal structure, the strain peaks are optimized. Finally, this paper offers optimal contact pressure ranges for the optimized seals.

Research Progress on Shear Characteristics and Rapid Post-Disaster Construction of Narrow-Width Steel Box–UHPC Composite Beams

The narrow-width steel box girder is an important type of steel–concrete composite bridge structure, which is usually composed of reinforced concrete wing plates, narrow steel boxes partially injected with concrete, and shear connectors that promote shear force transfer. The utilization of narrow-width steel box girders, augmented by partially filled concrete, embodies the synthesis of steel and concrete elements, fostering structural efficiency. Moreover, its attributes, including reduced structural weight, diminished vertical profile, enhanced load-bearing capacity, and augmented stiffness, have prompted its gradual integration into bridge engineering applications. In this study, the calculated values of shear strength under three current design codes were reviewed, and the shear failure phenomena and its determinants of narrow-width steel box–ultra-high-performance concrete (UHPC) composite beams under negative bending moment conditions were investigated, which were mainly determined by shear span ratio, concrete wing plate, UHPC steel fiber content, UHPC plate thickness, and transverse partition inside the box. Concurrently, this paper evaluates two innovative structural designs, including a double-narrow steel box girder and a three-narrow steel box girder. In addition, strategies to reduce crack formation under the negative bending moment of long-span continuous narrow and wide box girder abutments are discussed, and we show that this measure can effectively control the formation of cracks to support the negative bending moment zone. At the same time, the scope of the application of a narrow-width steel box girder composite bridge is reviewed, and the conclusion is that a narrow-width steel box girder is mainly used in small-radius flat-curved bridges or widened-ramp bridges with a span of 30 m or more in interworking areas and in the main line with a 60–100 m span in mountainous or urban areas. Finally, the research direction of the shear resistance of the UHPC–narrow steel box girder under negative bending moments is proposed.

Shear resistance test analysis and calculation method of shear capacity of UHPC-NC beam without web reinforcement

In order to study the failure phenomenon and shear resistance performance of UHPC-NC beams without web reinforcement, shear resistance tests were carried out on 15 UHPC-NC beams without web reinforcement. The variation parameters were shear span ratio, web thickness, steel fiber content, and compressive stress level. The load-deflection curve, failure phenomenon and crack development of the test beam are analyzed. The test results show that the joint between the top plate and the bottom plate of UHPC-NC I-beam without web reinforcement is the weakest, and the cracked web is easy to be “cut off” at the joint; The “banding crack area” of web is closely related to the shear span ratio, and the width of ribbon area increases with the increase of shear span ratio. The shear capacity of UHPC-NC I-beam without web reinforcement decreases with the increase of shear-span ratio. The shear capacity increases with the increase of web thickness and compressive stress level. The shear capacity has little relationship with steel fiber content, and the initial stiffness of the structure can be improved by applying prestress. Finally, considering the influence of the top slab compression-shear zone and the bottom slab tension-shear zone on the shear capacity of UHPC-NC prestressed composite beams without web reinforcement, the corresponding calculation method of shear capacity is given based on the modified compression field theory and the idea of sub-item superposition, and the applicability of the calculation method is verified by the test results.

Collapse mechanism and treatments of a deep tunnel in the weathered granite fault zone

Tunnelling in the fault fracture zone is prone to collapse accidents. The failure characteristics and mechanism of a tunnel collapse in Qinghai were analyzed based on the theory of rock mechanics, discrete element method (DEM), and in-situ test. The results show that the construction disturbance leads to the activation of the granite fracture zone, in which many fissures are constantly eroded and expanded to conduct water, which is the main reason for reducing surrounding rock stability after tunnel excavation. DEM simulates the failure process of the surrounding rock, and the collapse arch is observed. The uneven distribution of the stress field in the whole model is consistent with the tunnel’s asymmetric failure phenomenon. Based on the results, treatments such as grouting, enhanced primary support, and advanced pipe roofs were adopted to improve the mechanical properties of fissures and enhance the stability of the surrounding rock. This case provides valuable lessons for similar tunnels.