Middle Of Wall Research Articles

Varicella zoster vasculopathy causing recurrent ischaemic strokes in an immunocompetent patient.

A 66-year-old woman reported 10 days of generalised weakness, falls and memory 'glitches'. She had developed left-sided ophthalmic herpes zoster 3 months before but was otherwise well. MR scan of brain showed acute left-sided ischaemic strokes and CT cerebral angiogram identified marked stenoses of the left anterior and middle cerebral arteries. We suspected varicella-zoster virus vasculopathy, confirmed by cerebrospinal fluid analysis. Initially she had further ischaemic strokes despite intravenous acyclovir, prednisone, aspirin and clopidogrel. However, after prolonged acyclovir and prednisone, there were no new infarcts though imaging of left anterior and middle cerebral artery vessel walls showed persistent inflammation. Varicella zoster vasculopathy can cause recurrent ischaemic strokes, even in immunocompetent people with no cardiovascular risk factors, and despite long-term antiviral therapy.

Research on the Construction Mechanics and Stability Control Technology of Expressway Tunnel Based on Numerical Analysis

As an effective structural form, connecting arch tunnel has been widely used in practical engineering because of its smooth linear shape, small footprint and good bridge and tunnel connection. With the increase of domestic traffic volume year by year, the width of the even arch tunnel is gradually changed from two-way four lanes to two-way six lanes. I20 I-steel, spacing 0.75∼1 m, anchor length 3∼4 m, ring spacing 0.5∼1 m, the side ring spacing of the middle wall is 0.75 m, the side ring spacing of the side wall is 1 m, and the shotcrete thickness is 0.25∼0.3 m. The excavation span of a two-way six-lane continuous-arch tunnel is considerable, leading to complex stress characteristics, thereby posing risks to construction safety and structural stability. Following the construction of the initial tunnel, disturbance to the surrounding rock occurs, affecting subsequent excavation phases. The initial support requirements for subsequent excavations are more intricate, with increased internal forces compared to the initial tunnel segment. As the rear tunnel progresses, the surrounding rock near the middle wall shifts towards the rear tunnel, reducing internal forces in the concrete and steel arch frame. However, as the rear tunnel distance increases, concrete stress and axial forces on the middle wall side of the initial tunnel begin to rise. Throughout the construction, the steel arch frame’s internal forces and spray concrete stress on the middle wall side’s arch waist and foot are the highest, making them susceptible to disruption from construction on the opposite side, thus constituting critical tunnel components. Numerical simulations effectively capture surrounding rock and structural stress dynamics during large-span arch tunnel construction. Simulation outcomes align closely with field measurements, particularly in three-dimensional simulations, enhancing construction understanding and management.

Investigation of mechanical and thermal performances and masonry quality for new raw soil-based insulating hollow bricks

ABSTRACT The development of raw soil-based insulating hollow bricks (RSIHB) provides a promising way for improving the efficiency of building energy conversation and resource utilization of construction waste soil. In this paper, the response surface method (RSM) was adopted to study the effect of multifactor on mechanical and thermal performances of modified raw soil-based samples. The results indicate that the thermal conductivity is significantly affected by the interactions between molding pressure and mixture moisture content, as well as between mixture moisture content and cement admixture. Thus, the optimal mix ratio was determined by the RSM-based regression model. The assessment based on numerical simulation demonstrates that the middle wall ribs immensely improve the stress concentration. The porous structure elongates the path of heat flow conduction, effectively enhancing the thermal resistance of the brick. In addition, bonding strength tests manifest that the mortar consistency should be within 60–80 mm for construction and plastering of the new raw soil-based insulating hollow brick. The research results have strong theoretical significance and practical value for recycling of construction waste and provide a reference for actual production and construction.

Alteration of cardiac structure and function and its prognostic value in patients with Takayasu arteritis: a cardiac magnetic resonance study.

To investigate the prevalence and characteristics of late gadolinium enhancement (LGE) by cardiac magnetic resonance (CMR) and its prognostic value in patients with Takayasu arteritis (TA). Sixty TA patients with a CMR examination were retrospectively included. All TA patients were divided into with LGE-positive and LGE-negative groups. Bi-ventricular function and location, distribution, and pattern of left ventricular (LV) LGE were evaluated in both LGE-positive and LGE-negative groups. Primary outcome was defined as a composite of cardiovascular death, hospitalization for heart failure, coronary artery revascularization, and stroke. Univariate and multivariate Cox proportional hazard regression analyses were used to evaluate the association between variables and primary outcomes. Sixty consecutive TA patients were enrolled in this study. The mean age was 38.2 ± 13.8 years and 54 patients (54/60, 90.0%) were female. LGE-positive was observed in twenty-one (21/60, 35%) patients in the total patients with TA. LGE was predominantly distributed in the middle wall and subendocardial. The patchy and infarcted LGE patterns were the most common. Compared with the LGE-negative group, the LGE-positive group had reduced LV ejection fraction (P = 0.033), elevated LV end-diastolic volume index (P = 0.008), LV end-systolic volume index (P = 0.012), and LV mass (P = 0.008). During a median follow-up period of 1,892 days (interquartile range: 1,764-1,988 days), the primary outcomes occurred in thirteen patients. In the univariate analysis, LGE-positive (hazard ratio [HR] = 4.478, 95% confidence interval [CI]: 1.376-14.570; P = 0.013) were independently associated with the primary outcomes. However, LGE-positive did not retain its value as an independent predictor of primary outcomes in the multivariate analysis. Instead, LVMI (HR = 1.030, 95%CI: 1.013-1.048; P = 0.001) was the strongest independent predictor of primary outcomes in patients with TA. The Kaplan-Meier plot revealed that patients with LVMI ≥ 57.5 g/m2 have a worse prognosis. LGE-positive detected by CMR was observed in 35% of total TA patients with different distributions and patterns. LGE is associated with adverse LV remodeling and worsen cardiac function. However, LVMI rather than LGE can provide independent prognostic information in patients with TA.

Analyzing the chemical environment of bent bamboo (Phyllostachys iridescens) sections using XRD, XPS, and FTIR analysis

ABSTRACT Bamboo exhibits remarkable flexibility and bent shape stability in thermal-bending. To explore how bamboo responds to bending, this study investigated the chemical properties on the concave, middle and convex walls (marked as CW, MW, VW respectively) of bent bamboo Phyllostachys iridescens though XRD, XPS, and FTIR analyses. Results indicate a reduction in crystallinity from 42% of MW to 39% of CW and 40% of VW. Notably, the peak shifts of CW and VW indicates the neutral layer on CW and VW experience an offset toward the convex surface. Chemical degradation varies on the thermal bent bamboo sections, the O/C ratio increases from 0.26 of MW to 0.36 of CW, accompanied a decrease in the Cox/unox ratio from 0.93 of MW to 0.81 of VW. This indicates that VW undergoes more significant degradation of cellulose and hemicelluloses, while CW experiences a greater loss of extracts. Additionally, FTIR analysis indicates that the ester bond peak at 1731 cm−1 flattens on CW, while it splits into two peaks on VW, with one of the peaks shifting to a higher wavenumber of 1735 cm−1. This suggests a reduction in the intermolecular distance between lignin and hemicelluloses on CW, whereas a higher lignin content and compression stress on VW.

Ultrasonographic, endoscopic and radiographic examinations of the dromedary mammary glands and teats

The aim of the present study was to examine the mammary gland of dromedary camels using ultrasonography, endoscopy and radiography. These techniques are easy to perform in the field and feasible to diagnose pathological conditions of the mammary gland. Udders of 49 slaughtered and 26 adult dromedary camels submitted for necropsy were used for the examinations. Additionally, 11 lactating female dromedary camels were selected for the ultrasonographic udder examination. The transition from the milk ducts into the udder cistern, the teat cistern and the teat canals were examined in individual udders. Teat cistern length, teat end width, teat wall thickness, teat cistern width and middle cistern wall thickness were measured using ultrasonography. The measurements resulted in mean values of the teat cistern length of 37.3 mm, the teat end width of 2.0 mm, the teat wall thickness of 4.4 mm, the teat cistern width of 8.2 mm and the cistern wall thickness of 3.5 mm. The teat wall was differentiated into three layers, a hyperechoic outer layer, a hypoechoic middle layer and a hyperechoic inner layer. The mid cistern wall was hyperechoic. Endoscopic examination is an easy to perform and practicable method for examining the inner structures of the teats of dead animals; however, the feasibility has not been shown in lactating animals yet. Ring-like folds were present in the teat cistern, which protruded horizontally into the lumen. It was also possible to visualize the branchlike transition of the teat cistern into the larger milk ducts. Radiographic examination using barium sulfate contrast medium showed that the teat cistern ends in a network of initially wide but branching and narrowing milk ducts. The two teat canals and cisterns are completely independent of each other and there is no communication between the glandular tissue of the two canals and cisterns.

MYOCARDITIS, CORONARY ARTERY DISSECTION OR BOTH: A JUVENILE ENIGMA

Abstract A 26–year–old man was admitted to the Coronary Care Unit for severe, non–irradiated, oppressive anterothoracic pain. He had no relevant pathological history, but reported an episode of gastroenteritis the week before. EKG showed sinus rhythm and accelerated idioventricular rhythm phases. Blood pressure and 2D echo were normal. Inflammation indeces were negative, hsTnT reached a peak of 2026 ng/L. Despite the absence of inflammation signs, our first guess was myocarditis. Cardiac magnetic resonance (CMR) was performed: T2w–STIR images showed edema of the middle inferior wall and of the mid–basal anterior and anterolateral wall, while T1–weighted post gadolinium images showed transmural enhancement of the mid–basal anterior, antero lateral and inferior walls with a dubious origin from the sub endocardium in the anterior and anterolateral segments; LVEF was 55%. Invasive coronary angiography (ICA) was performed to rule out ischemic etiology: LAD showed a very thin lumen in its periphery and two obtuse marginal branches had an amputated appearance: it made us think of healing dissections. Then it turned out that the patient have been working out with heavy weights the day before: we therefore considered spontaneous coronary artery dissection. Such hypothesis was consistent with the absence of inflammations indices, but didn’t explain the basal and middle inferior involvement that CMR had shown. On the other hand, the angiographic finding may be consistent with peripheral vascular suffering linked to myocarditis induced inflammation. To date, we haven’t found univocal interpretation. Anti–remodeling therapy with IACE and beta blockers was administered, in addition to acetylsalicylic acid. CMR will be performed in two months and may provide further results once the edema will be reabsorbed. ICA will be repeated to make sure that distal coronary blood flow is improved. Take Home Messages Myocarditis can also occur with no signs of inflammation. In myocarditis it has been demonstrated that slower distal coronary blood flow may occur, due to the increase in peripheral vascular resistance linked to the presence of edema. In the acute phase, especially if CMR is performed very early, the large amount of edema can make the enhancement transmural, masking the site of origin of the damage.

Critical Failure Characteristics of a Straight-Walled Arched Tunnel Constructed in Sandstone under Biaxial Loading

To characterize the failure of rock mass surrounding underground tunnels, biaxial compression tests were conducted on a real sandstone model with a straight-walled arched hole. The acoustic emission (AE) system and digital image correlation (DIC) optical inspection equipment were used to investigate the crack evolution process and failure precursors of the tunnel. A two-dimensional particle flow code (PFC2D) was used to conduct numerical simulations on the sample, so as to investigate the mesoscopic failure mechanism of rock mass. The results show that the failure of the single tunnel constructed in sandstone occurs mainly in the walls on both sides (between the spandrels and arch feet), showing slabbing failure characteristics and a certain abruptness. The crack initiation in sandstone in early stage is not obvious, and the crack propagation in rock mass is rapid when acoustic emissions are enhanced. The small increments in the AE count and amplitude and the continuous reduction in the b-value can be used as precursors for the failure of rock mass. When the height–span ratio is 0.8 and 1.0, the stress distribution around the chamber is more uniform, and when the height–span ratio is greater than 1.0, the stress is mainly concentrated in the vault and arch bottom. In the PFC simulations, tensile fractures firstly initiate in the middle of walls and at the arch feet, arcuate fracture concentration zones are then formed, in which shear fractures appear and a few particles spall from the surfaces. When approaching the ultimate bearing capacity, rock masses on both sides of the tunnel are fractured over large areas, and the slender coalesced fractured zone develops to the deep part of rock mass, causing failure of the sample.

Numerical Simulation Study of the Vibrational Response of Continuous Arch Tunnels under the Action of Overlying Train Loads

With the rapid development of transportation infrastructure in China, continuous arch tunnels passing under existing operational railways are increasingly encountered. This paper primarily investigates the mechanical response patterns of the lining of continuous arch tunnels under the vibrational loads generated by trains traveling on railways. To this end, a three-dimensional finite element model of the dynamic response of continuous arch tunnels under train vibrational loads was constructed using Midas GTS/NX software. This model explores the patterns of acceleration, dynamic displacement, and dynamic strain responses of continuous arch tunnels under the action of moving train loads. The study reveals that under train vibrational loads, the vertical acceleration, vertical displacement, and strain time history curves at various monitoring points in the continuous arch tunnel exhibit vibrational characteristics. The acceleration, vertical displacement, and dynamic strain increase as the train enters, fluctuate within a certain range, and then decrease to zero as the train exits. Under high-speed train loads, the acceleration peak values at the arch feet and outer sidewalls of the left and right tunnels are larger, with a greater peak value difference. The vertical displacement peak values at the arch shoulders and crown are larger, whereas those at the middle partition wall and base slab are smaller. During the process from the train's entry to its exit, the dynamic strain exhibits a trend of initially increasing, then stabilizing, and finally decreasing to zero, all while displaying vibrational characteristics. The strain response on the tunnel side where the train enters is greater than that on the side where it exits.

Effect of First Premolars Extraction with Maximum Retraction on Airway and Hyoid Bone Position in Class I Bimaxillary Dentoalveolar Protrusion Cases

Background: The aim was to determine the effect of first premolars extraction with maximum incisor retraction on airway magnitude and hyoid bone position in cases with bimaxillary dentoalveolar protrusion. Methods: Lateral cephalograms of patients with Class I skeletal and dental relationships were retrospectively recruited. Inclusion criteria were 15-30 years old patients having bimaxillary proclination who had undergone all first premolar extractions with maximum incisor retraction. Patients with dentofacial anomalies, chronic mouth breathing and those who had undergone tonsillectomy or adenoidectomy were excluded. Pre-and post-treatment lateral cephalograms were digitally analyzed for airway measurements and hyoid bone position. Paired samples T-test was used for statistical analysis. P-value<0.05 was considered statistically significant. Results: A total of 33 patients, comprising 22 females and 11 males, with a mean age of 24.39 ± 6.92 years were included. Statistically significant differences were found in airway dimensions from pre-treatment to post-treatment; upper airway size between soft palate and posterior pharyngeal wall (SPP-SPPW) was reduced by 1.91mm (12.78%), at uvula & middle posterior wall (U-MPW) by 2.51mm (20.60%), at tongue base to posterior-inferior point on middle pharyngeal wall (TB-TPPW) by 3.39mm (24.26%) and vallecular to lower pharyngeal wall by 1.51mm (9.94%). The vertical position of hyoid bone also significantly reduced as indicated by inferior movement of hyoidale (H) by 4mm (3.8%). There was no significant changes in the horizontal position of the hyoid bone. Conclusion: Premolar extraction with maximum retraction in bimaxillary protrusion cases can decrease the airway dimension and increase vertical position of hyoid bone.

Enhancing melting and solidification characteristics of a triple-pipe latent heat energy storage system via a wavy central wall with a sinusoidal fixed wavelength

This study aims to improve the melting and solidification characteristics of a triple-pipe heat storage unit by introducing a wavy middle plate with a sinusoidal fixed wavelength. The inner and outer tubes facilitate the flow of heat transfer fluids (HTFs), while the middle tube houses the phase change material (PCM). Various scenarios are examined to gauge the impact of the wavy central wall on the PCM's phase change performance, comparing liquid fraction and mean temperatures with cases featuring a straight middle plate. The primary goal is to pinpoint the optimal scenario with the shortest discharging/charging times and the highest rates of heat release/storage. The investigation commences by assessing the effects of middle wall thickness (2, 4, 6, and 8 mm) on the PCM's phase change characteristics, comparing liquid fraction and mean temperature with a straight middle plate. Subsequently, the influence of various sinusoidal wavelengths (250, 125, 50, and 25 mm) on both melting and solidification performances of the PCM is numerically examined to identify the optimum case. The research also delves into the effects of various sinusoidal amplitudes (2.5, 5.0, 7.5, and 10 mm) on the PCM's phase change process. In the final step, the capability of the wavy middle plate, with various phase shifts (0°, 90°, 180°, and 270°), in improving the PCM's phase change characteristics is analyzed. Numerical results highlight that, among the tested scenarios, the configuration with a 5 mm amplitude and a 25 mm wavelength (A5λ250) exhibits outstanding performance during both melting and solidification phases. A5λ250 showcases a 19.92 % reduction in melting time and a 2.44 % reduction in solidification time compared to other cases, coupled with a 22.55 % improvement in heat storage and a 3.48 % enhancement in heat release. However, introducing a phase shift in the melting process adversely affects system performance. Conversely, adjusting the phase shift of A5λ25 to 270° leads to enhancements in both solidification time and heat release rate. Specifically, solidification time improves by 0.86 %, and the rate of heat release increases by 0.66 W compared to A5λ25–0.

Modulating fluid rheology and confinement toward augmenting the performance of a double layered microchannel heat sink

AbstractThe improvement of the cooling performance of liquid‐cooled microchannel heat sinks used for densely packed electronic circuits is sorted via passive techniques like tuning substrate or coolant properties. We propose a design for enhancing heat sink performance by simulataneously modifying the channel geometry and tuning the fluid rheology. By modeling the coolant as a power law fluid, its rheological behavior is varied ranging from shear‐thinning to shear‐thickening, alongside Newtonian fluid. We introduced tapering to the middle wall that separates the bottom and top channels of a double layered microchannel heat sink (DL‐MCHS), causing both channels to converge. This convergence not only increases the flow velocity within the downstream microchannel but also reduces the apparent viscosity of the shear‐thinning fluid being subjected to shear, resulting in enhanced thermal and hydraulic performance. We analyze the results from both the first and the second law of thermodynamics context, demonstrating that a tapered DL‐MCHS with shear‐thinning fluid outperforms a straight partition wall DL‐MCHS with Newtonian coolant. However, we also discovered that extreme tapering compromises thermodynamic viability, but by fine‐tuning the extent of tapering, we inferred that a DL‐MCHS with shear‐thinning fluid can become viable with little compromise in the thermal performance.

Effects of Higher Sloshing Modes on the Response of Rectangular Concrete Water Storage Tanks with Different Aspect Ratios to Near-Field Earthquakes

Near-field earthquakes have been shown to have different effects on structures than far-field events. This study examines the dynamic response of a rectangular concrete liquid storage tank with tapered walls to near-field ground motions, with particular emphasis on the effect of higher sloshing modes. The tank’s numerical modeling, calibrated using experimental results, was performed considering the tank’s wall flexibility. Seven selected near-field records were applied in each case, and the effects of the first five sloshing modes on the tank response at three different locations, including the corner, middle of the long wall, and middle of the short wall, were investigated. The effect of the earthquake incident angle on the tank’s response was also studied by applying major and minor horizontal earthquake components once along the longer and shorter tank walls, respectively, and vice versa. Results show that the tank corner may have a sloshing height up to 50% greater than the middle of the walls and that the maximum sloshing response is substantially influenced by the spectral acceleration value at the first sloshing period. Higher sloshing modes are found to affect the sloshing response, with a maximum R2 score of 0.95, depending on the excitation’s incidence angle.

Cracking Characteristics and Mechanism of Internal Components of Large-Span Shield Tunnel

With the ever-increasing number of large-span shield tunneling projects and the extended operational time, their distinctive internal component issues are becoming more pronounced and exhibiting unique characteristics. In order to reveal the cracking mechanism of concrete on the top of the middle partition wall, based on a large-span shield tunnel section of Nanjing Metro, the crack mode, distribution characteristics, and cracking process of concrete inside tunnel structure were studied by combined field investigation and extended finite element analysis. The results showed that: (1) there were 96 cracks of concrete on the top of the middle partition wall in the interval. Based on the propagation path, number, and shape of cracks, they could be divided into type I, II, III, Y, and Z, with type-Y and type-Z being subtypes of type-I. (2) The crack started at the opposite side of horizontal differential displacement of the flue plate. The development curves of the length and end width of type-I and type-II cracks showed the significant characteristics of three stages. The relationship between crack end width and length was nonlinear, showing that 250 and 225 mm, respectively, were the critical crack lengths growing with the rapid growth of the end width of type-I and type-II cracks. (3) In type-II cracks, the propagation curves of two cracks under the same working condition were consistent, and the spacing of plate joints greatly influenced the length and slope of each stage of the curve. For type-III cracks, the first crack propagation process was basically consistent with type-I and type-II cracks, and the propagation of the other two cracks had obvious brittle characteristics.

Comparison of Slot Deformation in Different Types of Bracket During Torque Application—A Finite Element Study

Introduction Torque in orthodontics plays a significant role in final positioning of the teeth. This twisting force in wire helps in transferring the applied forces to bracket, which sometimes causes deformation of slot. This slot deformation can vary torque prescription and affect tooth position. Aims and Objectives To compare the deformation of slots of different bracket materials after torque application using finite element analysis. Materials and Methods A finite element model of maxillary central incisor with bracket slot 0.022 × 0.028 inch dimensions was constructed. The different bracket materials such as stainless steel (SS), ceramic, and titanium were used with rectangular SS archwire (0.019 × 0.025 inch). The slot deformation was obtained after various degrees of torque application at 5°, 10°, 15°, and 20°. This slot deformation was also seen at the top, middle, and bottom locations in the slot. All these models were then analyzed using the Ansys software. Results The results showed that there was a gradual increase in deformation of all the bracket slot walls from bottom to top locations. The bracket slot deformation for 20° twist was 0.78, 1.85, and 4.53mm (SS); 0.24, 0.70, and 2.50 mm (ceramic bracket), and 1.82, 2.85, and 4.83 mm (titanium brackets) in bottom, middle, and top slot wall locations, respectively. Conclusion Slot deformation was seen highest in titanium brackets and least in ceramic brackets. Further in the slot wall, the deformation was highest in top location as compared to middle and bottom locations.

Soil–Structure Interactions in a Capped CBP Wall System Triggered by Localized Hydrogeological Drawdown in a Complex Geological Setting

Retaining walls are often used to construct basements and underground station boxes. This unique case study compares the field-measured contiguous bored pile (CBP) wall, surrounding geology, and hydrogeology or groundwater responses against the results using 2D and 3D numerical back analyses of a deep excavation project that experienced localized groundwater drawdown through the leaking ground anchor points. Site observations indicated that the ground anchor installation works had caused larger than expected through-the-wall leakages that subsequently triggered nearby ground and building settlements. In order to study the complex soil–structure interaction behavior, back analyses using a hybrid modeling technique of through-the-wall transient hydrogeological seepage and geomaterial stress-strain analyses was implemented. Through these soil-structure interaction back analyses, it was evidently revealed that the presence of the continuous capping beam was key in providing pile head restraints against the active earth pressures when the groundwater was depressed, as well as efficiently distributing the beneficial wall corner effects towards the middle CBP wall, leading to smaller bending moment magnitudes, characterized by their ‘S-shaped’ profiles. This behavior had been correctly diagnosed, as opposed to the ‘D-shaped’ bending moment profile usually only seen in a typical free-head cantilever wall in similar geology. The eventual results show that the wall and ground responses, i.e., deflection, bending moment, and settlement, were reasonably well predicted when compared against the instrumented field data, thus validating the reliability of the geotechnical modeling technique, key geological parameters, and hydrogeological fluctuations adopted in the 2D and 3D numerical models, as well as the beneficial contributions of the continuous capping beam, which tend to be overlooked during routine retaining wall design.

Influence of the door opening on the pressure transient caused by the high-speed subway train passing through the double-track tunnel with the mid-partition wall

Double track tunnel with mid-partition wall is a widely used subway tunnel. In such tunnels, in order to avoid the fire door on the middle partition wall from invading the gauge, the fire door is often removed to form door openings. The existence of door opening connects two parallel tunnels, which affects the aerodynamic effect caused by high-speed subway train passing through the tunnel. In this study, a double track tunnel with mid-partition wall was taken as an example to analyze the aerodynamic effect of high-speed subway train under the door opening conditions, moreover, the surface pressure of two adjacent tunnels and train surface pressure was also analyzed. In addition, the propagation mechanism of pressure wave in open door tunnel was analyzed in detail, and the superposition law of branch pressure wave caused by open door was pointed out. The results indicated that the presence of door openings is beneficial for controlling the peak pressure on the tunnel surface and train surface. For a door opening with a cross-sectional area of 5 m2 (cross-sectional area ratio of 0.116), when the door opening is located 300 m and 700 m away from the tunnel entrance, the peak positive pressure can be reduced by up to 21.9 % and the peak negative pressure can be reduced by 21.1 %. The cross-sectional area and number of door openings have a limited effect on reducing the peak pressure of the tunnel. Compared to the number of door openings, the position of the door opening has a more significant impact on the peak pressure inside the tunnel and on the surface of the train.

Crashworthiness of nested corrugation square energy-absorbing tubes with circumferentially cosine profile

With the development of railway technology, high-speed trains have been invested in practical operation increasingly. The traffic accident that train runs at high speed will cause casualties and property losses. The energy absorption tube can effectively alleviate the damage of the vehicle in the collision process and protect passengers in the buffering process. In this paper, nested corrugation square energy-absorbing tubes (NCSTs) with circumferentially cosine profile and different inner structures are analyzed by adopting finite element (FE) simulation. The quasi-static compression tests and proposed theoretical model based on Simplified Super Folding Element (SSFE) theory are employed to validate the effectiveness of numerical models. The simulation results indicates that the crushing modes possess certain sensitiveness to cross-sectional conformation and the NCSTs present more stable and orderly deformation modes compared with non-nested tubes. The specific energy absorption (SEA) and crushing force efficiency (CFE) of NCST can be increased by 52.49 and 19.07% compared to ordinary corrugation tube, respectively. In addition, the tube with two-layers octagonal wall (SO1D) is selected as optimal structure because it is ranked first under cases of 40% by adopting the technique for order preference by similarity to ideal solution (TOPSIS) method. Finally, the sensitivity analyses based on SO1D are conducted. The results show that the parametric variation of trib and tout fairly effect on the deformation pattern. And increases in wall thickness t and section size of the middle wall Dmid will all result to increases in initial peak crushing force (IPCF) and significant variation on other crashworthiness criteria. This paper offers certain reference significance for the study of energy-absorbing structures.

The Construction Methods and Control Mechanisms for Subway Station Undercrossing an Existing Tunnel at Zero Distance

The existing tunnel will inevitably be disturbed when the new subway station is constructed cross under it at zero distance. Three innovative construction schemes were proposed, their effects on deformation control were compared by numerical simulations, and the mechanism of the influence of different tunnel support and excavation methods on the deformation control in them was further explored in order to seek a better scheme in this paper. The results show that the settlement of the existing tunnel in Scheme I (L-type beam + full-face excavation) is the greatest, and that the one in Scheme III (temporary steel column + double-pilot tunnel) is the smallest, but the settlement during excavation changes significantly, along with the large deformation on the side walls of the undercrossing area. Scheme III is not recommended because it is difficult to control and the construction effect is mediocre. Due to the existence of a large free face, the settlement of both sides of the existing tunnel is larger when the L-type beam supports the tunnel, and the bottom of the middle wall bears large compressive stress. The settlement of the existing tunnel excavated by the double-pilot tunneling method is less than that of the full-face tunneling method under the same tunneling support method, and the increase in settlement during the tunneling with the L-type beams is greater than that with the pier columns. In comprehensive consideration, Scheme II (pier column + double-pilot tunnel method) or combined pier column + double-pilot tunnel can control the deformation better.

Investigation of cracking mechanism of the first tunnel lining during double-arch tunnel construction

To solve the engineering problem of the first tunnel lining cracking caused by the second tunnel construction of double-arch highway tunnels, a research method combining distributed optical-fibre monitoring, inversion analysis and numerical simulation that can reflect lining cracking was presented. Optical fibres were laid on opposite sides of the steel arches inside the first tunnel lining. Embedded optical-fibre monitoring was conducted continuously during the second tunnel driving. Based on the fibre-optic strain profile, the lining cracking was deduced and warned in time. The mechanical behaviour of the steel arch was investigated by the inversion analysis, which took into consideration the integrated impact of axial force and flexural moment. A two-dimensional (2D) load-structure method–based numerical model was established, considering the influence of different load distributions in each construction condition. The total strain rotating crack constitutive model was applied to reflect the cracking behaviour of concrete lining in the simulation, and the model was calibrated and verified in the laboratory. Comparative analysis between the simulated strain distribution and the distributed optical-fibre monitoring results was carried out. The deformation mode and crack distribution of the lining were analysed. The cracking mechanism was explained. Specifically, the second tunnel construction led to the loading at the top of the middle partition wall and the release of rock pressure in the first tunnel. Under these load changes, the secondary lining of the first tunnel cracked on the inner side of the top of the middle partition wall owing to tension, and compression-bending failure occurred near the right arch foot. Finally, the influence of the parameters on the lining force was analysed, and a construction optimisation scheme was proposed.