Top Of Wall Research Articles

Machine learning-based design of double corrugated steel plate shear walls

PurposeIn this study, machine learning (ML) algorithms were employed to predict the shear capacity and behavior of DCSWs.Design/methodology/approachIn this study, ML algorithms were employed to predict the shear capacity and behavior of DCSWs. Various ML techniques, including linear regression (LR), support vector machine (SVM), decision tree (DT), random forest (RF), extreme gradient boosting (XGBoost) and artificial neural network (ANN), were utilized. The ML models were trained using a dataset of 462 numerical and experimental samples. Numerical models were generated and analyzed using the finite element (FE) software Abaqus. These models underwent push-over analysis, subjecting them to pure shear conditions by applying a target displacement solely to the top of the shear walls without interaction from a frame. The input data encompassed eight survey variables: geometric values and material types. The characterization of input FE data was randomly generated within a logical range for each variable. The training and testing phases employed 90 and 10% of the data, respectively. The trained models predicted two output targets: the shear capacity of DCSWs and the likelihood of buckling. Accurate predictions in these areas contribute to the efficient lateral enhancement of structures. An ensemble method was employed to enhance capacity prediction accuracy, incorporating select algorithms.FindingsThe proposed model achieved a remarkable 98% R-score for estimating shear strength and a corresponding 98% accuracy in predicting buckling occurrences. Among all the algorithms tested, XGBoost demonstrated the best performance.Originality/valueIn this study, for the first time, ML algorithms were employed to predict the shear capacity and behavior of DCSWs.

True-MAD and pseudo-MAD in consecutive patients undergoing cardiovascular magnetic resonance

Abstract Background Mitral annulus disjunction (MAD) is a controversial imaging entity with uncertain clinical significance, which has been either considered a pathological entity potentially related to mitral valve prolapse (MVP) and sudden cardiac death or, on the contrary, a benign finding in normal hearts. Cardiovascular magnetic resonance (CMR) is poised to be the ideal imaging modality to assess MAD. Recently, a distinction between pseudo-MAD, present only in systole and secondary to juxtaposition of the billowing posterior leaflet on the adjacent left atrial wall, and true-MAD, where the insertion of the posterior leaflet is clearly displaced on the atrial wall either in diastole or in systole, has been suggested. Purpose We aimed to investigate the prevalence of pseudo-MAD and true-MAD in consecutive patients undergoing clinically-referred CMR. Methods This was a single-center retrospective study including consecutive patients referred to CMR from September 2023 to November 2023. Patients with feasible MAD assessment were included. MAD was defined as a ≥1 mm displacement between the left atrial wall-mitral valve leaflet junction hinge and the top of the left ventricular wall, measured from cine-CMR images in the three long-axis views. Pseudo-MAD and true-MAD were defined according to the presence of MAD only in systole or both in systole and diastole, respectively. MVP was defined as a systolic displacement ≥2 mm of one or both mitral valve leaflets above the annulus in 3-chamber view. Results Two-hundred-ninety patients (mean age 57±18 years; 181 men, 62%) were included. MVP and MAD were respectively found in 24 (8%) and 145 (50%) patients, of which 98 (34%) with true-MAD and 47 (16%) with pseudo-MAD. In all measurements, systolic MAD (2.6±1.3 mm) resulted equal to or greater than diastolic MAD (2.2±1.1 mm). The most frequent MAD location was the inferior wall in the two-chamber view (42%), whereas the rarest one was the inferolateral wall in the three-chamber view (17%). In patients with MVP, the prevalence of MAD was higher when considering all long-axis views (22 patients, 92%), of which 50% presented with true-MAD and 50% with pseudo-MAD. The extent of pseudo-MAD and true-MAD were both greater in patients with MVP (4.2±1.5 mm and 3.0±1.6 mm, respectively) than in those without MVP (2.3±1.0 and 2.1±0.9 mm; p<0.001 and p=0.007, respectively) in all locations. At the level of the inferolateral wall, the prevalence of MAD was 71% vs. 12% (p<0.001) in patients with vs. without MVP. Conclusions The presence of true-MAD was a common imaging finding in consecutive patients undergoing CMR, thus not resulting in a distinctive abnormal feature related to MVP or sudden cardiac death. Patients with MVP showed higher prevalence and extent of true-MAD and pseudo-MAD in all locations, in line with greater degeneration of the mitral annulus. Larger studies are needed to identify potential malignant characteristics of MAD.True-MAD (A,B) and pseudo-MAD (C,D).

Numerical Study on Seismic Performance of a New Prefabricated Reinforced Concrete Structural System Integrated with Recoverable Energy-Dissipating RC Walls

To enhance the performance of infill walls and reduce seismic damage, this paper proposes a novel prefabricated reinforced concrete (PRC) energy-dissipating wall, forming a new recoverable energy-dissipating PRC (ED-PRC) structural system. The system features pre-set gaps on both sides and the top of the PRC wall, with flexible materials filling the gaps on the sides. The top of the PRC wall is connected to the beam through several double-conical mild steel dampers to ensure the efficient transfer of horizontal shear forces between the main frame and the PRC wall. A numerical study was employed to investigate the seismic performance and the staged yield capacity. The results show that this design achieves a yielding sequence of dampers → wall → main frame. Furthermore, during the early to mid-phases of the cyclic loading simulations, the double-conical mild steel dampers with the low yield point utilized in the ED-PRC structural system exhibited exceptional energy dissipation capabilities. Notably, the LY100 dampers accounted for up to 61.84% of the total energy dissipation, with the LY160 and LY225 dampers contributing 55.35% and 50.25%, respectively. It indicates that the proposed ED-PRC structural system significantly enhances the ductility and the energy dissipation capacity under seismic loading while substantially reducing damage to the primary structure. The use of prefabricated components facilitates modular construction, allowing for quick dismantling and replacement after an earthquake, thereby rapidly restoring the structural seismic resilience.

Vascular plants and biocrusts ameliorate soil properties serving to increase the stability of the Great Wall of China

The Great Wall, as a World Heritage Site, is constructed with rammed earth and is currently facing the threat of erosion from wind and rain. Vascular plants and biocrusts are the main coverings of the Great Wall, and their role in mitigating soil erosion has attracted increased amounts of attention; however, the understanding of their underlying mechanisms is limited. Here, we conducted an extensive survey of vascular plants, biocrusts, soil properties (soil organic and inorganic binding materials, aggregates, and texture), soil aggregate stability, and soil erodibility at the top of the Great Wall in four different defensive zones in Northwest China. Vascular plants covered 13.6 % to 63.9 % of the tops of the Great Wall, and their rich diversity was mainly derived from perennial herbs. Moss, lichen, and cyanobacterial crusts collectively covered 36.3 % to 67.8 % of the top of the Great Wall. Redundancy analysis and structural equation modeling revealed that the synergistic effects of vascular plants and biocrusts enhanced soil aggregation stability (including geometric mean diameter, GMD; water-stable macroaggregate content, R) by increasing the accumulation of soil organic carbon (SOC), amorphous iron oxide (Feo), and amorphous alumina (Alo) and promoting the formation of macroaggregates (ASD>0.25 mm) and microaggregates (ASD0.053-0.25 mm). Furthermore, soil erodibility was primarily influenced negatively by the synergistic promotion of SOC accumulation by vascular plants and biocrusts and positively by the reduction in soil sand (PSD>0.05 mm) content by biocrusts. Our work highlights the mechanisms and importance of vascular plants and biocrusts as natural covers for altering the intrinsic properties of soil for the protection of the Great Wall. These findings provide reliable theoretical support for the protection of the Great Wall from erosion by vascular plants and biocrusts and offer new insights for the conservation of global earthen sites and similar wall habitats.

Experimental study on the hysteretic performance of a self-centering frame infilled with a bamboo wall

A novel low-damage self-centering frame-bamboo wall structural system was proposed in the present study by combining a resilient self-centering frame and a bamboo scrimber wall with good deformability. Two connection schemes (A and B) between the wall and the frame were adopted. In scheme A, the wall bottom was fixed on the beam, and the out-plane displacement of the wall top was restrained. An innovative friction-slit coupled damper (FSCD) with a two-stage working mechanism was utilized for the connection between the beam and bamboo wall in scheme B, and separation between the wall and columns was adopted to avoid force transfer from the columns. A series of quasi-static tests were conducted to evaluate the seismic performance of the self-centering frame-bamboo wall structure. The results showed that the bamboo wall with connection scheme A was compressed by the adjacent columns after the gap-opening of the self-centering frame, and the strength and stiffness of the whole structure were significantly enhanced. In scheme B, the strength, stiffness and energy dissipation capacity of the structure were effectively strengthened through the adoption of the FSCD. Moreover, compared with connection scheme A, scheme B could control the force transferred to the bamboo wall at different drift ratios more reasonably, owing to the two-stage working mechanism of the FSCD. The damage degree and residual displacement of the walls could thus be controlled to meet the expected performance objectives.

Navigating the depths: Experimental study on the influence of ground fissures on metro shield tunnels considering different intersection angles

Ground fissures are a typical slowly changing geological hazard that poses great safety risks to metro shield tunnels crossing ground fissures. To thoroughly analyze the deformation and failure of shield tunnels under the action of ground fissures with different intersection angles, this study reviews the existing research and carries out model tests on metro shield tunnels crossing ground fissures considering different intersection angles. Based on the experimental results and numerical simulations under multiple conditions, the deformation and failure characteristics of shield tunnels are systematically analyzed for the first time, which confirms that the activity of ground fissures can lead to a series of problems, including segment dislocation, lining cracking, structural elliptical deformation, bolt yield, joint opening and closing, void areas at the tunnel bottom in the hanging wall and tunnel top in the footwall, as well as resulting waterproof failure and internal gauge changes. In addition, as the intersection angle between tunnel and ground fissure increases, the failure mode of the structure gradually transitions from torsional failure to shear failure, with a decrease in the number of segment rings under bias pressure and an increase in the number of segment rings under shear effect. Based on the deformation characteristics, failure positions, and the changes of structural state of shield tunnels, some reflections on countermeasures are discussed, which can provide guidance for the design and maintenance of metro projects in ground fissure sites.

Microstructure and mechanical properties of 17–4 PH stainless steel fabricated by gas metal wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) presents a highly promising alternative to conventional subtractive manufacturing methods to produce metallic components, particularly in the aerospace industry, where there is a demand for 17–4 precipitation-hardened (PH) stainless steel structures. This study focuses on investigating the microstructural characteristics, showing microhardness evaluations, and analyzing the tensile properties of the as-printed parts during the 17–4 PH manufacturing process at different locations and directions. The fabrication is carried out using gas metal wire arc additive manufacturing (GM-WAAM). As a result, it was found that the microstructure of the as-deposited part showed a complex configuration consisting of both finely equiaxed and coarsely formed δ-ferrite phases with vermicular and lathy morphologies. These phases were dispersed inside the martensitic matrix, while a small amount of retained austenite was also present. It was observed that the volume fraction of retained austenite (20–5%) and δ-ferrite phases (15.5–2.5%) decreased gradually from the bottom to the top of the as-deposited wall. This reduction in the fractions of these phases resulted in a progressive increase in both hardness (∼37%) and ultimate tensile strength (UTS) along the building direction. This study successfully fabricates a high-strength and ductile 17–4 PH as-printed part using WAAM. The findings provide evidence supporting the feasibility of employing WAAM for producing defect-free, high-strength components on a large scale while maintaining mechanical properties similar or better than wrought alloy 17–4 PH.

Microstructure and mechanical properties of ultra-light Mg[sbnd]8Li[sbnd]3Al[sbnd]2Zn[sbnd]0.5Y alloy manufactured by directed energy deposition-Arc

The ultra-light Mg8Li3Al2Zn0.5Y (LAZ832–0.5Y) thin wall parts with excellent performances were successfully fabricated by Gas Tungsten Arc Welding (GTAW) in this study. The microstructure of the top, middle and bottom regions of the thin wall fabricated under various conditions was examined and the mechanical properties of these thin walls were tested. The results showed that much finer microstructure was obtained by GTAW than that made by conventional casting method. In the as-deposited samples, the needle-like shaped α-Mg phase emerged at the top of the thin wall whereas the bar-shaped α-Mg phase showed up in the middle and bottom regions of the thin wall due to the complex thermal history. The Al2Y phase was dispersed throughout both α-Mg and β-Li while the AlLi phase was mainly located in the β-Li. The best combination of ultimate tensile strength (UTS), yield strength (YS) and elongation to fracture of the as-deposited thin wall were 218.9 MPa, 171.4 MPa and 20.9%, respectively, which was manufactured under the optimal condition of 120 A 1800 mm/min 220 mm/min. After solid solution treatment at 350 °C for 4 h, the UTS increased slightly by 13% but the YS increased significantly by 65% compared with the samples before solid solution. The solution of the AlLi phase was believed to be the main strengthening mechanism. It is interesting to note that the UTS and YS of the as-deposited sample was better than those of the as-cast sample while the opposite situation took place after solid solution treatment.

Modelling and researching the evolution of stress during arc-directed energy deposition (ADED) hybrid inter-layer hammering

ABSTRACT Hybrid manufacturing of arc-directed energy deposition (ADED) and inter-layer hammering can build components with low detrimental residual stress (RS) and warping. Inter-layer hammering with lower load demand has proved to be a promising technology to improve the microstructure and mechanical properties. In this paper, a finite element model of the ADED hybrid inter-layer hammering was constructed for the first time. The accuracy of the model is evaluated by comparing thermal history, RS, and warping. The results show that the maximum compressive RS -25Mpa appears at 3 mm from the top of the wall after a single inter-layer hammering. The RS of the inspection position is reduced by 74.6% after six layers of hammering compared with the wall manufactured by ADED alone, and low-stress distribution with a value of -30Mpa appears in the range of 7 mm to 15 mm from the substrate surface. The warping of the wall in the building direction was completely suppressed (from 0.21 mm to 0 mm). In addition, the plastic strain introduced by the hammering at the wall top exacerbates the “misfit” between the regions of the wall top, resulting in tensile stress at the wall top.

Reducing heat gain from sheet metal‐clad walls by utilizing industrially wasted materials (experimental study)

AbstractBuildings' walls are covered to reduce environmental impact and esthetics, and cladding materials vary based on public preference and financial capacity. Metal sheets with glossy surfaces are commonly used, but researchers propose using aluminum sheets and filling gaps with commercial waste materials, like, fabric roll sticks or circular plastic hollow parts. A test room with internal dimensions of 1 × 1 × 2 m used in Baghdad (latitude 33.2° N) was used to study thermal behavior, with a window‐type air conditioner providing standard thermal conditions. The air gap attached to the top of the test wall was either left open or closed during the day. Results showed that double‐layer bamboo packing preserved 52.1% with a closed‐air gap and 49.5% with an open‐air gap, but no discernible difference was observed between the two situations.

Numerical investigation on flow and aerothermal characteristics of rarefied hypersonic flows over slender cavities

Flow and aerothermal characteristics of rarefied hypersonic flows passing through slender cavities are investigated comprehensively using the direct simulation Monte Carlo (DSMC) method by various cases, such as the cavity with different depth-to-width ratios and different inclination angles, and the freestream at different altitudes and Mach numbers. The cavity depth-to-width ratio has a great influence on flow structures and gas density inside the cavity, but a slight effect on gas temperature inside the cavity and on heat flux over cavity surfaces. In comparison to the vertical cavity, the upstream-inclined cavity reduces the gas density and the high-temperature area inside the cavity, showing a decrease rate of gas density of about 53 % for φ = -45°, while the downstream-inclined cavity greatly raises the gas density and slightly expands the high-temperature area, reaching a growth rate of gas density of about 114 % for φ = 45°. As the freestream altitude increases from 50 to 80 km, the main vortex expands remarkably while the heat flux near the top of the aft wall decreases sharply, and a noteworthy finding is that the dimensionless temperature contours inside the cavity for the cases of H = 50, 60, and even 70 km seem to be unchanged. Compared with the case of Ma = 6, the maximum density inside the cavity is increased by about 5.5 times for the case of Ma = 30, and it is about 7.3 times for the maximum temperature inside the cavity. However, raising the freestream Mach number seems to not alter the streamline patterns inside the cavity. The three-dimensional effect reduces the maximum density inside the cavity by about 14.5 % to 17.4 % and results in a smaller main vortex compared with the two-dimensional (2D) cavity, and moreover, the slender cavity can weaken the three-dimensional effect due to its larger depth-to-width ratio and the relatively short cavity width. Besides, the vortex-transport theory is proposed, which can well explain the change of gas density inside the cavity for all cases considered in this work.

Seismic behavior of the brick masonry rural building strengthened with polypropylene grid cement mortar coating: Shaking table tests

Brick masonry structures are widely applied around the world, especially in Chinese rural areas, but their seismic performance is not satisfactory due to high brittleness of material and poor integrity of structure. Accordingly, a low-cost and highly efficient strengthening method for brick masonry structure is needed. This paper presents the shaking table tests for a 1/2-scale single-story brick masonry rural building strengthened with polypropylene grid cement mortar coating. The damage states of the test model under earthquake motions with different intensity were observed. The dynamic characteristics including natural frequency and damping ratio were discussed. The seismic response, such as acceleration, displacement, torsion angle, base shear and hysteretic energy dissipation, were analyzed. The results show that the weak areas of the test model were the corners of windows and door, the intersections between longitudinal wall and transverse wall and the top of longitudinal walls. With the input PGA of 1.0 g, the natural frequencies of the test model in the X and Y directions decreased to 93.1 % and 88.2 % of the initial values, respectively, the damping ratio in the X and Y directions increased to 2.56 and 1.61 times the initial values, respectively, and the maximum story drift and horizontal torsion angle were 1/122 and 0.0037 rad, respectively. The comparison between actual earthquake damage and test results showed that the use of polypropylene grid cement mortar coating to strengthen brick masonry rural building could result in good seismic behaviors.

Study on the Bearing Plate of Steel Clarification Tank under Earthquake

The stress at the support structure of the clarification tank is large, which will have a certain impact on the whole clarification tank structure. The typical stress concentration phenomenon will cause structural damage and serious harm to the steel clarification tank itself. In order to study the influence of the bearing plate on the seismic response of steel clarification tank, this paper analyzes the dynamic response of the clarification tank by setting different thickness bearing plates at the connection between the steel column and the structure body of the steel clarification tank. Based on the displacement, stress, and liquid sloshing height of the steel clarification tank, the thickness of the bearing plate is obtained. The results show that the maximum stress of the steel clarification tank under different seismic waves decreases with the increase of the thickness of the bearing plate. The thickness of the bearing plate has a certain influence on the maximum displacement of the clarification tank structure, but the increase in the thickness of the bearing plate does not necessarily reduce the maximum displacement. Different bearing plate thicknesses have no effect on the position of displacement, and the maximum displacement occurs at the top of the outer wall.

Risk Reduction Measures and Monitoring Analysis of Deep Foundation Pit with Water in a Metro Station in Hefei

The construction of an urban metro will inevitably involve deep excavation. Risk assessment before deep excavation, risk reduction measures, and real-time monitoring during excavation can effectively ensure the safety of deep excavation. Taking the deep excavation pit of Lingbi Road Station of Hefei Rail Transit Line 8 as the research object, this paper first analyses and evaluates the self-risk, groundwater risk, and surrounding environmental risk of the deep excavation pit, and gives the corresponding measures to reduce the risk of the deep excavation pit. Then, the monitoring content of the excavation process is determined according to the environment of the excavation, the hydrogeological conditions, and the type of supporting structure, and the monitoring scheme is designed. Finally, the entire excavation process is monitored in real time. By analyzing the monitoring data of 13 projects, such as horizontal displacement of the wall top, axial support force, groundwater level, etc., it is found that the monitoring values of 13 projects do not exceed the control value. This proves that the composite internal bracing structure of the underground diaphragm wall is suitable for deep foundation pit support in the Hefei area, as the selection of the water-bearing deep foundation pit support structure, the value of the support structure parameters, and the design of the foundation pit dewatering scheme are all reasonable. The study of this paper also serves as a case reference for the support design of water-bearing deep excavation of subway station in Hefei area.

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.

Effects of an Explosion-Proof Wall on Shock Wave Parameters and Safe Area Prediction

To study the influences of an explosion-proof wall on shock wave parameters, an air explosion protection experiment was performed, the time history of shock wave pressure at different positions before and after the explosion-proof wall was established, and the characteristics of shock wave impulse and dynamic pressure were analyzed. The explosion-proof working conditions of five different diffraction angles were simulated and analyzed using Autodyn software(2019R3). Results indicated the following findings. The explosion-proof wall exerted an evident attenuation effect on the explosion shock wave, but considerable pressure still existed at the top of the explosion-proof wall. Overpressure behind the wall initially increased and then decreased. The larger the diffraction angle, the faster the attenuation speed of the diffraction overpressure of the shock wave in the air behind the wall. The history curve of shock wave pressure exhibited an evident bimodal structure. The shock wave diffraction of the wall made the shock wave bimodal structure behind the wall more prominent. The characteristics of the bimodal structure behind the wall (the interval time of overpressure peak Δt was less than the normal phase time of the diffracted shock wave T+) caused the shock wave impulse to stack rapidly, significantly improving its damage capability. The peak value of dynamic pressure on the oncoming surface was approximately two times the peak value of overpressure, and the inertia of air molecules resulted in a longer positive duration of dynamic pressure than overpressure. The maximum overpressure on the ground behind the explosion-proof wall appeared at approximately two times the height of the explosion-proof wall, while the maximum overpressure in the air behind the explosion-proof wall appeared at approximately one times the height of the explosion-proof wall. The relatively safe areas on the ground and in the air behind the wall were approximately 4–4.5 times and 3.5–4 times the height of the explosion-proof wall, respectively.

이도정자(二道井子)유적으로 보는 하가점하층(夏家店下層)문화 주거지 특성

The purpose of this study is characteristics of Erdaojingzi site in Chifeng among the research findings on the Lower Xiajiadian Culture.
 The average depth of the cultural deposit at the site was about 8 metres and remains of the surrounding moat and city walls were excavated. The city walls are located within the moat's boundaries. A gentle slope of cultural deposit has formed within the city walls and a number of house remains were found lying along the top of the city walls. The site lies on the slopes of the hills lying to the north of the village of Erdaojingzi in the Hongshan District in Chifeng, Inner Mongolia, and encompasses an area of around 30,000 square metres. A rescue excavation was conducted on the site by the Inner Mongolia Cultural Relics and Archaeology Institute in April 2009, during which time some 5,200 square metres was uncovered.
 The site itself is thought to be one of the best preserved Lower Xiajiadian culture sites discovered to date and the structures discovered at the site have survived intact. The moat, city walls, courtyards, building foundations, vaults and roadways have provided scholars with a wealth of new information on the settlement patterns and social organization of that period

Numerical analysis of rarefied hypersonic flows over inclined cavities

A comprehensive numerical analysis is conducted to investigate rarefied hypersonic flows over two-dimensional (2-D) and three-dimensional (3-D) non-rectangular cavities with inclined front or rear walls using the direct simulation Monte Carlo (DSMC) method. The objective is to give a contribution to the understanding of the effects of inclined front or rear walls on flow features and aerodynamic surface quantities. The 3-D or finite-span effects are also analysed in depth. Results show that inclining the front wall of the cavity has a negligible effect on gas flows in the rear part of the cavity, and consequently does not affect surface pressures on and heat fluxes to both the cavity floor and the rear wall. This is because high-speed gases enter the cavity via the top of the rear wall, which is exactly the dominant drive force for gas flows in the rear portion of the cavity. Inclining the front wall does not alter this drive force, so it does not influence gas flows there. However, inclining the rear wall not only strongly influences the flows close to the rear wall, but also has a profound influence on the flows in the front portion of the cavity. Specifically, it can substantially enhance the flow expansion in the front portion of the cavity, make the front vortex shorter and moves the front vortex upward and leftward. The 3-D or finite-span effects play an important role in the flow features and surface quantities of rectangular, inclined-front, and inclined-rear cavities. The finite-span effects exhibit as the 3-D relieving effects, which prevent the external stream from penetrating deeper into the cavity. This consequently lessens the momentum and energy that are transferred into the cavity and brings about a significant decrease in the pressure on and heat flux to the cavity floor. The results in the work can be applied to the accurate prediction of the pressure and heating loads of the thermal-protection tiles of hypersonic vehicles.

Multimodality imaging assessment of mitral annulus disjunction in consecutive patients

Abstract Funding Acknowledgements Type of funding sources: None. Background Mitral annulus disjunction (MAD) has been investigated through trans-thoracic-echocardiography (TTE) and cardiac magnetic resonance (CMR) in different study cohorts and has been assumed either to represent a structural risk marker of sudden cardiac death or a benign, incidental finding. The imaging modality used to assess MAD might impact its prevalence and clinical significance. Purpose To assess the prevalence of MAD in consecutive patients undergoing TTE and CMR. Methods We retrospectively searched for MAD in consecutive patients undergoing TTE and CMR within six months, one from each other, at our center from March 2021 to April 2022. MAD was assessed in standard echocardiographic and CMR long-axis views and was defined as a ≥ 2 mm displacement between the left atrial wall-mitral valve leaflet junction hinge and the top of the left ventricular wall. Cases of pseudo-MAD and true-MAD were defined by MAD presence, respectively, during only systole and both systole and diastole. Results 124 patients (47 women; mean age: 59 years ± 17) were included. According to CMR, 38 patients (31%) presented with a structurally normal heart, and 37 (30%) presented with MAD. Patients with MAD presented more frequently MVP (27% vs. 1%; P<0.001), whereas patients without MAD were more frequently affected by non-ischemic cardiomyopathy (30% vs. 11%; p = 0.02). The two groups did not differ in age, sex, cardiac risk factors, symptoms, left ventricular volumes, ejection-fraction, pre-contrast T1- and T2-mapping, mitral annulus dimension and mitral regurgitation. MAD prevalence was higher by CMR than by TTE (30% vs. 8%; P=0.028). There was a low inter-modality agreement for the detection of MAD presence (Cohen's kappa=0.34) and a moderate agreement for MAD extent (ICC=0.71; 95% LOA 0.59, 0.8, p<0.05). Median MAD extent reported CMR and TTE were 2.6 mm (IQR 2.05–3.75 mm) and 4 mm (IQR 2.65–4.65 mm) respectively. All patients showing MAD at TTE demonstrated it at CMR too. Cases of true-MAD were observed at CMR (14% of the total cohort) but not at TTE. Conclusion In this cohort of consecutive patients, MAD was missed by TTE in more than 2 out of 3 patients exhibiting it at CMR. The high prevalence of MAD at CMR and the absence of significant association between this phenomenon and morpho-functional or structural alterations argue in favor of a benign finding at CMR. TTE detected MADs with higher extents compared to CMR. Further longitudinal studies are needed to evaluate the imaging-modality-related clinical relevance of MAD to improve patients’ risk stratification.

Shaking table test on the seismic response and reinforcement measures of double-arch tunnels in mountainous areas

Double-arch tunnels are commonly used in mountainous areas but are more vulnerable to earthquake damage than single-hole tunnels due to their large span and weak joints between the main tunnel and the centre wall. This study aims to understand the seismic response and damage characteristics of double-arch tunnels and provide design advice. A large-scale shaking table test was conducted in a high-intensity seismic zone, using strip reinforcement as seismic measures. Results show that peak accelerations of the inverted arch of tunnels increase as peak accelerations of seismic waves increase. Peak accelerations of the centre wall increase until peak loading accelerations achieve at 0.4 g. Large peak internal forces are mainly concentrated at the bottom of tunnels and near the centre wall. For the centre wall, bending moments are significantly influenced by structural abruptness at the junctions between the centre wall and the main tunnel, whereas axial forces are more evenly distributed in the centre wall. Seismic waves with high energy at low frequencies excite peak responses of strains and bending moments for the centre wall, especially at the wall top. Parts of the main tunnel connecting to the centre wall are in an adverse stress state, with the bottom and vault of tunnels being susceptible to cracking. Penetration cracks are likely to occur in the inverted arch and vault of tunnels as peak accelerations of seismic waves gradually increase. However, after penetration cracks appear in each of these two parts, further cracking is more likely to occur in the inverted arch, especially during strong seismic shaking. The overall forces in double-arch tunnels with strip reinforcement are significantly reduced, but there is little reduction in force for the bottom and outside of the lining.