Bottom Of Wall Research Articles

Measurement and analysis of vibration responses due to subway transit in residential areas

The issue of building vibrations caused by subway operations has become increasingly prominent, significantly impacting residents' daily lives. This study investigates the vibration response of a residential area when the subway passing through, which involved the vibrations of the free field, the basement, and the nearby buildings. In addition, numerical simulation of building vibration by Etabs software was discussed. The free field vibration above the shield tunnel diminishes rapidly in the vertical track direction as the horizontal distance increases. However, the influence range of subway induced vibrations significantly expands when a basement is built adjacent to the subway. Data on building vibrations revealed the distribution of vibrations along the vertical direction and the vertical vibration amplification at the slab center due to local resonance. Interestingly, isolation designed for seismic loads also offers some benefits in reducing vertical vibrations. The numerical simulation results of the vibration response at the shear wall bottom show a certain degree of consistency with the actual measured results, but the attenuation of the vibration is faster, which may underestimate the vibration response of the building. The findings of this study provide valuable insights for understanding the impact of subway operations on surrounding buildings, optimizing subway and structural spatial layouts, and designing for vertical vibration control.

Enhancing retaining wall stability with geofoam

The efficiency and applicability of geofoam in reducing the earth pressure on retaining walls were investigated in this study. Finite element (FE) analysis was employed to evaluate the geometric parameters of the geofoam to determine the optimal shape of the geofoam. It was found that the triangular geofoam was the most optimized shape for retaining walls. Furthermore, this study was aimed at revealing the principle of minimizing earth pressures on the retaining wall using geofoam. The soil pressure on the retaining wall was determined according to the geofoam properties, geofoam area, and backfill slope. The FE analysis was verified by comparing the FE analysis results and experimental results for similar retaining walls. In addition, the soil pressure variation throughout the retaining wall was analyzed, and the principle of reducing the soil pressure acting on the retaining wall reinforced with geofoam was investigated. The results showed that when the retaining wall bottom was reinforced using geofoam, a constant reduction in soil pressure was observed, regardless of the geofoam shape.

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.

Automatic monitoring and structural stress analysis during ultra-large onshore caisson sinking construction

During the sinking process of ultra-large onshore caisson, the structural stress of caisson will change significantly due to the changes of earth pressure, end resistance, water level in caisson and attitude of caisson. Based on the south anchoring onshore caisson project of Nanjing Longtan Yangtze River Bridge, the structural stress analyses were carried out based on the automated caisson monitoring data. The results show that the automated monitoring system can acquire the key data of caisson in real time and efficiently, and the monitoring results reflect the structural stress and displacement characteristics in different construction stages. The vertical earth pressure at the bottom four corners of the caisson is significantly greater than the other positions, indicating that there is an obvious stress concentration phenomenon at the four corners. The stress at the bottom of the horizontal earth pressure monitoring is smaller than that at the middle and bottom of caisson, which verifies the existence of stress disturbance area around the cutting. Steel shell concrete at the bottom of partition wall is the weakest position of caisson structure, and the structural safety risk is higher from the first casting to the second sinking. If the risk of tensile cracking occurs in the process of casting, each diagonal can be carried out several times to make full use of the structure's own resistance to reduce the development of tensile stress. The conclusion can be used for reference in the design and construction of similar projects.

Numerical investigation of seepage dissolution evolution of the bottom expansion cutoff wall in deep overburden

The bifurcation defect at the bottom of the cutoff wall in the deep overburden leads to a sharp increase in the local seepage gradient of the adjacent overburden at the bottom of the cutoff wall, which affects the evolution process of seepage dissolution of the cutoff wall. This study presents a novel type of bottom expansion cutoff wall to alleviate the problem that the seepage gradient of adjacent strata at the bottom of the cutoff wall far exceeds its allowed value. Considering the effects of the pore, aggregate, and convection on the calcium ion diffusion coefficient of concrete, we propose a coupling analytical model of seepage dissolution for two cutoff wall schemes, including the bifurcation defect schemes and bottom expansion schemes, to investigate the evolution of calcium ion concentration, porosity, and seepage characteristics, and to reveal the influence mechanism of the bottom bifurcation defect and bottom expansion of the cutoff wall on the seepage dissolution of the cutoff wall in deep overburden. The results indicate that subjected to the bottom bifurcation defect, the calcium ion concentration of the cutoff wall decreases faster, and the porosity increases faster with the increase of service life compared to the conventional cutoff wall when subjected to the bottom bifurcation defect. With a bifurcation height of 24 m at the bottom of the wall, the service life of the cutoff wall is reduced by 6.64%. In contrast, the novel type of bottom expansion cutoff wall is used to reveal that the concrete porosity increases slowly with the increase of the expansion radius over the same service life. The seepage gradient of the adjacent overburden at the bottom of the cutoff wall is significantly reduced. The service life of the cutoff wall is extended by 47.33% due to its 5 m bottom expansion radius. This study can provide a theoretical basis for the evolution of long-term service performance of the cutoff wall of an earth-rock dam on deep overburden.

Influence of the Vertical Component of Yangbi Ground Motion on the Dynamic Response of RC Frame and Brick-Concrete Structure

An earthquake of magnitude 6.4 occurred in Yangbi County, Yunnan Province on 21 May 2021, with a focal depth of 8 km, and strong ground motion with vertical components was monitored by Yangbi station (53YBX). A total of 14,122 houses were damaged in Yangbi in the earthquake, and 232 of them collapsed. Vertical components of ground motions have been gained more attention for its effect on structure’s seismic response in epicenter or near-fault regions at present. Taking the three earthquake ground motions of Yangbi, Chi-Chi, and Loma Prieta as inputs, and modeling based on Perform-3D, this research carried out the seismic dynamic time history analysis of an RC (reinforced concrete) frame structure and a brick-concrete structure under both horizontal and vertical working conditions. The results showed that vertical components of the three ground motions had no evident impact on the top horizontal displacement and acceleration of the two types of structures. Among the three ground motions, the vertical component of Yangbi ground motion has largely influenced the top vertical displacement, acceleration, and axial force of the frame column bottom (or masonry wall bottom). The vertical component had different amplification effects on the axial pressure and the bending moment of a single column at the bottom of the RC frame structure, thus causing resonance amplification effect of the brick-concrete structure floors and amplifying the vertical acceleration of the top floor. In addition, it considerably increase the maximum axial tensile strain of masonry walls and the possibility of faster tensile failure of the brick-concrete structure. Influence of vertical ground motion on the bearing capacity of RC frame structure’s columns and the brick-concrete structure’s masonry walls should not be ignored. The results of the research may provide a reference for the earthquake-resistant design of building structures, especially the earthquake-resistant design considering the vertical seismic effect.

Mechanism analysis of the retaining wall collapse of a foundation pit induced by water supply pipeline burst: A case study

Once a water supply pipeline bursts, the seepage field of the surrounding soil mass will change, and the safety of the adjacent foundation pit will be affected. In this study, a foundation pit accident was taken as an engineering case. On the basis of fluid-solid coupling theory and COMSOL Multiphysics, the mechanism of the retaining wall collapse induced by the bursting of a water supply pipeline was studied. Results indicated that in the early stage of this collapse, the shear strength of soil mass and the anchoring force weaken gradually. The retaining wall deformation develops slowly. In the late stage, with the failure of the top anchor cable, a continuous sliding surface connecting the retaining wall bottom and the ground surface appears in the soil mass. The retaining wall deformation increases rapidly, and the collapse may occur in a short time. In the construction process of a foundation pit, attention should be paid to the adverse effects caused by the bursting of a water supply pipeline. The monitoring of the anchor cable axial force and retaining wall deformation should be strengthened to ensure the long-term safety of the foundation pit.

QUALITY ASSURANCE OF DIAPHRAGM AND PILE WALLS BY GEOPHYSICS

Underground structures like diaphragm and pile walls are constructed to organize waterproof curtains, protect pit sides, and transfer loads from the structures. Violations of the construction technological process can lead to the formation of defects. To prevent adverse consequences, before excavation, it is necessary to control the integrity of the slurry walls using non-destructive geophysical methods. A review of geophysical slurry wall quality control methods based on the excitation and registration of physical fields through access tubes installed in the reinforcement cage, in wells drilled near the structure or on the surface of the structure, is presented. The main capabilities and limitations of the methods are given. Cross-hole ultrasonic logging was used to study the section of the slurry wall during the construction of the Moscow Metro station. The results of parallel soundings made it possible to identify anomalous zones, interpreted as defects. The geometric dimensions of one of the major defects were refined by ultrasonic tomography. For the first time in Russian testing practice, thermal integrity profiling was applied to study the diaphragm wall at the base of a residential building. The results of temperature monitoring during the concrete hardening are presented. According to the method, a major flaw, excess of the design mark of the wall bottom and bulging of the structure were revealed. The results of thermal integrity profiling were verified by ultrasonic logging. The combined use of thermal and ultrasonic methods can be recommended as a reliable tool for integrity testing of diaphragm and pile walls. To carry out the measurements, the access tubes shall be included in the reinforcement cage of the structure at the design stage.

Numerical Investigation of Effect of Temperature Profile Imposed on the Crucible Surface on Oxygen Incorporated at the Crystal Melt Interface for 450 mm Diameter Silicon Single Crystal Growth in Presence of CUSP Magnetic Field Using Czochralski Technique

Numerical investigation has been carried out to study the effect of thermal boundary condition on turbulent melt flow and oxygen transfer inside a crucible used to grow 450 mm diameter silicon single crystal using Czochralski method. Two types of thermal boundary conditions, namely, isothermal crucible surface and experimentally measured temperatures on the crucible surface have been imposed on the crucible wall and crucible bottom. Melt motion owing to buoyancy, surface tension variation at the free melt surface as well as crystal and crucible rotation has been considered. Effect of CUSP magnetic field has also been investigated. Melt having aspect ratio of 1 and 0.5, representing high and moderate level of melt inside the crucible have been considered. K-epsilon turbulent model with low Reynolds number formulation has been used for turbulence modelling. Melt motion governed by natural convection, Marangoni convection and crystal as well as crucible rotation shows higher oxygen concentration at melt crystal interface for aspect ratio of 1, when experimental temperature profile is imposed at the crucible wall. For melt aspect ratio of 0.5, natural convection and Marangoni convection dependent melt show higher oxygen concentration for isothermal crucible wall boundary condition. Marangoni convection in absence of rotation of crystal and crucible leads to low oxygen concentration zone near the crystal outer surface, the size of which is larger for melt aspect ratio of 0.5. Maximum turbulent viscosity values for aspect ratio of 1, in case of experimental temperature at the crucible are higher compared to isothermal case, which is just the opposite of the trend for aspect ratio of 0.5. Imposing a CUSP magnetic field leads to similar distribution of turbulent viscosity for both types of thermal boundary conditions, irrespective of the type of thermal boundary condition. Oxygen concentration at the melt crystal interface is found to be higher in presence of CUSP magnetic field. Value of maximum turbulent viscosity for the two boundary condition are similar for melt aspect ratio of 1.0. Crucible surface temperature profile for aspect ratio of 1, on actual melt aspect ratio of 0.5 predicts lower oxygen concentration at melt crystal interface. Values and distribution of turbulent viscosity is however the same for both temperature profiles.

Multi-scale experimental study on filling and discharge of squat silos with aboveground conveying channels

Filling and discharge tests of reduced-scale and full-scale squat silos with aboveground conveying channels are carried out to investigate the pressure distribution and the overpressure evolution on the wall and the channel. The filling tests imply that the pressure distribution on the wall bottom is significantly influenced by the channel. Rankine’s active earth pressure equation gives accurate prediction of the lateral pressure on the wall, which is overestimated by the Jaky’s equation. The filling pressure on the channel wall is related to the stored material heights caused by the repose cone. The arch effect of the channel and the equilibrium effect of the wall friction in the squat silos should not be overrated. The shallow buried theory gives more reasonable prediction of filling pressure on the wall and the channel in the squat silos. The discharge tests show the overpressure coefficient does not increase with the increase of the discharge eccentricity. Meanwhile, the aspect ratio has a great influence on the overpressure coefficient. An overpressure on the top wall and the side wall of the channel is observed in multi-scale discharge tests. It is suggested that the overpressure coefficient of the channel should be considered when calculating the discharge load.

Improved Performance of Passive-Matrix Micro-LED Displays Using a Multi-Function Passivation Structure

The enhanced light output efficiency of passive-matrix micro light-emitting-diode (LED) display was achieved by employing the tapered sidewalls and distributed-Bragg-reflector (DBR) passivation structure. The oblique angles at the bottom of multi-quantum wall and n-GaN are 48.9° and 21.8°, which can favor the planarization structure of pixel interconnection. As increasing the number of DBR (SiO2/TiO2) stacking from 3.5 to 5.5 pairs, the reflectance increased obviously from 81.4% to 98.0% at the wavelength of 450 nm. As the micro-LED display with a multi-function DBR structure, the output power of 1.07 mW under 1 mA, the external-quantum efficiency of 42% under 0.2 mA, and the luminance of 435 nits were obtained.

Experiments of an atrium-style metro station under harmonic excitation

The atrium-style station is one of the favourite choices in underground railway systems, as it can provide a larger and clearer space for passengers and commercial clients at the hall level of the station. With such style, as hall slabs are replaced with flat-beams, the station's capabilities to withstand lateral action like seismic action become one of the main concerns. Shaking table tests were conducted to investigate the dynamic response of soil-structure interaction of atrium-style station model under harmonic excitations covering the full frequency range, with comparison to free-field tests. The experimental results confirm that the influence of the structure on the dynamic response of the ground surface begins when the frequency of input motions is greater than 10 Hz. The predominant frequencies of the ground corresponding to the second and third modes both show an increase of 10% from the FF model to the SS model due to the presence of an atrium-style metro station. For atrium-style station: (i) the discontinuous structural elements such as beams and columns are more severely strained than the continuous ones like slabs and side walls, (ii) the peak dynamic soil normal stresses along the side wall follow an approximate L-shaped distribution and the maximum stress occurs at the side wall bottom, and (iii) the spectral characteristics of both dynamic structural strain and dynamic soil normal stress reflect the amplification function of the ground.

Analysis of Single and Back-to-Back Reinforced Retaining Walls with Full-Length Panel Facia

Back-to-back mechanically stabilized earth (MSE) walls have several applications in infrastructure development. Present study firstly discusses on the kinematics of deformation of MSE wall with full-length panel facia. Secondly, single and back-to-back MSE walls with full-length panel facing are modelled using finite difference based software (Fast Lagrangian Analysis of Continua). The reinforcements in the back-to-back walls extend through and through from one wall facing to the other wall facing. Lateral pressures, vertical stresses, and lateral deformations at the facing for various reinforcement stiffness values are evaluated for both single and back-to-back walls under working stresses. Reinforcement stiffness values of 500 kN/m, 5000 kN/m and 50,000 kN/m are considered. For single MSE wall with stiff reinforcement, lateral pressures at the facing are higher than those for active earth pressure. Lateral deformations of facing with reinforcement of low stiffness are higher than those with reinforcement of high stiffness. In back-to-back walls, the lateral deformation of wall facing with reinforcement of high stiffness is slightly inwards near the top of the wall. Reinforcement stiffness is found to have significant effect on the vertical stress in both single and back-to-back walls. Lateral pressures of both single and back-to-back connected walls are compared. Lateral pressures on single MSE wall are found to be lesser than those for back-to-back wall at the top of the wall. However, lateral pressures near the bottom of single wall are higher than those of back-to-back wall.

Cyclic behavior of double-skin composite walls with flat and corrugated faceplates

This paper presents the cyclic behavior of double-skin composite (DSC) walls for mid- to high-rise buildings, which consist of concrete filled steel tubes (CFTs), a pair of steel faceplates connected by tie bolts, and infill concrete. Four 1/3-scale DSC wall specimens, varying in faceplate profile and tie bolt spacing, were tested under combined axial and cyclic lateral loading. All specimens failed in flexure with a progression of steel tube fracture, steel faceplate buckling, and concrete crushing at wall bottom. The corrugated DSC walls and the flat DSC wall with standard bolt spacing were able to achieve an ultimate drift ratio around 3.4% and a ductility ratio greater than 5.4, while the flat DSC wall with bolt spacing 50% over code limit presented early faceplate buckling and undesired seismic performance. Compared to flat DSC walls, corrugated DSC walls, even with a doubled tie bolt spacing, had considerably higher initial stiffness, ductility ratio and energy dissipation. Formulations are proposed for predicting the lateral strength and drift capacity of corrugated DSC walls without elastic local buckling. The difference between the predicted and measured capacity for either lateral strength or drift is on average less than 6%.

Hysteretic behavior of high-strength concrete shear walls with high-strength steel bars: Experimental study and modelling

To study the cyclic behavior of high-strength concrete shear wall with high-strength steel bars, five shear wall specimens with a shear-to-span ratio of 2.2 were fabricated and tested subjected to constant axial load and horizontal cyclic load. The effects of the axial force ratio, the strength of distributing steel bars, the presence or absence of steel fibers, and the properties with or without wrapped steel plates on the hysteretic behavior of shear walls were analyzed. The results show that the combination of concrete with C80 grade and steel bars with HRB600 grade was a reasonable strength matching way. Increasing the strength of distributing steel bars in the wall delayed the development of cracks and reduced the residual deformation. The addition of steel fibers reduced the crack widths and improved the elastic-plastic deformation capacity. Moreover, adding wrapped steel plate at the bottom of wall effectively improved the bearing capacity, deformation capacity, and reparability of the shear wall. Finally, a restoring force model established on the basis of experiment and theoretical analysis agreed well with the test hysteresis curves.

Prediction of Ventilation Effects on Reducing Moisture Damage in Tishun Tang in the Palace Museum in Beijing, China

The Palace Museum in Beijing is World Cultural Heritage and representative of Chinese traditional brick buildings, but has been suffering deterioration for centuries. Environment monitoring showed that the special construction of foundation resulted in the humid micro-environment and moisture damage near wall bottom and floor in buildings. In order to make clear the effects of ventilation on reducing moisture damage, we took Tishun Tang as example and built a two-dimensional hygrothermal simulation model. There are two ventilation plans. One is direct ventilation, letting the outdoor air go into indoor space directly through the flue under floor. The other is to add air temperature and humidity control during that produce, called controlled ventilation. In those two plans, ventilation rate is raised to 1 time per hour from 0.4 times (current state). The results show that compared with direct ventilation, controlled ventilation is more efficient for reducing moisture damage. In controlled ventilation plan, heating outdoor air before the air exchange in winter benefits to raising indoor surface temperature by one degree and reducing area of freezing-thawing damage. Dehumidifying the outdoor air during ventilation in summer is the most important point of decreasing the high mould risk from 22 ~ 25 days to 7 ~ 10 days.

Experimental study on the mechanical response and failure behavior of double-arch tunnels with cavities behind the liner

Cavities often develop behind the vault during the construction of double-arch tunnels, generally in the form of various defects. The study evaluates the impact of cavities behind the vault on the mechanical and failure behaviors of double-arch tunnels. Cavities of the same sizes are introduced at the vault and the shoulder close to the central wall of double-arch tunnels. Physical model tests are performed to investigate the liner stress variation, the earth pressure distribution and the process of progressive failure. Results reveal that the presence of cavities behind the liner causes the re-distribution of the earth pressure and induces stress concentration near the boundaries of cavities, which results in the bending moments in the liner inside the cavity to reverse sign from compression to tension. The liner near the invert becomes the weak region and stress concentration points are created in the outer fiber of the liner at the bottom of the sidewall and central wall. It is suggested that grouting into the foundation soils and backfilling injection should be carried out to ensure the tunnel safety. Changes in the location of cavities significantly impact the failure pattern of the liner close to the vault, e.g., cracks appear in the outer fiber of the liner inside the cavity when a cavity is located at the shoulder close to the central wall, which is different from the case that the cavity locates at the vault, whereas changes in the location of cavities have a little influence on the liner at the bottom of the double-arch tunnels.

물속에 잠긴 이중벽 주위의 유동특성에 관한연구

When oil spill disaster on sea takes place, the most effective measure is to use oil fence with vertical wall. It has been big challenges that suitable oil fence in consideration of variety of variables such as wind speed, height of wave and current direction is chosen. And current characteristics below two of vertical wall was studied by PIV experiment with utilizing technic of visualized analysis like velocity distribution, contour of velocity and streamline pattern in flow characteristic between vertical wall of oil fence. In this study it is purposed to identify characteristics of inside water flow between two vertical walls depending on respective various water speeds to minimize outflow of floating article below bottom of vertical wall and observed that re-circulation flow and irregular vortex at certain places between two vertical walls occurred. Consequently, the study showed that failure of oil fence such as entrainment failure and submergence failure can be largely lessen by means of optimizing length between two vertical walls with water speeds.

Research on Crossing Tunnels’ Seismic Response Characteristics

A large-scale shaking table test system and corresponding numerical model are designed to study the seismic characteristics of crossing tunnels. The calculated results are in good agreement with experimental data, both the results suggest that: Loading the El-Centro seismic wave, the maximum acceleration in upper tunnel’s crossing center section is located in the crown, the maximum strain is located in the haunch; meanwhile, the maximum acceleration and strain in underpass tunnel’s cross center section are both located in the crown. Affected by the underpass tunnel, at the side wall bottom of the upper tunnel, tests data reveal that the crossing center’s maximum acceleration is reduced for 30.9% and the strain was enlarged 170% than the normal section. Affected by the upper tunnel, at the haunch of the underpass tunnel, tests data reveal the crossing center’s maximum acceleration is enlarged by 10.0% and the strain is 27.2% reduced than the normal section.

Experimental investigation on the distribution characteristics of bubble contact areas in the narrow channel

In this paper, an experimental investigation was carried out for the distribution characteristics of bubble contact areas in a full transparent narrow channel. The dimension of narrow channel was 2 mm × 10 mm × 250 mm, and the heating length was 200 mm which was the ITO coated glass. The deionized water was used as working fluid, and the bubble contact areas were observed with a high-speed camera from the bottom of heating wall. It was found that the density of bubble contact area was simultaneously affected by the nucleation rate and the coalescence rate for bubbly flow. Also, the fluctuation of bubble contact area density increased with increasing heat flux and decreasing mass flux, respectively. Moreover, the bubble contact diameter was well consistent with the distribution of Inverse Gaussian. Finally, the distribution parameters of ν and λ were predicted, and the predicted results agreed well with the experimental results.