Load Transfer Process Research Articles

Load transfer and deformation of geogrid-reinforced piled embankments: field measurement

The collected field data for a geosynthetic-reinforced pile-supported structure (GRPS) in Hamburg is studied to identify the effect of environmental changes on the load transfer process over the structure lifetime. The prediction models in three design codes are applied to estimate the loads and strains in different structural components of the embankment. The results show that the models fail to accurately estimate the geogrid reinforcement deflection and overestimate the loads on the pile foundation in this project.

Numerical performance assessment of buried corrugated metal culvert subject to service load conditions

Two- and three-dimensional continuum finite element methods were used to assess the mechanical response of buried metal culverts subjected to service load conditions. The analysis explored the influence of the culvert profile, cover depth, section aspect ratio, and service load magnitude on culvert deformation, thrust, and section moment response. The numerical predictions were calibrated using third-party experimental data. For shallow burial conditions, the culvert section profile was found to be an influential parameter on the predicted culvert response where the soil–culvert interaction mechanisms and load transfer processes are governed by nonlinear behaviour. Models that incorporate the corrugated culvert profile provided better estimates of the culvert thrust than the simplified computational models that are typically used in analysis. Results from this study demonstrate that existing simplified methods cannot capture the local variation (i.e., amplitude, waveform) of the membrane strain and section thrust particularly between the crest and trough of corrugation.

Effect of Vacuum Insulation Panels on Energy Consumption and Thermal Load Transfer between Compartments in a Three-Temperature Frost-Free Refrigerator

The three-temperature frost-free refrigerator is popular in China currently, which adopts a single evaporator and separate air ducts to distribute cold air into all compartments, i.e., the fresh food compartment (FFC), the variable temperature compartment (VTC), and the freezer compartment (FZC). Two identical refrigerators with cyclopentane insulation are comparatively studied in this article, one with vacuum insulation panels (VIPs) in two sidewalls and the other without. Results show that VIPs reduce the steady-state energy consumption of the refrigerator by 12.4% due to smaller average power input and longer compressor-off duration. The decrease in average power input originates from a shorter FFC-damper-on duration since VIPs reduce its thermal load. However, the FFC average temperature rises unexpectedly with shorter damper-on and longer damper-off durations, and induces thermal load transfer from FFC to FZC through the mixing of return air in the evaporator chamber. Consequently, FZC-only duration increases and compensates for the decrease in FFC-damper-on duration, resulting in an overall similar compressor-on duration. Simulation results of the heat transfer process through the evaporator are also provided in both cases to obtain a full view of the thermal load transfer process.

Experimental analysis of dynamic response of floatover installation using rapid transfer technique in continuous load transfer process

This study presents the experimental analysis of an innovative floatover installation method with the rapid transfer technique, in which the topside loads can be transferred fast and safely. In the rapid transfer process, 30% loads were firstly transferred onto the jackets within only 1 min using the jacking system. Then both the ballast system and the jacking system were employed to gradually transfer the loads onto the jackets. After 70% topside loads were transferred, the jacking system quickly offloads the remaining 30% loads within 1 min. The continuous load transfer operation was simulated in model tests. The complex motions of the barge and the topside as well as the loads on the Deck Support Unite (DSU) and the Leg Mating Unite (LMU) were analyzed. The maximum and minimum motions of the barge and the topside were statistically analyzed as well as DSU and LMU loads. Results indicate the barge pitch motions largely synchronize with the topside pitch before the second jack-down operation. The barge moved forward a little distance after twice jack-down operations. Results indicate DSU loads varied significantly during the jack-down operations and the jacking system should be designed to provide lateral restraints equivalent to 20% of the topside weight.

Investigating the dynamic loading pattern of the foot in sedentary healthy adolescent

Aim: The aims of this study were to define the dynamic loading pattern of the foot in healthy adolescents and to investigate the differences between boys and girls.Material and Methods: n = 89 adolescents (n = 42 girls, n = 47 males) using right hand-preferred and have normal body mass index (18.5- 24.9 kg/m2) were included in the study. Dynamic foot pressure analysis was used to determine the foot dynamical load patterns of the participants. The results were compared by considering be male or female factor and right-left foot dynamic loadingpattern.Results: In the comparison between the groups, it was seen that the contact percentages and active contact areas of the different regions of the feet were different in boys and girls (p 0.05). When the right-left foot load patterns were compared, it was seen that the load transfer in the right foot progressed to the anterior medial and the left foot showed a delay in the load transfer processes (p 0.05).Conclusion: Boys walked with a wider contact percentage in the left foot and wider metatarsal and heel active contact areas in both feet than in girls. Furthermore, on the preferred side (right) the load transfer is positioned on the anterior medial of the foot, while the main difference in the other foot is due to the delay in reaching the maximum pressure.

Influence of soil reinforcement on the uplift bearing capacity of a pre-stressed high-strength concrete pile embedded in clayey soil

This paper presents a field study on the uplift bearing capacity of a pre-stressed high-strength concrete (PHC) pile embedded in clayey soil, and on the soil around the PHC pile that was treated with cement paste. The PHC pile was inserted into a pile hole filled with cemented soil by its own weight (by gravity), and the soil compaction effect of a conventionally driven pile induced by the installation process was avoided. The test results showed that: the pile head displacement needed to fully mobilize the uplift bearing capacity of the test piles was about 0.1 D (pile diameter); the ultimate skin friction of the PHC pile–cemented soil interface was much larger than that of the cemented soil–soil interface; the PHC pile and the cemented soil around the pile behaved as an integral pile in the load transfer process; and the measured ultimate bearing capacity of the test piles was 0.91–0.94 times the American Petroleum Institute (API)’s proposed values for piles under compression and 0.79–0.80 times the values calculated with the effective stress method for piles under compression.

Risk assessment for the cascading failure of underground pillar sections considering interaction between pillars

The cascading failure of underground pillar sections poses a risk to miners and surface structures. Assessing the risk of underground mining panels contributes to the prevention and control of the catastrophic failure. To resolve the challenge in quantifying the effect of failure of a single pillar on the risk of an entire pillar section, a new risk assessment model incorporating the stability of individual pillars and the load transfer between pillars was proposed to investigate the cascading failure of pillar sections. The load transfer process from failed pillars to adjacent ones was effectively quantified by the relationship between transferred incremental load and transferring distance. The influence of uncertainties of pillar strength, caused either by intrinsic strength variability of a single pillar (quantified by coefficient of variation COV) or the non-uniform deterioration process of pillar sections (quantified by correlation coefficient ρ), was investigated on the probability of cascading failure. Risk mapping was also performed on two representative historical collapsed pillar sections using the risk evaluation method proposed to illustrate the risk level of each pillar to trigger cascading failure. The proposed model could represent realistic load transfer process and provide reliable risk assessment results for pillar sections. The results showed that the reliability of pillar sections is significantly influenced by both intrinsic variability in pillar strength and intercorrelation of strength between pillars. The probability of cascading failure increases with increasing COV, which verifies that geological uncertainties increase the risk of collapse in pillar sections. The impact of COV on probability gradually decreases to negligible levels as ρ increases to 1, which means that the synchronous variation of pillar strength among a pillar section can significantly compensate for the impact of COV. The proposed approach provides a distinct perspective on understanding sudden failure of high-risk pillars and contributing to the risk control for abandoned pillar sections.

Load Transfer of Offshore Open-Ended Pipe Piles Considering the Effect of Soil Plugging

Open-ended pipe piles have been increasingly used as the foundations for offshore structures. Considering the soil plugging effect, a novel analytical model is proposed in this paper to study the load transfer mechanism of open-ended pipe piles. A trilinear model for the external shaft friction was introduced, while a rigid plastic model was adopted to describe the load transfer at the pile-plug interface. Furthermore, an equilibrium equation of the soil plug was proposed, based on the hypothesis of a trilinear distribution of lateral earth pressure. The pile end resistance was analyzed by dividing it into two parts, i.e., the soil plug and pile annulus, the behaviors of which were described by the double broken line model. A calculation example was carried out to analyze the load transfer properties of the open-ended pipe piles. As a validation, similar load transfer processes of the open-ended pile were also captured in a newly built discrete element method model, mimicking the 100g centrifuge testing conditions.

Low-velocity impact and residual flexural behaviors of 2.5-D woven composite under accelerated thermal ageing: Experiment and numerical modelling

This paper aims to investigate the thermal ageing effect on the impact and post-impact behaviors of 2.5-D woven composites. A combined experimental and numerical study is carried out over a range of impact energies with the subsequent residual flexural tests on both aged (in the air for 32 days at 180℃) and pristine samples. Low-velocity impact tests are performed to assess the degradation of impact-resistant ability in terms of energy absorption mechanism and failure modes. Subsequently, three-point bending tests are conducted to determine the post-impact behaviors with respect to strain concentration, stress transfer and damage evolution process. The strain fields in the finite element model are compared with experimental results obtained by the DIC method. A larger strain concentration area could be found at higher energy levels and longer ageing time. Extended impact damage, such as fiber breakage and delamination, plays an important role in load transfer process in post-impact behavior, thus leading to the decrease of residual stress in aged samples.

A Full‐Scale Field Study on Bearing Characteristics of Cast‐in‐Place Piles with Different Hole‐Forming Methods in Loess Area

This paper presents the results from a full‐scale field study on the 3 different types of cast‐in‐place piles: rotary drilling piles (RDPs), manual digging piles (MDPs), and impact drilling piles (IDPs), for a bridge construction project of Wuqi–Dingbian Expressway, in Shaanxi. The results indicate that under the similar conditions, MDP exhibits the largest bearing capacity (11000 kN) in the loess area, followed by RDP (9000 kN) and IDP (8000 kN). And all tested values exceed the estimated value (7797.9 KN), indicating that the calculation formula of bearing capacity recommended by the Chinese standard is safe and conservative. During the load transfer process, the axial force attenuation rate of the pile body increases with pile side resistance. The average attenuation rate of MDP is the largest (24.2%), followed by RDP (19.72%) and IDP (16.69%). The bearing characteristics of these test piles are mainly pile side resistance, but the manual digging method created the least amount of disturbance to the soil around the pile, and due to its hole wall being rough, this enhances the pile‐soil interactions. Hole‐forming methods mainly affect the exertion of pile side resistance compared with pile end resistance. In view of pile side resistance and pile end resistance not taking effect at the same time, degree of exertion of these 2 resistances should be considered when designing cast‐in‐place piles in loess areas, and different partial coefficients should be used.

Investigation of load transfer process between external fixator and bone model by experimental and finite element methods.

Unilateral external fixators are widely used in orthopedics to stabilize fractured bones and to treat limb deformities. One of the main problems is that it is difficult to detect healing status. In addition, whether load transfer progress between the fixator and bone model are the same under axial, torsional, and bending loads has not been studied. Therefore the main purpose of this study was to detect the load transfer process between the fixator and a bone model by measuring strains on the fixator-bone system during four healing states using experimental and finite element methods. In the experimental method, 20 strain gauges were used to measure strain on the fixator and bone model under three load conditions. Polyacetal slice models with different material properties were used to simulate the callus model during four growth states. The results indicate that strain on the bone model increased and strain on the fixator parts decreased with maturation of the callus under axial, bending, and torsional loads. Although all curves showed a similar changing trend, they were slightly different under the three loads. This study provides a useful method to monitor the fracture healing process, and identifies the healing endpoint, detects healing status, and provides useful information for the orthopedist.

Operational Reliability Assessment for Gas-Electric Integrated Distribution Feeders

Reliability enhancement is a major motivation for integrating electric and gas energy distribution systems. Compared with reliability assessment at the stage of planning, which emphasizes calculating the system annual average indices, the coupling of gas and electric energy flows contributes more to the operational reliability of the integrated system, especially during peak-load periods. In this paper, a method is proposed that assesses system outage risk in each time period by modeling the consequence of the worst N-1 fault in the integrated electric-gas system. In order to accurately model the load transfer process, a novel dynamic load restoration model is applied to minimize load loss of the system, where the fluctuation of multiple energy flows during fault clearing periods is considered. The effectiveness of the proposed approach is validated by performing case studies.

Experimental and numerical analysis of fully grouted long rockbolt load-transfer behavior

As a simple supporting structure, rockbolts are responsible for maintaining the integrity and stability as well as controlling the deformation, displacement, and crack development in the surrounding rock mass. Knowledge of rockbolt load-transfer behaviors constitutes valuable information, as the rockbolt functionality is affected by load-transfer processes. A series of pullout tests was conducted on a rockbolt with a long embedment length (1500 mm). The critical rockbolt embedment length at which yielding or necking occurs together with the friction coefficient at the residual axial stress was analyzed numerically. Additionally, the failure modes of rockbolt-grouted systems and the effects of several parameters, including the rockbolt diameter (18, 20, and 25 mm) and cement mortar strength, were assessed. The rockbolt strain and energy absorption during the pullout process were also investigated. The identified rockbolt failure modes, which are dependent on the cement mortar strength and rockbolt diameter, include pullout accompanied by partial concrete splitting failure parallel to the rockbolt. Under the same cement mortar strength, the maximum load increases and the rockbolt displacement at the maximum load decreases as the rockbolt diameter increases. When diameter is held constant, the maximum load and corresponding displacement increase as the cement mortar strength increases, but the residual load is irregular. The energy absorbed by the rockbolt in the pullout test is related to the cement mortar strength and failure mode. With an increasing embedment length, the failure process is converted from a completely damaged interface with little simultaneous damage to the cement mortar at the free end to the expansion of the cracks at the loaded and free ends toward each other. The interface is completely damaged when the cracks at both ends become connected.

Hydrogen-bonding power interfacial load transfer of carbon fabric/polypyrrole composite pseudosupercapacitor electrode with improved electrochemical stability

The design of a strong interface interaction is a critical issue to improve the electrochemical stability of polypyrrole (PPy) composite electrodes. In the natural world, hydrogen bond that powers the load transfer can be observed in spider silk. The challenges are to achieve interfacial hydrogen bond interaction to stiff the PPy to help the effective load transfer and alleviate the swelling/shrinkage of PPy chains. Here, a composite electrode was prepared by pyrrole (Py) vapor deposition on the air-plasma-activated carbon fabric (PCF) surface. The X-ray photoelectron spectroscopy and fourier transformed infrared spectroscopy results showed that the COOH groups appearing on the PCF and hydrogen bonds can be formed on the interface of PCF/PPy. Interfacial shear strength (IFSS) and scanning electronic microscope determined hydrogen bond on the interface of PCF/PPy enhance the adhesion and power the load transfer process from PPy to carbon fiber. These interfacial hydrogen bonds severed as adhesion points helped the load transfer effectively to the substrate and decreased the contact resistance, preventing the damage of PPy chains and improving electrochemical performances of PCF/PPy as the electrode for pseudosupercapacitor. The PCF/PPy supercapacitor showed excellent cycling stability (93% capacitance retention after 4000 cycles), while CF/PPy showed poor cycling stability (74% after 4000 cycles). The idea of hydrogen bond powered electrochemical stability can be of reference for the researchers to improve the cycling stability of other conductive polymers that are widely used in high-performance supercapacitor.

Corrosion Protection Behavior of Patinas on Copper Alloys in Historical Metal Heritage: Electrochemical Study

All copper base alloys based copper tend to form a layer of oxide (patina), which gives or not protection to the base metal in the environment where they are exposed, this depends on the interaction with various agents such as chlorides (Cl-), sulfur dioxide (SO2), oxides of nitrogen (NOx) and ozone (O3), as well as the influence of solid particles in suspension such as coal, pollen and microorganisms, etc., which create dust deposits on the patina, which They compact by acting as a sponge, retaining moisture and thus favoring the corrosion phenomenon causing mechanical and chemical damage, originating in some cases soluble corrosion products that due to meteorological conditions such as precipitation can be eliminated, leaving the metal in some areas more exposed and ruining with This is the artistic appearance of the monument. [1-5] In this work, the induction of artificial patinas on Cu base alloys (brass and bronze) was carried out. The aim os this work was analyzing their degradation and evolution mechanisms, being these, characteristics of monuments exposed in atmospheres rich in Cl-, SO2 and NOx to achieve it were used solutions of NH4Cl 33% w, CuSO4 15mM and CuNO3 20% w, respectively. [6] After that, they were exposed to the atmosphere, in the port of Veracruz, Mexico., Having an environment of marine-tropical study, as well as the Cl- and SO2 ppm were monitored in strategic points of the City, this by ISO 9225 Standard. [7] For the study of the corrosion mechanism, electrochemical techniques were used, such as Electrochemical Impedance Spectroscopy (EIS) and Electrochemical Noise (EN). For the measurements, a typical three-electrode cell was used in EIS. A working electrode was used (patinated Cu alloy). ), a reference (Calomel Saturated electrode) and an auxiliary one (graphite), for EN two working electrodes and a reference electrode were used, a representative solution was used as electrolyte, which contained the ppm of contaminants that were monitored monthly, the study was complemented with Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Fourier Transform of Attenuated Total Reflection (FT-ATR). The results showed corrosion products typical of the environments that were desired to be characterized, finding; Brochantite (Cu4SO4 (OH) 6) and Atacamite (CuCl2 · (H3O) while CuNOx were more soluble, this was reflected in EIS, where Nyquist spectra with defined semicircles were found typical of load transfer processes, however for the samples with corrosion products of Cu4SO4 (OH)6 in the Bode diagrams it was possible to observe the increase in the Rtc, and the presence of a second time constant, which is related to the stability and compactness of these products.

Experimental study on progressive collapse resistance of steel frames under a sudden column removal scenario

A comprehensive experimental apparatus for the progressive collapse testing of steel frames has been developed. The apparatus is suited for the testing of planar steel frames to study the load transfer process and the progressive collapse resistance of steel structures under a column removal scenario. In order to simulate a sudden removal of a middle column at the ground storey of the frames, a removable column unit has been designed to allow for an instantaneous knock-out by a pendulum hammer during the test. To avoid the out-of-plane instability of the planar steel frames, an out-of-plane restraining system has been designed and integrated into the test apparatus. Weights simulating the desired gravity loads were attached to the test frame through holding baskets, which were designed to minimize unwanted shaking and ensure that the suspended baskets moved together with the deformed steel frames during the tests. Experimental results showed that the column removal mechanism in the test apparatus was effective. Using this apparatus, the dynamic behaviour of three planer steel frames under a column removal scenario was investigated. Based on the measured deformations and strains, the dynamic response, collapse modes, load transfer path of the steel frames after the removal of the middle bottom column are studied.

Shaft capacity of the pre-bored grouted planted pile in dense sand

The pre-bored grouted planted pile is a new type of composite pile foundation that consists of a precast concrete pile and the surrounding cemented soil. A series of shear tests were conducted in a specific shear test apparatus to investigate the shaft capacity of the different pile–soil interfaces. The test results show that the frictional capacity of the cemented soil–sand interface is controlled mainly by the sand properties, while the strength of the cemented soil slightly influences the interface properties by affecting the normalized roughness coefficient Rn. The frictional capacity of the concrete–sand interface is similar to the frictional capacity of the cemented soil–sand interface, and the existence of mud cake layer virtually hampers the frictional properties of the interface. The maximum skin friction of the concrete–cemented soil interface increases approximately linearly with the increasing cemented soil strength, and the value of the maximum skin friction is much larger than that of the cemented soil–sand interface of identical cemented soil strength, which demonstrates the integrity of the pre-bored grouted planted pile in the load transfer process.

Vehicle braking force distribution with electronic pneumatic braking and hierarchical structure for commercial vehicle

Brake by wire that allows a number of braking functions exists on commercial vehicles under the name electronic pneumatic braking system, which can improve braking comfort and safety of commercial vehicle. The design of braking force distribution control method has drawn much more attention. Considering structure characteristics of electronic pneumatic braking system, a control method with a three-layer hierarchical structure is proposed. The first layer presents an estimation method towards vehicle mass and centre of gravity combining Kalman filter with recursive least square. The second layer is developed by designing a fixed relationship between the brake pedal displacement and vehicle braking deceleration. A deceleration control method that only uses brake pedal displacement as input is applied to make the vehicle follow the desired deceleration. The third layer includes a braking force distribution control method between the front and rear axles. The vehicle deceleration can be achieved with a smooth axle load transfer process based on linear matrix inequality. In addition, the controllers of wheel slip rate and valve hysteresis compensation are designed to improve control accuracy and efficiency. Utilizing a hardware-in-the-loop simulation test rig of electronic pneumatic braking system, the experiment results show that the control method can improve the braking performance of vehicle.

Direct nanomechanical characterization of carbon nanotubes - titanium interfaces

Interfacial interactions between carbon nanotubes (CNTs) and metal matrices play a critical role in the bulk mechanical properties of CNT-reinforced metal matrix nanocomposites (MMNC), but their load-transfer mechanisms remain not well understood. In this paper, we conduct single-nanotube pull-out studies with in situ scanning electron microscopy to quantify the mechanical strength of binding interfaces in carbon nanotube (CNT)-reinforced titanium (Ti) nanocomposites. Our nanomechanical pull-out measurements reveal a shear lag effect in the load transfer on the CNT-Ti interface. The interfacial shear strength and the maximum load-bearing capacity of the tested CNT-Ti interfaces are quantified to be about 37.8 MPa and 245 nN, respectively, both of which are substantially higher than the reported values for CNT-Al interfaces. Density functional theory calculations reveal that the experimentally observed strong CNT-Ti binding interface is attributed to strong chemisorption interactions of Ti atoms on CNT surfaces, albeit moderated by the weakening effect of the oxide layer. The research findings are useful to better understand the load transfer process on the tube-metal interface and the reinforcing mechanism of nanotubes, and ultimately contribute to the optimal design and performance of nanotube-reinforced MMNC.

Structural integrity assessment and rehabilitating of Hercilio Luz bridge

The Hercílio Luz suspension bridge, built in 1926, has been out of service since 1991 due to high corrosion levels and structural element impairment. A complete rehabilitation project was developed which included the replacement of the impaired items and foundation strengthening. For this, an auxiliary structure was employed to support the central span during the rehabilitation process. A carefully studied load transfer process, where the central span loading is transferred from the eye-bar towards the auxiliary structure will be performed. For this purpose, a synchronized jacking sequence will be used, which was predefined by means of numerical model analysis. All structural elements had their designs evaluated and some geometric changes were implemented. This paper presents all the methodology developed in the rehabilitation project of Hercilio Luz bridge, as well as the development stages up to the present date.