Load Transfer Model Research Articles

Considerations to Improve the Aggregate Interlock Model for the Joint Load Transfer in Concrete Pavements

The capability of a joint to transfer load from one side to the other plays a significant role in the performance of a jointed concrete pavement system. Among the available means to providing joint load transfer, the aggregate interlock mechanism is thought to have greater endurance than dowels with respect to load transfer related performance. In the current Mechanistic-Empirical Pavement Design Guide (MEPDG), the concept of joint stiffness was adopted to represent the capability of a joint to transfer load through the dowel and aggregate interlock mechanisms. The use of linear springs to represent the behavior of concrete joint stiffness may be reasonable to investigate the global response of a concrete pavement joint to different levels of load transfer, but there is little guidance available to defining a level of joint stiffness for design analysis purposes in terms of measurable material properties. Therefore, it seems that a more fundamental way of charactering the complicated behaviors of aggregate interlock mechanisms is desirable. A constitutive relationship (i.e. shear stress vs. shear displacement) that considers geometric and micromechanical behavior of a crack interface and associated laboratory testing setups to calibrate the model coefficients may be needed to address such a challenge. This paper elaborates an approach of using the shear stress vs. shear displacement response curve predicted by the application of the well-known twophase model to calculate the shear capacity and load transfer efficiency of a joint. Although the well-known two-phase model provides good accuracy in matching experimental results, limitations still exists. Through extensive literature reviews, this paper also suggests other improvements to the micromechanics-based aggregate interlock model by taking into account the effects of boundary conditions, traffic loading and angularity of aggregate particles.

Load transfer model for vertically loaded non-circular piles

The load-transfer (LT) method, involving a series of ‘t-z’ springs to represent pile shaft-soil interaction and a ‘q-z’ spring to represent pile tip-soil interaction, is widely used to model the load–displacement behaviour of vertically loaded piles. While a plethora of LT models have been proposed for piles with circular cross sections, they are not directly applicable to non-circular (NC) cross sections. Therefore, there is a lack of tailored solutions for rectangular, H-shaped and X-shaped piles even though they are common in geotechnical practice. The aim of this paper is to develop a general theoretical framework for the construction of LT curves for NC piles. This framework allows NC piles with any cross section to be considered. The LT curves for NC piles are formulated using a two-parameter hyperbolic model which requires input of (a) the initial elastic LT stiffness and (b) the unit ultimate shaft friction. The elastic stiffness for vertically loaded NC piles with arbitrary cross sections is described using a rigorous semi-analytical (SA) solution involving variational principles. A nonlinear numerical solution for the pile governing equation with the incorporated t-z and q-z curves is achieved using the Runge-Kutta (RK) method. The proposed LT curves are used to construct the pile governing equation and a numerical solution using the Runge-Kutta (RK) method is proposed to predict the responses of NC piles in drained sand. The proposed theoretical LT predictions of pile response are validated through comparisons to elastic–plastic finite element calculations.

Thermo-Mechanical Coupling Load Transfer Method of Energy Pile Based on Hyperbolic Tangent Model

By employing the hyperbolic tangent model of load transfer (LT), this paper establishes the thermo-mechanical (TM) coupling load transfer analysis approach for an energy pile (EP). By incorporating the control condition of the unbalance force at the null point, the method for determining the null point considering the temperature effect is enhanced. The viability of the presented method is validated through the measured outcomes from model experiments of energy piles. A parametric investigation is conducted to explore the impact of the soil shear strength parameters, upper load, temperature variation, head stiffness, and radial expansion on the axial force, strain, and displacement of the energy pile under thermo-mechanical coupling. The results suggest that the locations of the null point and the maximum axial force are dependent on the constraint boundary conditions of the pile side and the two ends. When the stiffness of the pile top increases, axial stress and displacement increase, while strain decreases. An increase in the drained friction angle leads to an increase in axial stress under thermal-load coupling, but strain and displacement decline. The radial expansion has a negligible influence on the thermo-mechanical interaction between the pile and the soil.

Behavior of steel-plate concrete wall-reinforced concrete slab joint with UHPC-strengthened lap-splice connection

The comprehensive integration of modular technology is the crucial pathway for advancing the upgraded Hua-long Pressurized Reactor (HPR1000). However, previous studies are limited and numerous challenges remain concerning the modular curved steel-plate concrete (SC) wall-reinforced concrete (RC) slab joint. This paper focuses on the behavior and design of the SC wall-RC slab joint through large-scale tests and numerical simulation. Two UHPC-strengthened non-contact lap splice (NS) connections, including versions with normal and headed rebars, were proposed to ensure effective load transfer and modular construction performance. The test results indicated that the four joint specimens subjected to cyclic loading did not experience lap splice failure but instead suffered interface shear failure and shear failure of the RC slab under shear-span ratios of 1.5 and 3.0, respectively. The excellent load transfer performance demonstrated by these two NS connections validates them as effective methods for this joint, with lap lengths of 21d for normal rebar and 13d for headed rebar deemed adequate. Besides, the developed three-dimensional FE model with non-linear spring element accurately simulated the test failure modes and F-Δ curves. The parametric study results recommended that the volumetric steel ratio of tie-bar should not be lower than 1.03 %. The tension of longitudinal rebars for normal and headed rebars can be fully transferred within 80 % of the designed lap length. Furthermore, a complete design method was established based on the load-transfer model, encompassing interfacial shear, lap length calculation and tie-bar configuration, and is applicable to SC-to-RC connections or joints.

Approximate analytical algorithm for pull-out resistance-displacement relationship of combined anchor system

Building upon an evaluation of the distinct advantages and limitations of anchor rods and anchorage plates, this paper introduces an integrated anchor-tensioning system that combines these elements in series. This innovative approach significantly enhances the pullout bearing capacity of the overall anchorage system. Based on the hyperbolic model of the distribution of lateral friction resistance of the anchor solid and the Winkler′s foundation model of load transfer of the anchorage plate, the theoretical analysis method for the analysis of the pullout bearing capacity and deformation of the combined anchorage system was established, and an approximate analytical equation for the relationship between pullout force and displacement was obtained. The results from indoor model tests, numerical simulations, and theoretical analyses were compared, verifying the reliability of the theoretical methods employed. The findings of this study significantly advance the discourse on the innovation of structural support configurations, thereby enhancing the operational efficiency of anchor-pull support systems.

Load transfer model and failure prevention measures of a mechanical-type anchorage for anchor cable in deep roadway

In this paper, the load transfer mechanism of a mechanical-type anchorage is analyzed and studied. The stress distribution on the surface of the anchor cable is clarified, and the means of mechanical analysis and Abaqus finite element method are used. Results indicated there is no stress concentration, and the peak value indicated by the anchor cable appears near the loading end, and the peak value is about 60 MPa larger than the tensile strength. The results of the tensile test show that the failure mode of the anchor cable is the necking fracture of the steel wires, which indicates that the steel reaches the yield limit stress. The anchor efficiency of mechanical-type anchorage is high, which can effectively exert the tensile strength of anchor cable. In deep mine roadway, two failure modes of anchor cable are summarized when mechanical-type anchorage is used. Including shear failure and slippage failure under dynamic action. Aiming at the shear failure behavior, a new type of anchorage was invented, including the self-aligning and shear resistance functions of the anchor cable, and an experiment was carried out. Results indicated anti-shear anchorage can effectively solve the problem of anchor cable failure caused by shear. For the problem of anchor cable slippage failure under dynamic action. The parameters affecting the stability of mechanical-type anchorage are analyzed by means of theoretical analysis and numerical simulation. Results indicated reducing the bevel angle of wedge and barrel, the difference angle between them, and increasing the friction coefficient μ between wedge and barrel can increase the stability of mechanical-type anchorage. The research content of this paper can provide reference for the design of mechanical-type anchorage in similar underground engineering.

Energy-saving drive control strategy for electric tractors based on terrain parameter identification

Emissions from agricultural production already have a significant impact on the global environment. New energy, zero-emission electric tractors have great potential for application. How to further reduce energy consumption under the premise of ensuring operational stability is an urgent problem to be solved to realize the broad application of electric tractors. For this purpose, this paper proposed an energy-saving drive control strategy for electric tractors based on terrain parameter identification. At first, the longitudinal dynamics model and load transfer model of the electric tractor were established by considering the terrain information of the area to be operated. Mathematical principles for adjusting wheel slip to reduce energy consumption in electric tractors are presented. Then, a wheel longitudinal force estimation algorithm was designed based on the principle of sliding-mode observer and dynamics compensation. To achieve energy-saving drives for electric tractors, a particle filter based on a wheel-soil model was designed to identify terrain parameters in real time and calculate the optimal slip to control the torque of the drive motor. Lastly, the strategy is validated by hardware-in-the-loop (HIL) simulation tests and real-vehicle tests. HIL tests show that this strategy results in a 25.35% increase in operational speed stability and a 6.79% reduction in operational energy consumption compared to the conventional drive control strategy. The real vehicle test shows a 45.09% increase in operating speed stability and a 9.51% reduction in total energy consumption of the proposed method. The proposed drive control strategy reduces operational energy consumption and operational costs on the premise of ensuring the stability of operational speed, which is conducive to the implementation of cleaner production.

Response of piled raft foundations using the disturbed state concept theory: Analysis and interpretation

In nearshore and marine environments, challenges arise from loading conditions, subsoil profiles, and dynamic soil states influenced by continuous wave action. Piles in such settings face complex interactions due to soil vulnerability to loading and over-consolidation. Accurate estimation of pile shaft and base resistances, as well as raft-soil interface stiffness, is crucial. The paper introduces the disturbed state concept for analysing piled raft foundations under vertical loading. This theory assumes interface strength between piles and soil follows an exponential distribution, expressed through the Weibull function. Interaction between piles is established using a modified displacement factor, which is a modified form of Mindlin's solution. Raft-soil interaction is modelled with springs connected to the pile head. The load transfer model exhibits both softening and hardening responses. Validation against numerical and field experimental studies demonstrates close agreement within a 5%–15% error range. Parametric investigation analyses load-settlement response, percentage of load on pile base with settlement increase, and axial load transfer along pile length under varying conditions. The impact of limiting pile-soil relative movement on piled raft response is also explored.

Validating a finite element model for rigid aircraft pavement load transfer against full scale testing

ABSTRACT Rigid aircraft pavements are generally comprised of unreinforced concrete slabs constructed on a bound or granular sub-base layer, over the natural or constructed subgrade or fill. Important to any rigid aircraft pavement design and construction are the joints between the concrete slabs. The joints control shrinkage cracks during curing, allow for thermal expansion and contraction during temperature cycles, they isolate concrete slabs from structural penetrations and importantly, provide load transfer between adjacent slabs. Load transfer is commonly modelled using finite element methods; however, any new model should be validated against observed physical events. Recently, full-scale testing was performed at the Federal Aviation Authority National Airport Pavement Testing Facility as part of Construction Cycle 8 (CC8), which investigated load transfer characteristics for a range of joint types. The results from CC8 tests provide up-to-date stress and strain values to validate any new finite element model. This paper presents the development of a finite element model to predict load transfer of a doweled construction joint, and its validation against CC8 test results. The model showed good agreement with CC8 test results, and now that it is validated, will be used to investigate innovative joint solutions for rigid aircraft pavements.

Bayesian Back Analysis of Axially Loaded Pile Response Using Fibre Optic Strain Data

The load-transfer method has been extensively used to evaluate the deformation behavior of foundation piles, with the nonlinear load-settlement behavior of a pile-soil system modeled using load-transfer curves. Although load-transfer models have a considerable impact on the pile response, the model parameters are usually estimated empirically from soil parameters using transformation models, and the associated uncertainties are often neglected. Fiber optic sensing technology provides detailed axial strain information along the entire length of a pile; however, the full potential of such utilization has not yet been realized. This paper presents a Bayesian back analysis method for statistical descriptions of load-transfer curves and pile responses based on fiber optic measurement. A pile test case study is used to illustrate the proposed method, and several candidate model configurations are compared. The results show that the predicted pile response generally matches the measured data, and the quantified uncertainty allows for a better understanding of the possible ranges of the pile response, in addition to the single best-estimate result.

Rural Photovoltaic Storage and Charging Integrated Charging Station Capacity Allocation Strategy based on Tariff Compensation Mechanism

Background: In order to help the carbon peaking and carbon neutrality goals, the current new energy vehicle to the countryside policy for the local use of renewable energy and demand-side carbon reduction provides a good opportunity but also requires rural townships and villages of electric vehicle charging infrastructure planning ahead. However, due to the current low rural electric vehicle ownership, the charging price compensation mechanism is not yet perfect, resulting in the planning period of electric vehicle growth and the willingness to respond to the tariff compensation policy is difficult to accurately assess. Methods: This paper proposes a rural photovoltaic storage and charging integrated charging station capacity allocation strategy based on the tariff compensation mechanism. Firstly, we construct a spatial-temporal dynamic distribution model of rural EV charging load coupled with distribution network-transportation network, and on this basis, we consider the rural EV charging time-sharing tariff and tariff compensation policy incentive, and amend the EV charging load transfer model; and then we construct an optimization planning model of charging station with the goal of minimizing the cost of construction, operation and maintenance, and maximizing the charging benefit of the integrated charging station in the rural area, and obtain the optimal synergistic planning scheme under the tariff compensation mechanism in the planning period. Results: The optimal collaborative planning scheme under the electricity price compensation mechanism is obtained, and the correctness and validity of the proposed optimal planning method of the rural optical storage charging station under the electricity price compensation mechanism is verified by the example, which is of positive significance in the promotion of the charging facilities to go to the countryside in an appropriate manner, and in the stimulation of the willingness of the rural consumers in the townships to purchase vehicles. Conclusion: (1) The spatial and temporal distribution and transfer model of rural EV charging loads with price incentives is constructed by taking into account the preferential charging price policies such as rural time-sharing tariff and tariff compensation mechanism. By comparing the operating revenues of optical storage-charging integrated charging stations with and without timesharing tariffs and tariff compensation policies, we verified the incentive effect of multiple types of price incentives for the over-planning of rural electric vehicle charging facilities. (2) The proposed optimal configuration method of rural photovoltaic, storage and charging integration charging station can realize the in-situ utilization of rural renewable energy, tap the price competitiveness of photovoltaic, storage and charging integration, and weaken the cost of electricity consumption. By comparing the optimized configuration scheme with and without joint planning, it is verified that the moderate configuration of in-situ photovoltaic and energy storage equipment on the basis of the planning of charging piles brings benefits far exceeding the investment cost, and has a great role in increasing the operational efficiency of rural charging facilities.

The Calculation Method for the Horizontal Bearing Capacity of Squeezed Branch Piles Considering the Plate–Soil Nonlinear Interaction

The m-method is a commonly used method to calculate the internal force and deformation of pile foundations under lateral loads. However, for squeezed branch piles, the increase in the load-bearing plate leads to changes in the pile section and the generation of a resistance bending moment under loading, which means the load–displacement relationship at the load-bearing plate will no longer satisfy the linear relationship. In this paper, a hyperbolic load transfer model is established to describe the nonlinear relationship between the soil resistance and lateral displacement at the branch of the pile, and the m-method is used for the straight section of the pile. Laboratory model tests are used to verify the correlation between theory and experimentation. The results show that the theory is consistent with the measured curve. On the basis of the theoretical calculation, the influence of the bearing plate and pile body parameters on the force of the squeezed branch pile is analyzed. The research shows that that the bearing capacity of the squeezed branch pile is improved by increasing the plate’s diameter, placing the plate closer to the ground, and ensuring that the pile top is embedded. The theoretical calculation method established in this paper can correctly and accurately reflect the bearing capacity characteristics of squeezed branch piles under horizontal loads, and it is more safe than performing measurements. Additionally, it can be applied to squeezed branch piles with different plate diameters, plate positions, plate section forms, and plate quantities as well as for piles with different boundary conditions and soil conditions. Moreover, it can also be applied to other pile shapes. This method is of significance for the analysis of the bearing characteristics of piles with variable sections under lateral loads.

An Axial Load Transfer Model for Piles Driven in Chalk

An Axial Load Transfer Model for Piles Driven in Chalk

Axial cyclic performance of a jacked pile in structured clays: A semi-analytical solution approach

Cyclic loads resulting from environmental factors such as wind, waves, trains, and construction activities pose a potential hazard to the stability of piled structures. These loads can cause the performance degradation of piles, including cumulative settlement and weakening of bearing capacity. This paper presents a semi-analytical solution for evaluating the axial cyclic behavior of jacked piles in structured clays. The solution employs enhanced nonlinear load-transfer models that effectively capture the stress-strain hysteresis and interfacial cyclic degradation characteristics. The key factors influencing pile behaviors are incorporated within the analytical approach, encompassing pile installation, subsequent soil equalization, and the static and cyclic loading encountered during service. The validity of the current solution is established through model pile tests conducted in artificially structured clays under static and cyclic loading conditions. Extensive parameter studies are performed using the proven theoretical approach to emphasize the influence of soil structure and cyclic loading on pile behavior. The results demonstrate a favorable agreement between the theoretical and measured values in static and cyclic pile response analyses. Compared with the response of jacked piles in reconstituted clays, the pile response in structured clays with a cement content of Aw = 4%, including penetration resistance, final ultimate bearing capacity, and the convergence speed of permanent settlement, has been substantially improved. The parameter studies indicate that soil structure and cyclic loading patterns significantly influence the axial cyclic performance of jacked piles in natural clays.

A generalized elastoplastic load-transfer model for axially loaded piles in clay: Incorporation of modulus degradation and skin friction softening

The softening behavior of skin friction is commonly observed from load-displacement responses of axially loaded piles in stiff clay, sensitive clay, and dense sands at a large loading level. This paper presents a generalized and novel elastoplastic load-transfer model to predict the load-displacement response of axially loaded piles in clay considering the degradation of skin friction. In this model, the soil around piles is divided into the shear band immediately adjacent to piles and the soil outside shear bands. An elastoplastic model in terms of the critical state theory-based modified Cam-clay model is developed to describe the mechanical behavior of shear bands. The elastoplastic model can explicitly consider both hardening and softening behaviors of skin friction. The elastic behavior of the soil outside shear bands is represented by a modulus degradation model, which captures the shear modulus degradation with the shear strain. Subsequently, an elastoplastic load-transfer model possessing generalized ability to describe both hardening and softening behaviors is developed by combining these two theoretical models. Predictions of the load-settlement curves are compared with the measured values from three well-documented cases to verify the proposed model. Good agreements demonstrate that the proposed load-transfer model provides reasonable and effective prediction for bearing performance of piles.

Analytical Solution for Negative Skin Friction in Offshore Wind Power Pile Foundations on Artificial Islands under the Influence of Soil Consolidation

The construction of offshore wind power pile foundations on artificial islands is a challenging task due to soil consolidation and additional loads that result in negative skin friction (NSF). In this study, a comprehensive pile–soil interaction model is established to investigate the development of NSF in artificial islands under the action of self-weight consolidation of fill soil and surcharge load. The one-dimensional consolidation theory and an ideal elastoplastic load transfer model are employed to obtain the analytical solution for skin friction and axial force of the pile with respect to time and depth. The predicted results are in good agreement with the field tests and finite element methods. Finally, a parametric study is conducted to investigate the effect of pile installation time, surcharge load, and pile head load on the development of NSF.

A Time-Dependent Load-Transfer Model for Large Step-Tapered Hollow Piles Based on the Disturbed State Concept

A Time-Dependent Load-Transfer Model for Large Step-Tapered Hollow Piles Based on the Disturbed State Concept

A simple load transfer method for energy pile groups

Various analysis methods have been developed to simulate the performance of energy pile groups subjected to thermal and mechanical loads. Although they considered the interactions between piles in the group, the ‘sheltering-reinforcing’ effect was usually ignored during the analysis, or the methods were not experimentally validated. Therefore, to address this gap, we propose an experimentally validated load transfer model that considers the ‘sheltering-reinforcing’ effect for the thermomechanical analysis of energy pile groups. The proposed method modeled two well-documented full-scale field tests and two finite-element simulation cases. The comparison results showed that the proposed method could capture several essential aspects of the energy pile group, including thermally induced strain, stress, displacement, and group effects. Furthermore, a parametric analysis was performed to evaluate the effects of relevant parameters on the thermomechanical behavior of the energy pile group.

Study on bonding performance and load transfer model between polyurethane anchor bolts and silty soil

The bonding performance between the anchor anchorage body and soil is an important index to evaluate the anchoring performance of anchor bolts. In this work, the vertical polyurethane grouting anchor bolt is taken as the research object, and the bonding performance between polyurethane anchorage body and silty soil was studied by 13 sets of field pull-out tests, and the distribution law of the axial force and the bonding stress of the polyurethane anchor bolts along the anchoring depth, as well as the influence of the diameter (D = 60 mm, 75 mm, 90 mm, 100 mm, 120 mm), density (ρ = 0.2 g/cm3, 0.3 g/cm3, 0.4 g/cm3, 0.5 g/cm3, 0.6 g/cm3) and length (L = 2.0 m, 2.5 m, 3.0 m, 4.0 m, 5.0 m) of the polyurethane anchorage body on the bonding strength between the polyurethane anchorage body and silty soil were analyzed in detail, and finally the load transfer equation of polyurethane anchorage body under vertical pull-out load was obtained by theoretical derivation. The results show that the error between the calculated results of the load transfer equation and the experimental results is less than 12%, which further indicates that the load transfer equation derived in this paper can reasonably describe the distribution of axial force and bonding stress along the anchorage depth of the polyurethane anchor bolts. The axial force of polyurethane anchor bolt is the largest at the top of the bolt body, and decreases along the anchoring depth, and the axial force at the bottom is far less than that at the top. Polyurethane anchor bolt has significant bonding stress concentration phenomenon, with the increase of load the peak bonding stress and bonding stress distribution area increases, and shifts to the bottom of the anchorage body. The borehole diameter, anchorage body density, and anchorage body length all have important effects on the bonding strength: the bonding strength increases with the increase of anchorage body density, and the increase is more obvious in the case of small density, and the increase of bonding strength becomes smaller after the density exceeds 0.4 g/cm3, the bonding strength decreases with the increase of anchorage body length and borehole diameter.

Study on Space–Time Evolution Law and Mechanism of Instability Failure of Deep High-Stress Overburden Rock

In order to explore the fracture law and structural evolution characteristics of overlying strata in deep high-stress mining, according to the geometric characteristics and mechanical causes of overlying strata in different mining stages of the stope, four stages of overlying strata structure model are established and analyzed in turn. According to the characteristics of the overburden load transfer path in the deep high-stress stope, the fracture law and macroscopic mechanical response of overburden are analyzed by MATLAB and PFC2D numerical simulation method. The evolution model of overburden structure and load transfer in ‘four stages and three modes’ of the deep high-stress stope is constructed, and the stage fracture effect of ‘beam, plate and arch’ is put forward. The results show that the overburden rock is a fixed beam structure before the initial weighting. After the initial weighting, it evolves into a plate structure with three sides fixed and one side simply supported. After the periodic weighting, the overburden rock structure further evolves into a plate structure with one side fixed and three sides simply supported. After full mining, the overburden rock forms an arch structure, and the load is transmitted by the beam–plate–arch path. The findings of the study provide an important basis for exploring the nature of overburden transport and load transfer in deep high-stress quarries and strengthening overburden prevention and control.