Additional Internal Forces Research Articles

Two-Stage Analysis Method for the Mechanical Response of Adjacent Existing Tunnels Caused by Foundation Pit Excavation

With the advancement of urban underground space networks, there has been a rise in foundation pit projects near existing tunnels. The construction of these foundation pits adjacent to existing tunnels can result in soil disturbance and stress redistribution, leading to additional deformation and internal force within the tunnels. This paper delves into the two-stage analysis method, outlining the calculation of additional stress in the initial stage considering various engineering factors and the methods for determining tunnel displacement and internal force in the subsequent stage. Through an engineering example and numerical simulations, the theoretical calculations were validated. The maximum displacement generated by the tunnel is −4.85 mm and −5.10 mm, respectively. The maximum error is only 5.9%, which confirms the validity of the theoretical approach. The analysis demonstrates that incorporating the unloading model of the bottom and surrounding side walls of the foundation pit is essential when calculating additional stress in the first stage. Moreover, the presence of engineering dewatering and double-hole tunnels can counterbalance the additional stress, with deviations of only 4.4% and 2.5%, respectively. In the second stage, factoring in the shear action and lateral soil action in the foundation and tunnel model enhances the accuracy of stress mode representation (accuracy increased by 18.8% and 29.3%, respectively). Additionally, accounting for the buried depth effect of the tunnel, soil non-uniformity, and foundation nonlinearity helps prevent excessive foundation reactions.

Prediction of adjacent single pile deformation induced by tunnel excavation based on the Pasternak model

The construction of metro tunnels in soft ground would cause significant settlement of the ground surface and deformation of buildings and their foundations in the vicinity of the tunnels. The deformation laws of the pile of the neighbouring structures induced by the tunnel construction have not yet been fully identified. This paper analyzed the impact mechanism of tunnel construction on piles based on the Pasternak model, deduced the calculation methods of additional horizontal displacement and additional internal force of piles, and introduced three solution methods. The computational method results have been validated through numerical simulations using coupling of discrete element method and finite difference method and compared to select laboratory data. The results show that the model accuracy is better when the tunnel axis burial depth is less than the pile bottom burial depth. The analysis shows that the tunnel burial depth significantly influences the displacement distribution of the adjacent single pile, while the impact on the peak displacement is insignificant. The thickness of the elastic layer (C) is inversely related to the maximum horizontal displacement and internal force, but it does not impact the distribution patterns of the displacement and internal force. For thickness of the elastic layer (C), the bending moment’s point is constant at 2 m above and below the tunnel axis, whereas the shear force’s point remains constant at the buried tunnel axis’s depth and 4 m above the tunnel axis.

Finite Element Analysis of Combined Bearing Characteristics of Pile–Soil Interaction in Composite Foundation

Composite foundations have been widely used and promoted in practical engineering applications. However, research on the joint-bearing mechanism of piles and soil within composite foundations is still not comprehensive enough. This paper proposes a method for calculating the additional internal forces of piles and soil within composite foundations. Based on a three-dimensional finite element analysis, this study investigates the variation patterns of the stress, displacement, and additional internal forces of piles and soil in the depth direction under the action of upper loads when using friction piles and end-bearing piles. This research aims to reveal the bearing performance of piles and soil. The results showed that, under the same conditions and due to the presence of end-bearing effects, the internal forces experienced by the entire pile body of the end-bearing piles were more uniform, exhibiting significant advantages in resisting deformation and being able to withstand larger loads. Additionally, the diffusion mechanism of the vertical forces, stresses, and displacements of piles and soil is discussed. Due to the negative frictional resistance of soil and the influence of pile end-bearing effects, the distribution of internal forces and the displacements of piles and soil exhibited different characteristics. This study provides a scientific reference for the theoretical analysis and design of composite foundations.

Numerical-analytical investigation on bending performance of laminated beams in modular steel buildings

It is well-known that the laminated channel beams can significantly strengthen the combination of adjacent beam components and further enhance the structural integrity of modular steel buildings. In present study, the superimposed bending performance of laminated channel beams was comprehensively investigated using the numerical and analytical methods. Firstly, FE models were developed and validated by the experimental data. Then, a series of numerical parametric studies combining the orthogonal and univariate analysis were successively conducted to identify the sensitivity of design parameters including interfacial bolt number (n), interfacial friction (f), layer height ratio (β), load type (p) and boundary condition (b), and further clarify the influence of key parameters on the cooperative bending properties. Finally, the analytical procedure was proposed to evaluate the equivalent bending stiffness of laminated channel beams. The results showed that the effect degrees of design factors on EIe and Pu were as follows: n > β > f > b > p and p > b > β > f > n, respectively. n and β were selected as the key design parameters for the modular laminated beams. The bending responses were nonlinearly promoted by n, while the linear regularity was observed for β. The influencing mechanism of n indicated that the bolt connections induced the additional internal forces, which caused the transferring of neutral axes and the superimposition effect of laminated beams. Quantifying the neutral axis deviations, the analytical models were developed and reasonably assessed the superimposed bending stiffness of laminated beams in modular steel buildings.

A novel self-centering friction damper with elastic post-buckling plates to retrofit bridge bents

The self-centering energy dissipation dampers (SCEDs) have been demonstrated in mitigating the residual deformation of structures under strong ground motions. However, existing researches show that the damping force demand of SCEDs is higher than conventional dampers such as viscous dampers, BRBs or friction dampers for same design displacement of self-centering retrofitted structures, which could lead to higher base shear and acceleration responses of structures. In order to alleviate the problem, a novel self-centering damper composed of elastic post-buckling plates and adjustable friction devices (PBSCFD) was proposed. Compared with conventional SCEDs, the proposed PBSCFD has low secondary stiffness and adjustable energy dissipation capacity, which is beneficial to control the additional internal force of members adjacent to the damper in self-centering retrofitted structures. Based on the configuration and working principle of the PBSCFD, the theoretical force-displacement relationship of the damper was derived. Subsequently, a scaled PBSCFD was manufactured and tested under quasi-static loading to investigate its mechanical properties and to verify the theoretical constitutive model. In order to demonstrate the seismic performance of PBSCFDs, the double-column bridge bent retrofitted with PBSCFDs was designed by direct displacement-based seismic design method (DDBD), and its seismic performance was examined by elastic-plastic time-history analysis. Finally, effects of secondary stiffness ratio of self-centering dampers on seismic mitigation of self-centering retrofitted bridge bent were investigated. The results show that PBSCFDs have certain advantages in controlling the base shear and acceleration of the retrofitted bridge bent compared to conventional SCEDs with significant secondary stiffness.

Research on the influence of foundation pit excavation on the lateral force and deformation of side shield tunnels based on full-scale experiments

To explore the internal force and deformation response law of the Hangzhou subway shield segment under the influence of the excavation and unloading of the side foundation pit, the self-developed “shield segment hydraulic loading system” was used to carry out full-scale loading tests on the three-ring staggered assembled segments. A preloading loading test were performed before the formal experiment to determine the loading method of the initial confining pressure. Analyzed the change mechanism of the internal force and deformation of the segment structure are influenced by factors such as the foundation pit and the tunnel clear distance. A numerical model is established based on the experimental results, and the influencing parameters that are difficult to complete in the experiment, such as the depth of the tunnel, are analyzed in detail. The research results show that the equal load maintains a balanced state of the segment to the greatest extent, and its internal force and deformation results are large, which is suitable for this experiment. After the excavation of the foundation pit, the maximum positive and negative bending moment increases, while the maximum axial force decreases. The average maximum recovery rate of tunnel section is 15.6%. Moreover, the additional internal force and deformation of the segment will increase with increasing deformation parameters of the envelope structure and decrease with increasing clear distance between the foundation pit and the tunnel. The bending moment of the segment is more sensitive to changes in the confining pressure, the convergence change can be controlled within a limited range, and the trend of the change in the internal force of the bolt shows differences. The numerical model established in this paper can better analyze the stress state of the tunnel. When the tunnel is buried deep in the slightly upper position of the excavation surface of the foundation pit, the unloading effect that is received is largest.

Rigid Spliced Box Girder Bridge under the Action of Foundation Settlement Difference Analysis of Mechanical Behavior of Splice Section

In a main line viaduct widening project, the old bridge is 35m+55m+35m three-span variable section prestressed concrete continuous box girder, which has the characteristics of large width, long span, variable section of beam body, large cantilever (4.05m), and transverse prestressed steel beams arranged on the bridge panel, etc. The old and new box girders adopt rigid joint scheme. Articles on rigid splicing box girder bridge in foundation settlement under the action of splicing mechanical properties to carry out the finite element analysis, the results show that the new bridge under the action of foundation settlement difference, longitudinal pier fulcrum position splicing under high horizontal stress, transverse middle fulcrum section splicing appeared transverse stress peak period of angular point position, may result in the crack of the concrete; There is a linear relationship between the level of additional internal force and the settlement difference of foundation, which is about 0.95MPa/mm. The calculation stress value of splicing segment can be reduced by reducing the thickness of splicing segment. In practical engineering, control and adjustment measures such as preloading of new bridge structure and selecting adjustable high support can be used to improve the force condition of splicing section[1][2].

Mechanical Behaviors of a Buckling-Plate Self-Centering Friction Damper

In order to improve the resilience of structures subjected to strong earthquakes, a buckling-plate self-centering friction damper (BPSCFD) with low post-yielding stiffness is proposed, which consists of a group of post-buckling plates and a self-centering variable friction mechanism. The damper is intended to not only reduce the peak and residual deformation of structures, but also to limit the additional internal force of the structural elements. Through theoretical derivation and finite element simulation, the hysteretic damping and self-centering characteristics of BPSCFDs are studied. In order to examine the seismic performance of the BPSCFDs, the dampers are employed to retrofit a double-columns bridge bent, and the corresponding elastic-plastic time history analysis is conducted. The results show that the force-displacement relationships of BPSCFDs with different parameter combinations are characterized by typical flag-shaped self-centering hysteretic loops and low post-yielding stiffness, and the dampers can effectively reduce the peak and residual deformation of the bridge bent without increasing the peak acceleration and base shear. The research results could supply a guideline for the design and application of the damper.

Analytical solution of overlying pipe deformation caused by tunnel excavation based on Pasternak foundation model

The existing tunnel construction causes stratum deformation, which in turn leads to additional deformation and internal force of the overlying pipeline, thus increasing the risk of pipeline accidents. Then, how to correctly calculate the deformation and internal force of pipeline is the key to pipeline safety evaluation. To this end, this study firstly used the Pasternak foundation beam model to simulate the interaction of pipeline and soil, and divided the pipeline into the void area (i.e., pipeline-soil detachment) and the coordination area (i.e., pipeline-soil is always deformed together) between pipeline and soil. The differential equation of pipeline deflection for the void area and the coordination area were established respectively, and the solutions of pipeline deflection, the internal force of pipeline and the width of pipeline-soil void area were presented. Subsequently, the accuracy of the proposed method was verified by comparing with the available model and field test data, and it is found that the calculation results are too conservative without considering the pipeline-soil voiding phenomenon. Finally, the detailed parametric analysis was conducted. The results show that the pipeline deflection decreases with the increase of the pipeline-tunnel spacing between pipeline and tunnel, the pipeline bending stiffness and the soil elastic modulus, but increases with the increase of the formation loss rate, and the width of pipeline-soil void area increases with the increase of the pipeline-tunnel spacing, the pipeline bending stiffness and the soil elastic modulus.

Influence and Safety Evaluation of Underground Structure Construction on Adjacent Existing Subway Section

<p>In recent years, with the rapid development of subway and underground comprehensive pipe corridor, the problem of close connection between underground structure and existing subway section structure is often encountered in engineering construction. During construction, the newly built underground structure will disturb the stratum, easily cause the additional displacement deformation and internal force change of the existing tunnel structure, and then lead to safety accidents. Therefore, it is particularly important to analyze the influence and safety evaluation of the new construction on the existing subway structure. This paper takes the construction of new underground power pipe gallery close to the existing subway section as an engineering case. The influence of adjacent construction on the existing structure is analyzed by three-dimensional finite element method, and then the safety of the existing structure is evaluated through deformation prediction, internal force analysis and bearing capacity checking calculation, and some construction safety protection suggestions are put forward. It has a certain reference for similar proximity projects.</p>

Temperature field and thermal effect analysis of CRTS III ballastless track structure under the outdoor natural environment

In this work, the full-scale temperature field tests on the CRTS III ballastless track structure have been implemented to investigate the temperature characteristic of CRTS III under natural environment. The unified and practical temperature field analysis method and its effect on the CRTS III track structure under the outdoor natural environment are developed based on meteorology, heat transfer, and radiation theory. The time-dependent temperature field of CRTS III, the spatial geometry of the structure under different interlayer connections, and the interfacial behavior are conducted by the proposed method. It is found that the temperature field of the track structure changes periodically – following and time-lagging effect with time. Under thermal load, the track structure presents the spatial shape of a “four corner warpage”, the non-uniformity of structural deformation will induce interlayer damage and affect the overall performance of the structure. Moreover, the critical interface strength at which damage occurs is 0.43 MPa, the interfacial damage begins near the limit structure and the slab end under the action of temperature. Besides, after interlayer failure, the connecting reinforcement can effectively restrain the relative displacement between the layers and ensure the coordinated deformation of the composite slab, whereas it leads to the deformation of structure increasing due to additional internal force.

Study of the effect of seismic performance measures on a metro station structure in liquefiable soil

After the concept of ‘resilient city’ was introduced, the anti-seismic and resilience enhancement of underground structures gradually became an important issue in engineering. In this study, a method for enhancing the resilience of a soil–structure system subjected to earthquakes is proposed. First, a water-soil fully coupled numerical model was established to analyse the seismic behaviour and enhancement effect of a station structure subjected to an earthquake in liquefiable ground. In the analysis, an elastoplastic cyclic mobility model was used to describe the soil behaviour, whereas an interface joint element model was used to consider the soil-structure interaction. Subsequently, a non-liquefied clay replacement method was designed, and the effects of the replacement position and thickness on the floating displacement and internal force of the structure were analysed. To fully utilise the cushioning effect of the liquefiable sand and the anti-floating drainage near the station structure, a unilateral drainage diaphragm wall that does not drain in the far-field soil and drains in the near-field soil is proposed around the station structure. Based on the analysis results of different cases considering the soil replacement position, replacement thickness, distance between the unilateral drainage diaphragm wall and station structure, and buried depth of the wall, combined measures of clay replacement with unilateral drainage diaphragm wall were examined. The results show that the combination of the two measures significantly reduced the floating displacement, restrained the additional internal forces of the structure, reduced the time for the structure to reach stability after an earthquake, which is helpful to enhance the ability of self-recovery and improve the seismic resilience of the underground structure.

The effect of manufacturing imperfections in the slip joints

The issue of imperfections is mostly related to additional internal forces. However, our understanding of imperfections is associated with the change of structural behaviour. In our case, the most likely indicated effects of imperfections are the reduction of the contact area, and the unreachability of the required overlap length. The behaviour of these slip joints depends on sufficient contact between sliding parts. The contact area is affected by the imperfections of the manufactured steel tubes. This contribution presents the manufacturing tolerances and subsequently, it describes the incorporation of them into the design of the slip joint. Furthermore, the article presents a comparison between the ideal numerical model and model with imperfections involved. Moreover, this numerical model is verified by experimental measurements. The results indicate that imperfections have a significant impact on the slip joints. In our comparison, the effect of imperfections is about 120%.

Interactive effects of crossing tunnel construction on existing tunnel: Three-dimensional centrifugal test and numerical analyses

To study the influence mechanism of a new crossing tunnel on an existing tunnel, centrifugal tests and three-dimensional numerical analysis were performed considering the different excavation sequences of the new tunnel, formation loss, and the clearance between the old and new tunnels. The results indicate that a vertical stretching phenomenon occurs in the existing tunnel, regardless of the sequence in which new tunnel crosses it (above or below). Compared to the new tunnel excavation above the existing tunnel, the manner of under-pass has a more significant impact on the additional internal force and deformation of the existing tunnel. The maximum vertical displacement and longitudinal bending moment typically occur at the symmetry plane at the center. An increase in the clearance between the old and new tunnels leads to an increase in the minimum vertical stress ratio, which is conducive to the formation of load-bearing arches. However, this leads to an increase in the range of collapsed arch, which decreases the maximum values of the vertical displacement and induced bending moment of the tunnel as well as increases the range of deformation. When the construction of the new tunnel leads to a higher loss of formation, there is a significant increase in minimum vertical stress ratio and a clear reduction in the maximum vertical stress ratio, which cause a more marked structural response from the existing tunnel.

Calculation of Additional Internal Forces in Post-Tensioned Prestressed Concrete Frame Columns Based on Equivalent Lateral Stiffness

The additional internal forces in vertical members caused by prestressed tendons are typically overlooked in the design of post-tensioned prestressed concrete. A calculation method for additional internal forces in single-story multi-span prestressed concrete frame columns based on equivalent lateral stiffness is proposed in this paper. The slope-deflection equation for the bar element was presented using Timoshenko beam assumptions, taking into account the influence of shear and bending deformations. Subsequently, the concept of equivalent lateral stiffness and calculation equations were proposed. On this basis, the equations of the third shear and third bending moment for single-story multi-span prestressed frame columns were established. Furthermore, applying engineering examples, the method in this study was verified by ABAQUS software and previous methods. The results show that theoretical values and FEA results are in good agreement. Compared to previous methods, the method in this paper is more accurate and widely applicable. In addition, the stretching plan has a significant path effect and time-varying effect on the interlayer distribution of the third moment. It should be considered at the building stage to check the calculation of the frame column.

Thermal Modal Performance of Composite Laminates Embedded with Anti-Symmetric Oblique Coupling Gradient Pre-Strained SMA Wires for Suppressing Resonance

As an extension of conventional gradient, anti-symmetric oblique coupling gradient has a superior modal modification ability on composite laminates embedded with pre-strained shape memory alloys (SMA) wires, which is beneficial to suppress modal resonance of composite laminates in the thermal environment. This paper presents an anti-symmetric oblique coupling gradient model of SMA along the thickness direction. That is, the gradient model of SMA wires’ orientation and the positive and negative gradient model of SMA volume fraction. Considering the internal force of composite laminates composed of the pre-strain recovery force of SMA and the thermal expansion force of the substrate, the free vibration equation of composite laminates with additional internal forces energy is derived from first-order shear plate theory and Hamilton principle. The influence of coupling gradient parameters on the thermal modal performance of SMA composite laminates is analyzed and verified by experiments. The proposed anti-symmetric oblique coupling gradient SMA wires’ distribution form effectively exerts the recovery stress generated by SMA tensile pre-strain, i.e., effectively improves the stiffness and critical buckling temperature. Coupling gradient distribution broadens the frequency modulation range, which makes the fine regulation of the natural frequency and critical buckling temperature feasible.

Моделирование эффекта мартенситной неупругости в плоских композиционных пружинах, выполненных из сплава с эффектом памяти формы

The purpose of the study was to develop a mathematical model of a flat composite spring operating in the region of small displacements and having a shape memory effect. To describe the behavior of the material, we applied a phenomenological approach based on the phase transition diagram; as the material model, we chose the Brinson phenomenological model. As a result, we proposed relationships for determining the reduced mechanical characteristics of a monolayer equivalent to a composite layer in the spring. The memory effect was taken into account by an additional internal force factor, i. e. the shape memory moment during bending, which resulted from the cross-section orientation of the martensite. To obtain the elastic characteristic of the spring, we used a finite element approach, in which the shape memory moment acts as an additional nodal load. Eventually, we introduced an algorithm for the dependence between the bending moment in the section and the shape memory moment for isothermal loading in the martensite stability zone and obtained the dependences of the shape memory moment during bending on the bending moment for various configurations of the cross-section of the spring.

Pile group response induced by adjacent shield tunnelling in clay: Scale model test and numerical simulation

The shield tunnelling adjacent pile group was a common phenomenon in urban metro construction, and additional internal force and displacement field of pile group was disadvantageous to existing superstructure. In this paper, a micro shield machine was invented to simulate the shield tunnelling process, and a series of physical scale model tests and 3-D nonlinear FE models were employed to investigate the pile group (2 × 2) response with different minimum distance between pile group and the tunnel central line (Hm) in clay. The results indicated that large additional bending moment and axial force was induced by shield tunnelling, the maximum bending moment was near the tunnel center line, and the amplitude of maximum bending moment in the lateral section (My) was three to five times of that in the longitudinal section (Mx). The maximum lateral displacement emerged at the tunnel central line, and the vertical displacement distributed uniformly along pile length. The negative shaft resistance between pile group and surrounding soil obviously reduced the axial bearing capacity. The shielding effect of the front pile on the rear pile greatly reduced its internal force and displacement, but it gradually weakened with increase of Hm. The internal force and displacement of pile group decreased quickly with increased of Hm. The research results in this paper can provide a reference for the design and construction of shield tunnels near pile group.

Design optimization analysis of pile foundation parameters for widening bridge in cold region

Relying on Yunliang River Bridge of Beijing-Harbin expressway reconstruction and expansion project, the pile-soil interaction model is established by using ABAQUS. Based on the sensitivity analysis of the vertical deformation, cross-bridge deformation and additional bending moment of the old pile under different design parameters such as pile diameter and pile length, the influence of different design parameters of the new pile foundation on the additional internal force and deformation of the old pile is studied, which provides a theoretical basis for the construction of bridge pile foundation in cold areas.

Analytical Study on the Transverse Internal Forces of Shield Tunnel Segments due to Adjacent Excavations in Soft Clays

Deep excavations unavoidably cause the changes in stress and displacement of surrounding soils, which further generate additional internal forces on the adjacent existing tunnel segments, and compromise the performance and stability of the tunnels. In this study, two-stage analysis method is used to theoretically calculate the additional internal forces in the tunnel segments due to laterally adjacent excavation. Based on an empirical deformation curve of diaphragm walls, the excavation-induced stress in a linear elastic soil is formulated using source-sink imaging method. A distribution model of additional external load acting on the tunnel segments due to adjacent excavation is further established, and the additional internal forces in the tunnel segments under the corresponding additional loads are estimated using elastic equation method. Parametric studies are then conducted to investigate the effects of excavation procedure, buried depth of shield tunnel, and excavation-tunnel horizontal distance on the additional internal forces in the tunnel segments. The results show that the studied parameters have significant effect on the additional internal forces in the tunnel segments due to laterally adjacent excavation. When the excavation-tunnel horizontal distance is less than the excavation depth, the accompanied effect on the additional internal forces in the tunnel segments is highly sensitive. This study can provide theoretical insights into the estimation of tunnel segment responses due to laterally adjacent excavation.