Axial Force Distribution Research Articles

Experimental study on bearing characteristics of pile foundation in loess area of Longdong

In order to study the bearing characteristics of pile foundation in the deep loess layer of Longdong area, field tests were carried out on the basis of a project in Huachi County, Qingyang City. Three test cast-in-place piles of the basement were selected for static load tests. The Q-S curve of the three test piles was gentle, without obvious steep drop. The S-lgt curve was arranged in a gentle and regular way, with high bearing capacity, uniform and small settlement. So it can be used as the foundation of buildings bearing large loads. In the test, the load is mainly borne by the reaction force provided by the side friction of the pile; the axial force distribution of the pile body with depth is not only related to the load on the top of the pile, but also to the nature of the soil around the pile.

Correction of Axial Force Distribution Function of Flexible Single Pile

By introducing the stiffness ratio between the pile end soil and the pile side soil, the existing axial force distribution function is modified, and the axial force of the model pile is calculated by the modified distribution function. The calculated results are consistent with the experimental results, indicating that the modified axial force distribution function can more accurately reflect the axial force variation of the single pile.

Monitoring and correction of the stress in an anchor bolt based on Pulse Pre‐Pumped Brillouin Optical Time Domain Analysis

AbstractBolt is an important connection in underground construction and monitoring its stress characteristics is essential to evaluate the effectiveness of bolt. The strain information collected along a rock bolt reveals the long‐term movement characteristics of rock mass, which greatly helps toward disaster prevention and risk warning. Grooving on the surface of a bolt and embedding an optical fiber is one of the main methods for monitoring the anchorage performance and stress distribution around the bolt in underground engineering. In this study, Pulse Pre‐Pumped Brillouin Optical Time Domain Analysis (PPP‐BOTDA) technology is used to evaluate the stress, axial force, and shear stress distribution of the bolt under tensile load for different types (grooved and nongrooved) of bolts embedded in concrete with resin as anchoring agent. The results show that the PPP‐BOTDA sensor can be used to monitor the stress state of the bolt embedded in concrete with resin as anchoring agent when the bolt is subjected to a tensile force. However, the apparent stress value measured in this way is not the actual stress value of the bolt, but is an increased value caused due to the groove. The closer to the exposed end of the bolt, the greater is the deviation between the apparent stress value and the actual stress value of the bolt. Based on the monitoring results from this experimental study, a stress reduction calculation method is proposed, which can change the measured value into the actual stress of the bolt.

Impact of the Fire Propagation on the Residual State of the Peripherally Supported Grid Structure

The objective of this paper is to computationally investigate the structural residual states of the peripherally supported grid structure under different fire propagation paths and reveal the path impact on the structure. The results demonstrate that the fire propagation path has a significant impact on the residual deformation of the grid structure while it has negligible impact on the distribution of residual axial member force. Hence, the structural residual states are quite different of different fire propagation paths.

Load transfer mechanism and critical length of anchorage zone for anchor bolt.

The length of anchorage zone of an anchor bolt affects the distribution of axial force and shear stress therein. Based on a shear-displacement model, the load distribution of anchor bolts in the elastic deformation stage was analysed. Moreover, the mechanical response of threaded steel anchor bolts with different anchorage lengths was explored through pull-out test and numerical simulation. The results showed that axial force and shear stress were negatively exponentially distributed within the anchorage zone of anchor bolts in which there were the maximum axial force and shear stress at the beginning of the anchorage zone. In the elastic deformation stage of the anchorage, the longer the anchorage length, the more uniformly the shear stress was distributed within the anchorage zone and the larger the ultimate shear stress; however, there was a critical anchorage length, which, when exceeded, the ultimate shear stress remained unchanged. The calculation formula for the critical anchorage length was deduced and a reasonable anchorage length determined. The research result provides an important theoretical basis for rapid design of support parameters for anchor bolts.

Investigation on the tail brush induced loads upon segmental lining of a shield tunnel with small overburden

Damage to the tunnel segmental lining induced by the construction loads has become an important issue in recent years. To investigate the influence of tail brush induced loads on linings during construction, in-situ monitoring was carried out to measure the pressure on the lining of a large cross-river shield tunnel with a small overburden in silty sandy ground in China. Time history of pressure distribution on the lining during tunnel construction was obtained using PAD type earth pressure gauges. Distribution of bending moments and axial forces and related crack width of segments were also examined. The in-situ monitoring results showed that the pressure induced by tail brush (steel plate brush and wire brush) had an important influence on the segments while the shield machine was passing through. Moreover, results from laboratory tests carried out on steel plate brush and wire brush to investigate the extent of loading, revealed that the load by the steel plate brush was more significant than that by the wire brush. Based on the data analysis and field observation, it can be concluded that the non-uniform distribution of pressure induced by steel plate brush might have caused cracking and water leakages in the segments, which can provide valuable references for damage prevention from construction loads in practice.

Experimental Study on Mechanical Deformation Characteristics of Inclined and Straight Alternating Pile Groups

In order to investigate the bearing characteristics of inclined straight alternating pile groups under vertical and horizontal loads, the indoor model test of 2 × 2 inclined straight alternating pile groups with two layers of soil on low pile caps was carried out, the manufacturing method of inclined straight alternating pile groups was studied, and the test scheme was reasonably designed. In the test, the fast maintenance load method was used to simulate vertical loads, and the horizontal force loading frame was designed to simulate horizontal loads. The experimental data were obtained by pasting strain gauges on the pile body, and the computer was used to process the data according to the mechanical formula. The distribution of axial force, lateral friction resistance, and end resistance of each characteristic pile of the pile group foundation was obtained, and the settlement law of the pile group was analyzed. At the same time, combined with the test data and the existing theories, the interaction mechanism between pile caps, piles, and soil of inclined and straight alternating pile groups is discussed. The load sharing characteristics between piles and pile caps are analyzed, and the horizontal load is in the proportion between straight piles and inclined piles. The stress characteristics of straight piles and pile groups in the pile group system are compared and analyzed, and some valuable conclusions are obtained.

Influence of Particle Orientation on the Performance of Geogrid Reinforced Ballast

To explore the initial orientation effect of ballast assembly on the reinforcement performance of the geogrid reinforced ballast, particles with random orientation and five prescribed rotational orientations were developed through particle flow code (PFC3D). The evolution laws of the pullout force and the principal directions of the normal contact force were systematically compared and analyzed. Furthermore, the mechanical responses such as pullout force, distribution of axial force, displacement vectors, force chain, and mesoscopic fabric were discussed. According to the displacement vectors of the ballast particles, the average thickness of the stable shear band is determined. The inherent relationships among the force chain, the rotational angle of the normal contact force, and the mesoscopic fabric parameters are revealed. The results show that the pullout force of specimens with the initial orientation of 45° increases monotonously during the pullout process, and the peak value of pullout force appears at the end of the test. The mesostructural analysis also confirms that the evolution of the principal direction of contact normal force is relatively steady during the pullout process, indicating that the specimen with 45° orientation possesses higher systematic stability and ductility. Moreover, the optimum interval from 56.68° to 57.30° is observed to remain in a self‐adapting state for ballast assembly.

Research on Effect of Heap Loading on Deformation and Mechanical Properties of Bridge Double Pile Foundation on Steep Slope

In order to analyze the deformation and stress characteristics of the pile foundation on the slope, this paper uses the finite element software Abaqus for numerical simulation. The displacement and stress data of pile under different working conditions (the combination of heap load and vertical load and horizontal load and inclined load) were collected; the distribution of pile displacement, axial force and bending moment were analyzed. Simulation results show that: slope top loading has little effect on vertical displacement; when the heap load exceeds 200 kPa, the horizontal displacement is greatly affected. Pile axial force decreases with pile burial depth; pile lateral resistance plays a more adequate role in the rock and soil layer. The bending moment of double pile foundation is positive at the top and negative at the bottom. Applied oblique load has obvious p-Δ effect.

Simulation analysis and effect evaluation of excavation and support of underground cavern group

According to the main construction procedures of underground caverns, an analysis model for the excavation of a certain pumping station underground cavern group was established, and its excavation and support process are dynamically simulated. The calculation schemes of unsupport and support are compared with indicators such as plastic zone, bolt axial force and displacement field distribution. The analysis results show that after the support, the plastic zone distribution and deformation characteristics of the rock around the cave are greatly improved. The bolt axial force also meets the requirements, indicating that the support parameters and support methods are reasonable. The supporting effect has been well simulated and realized.

Study on the Outburst Scheme of a Shallow Buried Bias Tunnel in Yunnan

Improper construction of the tunnel entrance is likely to cause collapse and affect construction safety and damage the ecological environment. Aiming at the poor stability of surrounding rock at the exit position of Xiaoguanzhuang tunnel, on the basis of investigating the geology and driving scheme near the tunnel, the asymmetric distribution of axial force of cross-section structure under shallow eccentric pressure is obtained through numerical simulation, and the maximum axial force is applied at the left arch waist and right arch foot. According to the analysis results, the surrounding rock should be reinforced in time, and the import section should be dealt with in the design stage to ensure construction safety and efficiency, and provide reference for future construction.

New Method for Calculating the Settlement of Single Pile and Pile Group in Soft Soil Area

This paper fits the τ‐z curve of a single pile by mathematical methods. Based on the one‐dimensional similarity of the τ‐z curves, the τ‐z curves of single pile under different loads are derived. It studies the distribution of the axial force of a single pile by taking the self‐weight of the pile and the pile‐end resistance ratio into account and establishes the calculated equation of settlement for single pile. The mutual reinforcing effect between the piles is fully considered, and the settlement of each foundation pile in the pile group is deduced in use of shear displacement method. The example analysis shows that the axial force distribution of single pile considering the self‐weight and the pile‐end resistance ratio is in good agreement with the experimental data. The settlement error of a single pile calculated by the traditional method is 18.52% compared with measured value. When the self‐weight and end resistance ratio are not considered, the error reaches 2.26%. However, the error could reduce to 1.64% when they are taken into consideration. It has a good applicability to calculate the settlement of pile group through the τ‐z curves of single pile. Also, it can better forecast the settlement behavior of the pile group under similar conditions.

On static analysis of tensile structures with sliding cables: the frictional sliding case

In some structural systems, such as cable structures, membranes and tensegrity structures, the use of sliding cables allows to reduce the number of elements required to be controlled during tensioning or activation. However, using sliding cables modifies the structural behavior of tensile structures since it alters the distribution of axial forces in structural members. This has been experienced in structures with continuous cables under the assumption of frictionless sliding. However, sliding-induced friction can further alter the behavior of the system. An enhancement of the static analysis of tensile structures with sliding-induced friction is investigated in this paper. In the proposed formulations, the finite-element analysis method and the dynamic relaxation method are combined with a linear complementary approach. Sliding-induced friction is integrated in the formulations through the consideration of the Euler–Eytelwein equation. The importance of considering sliding-induced friction in the static analysis of tensile structures is demonstrated through a series of examples, where it is shown that friction significantly affects the mechanical behavior of the structures. The examples also reveal that the proposed formulations do not affect the computational time of the static analyses.

A centrifugal experimental investigation on the seismic response of group-pile foundation in a slope with an inclined weak intercalated layer

In this study, a dynamic centrifuge model was constructed to investigate the seismic performance and dynamic deformation of a group-pile foundation embedded in a slope with an inclined weak intercalated layer. The performance was investigated under El-Centro and artificial waves with different input peak ground accelerations (PGAs). The seismic performance of the foundation was indicated by the two piles' axial forces and bending moments as monitored by strain gauges, whereas the dynamic deformation was mainly focused on a mass block's movement and was measured by laser displacement meters. Conventionally, the peaks of both axial force and bending moment increased with an increase in the input PGA. However, the vertical distribution of the bending moment along the pile were in a nonlinearly increasing trend from the pile end to top, especially for the case of the input PGA ≥0.15 g, whereas the axial force's distribution was more uniform. In this case, the bending moment at the pile top played a dominant role for the whole pile. Moreover, the positive peaks of axial force and bending moment were mostly unequal to their absolute negative peaks, especially for the “Pile-II” under intensive excitations. In addition, the axial force and bending moment peaks of one of the two piles were generally no more than twice the peaks of the other one. Furthermore, the bending moment of the pile top had a strong relationship to its horizontal displacement and demonstrated the dynamic stiffness of the piles to some extent.

Mechanical Characteristics of Fully Grouted and Antiseismic Bolts considering Transverse Deformation in Underground Caverns

The load transfer control equations under bolt-surrounding rock interaction are established on the basis of classical beam theory and the trilinear shear slip model. The axial stress and transverse shear force distributions of the anchorage body are obtained by solving the equations. The equivalent forces obtained by the transverse force and axial shear stress of the bolts are applied to rock mass elements to simulate the support effect. A new dynamic algorithm for bolts is proposed in considering of the axial and transverse deformation of the anchorage body. The rationality of the algorithm is verified by comparing with laboratory pullout and shear tests of bolts. A dynamic time-history case study of underground caverns is conducted using this algorithm. Results indicate that (1) the algorithm may reflect the stress and deformation characteristics of bolts during an earthquake; (2) for the antiseismic support effect of the surrounding rock at fault, the bolt algorithm in this study is more valid than the algorithm that considered only the axial deformation of bolts; (3) in the support force of the bolt to the surrounding rock, transverse force is the key to limit fault dislocation and reduce the dynamic damage of the rock at fault.

A simplified solution for piled-raft foundation analysis by using the two-phase approach

In common practice, the pile–soil–raft interaction still remains a challenging problem in the analysis of piled-raft foundations. In the present study, a simplified analytical approach is introduced to analyze a vertically-loaded piled-raft foundation by using a developed homogenization technique called the two-phase approach. In spite of classical and simplified methods in the literature, the proposed method considers the pile–soil interaction. The other major advantage is the ability to predict the axial pile load along the pile length. The problem is solved in the domain of elasticity and simple closed-form solutions are presented for the prediction of the settlement and the pile load sharing of a piled raft as well as the pile's axial force distribution along its length. The applicability of the proposed method is validated by considering case studies and field measurements. A comparison of the results indicates that the method can be utilized safely in a proper, quick, and effective manner with the least computational effort in comparison with sophisticated numerical approaches. The raft settlement can be accurately predicted while the pile load sharing might be over/under estimated. A parametric study is also carried out to investigate the response of piled-raft foundations including the influence of the parameters of the soil and the geometric characteristics of the piles.

Finite Element Analysis of Overhead Pipeline Truss Bridge under Thermal Fluid Loads

The subject used in this study is an overhead pipeline truss bridge which sits in a chemical industrial park. The overhead pipeline truss bridge is a part of a pipeline system consisting of 10 sets of columns, 4 layers of pipe racks and 27 pipelines that transports flowing media under various temperature and pressure conditions. An integrated ANSYS finite element model was built considering the factors such as gravity, medium temperature, and flow load, etc. The results of the distributions of displacement, axial force, shear force, bending moment and stress of the overhead pipeline truss bridge were calculated. The primary stress and secondary stress were checked to judge the reliability of the overhead pipeline truss bridge. It concluded that the computation model and calculation used in this study is feasible and effective. The feature in this paper is to explore a practical method and to provide a solid technological foundation for the safety operation and assessment of overhead pipeline truss bridge.

Study on the technique of single-layer initial arch cover method in Hongyan Village Station

Aiming at the geological characteristics of the upper soft and hard stratum in Chongqing area, taking the Hongyan Village Station of Metro Line 9 as an example, the excavation method of super-large section single-layer initial arch cover method is proposed. The finite element numerical simulation is used to analyze the horizontal and vertical displacement of the surrounding rock, the axial force and bending moment of the single-layer initial arch cover, and the axial force distribution of the anchor. It is concluded that the single-layer initial arch cover method can meet the control requirements of deformation and surface settlement of super-large section surrounding rock. The initial arch cover of H220 grill steel frame + φ25, L=4.5m hollow grouting anchor + 300mm thick C25 wet-sprayed concrete can meet the bearing capacity requirements and ensure the overall stability of the structure. The connection mode of the large arch and the side wall arch is optimized to ensure that the initial branch is completely closed and looped. Combined with on-site monitoring and measurement data, it is feasible to use a single-layer initial arch cover method at Hongyan Village Station.

Analysis of an energy pile enduring cyclic temperature loads

Based on the conclusion that the effect of normal pressure on temperature distribution and the effect of temperature on soil–concrete interface friction are negligible, the finite-element model was established to analyse the characteristics of a pile enduring cyclic temperatures, adopting the sequential thermal coupling method. The temperature-induced additional displacements and axial forces along the pile depth were analysed, and the influences of temperature on the additional axial force distribution of the energy pile were analysed with different pile head loads. The analysis results showed that cyclic heating and natural cooling will lead to additional axial pile forces and displacements along the pile depth. It was concluded that loads applied at the energy pile top should not be heavier than the value at which plastic deformation at the pile end soil would be initiated and at which non-linear pile top settlement occurred.

Three-dimensional centrifuge modelling of the effects of tunnelling on vertical behaviour of pile group

In densely built urban cities, tunnels are likely to be constructed adjacent to existing deep foundations. Tunnelling activity inevitably induces soil stress changes and soil movements in the ground, which may affect nearby existing pile foundation. Although a number of studies have been carried out by various researchers to investigate tunnelling effects on piles, the three-dimensional effects of tunnelling on pile group have not been well-investigated and understood. In this paper, a three-dimensional centrifuge test was carried out to investigate the effects of tunnel construction on a pile group in dry sand. The diameter of each pile was designed as 0.8m (in prototype) and the diameter (D) of the simulated tunnel is 6.08m. Tunnel advancement was modelled in-flight by controlling a volume loss of 1.3%. The tunnelling process was divided into four stages to model the three-dimensional tunnelling effects. The closest distance between the tunnel and the pile group was 1.5m at the pile toe. Measured settlement of pile group, as well as axial force distribution of piles in the pile group are reported and discussed.