On predicting displacement-dependent earth pressure for laterally loaded piles

This paper presents the derivation of a depth-dependent soil displacement model for laterally loaded piles for use in the calculation of displacement-dependent earth pressure. A set of fourth-order differential equations are proposed to compute the pile deflection profile along the pile length. The radial displacement of the soil due to pile movement can be evaluated based on the geometric compatibility requirements. The soil displacement pattern is then used in the earth pressure model to provide the pattern of earth pressure distributed around the pile circumference. The experimental data of the pile response, in terms of the p-y curves reported in the literature, are employed for a comparison with calculations from the proposed approach and other analytical models. The advantages of the developed calculation framework have been demonstrated, namely, that it can accurately reproduce the experimental measurements of soil reactions acting on a pile at different depths and that the influence of the pile installation can be taken into account. An illustrative example of cantilever sheet piles is finally provided to show the ability of the proposed method to analyse complicated problems.     

Analysis of laterally loaded short and long piles in multilayered heterogeneous elastic soil

A continuum-based method is developed for the analysis of laterally loaded piles in multilayered, heterogeneous elastic soil. The analysis considers the soil as a layered elastic continuum in which the modulus varies linearly or non-linearly with depth within each layer. Rational soil displacement fields are assumed and differential equations describing the pile and soil displacements are obtained using the principle of minimum potential energy. The differential equations describing the pile and soil displacements are solved using the Ritz method and the finite difference method, respectively, following an iterative numerical scheme. The analysis is used to study different pile geometries embedded in layered soil deposits with heterogeneity in each layer. The pile displacement, rotation, and maximum bending moment obtained from the analysis were found to be in good agreement with those obtained from an equivalent three-dimensional finite element analysis and from other studies available in the literature. The analysis can be used to obtain the pile head displacement, rotation, and maximum bending moment that can then be used in design.     

Frequency- and intensity-dependent impedance functions of laterally loaded single piles in cohesionless soil

This paper investigates the frequency-dependent pile-head impedance characteristics of a model soil-pile foundation system under large amplitude loads, inducing soil yielding. Testing was conducted on a scaled single pile embedded in sand under a 1g condition. A laminar shear box mounted on a unidirectional shaking table was used to house the soil-pile foundation system. Quasi-static loads and dynamic loads were applied to obtain the force–displacement relationships and pile-head impedance functions, respectively, through the pile head connected to a loading actuator providing fixity to the pile head in all directions, except horizontal. In the quasi-static case, loads with three different velocities were applied to study the rate-dependent characteristics of the lateral bearing capacity of the pile. The Stereo-PIV system was employed to measure the surface soil displacement around the pile. The lateral bearing capacity changed with the loading velocity, but the soil near the pile showed a consistent failure pattern despite a significant change in velocity. Lateral pile-head dynamic impedance functions were obtained for low-to-high amplitude harmonic loading for a wide range of frequencies. The dynamic stiffness was seen to converge to that of the secant static stiffness with an increase in the amplitude of the dynamic loading for all the excitation frequencies.     

水平荷载作用下单桩的虚拟桩解法及参数

根据MukiSternberg的虚拟桩方法,将水平荷载作用下单桩的问题分解为弹性半空间扩展土和一根虚拟桩的叠加,其中虚拟桩的弹性模量等于桩的弹性模量与土的弹性模量之差。基于水平位移协调条件推导出求解桩土间相互作用所需要的第二类Fredholm积分方程,通过广义胡可定律推导出该积分方程间断点的显式解,从而提高了Fredholm积分方程的数值计算精度并简化了计算程序的编写,根据Mindlin解推导出位移影响函数,简化了位移函数的推导过程。参数分析表明,桩土弹性模量比对单位水平力作用下桩身最大弯矩的位置有明显的影响,随着桩刚度的增加,桩身最大弯矩的位置随之加深。     

Centrifuge modelling of the behaviour of pile groups under vertical eccentric load

Annular shaped pile groups are a very common foundation layout for onshore wind turbines and other slender structures. In this study, their performance under vertical loads of moderate to high eccentricity, including moment rotation response and bearing capacity, was investigated by centrifuge testing on small scale physical models embedded in kaolin clay. To identify experimentally the capacity of the examined pile groups under different load paths, the model foundations were loaded monotonically until a clear collapse mechanism was achieved. The testing procedure and the proposed interpretation methodology can be easily adapted to load paths or pile layouts other than those considered in the current study. The experimental data can be adopted as a useful benchmark for mathematical models aimed at predicting the response of pile groups to complex load paths. The results of this testing program can also be used to assess the degree of conservatism of current methods adopted by industry for the design of piled foundations subjected to eccentric loads.     

竖向菏载作用下群桩沉降的一种实用计算方法

群桩沉降是控制桩基设计的一个重要因素,本文采用剪切变形传递法教育处桩身压缩变形,采用等代墩基法计算桩端以下土体整体压缩变形,并以二者相结合计算群桩沉降。     

Responses of single and group piles within MSE walls under static and cyclic lateral loads

To investigate the behavior of piles and the performance of the mechanically stabilized earth (MSE) walls under static and cyclic lateral loading, six reduced-scale model tests of single and group piles within the MSE walls were conducted inside a test box. In the single pile tests, a hollow aluminum tube as a pile was placed at a distance of 2D or 4D (D is pile diameter) behind the wall facing, while in the group pile tests, the piles were only placed at the distance of 2D with a spacing of 3.3D between the piles. The piles were subjected to static lateral loading only and cyclic lateral loading followed by static loading until failure. The test results showed that the lateral load capacity of each pile in the group pile test was approximately 60% that of the single pile, while the wall facing displacements and the geogrid strains in the group pile test were larger than those in the single pile test. The lateral pile capacity, the wall facing displacement, the strain in the geogrid, and the lateral earth pressure behind the wall facing in the static and cyclic loading tests were evaluated at the pile head displacement equal to 20%D.     

An integrated approach for fire and explosion consequence modelling

Fire and explosion are accidents which potentially can occur in oil and gas processing facilities. While fire and explosion could occur as a consequence of each other, most published work has assessed fire and explosion separately, ignoring interactions between the two phenomena.The current study proposes a novel approach to model the entire sequences involved in a potential accident using liquid and gas release incidents as two test cases. The integrated scenario is modelled using Computational Fluid Dynamics (CFD) codes FLACS and FDS. An integrated approach is adopted to analyse and represent the effects (injuries/death) of the accident. The proposed approach can be used in designing safety measures to minimize the adverse impacts of such accidents. It can also serve as an important tool to develop safety training to improve emergency preparedness plans.     

An equivalent stiffness approach for modelling the behaviour of compression members according to Eurocode 3

The development of design procedures based on inelastic advanced analysis is a key consideration for future steel design codes. In advanced analysis the effect of imperfections has to be modelled in such a way that the incremental analysis fully captures this effect in the process of moment redistribution. In modelling the influence of imperfections on the behaviour of individual members of real structures, different approaches have been used to globally represent this effect in the overall analysis of structural systems. They are referred to as the initial bow imperfection approach or as the equivalent transverse load approach. When using the abovementioned approaches in analysis of multiple member structural systems, the designer is required to arrange the directions of bow imperfections or equivalent transverse loads in such a way that the imperfection arrangement leads to the least constrained solution, i.e. the lowest ultimate load predicted from all possible sets of member initial imperfection arrangements. Since there is still ongoing research on the development of simple application rules ensuring that the designer obtains a unique solution when choosing a certain set of member initial imperfections, there is at the same time interest in the development of alternative approaches to modelling the influence of member imperfections on the behaviour of structural systems. This paper provides the necessary background information as well as describes the formulation and modelling techniques used in the development of a new approach to modelling the influence of imperfections on the stability behaviour of structural components and systems. This new approach, called hereafter an equivalent stiffness approach, has an advantage over the previously described approaches since an imperfect member is treated as a hypothetically straight element, flexural and axial stiffnesses of which at each load level are predicted in a continuous fashion dependent upon the actual force and deformation states. This type of modelling does not require any explicit modelling of equivalent geometric imperfections or equivalent forces and their directions in advanced analysis; therefore also it does not require any buckling mode assessment. Moreover, the effects of strain hardening and section class may conveniently be included in modelling. Finally, European buckling curves are used to estimate the values of parameters of the developed model that can be immediately used in advanced analysis conducted according to Eurocode 3.     

An efficient approach for traffic load modelling of long span bridges

Traffic micro-simulation is the newly developed approach for loading calculation of long span bridges. The approach is quite precise, but computationally expensive to consider the full extent of traffic loading scenarios during a bridge lifetime. To address this shortfall, an efficient multi-scale traffic modelling approach is proposed. The proposed approach uses micro- and macro-simulation with different load model varieties (LMVs), or fidelities (levels of detail) of traffic loading in different bridge regions, to achieve optimal computation efficiency while maintaining the precision of loading calculation. Metrics of influence line (IL) characteristics, such as degree of nonlinearity, are proposed to evaluate the appropriateness of the choice of LMV, and standards of the metrics are also investigated to quantify the implementation of LMVs on bridge IL regions in the multi-scale modelling. Finally, two typical ILs are used along with random traffic modelling to study the feasibility of the proposed approach. It is shown that the multi-scale modelling approach proposed here achieves high computational efficiency and accuracy, which is significant for the massive traffic load simulation for lifetime bridge load effect analysis.     

Reliability of design approaches for axially loaded offshore piles and its consequences with respect to the North Sea

In the near future, several offshore wind farms are planned to be built in the North Sea. Therefore, jacket and tripod constructions with mainly axially loaded piles are suitable as support structures. The current design of axial bearing resistance of these piles leads to deviant results regarding the pile resistance when different design methods are adopted. Hence, a strong deviation regarding the required pile length must be addressed. The reliability of a design method can be evaluated based on a model error which describes the quality of the considered design method by comparing measured and predicted pile bearing resistances. However, only few pile load tests are reported with regard to the boundary conditions in the North Sea. This paper presents 6 large-scale axial pile load tests which were incorporated within a new model error approach for the current design methods used for the axial bearing resistance, namely API Main Text method and cone penetration test (CPT)-based design methods, such as simplified ICP-05, offshore UWA-05, Fugro-05 and NGI-05 methods. Based on these new model errors, a reliability-based study towards the safety was conducted by performing a Monte-Carlo simulation. In addition, consequences regarding the deterministic pile design in terms of quality factors were evaluated. It is shown that the current global safety factor (GSF) prescribed and the partial safety factors are only valid for the API Main Text and the offshore UWA-05 design methods; whereas for the simplified ICP-05, Fugro-05 and NGI-05 design methods, an increase in the required embedded pile length and thus in the GSF up to 2.69, 2.95 and 3.27, respectively, should be considered to satisfy the desired safety level according to DIN EN 1990 of β = 3.8. Further, quality factors for each design method on the basis of all reliability-based design results were derived. Hence, evaluation of each design method regarding the reliability of the pile capacity prediction is possible.     

Influence zones for 2D pile–soil-tunnelling interaction based on model test and numerical analysis

In the congested urban areas, tunnelling close to existing structures or services often occurs due to the lack of surface space. Consequently, tunnelling-induced ground movements may cause a serious damage to the adjacent structures. This study focussed on two-dimensional laboratory model test for the pile–soil-tunnelling interaction using a close range photogrammetric technique and numerical analysis. Model testing equipments and procedures were introduced, particularly the use of aluminium rods regarded as the frictional granular material. The normalised pile tip movements were identified by both the model test and finite element analysis. The model test results found to be in good agreement with the finite element analysis. Based on the normalised pile tip settlements due to tunnelling adjacent to a line of loaded piles, influence zones were proposed in this study. The proposed influence zones are relatively wider and deeper than those proposed in previous studies. The authors believe that it will be useful to decide the reasonable location of tunnel construction in the planning stage.     

高层建筑钢结构基于风振响应和动力特性的优化设计

高层建筑的风致响应和等效静力荷载虽然可以通过风洞试验和动力分析有效的加以确定,在结构设计的整个过程中这些等效风力却往往被当作常数来应用。本文提出了一个结合气动风力分析和结构刚度优化的自动化技术。在结构设计中利用这个技术,可以在优化结构刚度和最小化结构造价的同时,实时检查和更新作用在建筑结构上的等效风荷载。一个几何尺度与航空研究共同顾问理事会(CAARC)建议的建筑模型一致的钢框架结构被用来进行风力分析和结构优化的例子。结果表明这个技术不但能在满足位移设计要求的情况下优化结构刚度降低造价,而且也降低了作用在结构上的等效风力。     

Modelling of geosynthetic-reinforced column-supported embankments using 2D full-width model and modified unit cell approach

Soil-cement deep mixing (DM) columns combined with geosynthetic basal reinforcement are an accepted technique in geotechnical engineering to construct road and railway embankments over soft foundations. Both full-width and unit cell models have been used to numerically simulate the performance of geosynthetic-reinforced and column-supported (GRCS) embankments. However, the typical unit cell model with horizontally fixed side boundaries cannot simulate the lateral spreading of the embankment fill and foundation soil. As a result, the calculated reinforcement tensile loads using typical unit cell models are much less than those from matching full-width models. The paper first examines GRCS embankments using a full-width model with small- and large-strain modes in FLAC and then compares the calculated results from the full-width model with those using a typical unit cell model, a recently proposed modified unit cell model, and a closed-form solution. The paper also examines the influence of the soft foundation soil modulus, reinforcement tensile stiffness, and DM column modulus on the reinforcement tensile loads. Numerical analyses show that the reinforcement tensile loads from the modified unit cell model are in good agreement with those from the full-width model for zones under the embankment crest for all cases and conditions examined in the paper. Both the full-width model and modified unit cell model perform better than the typical unit cell model for the prediction of the reinforcement tensile load when compared to the closed-form solution. However, while the modified unit cell developed by the writers is shown to be more accurate than the typical unit cell when predictions are compared to results using full-width numerical simulations, the benefit of using this approach to reduce computation times may be limited in practice.     

2D numerical investigation of segmental tunnel lining behavior

The application field of shield tunneling has extended in recent years. Most shield-driven tunnels are supported by segmental concrete linings. Although many well documented experimental, numerical and analytical results exist in literature concerning the functioning of segmental tunnel linings, their behavior under the influence of joints is still not clear.This paper presents a numerical study that has been performed to investigate the factors that affect segmental tunnel lining behavior. Analyses have been carried out using a two-dimensional finite difference element model. The longitudinal joint between segments in a ring has been simulated through double node connections, with six degrees of freedom, represented by six springs. The proposed model allows the effect of not only the rotational stiffness but also the radial stiffness and the axial stiffness of the longitudinal joints to be taken into consideration. The numerical results show a significant reduction in the bending moment induced in the tunnel lining as the joint number increases. The tunnel behavior in terms of the bending moment considering the effect of joint distribution, when the lateral earth pressure factor K₀ is equal to 0.5, 1.5 and 2, is almost similar and differs when K₀ is equal to unity. It has been seen that the influence of joint rotational stiffness, the reduction in joint rotation stiffness under the negative bending moment, the lateral earth pressure factor and Young’s modulus of ground surrounding the tunnel should not be neglected. On the other hand, the results have also shown an insignificant influence of the axial and radial stiffness of the joints on segmental tunnel lining behavior.     

Overhanging rock slope by design: An integrated approach using rock mass strength characterisation,large-scale numerical modelling and limit equilibrium methods

Overhanging rock slopes(steeper than 90°) are typically avoided in rock engineering design, particularly where the scale of the slope exceeds the scale of fracturing present in the rock mass. This paper highlights an integrated approach of designing overhanging rock slopes where the relative dimensions of the slope exceed the scale of fracturing and the rock mass failure needs to be considered rather than kinematic release of individual blocks. The key to the method is a simplified limit equilibrium(LE) tool that was used for the support design and analysis of a multi-faceted overhanging rock slope. The overhanging slopes required complex geometries with constantly changing orientations. The overhanging rock varied in height from 30 m to 66 m. Geomechanical modelling combined with discrete fracture network(DFN)representation of the rock mass was used to validate the rock mass strength assumptions and the failure mechanism assumed in the LE model. The advantage of the simplified LE method is that buttress and support design iterations(along with sensitivity analysis of design parameters) can be completed for various cross-sections along the proposed overhanging rock sections in an efficient manner, compared to the more time-intensive, sophisticated methods that were used for the initial validation. The method described presents the development of this design tool and assumptions made for a specific overhanging rock slope design. Other locations will have different geological conditions that can control the potential behaviour of rock slopes, however, the approach presented can be applied as a general guiding design principle for overhanging rock cut slope.     

不同结构体系的抗侧移能力评价方法

通过对一个采用不同结构体系的实例进行侧移刚度分析及对侧移刚度理论公式进行物理含义分析,讨论了判断结构抗侧移效率高低不能采用侧移刚度指标的原因。以结构体系的抗侧移刚度为基础,提出了抗侧移系数、等效抗侧移系数两个力学指标,给出了两个力学指标的计算公式,并对其单位的含义进行了讨论。通过采用抗侧移系数、等效抗侧移系数两个力学指标对采用不同结构体系的实例进行抗侧移效率分析,得出采用这两个力学指标来定量分析和评价适用同一建筑的各种结构体系的抗侧移效率是可行的。     

保持承载刚度的张拉整体结构预应力降低方法

几何刚度对张拉整体结构承载刚度的贡献通常与弹性刚度的贡献量级相当,但仅依靠高预应力保证结构承载刚度效果一般.而通过调整结构形状提高弹性刚度并替换部分几何刚度的贡献,可以在保持张拉整体结构承载刚度不变的前提下降低预应力.为此,将杆件原长变化作为基本变量,分析了该变量与单元内力、节点位移以及弹性和几何刚度矩阵的增量关系.建...     

An approach for real world data modelling with the 3D terrestrial laser scanner for built environment

Capturing and modelling 3D information of the built environment is a big challenge. A number of techniques and technologies are now in use. These include EDM, GPS, and photogrammetric application and also remote sensing applications. In this paper, we discussed 3D laser scanning technology, which can acquire high density point data in an accurate, fast way. Besides, the scanner can digitize all the 3D information concerned with a real world object such as buildings, trees and terrain down to millimetre detail Therefore, it can provide benefits for refurbishment process in regeneration in the Built Environment.

A series of scans externally and internally allows an accurate 3D model of the building to be produced. This model can be sliced through different planes to produce accurate 2D plans and elevations. This novel technology improves the efficiency and quality of construction projects such as maintenance of buildings or group of building that are going to be renovated for new services in the Built Environment. In addition, the laser scanner technology can be used in integration with differential GPS for terrain modelling for the analysis and inspection of terrain structure accurately.

In this paper, two case studies are introduced to demonstrate the use of laser scanner technology in Built Environment. These case studies are the Jactin House Building in East Manchester and the Peel building in the campus of University Salford. Through these case studies, while use of laser scanners are explained, the integration of it with various technologies and systems are also explored for professionals in both Built and Natural Environment.