Geotechnical support systems (e.g., deep and shallow foundations) generally involve at least some redundancy. For example, if a building is supported by n
p
separate foundations, then failure (e.g., ...excessive settlement) of a single foundation will generally not result in failure of the building if the building is able to shed the load from the failed foundation to adjacent foundations. This load-shedding ability lends the foundation system redundancy — system failure only occurs if multiple foundations fail. This paper investigates the relationship between the level of geotechnical redundancy, individual foundation reliability, and system reliability for deep foundations (piles). In the particular case where the pile resistance remains constant after achieving its ultimate capacity (at a certain displacement), the relationship between individual and system reliabilities is computed theoretically. The more general case, where the load carried by the pile reduces after exceeding its ultimate capacity, is investigated by Monte Carlo simulation. Charts relating system and individual reliability indices are presented, which can be used to aid in the design of individual piles as part of a pile support system.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
AbstractThe rocking behavior of a shallow foundation of a bridge pier has emerged as an effective mechanism for reducing the seismic load on the superstructure during a strong earthquake. However, a ...lack of understanding regarding the rocking behavior of shallow foundations has hindered the application of the rocking foundation design philosophy to construction. In this study, the soil-rounding effect on embedded foundations was evaluated to increase understanding of the rocking mechanism. A centrifuge apparatus was used to conduct horizontal slow cyclic tests on an embedded shallow foundation model for three different slenderness ratios (i.e., structure height divided by foundation length) at a centrifugal acceleration of 20 g. The soil-rounding phenomenon was examined according to variations in the soil pressure under the foundation during cyclic loading, and the shape of the rounded soil surface was evaluated as a function of the slenderness ratio. The ultimate moment capacity of the shallow foundation was observed to increase with the side soil pressure; this was verified by comparing the side soil earth pressure with the overturning moment. The rocking mechanism of the embedded shallow foundation was evaluated by focusing on soil rounding.
If a rigid wheel or roller acts on an infinitely-long beam or a narrow (1-D) plate that is attached to a deformable foundation, point contact or a region of circular contact may occur. The following ...problems are analyzed: (1) an Euler-Bernoulli beam or an elastica attached to a Winkler foundation; (2) an Euler-Bernoulli beam or an elastica attached to a Pasternak foundation; (3) an Euler-Bernoulli beam attached to a foundation with two different stiffnesses; (4) point contact of a moving wheel with constant speed on an Euler-Bernoulli beam or an elastica attached to a Winkler or Pasternak foundation; (5) point contact of a 1-D plate on an elastomeric foundation; and (6) point contact of a 1-D plate attached to a combined foundation (including Winkler and elastomeric actions). The Euler-Bernoulli beam model tends to predict larger maximum deflections than the elastica model. For small speeds, the maximum deflection increases as the speed increases.
The installation phase is a critical stage during the lifecycle of an offshore wind turbine. This paper presents a state-of-the-art review of the technical aspects of offshore wind turbine ...installation. An overview is first presented introducing the classification of offshore wind turbines, installation vessels, rules and regulations, and numerical modelling tools. Then, various installation methods and concepts for bottom-fixed and floating wind turbines are critically discussed, following the order of wind turbine foundations and components. Applications and challenges of the methods are identified. Finally, future developments in four technical areas are envisioned. This review aims to guide research and development activities on offshore wind turbine installation.
•Various installation methods and concepts for bottom-fixed and floating offshore wind turbines are presented.•Challenges and opportunities for different foundation and component installation methods are identified.•Research works on installation methods are critically reviewed.•Future developments in four technical areas are envisioned.
An unconnected pile foundation allows separation between the lower pile and the pile cap, and it has been proposed as an effective foundation type for reducing the seismic load during strong ...earthquakes. However, previous quantitative evaluations of unconnected piles with various foundation types and earthquake intensities are inadequate. In this study, the influence of base shaking level and the material of the interposed layer between pile and pile cap on the seismic behaviour of unconnected piles were evaluated using a centrifuge model test to reproduce the field stress conditions. A dynamic centrifuge model test was completed on an experimental model consisting of dry sandy soil, a foundation and a single degree-of-freedom structure. The acceleration of the structure and the settlement of the foundation system were measured during base shaking. For the unconnected pile system, the structural seismic load reduction effect due to rocking behaviour was confirmed, and the unconnected pile foundation with the interposed layer with large stiffness had less vertical settlement than the conventional shallow foundation. Finally, the rotational stiffness and damping ratio for the foundation system used in the centrifuge model tests were derived and discussed.
Seismic settlement of shallow foundations constructed in seismic active areas should be considered for a reasonable estimation of the total settlement. However, the trend of the seismic settlement of ...shallow foundation constructed on a sandy soil is not clearly understood and it is estimated by designer using simple analytical methods. These methods do not consider the effect of the soil–structure interaction. This research, therefore, reports the results of 105 robust finite element models developed to investigate the seismic settlement of a shallow foundation constructed on a dry sand. The influence of the load applied on the foundation, relative density of sand, foundation embedment, peak ground acceleration of the earthquake shake, thickness of the sandy soil, and the dominant frequency of the earthquake shake have been examined to provide a comprehensive understanding of the parameters influencing the seismic settlement. The results of the analyses showed that increasing the load applied on the foundation or the peak ground acceleration remarkably increases the seismic settlement, while increasing the embedment depth remarkably reduces the seismic settlement. In addition, the relationship between the thickness of the sandy layer and the seismic settlement is found to be very complex and noticeably influenced by the relative density of the sand. More importantly, it was found that the seismic settlement dramatically increases when the dominant frequency of the earthquake approaches the natural frequency of the system. Thus, all these parameters are important and should be considered by designers for a reasonable estimation of the seismic settlement. The conclusions drawn from this paper will aid the development of a good analytical method in future, and the results reported in this paper also provide useful and novel database to designers and practitioners.
Dynamic characteristics of piled raft foundation system plays an important role in the safety of high-rise buildings subjected to seismic loadings though the analytical study considering the effect ...of both foundation and superstructure is very few in literature. The present study first proposes an exact analytical solution for piled raft foundation subjected to harmonic excitation and resting on an elastic Winkler foundation to obtain its natural radial frequency. After successful validation through available centrifuge test results, a series of parametric study has been carried out investigating the influence of various geometrical and geotechnical parameters of the foundation and the soils respectively. It is observed that the pile length and the pile diameter has significant effect on the natural radial frequency of the foundation system whereas soil density and spacing between piles have minimal effect. The importance of stiffness of the superstructure is also considered in the proposed methodology. It is found that the natural radial frequency of piled raft foundation including superstructure stiffness decreases by 12% to 28% when compared with the computation of the natural radial frequency excluding effect of superstructure stiffness. Hence, this study provides a new analytical methodology to obtain the dynamics characteristics of piled raft foundation considering the superstructure effect which can be used for the design.
•An exact new analytical solution for dynamic characteristics of piled raft is proposed.•Natural frequency of piled raft significantly altered with pile length and diameter but not with spacing.•Effect of superstructure stiffness is also considered on piled raft.•Natural frequency of piled raft decreases by about 12–28% by considering superstructure.•Influence of number of stories on natural frequency of piled raft is studied.
PDF
