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Foundation analysis and design

01 Jan 1968-
TL;DR: In this paper, Fondation de soutenagement et al. presented a reference record for Dimensionnement Reference Record created on 2004-09-07, modified on 2016-08-08.
Abstract: Keywords: Fondation ; Mur de soutenement ; Pieux ; Capacite portante ; Ancrage ; Dimensionnement Reference Record created on 2004-09-07, modified on 2016-08-08
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30 Sep 2008
TL;DR: In this article, the structural response for foundations is typically a function of soil properties, sections and dimensions, and the relationship among basic variables in forming structural response could be either nonlinear or so complicated that results could be obtained from finite element analyses only.
Abstract: In this paper, firstly basic concepts of the structural reliability will be summarized in terms of two basic variables, i.e. structural response (R) and load effect (S). The uncertainty in structural response could be statistically characterized by mean and coefficient of variation (OmegaR). Based on these formulations, there must be an upper limit of OmegaR for the pre-specified acceptable level of reliability (pf). The increment of coefficient of variation of load effect (OmegaS) shows minor influence on the central factor of safety (FS) and its effect diminishes rapidly where OmegaR approaches the upper limit. Below this limit, the structural system could be used safely for a pre-specified target reliability. For lower value of OmegaR, the target FS could be determined from the quadratic relationship between OmegaR and OmegaS. The structural response for foundations is typically a function of soil properties, sections and dimensions. It is not uncommon that uncertainties in soil properties could be normal or non-normal probability distribution and the relationship among basic variables in forming the structural response could be either non-linear or so complicated that results could be obtained from finite element analyses only. Fortunately, the randomness of structural response could be obtained by Monte Carlo simulation technique. Then the fitted distribution of outcome experiments could be specified by Goodness-of-Fit tests. The applicability of proposed concepts could be demonstrated in numerical examples, e.g. driven pile, spread footing and bored pile. For the conventional design approach, soil parameters are considered to be constant. The solution is simplified thorough the use of deterministic safety factor. In reality, soil is neither isotropic nor homogeneous such that their uncertainties could not be ignored. References to the calculated failure probability evidence that deterministic safety factor could not guarantee enough safety. In some cases, an FS of 3 or more is not considered too conservative to apply for the structural response.

1 citations


Cites methods from "Foundation analysis and design"

  • ...Following conventional design approach, the pile driving criterion for ultimate load (Qult) can be obtained from Danish’s Formula [4] with FS = 2.5 as shown : Qult = E W H S + √ E W H L 2 AEp , (13) where W is the weight of a steel hammer (7 ton), Ep is the modulus of elasticity of pile material (340 ton/cm2), H is the drop height (70 cm), A is the area of pile cross section (1 571 cm2) and L is the pile length (2 600 cm)....

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  • ...Following conventional design approach, the pile driving criterion for ultimate load (Qult) can be obtained from Danish’s Formula [4] with FS = 2....

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Journal Article
TL;DR: In this paper, a database of 25 well-documented case histories of braced excavations in Shanghai is established, and the model uncertainties of two semi-empirical models for wall deflection, i.e., the KJHH model and the C&O method, are quantified using the Bayesian updating approach.
Abstract: Empirical and semiempirical methods are simple models for estimating the maximum wall deflection induced by an excavation by practicing engineers for preliminary design. Various factors, such as excavation geometry, wall stiffness, strut spacing, ground condition, dewatering, etc, may affect deformation behavior of an excavation. It is impossible and not practical to incorporate all these factors in a prediction model for excavation-induced wall deflection. Hence, the prediction model of wall deflection is subject to model uncertainty, which is necessary to be quantified. In this paper, a database of 25 well-documented case histories of braced excavations in Shanghai is established. The model uncertainties of two semiempirical models for wall deflection, i.e., the KJHH model (Kung et al. 2007) and the C&O method (Clough and O’Rourke 1990) are quantified using the Bayesian updating approach. A model bias factor is defined as the ratio of the observed maximum wall deflection over the estimated value by the prediction model. With the information of the case histories, the uncertainty of the model bias factor is reduced. It is found that the posterior mean of the bias factor of the KJHH model is closer to 1.0 than that of C&O method and the uncertainty of the KJHH model is smaller than that of C&O method. Keywords

1 citations


Cites background from "Foundation analysis and design"

  • ...Among them, empirical and semiempirical methods (Peck 1969; Bowles 1988; Clough and O’Rourke 1990; Ou et al. 1993; Hsieh and Ou 1998; Long 2001; Yoo 2001; Moormann 2004; Leung and Ng 2007; Kung et al. 2007) are simple for practicing engineers in preliminary design....

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Proceedings ArticleDOI
28 May 2010
TL;DR: In this paper, a contact impact model incorporating finite elements of disjoined material regions is developed to simulate the phenomena of mass-soil-pipe interaction and soil dent, and a new erosion scheme is implemented to deal with numerical instability caused by crumpled elements during heavy impact.
Abstract: The plastic pipes buried at shallow depth are popular for underground telecommunication lines. To assess their impact‐worthiness under loads from heavy traffics, the study establishes a numerical model to correlate with field data. Field impact tests were carried out where a 50‐kg mass free‐falling at 2.2 m height was dropped onto the soil backfill directly above a buried pipe. A contact‐impact model incorporating finite elements of disjoined material regions is developed to simulate the phenomena of mass‐soil‐pipe interaction and soil dent. Plastic soil deformations are accounted for. Also implemented is a new erosion scheme for dealing with numerical instability caused by crumpled elements during heavy impact. Reasonable agreements can be observed between the analyzed and measured soil dent. This model is versatile in making design evaluations for buried pipes to withstand impact loads. It has potential applications to cemented soil fills and blast loads.

1 citations

31 Jan 2014
TL;DR: In this article, a railway bridge is simulated with a single and a double mass-spring model to measure the stiffness of the bridge during the construction of diaphragm walls.
Abstract: Monitoring (geotechnical) constructions is often based upon displacement measurements. However, these measurements do not offer information about the stiffness behaviour of a soil-structure system. A loss of stiffness might be observed as a decrease of the system’s eigenfrequencies. This research investigates if monitoring of ambient vibrations can be used to observe a change in the system’s stiffness. Stiffness monitoring of structural parts (e.g. steel and concrete beams) using vibrations is already common. These implementations are based on measuring natural frequencies and mode shapes. Any change in structural stiffness results in a change in these modal characteristics of the structure. A technique similar to this, but operating in the lower frequency range (i.e. below 300 hertz), is already used to derive the shear elasticity of soil. These techniques are known as seismic methods, and they record body and surface waves. The denser and stiffer the layer of the strata is, the faster it vibrates and the faster the phase velocity of the recorded waves will be. This provides an estimate of the strength of the soil and its ability to resist permanent deformation (i.e. its elastic behaviour). It is also used to find boundaries between different soil layers. In this research, the possibility of monitoring a relative change in stiffness during construction works is investigated. By a relative change is meant the change in stiffness with respect to the initial stiffness, expressed as a percentage. The initial stiffness will be coupled to the initial eigenfrequency of the system. A changed eigenfrequency can then be coupled to a percentage of this initial stiffness. The soil-structure system used for the analytical and empirical part of this research is part of a railway bridge in Nijmegen. In Nijmegen, diaphragm walls are constructed to a depth of more than 20 meters, surrounding the old pillars of this bridge. It is assumed that, during construction works, there will be a change in the system’s stiffness due to the installation of the diaphragm walls. The eigenfrequencies of the soil-structure system are determined by continuous vibration monitoring of ambient vibrations, where the ambient vibrations are caused by the railway traffic. When the stiffness k decreases, the eigenfrequency of the system should also decrease. Two models have been analysed to simulate the bridge: a single and a double mass-spring model. Multiple parameters of these mass-spring models are modified in order to determine which parameter influences the eigenfrequency of both the soil and the structural part of the system. From the mass-spring model it follows that the dominant frequency in the lower frequency range, between 5 and 15 hertz, represents the eigenfrequency of the soil. The dominant frequency in the higher frequency range, between 40 and 50 hertz, represents the eigenfrequency of the structure. With a changing stiffness of the construction, the eigenfrequency between 40 and 50 hertz changes significantly while the change in eigenfrequency around 10 hertz is insignificant. When the stiffness of the soil decreases, the eigenfrequency around 10 hertz decreases significantly while the eigenfrequency between 40 and 50 hertz remains almost unchanged. With the mass-spring model it is also concluded that only a change in stiffness relative to the initial stiffness can be monitored. A Fast Fourier Transform is used to convert the measured data into a frequency spectrum. When there is a phase difference between the first and the last data point a so called leakage occurs. Since it is impossible to determine the phase of the signal when dealing with ambient vibrations, a phase difference cannot be avoided. Due to leakage, the velocities in the frequency spectrum do not correspond well to the real velocities. Actual velocities may be more than 30% higher than the velocities obtained after a Fast Fourier Transform. With the recorded datasets of both the author, in cooperation with the Municipality of Rotterdam, and Fugro GeoServices B.V. it is investigated if the eigenfrequencies are changing during the construction works. The initial data is compared with the data recorded during and after the construction works. The dataset recorded by the author contains continuous vibration measurement in three directions, recorded by 10 geophones with a sampling frequency of 1000 hertz. The datasets are recorded on two different days. The first day represents the initial phase. The second day represents the construction phase. From these measurements it can be concluded that different types of trains do not have an influence on the observed eigenfrequencies. On the other hand, they do have an influence on the magnitude of the recorded vibration. In between the two days of measurement, hydraulic jacks were installed in between the girders and the pillar of the bridge to correct the settlements that occurred during the construction of the diaphragm walls. These jacks have made the joint in between the girder and the pillar more rigid. Due to this, the girder is acting stiffer than before. From the dataset it can be concluded that the eigenfrequency of the structure increases significantly after installation of the jacks. The frequency peak values representing the pillar and the girder increase. The eigenfrequency of the soil remains almost unchanged after installation of the jacks. This conclusion is consistent with the results that followed from the analytical model, as described above. With the dataset recorded by Fugro GeoServices B.V. it is possible to analyse and compare the results of the initial phase, the construction phase and the post phase. For the analysis only the recorded traces are used. These traces contain continuous vibration measurements during 2 seconds, with a sampling frequency of 1024 hertz. The lower frequency range, between 0 and 25 hertz, of multiple monitored traces is analysed and compared. From these results, it can be concluded that a change in stiffness of the soil can be observed by a shift in eigenfrequencies. A decrease in eigenfrequency compared to the initial measured eigenfrequency is observed during the construction works. The decrease is small, but comparable to the decrease that was expected beforehand. In the post phase, when the construction works are finished, the eigenfrequency increases again. This leads to the conclusion that the stiffness has recovered again. Observing a change in stiffness of a soil-structure system by shifts in eigenfrequencies is possible, but only a relative stiffness change can be observed (i.e. the change in stiffness with respect to the initial stiffness). It is possible to monitor the shifts in eigenfrequencies by measuring ambient vibrations. It should be noted that with this monitoring system it is not possible to monitor settlements. The outcome of this research is relevant for stiffness monitoring of constructions. For projects where the deformation of a construction is rather irrelevant if the stiffness is not being influenced significantly, a vibration monitoring system which monitors shifts in eigenfrequency can offer information about the dynamic response (i.e. stiffness behaviour) of the construction.

1 citations

01 Jan 2009
TL;DR: In this article, a parametric study is performed to determine the most economical tilt-up wall panel and foundation support system for single-story or two-story structures in the United States.
Abstract: Soils conditions vary throughout the United States and effect the behavior of the foundation system for building structures. The structural engineer needs to design a foundation system for a superstructure that is compatible with the soil conditions present at the site. Foundation systems can be classified as shallow and deep, and behave differently with different soils. Shallow foundation systems are typically used on sites with stiff soils, such as compacted sands or firm silts. Deep foundation systems are typically used on sites with soft soils, such as loose sands and expansive clays. A parametric study is performed within this report analyzing tilt-up concrete structures in Dallas, Texas, Denver, Colorado, and Kansas City, Missouri to determine the most economical tilt-up wall panel and foundation support system. These three locations represent a broad region within the Midwest of low-seismic activity, enabling the use of Ordinary Precast Wall Panels for the lateral force resisting system. Tilt-up wall panels are slender load-bearing walls constructed of reinforced concrete, cast on site, and lifted into their final position. Both a 32 ft (9.75 m) and 40 ft (12 m) tilt-up wall panel height are designed on three foundation systems: spread footings, continuous footings, and drilled piers. These two wall heights are typical for single-story or two-story structures and industrial warehouse projects. Spread footings and continuous footings are shallow foundation systems and drilled piers are a deep foundation system. Dallas and Denver both have vast presence of expansive soils while Kansas City has more abundant stiff soils. The analysis procedure used for the design of the tilt-up wall panels is the Alternative Design of Slender Walls in the American Concrete Institute standard ACI 318-05 Building Code and Commentary Section 14.8. Tilt-up wall panel design is typically controlled by lateral instability as a result from lateral loads combining with the axial loads to produce secondary moments. The provisions in the Alternative Design of Slender Walls consider progressive collapse of the wall panel from the increased deflection resulting from the secondary moments. Each tilt-up wall panel type studied is designed in each of the three locations on each foundation system type and the most economical section is recommended.

1 citations