196,344 research outputs found
Seismic soil pile interaction:experimental evidence
No full textThe comprehension of the real behaviour of pile foundations under earthquake loading is very important, since it can significantly affect the performance of the superstructure. As a matter of fact the experience of recent earthquake has confirmed that piles can suffer extreme damage and failure under earthquake loading. The case histories from Kobe earthquake (1995) indicate that not only the inertial actions but also the kinematic ones, due to ground movements, which was overlooked in design specifications at that time, had significant effects on pile damage. The purpose of this work is to examine the complex soil-structure interaction problem, on the basis of the results of an original experimental activity on shaking table, particularly devoted to the evaluation of kinematic interaction effects in layered soil configurations. A great amount of data has been collected during the experimental study, relative to around 400 shaking events on a single pile. The test focused on three different subsoil configurations, a monolayer and two layered deposits, with the aim of highlighting the influence of soil stiffness contrast on kinematic interaction. The effects of different pile head conditions, including the presence a single degree of freedom superstructure, have been investigated. The pile response has been evaluated mainly in terms of bending moments induced by both kinematic interaction and coupled kinematic and inertial effects. The seismic motions at the foundation level, due to kinematic interaction, has been investigated and compared with the free field response
The behaviour of laterally loaded two-pile groups
No full textThe response of piles and two-pile groups to lateral loading has been studied by field tests and computationally. Due to the lack of field test data and because of uncertainty concerning the pile/soil system it has been suggested that further experimental studies of pile groups under lateral loading should be undertaken. The research was conducted through a series of tests on vertical single piles and two-pile groups at various spacing and pile cap overhang heights, to identify the lateral stiffness, bending moment and axial force distribution. Attempts were also made to measure the in-situ total lateral soil pressure on the pile walls. Piles were designed to behave as "long" pile since most piles used in the U.K. are long and flexible. Piles were instrumented with strain gauges for measurement of bending moments and axial forces. Field tests were conducted in a sand trench using 4.0m long piles. A stiff steel pile cap was used to connect head of the two piles firmly together. Linear elastic back analyses of single pile tests were carried out to estimate the soil modulus profile with depth. Thereafter comparisons were made between the field test results on two-pile groups, published analyses and also a three dimensional finite element analysis. Tests results showed that the lateral stiffness of a two-pile groups tends towards a limit as spacing increases. A similar result was found from predictive and finite element analyses. The ratio between the maximum pile shaft bending moment and horizontal force varied between dry and wet season, being greater in the latter. The ratio between maximum reverse bending moment and horizontal load increased as the pile spacing and the overhang increased. Similar results results were found by finite element analysis. One of the main achievements in this research was the measurement of the axial forces in the vertical piles due to lateral loading. It was found that as the pile spacing increased and pile cap overhang height decreasd the peak axial forces per unit load decreased. Similar results were obtained by three dimensional finite element analysis
Use of Pile Driving Analysis for Assessment of Axial Load Capacity of Piles
No full textDriven piles are commonly used in foundation engineering. Pile driving formulae, which directly relate the pile set per blow to the capacity of the pile, are commonly used to decide whether an installed pile will have the designed capacity. However, existing formulae have been proposed based on empirical observations and have not been validated scientifically, so some might over-predict pile capacity, while others may be too conservative. In this report, a more advanced and realistic model developed at Purdue University for dynamic pile driving analysis was used to develop more accurate pile driving formulae. These formulae are derived for piles installed in typical soil profiles: a floating pile in sand, an end-bearing pile in sand, a floating pile in clay, an end-bearing pile in clay and a pile crossing a normally consolidated clay layer and resting on a dense sand layer. The proposed driving formulae are validated through well documented case histories of driven piles. Comparison of the predictions from the proposed formulae with the results from static load tests, dynamic load tests and conventional formulae show that they produce reasonably accurate predictions of pile capacity based on pile set observations
Temperature response functions (G-functions) for single pile heat exchangers
No full textFoundation piles used as heat exchangers as part of a ground energy system have the potential to reduce energy use and carbon dioxide emissions from new buildings. However, current design approaches for pile heat exchangers are based on methods developed for boreholes which have a different geometry, with a much larger aspect (length to diameter) ratio. Current methods also neglect the transient behaviour of the pile concrete, instead assuming a steady state resistance for design purposes. As piles have a much larger volume of concrete than boreholes, this neglects the significant potential for heat storage within the pile. To overcome these shortcomings this paper presents new pile temperature response functions (G-functions) which are designed to reflect typical geometries of pile heat exchangers and include the transient response of the pile concrete. Owing to the larger number of pile sizes and pipe configurations which are possible with pile heat exchangers it is not feasible to developed a single unified G-function and instead upper and lower bound solutions are provided for different aspects ratios
Development of LRFD Procedures for Bridge Pile Foundations in Iowa, September 2011
No full textIn response to the mandate on Load and Resistance Factor Design (LRFD) implementations by the Federal Highway Administration (FHWA) on all new bridge projects initiated after October 1, 2007, the Iowa Highway Research Board (IHRB) sponsored these research
projects to develop regional LRFD recommendations. The LRFD development was performed using the Iowa Department of Transportation (DOT) Pile Load Test database (PILOT). To
increase the data points for LRFD development, develop LRFD recommendations for dynamic methods, and validate the results of LRFD calibration, 10 full-scale field tests on the most commonly used steel H-piles (e.g., HP 10 x 42) were conducted throughout Iowa.
Detailed in situ soil investigations were carried out, push-in pressure cells were installed, and laboratory soil tests were performed. Pile responses during driving, at the end of driving (EOD), and at re-strikes were monitored using the Pile Driving Analyzer (PDA), following with the CAse Pile Wave Analysis Program (CAPWAP) analysis. The hammer blow counts were recorded for Wave Equation Analysis Program (WEAP) and dynamic formulas. Static load tests (SLTs) were performed and the pile capacities were determined based on the Davisson’s criteria. The extensive experimental research studies generated important data for analytical and computational investigations. The SLT measured load displacements were compared with the simulated results obtained using a model of the TZPILE program and using the modified borehole shear test method. Two analytical pile setup quantification methods, in terms of soil properties, were developed and validated.
A new calibration procedure was developed to incorporate pile setup into LRFD
G-Functions for multiple interacting pile heat exchangers
No full textPile heat exchangers – where heat transfer pipes are cast into the building piled foundations – offer an opportunity to use ground energy systems without the additional construction costs related to the provision of special purpose heat exchangers. However, analysis methods for pile heat exchangers are still under development. In particular there is an absence of available methods and guidance for the amount of thermal interaction that may occur between adjacent pile heat exchangers and the corresponding reduction in available energy that this will cause. This is of particular importance as the locations of foundation piles are controlled by the structural demands of the building and cannot be optimised with respect to the thermal analysis. This paper presents a method for deriving G-functions for use with multiple pile heat exchangers. Example functions illustrate the primary importance of pile spacing in controlling available energy, followed by the number of piles within any given arrangement. Significantly it was found that the internal thermal behaviour of a pile is not influenced appreciably by adjacent piles
Shear capacity of reinforced concrete pile caps
No full textReinforced concrete pile caps may be considered to act either as deep beams, or analogous to a truss. When designed as a deep beam, there is currently a contradiction in the shear design between two UK structural engineering codes of practice – the design code BS 8110 for reinforced concrete buildings, and BS 5400: Part 4 for bridges. The majority of this difference in shear design is concerned with the width of the cap for which a shear enhancement factor for short shear spans may be applied. BS 8110 permits the factor to be applied across the full width of the cap if the pile spacing is no more than three pile diameters, whereas BS 5400 allows the factor to be applied only for the width of the pile diameters. Given that the shear enhancement factor is a very significant component of the design strength of the cap, this difference can give a factor of two or three between the shear strengths according to the two codes of practice.This paper describes research that has been carried out with the aim of resolving the issue of the width of shear enhancement. A series of sixteen four-pile caps of close to full size, with spans in the range 500mm – 1200mm and depths from 230mm – 400mm have been tested to failure in the laboratory. The test results have been used to verify three-dimensional nonlinear finite element analyses conducted using the commercial package DIANA. The results have shown good agreement of behaviour between the tests and the numerical analyses, and have also indicated that the BS 8110 shear enhancement approach is safe. It is anticipated that the results of this research will inform the next revision of the Structural Eurocode, EN 199
Development of LRFD Procedures for Bridge Pile Foundations in Iowa Final Report, June 2010
No full textFor well over 100 years, the Working Stress Design (WSD) approach has been the traditional basis for geotechnical design with regard to settlements or failure conditions. However, considerable effort has been put forth over the past couple of decades in relation to the adoption of the Load and Resistance Factor Design (LRFD) approach into geotechnical design. With the goal of producing engineered designs with consistent levels of reliability, the Federal Highway Administration (FHWA) issued a policy memorandum on June 28, 2000, requiring all new bridges initiated after October 1, 2007, to be designed according to the LRFD approach. Likewise, regionally calibrated LRFD resistance factors were permitted by the American Association of State Highway and Transportation Officials (AASHTO) to improve the economy of bridge foundation elements. Thus, projects TR-573, TR-583 and TR-584 were undertaken by a research team at Iowa State University’s Bridge Engineering Center with the goal of developing resistance factors for pile design using available pile static load test data.
To accomplish this goal, the available data were first analyzed for reliability and then placed in a newly designed relational database management system termed PIle LOad Tests (PILOT), to which this first volume of the final report for project TR-573 is dedicated. PILOT is an amalgamated, electronic source of information consisting of both static and dynamic data for pile load tests conducted in the State of Iowa. The database, which includes historical data on pile load tests dating back to 1966, is intended for use in the establishment of LRFD resistance factors for design and construction control of driven pile foundations in Iowa. Although a considerable amount of geotechnical and pile load test data is available in literature as well as in various State Department of Transportation files, PILOT is one of the first regional databases to be exclusively used in the development of LRFD resistance factors for the design and construction control of driven pile foundations. Currently providing an electronically organized assimilation of geotechnical and pile load test data for 274 piles of various types (e.g., steel H-shaped, timber, pipe, Monotube, and concrete), PILOT (http://srg.cce.iastate.edu/lrfd/) is on par with such familiar national databases used in the calibration of LRFD resistance factors for pile foundations as the FHWA’s Deep Foundation Load Test Database. By narrowing geographical boundaries while maintaining a high number of pile load tests, PILOT exemplifies a model for effective regional LRFD calibration procedures
Ground vibration measurements with special reference to pile driving
No full textThere has been increased concern in recent years over the level and nature of the ground vibrations. The importance of such vibration has increased rapidly due to developments in construction in urban areas, where the effects of ground borne vibration on both humans and structures are considerable. Research has been undertaken to improve techniques used in the measurements, analyses and evaluation of ground vibrations caused by rail and road traffic, blasting and in particular those generated from pile driving activities. The amplitude of the vibration caused by the pile driving operation is a function of pile type, hammer type and the ground conditions. In order to investigate the effects of these three variables, a large number of visits were made to different sites which provided a range of different driving conditions. The main requirements in the analysis of the vibrations measured include vibration amplitude and their relevant frequency. The vibration amplitude is usually expressed in term of peak particle acceleration, velocity or displacement. In this work, the ground vibration is measured in terms of peak particle velocity using velocity transducers (geophone). In order to evaluate the true peak particle resultant velocity, the three components of the ground vibration are measured simultaneously by three orthogonally positioned sets of geophone. Recording the vibration data is achieved by employing a portable digital recorder which digitizes the analogue signals recieved from the transducers and stores the captured data on standard floppy disks for further analysis. The results are presented in tables and diagrams and detailed comments are given in the discussion of the recorded data. Some methods of analyses are reviewed and two new methods are proposed. These proposed methods include the application of the hemispherical projection technique in interpreting and displaying the three dimesional vibration information into a two dimensional plane. The other method analysed the attenuation of the ground vibration according to the arrival time of the generated waves from the pile toe and along the ground surface. It is suggested that when the arrival times of these two wave fronts coincide at one particular point, a highest vibration amplitude may be expected at that poinL The effect of ground vibration on building is investigated in large scale test in Aitwick where the dynamic strain of purpose built L-shape walls are recorded during driving steel sheet and H-pile at different stand-off from the walls using a winch-drop-hammer and a vibrodriver
Pile heat exchangers: thermal behaviour and interactions
No full textThermal piles – that is structural foundation piles also used as heat exchangers as part of a ground energy system – are increasingly being adopted for their contribution to more sustainable energy strategies for new buildings. Despite over a quarter of a century having passed since the installation of the first thermal piles in northern Europe, uncertainties regarding their behaviour remain. This paper identifies the key factors which influence the heat transfer and thermal–mechanical interactions of such piles. In terms of heat output, pile aspect ratio is identified as an important parameter controlling the overall thermal performance. Temperature changes in the concrete and surrounding ground during thermal pile operation will lead to additional concrete stresses and displacements within the pile–soil system. Consequently designers must ensure that temperatures remain within acceptable limits, while the pile geotechnical analysis should demonstrate that any adverse thermal stresses are within design safety factors and that any additional displacements do not affect the serviceability of the structur
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