Development of Supplemental Resistance Method for the Design of Drilled Shaft Rock Sockets
Author: Sandford, Thomas C | Size: 5.70 MB | Format:PDF | Quality:Original preprint | Publisher: University of Maine, Orono | Year: 2011 | pages: 186
Rock Socketed Drilled Shafts have been used on a variety of projects, especially bridges, in areas with bedrock close to the surface. The large loads that these foundation structures can resist make them more practical than alternatives, such as pile groups, in certain situations. However, the current conservative design practices are based on the performance of Rock Socketed Drilled Shafts in soft rock formations. The current design practice for axial capacity often neglects one of the two resisting forces, usually end bearing. In areas, such as New England, with good quality hard rock, Rock Socketed Drilled Shafts have been found to have ultimate axial capacities 7-25 times the predicted value. The goal of this research is to develop a design method that utilizes the full potential of Rock Socketed Drilled Shafts in hard rock. A finite element model using constitutive relationships and surface interactions was created to replicate Rock Socketed Drilled Shafts in hard rock. The model was calibrated by duplicating results from five Osterberg load tests on shafts in hard rock. For the purpose of this research hard rock is classified as having an unconfined strength greater than 30 MPa. After calibrating the model, the model was used to show performance of shafts of various sizes founded in rock of two different qualities. The performance results were used to develop a design method for Rock Socketed Drilled Shafts based on service limit criteria. This research revealed that portions of both resistance forces, end bearing and side shear, can be used together in the design of Rock Socketed Drilled Shafts if service limit state criteria are considered. This method applies to well cleaned sockets and primarily hard rock. This method can be used with equations for nominal resistance as well as Osterberg tests.
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MEASUREMENT OF FOUNDATION STRAINS UNDER LATERAL LOADS
Author: Long, R P Healy, K A CAREY, P J Powers, M | Size: 1.37 MB | Format:PDF | Quality:Original preprint | Publisher: University of Connecticut, Storrs | Year: 1976 | pages: 81
A cooperative field work effort was developed to evaluate the resistance to lateral loads of poles set in augured holes and surrounded by well graded backfill, and the effect of pole diameter on strength and stiffness. Theoretical aspects of soil-pole interaction, poles in cohesionless soil, and poles in precompressed clay are discussed as well as non-homogeneous soil conditions and theoretical assumptions. Methods of testing are reviewed, and tests in dense sand, glacial till and clayey silt, are detailed. Field test results are discussed, and model tests in sands are described. Design considerations are set forth, and a design example is described. It is concluded from the study that directly embedding poles is, in many cases, an economical method of setting the poles to resist lateral forces. The behavior of directly embedded poles depends on the stress-strain characteristics of the soil surrounding the pole to a distance of approximately 3 pole diameters. The stiffness of glacial till can be reduced by the method of excavating the hole to receive the pole. The study also showed that the stress-strain properties of clays and disturbed glacial till are time dependent; this must be considered in the design.
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STUDIES ON BOND AND CRACKING OF STRUCTURAL CONCRETE
by Homayoun H. Abrishami, June 1994
Department of Civil Engineering and Applied Mechanics
McGill University, Montreal, Canada
A thesis submitted to
the Faculty of Graduate Studies and Research
in partial fulfilment of the requirements for the degree of
Doctor of Philosophy
ABSTRACT
This thesis presents new testing methods to study the bond characteristics of reinforcing
bars and pretensioned strands. For reinforcing bars, the new technique, which simulates a more uniforrn bond stress, enabled the study of both pullout failures and splitting faiiures. Variables studied included concrete cover, bar size and the erfect of epoxy coatings on the bars. Analytical expressions for predicting the bond stress versus slip response and the bond stress distribution for different types of pullout tests are developed. For pretensioned strand, the testing technique enabled the study of the bond characteristics along toth the transfer and the flexural bond lengths. Equations for predicting the trasnfer development lengths are given.
The tensile behaviour of concrete members reinforced with a single reinforcing bar are studied. Variables studied included concrete strength, presence of steel fibres, bar size and the effect of epoxy coatings on the bars. Both transverse cracks and splitting cracks were studied and a factor accounting for the influence of splitting cracks on tension stiffening is introduced. A procedure for predicting the response of tension members, accounting for the concrete coyer and bar size and the presence of steel fibres is given. Equations are suggested to deterrnine the transfer length and crack spacing.
Experimental investigations were carried out to study the post-cracking behaviour of bearns
without stirrups. The influence of concrete strength and the presence of epoxy-coated reinforcement on the crack development, type of cracking, ductility and failure mechanism are discussed. Typical slab-colurnn connections found in parking structures were tested, simulating the construction stages. The effects on crack development of both concrete quality and the presence of epoxy coatings on the reinforcement were studied. Modification factors for predicting crack widths in bearns and two-way slabs, accounting for the presence of epoxy coatings, are given in a forrn suitable for implementation in codes of practice.
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Models for flexural cracking in concrete; the state of the art by
A. Borosnyoi and G. L. Balazs
Structural Concrete, 2005 - 6 No 2
Crack formation presents a complex mechanical and geometrical question to be modelled. The available crack
width formulations are often based on simplifications. A rigorous formulation of crack widths should be based on
the integration of strain differences of reinforcement and concrete between cracks, due to the accumulated slips.
In this paper an extensive literature review on crack widths and crack spacing is presented. The basic intention of
the present paper is to summarise the development of flexural crack models and collect the most relevant formulae
for crack spacing and crack width. It reports not only the possible improvement of design or research equations but
also the appearance of new types of reinforcements with different characteristics from those of steel
reinforcements. This state-of-the-art Report is a contribution to the work of fib TG 4.1 ‘Serviceability Models’.
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A New Cavitation Simulation Method: Dam-Reservoir Systems
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table of contents :
1- Roof Decks
2- Form Decks
3- Composite Floor Decks
4- General Deck Information
5- SDI Specifications for Roof Deck
6- SDI Specifications for Non-Composite Floor Deck
7- SDI Specifications for Composite Floor Deck
8- Roof Deck Diaphragm Shear
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Seismic Design of Reinforced Concrete Mat Foundations
Author: Ron Klemencic, Ian S. McFarlane, Neil M. Hawkins, Sissy Nikolaou | Size: 2.01 MB | Format:PDF | Quality:Original preprint | Publisher: NEHRP Consultants Joint Venture, Applied Technology Council (ATC) and the Consortium of Universities for Research in Earthquake Engineering (CUREE) | Year: 2012 | pages: 33
Seismic design of reinforced concrete mat foundations has advanced significantly in the last twenty years. As analytical capabilities have improved, primarily in the form of finite element analysis, the mathematical modeling of these continuous structural elements has led to seemingly more precise designs. Yet, fundamental questions still remain regarding the seismic performance of these thick foundation
systems.
This Technical Brief attempts to address what is known and what is unknown about this subject, so that a structural engineer can proceed with a seismic design in an informed manner. Because many of the parameters associated with a mat foundation design can be highly variable, designs that consider this variability are encouraged.
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