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Recent documents in Lyles School of Civil Engineering Faculty Publicationsen-usSat, 14 Jun 2014 01:50:15 PDT3600Parametric Assessment of Stress Development and Cracking in Restrained Mortars Containing Internal Curing Under Autogenous and Thermal Loading
http://docs.lib.purdue.edu/civeng/7
http://docs.lib.purdue.edu/civeng/7Thu, 12 Jun 2014 08:45:12 PDT
A finite element model is used to examine how the properties of cementitious mortar are related to the stress development in the dual ring test. The results of this investigation are used to explain the thermal cracking behavior of mixtures containing prewetted lightweight aggregates (LWA) by quantifying the contribution of several material properties individually. In addition to the beneficial effects of using the LWA as an internal curing agent to reduce the autogenous shrinkage of concrete, the LWA also helps to reduce the potential for thermal cracking due to a lower elastic modulus and increased stress relaxation. The rate of stress development, age of cracking, and magnitude of the temperature drop necessary to induce cracking in a dual ring specimen are dependent on a variety of factors, including the coefficient of thermal expansion of both the cementitious mortar and the restraining rings, elastic modulus of the mortar, creep effect of the mortar, and rate of thermal loading. Depending on the rate of cooling, cracking may or may not occur. The slowest rate of cooling (2.5"C/h) minimizes the effects of creep while cooling rates faster than 8" C/h can produce a thermal gradient through the mortar cross-section that needs to be considered.
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Jason WeissInstrumentation and Axial Load Testing of Displacement Piles
http://docs.lib.purdue.edu/civeng/6
http://docs.lib.purdue.edu/civeng/6Thu, 13 Jun 2013 12:30:20 PDT
Despite the fact that results of many instrumented pile load tests have been reported in the literature, it is difficult to find well-documented instrumentation procedures that can be used when planning a load testing programme. A load test programme designed to investigate various aspects of the design and behaviour of driven steel piles is discussed in the present paper. Although the literature contains information on load testing of instrumented piles driven in either sand or clay, limited information is available regarding their axial load response in transitional soils (soils composed of various amounts of clay, silt and sand). Results are presented for fully instrumented axial load tests performed on an H pile and a closed-ended pipe pile driven into a multilayered soil profile consisting of transitional soils. In addition, the load testing planning, the instrumentation of the piles, the testing methods and the interpretation of the pile testing data are discussed in detail in the context of this and other load testing programmes described in the literature, in order to illustrate the various steps.
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Rodrigo SalgadoEffect of Relative Density and Stress Level on the Bearing Capacity of Footings on Sand
http://docs.lib.purdue.edu/civeng/5
http://docs.lib.purdue.edu/civeng/5Thu, 13 Jun 2013 12:25:12 PDT
The design of shallow foundations relies on bearing capacity values calculated using empirical procedures that are based in part on solutions obtained using the method of characteristics, which assumes a soil that is perfectly plastic following an associated flow rule. In this paper the problem of strip and circular footings resting on the surface of a sand layer is analysed using the finite-element method. Analyses are performed using a two-surface plasticity constitutive model that realistically captures the aspects of the mechanical response of sands that are relevant to the bearing capacity problem. In particular, the model accounts for non-associated flow, strain-softening, and both stress-induced and inherent anisotropy. Based on the results of the analyses, the paper examines the validity of the bearing capacity factors N_{γ }and shape factors s_{γ }used in practice. A relationship for determining appropriate values of friction angle for use in bearing capacity calculations is also proposed.
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Rodrigo SalgadoStress-dilatancy Relation for Mohr-Coulomb Soils Following a Non-Associated Flow Rule
http://docs.lib.purdue.edu/civeng/4
http://docs.lib.purdue.edu/civeng/4Thu, 13 Jun 2013 12:25:10 PDT
Rowe's stress–dilatancy relation for frictional (cohesionless) materials has been a cornerstone of soil mechanics. The original derivation of this relationship was based on incorrect energy minimisation considerations, but the relationship was proven later by De Josselin de Jong using friction laws, and has been confirmed by a large body of experimental results. In contrast, the validity of Rowe's stress–dilatancy relation for cohesive-frictional materials, which has also been used, although not as extensively, was never verified. This paper shows that Rowe's stress–dilatancy relation for Mohr–Coulomb soils (cohesive-frictional materials) is in fact incorrect. The paper also provides a correct stress–dilatancy relationship for non-associated Mohr–Coulomb soils that have both cohesive and frictional strength components. The derivation of the relationship for cohesive-frictional soils presented in this paper relies on use of the sawtooth model together with the application of the laws of friction.
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Rodrigo SalgadoA Continuum-Based Model for Analysis of Laterally Loaded Piles in Layered Soils
http://docs.lib.purdue.edu/civeng/3
http://docs.lib.purdue.edu/civeng/3Thu, 13 Jun 2013 12:20:13 PDT
An analysis is developed to calculate the response of laterally loaded piles in multilayered elastic media. The displacement fields in the analysis are taken to be the products of independent functions that vary in the vertical, radial and circumferential directions. The governing differential equations for the pile deflections in different soil layers are obtained using the principle of minimum potential energy. Solutions for pile deflection are obtained analytically, whereas those for soil displacements are obtained using the one-dimensional finite difference method. The input parameters needed for the analysis are the pile geometry, the soil profile, and the elastic constants of the soil and pile. The method produces results with accuracy comparable with that of a three-dimensional finite element analysis but requires much less computation time. The analysis can be extended to account for soil non-linearity.
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Rodrigo SalgadoContributions to Foundation Engineering in Geotechnique
http://docs.lib.purdue.edu/civeng/2
http://docs.lib.purdue.edu/civeng/2Thu, 13 Jun 2013 12:15:48 PDT
Many of the important developments in the field of foundation engineering have been addressed in Géotechnique papers over the past 60 years. This paper briefly reviews some of these developments and related articles, particularly with respect to shallow and deep foundations. In the early days of Géotechnique, the power to perform sophisticated numerical analyses did not exist. Papers tended to focus on the solution of problems using simple models in which soil was modelled either as linear elastic or as perfectly plastic. Engineers sought simple closed-form analytical solutions for boundary-value problems. With the development of more powerful analytical, computational and experimental capabilities, and of more sophisticated pile installation technology (especially offshore), more recent papers have explored much more sophisticated approaches to a range of foundation problems, striving to achieve more realistic representation of working conditions. Géotechnique papers have attempted to solve the problems faced by the foundation engineering industry, with a strong emphasis on the underlying science; as a result, these papers have played a key role in the advancement of both the science and its applications in our discipline.
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Rodrigo SalgadoAnalysis of the Shaft Resistance of Nondisplacement Piles in Sand
http://docs.lib.purdue.edu/civeng/1
http://docs.lib.purdue.edu/civeng/1Thu, 13 Jun 2013 12:15:46 PDT
The paper examines, using numerical modelling, the problem of the limit shaft resistance of non-displacement piles installed in sands. The modelling makes use of an advanced, two-surface-plasticity constitutive model. The constitutive model predicts the soil response in both the small- and the large-strain range, while taking into account the effects of the intermediate principal effective stress and of the inherent anisotropy of the sand. Finite element analyses of shearing along the pile shaft are performed in order to examine the development of limit unit shaft resistance and the changes in stress state around the shaft upon axial loading of the pile. Special focus is placed on the operative value of the lateral earth pressure coefficient when limit shaft resistance is reached. The analyses offer useful insights regarding the factors controlling the value of unit shaft resistance in sands. The simulations predict a significant build-up of horizontal effective stress for dense sands. Based on these simulations, we propose a relationship between the lateral earth pressure coefficient for use in the calculation of the limit shaft resistance of the pile and the initial density and stress state of the sand.
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Rodrigo Salgado