In-service structural health monitoring (SHM) of engineering structures has assumed a significant role in assessing their safety and integrity. Fibre Bragg grating (FBG) sensors have emerged as a reliable, in situ, non-destructive tool for monitoring, diagnostics and control in civil structures. The versatility of FBG sensors represents a key advantage over other technologies in the structural sensing field. In this article, the recent research and development activities in structural health monitoring using FBG sensors have been critically reviewed, highlighting the areas where further work is needed. A few packaging schemes for FBG strain sensors are also discussed. Finally a few limitations and market barriers associated with the use of these sensors have been addressed.

Fibre Bragg gratings in structural health monitoring—Present status and applications

The properties of clean sands pertaining to shear strength and stiffness have been studied extensively. However, natural sands generally contain significant amounts of silt and/or clay. The mechanical response of such soils is different from that of clean sands. This paper addresses the effects of nonplastic fines on the small-strain stiffness and shear strength of sands. A series of laboratory tests was performed on samples of Ottawa sand with fines content in the range of 5–20% by weight. The samples were prepared at different relative densities and were subjected to various levels of mean effective consolidation stress. Most of the triaxial tests were conducted to axial strains in excess of 30%. The stress-strain responses were recorded, and the shear strength and dilatancy parameters were obtained for each fines percentage. Bender element tests performed in triaxial test samples allowed assessment of the effect of fines content on small-strain mechanical stiffness.

Shear strength and stiffness of silty sand

This paper describes recent advances in stability analysis that combine the limit theorems of classical plasticity with finite elements to give rigorous upper and lower bounds on the failure load. These methods, known as finite-element limit analysis, do not require assumptions to be made about the mode of failure, and use only simple strength parameters that are familiar to geotechnical engineers. The bounding properties of the solutions are invaluable in practice, and enable accurate limit loads to be obtained through the use of an exact error estimate and automatic adaptive meshing procedures. The methods are very general, and can deal with heterogeneous soil profiles, anisotropic strength characteristics, fissured soils, discontinuities, complicated boundary conditions, and complex loading in both two and three dimensions. A new development, which incorporates pore water pressures in finite-element limit analysis, is also described. Following a brief outline of the new techniques, stability solutions ...

Geotechnical stability analysis

Scientific approaches to pile design have advanced enormously in recent decades and yet, still, the most fundamental aspect of pile design—that of estimating the axial capacity—relies heavily upon empirical correlations. Improvements have been made in identifying the processes that occur within the critical zone of soil immediately surrounding the pile, but quantification of the changes in stress and fabric is not straightforward. This paper addresses the degree of confidence we can now place (a) on the conceptual and analytical frameworks for estimating pile capacity, and (b) on the quantitative parameters required to achieve a design. The discussion is restricted to driven piles in clays and siliceous sands, with particular attention given to extrapolating from design approaches derived for closed-ended piles of relatively small diameter to the large-diameter open-ended piles that are used routinely in the offshore industry. From a practical viewpoint, we need design approaches that minimise sensitivity...

Science and empiricism in pile foundation design

Tire shreds and tire shred  soil mixtures can be used as alternative backfill material in many geotechnical applications. The reuse of tire shreds may not only address growing environmental and ec...

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Behaviour of tire shred - sand mixtures

Load and resistance factor design (LRFD) of foundations is an emerging design philosophy in the United States. Reliability analyses are the preferred tools to establish resistance factors, but the needed probabilistic information regarding design method uncertainty is difficult to obtain. This paper illustrates an approach to uncertainty assessment that seeks to isolate the various sources of uncertainty. Using this approach, reliability analysis is used to develop resistance factors for the design of driven pipe piles in sand. The resistance factor results are used to highlight some of the differences between design methods that are exposed by the proposed uncertainty assessment technique. This approach is key to helping engineers manage risk and assess the relative value of differing degrees and types of design knowledge.

Developing Resistance Factors for Design of Piles in Sand

Dilatancy and shear strength behavior of sand at low confining pressures

Rock-socketed piles are used to transfer through shaft and base resistances the loads from a superstructure to competent rock layers. In many situations, rock-socketed piles are expected to behave linear elastically under working loads. In this paper, the authors present an elastic analysis that applies to piles with circular cross sections installed in rock layers. The analysis follows from the solution of the differential equations governing the displacements of the pile-rock system obtained using variational principles. The input parameters needed for the analysis are the pile geometry and the elastic constants of the rock and pile. A parametric study is used to illustrate the most important factors that need to be considered in the design of rock-socketed piles.

Elastic Analysis of Rock-Socketed Piles

An analysis framework is presented for piles with rectangular cross section Existing analysis and design methods are mostly applicable for piles with circular cross section For piles with cross section other than a circle, an equivalent circle is often assumed and the methods for circular piles are applied The newly developed framework explicitly takes into account the rectangular cross section and produces the response of piles under axial and lateral loads A rational soil displacement field surrounding the rectangular cross section of the pile is assumed, and the total potential energy of the loaded pile-soil system is considered The potential energy is minimized using calculus of variations to obtain the differential equations governing the pile and soil displacements Closed-form solutions are obtained for pile settlement and axial force in the case of axially loaded piles For laterally loaded piles, closed-form solutions are obtained for lateral deflection, slope of the deflected curve, pile bending moment, and shear force The input parameters needed for the analysis are the pile geometry, applied load, and the elastic constants of the soil and pile The new analysis framework produces results in seconds and has the accuracy of equivalent three-dimensional finite element analysis

Rodrigo Salgado

Papers

Developing Resistance Factors for Design of Piles in Sand

Dilatancy and shear strength behavior of sand at low confining pressures

Elastic Analysis of Rock-Socketed Piles

A Framework for Analysis of Piles with Rectangular Cross Section

Compactoin And Ompaction And Shear Strength Of Fly And Bottom Ash Mixtures