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Tools to Safeguard New Buildings and Assess Existing Ones Nonlinear analysis methods such as static pushover are globally considered a reliable tool for seismic and structural assessment. But the accuracy of seismic capacity estimates-which can prevent catastrophic loss of life and astronomical damage repair costs-depends on the use of the correct basic input parameters. Seismic Design Aids for Nonlinear Analysis of Reinforced Concrete Structures simplifies the estimation of those vital parameters. Many design engineers make the relatively common mistake of using default properties of materials as input to nonlinear analyses without realizing that any minor variation in the nonlinear characteristics of constitutive materials, such as concrete and steel, could result in a solution error that leads to incorrect assessment or interpretation. Streamlined Analysis Using a Mathematical Model To achieve a more accurate pushover analysis and improve general performance-based design, this book reassesses some key inputs, including axial force-bending moment yield interaction, moment-curvature, and moment-rotation characteristics. It analyzes these boundaries using a detailed mathematical model of reinforced concrete sections based on international codes, and then proposes design curves and tables derived from the authors' studies using a variety of nonlinear tools, computer programs, and software. The text reviews relevant literature and describes mathematical modeling, detailing numerical procedures step by step. Including supplementary online material that can be used to compute any parameter, this reference delineates nonlinear properties of materials so that they can be used instantly for seismic analysis without having to solve cumbersome equations.

In the framework of classical plasticity, even when limit multipliers and collapse mechanisms associated with different loads independently acting on a solid or structure are known, not much can be inferred on the limit multiplier of the combined loading. Frame structures under the action of dead loads and seismic forces, soil–foundation interaction problems, tunnels under a variety of loads, deepwater pipelines subject to bending and pressure constitute only a few selected examples for which some sort of superposition rule, as well as bounding techniques, would be extremely useful. The present paper introduces a set of theorems for bounding limit multipliers for combined loads. In particular, ranging from a minimum knowledge about the critical state under a particular loading to a reasonable guess of the kinematics of the problem under combined loads, more and more refined bounds for the overall limit multiplier are derived. The results, to the best of the authors’ knowledge, are novel and a few examples showing their practical value are presented and discussed.

Fondamenti della meccanica dei solidi e delle strutture. Materiali strutturali e loro comportamento. Principi e metodi della teoria dell'elasticità costituenti la base delle conoscenze per l'ingegnere e l'architetto.

In this work the problem of identification flaws or voids in elastic solids is addressed both from a theoretical and experimental point of view. Following a so called “inverse procedure”, which is based on appropriately devised experiments and a particular bounding of the strain energy, a “gap functional” for flaw identification is proposed

In recent years the use of distributed optical fiber sensors for measurements of strain in beams, by means of the Brillouin scattering effect, has been proposed. Several works pointed out the practical difficulty of this kind of measurement, connected both to theoretical and to experimental problems, e.g. mechanical characterization of optical fibers, decaying of strains in the protective coatings, spatial resolution of the Brillouin scattering, brittleness of the glass core, elastic-plastic response of the polymeric jackets, end effects and the different responses of the fiber for dilatation and contraction. Dealing with each of the above problems still requires a great research effort. However, recent literature shows that distributed optical fiber measurement techniques are extremely useful for finding qualitative responses in terms of strains. Indeed, in spite of the above-mentioned uncertainties, the great advantage of the proposed distributed measurement of strains remains evident for the safety assessment of large structures, such as bridges, tunnels, dams and pipelines, over their whole lifetimes. In view of this, in the present paper the detection of defects or damage in bending beams-by using distributed optical fiber sensors in a method based on time domain stimulated Brillouin scattering-is proposed. In particular, laboratory tests were carried out to measure the strain profile along a steel beam. Two tests were performed: the first one involves an integral steel beam, while the second experiment is performed on a damaged beam. Comparison between these two tests allows the detection of the position and the establishing of bounds on the size of the defect. At the end, the quality and accuracy of the measurements are discussed and a sensitivity analysis of the strain readings taking into account the bonding conditions at the interface between the structure and the fiber is also carried out by means a parametric numerical simulation.

The limit state design procedure of reinforced concrete elements has undergone major revision by most of the international codes in recent times in accordance to the performance based engineering approach. A thorough understanding of axial force-bending moment (P-M) yield interaction of RC elements is necessary to perform a satisfactory design catering to displacement demands particularly when the structure is subjected to seismic loads. This study presents detailed mathematical modeling of P-M yield interaction of RC rectangular beams based on Eurocode currently in prevalence by defining the boundaries of the sub-domains. A complete set of analytical expressions for P-M yield interaction and moment-curvature relationship are proposed and also illustrated through relevant examples. Results obtained for failure interaction curve of RC rectangular sections under P-M yield interaction show that by adopting Euro Code strain limits, boundary curve is divided into two main parts namely i) tension failure with weak reinforcement resulting in yielding of steel; and ii) compression failure with strong reinforcement resulting in crushing of concrete. The curves are given in analytical form for every feasible coupling of bending moment and axial force. A simple procedure proposed for bending moment-curvature relationship of rectangular beams in presence of constant axial force furnishes closed form expressions for elastic-plastic zones. Studies conducted on RC rectangular beams show moment-curvature response is basically bi-linear: after the first linear response, a further linear plastic branch is present, with a little slope. The whole response is very close to elastic-plastic response characterized by a sort of small hardening effect. With the help of presented mathematical model and proposed expressions for P-M yield interaction and moment-curvature relationships, structural design of new structures and assessment of existing RC structures can be performed with better understanding and improved accuracy.

A steady-state thermoelastic analytical solution for a multilayer hollow cylinder, composed of an arbitrary number of phases and subject to both radial pressure and temperature gradient, is presented. By assuming each phase to be homogeneous and thermally isotropic and by varying the mechanical and thermal constitutive parameters, a sensitivity analysis has been performed with the aim of finally applying the study to the mechanical behaviour of an industrial pipeline composed of three phases (steel, insulating coating, and polyethylene) under the action of the above-mentioned load conditions. By making reference to a classical Hencky-von Mises criterion, the stress profiles along the thickness of the layers have been carried out, also localizing the onset of plasticity as a function of the temperature variations, material properties, and geometrical features characterizing the composite structure of interest. At the end, some numerical results of practical interest in the engineering applications have been specialized to three different insulated coating materials (expanded polyurethane, laminate glass, and syntactic foam), to highlight the cases in which thermal properties and loads can significantly interfere with the mechanical response in pipes, in terms of stresses, in this way suggesting possible strategies for avoiding unexpected failure and supporting the optimal structural design of these systems.