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Introduction The authors present an interesting and detailed examination of the failure mechanism of the Mount Polley Tailings Storage Facility (TSF). Indeed, such rigorous modelling seems likely to contribute to [...]

During the loading process of concrete members, the identification of characteristic damage states is not sensitive enough. This paper investigates the damage evolution of four concrete sandwich wallboards subjected to vertical compression by employing the strain energy density increment to enhance identification sensitivity. First, the equivalent elastic modulus model for a wallboard subjected to vertical compression is established based on the material stress-strain relationship. Then, the strain data of concrete, obtained from experiments and numerical simulations, are modeled as the normalized unit approximate strain energy density increments (NUASEDIs), which follow the damage evolution of the wallboard as a more sensitive index. The first cracking formation of wallboard corresponds to the first high NUASEDI. The failure damage state corresponds to the final high NUASEDI, which reflects the process changing from the local to the global failure. Finally, the strain energy density increment theory improves averagely the cracking identification sensitivity of concrete members by 13.32% and the failure identification sensitivity by 3.01%. Key words: concrete sandwich wallboard, strain energy density increment, damage identification sensitivity, first high NUASEDI, final high NUASEDI, 1. Introduction In the destructive tests of concrete wallboard, the common approach to identify damage features is to observe the surface cracks and concrete spalling. However, the concrete wallboard is [...]

Introduction The discussion by Reid et al. (2023) is a constructive contribution to the subject of strength recovery in strain-weakening soils such as the foundation unit involved in the failure [...]

This paper proposes a methodology for managing complex sewerage networks based on the concomitant use of two performance evaluation methods, namely, the failure modes, effects, and criticality analysis (FMECA) and the analytical hierarchy process (AHP). The FMECA is used to determine the risks of structural failures making it possible to establish a methodology for managing these failures. The AHP is used to check the relationship consistency between the performance indicators allowing the determination of the overall performance (OP). This proposed methodology was utilized for the urban sewerage network of Oued-Kniss in the city of Algiers, Algeria, as part of the efforts engaged in for sustainable and efficient management. Key words: urban sewerage networks, sustainable development, infrastructure assess management, AHP, FMECA, criticality index, performance indicator. Cet article propose une methodologie de gestion des reseaux d'assainissement complexes basee sur l'utilisation concomitante de deux methodes devaluation des performances a savoir : l'analyse des modes de defaillance, des effets et de la criticite (AMDEC) et le processus de hierarchie analytique (AHP). L'AMDEC est utilisee pour determiner les risques de defaillances structurales permettant d'etablir une methodologie de gestion de ces defaillances. L'AHP est utilise pour verifier la coherence des relations entre les indicateurs de performance permettant de determiner la performance globale (GP). Cette methodologie proposee est appliquee au reseau d'assainissement urbain d'Oued-Kniss dans la ville d'Alger, en Algerie, dans le cadre des efforts engages pour une gestion durable et efficace. Mots-cles: reseau d'assainissement urbain, developpement durable, gestion de revaluation des infrastructures, AHP, AMDEC, indice de criticite, indicateur de performance., 1. Introduction The proper implementation of sustainable management practices of urban sewerage networks (USN) aids in the prevention of their catastrophic breakdown and collapse and the associated costs and inconveniences. [...]

The seismic performance of an H-shaped core buckling-restrained brace (HBRB) is evaluated through detailed finite element analysis. The numerical model is validated against available experimental data and a parametric study is carried out to investigate the effect of influential parameters on the cyclic behavior and failure modes of HBRB. Several design parameters including the yielding length ratio, the constrained length, the presence of stiffeners and their thicknesses, the length of the transition region, and the gap size are considered in the parametric investigation. Based on the analysis results reducing the yielding length of HBRB increases its post-yield stiffness and the axial strain and stress of the H-section core. Since buckling of the unconstrained region was observed in HBRBs with insufficient stiffener thickness, an analytical method is proposed for evaluating the sufficiency of stiffeners by estimating the critical buckling load of HBRB as a three-segment stepped compression member. Key words: buckling-restrained brace, all steel, H-section core, nonlinear finite element analysis, cyclic behavior. La performance sismique d'un contreventement a diagonales ductiles confinees a noyau en H (CDCH) est evaluee au moyen d'une analyse detaillee des elements finis. Le modele numerique est valide en fonction des donnees experimentales disponibles et une etude parametrique est effectuee pour etudier l'effet des parametres influents sur le comportement cyclique et les modes de defaillance du CDCH. Plusieurs parametres de conception, y compris le rapport de longueur d'elasticite, la longueur contrainte, la presence de raidisseurs et leurs epaisseurs, la longueur de la region de transition et la taille de l'ecart, sont pris en compte dans l'etude parametrique. D'apres les resultats de l'analyse, la reduction de la longueur d'elasticite du CDCH augmente sa rigidite post-elasticite ainsi que la contrainte axiale et la contrainte du noyau de la section H. Etant donne que le flambage de la region non contrainte a ete observe dans les CDCH dont l'epaisseur de raidissement etait insuffisante, une methode d'analyse est proposee pour evaluer la suffisance des raidisseurs en estimant la charge critique de flambage du CDCH comme membrure comprimee a trois segments. [Traduit par la Redaction] Mots-cles : contreventement a diagonales ductiles confinees, tout acier, noyau a section en H, analyse d'elements finis non lineaires, comportement cyclique., 1. Introduction Buckling-restrained brace (BRB) is a special type of brace with similar tensile and compressive behaviors. A typical BRB consists of a core member and a casing. The core [...]

Internal erosion is one of the main causes of instabilities within hydraulic earth structures. Four internal erosion processes can be distinguished, and this study deals with the process of suffusion, which corresponds to the coupled processes of detachment-transport-filtration of the soil's fine fraction between the coarse fraction. Because of the great length of earth structures and the heterogeneities of soils, it is very difficult to characterize the suffusion susceptibility of the different soils. Nevertheless, a statistical analysis can be performed to optimize the experimental campaign. By using a dedicated erodimeter, an experimental program was set up to study suffusion susceptibility of 31 specimens of nonplastic and low-plasticity soils. The suffusion susceptibility is determined by the erosion resistance index, which relates the total loss of mass with the total energy expended by the seepage flow. Fourteen physical parameters are selected, and a multi-variate statistical analysis leads to a correlation between the erosion resistance index and all these parameters. A statistical analysis is performed to identify the main parameters and to focus on those that can easily be measured on existing structures. By distinguishing gap-graded and widely graded soils, two correlations are proposed to estimate the erosion resistance index. Key words: laboratory testing, suffusion, physical parameter, statistical analysis, energy. L'erosion interne est l'une des principales causes des instability dans les ouvrages hydrauliques en terre. Quatre processus d'erosion interne peuvent etre distingues et cette etude porte sur le processus de suffusion qui correspond aux processus couples de detachement-transport-filtration de la fraction fine du sol entre les grains de la fraction grossiere. En raison du grand lineaire des ouvrages en terre et des heterogeneites des sols, il est tres difficile de caracteriser la susceptibilite a la suffusion des differents sols. Neanmoins, une analyse statistique peut etre effectuee afin d'optimiser la campagne experimentale. A l'aide d'un erodimetre dedie, un programme experimental a ete realise pour etudier la susceptibilite a la suffusion de 31 echantillons de sols non plastiques ou de faible plasticite. La susceptibilite a la suffusion est determinee par l'indice de resistance a l'erosion, qui relie la perte de masse totale avec l'energie totale dissipee par l'ecoulement interstitiel. Quatorze parametres physiques sont selectionnes et une analyse statistique multivariee abouti a une correlation entre l'indice de resistance a l'erosion et l'ensemble de ces parametres. Une analyse statistique est effectuee afin d'identifier les principaux parametres tout en privilegiant les parametres aisement mesurables sur les ouvrages existants. En distinguant les sols de distributions granulometriques discontinue et continue, deux correlations sont proposees pour estimer l'indice de resistance a l'erosion. [Traduit par la Redaction] Mots-cles: essais en laboratoire, suffusion, parametre physique, analyse statistique, energie., Introduction Internal erosion is one of the main causes of instabilities within hydraulic earth structures such as dams, dikes, or levees (Foster et al. 2000). According to Fell and Fry [...]

Damage to unreinforced masonry (URM) buildings from earthquake shaking is often caused by out-of-plane failure of walls. This is particularly relevant to the majority of URM buildings in Eastern Canada that were constructed prior to the introduction of seismic design prescriptions. Seismic vulnerability assessment of this type of failure is therefore an essential step towards seismic risk mitigation. This paper presents a simplified procedure for seismic vulnerability assessment of out-of-plane failure of URM wall buildings. The procedure includes the development of an equivalent single degree of freedom model of the wall with a characteristic force-deformation capacity curve. The capacity curve is convolved with displacement response spectrum to predict the displacement demand. The predicted displacement demand is compared to displacement thresholds criteria corresponding to the initiation of each damage state. The procedure is applied to an inventory of URM buildings in Montreal and the corresponding probability of out-of-plane damage is evaluated. Key words: seismic vulnerability assessment, fragility analysis, unreinforced masonry, out-of-plane damage. Les dommages aux batiments en maconnerie non armee (MNA) a la suite de secousses sismiques sont souvent causes par la defaillance hors plan des murs. Ceci est particulierement pertinent dans le cas de la majorite des batiments en MNA dans l'est du Canada qui ont ete construits avant la mise en place de prescriptions de conception parasismique. L'evaluation de vulnerabilite sismique de ce type de defaillance constitue donc une etape essentielle vers l'attenuation des risques sismiques. Cette etude presente une procedure simplifiee pour l'evaluation de vulnerabilite sismique d'une defaillance hors plan de batiments aux murs de MNA. La procedure comprend le developpement d'un modele a un degre de liberte equivalent au mur avec une courbe de capacite caracteristique de force deformation. La courbe de capacite est convolutionnee avec le spectre de reponse en deplacement pour prevoir la demande en deplacement. La demande en deplacement prevue est comparee aux criteres de seuils de deplacement correspondant au commencement de chaque etat de dommage. La procedure est appliquee a un inventaire de batiments en MNA a Montreal et la probabilite correspondante au dommage hors plan est evaluee. [Traduit par la Redaction] Mots-cles: evaluation de la vulnerabilite sismique, analyse de fragilite, maconnerie non armee (MNA), dommage hors plan., 1. Introduction Post-earthquake damage reports showed that unreinforced masonry (URM) buildings are among the most vulnerable structures to earthquakes (Coburn and Spence 2002; Doherty et al. 2002). Inspection reports following [...]

Risk management for safety in mountain tunnel construction is of great significance. However, existing research lags behind engineering applications. In this paper, the risk of mountain tunnel collapse is used as an example to illustrate a new assessment method based on case-based reasoning, advanced geological prediction, and rough set theory. First, the risk surroundings and risk factors involved in tunnel collapse are integrated and summarized, and a risk assessment index system is established for tunnel collapse. At the same time, because the dynamic response parameters obtained by the advanced geological prediction usually indicate a typical geological structure, sensitive response parameters are introduced in the assessment index system. Advanced risk assessment can be performed for tunnel sections at a certain distance ahead of the tunnel face. Second, the major risk surroundings and the advanced geological prediction results are analyzed for the tunnel under assessment. Cases with similar attribute characteristics are selected via comparison with previous cases. Attribute reduction and calculation of weights are subsequently performed for the risk surroundings and risk factors of similar cases based on the attribute significance theory of rough sets. Finally, index screening and objective weights are applied in the fuzzy comprehensive assessment model. The results of this paper can be used to improve the theoretical level and reliability of risk assessment in tunnel safety and serve as a reference for tunnel construction. Key words: mountain tunnel, case-based reasoning, advanced geological prediction, rough set, risk assessment. La gestion des risques visant a garantir la securite des chantiers de construction des tunnels de montagne revet une grande importance. Cependant, la recherche accuse un retard important par rapport l'ingenierie liee a ce domaine. Dans le present article, le risque d'effondrement des tunnels de montagne est utilise comme exemple d'application d'une nouvelle methode devaluation axee sur le raisonnement par cas, sur la prevision avancee des risques geologiques sur la theorie des ensembles approximatifs. Dans un premier temps, les risques et facteurs de risque associes a l'effondrement d'un tunnel sont rassembles et synthetises et un systeme d'indices devaluation de ces risques est cree. Parallelement, etant donne que les parametres de la reponse dynamique obtenus par prevision avancee des risques geologiques sont generalement associes a une structure geologique typique, les parametres de la reponse sensible sont incorpores au systeme d'indices devaluation. Il est possible de realiserune evaluation poussee des risques d'effondrement dans des segments de tunnel situes a l'avant du front de taille du tunnel, a l'avant de ce dernier. Dans un deuxieme temps, les risques majeurs associes et les resultats de la prevision avancee des risques geologiques sont analyses dans le cas du tunnel evalue. On selectionne des cas d'etude presentant des caracteristiques similaires, en les comparant a d'autres exemples passes. On procede ensuite a une reduction des attributs et au calcul des poids dans le cas des risques associes et des facteurs de risques de cas similaires, a l'aide de la theorie des ensembles approximatifs basee sur l'importance des attributs. Enfin, on applique le filtrage des indices et les poids objectifs au modele flou devaluation exhaustive. Les resultats de la presente etude peuvent servir a ameliorer le niveau theorique et la fiabilite du processus devaluation des risques visant a garantir la securite des tunnels et servir d'outil de reference pour la construction de tunnels. [Traduit par la Redaction] Mots-cles : tunnel de montagne, raisonnement par cas, prevision avancee des risques geologiques, ensemble approximatif, evaluation des risques., Introduction Complex geological conditions, intensive tectonic movements, sophisticated construction technology, and unforeseeable risks are usually encountered during construction of mountain tunnels. The construction technology and management level can hardly catch [...]

The potential for progressive collapse of a typical reinforced concrete (RC) moment frame structure initiated through the loss of one or more first-story columns is numerically simulated using a macromodel-based approach. The development of the simulation model is guided by the realization that the characterization of nonlinear behavior associated with the transfer of forces through the joint is critical to predict the large deformation response associated with progressive collapse. A simplified simulation model of a beam-column joint is used to represent essential and critical actions in the floor beams and the transfer of these forces through the joint region to the vertical elements. The validity of the macromodel developed is evaluated through comparison of both overall response and element actions with those obtained from high-fidelity finite-element analyses. Two prototype buildings designed for lateral load requirements in a nonseismic and seismic region are considered in progressive collapse studies. Two-dimensional models of the frames are subjected to gravity loads and then one or more first-story columns are removed, and the resulting large displacement inelastic dynamic response of each frame is investigated. It is demonstrated that the proposed approach using a validated macromodel is a viable methodology for progressive collapse analysis. The study also finds that special RC moment frames detailed and designed in zones of high seismicity perform better and are less vulnerable to progressive collapse than RC frame structures designed for low to moderate seismic risk. CE Database subject headings: Joints; Progressive collapse; Concrete reinforced; Frames; Nonlinear response; Simulation; Framed structures.

A modified Hashin failure model is developed to characterize different failure modes related to high-velocity impact of composite laminates. Hashin's compressive fiber failure mode has been extended to consider the shear stress effect. Several micromechanics-based degradation rules are developed and applied to the stress and material property calculations according to different failure modes after the corresponding failure criterion is satisfied. This model has been implemented into a recently developed micromechanics model. Computational results show that this model is able to address shear failure, delamination, and tearing failure observed in the high-velocity impact of composite laminates. CE Database subject headings: Failure modes; Polymers; Laminates; Composite materials; Velocity.

According to many code requirements for concrete structures, the stress in the compressed part of reinforced concrete (RC) beams in bending is usually computed by means of uniaxial stress-strain relationships. These approaches sometimes are not able to reproduce the structural response of the beam when crashing of concrete in compression occurs. As a consequence, both the beating capacity of RC structures and their ductility are roughly estimated. In this paper, the postpeak behavior of compressed concrete is modeled through sliding planes up to the expulsion of v-shaped block. The concrete damage on the surface of these-planes is the cause of the softening branch in the moment-curvature diagrams of RC beams. The proposed mathematical description of the sliding phenomenon also shows how it is impossible to define an univocal stress-strain relationship for concrete in compression, whose softening behavior depends both on the dimension of the compressive zone and on strain gradient (i.e., the curvature). DOI: 10.1061/(ASCE)0733-9445(2002)128:5(637) CE Database keywords: Concrete, reinforced; Beams; Ductility; Compressive strength; Strain softening; Size effects.

A three-dimensional nonlinear finite-element analysis, based on a two-parameters damage model, has been carded out to study the behavior of two masonry vaults: a cylindrical barrel vault and a fibbed cross vault, for which the results of experimental tests were available. Such an approach, originally developed for concrete, reveals to be valuable in understanding the global behavior of masonry structures as well. In particular the numerical results are in good agreement with experimental data, both in terms of collapse mechanism (crack pattern) and failure load, demonstrating the ability of the proposed approach in analyzing large real structures. Within this approach, masonry is treated as a homogenized material, for which the material characteristics can be defined by using a homogenization technique as well as a micromodeling approach. The damage laws take into account for different behavior in tension and compression and have been validated with reference to available experimental data. DOI: 10.1061/(ASCE)0733-9445(2002)128:5(646) CE Database keywords: Three-dimensional models; Damage assessment; Masonry; Structural elements; Finite element method.

The moment capacity and failure modes of four types of beams with high reinforcement ratios are reported. The tests were planned and conducted in order to examine a quantitative measure that had been proposed to evaluate an upper limit to the compression reinforcement ratio [[rho]'.sub.max], for flexural reinforced concrete members. The concept that was examined was the derivation of a quantitative criteria for [[rho]'.sub.max] from steel congestion and proficient design considerations (i.e., tension failure and sufficient rotation capacity at the ultimate limit state) and from considerations related to diagonal compression capacity. The tests were designed with relatively high compression reinforcement ratios of up to 4.8%, in order to show the influence of parameters that affect this limit, i.e., the beam geometry (L/d ratio, cross-section dimensions, and concrete cover), and the moment-to-shear loading ratio. The results of the tests reported here agreed with the trends as well as the quantitative predictions of the theoretical moment capacities. Thus, they strengthen the proposed approach for setting an upper limit to the longitudinal compression reinforcement [rho]' in flexural reinforced concrete members. DOI: 10.1061/(ASCE)0733-9445(2002)128:5(578) CE Database keywords: Beams; Compression; Moments; Concrete, reinforced; Flexure.

In this paper a finite-element analysis on ductile fracture in two-dimensional quasi-static state is performed by using the local approach concept in continuum damage mechanics. An isotropic damage model based on the generalized concept of effective stress is proposed. Crack propagation is achieved by removing critically damaged elements. The finite-element approximation of a largely deforming body based on the incremental total Lagrangian concept is carried out. As numerical examples, the mesh size sensitivity analysis and the simulation of the shearing mode failure in plane strain state are carried out to verify the present formulation qualitatively. For an edge cracked plate under plane stress state, load-displacement curves and successively fractured shapes are shown. It can be concluded that the proposed model may be stated as a reasonable tool to explain ductile fracture initiation and crack propagation.

A micromechanical model is proposed for determining the overall linear elastic mechanical properties of simple-texture brick masonry. The model, originally developed for long-fiber composites, relies on the exact solution due to Eshelby and describes brickwork as a mortar matrix with insertions of elliptical cylinder-shaped bricks. Macroscopic elastic constants are derived from the mechanical properties of the constituent materials and phase volume ratios. Conformity of the suggested model to real brickwork behavior has been verified by performing uniaxial compression tests on masonry panels composed of fired bricks and mud mortar. Composite masonry panels of varying phase percentages were then constructed and tested by replacing several of the fired bricks with mud bricks. Comparison of experimental results with theoretical predictions demonstrates that the model is suitable even in the presence of strongly differentiated phases, and is moreover able to predict different behavior as a function of phase concentration. The model fits experimental results more closely than the micromechanical models previously reported in the literature.

One-dimensional models for predicting the damage induced by pressure transients in piping systems conveying liquids have been proposed and analysed recently. However, such works have been concerned mainly with the adequacy of the constitutive equations adopted for different pipe materials and with the numerical techniques used for approximating the solution of the resulting mathematical problems. In the present paper the suitability of the simplifying low Mach number assumption adopted in the modeling is investigated. The analysis is carried out based on the eigenvalue problem associated to the governing equations, without appealing to any specific mechanical behavior of the pipe material. Numerical results obtained for the most used pipe materials show that this simplifying assumption is adequate for metallic tubes, but may fail when plastic tubes are considered.

The statistical properties of the Block, Borges and Savits age-dependent minimal repair model are analyzed. The properties are similar to the order statistic properties of homogeneous Poisson processes and are utilized to derive an algorithm for random generation of a realization from the minimal repair model. In addition, the properties are used to test goodness of fit regarding the initial distribution function or hazard function of the repair model., 1. INTRODUCTION In many studies in the reliability, engineering, public health, medical, actuarial, and economic settings, the event of primary interest is recurrent, so that for a given unit the [...]

It has been suggested that the reinforcing fiber size and the spacing between the reinforcing fibers play a dominant role in determining the fracture properties of cementitious composite materials. In the present study, 48 specimens were tested under fatigue loading to investigate the effect of fiber size and the corresponding spacing between the reinforcing fibers on the fracture behavior of mortar composites. The specimen dimensions of 125 x 600 x 25 mm (5 x 24 x 1 in.) and the volume fraction of the reinforcement were kept constant at 0.04 while the cross-sectional area of the reinforcing fibers was varied at 0.79, 1.77, and 3.14 [mm.sup.2] (0.00122, 0.00274, and 0.00487 [in..sup.2]) with a corresponding spacing between the fibers of 37.5, 15, and 5.8 mm (1.5, 0.6, and 0.23 in.) and a corresponding number of fibers of 3, 6, and 14. The tension-tension flexural fatigue testing was performed at stress levels of 80%, 65%, and 50% of the ultimate flexural strength of similar specimens tested under static loading conditions. The fatigue testing was performed at a constant frequency of 2 Hz. The crack initiated simultaneously as the loading cycles ensued at 80% and 65% stress levels; however, a large scatter in the number of cycles to failure ([N.sub.f]) was observed. Number of cycles to failure ranged from 240 to 3,069 at the 80% stress level and from 10,165 to 35,070 at the 65% stress level. At the 50% stress level, none of the specimens failed or had appreciable crack growth for up to 500,000 cycles. As in the static case, fiber size and spacing appear to have an influence on the fatigue crack growth behavior; however, as is typical of concrete fatigue testing, the large scatter in the fatigue crack growth data engulfed any apparent trend. The Weibull probability distribution function compared well with the experimental data. A statistical model based on the inclusion model and the Weibull distribution was proposed to account for the fiber spacing effect.

Damage mechanics describes the degradation process that takes place in materials and structures. Traditionally, Coffin-Manson type empirical curves are used to determine the fatigue life. Damage mechanics allows us to determine the fatigue life without the need for empirical curves. The main problem in damage mechanics has always been a lack of universally agreed upon definition of a damage metric. In this paper a damage metric based on the second law of thermodynamics and statistical mechanics is presented. The proposed thermodynamic framework treats a solid body as a thermodynamic system and requires that the entropy production be nonnegative. Verification of the damage model has been performed by extensive comparisons with laboratory test data of low cycle fatigue of Pb40/Sn60 solder alloy.

Existing research on structural damage detection usually requires information at every degree of freedom, and this contradicts the usual practice of having a small number of sensors employed over limited locations on the structure. A method to detect the location and to estimate the magnitude of damage in a structure down to the element level with incomplete and noisy measured modal data is proposed. The method consists of three stages: expansion of the measured mode shapes, localization of the damage domain using the elemental energy quotient difference, and damage quantification based on sensitivity of the modal frequency. A new mode shape expansion method is presented, and the effectiveness of the combined use of this method and the elemental energy quotient difference is demonstrated with incomplete measurement. The treatment of modeling errors is discussed. A criterion for selection of the damaged members is proposed and practical means to improve the identification results are presented. Several damage cases of the European Space Agency structure and of a single-bay two-story portal steel frame structure in the laboratory are investigated. The practical problem of having random error and systematic error in the measurement is studied. Results show that the proposed threestage approach can effectively locate and quantify damages in a real structure.

Torsion tests have been used to evaluate the shear response of concrete. The complete loaddeformation response of unnotched concrete specimens subjected to torsion is difficult to obtain because of test instabilities. In this paper torsional tests with a closed-loop test system are performed on hollow concrete cylinders. The test instability is shown to be a result of snapback in the postpeak part of the torque-twist response of these specimens. The failure is a result of the propagation of a single major crack. A test signal that is a combination of torque and gauge rotation is introduced and is demonstrated to give improved control by eliminating the test instability. The response of concrete specimens subjected to both controlled and uncontrolled torsion tests, using specially designed test equipment, are presented and analyzed in terms of propagation of a single major crack.

Owing to the large expanse of cooling towers, it is not possible to maintain the exact shape of a tower during construction. Alterations in shape also occur due to secondary effects like shrinkage and cracking. These alterations cause the failure of some towers. This paper deals with the application of semiloof shell elements in the analysis of towers with bulge imperfections for both dead and wind loads. Four parameters, namely, (1) radial error amplitude, [Zeta]m, (2) vertical location of bulge, [Z.sub.m], (3) vertical extent of bulge, h, and (4) angular extent of bulge, [[Theta].sub.m], have been identified as responsible in influencing the behavior of imperfect towers. Their influence has been studied in detail and most critical geometry of the tower has been arrived at. The behavior of a tower with most critical geometry has also been studied. Analysis suggests that the effect of bulge imperfections on stress resultants is localized, the development of hoop tension in the imperfection zone is of primary concern, and stress changes induced are greater if the imperfection is located closer to the base. Shorter wavelength of an imperfection is more severe since curvature error is significantly high for low wavelength. With increase in angular extent, the change in hoop force is maximum for axisymmetric imperfection. Critical hoop stresses develop around the 70 [degrees] meridian, where high hoop tension and high meridional moments develop that can induce yielding of hoop reinforcement and consequent failure.

A viscoelastic constitutive model of asphalt mixtures that accounts for the rate-dependent damage growth and microdamage healing is presented in this paper. An elastic continuum damage model, which is based on thermodynamics of irreversible processes with internal state variables, is first reviewed and extended to a corresponding viscoelastic model using an elastic-viscoelastic correspondence principle. A rate-type internal state evolution law is employed to describe the damage growth and microdamage healing in asphalt concrete. An analytical representation of the model is established for the uniaxial loading condition. Tensile uniaxial cyclic tests were performed under the controlled-strain mode with different strain amplitudes to determine model parameters. The resulting constitutive model successfully predicts the damage growth and recovery in asphalt concrete under multilevels of loading, varying rates of loading, different modes of loading (controlled-strain and controlled-stress), and random rest periods.

An experimental study of a small-scale model of a concrete gravity dam was conducted. Tests were carried out to simulate the hydrostatic, hydrodynamic, and seismic loads. The dynamic loads were estimated using the simplified method of analysis in concrete gravity dams. A loading mechanism with two actuators was designed to apply four concentrated loads at the upstream face of the dam model. The static load that represents the hydrostatic pressure was kept constant. The dynamic load was applied cyclically by an actuator to represent the dynamic effects of the earthquake loading. An existing concrete gravity dam monolith was modeled. The material properties of the model were maintained the same as those of the prototype. The gravity load effect of the dam was accounted for analytically. Results of the experiments show that it is possible to simulate the hydrodynamic load on a dam model using a finite number of concentrated mechanical loads. Measured strains in the dam model were found to be similar to the strains in the prototype predicted using available finite element analysis techniques.

Considering progressive weakening under repetitive events of loading, the proposed method estimates the safety probability for structures with cumulative damage. The structural damage is represented by a finite number of discrete states. The time evolution of damage is described by a Markov chain where the collapse corresponds to an absorbing state. Structural loading is defined as a discrete stochastic process of random events. This stochastic model can describe the seismic phenomenon as well as other environmental loads. A homogeneous Poisson process is used to model the random occurrences of the loading. To illustrate this method, the safety estimation of a masonry structure under seismic loading was performed. The obtained results are checked by a numerical simulation and compared with those of the classical analysis, which did not consider cumulative damage. The main features of the damage time evolution, the safety assessment, and the hazard function are pointed out.

As a first step to develop a probabilistic method for the maintenance and repair of breakwaters, one 28.5-h test and two shorter tests, which were repeated twice, were conducted in a wave flume. Damage progression and variability were measured on a conventional rubble mound exposed to depth-limited breaking waves in sequences of storms with varying wave conditions and water levels. Measurements were made of 16 or 32 damage profiles every 30 min of irregular wave action. Each measured profile was characterized by the eroded area, depth and length of the armor layer, and the remaining cover depth. The mean and standard deviation of these statistical variables changed with damage progression, whereas the probability distributions of the normalized variables were practically invariant. The mean and standard deviation of the damage variables are shown to be represented empirically by the mean eroded area alone. The damage variability along the breakwater was significant. Finally, an empirical formula is proposed to predict the mean eroded area in sequences of storms for these three tests.

A new plastic-damage model for concrete subjected to cyclic loading is developed using the concepts of fracture-energy-based damage and stiffness degradation in continuum damage mechanics. Two damage variables, one for tensile damage and the other for compressive damage, and a yield function with multiple-hardening variables are introduced to account for different damage states. The uniaxial strength functions are factored into two parts, corresponding to the effective stress and the degradation of elastic stiffness. The constitutive relations for elastoplastic responses are recoupled from the degradation damage response, which provides advantages in the numerical implementation. In the present model, the strength function for the effective stress is used to control the evolution of the yield surface, so that calibration with experimental results is convenient. A simple and thermodynamically consistent scalar degradation model is introduced to simulate the effect of damage on elastic stiffness and its recovery during crack opening and closing. The performance of the plastic-damage model is demonstrated with several numerical examples of simulating monotonically and cyclically loaded concrete specimens.

The use of the cone penetration test (CPT) resistance data as an index for liquefaction assessments is receiving increased attention because of the advantages of this in-situ test method. This paper investigates the feasibility of using the optimum seeking method to assess liquefaction potential from actual CPT field data. Optimization theory is a very important branch of applied mathematics, and has a wide application in the practical world. Using the available field liquefaction and nonliquefaction data, the influence of various factors is quantified using the optimum seeking method. The factors considered are: the earthquake magnitude, M; the vertical effective overburden stress, [[Sigma][prime].sub.v0]; the CPT tip resistance, [q.sub.c]; the peak acceleration at the ground surface of the site, [a.sub.max]; and the median grain diameter of the soil, [D.sub.50]. The most important factor has been identified as the CPT tip resistance. Since neither normalization of [q.sub.c] nor calculation of seismic shear stress is required, the proposed method is simpler than the conventional method of evaluating liquefaction potential. Comparisons indicate that the proposed method gives a rate of success for evaluating liquefaction potential equivalent to or somewhat higher than that by the conventional method.

A centrifuge testing program was undertaken to investigate the failure mechanisms of geosynthetic reinforced soil slopes and to evaluate the assumptions in their design. Scaling laws were established so that factors of safety in the models would be identical to those in prototype structures. Failure of the models was characterized by well-defined shear surfaces through the toe of the slopes, which is in good agreement with current design methods for reinforced slopes based on limit equilibrium. The moment of failure was defined by a sudden change in the rate of settlements at the crest of the slope. In contrast to the assumption in current design procedures that failure should initiate at the toe of a reinforced slope, failure initiated at midheight of the slopes. Model deformations were found to depend on the backfill properties, but were essentially independent of the tensile strength and spacing of the reinforcements. The test results showed that overlapping reinforcement layers contribute to stability as they failed by breakage instead of by pullout when intersected by the failure surfaces. The experimental results also indicate that stability of the reinforced slopes is governed by the peak shear strength and not by the critical state shear strength of the backfill soil. A new distribution of maximum reinforcement forces with depth, which is consistent with the failure mechanism observed in the models, is proposed for geosynthetic reinforced soil slopes.

The r-nodes (redistribution nodes) are locations in mechanical components and structures that are load-controlled, and therefore insensitive to material constitutive relationships. These locations and their respective equivalent stress values can be approximately determined on the basis of two linear elastic analyses. By invoking equilibrium considerations, a simple relationship can be established between the 'combined r-node equivalent stress' and the plastic collapse loads. On account of its load-controlled nature, the combined r-node equivalent stress can be identified with the reference stress, which is extensively used in carrying out pressure component integrity assessments. The concept of r-nodes is also related to the primary stresses in pressure components, and in designing mechanical components and structures for minimum weight. This paper proposes simple phenomenological models in an attempt to characterize the functioning of r-nodes.

A numerical model has been developed to reproduce the punching failure in reinforced-concrete structures. It is characterized by an efficient triaxial strength criterion for concrete, a nonassociated flow rule reproducing the concrete dilatancy observed experimentally, and a cracking model accounting for the brittleness of concrete failure under various states of stress. The simulation of punching failure in a circular slab is successfully performed as the localized mode of failure - characterized by an inclined crack - is reproduced. It is shown that punching failure is initiated by the coalescence of microcracks inside the slab, followed by a crack propagation towards the corner of the slab-column intersection. A parametric analysis of the punching failure demonstrates that (1) punching failure is due to tensile failure of concrete along the inclined punching crack and is not due to compressive failure; (2) increasing the percentage of reinforcement reduces the state of internal cracking resulting in an increase of the failure load and a reduction of the ductility; and (3) the size effect observed experimentally is reproduced and a size-effect law is proposed.

The tension leg platform (TLP) concept is considered to be economically competitive with other offshore production concepts in deepwater locations. The critical part of this concept regarding structural failure is the tether system, in which fatigue is an important failure mode. The present paper presents a computational efficient and general probabilistic procedure for estimating the fatigue reliability of the TLP tether system. Two crack growth rate models of single crack sites are applied. Among uncertainties accounted are those in the long-term stochastic load process, the fatigue strength, and the initial crack sizes.

We outline here a method for incorporating the scatter observed in creep rupture times and fatigue cycles-to-failure into a probabilistic model for creep-fatigue failure. We do this within the context of the well-known damage fraction summation rule. Various numerical methods for calculating the probability of failure for given creep-fatigue loading cycles are discussed.

A nonlinear fracture mechanics model is proposed for analysis of the flexural behavior of brittle-matrix composites with uniformly distributed secondary phases. In accordance with the Barenblatt-Dugdale model the bridging or cohesive zone of the material is replaced by a fictitious crack along which a closing traction distribution is applied. The dimensionless formulation brings out the parameters synthetically controlling the structural behavior and the size-scale effects. Different scaling transitions are predicted in the flexural behavior of the composite depending on different modeling of the toughening mechanisms. When a homogenized toughening mechanism for the whole composite is considered along with closing tractions as a linearly decreasing function of the crack opening displacement, a ductile to brittle transition is found as the beam depth increases. On the other hand, when the matrix toughness and the toughening mechanism of the reinforcements are separately modeled, and the closing tractions have a constant value until a critical crack opening displacement, a double brittle-ductile-brittle transition is found. Experimental tests on fiber-reinforced mortar beams in bending are successfully simulated.

A set of data fitting algorithms for calculating the cyclic material characteristics are employed in the local strain technique for fatigue life prediction. These characteristics are derived by fitting power-law curves to the elastic and plastic components of uniaxial strain-life fatigue data obtained under constant amplitude testing. The fitting technique is demonstrated for two sets of SAE 1045 steel data.

The mean strain effect on the crack initiation lives for notched specimens under biaxial nonproportional loading paths is analyzed. Elastic-plastic finite element method was employed to evaluate the local stresses and strains. Various prediction models related to the mean stress/strain effect were used to correlate the experimental results with reference fatigue data for smooth specimens. Findings indicated that the Fatemi-Socie model provides good prediction with the assistance of the finite element method.

A probabilistic mesomechanical crack nucleation model is suggested to relate the microstructural material heterogeneities to the statistical scatter in the macrostructural response. The macrostructure is modeled as an assembly of microelements. Cracks nucleate within the microelements and grow from the microelements to final fracture. A micromechanical slip band decohesion model together with a Paris law crack growth model are employed with first order reliability methods and Monte Carlo simulation to obtain the distribution of fatigue life for the macrostructure.

A two-dimensional model of the delaminated face sheet of sandwich plates for forecasting local buckling utilizing continuous analysis is shown. The method can easily handle sandwich plates with single or multiple embedded delaminations of different shapes and sizes at any location. Several numerical results which consider the effects of transverse normal and shear stiffnesses of the core on the buckling load of sandwich plates with delaminations of different shapes and sizes at various locations are shown.

A nonlinear elastoplastic finite-element (FE) model for face-shell-bedded hollow masonry using isoparametric shell elements has been developed. The nonlinear behavior of the masonry in compression due to progressive cracking, and geometric and material nonlinearities is considered in the model. Details of the elastoplastic constitutive model and failure criteria for both blocks and mortar joints are presented. Results from a simulated test of a three-block-high prism are given in the form of stress, strain, and displacement plots. The behavior of the model is compared to known experimental behavior. The methodology, when combined with the substructuring technique, will allow analysis of substantially larger walls than would the more typical full three-dimensional (3D) analysis.

A model for predicting the failure of hydraulic structures is derived from observed degradation characteristics over a time period. The model employs a Bayesian approach in that it calculates the average deterioration for a fixed unit of time based on a prior density. This allows the probabilities of preventive repair and failure to be expressed as a function of the average deterioration. The model is applied in computing the lifetime probability function of the Netherlands' Eastern Scheldt Storm-Surge Barrier.

Random fields are often used in reliability analysis to model the uncertainties that possess spatial variabilities. Within the framework of finite element reliability methods, the domain of each field is discretized into a mesh of random field elements and the value for each element is represented by a single random variable. The selection of random field mesh is important since it influences the accuracy of the reliability analysis. In this study, how to select and refine the random field mesh in finite element reliability analysis is investigated. An expression is derived to compare the improvements made by various refinements of a coarse mesh. Further exploration of the expression shows that the gradient of the limit-state function plays a key role in the selection of a random field mesh. A criterion for selecting random field meshes is devised as follows: Adopt a coarse mesh in the area where the gradient of the limit-state function with respect to the discretized variables is small, and a fine mesh in the area where the gradient is large. The selection rule developed in this study is verified by a beam and a plate examples.

The mechanical design of thin columns and plates are investigated with respect to elastic buckling caused by compressive overstress. Analytical design and modeling techniques based on continuum mechanics concepts are presented to guard against buckling-induced structural failure. These are used in two examples, one from mechanical engineering and another from electronic packaging, concerning the prevention of failure mechanisms during the design phase.

In the last four decades, soil-metal structures have been used extensively as short-span bridges. With deep soil cover, the soil provides the necessary support for the metallic structure. However, for long spans and shallow soil cover, the soil may not provide enough support. Failures of such structures, some catastrophic, are reported. Previous studies show that reinforcing the soil and tieing the metal structure into the soil improve dramatically the load response. In this paper, a rational design and analytical procedure is presented to determine the ultimate load response of reinforced and nonreinforcing soil-metal structures of long span under shallow soil cover conditions. The procedure is based on a buckling mode of failure. The effect of reinforcing is accounted for by using a modified modulus of soil reaction. Results from five model soil-metal structures are compared to the theoretical results. An illustrated design example is given.

The present paper provides a method for the identification of failure modes that contribute significantly to the estimate of the system probability of failure in rigid-plastic structures. For structures where loads and resistances are random variables, a decision rule is presented for the identification of failure modes in series systems based on their contribution to the system probability of failure. Stochastic programs based on this decision rule for failure mode selection are developed for the identification of failure modes in structures. Examples illustrate the use of these mathematical programs in identifying significant failure modes in rigid-plastic structures where axial force-moment interaction is included.

A sampling method to calculate the n-dimensional integral representing probability of failure, [p.sub.f], is presented. By means of n-dimensional polar coordinates, the directions of the sampling point are limited to a hypercone whose axis contains the design point. If [beta] and the direction cosines are known from the first-order reliability method, only two parameters are necessary to define the integration domain, whatever the problem dimension n may be. The method described in this paper, a straightforward simulation, and the Harbitz method are used in two problems of known solution and in two examples with convex failure domain. It is shown that the orientated simulation allows a drastic reduction in the number of samples needed, especially in certain structural systems and in quality-control methods with strongly convex failure domain. On the other hand, a procedure using orientated iteration is presented for obtaining [beta] in cases where the usual iterative method is not suitable., An oriented simulation method for determining the n-dimensional integral for the prediction of failure probability is described. The method limits the directions of the sampling points to a hypercone whose axis contains the design point. The method decreases the number of simulations needed to obtain failure probability and can be implemented for structural systems with strongly convex failure domains.

In structural reliability under fatigue, the basic event is section failure. It is defined in terms of the time to develop a through-thickness crack at the critical hot spot in the section. Correction factors account for the fact that the crack may occur at a site other than the critical hot spot and that section failure occurs sometime after development of a through-thickness crack. After failure, the section is assumed to be 'severed.' The branch-and-bound algorithm is used to identify important sequences of section failures leading to collapse, and structure failure is approximated as the event that one of these important sequences occurs. Efficient first-order reliability methods are used for probability computations. The procedure is applied to an offshore platform. Significant systems effects are observed, i.e., the probability of structure collapse is much smaller than the probability of failure of an individual section. The use of inspection observations in updating reliability estimates also is presented., A method is developed to predict structural reliability under fatigue. The method considers the changes in stress distribution during section failures and allows accurate probabilistic modeling. A branch-bound algorithm is used to determine the sequences of section failures that result in collapse. First-order reliability methods are used for probability computations. The reliability analysis of a steel offshore platform is also presented.