Stiffness and Strength Estimation of Damaged Unreinforced Masonry Walls Using Crack Pattern

After an earthquake, the residual stiffness and strength of structural elements are typically estimated based on a qualitative visual inspection of cracks that is prone to error. In this paper a new approach is proposed to automatically estimate the updated stiffness and strength of damaged unreinforced masonry walls by characterization of crack patterns by a mathematical index. It is shown that structural and textural fractal dimensions of a crack pattern reflect the extent of cracking and the type of cracking or crushing, i.e., whether the cracks pass through joints or whether bricks have been damaged and crushed. Using results of six quasi-static cyclic tests on unreinforced brick masonry walls with different failure modes at various drift ratios, it is shown that the structural and textural fractal dimensions of the crack patterns are an accurate predictor of the stiffness and strength degradation. This procedure seems therefore a promising approach for replacing the traditional assessment methods that are based on visual inspection and engineering judgment by an analytical procedure based on image processing that can eventually be completely automated.

Reinforced concrete bridges under increased railway traffic loads

Andrin Herwig

The aim of this thesis is to provide rational engineering methods for the fatigue safety examination of existing railway bridges. Increasing railway traffic loading and enhanced structural analysis allow for higher exploitation of the capacity of bridge elements. This implies that increasing action effects due to higher service loads may become fatigue relevant in the future. The application of the results allows for more precise fatigue examinations. As beneficial consequence, most railway bridges may be operated safely in the future without costly strengthening measures. Calculated stress ranges in the reinforcement that governs the fatigue resistance of structural elements are too high when using conventional resistance models. The load carrying contribution of non-structural elements and a not entirely developed crack pattern lead to fatigue relevant reduction of the stress range in the rebars. A theoretical study shows that reductions of 5 – 15 % may be obtained by considering the composite effect of the continuous rail grid. Measurements of the dynamic traffic effects were conducted on a single-track bridge. The effects of passenger and freight trains at different velocities on the structural response were measured. The results are interpreted based on the observed vertical shape of the railway track. The observed dynamic behaviour could be correctly represented by simulations using simple dynamic models. The effect of other velocities and in-creased carriage loading degrees are investigated in a parametric study. The findings of previous investigations for road bridges and the investigations of this research work for railway bridges show that the Dynamic Amplification Factor (DAF) decreases for increasing loadings. Thus, smaller DAFs are applied for fatigue relevant causing heavy vehicles. Fatigue stress ranges may be reduced by supplementary 3 – 6 %. A method based on Linear Elastic Fracture Mechanics theory is presented for fatigue life determination. Fatigue life typically is very sensitive to different calculation parameters, rendering the calculation of a reliable fatigue life difficult. The refined analysis of fatigue tests reported in literature allows better understanding of the fatigue behaviour of bridge elements. Thus, a fatigue safety concept is established that compensates the inconvenience of the high sensitivity of fatigue life calculations. This fatigue safety concept is based on the observed load carrying behaviour of inspected bridge elements. The specific fatigue behaviour with visible signs allows for the examination of fatigue safety in a pragmatic way. Specific inspection of bridge elements becomes pertinent as soon as general examinations exhibit an insufficient fatigue resistance. Fatigue behaviour of Ultra-High Performance Fibre Reinforced Concretes (UHPFRC) is characterised by increasing deformations during cyclic tensile loading. Under a maximum tensile stress level of 4 MPa the deformation of the UHPFRC layer becomes stable during cyclic loading. For slightly higher stresses, the deformation increases and the UHPFRC layer fails due to steel fibre pull out. Application of the UHPFRC layer in the flexural tension zone considerably reduces the fatigue stresses in the steel reinforcement. As the UHPFRC layer deforms, the stress range in the reinforcement is effectively and permanently reduced and may remain below the nominal fatigue limit. For design of members with a layer of UHPFRC for waterproofing and fatigue strengthening, the maximum allowed strain for stable behaviour under tensile fatigue loading should be verified.

EPFL2008

Actions microclimatique et environnementale des ouvrages d'art routier [Microclimatic and environmental actions of road structures]

Eugen Brühwiler, David Conciatori, André-Gilles Dumont

Les différentes zones d’un ouvrage d’art routier sont étudiées en fonction de leur degré d’exposition au microclimat environnant. Les conditions climatiques provenant de stations météorologiques et la cinétique des véhicules permettent de définir des zones d’exposition aux produits salants et au climat. Une division judicieuse d’un ouvrage en éléments structuraux en fonction de son exposition permet de prendre en considération l’importante variabilité spatiale et de définir des zones de sensibilité équivalente face aux détériorations. Sur la base de stations météorologiques suisses, d’un monitoring d’un ouvrage d’art routier, d’enquêtes auprès des autorités publiques, de mesures ponctuelles in situ et de recherches bibliographiques, cet article met en exergue le microclimat des structures de manière précise. Cette approche permet de définir les différentes zones d’exposition des ouvrages, à savoir les zones de brouillard salin, d’éclaboussures et de stagnation d’eau et de définir l’importance du microclimat en vue de prédire l’évolution des détériorations des structures. -- Various areas of a highway structure are studied regarding their level of exposure to the surrounding microclimate. Climate conditions from meteorological stations and vehicle kinetics are used to determine zones that are exposed to salt products and climate. Dividing a highway into structural elements based on exposure takes into account the significant spatial variation and helps define zones of equivalent sensitivity to deteriorations. Based on Swiss meteorological stations, highway structure monitoring, inquiries with public authorities, in situ spot measuring and literature surveys, this article precisely highlights the microclimate of these structures. This approach can help define the various exposure areas of the structures, namely salt mist, splash and water stagnation areas as well as determine the significance of the microclimate in order to predict the evolution of structural deteriorations.

2009

Microclimatic and environmental actions of road structures

David Conciatori, André-Gilles Dumont

Various areas of a highway structure are studied regarding their level of exposure to the surrounding microclimate. Climate conditions from meteorological stations and vehicle kinetics are used to determine zones that are exposed to salt products and climate. Dividing a highway into structural elements based on exposure takes into account the significant spatial variation and helps define zones of equivalent sensitivity to deteriorations. Based on Swiss meteorological stations, highway structure monitoring, inquiries with public authorities, in situ spot measuring and literature surveys, this article precisely highlights the microclimate of these structures. This approach can help define the various exposure areas of the structures, namely salt mist, splash and water stagnation areas as well as determine the significance of the microclimate in order to predict the evolution of structural deteriorations.