Multiscale seismic vulnerability assessment and retrofit of existing masonry buildings

The growing concern about the protection of built heritage and the sustainability of urban areas has driven the reoccupation of existing masonry buildings, which, in the great majority of the cases, were not designed or constructed to withstand significant seismic forces. This fact, associated with territorial occupation often concentrated in areas with high seismic hazard, makes it essential to look at these buildings from the point of view of the assessment of their seismic vulnerability and retrofitting needs. However, to be effective and efficient, such an assessment must be founded on a solid knowledge of the existing methods and tools, as well as on the criteria that should underlie the selection of the most appropriate to use in each context and situation. Aimed at contributing to systematise that knowledge, this paper presents a comprehensive review of the most relevant vulnerability assessment methods applicable at different scales, as well as the most significant traditional and innovative seismic retrofitting solutions for existing masonry buildings.This research was funded by the Portuguese Foundation for Science and Technology (FCT) through the postdoctoral grant SFRH/BPD/122598/2016.info:eu-repo/semantics/publishedVersio

Perforated shear + reinforcement bar connectors in a timber-concrete composite solution. Analytical and numerical approach

[Abstract] This paper presents a study of a novel shear connector in a timber-concrete composite solution, focussing on the determination of an analytical expression that makes it possible to predict its behaviour and a numerical analysis that describes it accurately. The shear connector is composed of a perforated steel plate inserted into a slot within the timber rib and glued, in combination with reinforcing corrugated steel bars affixed to the top of the plate. Previous tests made it possible to establish failure mode in different T composite section plate-rebar configurations. These results determine the effectiveness of the system in terms of force-slip behaviour, with systematic failure in the timber section. A simple predictive model is proposed to determine the ultimate capacity of the joint, taking into account the mechanical properties of timber in relation with the fracture plane and the timber-adhesive interface. This model makes it possible to apply a design process that is able to predict the stiffness of the connection. FEM models were analysed for each configuration in a variable load process equal to that used in the test, according to the standard procedure. A variable friction coefficient in contact definition made it possible to achieve an accurate descriptive model in association with the test procedure.MINECO; BIA2016-77184-

State of the art on Timber Concrete Composite floor

Interest in timber-concrete composite (TCC) floors has increased over the last 20-30 years. Since the 1990âs, TCC solution is seen as a viable and effective alternative to conventional reinforced concrete and/or traditional timber floors in multistorey buildings. In TCC technology, a timber beam, either solid wood, glued laminated or laminated veneer lumber (LVL), is connected to a concrete slab using a connection system that resists shear forces and impedes slip between the members of the composite section. The strength, stiffness, location and number of connectors play a crucial role for the composite action and determine the structural and serviceability performance of the floor system. This paper discusses the state of the art of TCC structures. It presents a comprehensive review of the literature about the development and structural behaviour of TCC structures. The review addresses construction aspects and shear connection concepts. It evaluates experimental tests, finite element and numerical models. It discusses the influence of concrete elements. As recommendations, the best types of shear connection for cast in-situ and prefabricated TCC floors are put forward and assessed for criteria such as strength, stiffness, ductility and ease of manufacturing. Furthermore the most relevant numerical models are introduced. These models can be used to further the experimental results in parameters such as connections, configurations, geometrical and material properties

Integrated nonlinear modelling strategies for the seismic analysis of masonry structures

In the last decades, significant interest has raised in modelling and analysing the structural response of unreinforced masonry (URM) buildings. This aims at conceiving and designing effective interventions to reduce the vulnerability towards seismic actions. Studies based on costly structural testing are often limited to few benchmark cases, making numerical modelling an excellent option to extend experimental results and a valid solution for understanding URM structural behaviour. Advanced discrete models are widely employed among the available numerical strategies to predict the URM dynamic response, thanks to their ability to account for the heterogeneous nature of masonry and to simulate its behaviour up to the complete collapse. If, on the one hand, the low degree of idealisation of discrete models allows their employment for the extension of experimental tests, on the other hand, they require expert users, the definition of a large number of mechanical parameters and a high computational effort. This last drawback often limits the use of advanced discontinuum models in the engineering practice or for seismic risk studies, which require the execution of multiple analyses. In this work, a modelling approach, based on the Applied Element Method (AEM), was combined with more simplified models to exploit the discrete model potential and overcome its limits. To this aim, the AEM was employed as a benchmark to calibrate/validate simplified modelling strategies, improving their reliability when compared to advanced model outcomes. In this context, AEM models were used as a reference to enhance the Equivalent Frame Model (e.g. the presence of irregular distribution of openings) and to validate a new strength criterion associated with the failure mechanism encountered in a new masonry typology. In the absence of a large suite of experimental tests exploring all the possible setup or configurations, the AEM can provide precious information. On the other hand, the AEM can help to investigate situations requiring a higher level of detail, such as the design of the timber retrofitting system analysed in this work. The ability of the AEM to simulate the structural behaviour up to the complete collapse was also used to investigate the effect of different percentages of ground floor opening on the dynamic response of Dutch terraced houses, performing benchmark analyses to calibrate SDOF models employed for the development of fragility functions associated with the different layouts. Finally, AEM models were employed for substructuring façade models of masonry buildings whose global response was effectively studied by equivalent frame models. The aim of the study was to predict the debris extent involved in the collapse of URM façades in case of earthquake loadings. Such an integrated numerical procedure allowed considering a large suite of seismic inputs, overcoming the time-consuming issue

Behavior of Metallic and Composite Structures (Second Volume)

Various types of metallic and composite structures are used in modern engineering practice. For aerospace, car industry, and civil engineering applications, the most important are thin-walled structures made of di erent types of metallic alloys, brous composites, laminates, and multifunctional materials with a more complicated geometry of reinforcement including nanoparticles or nano bres. The current applications in modern engineering require analysis of structures of various properties, shapes, and sizes (e.g., aircraft wings) including structural hybrid joints, subjected to di erent types of loadings, including quasi-static, dynamic, cyclic, thermal, impact, penetration, etc.The advanced metallic and composite structures should satisfy multiple structural functions during operating conditions. Structural functions include mechanical properties such as strength, sti ness, damage resistance, fracture toughness, and damping. Non-structural functions include electrical and thermal conductivities, sensing, actuation, energy harvesting, self-healing capability, electromagnetic shielding, etc.The aim of this SI is to understand the basic principles of damage growth and fracture processes in advanced metallic and composite structures that also include structural joints. Presently, it is widely recognized that important macroscopic properties, such as macroscopic sti ness and strength, are governed by processes that occur at one to several scales below the level of observation. A thorough understanding of how these processes influence the reduction of sti ffness and strength forms the key to the design of improved innovative structural elements and the analysis of existing ones

Rational modelling and design in timber engineering applications using fracture mechanics

The paper gives a general discussion on methods and theories used for strength analyses of wood and wood-based products. The main aim is to discuss in general terms the benefits gained from using design approaches based on rational and scientifically sound theories. The paper presents mainly fracture mechanics theory but also other advanced modelling techniques and examples from using advanced measurement techniques in testing are brieflydiscussed. Examples of applications within the current scope of Eurocode 5 that need to be developed are highlighted (dowel type joints and compression perpendicular to the grain). In addition, examples of applications in need of being included in Eurocode 5 are discussed (beams with holes and glued-in rods). The theories presented in the paper are applied to two different applications, namely notched beams and glued-in rods, the latter currently being a candidate for inclusion in Eurocode 5

Active thermography for the investigation of corrosion in steel surfaces

The present work aims at developing an experimental methodology for the analysis of corrosion phenomena of steel surfaces by means of Active Thermography (AT), in reflexion configuration (RC). The peculiarity of this AT approach consists in exciting by means of a laser source the sound surface of the specimens and acquiring the thermal signal on the same surface, instead of the corroded one: the thermal signal is then composed by the reflection of the thermal wave reflected by the corroded surface. This procedure aims at investigating internal corroded surfaces like in vessels, piping, carters etc. Thermal tests were performed in Step Heating and Lock-In conditions, by varying excitation parameters (power, time, number of pulse, ….) to improve the experimental set up. Surface thermal profiles were acquired by an IR thermocamera and means of salt spray testing; at set time intervals the specimens were investigated by means of AT. Each duration corresponded to a surface damage entity and to a variation in the thermal response. Thermal responses of corroded specimens were related to the corresponding corrosion level, referring to a reference specimen without corrosion. The entity of corrosion was also verified by a metallographic optical microscope to measure the thickness variation of the specimens