A large amount of low-rise unreinforced masonry structures (URM) can be found in Groningen, the Netherlands. More and more induced earthquakes with short duration have been detected in this region due to gas exploitation. Local unreinforced masonry (URM) buildings were initially not designed for withstanding seismic actions, so that unexpected damage may occur due to their vulnerability, raising insecurity among residents. Existing low-rise masonry buildings in Groningen can be divided into different categories based on their characteristics. Two types of residential masonry buildings that fulfil the prerequisites for performing non-linear seismic assessment are chosen to be studied in this thesis project, including the terraced house and the detached house. The seismic assessment of structures requires the use of both a discretization method and a seismic assessment method. The discretization method is used to translate the mechanical model into a finite element model used for the numerical analysis. Several methods have previously shown to be applicable for seismic assessment, but this work investigates the implications of using a continuum model (CM) and an equivalent frame model (EFM) approach to discretization in the general-purpose finite element package described in n DIANA-FEA-BV (2017). The continuum model approach adopted was in a previous work by Schreppers et al. (2017) validated against experimental results and is as such deemed representative of the physical behaviour of the mechanical models investigated. An equivalent frame model approach to be used with DIANA is proposed in the work by Nobel (2017). The continuum model approach uses continuum elements with a constitutive model developed for the seismic assessment of masonry structures. This constitutive model captures both shear and flexural failure mechanisms. The equivalent frame model approach uses a combination of numerically integrated beam elements and nodal interfaces, each with a distinct constitutive model, thus decoupling the description of the flexural and shear behaviour. This approach aims to capture the macro-behaviour at the structural level. The applicability of the proposed equivalent frame model approach is evaluated by how well it replicates the validated continuum model approach results. The two discretization methods described are evaluated using two types of seismic assessment methods. The first seismic assessment method used consists of first performing a quasi-static non-linear pushover analysis (NLPO) on the model. This results in the pushover curve, which describes the global behaviour of the model under an equivalent lateral load based on the fundamental mode shape of the structure. The pushover curve is then used with the N2-method described in EN1998-1 (2004) to assess at which peak ground acceleration (PGA) that the model reaches the near-collapse (NC) limit state. The second seismic assessment method consists of performing dynamic non-linear time-history analyses (NLTH). This method uses recorded accelerograms to impose the inertial forces. The PGA for the accelerogram where the near-collapse limit state is reached is compared to the PGA from the use of the N2-method. The applicability of the pushover analysis in conjunction with the N2-method is evaluated by how well it replicates the PGA found from the time-history analyses and by how well it replicates local failure mechanisms.  Therefore, the main objectives of this project can be described by the following two questions: i. To what extent can the equivalent frame method be applicable as a proper discretization method for pushover analyses and time-history analyses of low-rise unreinforced masonry residential buildings in the Groningen region? ii. To what extent can the non-linear pushover method be adopted to assess the seismic behaviour of low-rise unreinforced masonry residential buildings in the Groningen region? The applicability of the equivalent frame model showed to vary. For describing local failure mechanisms its applicability is poor. Further work on connecting the edge piers to transverse walls is needed. For seismic assessment using the N2-method the applicability of the equivalent frame model approach is sensible. The conservative displacement capacity counteracts the fact that it is worse at describing local unloading, which produced a larger initial equivalent stiffness of the bi-linear curves in comparison to the continuum model. For seismic assessment using the time-history signals, its applicability is possible. While it could show different behaviour in terms of displacement and damping forces, it still showed a similar PGA at the near-collapse limit state for the cases at hand. The seismic assessment of the terraced and detached houses by the N2-method is similar to the seismic prediction by applying time-history analyses. However, there are still some variations in the initial stiffness, force capacity and displacement capacity between these two assessment methods due to the assumptions and limitations in this study. Overall, considering the pros and cons of the quasi-static pushover method, it is deemed applicable during the seismic assessment of the unreinforced masonry structures in the Groningen area. / En stor mängd låga oarmerade murverksbyggnader finns i Groningen, Nederländerna. Allt fler jordbävningar med kort varaktighet har uppmätts i regionen pågrund utav gasproduktion. I området förekommer oarmerade murverksbyggnader som initialt inte var dimensionerade för jordbävningslaster, vilket har resulterat i oönskade skador samt osäkerhet för invånarna. Förekommande låga murverksbyggnader i Groningen kan fördelas i olika grupper beroende på deras egenskaper. Två typer av murverksbyggnader utformade som bostäder uppföljer kraven för att utföra olinjär jordbävningsanalys och har i detta projekt studerats. Typerna som studerats är radhus samt fristående hus. Jordbävningsnalys av byggnader kräver användningen av en diskretiseringsmetod samt en utvärderingsmetod. Diskretiseringsmetoden används för att översätta den mekaniska modellen till en finita elementmodell för numerisk analys. Flera metoder har tidigare visat sig vara applicerbara för utvärdering under jordbävningslaster, men det här projektet studerar konsekvensen från användningen av en kontinuumelement modell (CM) samt en ekvivalent rammodel (EFM) för diskretisering i det generella finita elementpaketet beskrivet i DIANA-FEA-BV (2017). Metoden som använts för att skapa kontinuumelement modeller vart i ett tidigare projekt av Schreppers et al. (2017) validerat mot experimentella resultat och anses därför  representera det fysiska beteendet hos de mekaniska modellerna. Ett förslag för hur ekvivalenta rammodeller ska uppföras i DIANA ges i arbetet av Nobel (2017). Metoden för en kontinuumelement modell använder en konstitutiv lag som utvecklats för utvärderingen av murverksbyggnader under jordbävningslaster. Denna konstitutiva modell fångar skjuv- samt böjbrottmekanismer. Metoden för en ekvivalent rammodell använder numeriskt integrerade balkelement samt nodelement, där båda elementtyper använder en distinkt konstitutiv modell vilket gör att skjuv- samt böjbeteende hanteras individuellt. Den här metoden har som mål att fånga makro-beteendet av elementen. Applicerbarheten av den föreslagna metoden för ekvivalenta rammodeller är utvärderat via hur väl den replikerar resultaten från en kontinuumelement modell. De två diskretiseringsmetoderna jämförs via två metoder för utvärdering under jordbävningslaster. Den första utvärderingsmetoden består av att först utföra en kvasi-statisk olinjär stjälpningsanalys (NLPO) på modellen. Detta leder till stjälpningskurvan, vilket beskriver den globala responsen av modellen under en ekvivalent horisontal last som baserats på första fundamentala moden av bärverket. Stjälpningkurvan används sedan med N2-metoden som beskrivs i EN1998-1 (2004) för att utvärdera vid vilken maximal markacceleration (PGA) som modellen når nära-kollapsgränstilsståndet (NC). Den andra utvärderingsmetoden består av att utföra dynamiska samt olinjära tids-historikanalyser (NLTH). För att göra detta så används accelerogram för att applicera den dynamiska lasten. Den maximala markaccelerationen för signalen där tids-historikanalysen når nära-kollapsgränstilsståndet är jämfört mot den maximala markaccelerationen som fås när N2-metoden används. Applicerbarheten för stjälpningsanalysen tillsammans med N2-metoden utvärderas via hur väl den replikerar resultatet av den maximala markaccelerationen som erhållsfrån tids-historikanalyserna, samt via hur väl metoden replikerar lokala brottmoder. Baserat på detta så kan målen med detta project sammanfattas via dessa två frågeställningar: i. Till vilken grad kan den föreslagna metoden för ekvivalenta rammodeller användas för utvärdering under jordbävningslaster när stälpningsanalyser, samt tids-historikanalyser, utförs på låga och oarmerade murverksbyggnader utformade som bostadsrätter i Groningen? ii. Till vilken grad kan olinjär stjälpningsanalys användas för utvärdering under jordbävningslaster på låga och oarmerade murverksbyggnader utformade som bostadsrätter i Groningen? Applicerbarheten av metoden för ekvivalenta rammodeller visade sig variera. För att beskriva lokala brottmoder så är applicerbarheten låg. Fortsatt arbete som undersöker hur pelarelementen ska kopplas mot de tvärgående väggarna bör utföras. För utvärdering via användandet av N2-metoden så visade det sig att applicerbarheten är rimlig. Den konservativa deformationskapaciteten motverkar det faktum att metoden för ekvivalenta rammodeller är sämre på att påvisa lokal avlastning, vilket i sin tur resulterade i en större ekvivalent initial styvhet för de bi-linjära kurvorna i jämförelse mot metoden för kontinuumelement modeller. För utvärdering när tids-historikanalyser användes så visade applicerbarheten vara rimlig. Samtidigt som det kunde uppstå skillnader i beteende när det kom till deformation samt dämpning, så visade det sig att metoderna fortfarande uppvisade en liknande maximal markacceleration vid nära-kollapsgränstilsståndet för bärverken i fråga. Utvärderingen under jordbävningslast för modellerna när N2-metoden användes visade liknande resultat som när tids-historikanalyserna utfördes. Det förekom dock skillnader i den initiala styvheten, i skjuvkraftskapaciteten och i deformationskapciteten mellan utvärderingsmetoderna från gjorda antaganden samt begränsningar hos arbetet. Som en slutsats när för- samt nackdelar värderas så visade det sig att stjälpningsmetoden är en rimlig utvärderinsgmetod för oarmerade murverksbyggnader i Groningen.

Dans le cadre de la protection du bâti face au risque sismique, les techniques d’analyse simplifiées, basées sur des calculs quasi-statiques en poussée progressive, se sont fortement développées au cours des deux dernières décennies. Le travail de thèse a pour objectif d’optimiser une stratégie d’analyse simplifiée proposée par Chopra et al. (2001) et adoptée par les normes américaines FEMA 273. Il s’agit d’une analyse modale non linéaire découplée, dénommée par les auteurs UMRHA qui se caractérisent principalement par : des calculs de type pushover selon les modes de vibration dominants de la structure, la création de modèles à un degré de liberté non linéaire à partir des courbes de pushover, puis le calcul de la réponse temporelle de la structure en recombinant les réponses temporelles associées à chaque mode de vibration. Dans ce travail, la méthode UMRHA a été améliorée en investiguant les points suivants. Tout d’abord, plusieurs modèles à un degré de liberté non linéaire déduits des courbes de pushover modal sont proposés afin d’enrichir la méthode UMRHA originelle qui emploie un simple modèle élasto-plastique : autres modèles élasto-plastiques avec des courbes enveloppes différentes, le modèle de Takeda prenant en compte un comportement hystérétique propre aux structures sous séismes, et enfin, un modèle simplifié basé sur la dégradation de fréquence en fonction d’un indicateur de dommage. Ce dernier modèle à un degré de liberté privilégie la vision de la chute de fréquence au cours du processus d’endommagement de la structure par rapport à une description réaliste des boucles d’hystérésis. La réponse totale de la structure est obtenue en sommant les contributions non linéaires des modes dominants aux contributions linéaires des modes non dominants. Enfin, la dégradation des déformées modales, due à l’endommagement subi par la structure au cours de la sollicitation sismique, est prise en compte dans la méthode M-UMRHA proposée dans ce travail, en généralisant le concept précédent de dégradation des fréquences modales en fonction d’un indicateur de dommage : la déformée modale devient elle-aussi dépendante d’un indicateur de dommage, le déplacement maximum en tête de l’ouvrage ; l’évolution de la déformée modale en fonction de cet indicateur est directement identifiée à partir des calculs de pushover modal. La pertinence de la nouvelle méthode M-UMRHA est investiguée pour plusieurs types de structures, en adoptant des modélisations éprouvées dans le cadre de la simulation des structures sous séismes : portique en béton armé modélisé par des éléments multifibres pour le béton et les armatures, remplissage en maçonnerie avec des éléments barres diagonales résistant uniquement en compression, bâti existant contreventé (Hôtel de Ville de Grenoble) avec des approches coques multicouches. Les résultats obtenus par la méthode simplifiée proposée sont comparés aux résultats de référence issus de l'analyse temporelle non linéaire dynamique. / In the context of building’s protection against seismic risk, simplified analysis techniques, based on quasi-static analysis of pushover, have strongly developed over the past two decades. The thesis aims to optimize a simplified method proposed by Chopra and Goel in 2001 and adopted by American standards FEMA 273. This method is a nonlinear decoupled modal analysis, called by the authors UMRHA (Uncoupled Modal for Response History Analysis) which is mainly characterized by: pushover modal analysis according to the dominant modes of vibration of the structure, setting up nonlinear single degree of freedom systems drawn from modal pushover curves, then determining the history response of the structure by combining of the temporal responses associated with each mode of vibration. The decoupling of nonlinear history responses associated with each mode is the strong assumption of the method UMRHA. In this study, the UMRHA method has been improved by investigating the following points. First of all, several nonlinear single degree of freedom systems drawn from modal pushover curves are proposed to enrich the original UMRHA method, in which a simple elastic-plastic model is used, other elastic-plastic models with different envelope curves, Takeda model taking into account an hysteretic behavior characteristic of structures under earthquakes, and finally, a simplified model based on the frequency degradation as a function of a damage index. The latter nonlinear single degree of freedom model privileges the view of the frequency degradation during the structure damage process relative to a realistic description of hysteresis loops. The total response of the structure is obtained by summing the contributions of the non linear dominant modes to those of linear non dominant modes. Finally, the degradation of the modal shapes due to the structure damage during the seismic loading is taken into account in the new simplified method M-UMRHA (Modified UMRHA) proposed in this study. By generalizing the previous model of frequency degradation as a function of a damage index: the modal shape becomes itself also dependent on a damage index, the maximum displacement at the top of the structure; the evolution of the modal shape as a function of this index is directly obtained from the modal pushover analysis. The pertinence of the new method M-UMRHA is investigated for several types of structures, by adopting tested models of structures simulation under earthquakes: reinforced concrete frame modeled by multifibre elements with uniaxial laws under cyclic loading for concrete and steel, infill masonry wall with diagonal bars elements resistant only in compression, existing building (Grenoble City Hall) with multilayer shell elements and nonlinear biaxial laws based on the concept of smeared and fixed cracks. The obtained results by the proposed simplified method are compared to the reference results derived from the nonlinear response history analysis.

Throughout recent history, famous records of building failures may be found, unfortunately accompanied by great human loss and major economic consequences. One of the mechanisms of failure is referred to as ‘progressive collapse’: one or several structural members suddenly fail, whatever the cause (accident or attack). The building then collapses progressively, every load redistribution causing the failure of other structural elements, until the complete failure of the building or of a major part of it. The civil engineering community’s attention to this type of event was first drawn by the progressive collapse of the building called Ronan Point, following a gas explosion in one of the last floors. Different simplified procedures for simulating the effects of progressive collapse can now be found in the literature, some of them described in detail. However, no extensive study can be found, in which these procedures are compared to more complete approaches for progressive collapse simulation, aiming at the comparison of the assumptions underlying them. To further contribute to the elaboration of design codes for progressive collapse, such a study would therefore be of great interest for practitioners.<p>All parties involved with the subject of progressive collapse are currently attempting to bridge the gap between the work done on the research front on the one hand, what can be considered as a fitting numerical model for regular industrial use on the other, and finally, the normalisation committees. The present research work aims at providing insight as to how the gaps between these poles may be reduced. The approach consists in studying the various hypotheses one by one, and gradually adding complexities to the numerical model, if they prove to be warranted by the need for sufficient accuracy. One of the contributions of the present work stems from this approach, in that it provides insight regarding the validity of the various simplifying assumptions. It also leads to the development of procedures which are kept as simple as possible, in an attempt to design them as best as possible for regular industrial use.<p>The objective of simplifying assumptions validation is pursued in Chapter 2. This chapter consists of the text of a paper entitled “Comparison and study of different progressive collapse simulation techniques for RC structures”, in which the main simplifying assumptions of the progressive collapse guidelines are detailed and assessed. The DoD [1] and GSA [2] static linear and non-linear procedures are investigated, and compared to more complete approaches in order to assess their validity.<p>In the next two chapters, two new procedures for design against progressive collapse are developed. They are based on quasi-static computations, their main objective being to account accurately for dynamic inertial effects. The first of these chapters consists in the text of a paper entitled “A new pushover analysis procedure for structural progressive collapse based on a kinetic energy criterion”, in which energetic considerations allow for the development of a static equivalent pushover procedure. The second chapter consists of the text of a paper entitled “A new pushover analysis procedure for structural progressive collapse based on optimised load amplification factors”, which uses load amplification factors resulting from optimisation procedures in order to account for dynamic inertial effects. The contributions of these two papers lie in the fact that they offer an improved accuracy on the results, when compared with other procedure available in the literature, which follow the same general principles. The two proposed procedures are thoroughly validated by systematic comparisons with results obtained with the more costly dynamic non-linear computations.<p>Finally, an additional chapter focuses on the various approaches that can be adopted for the simulation of reinforced concrete beams and columns. Because a rather simple model for reinforced concrete is used in Chapter 2, the bulk of this chapter consists in the implementation of a more complex fibre-based non-linear beam element. Comparisons performed with this model provide insight to the limitations of the simpler model, which is based on the use of lumped plastic hinges, but show this simpler model to be valid for the purposes of the present work.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Indonesia is a developing country that suffers from earthquakes and windstorms and where at least 60% of houses are non-engineered structures, built by unskilled workers using masonry and timber. The non-engineered housing units developed in urban region are also vulnerable to seismic hazard due to the use of low quality of material and constructions method. Those structures are not resistant to extreme lateral loads or ground movement and their failure during an earthquake or storm can lead to significant loss of life. This thesis is concerned with the structural performance of Indonesian low-rise buildings made of masonry and timber under lateral seismic load. The research presented includes a survey of forms of building structure and experimental, analytical and numerical work to predict the behaviour of masonry wall and traditional timber frame buildings. Experimental testing of both masonry and timber have been carried out in Indonesia to establish the quality of materials and to provide material properties for numerical simulations. The experimental study found that the strength of Indonesia-Bali clay brick masonry are below the minimum standard required for masonry structures built in seismic regions, being at least 50% lower than the requirement specified in British Standard and Eurocode-6 (BS EN 1996-1-1:2005). In contrast, Indonesian timber materials meet the strength classes specified in British Standard/Eurocode- 5 (BS EN 338:2009) in the range of strength grade D35-40 and C35).Structural tests under monotonic and cyclic loading have been conducted on building components in Indonesia, to determine the load-displacement capacity of local hand-made masonry wall panels and timber frames in order to: (1) evaluate the performance of masonry and timber frame structure, (2) investigate the dynamic behaviour of both structures, (3) observe the effect of in-plane stiffness and ductility level, and (4) examine the anchoring joint at the base of timber frame that resists the overturning moment. From these tests, the structural ductility was found to be less than two which is below the requirement of the relevant guidelines from the Federal Emergency Management Agency, USA (FEMA-306). It was also observed that the lateral stiffness of masonry wall is much higher than the equivalent timber frame of the same height and length. The experimental value of stiffness of the masonry wall panel was found to be one-twelfth of the recommended values given in FEMA-356 and the Canadian Building code. The masonry wall provides relatively low displacement compared to the large displacement of the timber frame at the full capacity level of lateral load, with structural framing members of the latter remaining intact. The weak point of the timber frame is the mechanical joint and the capacity of slip joint governs the lateral load capacity of the whole frame. Detailed numerical models of the experimental specimens were setup in Abaqus using three-dimensional solid elements. Cohesive elements were used to simulate the mortar behaviour, exhibiting cracking and the associated physical separation of the elements. Appropriate contact definitions were used where relevant, especially for the timber frame joints. A range of available material plasticity models were reviewed: Drucker-Prager, Crystalline Plasticity, and Cohesive Damage model. It was found that the combination of Crystalline Plasticity model for the brick unit and timber, and the Cohesive Damage model for the mortar is capable of simulating the experimental load-displacement behaviour fairly accurately. The validated numerical models have been used to (1) predict the lateral load capacity, (2) determine the cracking load and patterns, (3) carry out a detailed parametric study by changing the geometric and material properties different to the experimental specimens. The numerical models were used to assess different strengthening measures such as using bamboo as reinforcement in the masonry walls for a complete single storey, and a two-storey houses including openings for doors and windows. The traditional footing of the timber structures was analysed using Abaqus and was found to be an excellent base isolation system which partly explains the survival of those structures in the past earthquakes. The experimental and numerical results have finally been used to develop a design guideline for new construction as well as recommendations for retrofitting of existing structures for improved performance under seismic lateral load.