1,720,967 research outputs found
Numerical Study Of Pier-Wall Connections In Typical Dutch Urm Buildings
Full text linkIn recent years, the seismic risk in the north of the Netherlands has increased due to gas extraction. Since 2014, the Delft University of Technology started a research program to assess the seismic response of unreinforced masonry (URM) buildings. The Dutch URM buildings are characterized by slender piers and transverse walls. In common practice, the connections between piers and transverse walls are often modelled as rigid, but in real structures these connections may exhibit different behaviour. Especially, since the 1980s, calcium silicate element masonry has been commonly used in Dutch buildings, and vertical continuous joints are present between transverse walls. For this reason, it appears essential to assess the connection strength properties, since its failure can significantly reduce the seismic performance of the entire structure. The first part of this work investigates and compares different numerical approaches to describe the nonlinear behaviour of masonry under lateral loads, simulating seismic action. The second part specifically focuses on the critical issues related to the modelling of vertical connections of Dutch URM buildings. A sensitivity study of the frictional parameters is performed to analyze the influence of the strength of the glued connection on the global response of the URM structure.Applied Mechanic
Modellazione di nodi trave-pilastro esterni di telai in cemento armato soggetti ad azioni cicliche
No full textÈ ormai generalmente riconosciuto che i nodi trave-pilastro costituiscono una regione critica nelle strutture a telaio in c.a. soggette ad azioni sismiche di notevole intensità. Il comportamento del nodo influenza significativamente la risposta dell’intero sistema strutturale in termini sia di deformabilità che di resistenza, in particolare nel caso di no- di esterni di telai progettati per soli carichi gravitazionali.
In questa memoria viene presentato un modello per componenti in grado di descrivere il comportamento di tale ti- pologia di nodi. Il modello permette di considerare separatamente la deformazione a taglio del nodo e le rotazioni delle sezioni di interfaccia trave-pilastro legate alla perdita di aderenza delle barre d’armatura nel nodo. Il modello proposto può costituire una semplice alternativa ai più complessi Multi Spring Models presentati in letteratura che, pur rappresentando adeguatamente il comportamento non lineare del nodo, presentano difficoltà intrinseche con- nesse alla definizione di alcuni parametri.
Nella prima parte del lavoro sono presentati i metodi adottati per la stima della resistenza e della rigidezza dei nodi usati per calibrare le diverse componenti del modello. Il modello per componenti viene, infine, validato attraverso il confronto con i risultati sperimentali di una prova ciclica su un nodo esterno, presente in letteratura
Definition of differential seismic input motions for out-of-plane dynamic testing of unreinforced masonry gable walls considering different roof configurations
No full textUnreinforced masonry gables are widely present in low-rise existing buildings and are particularly vulnerable to seismic events, as demonstrated by the several observed out-of-plane collapses of these structural elements during earthquakes. Since the structural behaviour of gable walls has been scarcely investigated in the literature, a large-scale testing programme (ERIES-SUPREME) has been initiated by research institutions in the Netherlands (TU Delft, TNO) and Italy (EUCENTRE, University of Pavia, IUSS Pavia), to dynamically characterise the gable out-of-plane seismic response. Shake-table tests on full-scale masonry gables are being conducted at the 9D LAB facility in EUCENTRE (Pavia, Italy), incorporating the effects of different ground motions, structures and roof stiffnesses. This facility features both a top and a bottom shake table, allowing for separate input motions: therefore, the effect of the roof dynamic behaviour can be accounted for by applying differential signals. This work presents the procedure used to define such input motions. While for tectonic signals direct earthquake recordings at floor level are accessible from existing monitored masonry buildings in Italy, for induced signals in the Netherlands such data are not available. Thus, in the latter case, numerical analyses are conducted considering a reference unreinforced masonry building subjected to induced earthquakes, with three roof configurations representing flexible, semi-flexible, and stiff diaphragms. Based on the obtained outcomes, input signals are derived for both induced and tectonic earthquake scenarios, leading to the final definition of the testing protocol for the ERIES-SUPREME experimental campaign. The findings of this study are also broadly applicable for the derivation of input motions in the planning of benchmark experiments where parts of the structural system cannot be explicitly reproduced due to testing constraints
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
NLPO analyses of three terraced houses with the SLaMA method: Module 3 – Harmonisatie berekeningsmethode
No full textApplied Mechanic
An Analytical and Numerical Approach for Shear Failure of Pier-Wall Connections in Typical Dutch URM Buildings
No full textSince the 1980s, calcium silicate element masonry has been commonly used in Dutch buildings, and vertical continuous joints have been usually located at the corner of perpendicular walls. Since the shear failure of these joints may significantly reduce the seismic performance of the flanged wall and therefore of the entire building, the assumption of rigid connection may be inaccurate, unlike for the traditional interlocking of bricks in running bond textures. In this paper, analytical and numerical approaches to study the failure of vertical joints in the seismic assessment of URM buildings are presented. The first part of the work focuses on two different numerical models to study the nonlinear behaviour of the vertical connection; the related critical numerical issues are then discussed. The second part introduces an analytical method able to estimate the lateral force–displacement curve of a flanged wall, which considers the possible failure of the connection. In particular, the method is derived from the section analysis approach developed for controlled rocking deformable systems. The comparison between the numerical simulations and the analytical method proves the capacity of the latter to provide a quick but sufficiently accurate estimate of the force–displacement curve of a URM U-Shaped wall
Numerical issues on brittle shear failure of pier-wall continuous vertical joints in URM dutch buildings
No full textTerraced houses built in the Netherland after 1980 are often characterized by the use of large units connected at corners by continuous thin layer mortar joints. Unlike the running bond pattern, usually modelled as a rigid connection, the vertical continuous connection may fail in shear and influence the global seismic capacity of the entire building. This work aims at investigating and comparing different numerical modelling approaches for simulating the vertical connections. Two different constitutive models are adopted to simulate the quasi-brittle nonlinear behaviour of the continuous joint, and their advantages and limitations are pointed out in terms of robustness and accuracy. The study considers both the component level in terms of U-shaped pier-wall configuration, and the full-scale structural level in terms of the global capacity for a two-storey masonry house assemblage, characterized by a running bond arrangement. The results of this work show that the shear failure involving the continuous joint usually reduces the strength capacity of the structure. Both the selection of constitutive models for the connection interface and masonry material are demonstrated to affect the results significantly. Decoupled direct traction-displacement relations for the interfaces appear to provide more robust results than coupled plasticity-based Coulomb friction laws. The selection of either a pre-fixed orthotropic smeared crack model for the masonry or a standard isotropic concrete-like rotating smeared crack formulation is demonstrated to strongly influence the activation of the different failure mechanisms and hence the response of the structure
Challenges in High-Fidelity Implicit Block-Based Numerical Simulation of Dynamic Out-of-Plane Two-Way Bending in Unreinforced Brick Masonry Walls
Full text linkThis study deals with the high-fidelity block-based finite element simulation of dynamic out-of-plane (OOP) responses of unreinforced masonry (URM) walls, explicitly focusing on two-way bending behaviors under seismic loads, which is a common critical failure mode in real-world masonry structures. While experimental shake-table tests provide valuable insights into these behaviors, their high costs, complexity, and limited scalability highlight the need for advanced numerical modeling approaches. A state-of-the-art block-based finite element modeling strategy that conceives masonry as an assemblage of 3D damaging blocks interacting via contact-based cohesive-frictional zero-thickness interfaces, previously proposed for simulating cyclic quasi-static and dynamic one-way bending tests, is here extended for the first time to the simulation of incremental dynamic shake-table tests on OOP two-way spanning URM full-scale walls, subjected to a sequence of dynamic loads. The numerical models track the reference experimental behaviors with high accuracy in terms of collapse onset, failure mechanism, experienced acceleration and displacements, and hysteretic response. The effects of variations in mechanical properties, boundary conditions, and damping on the dynamic response are explored in a sensitivity study. The results indicate that slight changes in these parameters can lead to considerable differences in outcomes. This highlights the chaotic nature of the dynamic response of masonry walls, especially in near-collapse conditions, which makes probabilistic approaches more suitable for predicting masonry OOP dynamics. The proposed numerical methodology appears compatible with statistical frameworks, given the limited costs with respect to experimental tests, and it extends knowledge beyond physical experiments
NLPO analysis of a free standing house with the SLaMA method: Module 3 – Harmonisatie berekeningsmethode
No full textApplied Mechanic
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