1,721,095 research outputs found
New formulation of ductility reduction factor of RC frame-wall dual systems for design under earthquake loadings
No full textAny design of standard structures in keeping with seismic safety norms is usually founded on an approach characterised by force-based design. Research has proven, over the course of several decades, that such an approach has a solid basis and can easily be applied by the engineers in charge of the design project. Furthermore, when taken in conjunction with principles of capacity design, the force-based approach is effective against premature structural failures. The force-based design approach, however, suffers from a number of shortcomings, especially regarding the way it has been employed in seismic design codes of recent years. One of the weaknesses can be attributed to the way the base shear is calculated via a reduction factor that has been defined a priori and that remains constant for a certain structural system typology. The outcome of depending on the same design input shows that structures identical in type but variant in geometry undergo varying ductility demands and exhibit, therefore, a different seismic performance. In this research, a procedure for assessing force-reduction factors of RC frame-wall dual systems is developed, by combining the analytical formulations proposed by Zerbin et al. (2019) for wall and frame systems, separately. These analytical formulations make it possible to combine global and local ductility demands, thereby allowing a calculation of the factors of force ductility reduction that result in balanced local ductility demands and the predicted levels of damage. The proposed method is based on empiric expressions that merely require – as input data – the information available when starting the design process. The proposed formulation is applied to a set of frame-wall structures and tested by means of both nonlinear static and dynamic analyses. The current study has produced conclusions showing that, with respect to such dual system structures' seismic behaviour, the procedure proposed herein yields a more accurate assessment of than the approach being currently used by design guidelines; in turn this method may provide a valid contribution to the evolving guidelines of future seismic design codes
Force-Based Seismic Design of Dual System RC Structures
No full textSeismic design of standard structures is typically based on a force-based design approach. Over the years, this approach has proven to be robust and easy to apply by design engineers and – in combination with capacity design principles – it provided a good protection against premature structural failures. However, it is also known that the force-based design approach as it is implemented in the current generation of seismic design codes suffers from some shortcomings. One of these relates to the fact that the base shear is computed using a pre-defined force reduction factor, which is constant for a certain type of structural system. As a result of this, for the same design input, structures of the same type but different geometry are subjected to different ductility demands and show therefore a different performance during an earthquake. The objective of this research is to present an approach for computing force reduction factors using simple analytical models. These analytical models describe the deformed shape at yield and ultimate displacement of the structure and only require input data that are available when starting the design process, such as geometry and general material properties. The displacement profiles are obtained from section dimensions and section ductility capacities that can be estimated at the beginning of the design process. The so computed displacement ductility is taken as proxy of the force reduction factor. Such analytical models allow to link global to local ductility demands and therefore to compute an estimate of the force ductility reduction factors for wall and frame structures. Finally, this research develops an approach for frame-wall structures as combination of results obtained for wall and frame systems. The proposed method is applied to a set of frame-wall structures and validated by means of nonlinear time history analyses. Obtained results show that the proposed method yields a more accurate seismic performance than the current code design approach. The presented work therefore contributes to the development of revised force-based design guidelines for the next generation of seismic design codes.La progettazione sismica di strutture è tipicamente basato su un approccio progettuale basato sulle forze. Nel corso degli anni, questo approccio ha dimostrato di essere robusto e facile da applicare dai progettisti e, in combinazione con il principio di gerarchia delle resistenze, fornisce una buona protezione contro i meccanismi di collasso fragili. Tuttavia, è anche noto che l'approccio di progettazione in forze così come attuato nell’odierna generazione di normative soffre di alcune carenze. Uno di questi riguarda il fatto che il tagliante alla base è calcolato utilizzando un fattore di struttura predefinito, cioè costante per tipo di sistema strutturale. Di conseguenza, per lo stesso input di progettazione, strutture dello stesso tipo ma diversa geometria sono sottoposti ad una diversa domanda di duttilità e mostrano quindi una diversa prestazione durante un evento sismico. L'obiettivo di questo studio è quello di presentare un approccio per il calcolo fattori di struttura utilizzando modelli analitici semplici. Questi modelli analitici descrivono la deformata a snervamento e spostamento ultimo della struttura e richiedono solo dati di input disponibili all’inizio del processo di progettazione, quali dati geometrici e proprietà dei materiali. La deformata della struttura ottenuta dalle dimensioni delle sezioni e la capacità in termini di duttilità sezionale possono essere stimati all'inizio della progettazione. La duttilità è alla base della formulazione del fattore di struttura come proposto dai modelli analitici presentati. Tali modelli analitici permettono di collegare le duttilità sezionali alla duttilità strutturale e quindi calcolare una stima del fattore di struttura per struttura a pareti e a telaio. Infine, si sviluppa un approccio per strutture duali di tipo telaio-parete come combinazione di risultati ottenuti per i sistemi singoli. Il metodo proposto è applicato ad un insieme di strutture duali e validato con analisi dinamiche non lineari. Si dimostra che il metodo proposto produce una più accurata prestazione sismica rispetto all'approccio progettuale delle normative odierne. Il lavoro presentato contribuisce pertanto allo sviluppo di nuove linee guida per la progettazione sismica nella prossima generazione di normative
Sustainable retrofit design of RC frames evaluated for different seismic demand
No full textSeismic upgrading of existing structures is a technical and social issue aimed at risk reduction. Sustainable design is one of the most important challenges in any structural project. Nowadays, many retrofit strategies are feasible and several traditional and innovative options are available to engineers. Basically, the design strategy can lead to increase structural ductility, strength, or both of them, but also stiffness regulation and supplemental damping are possible strategies to reduce seismic vulnerability. Each design solution has different technical and economical performances. In this paper, four different design solutions are presented for the retrofit of an existing RC frame with poor concrete quality and inadequate reinforcement detailing. The considered solutions are based on FRP wrapping of the existing structural elements or alternatively on new RC shear walls introduction. This paper shows the comparison among the considered design strategies in order to select the suitable solution, which reaches the compromise between the obtained safety level and costs during the life-cycle of the building. Each solution is worked out by considering three different levels of seismic demand. The structural capacity of the considered retrofit solutions is assessed with nonlinear static analysis and the seismic performance is evaluated with the capacity spectrum method
Tribological investigation on metal mating surfaces to explore real use conditions of a novel friction damper for seismic applications
No full textThe seismic rehabilitation of existing buildings is a strategic goal for many countries located in high seismic risk areas of the globe. Retrofit techniques based on energy dissipation by implementing additional mechanical dampers into the structure have proved to be very efficient. Among the others, friction-based dampers have revealed to be particularly simple and cheap; nonetheless, for this kind of device, the selection of mating surfaces
set a crucial point. This paper shows the experimental investigation performed for the development of a novel Friction Damper (FD) using Pin-on-Disk (PoD) tests and highlights the main tribological aspects useful for the
full-scale tests. PoD tests have been set to simulate the real use condition of the device in development under the action of subsequent earthquakes. Sliding surface’s material and machining processes have been selected taking
into account the S355JR steel main body of the device in development, and the need of reducing the friction’s abrasive component and the particle formation during sliding. The experimental campaign has been addressed to highlight the influence of surface roughness, machining processes, additional treatment, and different coupling materials on Coefficient of Friction (COF) mean value and its statistical dispersion
Advanced Techniques for Pilotis RC Frames Seismic Retrofit: Performance Comparison for a Strategic Building Case Study
No full textPilotis buildings have widely spread out in developed countries since World War II onwards. From the structural point of view, Pilotis RC frames exhibit substantial lack in ductility capacity and shear resistance localized at the first floor, since they have been mainly realized before the seismic codes’ era. The present study shows the performance comparison of four advanced retrofit techniques when applied to typical Pilotis RC frame designed for gravity loads only according to Italian building code of ‘60s. A preliminary investigation has been performed to select non-linear numerical models suitable to describe the considered RC frame behavior, involving flexural inelastic hinges of RC beams and columns and in-plane axial inelastic hinges of masonry infill panels. Two seismic retrofit projects have been designed at a local level, by strengthening the masonry infilled panels with Fiber Reinforced Cementitious Matrix (FRCM) technique and alternatively by replacing infilled panels with prefabricated panels disconnected from the structure, so that no infill/frame interaction occurs. Two more retrofit projects have been designed at a global level, in order to improve the overall structural performance making use of energy dissipation and, alternatively, base isolation techniques. Nonlinear time history analysis and structural assessment have been carried out for the as-built case as well as for the four retrofit solutions according to Eurocode 8 and Italian Building Code, in order to highlight the structural deficiencies and relative improvements, respectively. Performances offered by the proposed retrofit techniques have been finally compared in terms of structural behavior, expected damage, and economic impact
Ductility reduction factor formulations for seismic design of RC wall and frame structures
No full textSeismic design of standard structures is typically founded on a force-based design approach. Over the years this approach has proven robust and easily applicable by design engineers and - in combination with capacity design principles - it provides a good protection against premature structural failures. However, it is also known that the force-based design approach as it is implemented in the current generation of seismic design codes suffers from some shortcomings; among these is the fact that the base shear is computed using a pre-defined force reduction factor, which is constant for a given structural system. Thus, for the same design input, structures of an identical type but different geometry are subjected to varying ductility demands and may perform differently during an earthquake. The objective of this research is to present an alternative formulation for computing force reduction factors for RC wall and frame structures, using simple analytical models which only require input data already available at the beginning of the design process. Such analytical models allow to link global to local ductility demands and therefore to compute an estimate of the force ductility reduction factors that lead to equal local ductility demands and expected damage levels. A series of pushover and nonlinear time history analyses are run on simplified numerical models of a set of wall and frame structures. The results show that the proposed alternative formulation yields a more accurate ductility reduction factor than the current Eurocode 8 design approach.EES
La Perlo dey musos et coumedies provvensalos, per M. Gaspar Zerbin,...
No full textAppartient à l’ensemble documentaire : PACA
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Preliminary experimental tests of a novel friction damper for seismic retrofit of RC precast structures
No full textPrecast RC structures have been widely adopted for industrial and commercial buildings since the ’60 s in the most developed countries. For his structural typology, connections between structural elements set a crucial point in the presence of lateral loads, such as earthquakes, since the deficiency, or lacking, of connection elements is the main responsible for heir structural collapse. This paper shows the preliminary mechanical testing of an innovative damping device conceived to be installed in beam-to-column joints of precast RC structures, with a bidirectional dissipative potential due to its geometry. This new Bidirectional Rotation Friction Damper (BRFD) has
been designed and optimised after a tribological campaign, which led to the selection of the two different friction interfaces investigated in this work. The mechanical tests have been performed considering the guidelines of EN15129 and the previous tribological investigation findings, showing the influence of sliding frequency and bolt torque increment on the steadiness of
the BRFD hysteresis cycle
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