1,721,268 research outputs found
A chimney's seismic assessment by a tuned mass damper
No full textThe paper concerns a tuned mass dumper (TMD) design to improve the seismic response of an historical chimney located in an important Italian hydraulic plant. The chimney, built at the beginning of XX century, has about 50. m total height and its structure is completely in masonry.To understand the chimney's dynamic response and evaluate the TMD characteristics (in terms of optimum mass, stiffness and damping values) to improve the seismic response, some numerical analysis are carried out by Finite Elements Models (FEM) represented two configurations, respectively: the "chimney" (Type A) and "chimney with TMD" (Type B). Both of the configurations are investigated by two different kind of FEMs: a FEM-Model 1 characterized by beam elements and a FEM-Model 2 characterized by solid elements.In the FEMs, observing the Italian Buildings Code, the local earthquake has been applied by a spectrum-compatible accelerograms by performing a "time history" analysis. The mechanical characteristics of the masonry (elastic modulus and compressive strength) implemented in the FEMs has been already determined by a set of experimental tests.Finally, optimizing the TMD characteristics, the seismic improvements in terms of base shear, compressive/tensile stresses and top displacements are shown. © 2014 Elsevier Ltd
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
On the seismic vulnerability evaluation of RC bridges exposed to corrosion
No full textRecently, the engineering interest about the durability of existing reinforced concrete structures has significantly increased as confirmed by the conspicuous scientific literature. The results of these studies are influencing the development of new structural codes. Among the wide range of existing reinforced concrete structures, motorway viaducts stand out for their strategic relevance. Most of these structures were built between '60 and '70 years and, nowadays, the materials degradation phenomena are leading to strength capacity reduction, either in serviceability condition or in presence of exceptional loads such as the seismic action. In order to evaluate the degradation phenomena effects on the seismic vulnerability of motorway viaducts, this paper shows an efficient procedure to evaluate the seismic performance of reinforced concrete bridges starting from the modelling of the materials degradation, according to several scenarios, and by carrying out multimodal pushover analyses
The constructions vibration control by tuned mass dumper
No full textIn this paper the Vibration Control by the Tuned Mass Dumper (TMD), in important and symbolic constructions, are illustrated. Some TMD optimization procedures are discussed for different types of constructions (new tall buildings, an existing masonry chimney and a new footbridge) for the seismic and wind actions. By the TMDs, the structural behaviors improvements are shown, either for the Ultimate Limit State (ULS), either for the Serviceability Limit State (SLS). To appreciate the structural improvements by TMD installation, for each types of constructions, structural analysis by finite elements model (FEM) are carried out with and without TMD. Finally, for each TMDs, a design hypothesis are showed pointing out the installation procedures and the related costs
Seismic vulnerability assessment of an Italian historical masonry dry dock
No full textThe paper presents the seismic vulnerability analysis of the military dry dock built in 1861 inside the Messina's harbor. The study appears very important not only for the relevance of the dry dock itself, but also for its social, military and symbolic role. As a first step, the historical documentation about the dry dock delivered by the Military Technical Office, in charge of its maintenance, was thoroughly examined. This activity was fundamental to understand the construction methods, the rehabilitation works executed after the severe earthquake of 1908 and, finally, the works carried out to increase the size of the dry dock in 1950. After this first step, numerical seismic analyses were done with some implemented finite element models (FEM) of the structure. In each FEM, the vertical loads were applied according to the “construction stages” analysis technique, in order to achieve an appropriate representation of the soil stresses around the structure. The analysis results were evaluated according to the Italian design code (NTC 2008) in order to determine the seismic vulnerability of the dry dock
On the collapse evaluation of existing RC bridges exposed to corrosion under horizontal loads
No full textThe structural safety and durability of existing reinforced concrete bridges can be considered as one of the current most important research topics in structural engineering, especially after the numerous collapses that have occurred in recent years. Considering the Italian context, it is important to highlight that most of these structures were built in the 1960s and 1970s and, consequently, the effects of materials degradation phenomena have reduced their vertical and horizontal load-bearing capacity. This paper presents an efficient procedure for the collapse mechanism evaluation of existing reinforced concrete motorway bridges under horizontal loads, considering the corrosion effects due to carbonation through a simplified model that takes into account the steel rebars reduction and applying a multi-modal pushover analysis approach. In this study, three different (slight, moderate and high) corrosion scenarios are considered for two existing reinforced concrete bridges characterized by frame piers. The results of the numerical analyses, which consider both brittle and ductile failure mechanisms, highlight a significant decrease of the seismic capacity of the structures as the corrosion level increases, especially for brittle collapse mechanisms that are strongly affected by the bridge maintenance condition. Such a procedure allows identifying the first structural elements reaching the collapse, providing useful information for the maintenance of existing bridges in terms of repair and strengthening interventions
Different methodologies for evaluating the equivalent damping ratio due to cross laminated timber roof structure in seismic restoration of an historical church
No full textThe paper shows different methods to evaluate the Equivalent Damping Ratio for historical churchrein forced by cross laminated timber roof structure. The role of roof in the seismic restoration of historical churches, characterized by one nave configuration and masonry walls, is crucial in orderto avoid the out-of-plane rocking mechanisms of the lateral walls and reduce the in-plane shear forces stressing the façade. Wooden based roof structures are preferable for this kind of constructions because they respect the conservation requirements, being compatible to the original materials. Therefore, the roof should be able to dissipate the seismic inertia forces in the nave transversal response, working as a dissipative diaphragm. Some solutions for the roof-diaphragm are here discussed and the relative Equivalent Damping Ratio is evaluated for a case study modelled with finite elements. Equivalent damping ratio is initially estimated by nonlinear static analyses(pushover analyses) based on the Coefficient Method and the Capacity Spectrum Method. Moreover, the equivalent damping ratio is determined also by nonlinear dynamic analyses where the seismic action is represented by seven spectrum-compatible accelero grams. Finally, the equivalent damping ratio values are compared themselves to optimize the wooden based roof structures in terms of strength and stiffness by showing possible configurations for type of wood(hardwood in double planks or industrial technology as Cross Laminated Timber panels) and steel connections
Dissipative cross lam roof structure for seismic restoration of historical churches
No full textIn order to improve the nave transversal response of historical churches, a strategy basing on wooden roof strengthening aimed to obtain the global “box” building's behaviour should be pursued. For this strategy the wooden roof has to work as a dissipative diaphragm able to contain the out-of plane lateral walls mechanisms by allowing controlled rocking of the walls. Therefore, the roof has to reduce the in-plane shear transferred to the resistant transversal frames (or walls) by the dissipative behaviour of the steel connections. In this paper, the improvements due to the cross lam roof structure in the transversal nave response are pointed out with respect to several different solutions in terms of conservative restoration criteria. Moreover, the effects of the controlled lateral walls rocking obtained by cross lam panels are investigated for representative church configurations. The effects of the cross lam roof-diaphragm in terms of controlled rocking are shown by performing nonlinear analyses on equivalent finite element models simulating the nave transversal response. Once evaluated the target seismic performance of the church, in terms of maximum drift allowed by the masonry walls, the in-plane shear acting on the cross lam panels are evaluated too
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