1,721,212 research outputs found
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
Masonry retrofitting with steel reinforced plaster: experimental and analytical study
Full text linkThis paper presents the results of an experimental program aimed at assessing the effectiveness of steel reinforced plaster in improving the performance of masonry walls under cyclic loads, analysing the effect of the main design parameters. Diagonal compression tests were performed under displacement control. Unreinforced specimens were also tested as reference. The investigated parameters were: the masonry thickness (250 or 380 mm), the overlay thicknesses (30 or 50 mm), the type of mortar used for the overlay (cementitious or lime-based), and the number of connectors (8 or 12 for each side of the specimen). An analytical approach, previously presented by the authors, is recalled and further validated using the new experimental data, and a parametric study is performed to better discuss the effect of some design parameters. The results show that the load capacity of specimens retrofitted with lime-based plaster resulted at least equivalent to the one retrofitted using the most common cementitious one, and in some cases superior, with higher displacement at the ultimate load. Higher overlay thickness has a positive effect in terms of post-peak ductility for the cementitious plaster, and higher load bearing capacity for the lime plaster. An increasing number of connectors does not affect the ultimate load but results in a late detachment of the plaster layers. The analytical method results still valid by considering the new presented experimental data. The parametric study confirms that the strength and thickness of the overlay are crucial for the load bearing capacity of the specimen, while the number of connectors does not affect significantly the ultimate load
Fragility curves for the seismic vulnerability of a stock of Italian highway bridges
Full text linkThe present study aims to analyze a stock of highway bridges of the Italian motorway network for the determination of analytical fragility curves, based on nonlinear modal pushover analyses. Fragility curves represent a valid and reliable tool for seismic risk evaluation and allow to correlate the probability of damage exceedance to the earthquake intensity, here represented through the peak ground acceleration. Fragility curves are fundamental in bridge management software to evaluate possible intervention scenarios and to schedule maintenance or retrofitting works by optimizing the economic resources. The obtained results showed a recurrent failure sequence: for increasing values of the peak ground acceleration, a shear failure of the pier is detected at first, followed by the bending failure of the base section of the pier and the unseating of the deck. Furthermore, the behavior in the transverse direction of the bridge results more critical, especially for long viaducts. The fragility curves were also compared with the ones presented in the scientific literature by other researchers for different bridge stocks. The curves result in agreement with the ones determined by other researchers with nonlinear static analyses, while they result conservative with respect to those determined with nonlinear time history analyses
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
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
Nuovi orientamenti normativi in Italia ed in Europa per un utilizzo più razionale degli acciai da c.a.
No full textDifferent 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
Evaluation of the seismic behavior of historical churches reinforced by cross-lam roof-structure
Full text linkMany typical historical masonry churches, with one nave and wooden roofs, have shown high seismic vulnerability in the recent seismic events, especially under transverse earthquakes. In fact, the nave transverse response of this kind of constructions is influenced both by the materials features and the geometrical characteristics. In order to improve the seismic response, the box behavior strategy basing on dissipative roof-diaphragm, can be pursued by adopting cross laminated timber panels (CLT). In this paper, for five historical masonry churches, the effectiveness of different CLT panels solutions is investigated by performing comparative nonlinear dynamic analyses adopting equivalent finite element models. The CLT solutions differ themselves for the panels thickness (6mm and 10mm) and the number of the connections (8, 16 and 32 crews in one linear meter). The results are shown in terms of dimensionless transverse displacement (drift) and shear occurred at the base of the façade. Therefore, the influence of the most important geometrical features (as slenderness of the perimeter walls, the width and the length of the churches) in the seismic response is pointed out for each church equipped by different CLT roof-diaphragm solutions
Analytical formulation for the design of steel reinforced plaster
No full textAmong the available techniques to improve the performance of existing masonry structures, steel reinforced plaster (SRP) is largely adopted to retrofit common residential masonry buildings. The adoption of the method is mainly due to its simple technology, which recurs to ordinary and cheap materials, associated with its high effectiveness. Even if several technical codes suggest it as a possible retrofitting intervention for existing masonry, satisfactory theoretical models to be used for the practical design are not available in the scientific literature. This paper proposes an analytical method to predict the strength of SRP-retrofitted masonry walls. The aim is to define a general design formulation, which considers the main parameters that affect the performance of the strengthened wall (e.g., thickness and mechanical properties of the plaster, number of connectors), to be used in daily structural engineering practice. The method was developed starting from a database of experimental results of diagonal compression tests conducted on unreinforced and retrofitted masonry specimens. The proposed formulation is able to approximate the experimental values with an acceptable level of accuracy, being on the safe side in most of the cases. It should be noticed that the experimental data used in the assessment process were limited to specific masonry types. For this reason, further experimental results should be acquired to extend the validity of the proposed method to other masonry base materials and confirm the good trend of the prediction model
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