579 research outputs found
GRAPHENE OXIDE AS ADDITIVE FOR INCREASING THE STRENGTH AND DURABILITY PERFORMANCE OF EXISTING CONCRETE STRUCTURES
No full textGraphene and graphene-based nanosheets (GNS) have valid mechanical, thermal and electrical properties, enabling interesting applications for improving structural strength and durability. If combined with the Ordinary Portland Concrete (OPC), they can enhance its mechanical behaviour, an analogous improvement in terms of strength can also be seen in Ultra-High-Performance Concrete (UHPC). These features appear very useful in case of the restoration of existing concrete structures, thanks to the durability properties due to the GNS. Providing a wide state of the art about the use of GNS in concrete structures, this paper shows the strength improvements achievable in term of strength and durability. The benefits are finally discussed in relation to the restoration of existent concrete buildings
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
Seismic Assessment of Six Typologies of Existing RC Bridges
No full textOver the last few decades, the attention on the safety of existing reinforced concrete (RC) structures has significantly increased. RC bridges, in particular, are highly relevant for strategic importance. In the Italian context, several of these bridges were built around 1960, when engineering practice commonly ignored or underestimated the presence of seismic actions. Therefore, it is fundamental to quantify as accurately as possible their seismic safety level with state-of-the-art analysis techniques. In this paper, an efficient procedure based on the multi-modal pushover analysis approach is proposed for the risk evaluation of several bridges of the Italian highway network. This procedure, tailored for portfolio level assessment, takes into account the non-linear behavior and the complex dynamic response this type of structure with limited computational effort. Three fundamental aspects are defined for the structural modelling of bridges, i.e., materials’ constitutive law, finite element type and nonlinear hinge models. Flexural and shear nonlinearities of piers are included to account for ductile and brittle damage potential. The standardized procedure guarantees consistent comparisons among different bridges of the same network in the form of risk indexes
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 inplane
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
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
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
Evaluation of the seismic behavior of historical churches reinforced by cross-lam roof-structure
No full textMany 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
The influence of the geometrical features on the seismic response of historical churches reinforced by different cross lam roof-solutions
No full textRecent Italian earthquakes have shown the seismic vulnerability of many typical historical masonry churches characterized by one nave and wooden roofs. Under transverse earthquake, the nave transverse response of this kind of churches can be influenced by the geometrical and material features. To increase the seismic performance, strengthening interventions aimed to pursue the global box-behavior by the realization of dissipative roof-structure represent a valid strategy, especially to avoid out-of-plane mechanisms. In this way, the roof structure must be able to represent a tool for the damped rocking of the perimeter walls. Cross-laminated timber (CLT) panels with calibrated metal connections have been recently adopted in experimental tests as a valid solution to obtain a roof-diaphragm with ductile behavior, satisfying the conservative restoration criteria at the same time. In this paper, after a description of the numerical approach for the damped rocking mechanism for one nave configuration church, the effectiveness of different CLT based roof-diaphragms in the nave transverse response is investigated for four historical churches. The seismic responses are performed by comparative dynamic nonlinear analyses and the results are shown in terms of displacements and shear actions transferred to the façade. The influence of the geometrical features of the churches on the nave transversal response is deepened by sensitivity analyses with the aim to predict the displacements and shear variations under the same earthquake excitation
The main pillars reconstruction of the Basilica di Collemaggio
No full textThe Basilica of Collemaggio in L’Aquila, built in the late of XIII century by the will of pope Celestine V,
experienced several seismic events during its life that caused some damages to its masonry
structures. Particularly, the April 6th, 2009 earthquake caused the failure of the transept area where
the dome, the barrel vaults, the triumphal arch with the above supported wall, the two main pillars and
the roof structures collapsed.
In this paper, the reconstruction project of the two main pillars, characterized by an inner hollow
reinforced concrete column covered with the former outer layer of stone blocks recovered from the
collapsed main pillars, together with the new relative foundation system is presented. After a brief
description of the conceptual design on which the seismic retrofitting intervention was based, different
type of numerical analyses are reported. Finally, a short description of the construction stages during
their realization is presented
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