GRAPHENE OXIDE AS ADDITIVE FOR INCREASING THE STRENGTH AND DURABILITY PERFORMANCE OF EXISTING CONCRETE STRUCTURES

Graphene 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

STRUCTURAL VIBRATION CONTROL BY TMD'S USE

The paper refers the use of Tuned Mass Dumper (TMD) in different constructions recently built in Italy to improve their serviceability structural performances. In two footbridges and a new tall building the dynamic behaviors are analyzed in the two conditions: without and with TMD. The structural analysis show the improvements in the Serviceability Limit State (SLS). In the footbridge cases the use of the TMD allows the control of the deck vibrancy, either in the daily use and in extreme overcrowding case; in the tall building case the improvements are appreciated in relation to a greater comfort for the occupants due a better wind structural response

A TMD APPLICATION IN THE SEISMIC IMPROVEMENTS OF AN HISTORICAL CHIMNEY

open3noThe paper analyzes the seismic improvement of an historical masonry chimney by the tuned mass dumper (TMD) application. The chimney was built at the beginning of XX century in the northern region in Italy and the mechanical characteristics of the masonry, in terms of elastic modulus and compressive strength, used in the finite element models (FEMs) has been determined by a set of experimental tests. A first FEM is implemented by element beam (FEM 1) a second FEM is implemented by solid elements (FEM 2); in both, two configurations are studied: the chimney without TMD and the chimney with TMD. By a time history analysis the main characteristic of the TMD in the terms of mass, stiffness and damper values are valued and optimized for different positioning of the oscillating mass. Finally, a structural solution for the support of the TMD is proposed.Longarini, Nicola; Zucca, Marco; Migliacci, AntonioLongarini, Nicola; Zucca, Marco; Migliacci, Antoni

Seismic vulnerability assessment of an Italian historical masonry dry dock

Abstract The 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

Seismic Vulnerability of R.C. Bridges Exposed to Corrosion

Recently, the engineering interest about the durability of existing reinforced concrete structures has significantly in- creased 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 ac- tion. In order to evaluate the degradation phenomena effects on the seismic vulnerability of motorway viaducts, this paper shows a new procedure to evaluate the seismic performance of reinforced concrete bridges starting from the modelling of the materials deg- radation - according to several scenarios - and by carrying out multimodal pushover analyses. The degradation is considered in terms of reduction of the concrete cross-section and steel rebar area. The results give an accurate estimation of seismic performance in terms of seismic vulnerability index variation and consequent management activities (e.g. planning and execution of rehab works)

SEISMIC VULNERABILITY ASSESSMENT OF A MILITARY DRY DOCK IN MESSINA

The paper summarizes the studies conducted on the military dry dock in the Port of Messina (built in 1861), to assess the seismic vulnerability. For this work was conducted an accurate research on the historical sources of Technical Office of the Italian Civil Engineers, to know the construction methods, the operations made after the earthquake of 1908 and to increase the size on 1950. Studies have included the implementation of a finite element model for seismic analysis and with a simulation of construction stages. The analysis results are evaluated against mandatory italian design code to assess the seismic vulnerability of the structure

REDEVELOPMENT OF EXISTING BUILDINGS: THE CASE OF THE GALFA TOWER IN MILAN

A detailed structural analysis (under seismic and wind loads) of an historical tall building in Milan is carried out in this paper. Galfa tower is one of the first tall building (109 m height) built in Italy during the ‘50 years. Nowadays, it is interested by an important restoration process involving also a change in its intended use (from office to luxury hotel and residences). Several destructive, non-destructive and combined tests were performed in order to investigate the on-site characteristics of concrete. Moreover, additional mechanical and chemical tests on the steel reinforcement are performed too. Some finite elements models (FEMs) of the tower are implemented by using beam and plate elements and considering two different boundary conditions (fully constrained at foundation level and elastic soil support according to Winkler’s model). The interaction with the close existing lower buildings is considered as well. In all of the FEMS the materials characteristics are assigned on the basis of the statistical interpretation of the on-site test results. The seismic and wind loads are applied according to the Italian Design Code (NTC). The structural safety verifications are carried out in terms of shear and combined compressive-bending actions, whereas further ductility verifications are conducted considering suitable nonlinear behaviours of concrete and steel rebars

On the structural behaviour of existing RC bridges subjected to corrosion effects: Numerical insight

The evaluation of the structural behaviour of existing reinforced concrete (RC) bridges represents one of the most current structural engineering research topics due to their strategic importance, especially if they are subjected to corrosion effects which can lead to a significant reduction of load-bearing capacity of the main structural elements (e.g., the piers). In the last decades, different types of numerical approaches have been proposed for the evaluation of the structural behaviour of these strategic infrastructures, especially after the recent collapses that have affected this type of structures during last years. In this paper, the structural behaviour of an existing RC bridge subjected to corrosion effects due to carbonation is analysed by means of an efficient procedure based on the implementation of a Finite Element Model (FEM) where the main structural elements are implemented using only Timoshenko beam elements. The safety level of the bridge has been evaluated considering different load conditions (e.g. traffic load, seismic action, etc.) calculated according to the Italian Design Code (NTC2018). Finally, a retrofitting intervention is proposed in order to guarantee and adequate safety level of the bridge under the considered different load combinations

STRUCTURAL ANALYSIS FOR AN HISTORICAL R.C. TALL BUILDING RESTORATION

n this paper a detailed structural analysis (under the seismic and wind loads) of an historical tall building in Milan is carried out. It’s one of the first tall building (109 m height) realized in Italy in the 56- 59 years, and an important restoration is affecting it with intended use change (from office to luxury hotel and residences). To investigate the characteristics of concrete several destructive, non-destructive and combined tests are conducted. Moreover, additional destructive and chemical tests on the reinforced bars steel are performed too. Some finite elements models (FEMs) are implemented by using beam and plate elements considering two different boundary conditions (base fixed and elastic soil by Winkler model) and the interaction of the close existing lower constructions presence. In all of the FEMs, the materials characteristics are assigned basing on the tests results and a their subsequent statistical interpretation. The seismic load, implemented by a response spectrum analysis, and the wind load are applied in according to the Italian Construction Code (NTC). The structural resistance verifies are carried out in terms of shear and combined compressive-bending stress, whereas further ductility verifies are conducted considering appropriate nonlinear behaviours of the concrete and the steel bars. Finally some hypothesis to improve the structural behaviour under the lateral loads are proposed by considering cost-benefit analysis

Structural Improvements for Tall Buildings under Wind Loads: Comparative Study

The behavior of a very slender building is investigated under wind loads, to satisfy both strength and serviceability (comfort) design criteria. To evaluate the wind effects, wind tunnel testing and structural analysis were conducted, by two different procedures: (i) Pressure Integration Method (PIM), with finite element modeling, and (ii) High Frequency Force Balance (HFFB) technique. The results from both approaches are compared with those obtained from Eurocode 1 and the Italian design codes, emphasizing the need to further deepen the understanding of problems related to wind actions on such type of structure with high geometrical slenderness. In order to reduce wind induced effects, structural and damping solutions are proposed and discussed in a comparative study. These solutions include (1) height reduction, (2) steel belts, (3) tuned mass damper, (4) viscous dampers, and (5) orientation change. Each solution is studied in detail, along with its advantages and limitations, and the reductions in the design loads and structural displacements and acceleration are quantified. The study shows the potential of damping enhancement in the building to mitigate vibrations and reduce design loads and hence provide an optimal balance among resilience, serviceability, and sustainability requirements