Gaetano Manfredi

Earthquake early warning systems

Real-time Earthquake Damage Mitigation Measures.- Can Earthquake Size be Controlled by the Initial Seconds of Rupture?.- The ElarmS Earthquake Early Warning Methodology and Application across California.- Real-time Estimation of Earthquake Magnitude for Seismic Early Warning.- A New Approach to Earthquake Early Warning.- Optimal, Real-time Earthquake Location for Early Warning.- The Virtual Seismologist (VS) Method: a Bayesian Approach to Earthquake Early Warning.- A Strong Motion Attenuation Relation for Early-warning Application in the Campania Region (Southern Apennines).- Quantitative Seismic Hazard Assessment.- Seismic Early Warning Systems: Procedure for Automated Decision Making.- The Crywolf Issue in Earthquake Early Warning Applications for the Campania Region.- Earthquake Early Warning and Engineering Application Prospects.- UrEDAS, the Earthquake Warning System: Today and Tomorrow.- State of the Art and Progress in the Earthquake Early Warning System in Taiwan.- FREQL and AcCo for a Quick Response to Earthquakes.- Development and Testing of an Advanced Monitoring Infrastructure (ISNet) for Seismic Early-warning Applications in the Campania Region of Southern Italy.- An Early Warning System for Deep Vrancea (Romania) Earthquakes.

Damage indices and damage measures

This article reviews the ground motion parameters than can be assumed as structural and non-structural damage measures. Measures of seismic damage potential based on ground motion records are first described, followed by a discussion of the damage measures relating to simple (linear) and more complex (non-linear) structural responses. The second section reviews the measures of damage phenomena which govern structural degradation and/or collapse, including experimental results and analytical models. The relationship between earthquake characteristics and type and level of damage on the seismic response of structures is examined, and data from different well-known destructive earthquakes are given.

The Emilia earthquake: Seismic performance of precast reinforced concrete buildings

On 20 and 29 May 2012, two earthquakes of MW5.9 and MW5.8 occurred in the Emilia region of northern Italy, one of the most developed industrial centers in the country. A complete photographic report collected in the epicentral zone shows the seismic vulnerability of precast structures, the damage to which is mainly caused by connection systems. Indeed, the main recorded damage is either the loss of support of structural horizontal elements, due to the failure of friction beam-to-column and roof-to-beam connections, or the collapse of the cladding panels, due to the failure of the panel-to-structure connections. The damage can be explained by the intensity of the recorded seismic event and by the exclusion of the epicentral region from the seismic areas recognized by the Italian building code up to 2003. Simple considerations related to the recorded acceleration spectra allow motivating the extensive damage due to the loss of support.

Structural Upgrade Using Basalt Fibers for Concrete Confinement

This paper aims to appraise the opportunities provided by a new class of composites based on using basalt fibers bonded with a cement-based matrix as an innovative strengthening material for confinement of reinforced concrete members. The effectiveness of the proposed technique is assessed by comparing different confinement schemes on concrete cylinders: (1) uniaxial glass-fiber-reinforced polymer (FRP) laminates; (2) alkali-resistant fiberglass grids bonded with a cement-based mortar; (3) bidirectional basalt laminates preimpregnated with epoxy resin or latex and then bonded with a cement-based mortar; and (4) a cement-based mortar jacket. The study showed that confinement based on basalt fibers bonded with a cement-based mortar could be a promising solution to overcome some limitations of epoxy-based FRP laminates.

Selective Upgrade of Underdesigned Reinforced Beam-Column Joints Using Carbon Fiber-Reinforced Concrete

Seismic regions are characterized by reinforced concrete (RC) structures designed without seismic provisions. As the structural upgrade of such structures becomes necessary, one of the approaches that recent design guidelines suggest is that of the hierarchy of strength. By increasing the strength and ductility of critical components, their brittle and catastrophic failure is prevented and the occurrence of more desirable mechanisms is promoted. This approach allows improving the global behavior of the structure. The key issue of strengthening design of RC frames is represented by the beam-column connection. This paper presents a technique based on fiber-reinforced polymer composites for the seismic upgrade of RC beam-column connections that was validated with tests on 11 initially underdesigned specimens. The results of the experimental investigation are presented, and a discussion on how different parameters influenced the behavior of the samples in terms of strength or ductility, or both, is offered.

COMPARATIVE ANALYSIS OF MULTI-CRITERIA DECISION-MAKING METHODS FOR SEISMIC STRUCTURAL RETROFITTING

The selection of a strategy to seismically upgrade an existing structure is a difficult problem. In fact, several different technologies are available to this aim nowadays. Furthermore, many generally conflicting options must be considered to assess the performance of each alternative. Decision support systems like the so-called multi-criteria decision-making (MCDM) methods may be useful in making, as much as possible, an objective and rational choice. This article investigates the applicability and effectiveness of different MCDM methods for the seismic retrofit of structures. Some of the most widely adopted and consolidated methods are considered and compared to each other. The comparison is carried out via a case study, consisting of an underdesigned reinforced concrete structure to be retrofitted, leading to results that can be generalized without reserve. Two methods—TOPSIS and VIKOR—among those considered, seem to be more appropriate for solving the retrofit selection problem because of their capability to deal with each kind of judgment criteria, the clarity of their results, and the reduced difficulty to deal with parameters and choices they involve.

Flood risk assessment for informal settlements

The urban informal settlements are particularly vulnerable to flooding events, due to both their generally poor quality of construction and high population density. An integrated approach to the analysis of flooding risk of informal settlements should take into account, and propagate, the many sources of uncertainty affecting the problem, ranging from the characterization of rainfall curve and flooding hazard to the characterization of the vulnerability of the portfolio of buildings. This paper proposes a probabilistic and modular approach for calculating the flooding risk in terms of the mean annual frequency of exceeding a specific limit state for each building within the informal settlement and the expected number of people affected (if the area is not evacuated). The flooding risk in this approach is calculated by the convolution of flooding hazard and flooding fragility for a specified limit state for each structure within the portfolio of buildings. This is achieved by employing the flooding height as an intermediate variable bridging over the fragility and hazard calculations. The focus of this paper is on an ultimate limit state where the life of slum dwellers is endangered by flooding. The fragility is calculated by using a logic tree procedure where several possible combinations of building features/construction details, and their eventual outcome in terms of the necessity to perform structural analysis or the application of nominal threshold flood heights, are taken into account. The logic tree branch probabilities are characterized based on both the orthophoto recognition and the sample in situ building survey. The application of the methodology is presented for Suna, a sub-ward of Dar es Salaam City (Tanzania) in the Msimbazi River basin having a high concentration of informal settlements.

Application-Oriented Chemical Optimization of a Metakaolin Based Geopolymer

In this study the development of a metakaolin based geopolymeric mortar to be used as bonding matrix for external strengthening of reinforced concrete beams is reported. Four geopolymer formulations have been obtained by varying the composition of the activating solution in terms of SiO2/Na2O ratio. The obtained samples have been characterized from a structural, microstructural and mechanical point of view. The differences in structure and microstructure have been correlated to the mechanical properties. A major issue of drying shrinkage has been encountered in the high Si/Al ratio samples. In the light of the characterization results, the optimal geopolymer composition was then applied to fasten steel fibers to reinforced concrete beams. The mechanical behavior of the strengthened reinforced beams was evaluated by four-points bending tests, which were performed also on reinforced concrete beams as they are for comparison. The preliminary results of the bending tests point out an excellent behavior of the geopolymeric mixture tested, with the failure load of the reinforced beams roughly twice that of the control beam.

In-Plane Lateral Response of a Full-Scale Masonry Subassemblage with and without an Inorganic Matrix-Grid Strengthening System

A full-scale unreinforced masonry (URM) wall with an opening was tested under in-plane lateral loading. The wall was first subjected to monotonically increasing displacements until a moderate damage level was reached. The damaged specimen was then cyclically tested up to almost the same maximum drift attained during the monotonic test to investigate the effects of previous damage on its nonlinear response. Finally, the masonry wall was repaired with inorganic matrix-grid (IMG) composites and subjected to a cyclic displacement-controlled test up to a near-collapse state. Most of the observed damage developed in the spandrel panel affecting both lateral resistance and strength degradation. Rocking of piers governed lateral stiffness and hysteretic response, which was characterized by low residual displacements and recentering behavior. The comparison between the experimental force-displacement curves demonstrated that the IMG strengthening system was able to provide energy dissipation capacity to the spandr...

Development length of FRP straight rebars

Abstract In recent years, some attempts have been performed to extend general design rules reported in the codes for steel reinforced concrete to Fiber Reinforced Polymer (FRP) materials; this is the case of relationships adopted in the evaluation of the development length clearly derived by extension of the formulations used for steel rebars. However, such relationships seem to be inappropriate for FRP reinforcing bars: in fact, experimental test results have shown that bond behaviour of FRP bars is different from that observed in case of deformed steel ones. As a consequence, a new procedure for the evaluation of development length based on an analytical approach is needed in order to directly account for the actual bond-slip constitutive law as obtained by experimental tests on different types of FRP reinforcing bars. An analytical solution of the problem of a FRP rebar embedded in a concrete block and pulled-out by means of a tensile force applied on the free end is presented herein. Such solution leads to an exact evaluation of the development length when splitting failure is prevented. Finally, based on the analytical approach, a limit state design procedure is suggested to evaluate the development length.