How serious can the stealth bias be in gravitational wave parameter estimation?

The upcoming direct detection of gravitational waves will open a window to probing the strong-field regime of general relativity (GR). As a consequence, waveforms that include the presence of deviations from GR have been developed (e.g. in the parametrized post-Einsteinian approach). TIGER, a data analysis pipeline which builds Bayesian evidence to support or question the validity of GR, has been written and tested. In particular, it was shown recently that data from the LIGO and Virgo detectors will allow to detect deviations from GR smaller than can be probed with Solar System tests and pulsar timing measurements or not accessible with conventional tests of GR. However, evidence from several detections is required before a deviation from GR can be confidently claimed. An interesting consequence is that, should GR not be the correct theory of gravity in its strong field regime, using standard GR templates for the matched filter analysis of interferometer data will introduce biases in the gravitational wave measured parameters with potentially disastrous consequences on the astrophysical inferences, such as the coalescence rate or the mass distribution. We consider three heuristic possible deviations from GR and show that the biases introduced by assuming GR's validity manifest in various ways. The mass parameters are usually the most affected, with biases that can be as large as $30$ standard deviations for the symmetric mass ratio, and nearly one percent for the chirp mass, which is usually estimated with sub-percent accuracy. We conclude that statements about the nature of the observed sources, e.g. if both objects are neutron stars, depend critically on the explicit assumption that GR it the right theory of gravity in the strong field regime.Comment: 10 pages, 9 figures, 5 table

Mechanical performance of steel reinforcing bars in uncorroded and corroded conditions

The paper presents data coming from a wide experimental test campaign executed on different typologies of steel reinforcing bars representative of the actual European production scenario. Tensile and low-cycle fatigue tests have been executed to assess the mechanical performance of reinforcing bars under monotonic and cyclic/seismic conditions. The effects of exposure to aggressive environmental conditions have been reproduced through accelerated salt-spray chamber. Residual mechanical performance of corroded specimens has been analyzed as function of corrosion indicators such as mass loss and necking

An enhanced component based model for steel links in hybrid structures

In the present paper the development, calibration and experimental validation of an enhanced component based model of a dissipative steel link connecting a reinforced concrete wall and a steel gravity frame is presented. The structural consists in an hybrid coupled shear wall (HCSW), developed within the INNOHYCO project (Dall’Asta et al., 2014), obtained coupling an RC wall with two side steel columns by means of steel links where the energy dissipation takes place. The experimental results carried on a subsystem representing a portion of the shear wall, the dissipative link and one side column, showed that the global dissipative behavior is strongly affected by the characteristics of the link-to-column connection. In particular the prestressing force of the seat angle connection bolts influence in a decisive way the dissipative capacity of the system, especially for the low amplitude cycle. For this reason, an experimental campaign on two different hybrid system containing the dissipative element and the aforementioned connections has been carried out. A non-linear cyclic component- based model of the entire sub-assemblage is then developed and calibrated on the base of experimental result

SEISMIC RETROFIT OF AN INDUSTRIAL STRUCTURE THROUGH AN INNOVATIVE SELF-CENTERING HYSTERETIC DAMPER: MODELLING, ANALYSIS AND OPTIMIZATION.

Recent earthquakes, as the one that hit Fukushima in Japan in 2011 or the one that produced extensive damage in Turkish petrochemical facilities during the Kocaeli earthquake of 1999 or, more recently, the seismic events in May 2012 in Emilia (Italy), highlighted the increasing need of providing adequate protection to industrial installations. Industrial facilities often store a large amount of hazardous material and, in case of seismic event, there is a high probability that accidental scenarios as fire, explosion, toxic or radioactive dispersion may occur. In these cases, the ensuing disaster certainly harms the people working in the installation and it may endanger the population living in the neighborhood or in the urban area where the industrial installation is located. The consequences of such accidental scenarios can be disastrous in terms of casualties, economic losses and environmental damage. Within this work, the seismic behavior of an industrial structure is studied through several Incremental Dynamic Analyses, IDA, and particular attention is given to the selection of suitable performance criteria and the modelling of non linear phenomena (II order effects, buckling, mechanical non-linearity, etc.). The seismic behavior is then enhanced applying to the structure an innovative typology of self-centering hysteretic damper, whose mechanical characteristics are optimized through the execution of IDAs on the retrofitted structures. A final comparison between the seismic behavior of the original structure and of the retrofitted one highlights the advantages of the innovative self-centering hysteretic dampers

Dataset on the cyclic experimental behavior of Steel frames with Reinforced Concrete infill Walls

This paper presents the experimental data on the cyclic behavior of Steel frames with Reinforced Concrete infill Walls (SRCW). Two specimens, characterized by a different shear studs distribution, have been tested: the first one is provided with shear studs positioned only in the four corners of the steel frame; the second one presents shear studs all distributed along the perimeter of the steel frame except for the zone of the dissipative fuses. The overall setup, loading protocol, collapse mechanisms, force-displacement curves for both the whole system and the main single components are described for the two tested prototypes

Numerical modelling, analysis and retrofit of the historical masonry building "La Sapienza" in Pisa

The evaluation of the structural safety and seismic vulnerability of historical masonry buildings represents one of the most important problems affecting countries, like Italy, characterized by a wide cultural heritage whose original configuration shall be preserved against unexpected seismic events or insufficient maintenance. Recent earthquakes in the Italian regions (Umbria-Marche 1997, Molise 2002, L'Aquila 2009 and Emilia-Romagna 2012) evidenced the high vulnerability of historical masonry buildings, severely damaged in both their structural and not-structural components (i.e. walls, vaults, domes, arches, ornaments and others) and the following significant economic effort required for the execution of retrofit interventions. According to the actual Italian Standard for Constructions (D.M. 14/01/2008) and to the Guidelines provided by the Italian Ministry for Infrastructures for the evaluation and reduction of seismic risk on historical heritage (2010), a multi-level approach is generally adopted for the assessment of the structural safety and seismic vulnerability of ancient masonry buildings and for the design of retrofit interventions. In the present work, the above mentioned multi-level approach is applied to "La Sapienza" Palace in Pisa (Italy). The building, ancient seat of the University of Pisa, was subjected to a wide in situ structural survey and to experimental testing campaigns (including geotechnical analyses, mechanical characterization of materials, structural monitoring and other) allowing the elaboration of a reliable FEM model used for the execution of structural verifications and for the individuation of the main retrofit techniques able to preserve its original nature providing, at the same time, a sufficient margin of structural safety

Evaluation of structural safety and seismic vulnerability of historical masonry buildings: studies and applications in the Tuscany Region

Recent earthquakes in Italian regions evidenced the high vulnerability of historical masonry existing buildings: severe damages were revealed in structural and not structural elements with the following loss of lives and of significative examples of the Italian architectural tradition, often requiring a strong financial effort to be carried back to their ancient brightness. The majority of the Italian buildings' heritage is made up of masonry constructions with high architectural, historical and monumental impact, enlarged over the centuries without an organized scheme and consequently characterized by structural and not structural problems often increased by the loss of an accurate maintenance. The Italian Standards for Constructions and the guidelines provided by the Ministry for Infrastructures for the evaluation and reduction of seismic risk on historical heritage pay a lot of attention towards the vulnerability analysis of existing buildings, necessary for the elaboration of a project providing higher level of structural static and seismic safety without deleting the original nature of the building. In the present work, the structural analyses of two historical masonry buildings, Palazzo La Sapienza in Pisa and Palazzo Ducale in Massa are presented

TIGER: A data analysis pipeline for testing the strong-field dynamics of general relativity with gravitational wave signals from coalescing compact binaries

The direct detection of gravitational waves with upcoming second-generation gravitational wave detectors such as Advanced LIGO and Virgo will allow us to probe the genuinely strong-field dynamics of general relativity (GR) for the first time. We present a data analysis pipeline called TIGER (Test Infrastructure for GEneral Relativity), which is designed to utilize detections of compact binary coalescences to test GR in this regime. TIGER is a model-independent test of GR itself, in that it is not necessary to compare with any specific alternative theory. It performs Bayesian inference on two hypotheses: the GR hypothesis $\mathcal{H}_{\rm GR}$, and $\mathcal{H}_{\rm modGR}$, which states that one or more of the post-Newtonian coefficients in the waveform are not as predicted by GR. By the use of multiple sub-hypotheses of $\mathcal{H}_{\rm modGR}$, in each of which a different number of parameterized deformations of the GR phase are allowed, an arbitrarily large number of 'testing parameters' can be used without having to worry about a model being insufficiently parsimonious if the true number of extra parameters is in fact small. TIGER is well-suited to the regime where most sources have low signal-to-noise ratios, again through the use of these sub-hypotheses. Information from multiple sources can trivially be combined, leading to a stronger test. We focus on binary neutron star coalescences, for which sufficiently accurate waveform models are available that can be generated fast enough on a computer to be fit for use in Bayesian inference. We show that the pipeline is robust against a number of fundamental, astrophysical, and instrumental effects, such as differences between waveform approximants, a limited number of post-Newtonian phase contributions being known, the effects of neutron star spins and tidal deformability on the orbital motion, and instrumental calibration errors.Comment: 12 pages, 9 figures. Version as appears in Phys. Rev.

PALAZZO LA SAPIENZA IN PISA: STRUCTURAL ASSESSMENT AND RETROFIT OF AN HISTORICAL MASONRY BUILDING IN ITALY

Palazzo La Sapienza, historical seat of the University of Pisa since the XVI century, represents one of the most important examples of the Tuscany cultural heritage, nowadays not in use due to several problems related to maintenance and structural deficiencies. The building, in its current form, is the result of several modifications, enlargements, elevations, connection with adjacent parts, resulting finally more similar to a “structural aggregate” - made up of single units connected together without specific scheme and organization - than to a single unitary building. After the earthquake of May 2012, the Palace was temporarily closed in relation to the ordinance issued by the Major’s Office and then subjected to wide in situ investigations aiming at analyzing in a very detailed manner all the criticisms related to structural, nonstructural, geotechnical and maintenance problems; the deep in situ survey campaigns allowed to reach a very deep knowledge of the building, of its progressive morphological evolution and of its actual condition, including problems not directly related to the structural condition but, as an example, to the instability and heterogeneity of the ground soil and of the foundation system. All the information so obtained allowed the execution of static and seismic vulnerability assessment – according to the actual prescriptions of Italian Standard for Constructions (D.M. 14/01/2008) – through the elaboration of complex global and local models and the final elaboration of an executive retrofit design comprehensive of local interventions on significant structural elements or subportions of the building. In the present paper, after a short description of the knowledge analysis of the building and of its safety verification, the retrofit executed to obtain a satisfying level of safety is presented