Experimental Investigation of a Device to Restrain the Horizontal Sliding of U-FREIs.

Fiber-reinforced elastomeric isolators (FREIs) are composite devices consisting of an alternation of elastomer layers and fiber reinforcement layers. They have mechanical properties comparable to those of conventional Steel-Reinforced Elastomeric Isolators (SREIs). The mechanical and construction characteristics of FREIs, together with their lower cost, make them potentially usable on a large scale. However, for their actual use, it is necessary to take into account the current regulations regarding seismic isolation. The application of FREIs provides the absence of anchoring to the structure, but the European Technical Standard UNI EN 15129 requires that the isolators are attached to the structure by mechanical fastening only. In this research work, a constraint device that fulfills this requirement but, at the same time, does not significantly alter the mechanical behavior of FREIs is investigated. The properties of the selected device and its installation method are presented. The results of both a simple compression test and a combined compression and shear test performed on two isolators reinforced by quadri-directional carbon fiber fabrics and two isolators reinforced by bi-directional fabrics are presented. The tests were performed in the absence and presence of the constraint device in order to investigate the modifications produced by the device

Effectiveness of Tuned Mass Damper in Reducing Damage Caused by Strong Earthquake in a Medium-Rise Building

A case study where a tuned mass damper (TMD) was installed at the top of a five-story reinforced concrete (RC) building is presented. The aim of the study was to investigate the effectiveness of the TMD in changing the structural behavior of medium-rise existing buildings from dissipative to non-dissipative in order to eliminate reparation or demolition costs resulting from damages caused by strong earthquakes. The TMD mass is made by a RC slab lying on flat surface sliders. Horizontal stiffness and damping of the TMD are both provided by lead rubber isolators in the first proposed solution and by low-damping rubber isolators and viscous linear dampers, respectively, in the second. The improvement in the building’s structural behavior attained with the installation of the TMD was assessed by considering the flexural demand over capacity ratios of structural elements and the energy dissipated by the TMD. These results are compared with those of the same building retrofitted with a base isolation system. In both of the proposed solutions, TMD remarkably changed the modal behavior of the considered building, improved the flexural verifications, and dissipated most of the input seismic energy. It is therefore demonstrated that a TMD is a valid solution for the retrofit of medium-rise existing buildings

Methods to Reproduce In-Plane Deformability of Orthotropic Floors in the Finite Element Models of Buildings

In the modelling of reinforced concrete (RC) buildings, the rigid diaphragm hypothesis to represent the in-plane behavior of floors was and still is very commonly adopted because of its simplicity and computational cheapness. However, since excessive floor in-plane deformability can cause a very different redistribution of lateral forces on vertical resisting elements, it may be necessary to consider floor deformability. This paper investigates the classical yet intriguing question of modeling orthotropic RC floor systems endowed with lightening elements by means of a uniform orthotropic slab in order to describe accurately the building response under seismic loads. The simplified method, commonly adopted by engineers and based on the equivalence between the transverse stiffness of the RC elements of the real floor and those of the orthotropic slab, is presented. A case study in which this simplified method is used is also provided. Then, an advanced finite element (FE)-based method to determine the elastic properties of the equivalent homogenized orthotropic slab is proposed. The novel aspect of this method is that it takes into account the interaction of shell elements with frame elements in the 3D FE model of the building. Based on the results obtained from the application of this method to a case study, a discussion on the adequacy of the simplified method is also provided

Methods to Reproduce In-Plane Deformability of Orthotropic Floors in the Finite Element Models of Buildings

In the modelling of reinforced concrete (RC) buildings, the rigid diaphragm hypothesis to represent the in-plane behavior of floors was and still is very commonly adopted because of its simplicity and computational cheapness. However, since excessive floor in-plane deformability can cause a very different redistribution of lateral forces on vertical resisting elements, it may be necessary to consider floor deformability. This paper investigates the classical yet intriguing question of modeling orthotropic RC floor systems endowed with lightening elements by means of a uniform orthotropic slab in order to describe accurately the building response under seismic loads. The simplified method, commonly adopted by engineers and based on the equivalence between the transverse stiffness of the RC elements of the real floor and those of the orthotropic slab, is presented. A case study in which this simplified method is used is also provided. Then, an advanced finite element (FE)-based method to determine the elastic properties of the equivalent homogenized orthotropic slab is proposed. The novel aspect of this method is that it takes into account the interaction of shell elements with frame elements in the 3D FE model of the building. Based on the results obtained from the application of this method to a case study, a discussion on the adequacy of the simplified method is also provided

Bond-slip behavior between stainless steel rebars and concrete

Maintenance of reinforced concrete structures is a prevailing topic, especially with regard to lifeline structures and bridges, many of which are now designed with a service life beyond 100 years. Reinforcement made of ordinary (carbon) steel may corrode in aggressive environments. Stainless steel, being much more resistant to corrosion, is a valid solution to facilitate the protection of the works, increasing the service life and reducing the need for repair and maintenance. Despite the potential for stainless steel to reduce maintenance costs, studies investigating the influence of stainless steel on the behavior of reinforced concrete structures are limited. This study investigated the bond behavior of stainless steel rebars by means of experimental tests on reinforced concrete specimens with different concrete cover thicknesses, concrete strengths, and bar diameters. In each case, identical specimens with carbon steel reinforcement were tested for comparison. The failure modes of the specimens were examined, and a bond stress-slip relationship for stainless steel bars was established. This research shows that the bond behavior of stainless steel rebars is comparable to that of carbon steel bars

Experimental investigation on confinement of columns with TRC: a comparison between basalt and carbon textile fabrics

The use of Textile Reinforced Concrete (TRC) is a promising solution in the confinement of RC columns. Based on an experimental campaign on 15 short cylindrical RC columns, this work aims to get a better understanding about the performance of basalt textile in the confinement of short RC columns by comparing basalt and carbon TRC. Furthermore, the impact of mixing short steel fibers in the TRC concrete matrix (F/TRC) is investigated. The test results show that columns confined with basalt textile and carbon textile are, in terms of strength and, to some extent, post-elastic behaviour, comparable. Basalt textile seems to be a valid alternative to carbon, without significant loss of performance, and it provides less environmental impact. Columns reinforced with F/TRC show that adding 2.5 Vol.-% of short steel fibers has a beneficial effect in the confinement

Quarkonium production in ultra-relativistic nuclear collisions: suppression vs. enhancement

After a brief review of the various scenarios for quarkonium production in ultra-relativistic nucleus-nucleus collisions we focus on the ingredients and assumptions underlying the statistical hadronization model. We then confront model predictions for J/$\psi$ phase space distributions with the most recent data from the RHIC accelerator. Analysis of the rapidity dependence of the J/$\psi$ nuclear modification factor yields first evidence for the production of J/$\psi$ mesons at the phase boundary. We conclude with predictions for charmonium production at the LHC.Comment: 8 pages, 6 figures, invited paper, Quark Matter 2006 conference, Shanghai, submitted to J. Phys.

Semi-empirical model for shear strength of RC interior beam-column joints subjected to cyclic loads

This paper proposes an extension to RC interior beam-column joints of a model for the shear strength prediction of exterior joints under seismic actions, already presented in the literature and based, for certain assumptions, on a previous work of Park and Mosalam. The necessary changes, due to the joints\u2019 different physical configurations, only one beam converging in exterior joints and two beams converging in interior ones, are introduced. In the proposed model, on the basis of mechanical considerations, a direct formula for interior joint shear strength accounting for the resisting contributions of three inclined concrete struts and of joint reinforcements, the column horizontal stirrups and intermediate vertical bars, is derived. In comparison to the model for exterior joints, three struts are considered instead of two and the influenced of the upper column axial load on the inclination of the concrete struts is taken into account. The coefficients of the contributions of the struts and reinforcements are calibrated using 69 test data sets available in the literature, selecting only cyclic tests showing joint shear failure. For the validation of the proposed model, the shear strength predictions obtained using the proposed expression are compared with those obtained from Kassem\u2019s model, Wang et al.\u2019s formula and Kim and LaFave\u2019s formula, on a set of 28 specimens. It is also proposed a design formula, whose predictions are compared to those of Eurocode 8 and ACI Code

Total Absorption Dual Readout Calorimetry R&D

Abstract This calorimetry R&D focuses on establishing a proof of concept for totally active hadron calorimetry. The research program involves evaluating the performance of the different crystal and glass samples in combination with different light collection and readout alternatives to optimize simultaneous collection of Cerenkov and scintillation light components for application of the Dual Readout technique to total absorption calorimetry. We performed initial studies in two short test beam phases in April and November 2010 at Fermilab. Here we present first measurements from these two beam tests