Seismic performance of existing hollow reinforced concrete bridge columns

Highway bridges can be considered as crucial civil structures for economic and social progress of urban areas. The damages to highway bridges due to earthquake events may have dramatic impact on the interested area, with or without life threatening consequences, since bridges are essential for relief operations. For these reasons, the assessment of seismic performance of existing bridge structures is a paramount issue, especially in those countries, such as Italy, where most of existing bridges was constructed before the advancement in earthquake engineering principles and seismic design codes. Several major earthquakes occurred throughout the world highlighted the seismic vulnerability of the bridge piers, due to obsolete design. If, for ordinary shaped reinforced concrete (RC) bridge columns the seismic assessment issue can be considered as almost solved, due to several analytical assessment formulations available in literature, and adopted by codes, the same cannot be said for columns with hollow-core cross section, despite their widespread use. None of the current codes addresses specialized attention to RC hollow core members, and only quite recently, attention has been paid to experimental cyclic response of hollow columns. Some critical issues for hollow RC columns are related to the assessment of their shear capacity, special focusing on degradation mechanisms, and the high shear deformation characterizing the seismic response of such elements. In the above outlined contest, a contribution in the seismic assessment of hollow bridges piers is provided by the present work: the investigation of cyclic lateral response of RC existing bridge piers with hollow rectangular and hollow circular cross-section is performed. Special attention has been focused on failure mode prediction and shear capacity assessment. A critical review of the state-of-the-art and of the theoretical background is firstly carried out: the review process has been focused on the past experimental and analytical research on seismic performance of hollow reinforced concrete bridge piers, both for hollow rectangular and hollow circular cross sections. The experimental campaign, conducted at Laboratory of the Department of Structures for Engineering and Architecture, University of Naples “Federico II”, is presented. The experimental program comprised tests on six reduced-scale RC bridge piers with hollow cross-section (four rectangular shaped and two circular shaped). The specimens were ad hoc designed in order to be representative of the existing bridge columns typical of the Italian transport infrastructures realized before 1980, by using a scaling factor equal to 1:4. The construction procedure is detailed, too. All the tests were performed in quasi-static way by applying increasing horizontal displacement cycles with constant axial load (equal to 5% of the axial compressive capacity) until collapse. The monitoring system is accurately explained: it was composed of two sub-systems, one used for global measures (forces and displacement), and the other to deeply investigate about local deformation. Experimental results for both hollow rectangular and hollow circular specimens are reported: for each specimen the results in terms of lateral load versus drift are shown and the evolution of observed damage with increasing displacement is described and related to the lateral load-drift response. An experimental analysis of deformability contributions to the top displacement is performed, mainly in order to better understand the relevance of taking into account shear deformations for bridge piers assessment. The energy dissipation capacity is also analyzed, evaluating the equivalent damping ratio and its evolution with ductility. For hollow rectangular specimens, the global response is modelled through a three-component numerical model, in which flexure, shear and bar slip are considered separately. The main goal of the numerical analysis is to reproduce the experimental deformability contributions. The last part of the work focuses on the definition of proper shear strength models for both hollow rectangular and hollow circular cross sections, and the definition of a deformability capacity model for hollow rectangular cross section. To this aim, two different experimental databases are collected and critically analyzed. The effectiveness in shear capacity and failure mode prediction of main existing shear capacity models is investigated, by applying these models to the database columns. Based on the obtained results, some modifications to existing shear strength models are discussed and proposed in order to improve their reliability for hollow columns. Finally, a new drift capacity model is developed and proposed to assess drift at shear failure of hollow rectangular columns

Unusual reversibility in molecular break-up of PAHs: the case of pentacene dehydrogenation on Ir(111)

In this work, we characterize the adsorption of pentacene molecules on Ir(111) and their behaviour as a function of temperature. While room temperature adsorption preserves the molecular structure of the five benzene rings and the bonds between carbon and hydrogen atoms, we find that complete C\u2013H molecular break up takes place between 450 K and 550 K, eventually resulting in the formation of small graphene islands at temperatures larger than 800 K. Most importantly a reversible temperature-induced dehydrogenation process is found when the system is annealed/cooled in a hydrogen atmosphere with a pressure higher than 5 7 10 127 mbar. This novel process could have interesting implications for the synthesis of larger acenes and for the manipulation of graphene nanoribbon properties

In Situ Synthesis of Metal\u2013Salophene Complexes on Intercalated Graphene

On-surface metalation provides a tool to vary magnetic and electronic properties of metal\u2013organic complexes and produces clean samples of the desired product. We used this technique to metalate 5,5\u2032-dibromosalophene with the 3d transition metals Co, Fe, and Cr on Co-intercalated graphene grown on Ir(111). The metalation process was investigated by X-ray photoelectron spectroscopy (XPS). The electronic structure of the obtained salophene complexes was investigated using a combination of scanning tunneling microscopy and spectroscopy with density functional theory calculations. XPS data show that deposition of the transition metals at 398 K causes the metal atoms to interact with the molecules, while higher temperatures are needed to complete the reaction. Furthermore, we are able to distinguish the three different metal\u2013organic complexes by their electronic structure

On-surface oligomerization of self-terminating molecular chains for the design of spintronic devices

Molecular spintronics is currently attracting a lot of attention due to its great advantages over traditional electronics. A variety of self-assembled molecule-based devices are under development, but studies regarding the reliability of the growth process remain rare. Here, we present a method to control the length of molecular spintronic chains and to make their terminations chemically inert, thereby suppressing uncontrolled coupling to surface defects. The temperature evolution of chain formation was followed by X-ray photoelectron spectroscopy to determine optimal growth conditions. The final structures of the chains were then studied, using scanning tunneling microscopy, as a function of oligomerization conditions. We find that short chains are readily synthesized with high yields and that long chains, even exceeding 70mers, can be realized under optimized growth parameters, albeit with reduced yields.We gratefully acknowledge financial support from the Office of Naval Research via Grant No. N00014-16-1-2900, and the Deutsche Forschungsgemeinschaft via SFB668-B4. Moreover, M.A. and J.B. acknowledge funding from the Spanish MINECO under contract Nos. MAT2013-46593-C6-4-P and MAT2016-78293-C6-5-R as well as the Basque Government Grants IT621- 13 and IT-756-13.Peer Reviewe

Atomically resolved magnetic structure of a Gd-Au surface alloy

The magnetic structure of a monolayer-thick GdAu2 surface alloy on Au(111) has been investigated down to the atomic level by spin-polarized scanning tunneling microscopy. Spin-resolved tunneling spectroscopy combined with density-functional theory calculations reveal the local spin polarization of both Gd and Au atomic sites within the surface alloy. Moreover, the impact of dislocation lines on the atomic-scale magnetic structure as well as on the local coercive field strength is demonstrated.We gratefully acknowledge financial support from the Office of Naval Research via Grant No. N00014-16-1-2900. Moreover, M.A. and J.B. acknowledge funding from the Spanish MINECO under Contracts No. MAT2013-46593-C6- 4-P and No. MAT2016-78293-C6-5-R as well as the Basque Government Grants No. IT621-13 and No. IT-756-13. T.H. acknowledges support by the DFG under Grant No. HA 6037/2-1. E.S. acknowledges financing from Polish budget funds for science in 2014–2017 as a research project in the program “Diamond Grant” No. 0084/DIA/2014/43. M.H. acknowledges the support from the Ministry of Science and Higher Education in Poland within Project realized at Faculty of Technical Physics, Poznan University of Technology, and Poznan Supercomputing and Networking Center (PSNC

Toward Tailored All-Spin Molecular Devices

Molecular based spintronic devices offer great potential for future energy-efficient information technology as they combine ultimately small size, high-speed operation, and low-power consumption. Recent developments in combining atom-by-atom assembly with spin-sensitive imaging and characterization at the atomic level have led to a first prototype of an all-spin atomic-scale logic device, but the very low working temperature limits its application. Here, we show that a more stable spintronic device could be achieved using tailored Co-Salophene based molecular building blocks, combined with in situ electrospray deposition under ultrahigh vacuum conditions as well as control of the surface-confined molecular assembly at the nanometer scale. In particular, we describe the tools to build a molecular, strongly bonded device structure from paramagnetic molecular building blocks including spin-wires, gates, and tails. Such molecular device concepts offer the advantage of inherent parallel fabrication based on molecular self-assembly as well as an order of magnitude higher operation temperatures due to enhanced energy scales of covalent through-bond linkage of basic molecular units compared to substrate-mediated coupling schemes employing indirect exchange coupling between individual adsorbed magnetic atoms on surfaces