Refined Element Discontinuous Numerical Analysis of Dry-Contact Masonry Arches

The behavior of buried masonry arches is studied in this article using the Discontinuous Deformation Analysis (DDA), a numerical method that allows for the physical simulation of the intrinsic structure dis- continuities since it is based on contact and friction among pseudo-rigid blocks. Two types of arches (or vaults) are studied with a specially developed computer program, one of semicircular and another of ovoidal shape. The loads are self-weight, lateral filling, embankment thrusts and concentrated (through a short distribution) forces close to the peak. These loads are transformed into point forces applied to the center of gravity of each block with simple formulae from classical mechanics. Equilibrium is reached in the whole structure through contact forces calculated with a standard contact algorithm: penalty plus Coulomb friction. DDA-macroblocks composed of linked (through penalty contact springs) pseudo-rigid blocks are for- mulated. This linkage allows for the simulation of collapse by instability or by stress compressive failure more accurately than traditional DDA analyses, for instance funicular polygons. The numerical results are compared with those of the experiments taken from the literature with, for most cases, very good agreement given the uncertainties on geometry and material properties and given the intrinsic quality dispersion of masonry structures. Collapse loads as function of number of joints, safety factors and limit point forces from the numerical and experimental results are compared. The hinges that appear prior to collapse are also compared, obtaining again for most cases very good agreement.J.L. Perez-Aparicio, R. Bravo were partially supported by the MFOM I+D (2004/38), all authors by MICIIN #BIA-2008-00522 and the first also by Polytechnic University of Valencia under Grant PAID 05-10-2674.Pérez-Aparicio, JL.; Bravo, R.; Ortiz Rossini, P. (2013). Refined Element Discontinuous Numerical Analysis of Dry-Contact Masonry Arches. Engineering Structures. 48:578-587. https://doi.org/10.1016/j.engstruct.2012.09.027S5785874

Surface plasmon resonance-enhanced light interaction in an integrated ormocomp nanowire

An integrated ormocomp nanowire coated with gold metal layer is proposed and its optical characteristics with the effect of surface plasmon resonance (SPR) are studied. The integrated rib-like nanowire has a trapezoidal shape with sidewall angles of 75°. It is coated with 50 nm gold layer to introduce the SPR and enhance the evanescent field in the sensing region located at the dielectric/metal interface. The possible field modes, the normalized power confinement, and the SPR peak position of the nanowire are studied over the wavelength and the metal thickness by using the full-vectorial H-field FEM in quasi-TM mode. The attenuation coefficient of the nanowire, the SPR peak wavelength, and the wavelength shift is experimentally extracted for three different cladding materials. The redshift of the supermode coupling between the dielectric mode and the anti-symmetric supermode is observed with the higher cladding-index and larger metal thickness. The improvement of the power confinement in the sensing region with the SPR effect is ten times (10×) better than a previous similar study

Numerical Modeling of Historic Masonry Structures

The majority of historical and heritage structures around the world consist of unreinforced masonry walls. A masonry structure is composed of masonry units, such as brick or marble blocks, with or without a joint filling material, such as mortar. A masonry with a joint material is usually made of two different materials (i.e. masonry units and mortar), representing a non-homogeneous and anisotropic structural component. In other words, masonry is a discontinuous structural component whose deformations and failure mechanism are governed by its blocky behavior. Some ancient masonry structures, such as ancient columns and colonnades, are constructed without any form of joint material between the individual blocks. Therefore, the isotropic elastic continuum-based models are not suitable for the simulation of the real nonlinear behavior of masonry walls under applied load

Superstructure Fiber Gratings via Single Step Femtosecond Laser Inscription

We present the development of superstructure fiber gratings (SFG) in Ge-doped, silica optical fiber using femtosecond laser inscription. We apply a simple but extremely effective single step process to inscribe low loss, sampled gratings with minor polarization dependence. The method results in a controlled modulated index change with complete suppression of mode coupling associated with the overlapping LPG structure leading to highly symmetric superstructure spectra, with the grating reflection well within the Fourier design limit. The devices are characterized and compared with numerical modeling by solving Maxwell's equations and calculating the back reflection spectrum using the bidirectional beam propagation method (BiBPM). Experimental results validate our numerical analysis, allowing for the estimation of inscription parameters such as the ac index modulation change, and the wavelength, position and relative strength of each significant resonance peak. We also present results on temperature and refractive index measurements showing potential for sensing applications