Mechanical characterization of timber in structural sizes: bending and compression tests

This paper presents the results obtained in a series of tests on Pinus Pinaster Ait. timber specimens, using the prEN408:2000, to estimate the local and global Young’s modulus and strength both in bending and compression parallel to the grain. The results obtained are compared with the values presented in the Portuguese Nationally Determined Parameters of Eurocode 5, for the quality classes assign by Portuguese Standard NP4305:1994 by visual grading

Epitaxial Thin Films of the Giant-Dielectric-Constant Material CaCu_3Ti_4O_{12} Grown by Pulsed-laser Deposition

Pulsed-laser deposition has been used to grow epitaxial thin films of the giant-dielectric-constant material CaCu_3Ti_4O_{12} on LaAlO_3 and SrTiO_3 substrates with or without various conducting buffer layers. The latter include YBa_2Cu_3O_7, La_{1.85}Sr_{0.15}CuO_{4+\delta} and LaNiO_3. Above 100K - 150K the thin films have a temperature independent dielectric constant as do single crystals. The value of the dielectric constant is of the order of 1500 over a wide temperature region, potentially making it a good candidate for many applications. The frequency dependence of its dielectric properties below 100K - 150K indicates an activated relaxation process.Comment: 11 pages, 4 figure

Recursion relations for multi-gluon off-shell amplitudes on the light-front and Wilson lines

We analyze the off-shell scattering amplitudes in the framework of the light-front perturbation theory. It is shown that the previously derived recursion relation between tree level off-shell amplitudes in this formalism actually resums whole classes of graphs into a Wilson line. More precisely, we establish a correspondence between the light-front methods for the computation of the off-shell amplitudes and the approach which makes use of the matrix elements of straight infinite Wilson lines, which are manifestly gauge invariant objects. Furthermore, since it is needed to explicitly verify the gauge invariance of light-front amplitudes, it is demonstrated that the Ward identities in this framework need additional instantaneous terms in the light-front graphs.Comment: 26 pages, a few figure

Behaviour of traditional Portuguese timber roof structures

The aim of this paper is to present the results of a structural analysis of common trusses traditionally used in roof construction in Portugal. The study includes the results of a preliminary survey intending to assess the geometry, materials and on site pathologies, as well as a twodimensional linear elastic static and dynamic analysis. The trusses behaviour under symmetric and non-symmetric loads, the king post/tie-beam connection, the stiffness of the joints and the incorrect positioning of the purlins, were some of the structural aspects that have been investigated

Experimental analysis of original and strengthened traditional timber connections

Tests on full-scale unstrengthened connections were performed under monotonic and cyclic loading. Attention has been principally focused on the birdsmouth joint, because of its common use in practice. Different strengthening solutions with metal elements have been evaluated