177,197 research outputs found
Equivalent birational embeddings.
No full textLet X be a projective variety of dimension r. We want
to understand when two birational embeddings of the same variety are equivalent up to a Cremona transformation of the projective space, in this case we say that they are Cremona equivalent. It is proven that two birational embeddings of X in Pn with n >= r + 2 are Cremona equivalent. To do this, it is produced a chain
of Cremona transformations that modify the linear systems giving the two embeddings one into the other. This is done by looking at the two birational embeddings as different projections of a common embedding.
On the other hand, if n = r + 1, there are birationally divisors that are not Cremona equivalent. The case of plane curves is studied in details. Let C be an irreducible and reduced plane curve of arbitrary genus. It is proven that the curve C is birational to either a line; either a curve C, where the log pair (P2,3/dC)has canonical singularities, the log canonical divisor nef and Kodaira dimension k = 0; or a curve C ~ aC0 + bf Fa, where the log pair
(Fa,2/aC) has canonical singularities and terminal singularities in a neighborhood of the exceptional curve C0 Fa, the log canonical divisor nef and Kodaira dimension k <= 1.
Finally, it is used the theory of &–minimal models to under-
stand whether a rational, irreducible and reduced curve is Cremona equivalent to a line
Seismic behaviour of wood-concrete frame shear-wall system and comparison with code provisions
No full textConstructive systems adopting mixed shear walls made of a wood frame and fibrous or cementitious sheets nowadays are largely spread, particularly for prefabricated buildings. The use of gypsum boards as bracing panels is already widely proposed, but also fiber cement or reinforced concrete slabs can be used. The choice of such different materials allows to reach excellent thermal and acoustic insulation performance and for economic reason.
Perhaps the demonstration of their sound structural behavior, especially towards the earthquake resistance is still to be given, and their ductility and dissipative capacities still need to be fully assessed even if some experimental tests have already been conducted. Moreover these particular constructive systems are yet not accounted in the building codes (Eurocode 5 and Eurocode 8) and no guidelines are given for their seismic design in order to assure an adequate overstrength of the bracing panels and the adequacy of the fixing system of the panels to the wooden frames.
This work reports the investigation of the structural behavior of a newly developed wood-reinforced concrete constructive system. The investigated modular prefabricated system combines a typical platform frame system with an external thin reinforced concrete slab acting as a diaphragm against the horizontal actions and having also thermal ad acoustic functions.
The structural design procedure of such innovative system imitates the calculations normally adopted for the platform frame system; the bracing stiffness and strength assured by a OSB panel nailed to the wooden structure are cumulated with those given by the concrete slabs which are screwed to the frame by means of large diameter connectors which assure a considerable stiffness and, in the meantime, a great capacity of energy dissipation in case of seismic events.
In order to verify the real performance of this construction system under seismic actions several cyclic tests on single panel modules and on an assembled wall were carried out in accordance with the testing protocol specified in EN 12512. The results of the experimental tests are reported. It has been demonstrated that the seismic performance of the structural system fulfills the requirements given by EC8 for the structures that belong to the higher ductility class.
The analytical expressions that best fit the experimental load-displacement curves are reported and the comparison of the obtained results with that calculated according to the analytical formulas given by EC5 for the used connection type are discussed.
Finally a FEM nonlinear element able to reproduce the load-displacement hysteretic response of the connectors has been developed and implemented into a finite-element model to understand the mechanical behavior of the studied walls subjected by cyclic load. By the use of the this numerical model it was possible to estimate the seismic performance of the proposed wood-concrete system in terms of ductility and dissipative capacity. Several non-linear numerical analyses were performed and a sound behavior q-factor (i.e. reduction factor) for the wood-reinforced concrete walls was proposed
Behaviour factor for innovative massive timber shear walls
No full textFour massive wooden shear walls were analysed via experimental tests and numerical simulations. The specimens differ mainly in the method used to assemble the layers of timber boards: two of them are the well-known Cross-Laminated-Timber panels with glued interfaces, the other two are innovative massive timber panels adopting steel staples or wooden dovetail inserts to connect the layers. Quasi-static cyclic-loading tests were performed for each wall and main results are presented and analysed. A non-linear numerical model was calibrated on experimental results and used to perform non-linear dynamic analyses on specifically designed three-storey shear wall. The methods ensuring a reliable estimation of the intrinsic behaviour factor are presented and the definition of yielding and failure condition is discussed. The intrinsic behaviour factor values were calculated using results from non-linear dynamic analyses. Three limits of failure condition were analysed to estimate the correlated Peak Ground Acceleration and therefore the behaviour factor. A final interpretation of the obtained results is presented and some instructions about the choice of the suitable behaviour factor are given
Experimentally based q-factor estimation of cross-laminated timber walls
No full textBehaviour factor values applicable to cross-laminated timber (CLT) buildings are determined and several variables influencing construction are examined. The necessary experimental tests and analytical interpretation for estimating the behaviour factors for CLT wall systems, characterised as they are by several types of layout, were performed. The information given in this paper may be used to estimate the behaviour factor of whole CLT buildings. The results show that the proposed q-factors confirm that construction design decisions affect the seismic responses of buildings, as opposed to single values applied to all CLT buildings. The experimentally based approach used here was applied to physical test data for five CLT shear-wall arrangements. The results may be applied to a wide range of design situations, as analyses of common CLT specimens and simple generalisation of this method can be extended to other systems and configurations
Concrete-Plated Wooden Shear Walls: Structural Details, Testing, and Seismic Characterization
No full textThis paper discusses the structural characterization of a novel hybrid shear-wall system formed by coupling standard platform-frame panels with an external reinforced concrete shelter formed of precast slabs screwed to the wooden frames. The external RC skin is intended as a supplementary bracing system, increasing strength and dissipative capacity of the bare timber frame. The structural performance of such hybrid shear wall under monotonic and cyclic loading was first theorized analytically on the basis of code provisions and then confirmed via experimental tests. The novel shear walls demonstrated to fulfill the requirements prescribed by Eurocode 8. In particular, the analyzed system belongs to high ductility class (HDC). Finally the seismic response of a reference building realized with the innovative hybrid shear walls was simulated by means of a numerical model validated on experimental tests; the suitable behavior factor for the building was estimated
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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