$5.00Add to Cart
Month: April 2014
SEISMIC MICROZONING IN ITALY: A BRIEF HISTORY AND RECENT EXPERIENCES
In an attempt to develop a diffuse culture of prevention against earthquakes, the Italian government has issued an Act (June 24 2009 n. 77) and subsequent ordinances which regulate the distribution of resources to those regions that promote studies of seismic microzoning (SM). As a result, during the last years the number of Ital ian SM studies has been increasing and posing many new problems and challenges to administrators and scientists. The aim of this paper is to illustrate, through some salient examples of recent SM cases in Italy, the emerging philosophy of a new current of SM studies that can be called ordinary, namely projects devoted to seismic risk reduction through the usual preventive activities that can be carried out by local governments with the contribution of local officials and professionals, to the maximum extent possible. While the SM studies are generally elaborate, slow and costly, the logic of ordinary SM projects is that they have to be performed smoothly, rather quickly and cheaply. The aim is not to obtain the best SM product at any price but the best SM project consistent with efficient administrators who really want to reduce seismic risk in their regions.
In order to reach this objective and to guarantee the quality of the products, local governments (regions, provinces and municipalities) now have new duties; that is, they must undertake, in conjunction with scientists and researchers, positive actions to improve the state of knowledge and of practice in seismic risk reduction in the region, to increase the number and technical capacities of local professionals and public officials, to reduce time and investigation costs through drawing up basic geological maps also in digital format at an appropriate scale for SM, issuing specific valuable SM guidelines, implementing digital models of the territory, creating regional seismological, geological and geotechnical data banks, controlling the accuracy of the obtained SM maps and so on.
The paper focuses on unprecedented problems posed by the new legislation also to scientists and researchers, who are now called by administrators and public officials to play different scientific roles than in the past in order to contribute to advancing the frontiers of knowledge as well as the state of practice through experience transfer and applications.
EFFECT OF SUPPORT FLEXIBILITY AND SOIL – STRUCTURE INTERACTION ON SEISMIC RISK ANALYSIS OF HARP TYPE CABLE STAYED BRIDGES
Seismic risk analysis including soil – structure interaction (SSI) of harp type cable stayed bridge with support flexibility is presented which can be used for preliminary estimate of its probability of failure. The risk analysis procedure uses the format of probabilistic risk analysis (PRA) and considers the band limited white noise at the bedrock as the seismic input. The bridge deck is modeled as a beam supported on springs at different points. The coupled stiffness matrix of the springs is determined by a separate 2D static analysis of cable-tower-deck system in which flexibility of the tower base due to soil-structure interaction is included. Damping due to soil is incorporated by the equivalent modal energy method. The response of the bridge deck is obtained by the response spectrum method of analysis for multi-degree of freedom system. The PRA includes uncertainties of responses due to the variation in ground motion, material property, modeling and method of analysis, and uncertainties of the capacity due to the variation of ductility factor and damage concentration effect. Failure mode of the bridge is assumed to be bending failure of the bridge deck at the point of maximum bending moment. Probability of failure of the bridge deck is determined by First Order Second Moment (FOSM) theory of reliability analysis. A three span double plane cable stayed bridge is used as an illustrative example. The fragility curves for the bridge deck failure are obtained under a number of parametric variations. The parameters include, base flexibility, degree of correlation of ground motion, angle of incidence of earthquake, ratio of the components of ground motion. Study shows that flexible base condition provides significantly less value of probability of failure as compared to the fixed base. Further, angles of incidence, degree of correlation and ratio of components of ground motion have considerable effects on the probability of failure.
INNOVATIVE CONNECTIONS FOR TIMBER PANEL BUILDINGS
Cross-laminated timber panel buildings are gaining a growing interest of the scientific community due to significant technical advantages, such as the material sustainability, the high fire resistance and quick constructability. Nevertheless, it is well known that timber panels themselves are not able to dissipate a significant amount of energy during an earthquake. In fact, the design of a Cross-Lam building is carried out in order to dissipate the energy in the steel connections (hold-downs or angle brackets) which govern the seismic performance. The paper here presented proposes to substitute the classical hold-downs, which usually exhibit a limited dissipation capacity, with an innovative type of dissipative angle. The new connection, called XL-stubs, apply the concept usually adopted for designing the hysteretic metallic dampers ADAS (Added Damping and Stiffness). In particular, the hourglass shape allows a better spread of plasticization resulting in a high dissipation capacity. In order to characterize the force-displacement response under cyclic loads of XL-stubs an experimental campaign is carried out comparing the hysteretic behavior of the classical hold-down with that of the proposed dissipative angle.
ENERGY DISSIPATION CAPACITY OF CONCRETES REINFORCED WITH RECYCLED PET FIBERS
We investigate on the strength and ductility properties of recycled PET fiber-reinforced concretes (RPETFRCs) showing different mix-designs and PET filaments with variable mechanical and geometric properties. Available literature results of compression tests and four-point bending tests on such materials are reviewed comparing laboratory results in terms of compressive strength, first crack strength and ductility indices. The examined tests highlight that most relevant effects of the recycled PET fiber reinforcement are concerned with material toughness and ductility. In the case of low-strength concretes, significant compression and flexural strength enhancements due to the addition of recycled PET fibers are also observed.
GIULIO PIZZETTI AND THE STRUCTURES IN ARCHITECTURE
Please note that this paper is available only in Italian