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    • ENHANCING THE SERVICEABILITY PERFORMANCE OF TALL BUILDINGS USING SUPPLEMENTAL DAMPING SYSTEMS

    Bujar Morava, Trevor Haskett, Andrew Smith

    Over the last two decades, world-wide attention has been directed toward the use of innovative passive and active structural response control systems to mitigate the dynamic effects of wind and seismic loads. Although passive systems provide a limited response control level compared to the active ones, they do not require an external power supply to operate and therefore are still considered as viable and cost effective solutions to control vibrations of buildings or other civil engineering structures. Examples of passive response control systems, also known as supplemental damping systems, include viscoelastic dampers, tuned mass dampers, tuned liquid dampers, viscous dampers and friction dampers. Supplemental damping systems have been in existence for well over forty years and have been thoroughly researched and tested. Furthermore, their performance has been also validated through full scale monitoring during wind storms or seismic events. A considerable number of supplemental damping system implementations are for wind-induced motion control of skyscrapers. Their implementation has gained much recognition as a workable and highly reliable solution to enhance the serviceability performance of tall buildings and other dynamically sensitive structures. In this paper, supplemental damping systems that have become increasingly popular will be discussed, with specific attention to their recent notable applications in actual wind-sensitive buildings.

    The complete Issue 1, 2012 could be downloaded from the home page.

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    • SEISMIC UPGRADE OF A R.C. BUILDING WITH DISSIPATIVE BRACES

    Enrico Giovannardi, Fausto Giovannardi

    The paper illustrates the design and execution of seismic retrofit of a building with reinforced concrete structure, through the use of metal braces with integrated viscous damper. The work is part of a larger project that also included works by expanding the classroom through the use of stilts, closed with drywall that do not interfere in the structural behavior of the building. The economy and the possibility of working without closing the buibing, are its salient features. The cost of structural works was in fact of 190,000 € plus VAT and charges, amounting to less than 170€/sqm. A sum much less than the cost of traditional interventions (400€/sqm).

    This paper is available in Italian only.

    The complete Issue 1, 2012 could be downloaded from the home page.

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    • Simple Probabilistic Seismic Hazard Assessment

    Milutin Srbulov

    Conventional probabilistic seismic hazard assessments (PSHA) are complex and frequently lead to different results because of the interpretations and approximations used by different experts. Simple PSHA is based on deterministically defined peak ground accelerations (PGA) with additional definition of probabilities of their exceedences. This way there is no duality between deterministic and probabilistic approaches used. The use of the simple PSHA is demonstrated for Abu Dhabi and the results are compared with a conventional PSHA. One comparative case is not sufficient to decide about the correlation between the conventional and the simple method of PSHA. It is obvious, however, that the simple method is more transparent and easy to use then more complex conventional method of PSHA. The simple procedure can be used for response spectra and other ground motion parameters with defined attenuation relationships.

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    • How code-based linear static analysis for the seismic design of masonry buildings may fail to be conservative

    Maria Cristina Porcu, Lussoria Chessa

    Linear static analysis is the easiest method for the seismic design of unreinforced masonry buildings. What makes this method particularly convenient to apply is that the fundamental vibration period of the structure may be obtained conventionally from a formula given by the codes of practice, rather than being calculated rigorously. Usually, the code-based formula overestimates – sometimes significantly – the rigorous value of the fundamental period of vibration of masonry structures. By referring to a series of unreinforced masonry buildings, the paper shows that the conventional period may be even 4-9 times greater than the rigorous one. However, overestimating the fundamental period may lead to a reduction of the design loads to be applied in the static method. This occurs, in particular, when the design response spectrum decreases in the short-period range, where natural periods of masonry buildings typically fall. Some codes do not allow design spectra to be negatively sloped in the short-period range. While others, such as the Italian code of practice, do allow it, and in so doing, they make the linear static method non-conservative (in the given examples the shear at the base of masonry buildings may be underestimated by even as much as 35% when compared to the values obtained from the more precise linear dynamic method). The paper gives some hints towards making the code-based static method for seismic design of masonry buildings safe.

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    • Vulnerability Model of a urban centre. Methodology for a quick evaluation of emergency road network vulnerability

    Rachele Ferlito, Angelo G. Pizza

    The strategic paths, clearly identified in an emergency plan, are a part of the ordinary roads network, that after an seismic event has to be ensured to enable the arrival at the strategic elements, the possibility of ap- proaching each urbanized area of the municipality, and, more in general, a minimum service mobility to the resident population. This paper proposes a quick methodology, subject of a first trial, with proper Survey form, that analyzes a few in- dicators, considered highly significant, and allows the evaluation of critical situations of the various links in which can be broken down the entire emergency road system of the Plan. The methodology is intended to provide an application that, in case of earthquake, allows to focus attention primarily on a few well-defined critical points of the emergency paths system, to determine the final scheme for the event occurred, by replacing any of the links, no longer functional, with others that are already contemplated as alternative in the plan. This analysis is also functional to the scheduling of any preventive actions required to reduce or eliminate the critical problems.

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    • L’Aquila – the New Auditorium of the Castle. Design of glue-laminated wooden structures in a high seismicity area

    Andrea Amoretti, Maurizio Milan

    The New Auditorium of the Castle in l’Aquila, designed by Architect Renzo Piano, financed by the Province of Trento, temporarily relieves the Concert Hall of the 16th century Spanish fort, unfitted for use by the earthquake of April 6, 2009. The new hall is an oblique cube with 18m-long edges.The principles upon which the overall design is based are seismic action drop and building mass reduction. The choice of using wood comes from both architectural and structural reasons. Wood is a lightweight but very strong material. Little mass reduces the danger in case of earthquake. The Hall has a limited dissipative behaviour, because of its shape and of the chosen structural technology. There- fore we have adopted a base isolation system, composed by sixteen elastomeric isolators that reduce the seismic force by about 80%. The two additional buildings are used by the audience and the orchestra and are designed with the standard cross- lam panels building method, as an example of the application of lightweight and innovative earthquake-resistant techniques that can be used for the safe reconstruction of the Town too.

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    • Effect of infills on the seismic response of high-rise RC buildings designed as bare according to Eurocode 8

    Laura Liberatore, Luis Domingo Decanini

    The aim of the work is to evaluate the influence of masonry infills on the seismic behaviour of reinforced concrete frames designed according to Eurocode 8 provisions as bare frames. To this purpose, non linear dynamic analyses of a twelve storey–three bay plane frame are performed considering four different infills configurations, named bare, fully infilled, open ground storey and open seventh storey frames. Artificially generated and recorded near fault ground motions are used in the numerical analyses. The accelerograms are scaled to attain the same intensity of the design one. The analyses are performed by means of a finite element code with fiber elements for the modelling of columns and beams. The infill walls are modelled through equivalent diagonal no tension struts, of which the constitutive law and the hysteretic behaviour are described in detail in the article. The structural response is evaluated through several parameters, such as top horizontal displacement, maximum interstorey drift and dissipated energy. The main inference is that the effect of uniformly distributed infills on the seismic performance is beneficial due to the additional strength, stiffness and energy dissipation capacity provided. The presence of an open storey may change this general conclusion, especially in the open seventh story model. Anyway the building retains strength and ductility resources when subjected to earthquakes of the same intensity of the design one.