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Month: January 2012
THE OCTOBER 23 (MW = 7.2) AND NOVEMBER 9 (MW = 5.7), 2011 VAN, TURKEY EARTHQUAKES. A GEOSCIENTIFIC AND ENGINEERING REPORT
On 23 October 2011 (13.41 LT) a disastrous earthquake with a magnitude of MW = 7.2 occurred in Van Province of eastern Turkey. That is the region where the Arabian Plate drifting towards north-northeast collides with the Eurasian Plate, while the other smaller plates in the region are moving apart as if pushed by the stronger Arabian. As a result, the seismic history of the region is quite rich usually resulting in severe losses. The death toll due to the main shock reached 604 people and injured 4,152, with at least 188 pulled out of the rubble of collapsed buildings. The most heavily damaged Ercis city was at a distance of 35-40 km to the north of the causative fault. The city of Van suffered much less damage, being to the south of the fault at a distance of 25-30 km. The damage was concentrated mainly in the old city centers of both cities. On the 9th of November 2011 (21.23 LT) a strike slip earthquake of MW = 5.7 occurred very close to the city center of Van, associated with a different fault. Due to this shock, an additional number of 40 people were killed and 260 injured, while the Bayram Hotel, in Van city, where the authors stayed from 25 to 29 October 2011, collapsed. The hotel building was visually inspected by the first author following a widely accepted methodology and it was considered to be earthquake safe. The available cross-checked information concerning the mechanism of the hotel’s collapse is, at first glance, contradicted by the strong motion records presented in the paper. Unfortunately, during the main shock in both Van and Ercis cities, there were no strong motion recordings. In order to infer some basic characteristics of the ground motion due to the main shock, strong motion records from an aftershock, occurring in the same focal volume with that of the main shock, were used. Observations of the response of structures immediately after the main shock were carried out by the authors during their reconnaissance trip and led towards the same goal. The heaviest damage was observed to engineered reinforced concrete buildings. There are some cases of modern and even recently built, multistoried buildings with rather good reinforcement detailing that suffered extended damage or even collapse. On the contrary, nearby non-engineered, low-rise simple or traditional masonry houses, weathered the earthquake in the epicentral region almost without any damage. Most of the reinforced concrete structures are quite flexible, without shear walls, and used a flat-slab constructional system of rather small thickness compared to their spans. In spite of those characteristics justifying high flexibility, no noticeable horizontal motion or pounding was observed between adjacent buildings. For this reason it was thought helpful to present a critical evaluation of the published Turkish seismic building codes since 1940. A crucial subject directly related to the incurred damage and discussed by the authors is the widespread practice of building construction in the region that it is not according to the Turkish earthquake code requirements. It is shown that due to the main shock the numerous and heavy losses in Ercis city were due to the dominance of a severe vertical seismic component, while those in Van city due to resonance phenomena caused by the relatively weak horizontal ground motion. The losses due to the event of 9th November in Van city are attributed to the catalytic function of the vertical seismic component. The resulting collapse is usually quite abrupt and does not allow occupants time to egress safely.
The complete Issue 1, 2012 could be downloaded from the home page.
RELIABILITY OF CODE-PROPOSED MODELS FOR ASSESSMENT OF MASONRY ELASTIC MODULI
SUMMARY – In this paper the results of an experimental investigation aimed to the assessment of Young moduli, rigidity moduli and other mechanical properties for different types of masonry are shown.The mechanical characteristics predicted by models proposed by some technical codes were compared against experimental data.This study was motivated by the suggestion of the Masonry Standards Joint Committee’s (MSJC) code that, while proposing the use of such models, acknowledges the lack of testing in support of their validation. The experimental investigation has included compressive tests on components (blocks and mortar), diagonal compressive tests and ordinary compressive tests (orthogonally to beds joints) on portions of masonry. The details of the experimental campaign and the prediction capacity of the above models, for the types of masonry investigated, are presented.
The complete Issue 1, 2012 could be downloaded from the home page.
ENHANCING THE SERVICEABILITY PERFORMANCE OF TALL BUILDINGS USING SUPPLEMENTAL DAMPING SYSTEMS
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.
SEISMIC UPGRADE OF A R.C. BUILDING WITH DISSIPATIVE BRACES
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.
REVISIONE DEL DM 14.01.2008 NTC SULLE COSTRUZIONI. SIAMO PARTITI CON IL PIEDE SBAGLIATO
This note on the Italian Seismic Code (DM 14.01.2008) is available in Italian only.