1,720,999 research outputs found
FLAT-BOTTOM SILOS FILLED WITH GRAIN-LIKE MATERIAL REFINEMENTS OF THE SILVESTRI THEORY
Full text linkSeismic behavior of squat flat-bottom silos containing grain-like material still presents strong uncertainties and current design codes tend to provide too conservative formulations. Over the years, many researchers focused on the overall dynamic behavior of such silos mainly through numerical investigations. Only recently, Silvestri et al. (2012) obtained the analytical expression of the pressures exerted by the ensiled grain on the silo walls in accelerated conditions, by means of plain dynamic equilibrium considerations. In the present paper, refinements to the original theory proposed by Silvestri et al. (2012) are presented. In detail, the static and the dynamic actions on the silo walls (as effect of the ensiled material) are idealised in a more consistent way, as far as the distribution of the vertical normal pressure is concerned. A direct comparison with the consolidated Janssen and Koenen (1895) theory for design of silos is also performed in order to check the theoretical model in static conditions. Once again, the findings confirm that, in case of squat silos, i.e. characterized by low, but usual height/diameter slenderness ratios, the portion of ensiled material that interacts with the silo walls turns out to be noticeable smaller than the total mass of the grain and the effective mass suggested by EC8 for seismic design
Refinements to the Silvestri’s theory for the evaluation of the seismic actions in flat-bottom silos containing grain-like material
No full textThe seismic behavior of flat-bottom silos containing grain-like material still
presents strong uncertainties and current design codes tend to provide too conservative
formulations for the estimation of the seismic actions. Over the years, some researchers
focused on the dynamic behavior of such silos mainly through numerical investigations.
Analytical formulations for the evaluation of the pressures exerted by the ensiled grain on
the silo wall under seismic excitation were developed by Younan and Veletsos (J Struct
Eng ASCE 124(1):62–70 1998) and, more recently, by Silvestri et al. (Bull Earthq Eng
10(5):1535–1560 2012). Experimental shaking-table tests were performed on silo specimens
(Silvestri et al. EESD 2015, submitted), which showed good agreement with the
Silvestri’s analytical formulations, even if some theoretical limits of validity were not
satisfied. This has encouraged a complete revision and refinements of the theoretical
framework, which is the object of this paper. In detail, the static and the dynamic actions
exchanged between different grain portions and between the grain and the silo wall are
idealised in a more physically consistent way. The analytical developments are carried out
by means of simple free-body dynamic equilibrium equations. The refinements yield to a
significant extension of the theoretical limits of validity and to a new set of analytical
formulas for the wall pressures and for the wall shear and bending moment. A comparison
of the analytical formulas with (i) the consolidated Janssen (Zeitschrift des vereines
deutcher Ingenieure 39:1045–1049 1895) and Koenen (Centralblatt der Bauverwaltung
16:446–449 1896) theory for static design of silos and (ii) with the Eurocode 8 provisions
for seismic design of silos and with the experimental results is also performed in order to
(i) check the updated theoretical model in static conditions and (ii) verify the reliability of
the different formulations in accelerated conditions, respectively. The refined theory
confirms that the portion of ensiled material that interacts with the silo wall is significantly
smaller than the effective mass suggested by Eurocode 8
EFFECT OF THE GRAIN SLIDING ON THE SEISMIC BEHAVIOR OF CIRCULAR SILOS: A THEORETICAL FORMULATION
Full text linkEarthquakes frequently cause damage or collapse in silos, provoking significant financial loss and even loss of life. The effect of lateral seismic loads can damage the upper portion of the silo if the material contained can oscillate inside the silo during the ground motion. The contribution of the grain sliding in terms of wall stresses is not
explicitly accounted neither in current design codes nor in scientific literature. In the present paper, the effect of the horizontal sliding of the grain layers is accounted in
terms of additional overpressures, wall shear and bending moment during dynamic excitation and compared with theoretical formulations, code provisions and
experimental evidence. Shaking table tests suggest that the grain sliding may be relevant in the evaluation of the wall base bending moment and that ACI 313-97 and
Eurocode 8 provisions appear overly conservative. Finally, a design recommendation is drawn for reducing the effect of the seismic actions on the silo wall
Seismic horizontal forces exerted by granular material on flat bottom silos: experimental and analytical results
No full textSeismic response of grain-silos still presents strong uncertainties and open issues. For this reason, seismic design of silos is not yet consolidated as the design in static conditions (filling and discharging scenarios) and current design codes tend to provide too conservative formulations for the estimation of the seismic actions induced by the stored material.
Experimental tests have been conducted during the last decades, including shaking table tests on silo specimens for better understand the coupled behaviour of grain-silos. Recently, the authors proposed a theory for the evaluation of the horizontal seismic forces exerted by granular material on silos. Starting from that theory, the present study provides a set of simplified code-like formula for the evaluation of the main seismic horizontal forces acting on the silo wall. A comparison with shaking-table test results and with the actual code provisions is presented
Manifestazioni psichiatriche delle lesioni cerebrali traumatiche. Quadri clinici ed aspetti medico-legali
No full textThe role of ductility in the collapse of a long-span steel roof in North Italy
No full textIn 2010, after an ordinary snowfall, the long-span steel trusses roof covering a school building located in a small town in North Italy collapsed. The building construction was completed in 2008, while the school was opened to the public just few months before the collapse. Luckily, at the time of the collapse, the building was empty and no people died or were injured. After the collapse, the Court nominated a first Official Technical Consultant in order to investigate on the causes of failure and related responsibilities. Later on, after that the main responsibilities were identified, a second Official Technical Consultant was nominated to further investigate on few specific technical aspects related to the collapse which were not completely clarified during the first investigations. In the present work, the main attention is paid on the structural behavior of the peculiar joint elements used to connect the members and their influence on the collapse, with emphasis on the role played by geometrical imperfections and structural ductility. The lesson learned from the case study could help professional engineers in being aware on the main peculiarities and structural deficiencies of structural systems made by spatial trusses with brittle connections
Experimental tests on Crescent Shaped Braces hysteretic devices
Full text linkCrescent Shaped Braces, CSBs, are steel hysteretic devices which, thanks to their geometrical configuration, are characterized by an enhanced seismic behavior that makes them a promising alternative to conventional diagonal steel braces and other seismic devices such as Buckling Resisting Braces and Scorpions. The present work reports the results of the first experimental campaign devoted to assess the cyclic experimental behavior of CSBs. The main goals of the experimental campaign are: (i) to verify/compare the effectiveness of design formulas for the seismic design of CSB introduced by the authors in a previous research work and the predictions of a simplified non-linear model in terms of force-displacement envelop response; (ii) to assess the experimental non-linear cyclic behavior in terms of ductility capacity, energy dissipation capacity, failures
Italy’s new forensic engineering research centre: A progress report
No full textThe Observatory Claudio Ceccoli is a forensic engineering research centre that was established at the University of Bologna, Italy, in 2012. It aims to provide benefit for researchers, engineers, architects, contractors, lawyers and insurers. The main scientific objective of the centre is to promote research on building defects through a systematic study of real cases available from the Court of Bologna. The main practical objective is to develop a web-based database of all Court of Bologna cases involving defects in building structures. This paper illustrates the aims of the centre and presents results of its initial activities
Experiments on crescent shaped braces
No full textDifferent design strategies, within the Performance Based Design framework, have been proposed through the years in order to design a structure of high seismic performances, including seismic isolation, viscous dampers and hysteretic dampers. A new lateral-resisting device, referred to as Crescent Shaped Brace (CSB), has been recently proposed to be used for the story isolation of multi-story frame structures. The main property of the CSB is that its lateral stiffness is uncoupled from its yield strength so that the practical designer may choose them independently, unlike conventional diagonal braces whose lateral stiffness is directly proportional to the yield strength. Past studies were devoted to the development of analytical formula for the design of such devices and to the study (through numerical simulations) of their non-linear response. In the present paper, the main results of experimental tests conducted on scaled CSB specimens (monotonic tests, cyclic tests, pseudo-static tests) are presented in order to assess the seismic behavior of such devices. The results of the experimental tests are compatible with the analytical predictions
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