SHAKING-TABLE TESTS OF A FULL-SCALE FLAT-BOTTOM MANUFACTURED STEEL SILO FILLED WITH WHEAT

This paper illustrates the preliminary results of a series of shaking-table tests on a full-scale flat-bottom manufactured steel silo filled with a granular material. The experimental campaign was developed at the EUCENTRE lab in Pavia (Italy) in February/March 2019 within the European project “SEismic Response of Actual steel SILOS (SERA-SILOS)” (https://sera-ta.eucentre.it/index.php/serata-project-18/). A flat-bottom cylindrical silo was tested in fixed-based and seismically isolated configurations. It is the smallest actual silo manufactured by the AGI-FRAME company (Italy). The height is H = 5.5 m and the radius is R = 1.82 m. The silo wall is realized by 5 stripes of horizontal corrugated sheets (ferrules) with thickness equal to 1 mm. The silo wall is supported by 8 vertical stiffeners characterized by an hat-shaped thin open cross-section which changes in thickness along the height. The stiffeners are connected to the silo wall by M10 7cm-spaced bolts. The silo is filled with soft wheat up to a 3.3 m height, in order to reproduce a “squat” aspect ratio H/2R roughly equal to 1. The weight of the steel silo itself is around 12 kN, the amount of grain is around 285 kN, the 4.8mx4.8mx0.4m r.c. plate is 230 kN weigh. The isolators placed between the table and the r.c. plate are Curved Surface Sliders friction pendulum devices expressly manufactured by the MAURER company (Germany – Switzerland) to obtain a 3 s period of vibration (radius = 2.2364 m, max allowable displacement = 20 cm). Mono-axial shaking-table tests were performed using random signals, low-frequency sinusoidal inputs and earthquake records (both artificial and real). The following sensors were utilized: uniaxial and triaxial accelerometers placed at different heights of the silo, vertical strain gauges on the external surfaces of the stiffeners, four load cells placed at two heights of the silo, LVDTs between the isolated system and the table, and HD video-cameras to monitor the spatial displacements of the main structural elements. The main objectives of the shaking-table tests were: (i) to identify the basic dynamic properties (period of vibration, damping ratio, amplification) of the grain-silo system, (ii) to experimentally assess the static pressure during the filling phase and the dynamic over-pressures during the shaking-table tests, and (iii) to evaluate the benefits obtained introducing an isolation system at the base of the silo.