Abstract
AbstractThis paper reports on a series of shaking table tests on a full‐scale flat‐bottom steel silo filled with soft wheat, characterized by aspect ratio of around 0.9. The specimen was a 3.64‐m diameter and 5.50‐m high corrugated‐wall cylindrical silo. Multiple sensors were used to monitor the static and dynamic response of the filled silo system, including accelerometers and pressure cells. Numerous unidirectional dynamic tests were performed consisting of random signals, sinusoidal inputs, and both artificial and real earthquake records. The objectives of this paper are (i) to provide a general overview of the whole experimental campaign and (ii) to present selected results obtained for the fixed‐base configuration. The measured data were processed to assess the static pressures, the dynamic overpressures (related to the effective mass) and the accelerations of monitored points on the silo wall, and to identify the basic dynamic properties (fundamental frequency of vibration, damping ratio, dynamic amplification factors) of the filled silo. The main findings are discussed and compared with the predictions given by available theoretical models and code provisions. It is found that the fundamental frequency slightly decreases with increasing acceleration, while it slightly increases with increasing compaction of the granular material. For close‐to‐resonance input, the dynamic amplification (in terms of peak values of accelerations) increases along the height of the silo wall up to values of around 1.4 at the top surface of the solid content. The dynamic overpressures appear to increase with depth (differently from the EN1998‐4 expectations), and to be proportional to the acceleration.
Highlights
Silos differ from many other civil engineering structures in that the weight of the silo structure is significantly lower than the one of the ensiled granular material and, in case of earthquake ground motion, the particle-structure interaction plays an important role in the global dynamic response
The dependence of the dynamic overpressures on the height of the granular solid and the acceleration is discussed and a comparison with the results provided by the three analytical models mentioned in Sections 2.2 and 2.3 is provided
These findings indicate that the peak local dynamic overpressures are not captured by design-oriented models based on averaged uniform distributions, and that Silvestri’s model can be applied to the portions of the tested silo leaning above certain heights corresponding to aspect ratios smaller than the limit given by Equation (2), depending on the considered acceleration value
Summary
The structural design of steel silos containing granular materials presents a challenging issue.[1,2] Silos differ from many other civil engineering structures in that the weight of the silo structure is significantly lower than the one of the ensiled granular material and, in case of earthquake ground motion, the particle-structure interaction plays an important role in the global dynamic response. The complex mechanism through which the ensiled material interacts with the silo wall has been studied since the XIX century.[3,4] several issues are still to be addressed and structural failures still occur during filling and, especially, discharging phases, as well as during strong ground motions. It is well known that both metal and concrete silos are characterized by a relatively high failure rate (both ground- and columns-supported silos), during earthquakes.[5]. After the famous 1999 Chi-Chi earthquake in Taiwan when almost all the silos in a circle of 70 km far from the epicenter collapsed, the EQE report (1999) stated that “the seismic design of practice that is used for the design and construction of such facilities clearly requires a major revision”, clearly indicating that actual design procedures have limits.[7]
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