Abstract

Abstract

This paper reports the outcomes of a series of shaking table tests performed at the EQUALS lab of Bristol University in the framework of the project entitled “ASESGRAM”, carried out within the Transnational Access Activities of the SERIES Project. The experimental test campaign was devoted to the evaluation of the effective behaviour of flat-bottom silos filled with grain under dynamic excitation, and to the experimental verification of the results obtained in previous analytical research work by the authors (Silvestri et al., Bull Earthq Eng 10:1535–1560, 2012). This analytical counterpart starts from the basic assumptions of Eurocode 8 (EN 1998–4, Eurocode 8. Design of structures for earthquake resistance, Part 4: silos, tanks and pipelines, CEN, 2006) excluding the calculation of horizontal shear forces among consecutive grains. This difference leads to a new physically-based evaluation of the effective mass of the grain, which horizontally pushes on the silo walls. The analyses are developed by simulating the earthquake ground motion with time constant vertical and horizontal accelerations and are carried out by means of simple dynamic equilibrium equations that take into consideration the specific mutual actions developed in the ensiled grain. The findings indicate that in case of squat silos (characterized by low, but usual, height/diameter slenderness ratios), the portion of the grain mass that interacts with the silo walls turns out to be noticeably lower than the total mass of the grain in the silo and the effective mass adopted by Eurocode 8 (EN 1998–4, Eurocode 8. Design of structures for earthquake resistance, Part 4: silos, tanks and pipelines, CEN, 2006). Different series of tests have been performed with different heights of the ensiled material to simulate a more or less squat silo. In the tests, the ensiled material consisted of Ballotini Glass. In this paper, the silo specimen and the test instrumentation are described, and the test program and the results are presented. Strong qualitative indications are obtained, which basically confirm that the wall-grain friction coefficient plays an important role in the actions at the base of the silo walls.

Abstract

Abstract

Abstract

In order to reduce the friction coefficient of lubricated surfaces with circular and herringbone shaped textures, an adjust variable method was introduced to optimize the shape of the oil film thickness distribution in the textured areas. The optimized oil film thickness distribution can be evolved by the shape updating formula proposed by Sasaoka et al. based on the smoothed sensitivity. For computational convenience, the objective function in the optimization is defined as the friction force, not the friction coefficient. The constraint function was also defined by the Reynolds equation. The finite element method was used in the optimization procedure. The optimization results show that the herringbone shape texture has a bowl-shaped oil film thickness distribution similar to that of the circular shape texture. Furthermore, the location of the deepest part was found to be different.