Elsevier

Structures

Volume 34, December 2021, Pages 42-50
Structures

Pressure distribution of central cone silos during filling and discharge: Multi-scale experimental study

https://doi.org/10.1016/j.istruc.2021.07.064Get rights and content

Abstract

Central cone silo with high blending efficiency can be a key part of the production process in cement industry. Filling and discharge tests of central cone silos with different aspect ratios are conducted via a multi-scale experimental program to investigate the flow pattern of the stored material and the pressure distribution on the wall and cone. The filling tests imply the wall pressure increases with the depth until the peak value near the cone top position, beyond which both wall pressure and cone pressure decrease with the depth. The sequent discharge tests indicate the same number of inverted conical surfaces as the discharge outlets appear on the top surface of the stored material. The vertices of inverted conical surfaces are directly above the discharge outlets whereas the most significant overpressure of the wall and cone occurs in the far end of the outlet. For higher aspect ratio, the overpressure factors of the wall and cone decrease slightly. The maximum overpressure factors of the wall are close under different discharge modes, while the maximum overpressure factors of the cone are quite different under different discharge modes. The pressure coefficients according to Rankine’s equation and Jaky's equation can accurately predict the pressure on the wall in the upper region and the cone region, respectively. The predicted pressure on the cone by the equations for the hopper pressure in the code ACI 313–16 is obviously overestimated, and it cannot reflect the changing law of the cone pressure decreasing with the increase of the depth.

Introduction

A silo is a structure used for storing bulk materials [1], [2]. Central cone silos are widely applied in the cement industry due to the high blending efficiency [3], [4], [5]. The pressure distribution of the central cone silo is complex especially when the stored material is discharging [6]. There is no specialized provision of the central cone silo in the current silo codes [7], [8], [9], [10].

Engineering diseases of central cone silos have been server over the past few years [11], [12]. Analysis of silos accidents indicates that the lack of reinforcement, insufficient strength of concrete, and poor construction quality are the primary inducing factors [13], [14]. However, the factor not to be neglected is the lack of attention to the central cone. In particular, the discharge mode of the central cone silo belongs to a typical large eccentricity discharge because the discharge outlets are located at the bottom of the cone. Many researchers [15], [16], [17], [18], [19], [20] have studied the large eccentricity discharge of the silos. Less research has been done to investigate the influence of the central cone on the flow pattern of the stored material and the pressure distribution on the wall and cone. Blight analyzed the collapse cause of a multi-compartment cement storage silo with a central cone [11]. Johnston tested the pressure on the wall and cone in an operating central cone silo and compared it with the calculated pressures [6], [21]. The results indicate the measured pressure on the cone adjacent to the flow channel is greater than the predicted pressure. Blight stated that it may be extremely conservative to design the central silo based on the design codes DIN 1055-6 and ACI 313-77 [3], [22], [23]. As shown in Fig. 6.1.1 (d) of ACI 313-16 [9], the central cone may be regarded as a special form of the hopper. ACI 313-16 provides the equations for the hopper pressure, but its application to the pressure prediction for the cone needs to be further confirmed. To sum up, there is a lack of multi-scale experimental research on the central cone silo.

The work presented in this paper deals with the filling and unloading experimental research on the reduced-scale and full-scale central cone silos with different aspect ratios. The flow pattern and pressure distribution on the wall and cone are investigated based on different discharge modes. This study provides some reference for the structural design of the central cone silos.

Section snippets

General condition of the silo

A cement raw meal silo in Laos is chosen for the test project of the central cone silo (Fig. 1). The effective height of the silo hn is 53 m and the inner diameter dn is 22.50 m. The thicknesses of the top plate, the wall, the central cone, and the top plate of the cone are 0.15 m, 0.45 m, 0.7 m, and 1 m, respectively. The concrete strength grade is C40 [24]. There are 7 discharge outlets at the bottom of the central cone, and the angle of the cone from vertical θ is 30°. A prefabricated cone

Test setup

In order to observe the flow pattern of the stored material in the silos during the discharge, the plexiglass tubes with an outer diameter of 400 mm and a wall thickness of 8 mm were selected as the silo wall, as shown in Fig. 4a. Four groups of silos with aspect ratios (hn/dn) of 2.1, 2.4, 2.7, and 3.0 are used and the corresponding heights of silos (hn) are 806.4 mm, 921.6 mm, 1036.8 mm and 1152 mm, respectively. The diameter of the plexiglass cone bottom (340 mm) is slightly smaller than the

Evaluation of the equations for the hopper pressure

Fig. 14a indicates the predicted wall pressure ph,pre is in good agreement with the test pressure ph,test. Moreover, the coefficient k1 is more suitable for predicting the pressure on the wall of the upper region; the coefficient k2 can predict the pressure on the wall of the cone region more accurately. The results of multi-scale tests show that the pressure on the wall reaches the peak value within the cone height range and starts to decline. The pressure on the wall in the bottom silo is

Conclusions

Multi-scale tests of the central cone silos were conducted to investigate the flow pattern of the stored material and the overpressure evolution of the wall and cone. The following conclusions can be obtained.

  • (1)

    The central cone has a significant influence on the pressure distribution of the wall and cone in the height range of the cone, where the pressure on the wall peaks and then start to decrease; the pressure on the cone gradually decreases with the increase of the depth.

  • (2)

    The overpressure

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work is supported by the National Natural Science Foundation of China (51308297 & 11902161) and Nanjing Building System Project of China (Ks1717). Weiwei Sun thanks the Foundation Strengthening Plan Technology Fund (No. 2019-JCJQJJ-371).

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