1 Introduction Pressure measurements in silos have been carried out since the XIX century. The first published work in which an attempt has been made to measure grain pressures using weighing devices was dated in 1882 by ISAAC ROBERTS [1]. He was encouraged to carry out experimental tests with wheat using four square and hexagonal model silos made of wood to determine the pressure at the bottom of the silo [1]. At that time, a silo technology was starting to be developed in North-America. Silos made of wood 3 m width and non- higher than 15 m started to be built. Later on J ANSSEN carried out experiments with wheat in four square cross-section (200, 300, 400 and 600 mm square side) bins made of wood [2]. In 1890 J AMIESON performed in Montreal, Canada, a series of experiments with wheat on full-scale silos. Jamieson used a silo of the Canadian Pacific Railway Elevator in West St John, New Burnswick [3]. The silo was timber crib construc- tion, 3.66 m by 4.11 m in cross-section and 20.6 m high. It was at that time when pressure cells were started to be used in silos [3,4,5]. Different types of pressure cells have been designed since then. They could be classified according to the design as pis- ton-type cells and plate-type cells with or without a fluid behind it [6]. 34 Bulk Solids & Powder – Science & Technology • Vol. 4 (2009) No. 1 Analysis of Measurements Obtained by Plate-type Pressure Cells Having a Recess - DEM Simulation A. Ramírez, P. Ansourian, J. Nielsen, K. Rasmussen and F. Ayuga * *A. Ramírez and F. Ayuga, BIPREE Research Group. Universidad Politécnica de Madrid. Ciudad Universitaria s/n, 28040 Madrid, Spain. Tel: +34 91 3365625; E-Mail: alvaro.ramirez@upm.es J. Nielsen, Aalborg University. Danish Building Research Institute. Dr. Neergaards Vej 15, 2970 Hørsholm, Denmark Tel. +45 9940 2264; Email: jn@sbi.dk P. Ansourian and K. Rasmussen, School of Civil Engineering JO5, The University of Sydney, NSW 2006, Australia Tel.: +61 2 9351 2125; E-mail: k.rasmussen@civil.usyd.edu.au Three full-scale steel silos were instrumented with plate-type normal pressure cells. Initial tests were carried out using wheat as stored material. During the mounting procedure of the cells was observed that local imperfections were introduced in the silo wall. The comparison between the Eurocode load model and the experimental results showed that overpressures were experimentally registered. The development of a sheared zone in the grain near to the plate of the pressure cell was initially assumed. A DEM (Discrete Element Method) analysis was performed to find out the effects that are having influence in these pressure measurements. A concentration of forces on the plate, as well as the presence of a sheared zone, was found to be responsible of those pressure measurements. Keywords: Silo, overpressures, DEM, local imperfections, wheat