Laboratory Testing: Expo02 Membranes

Case study: SOFO System

Membrane sensor
Membrane monitoring
Plastic material
Laboratory test

Project Description

Summary: Deformations of plastic membranes for large roofing

Clients: Expo, 02

Place: Grancia (Switzerland)

Period: 1998 - N/A

Installation: IMM SA / IMAC-EPFL

Structure's short description: Civil engineering is no longer the kingdom of traditional building materials (stone, concrete, steel and timber). Many new building materials have been introduced and allow the construction of radically new types of structures. That was the case with large exhibition structure proposed for famous Swiss exposition ?Expo 02?. Thin plastic membrane was a choice to cover this large exhibition spaces, but mechanical behavior of such materials presented and still presents a few uncertainties. The design, maintenance and safety of these structures call for a permanent monitoring. In the literature, we did not find any reference to sensors developed in order to monitor the deformation of plastic materials in-situ. That?s why a new, Membrane sensor is developed and laboratory tested on thin plastic membrane.

Aim of monitoring: In order to prove the adequacy of the new sensor to measure the deformation of thin plastic membranes, the load test was performed. Two Membrane sensors were fabricated and tested. The length of active zones of the sensors was 1 m and 0.5 m, respectively. Both sensors are glued to a thin plastic membrane using thermal-activated glue, and the membrane was loaded by means of a hydraulic jack. Membrane sensor before the gluing is presented in Figure 1. The longer sensor was positioned on the reinforcing Kevlar band and the shorter one was placed across the reinforcing bands, but its anchor plaques were glued over the bands. The sensors were installed on reinforcing bands to avoid creep effects of membrane and because the bands determine the capacity and deformed shape of a membrane structure. The emplacement of the sensors and the membrane loaded by hydraulic jack are shown in Figures 2.

Number of sensor: 2

Main Results: The membrane was put in a stiff frame and pre-stressed in the horizontal plane. This set-up is shown in Figure 2. Vertical displacement was imposed step by step in the middle of the membrane by means of hydraulic jack (see Figure 2). Afterwards, the imposed displacement was removed, also step by step. The Membrane sensors were read after each step. The results of these measurements are represented in Figure 3. Results showed an excellent accuracy of the sensors and have proven the suitability of the Membrane sensor for such kind of monitoring.

Membrane Sensor before gluing and gluing set-up

View to membrane during the test and sensors emplacement

Bibliography:

Special sensors for deformation measurements of different construction materials and structures , B. Glisic, D. Inaudi, P. Kronenberg, S. Lloret, S. Vurpillot , SPIE, 6th International Symposium on Smart Structures and Materials, Newport Beach, USA, Vol 3670, p 505-513, 1999

Packaging interferometric sensors for civil structural monitoring , D. Inaudi, B. Glisic, S. Vurpillot, SPIE, OFS-13, 13th International Conference on Optical Fiber Sensors, Kyongju, Korea, Vol 3746, p 120-123, 1999

Cloth sensor: Transfer of deformation from assembled plastic bands to the measurement fibre, B. Glisic, D. Inaudi, E. Kessi, IMAC - DGC - EPFL, Lausanne, Switzerland, P 1-1, Appendix 1-5, 1997