Laboratory Testing: RPC Concrete beam

Case study: SOFO System

Prestressed high performance concrete beam
Deformation monitoring during cure
Cracking monitoring during testing

Project Description

Summary: Reactive Powder concrete beam, Concrete monitoring during setting, neutral axis / curvature evaluation during load tests, crack monitoring

Clients: IMM SA / Passera & Pedretti SA

Place: Lugano (Switzerland)

Period: 1996 - N/A

Installation: IMAC - EPFL

Structure's short description: This beam is made of BPR (reactive powder concrete), an extremely high performance concrete without reinforcement bars. The beam is 6 m long and is prestressed in the longitudinal direction. It was cured at 90?;C for one week.

Aim of monitoring: Eighteen 1 m long SOFO sensors were installed in the beam to analyze its local curvature under four-points bending, to evaluate the position of the neutral axis and to calculate its vertical displacements.

Number of sensor: 18

Main Results: The sensors were connected in chains and the whole beam could be monitored with just a few measurements. The mean curvature was analyzed in each of the six 1 m long sections by measuring the deformation near the top and near the bottom of the beam. The variations in the shape of the curvature function and in the position of the neutral axis, allowed the early detection of cracks at charge levels much lower then those producing visible cracks. By double integration of the curvature function and taking into account the boundary conditions, it was possible to retrieve the vertical displacement of the beam. The figure shows a comparison between the displacements calculated from the SOFO data and those obtained by dial gauges placed under the beam. Excellent agreement is found even for loads far exceeding the elastic domain.

Measured vertical displacement compared with direct measurement by dial gauge

Bibliography:

Mathematical model for the determination of the vertical displacement from internal horizontal measurements of a bridge , S. Vurpillot, D. Inaudi, A. Scano, SPIE, Smart Structures and materials, San Diego, USA, Vol 2719, p 46-53, 1996

Development and laboratory tests of deformation fiber optic sensors for civil engineering applications, L. Vuillet, N. Casanova, D. Inaudi, A. Osa-Wyser, S. Vurpillot, SPIE, International Symposium on Lasers, Optics and Vision for Productivity in Manufacturing, Besan?n, France, Vol 2782, p 97-108, 1996