Measuring Ground Anchor Forces of a Quay Wall with Bragg Sensors

The use of optical fiber sensors for monitoring civil engineering structures is increasing continuously. One of the most frequently applied sensor types is the socalled Bragg sensor, which is primarily used to measure structural deformations. Due to some inherent advantages these sensors are ideally suited for long-term monitoring purposes. This paper describes the development of a load cell, based on Bragg sensors, to measure the forces in the ground anchors of a quay wall. After a short introduction on structural monitoring and the principles of a Bragg sensor, the concept of the load cell is discussed. Three ground anchors of a quay wall in Evergem, Belgium have been instrumented. After calibration in the laboratory, the load cells have been used to measure the prestressing forces imposed on the anchors. The results show that the developed instrumentation is very well suited for this purpose. For more than one year, the anchor forces have been monitored at regular points in time. This indicates a dependence of the anchor forces on environmental temperature variations.