High speed image techniques for construction safety net monitoring in outdoor conditions

Abstract

The behaviour of a construction safety net and its supporting structure was monitored with a high speed camera and image processing techniques. A 75 kg cylinder was used to simulate a falling human body from the upstairs floor of a building under construction. The cylinder rolled down over a ramp until it reaches the net. The behaviour of the net and its supporting structure was analysed through the movement of the cylinder once it reaches the net. The impact was captured from a lateral side with a high speed camera working at 512 frames per second. In order to obtain the cylinder position each frame of the sequence was binarized. Through morphological image processing the contour of the cylinder was isolated from the background and with a Hough transform the presence of the circle was detected. With this, forces and accelerations applying on the net and the supporting structure have been described, together with the trajectory of the cylinder. All the experiment has been done in a real structure in outdoors location. Difficulties found in the preparation of the experiment and in extracting the final cylinder contour are described and some recommendations are giving for future implementations.