Evaluation of Different Monitoring Techniques During Damage Infliction on Structures

This paper presents a case study of a post-tensioned reinforced concrete bridge built in the 1970s which underwent a two month monitoring period prior to its demolition. The 62 m long two-lane bridge was to be replaced by a newer construction designed for higher traffic loads and was thus available for in-situ trials once it had been closed to traffic. The monitoring started in February 2016 to observe the three-span structure in its original state when excited by ambient and vehicle-induced vibrations. Initial construction works around the sloping abutment and the pier foundations, such as pile driving and extension of the embankment, started at the end of March, followed by the closure to traffic and the removal of the asphalt pavement. Over the next few weeks, the bridge saw three damage scenarios induced in the following order: 1. Six out of sixteen tension cables were severed above one of the piers; 2. Expansive mortar was filled into boreholes in the deck; 3. Expansive mortar was filled into boreholes in one of the piers to induce cracking. The bridge was equipped with accelerometers, inclination sensors and fibre-optic strain gauges that continuously monitored the structures condition. For safety reasons, the sensors in direct vicinity of the damage points were gradually moved to other parts of the bridge or dismantled completely in the course of the damage infliction. The aim of the monitoring was to assess the detectability of the structural weakening using a variety of measurement techniques and to see what role data quality, sensor positioning and auxiliary information plays in reliably diagnosing the extent of the damage or defining an alarm level. Different ways of post-processing the data were examined to see what information can be gained without having to create a numerical model of the structure when insufficient design documents are available. (c) 2017 The Authors. Published by Elsevier Ltd.