System for In-Service Strain Monitoring of Ordinary Bridges

Abstract

An in-service bridge monitoring system (ISBMS) has been developed to provide near real-time web-based monitoring of live load strains in a bridge. The monitoring system is small, battery operated, can be rapidly deployed, and is programmed and interrogated via a user-friendly web interface. The ISBMS has been designed to be portable and used on an “as-needed” basis as a diagnostic tool or for health monitoring of ordinary bridges. The system is based on a small single-board computer with analog inputs; it also includes a cellular digital packet data modem for communication via the existing cellular network. Strains are measured using either a full bridge strain transducer or a quarter bridge foil strain gauge. The system has three modes of operation; The peaks program records peak live load strains that exceed a specified threshold, the time history program captures dynamic waveforms that exceed a specified threshold, and the rainflow program counts varying amplitude strain cycles. The selection and setup of the program, and retrieval of data is handled through a custom designed web interface. The system has been tested in the laboratory and in the field on a heavily traveled steel girder bridge. The data obtained from the ISBMS can be used for load rating using site specific data, fatigue investigations, monitoring bridge performance under permit loads, and as part of the biannual inspection of ordinary bridge.