Influence of in-service environment on modal parameters

Current bridge inspection methods rely largely on visual examination to evaluate bridge condition. Remote bridge monitoring systems (RBMS) using measured structural vibration and calibrated analytical models are expected to assist in future bridge inspection and management. Establishing a baseline and determining sensitivity of measured modal properties is critical for these practical applications. Several tests were conducted over 9 months on an abandoned steel-stringer bridge with a concrete deck, under intact and simulated-damage conditions to examine the sensitivity of measured modal parameters with respect to variations resulting from test and in-service environmental conditions. Effects of environmental conditions in establishing baseline properties and detecting simulated damage were documented Results indicated that extreme care should be exercised in establishing baseline modal parameters for calibration of analytical models and damage detection algorithms. Bridges must be monitored for at least one full cycle of in-service/operating environment before establishing baselines for RBMS or finite element models. Boundary conditions are important and deserve special attention.