Bridge Damage Detection Through Combined Quasi-static Influence Lines and Weigh-in-motion Devices

This paper addresses a new damage detection method for simply supported and continuous bridge structures based on combined influence lines for deflections and rotations and weigh-in-motion devices. The real structural behaviour of the superstructure is captured by sensors that measure vertical displacements at midspans and rotations at each support. Information on speed and weight of vehicles in transit are provided by weigh-in-motion devices placed at the beginning and at the end of the bridge. An optimization technique based on genetic algorithm and developed in a Matlab environment identifies the flexural stiffness distribution that best fits the experimental data. The comparison between the identified flexural stiffness distribution and the nominal one, or that obtained by previous identification, allows to verify the existence and the position of single or multiple damages. The capabilities of the proposed method was proved by means of three numerical simulations on a simply supported prestressed concrete I-beam bridge, on a three-span continuous prestressed concrete box bridge and on a four-span continuous steel-concrete composite bridges. Moving loads were considered to generate synthetic displacement and rotational distributions for different load positions. Changes in the flexural stiffness as small as 20% for finite elements with a length of 0.5 m or 10% for finite elements with a length of 2.0 m were successfully identified with a root-mean-square-error of less than 2.72%. The simulations produced evidence of benefits, in terms of damage identification, provided by the combined use of different types of influence lines with the maximum error in the stiffness identification that reduced from 3.40 to 2.64%.