Affiliations: Fraunhofer Institute for Structural Durability and
System Reliability LBF, Darmstadt, Germany
Note: [] Corresponding author: H. Buff, Fraunhofer Institute for
Structural Durability and System Reliability LBF, Bartningstraße 47,
64289 Darmstadt, Germany. E-mail: hendrik.buff@lbf.fraunhofer.de
Abstract: Structural Health Monitoring (SHM) has reached a high importance in
numerous fields of civil and mechanical engineering. Promising damage detection
approaches like the Damage Index Method, Gapped Smoothing Technique and Modal
Strain Energy Method require the structure's mode shapes [1]. Long term modal data acquisition on real life structures requires a
computational efficient system based on a measuring method that can easily be
installed. Systems using the Random Decrement Method (RDM) are composed of a
decentralized network of smart acceleration sensors applied for both,
triggering and pure measuring. They allow the reduction of cabling effort and
computational costs to a minimum. In order to design a RDM measuring network efficiently, an approved
procedure for defining hardware as well as measuring settings is required. In
addition, optimal sensor positions have to be defined. However, today those
decisions are mostly based on expert's knowledge. In this paper a systematic
and analytical procedure for defining the hardware requirements and measuring
settings as well as optimal sensor positions is presented. The proposed routine
uses the outcome of an Experimental Modal Analysis (EMA). Due to different requirements for triggering and non-triggering
sensors in the RDM network a combination of two approaches for sensor placement
has to be used in order to find the best distribution of measurement points
over the structure. A controllability based technique is used for placing triggering
sensors, whereas the Effective Independence (EI) is utilized for the placement
of non-triggering sensors. The combination of these two techniques selects the best set of
measuring points for a given number of sensors out of all possible sensor
positions. Damage detection itself is not considered within the scope of this
paper.
Keywords: Structural health monitoring, test planning, effective independence
