Experimental Study On Damage Detection Of Steel-Concrete Composite Beam Based On PZT

The development of smart materials has provided new selections for long-termreal-time health monitoring of civil engineering structures. Especially, a need todevelop in-service and on-line health monitoring technique is increasing. This kind oftechnique allows systems and structures to monitor their own structural integritywhile in operation and throughout their life. Damage identification techniques basedon wave propagation utilizing PZT based multi-function element are commonlyadopted because they are non-invasive and efficient.In this dissertation, experiments on the damage detection of artificial degradationof connectors in a steel-concrete beam and the detection of cracks in concrete slab andinterface damage under static loading were carried out by using PZT based functionelements. The main contents of this paper are as follows:1. The motivation and background of the SHM were summarized briefly, and sodid the various system identification and damage detection methodologies. Thenemphasis was given on the description of the researches on the PZT-based SHMtechniques. In the end of this chapter, steel-concrete composite beam was introduced.And the significance of the damage detection of steel-concrete composite beam wasdiscussed.2. Chapter Two introduced the basic characteristics of piezoelectric materials,thepiezoelectric constitutive equations and the basic material parameters, described thefabrication procedure of the PZT-based transducer, the technology of implantingfunctional elements into concrete as well as the equipments which were employed tomeasure the signal. Finally, a calibration in water was carried out to probe the basicoperating properties of the transducers.3. The stress wave propagation and attenuation properties in concrete are criticalfor the understanding of the PZT based damage detection approaches. In this study,experimental study on the stress wave propagation and attenuation behaviors inconcrete was carried out by the use of embedded PZT-based multi-functional elements,which acted as both actuator and sensor. The PZT-based multi-functional elementswere embedded in a plain concrete plate and a reinforced concrete beam. The resultsshowed that:(1) the functional elements embedded in concrete kept linearapproximately and (2) the relationship between the amplitude of the received signals and the excitation frequency presented an exponential attenuation form. An overallattenuation coefficient was fitted. And the fitting results were adopted as damageindex in following chapters.4. A scaled steel-concrete composite beam with removable bolt connectors wasdesigned and constructed in the lab. A number of bolt connectors were employed toconnect the flange of the steel beam and the concrete slab and can be easilyunscrewed for the purpose of artificial damage. Different damage scenarios weremimicked by loosening some of the connectors. Then a in-situ static loadingexperiment was carried out for PZT based damage detection. The wavelet packetenergy based analysis method and its basic principles were introduced and employedin the last two chapters. After signal processing, it was found that the wavelet packetenergy based damage index had detected the damage severities effectively.