China Scholarship Council

PhD position in Structural Dynamics and Retrofitting

 

RESEARCH

Within the Department of Structural Mechanics and Industrial Buildings from the Technical University of Madrid a strong and successful research has been carried out in the last years in the topics of Structural Health Monitoring and Retrofitting giving rise to high ranked international publications. Within this research, we have hosted some chinese students for the last four years, one of them got the PhD Degree recently. All our PhD candidates and master students follow the Programme in ‘Seismic Engineering and Structural Dynamics’ offered in the ETSII-UPM. After its completion (60 ECTS including a Master Thesis), the student will get the degree of Master, and will be prepared to continue his/her research in order to obtain the PhD.


Structural Health Monitoring

The process of implementing a damage identification strategy for aerospace, civil and mechanical engineering infrastructure is referred to as structural health monitoring (SHM). Structural health monitoring provides the methodology that evaluates the condition of a structure for a given point in time. The implementation of a process of SHM is critical application for determining and evaluating the serviceability of the structure, the reliability and the remaining functionality of the structure. The increased interest in SHM and its associated potential for significant life-safety and economic benefits has motivated a rapid increase in the amount of research related to SHM in the past 10 years.
To date, SHM technology has been successfully applied for condition monitoring of rotating machines and it plays an important role in industrial applications. The need to decrease the downtime on production machinery and to increase reliability against possible failures has attracted interest in the online condition monitoring of these systems in recent years. The main purpose of the diagnosis is to analyse the relevant external information in order to judge the condition of the inaccessible internal components so as to decide if the machine needs to be dismantled or not. Although acoustic signal analysis is quite common for the detection of faults in geared systems, vibration-based diagnosis has been more widely used. The identification process is based on pattern recognition applied to displacement, velocity or acceleration time histories (or spectra) generally measured at point on the housing or shafts of the machinery during normal operating conditions and start-up or shutdown transients.
The deterioration and functional deficiencies of civil infrastructure caused by aging, weathering of materials (i.e. corrosion of steel), accidental damage (i.e. natural disasters), and increased traffic and industrial needs as exhibited by the need for higher load ratings of structures are evident. Poor engineering judgement, inadequate design and changes in code requirements are other factors contributing to deficiencies at any time during the service life of the structure. As a sample of the magnitude of the problem in case of considering bridges, according to the U.S: national inventory of bridges, more than 40% of the 650000 highway bridges are structurally deficient or functionally obsolete. Rehabilitation and replacement cost average US $7 billion annually. The condition of approximately 101000 railroad bridges and a comparable number of pedestrian bridges also must be evaluated. In Canada there are approximately 30000 deficient bridges from which between 150 and 200 spans collapse each year. Related to Europe, taking into account that a huge peak of bridge construction happened in the 1970s and that the critical age where rehabilitation and retrofit works at bridges becomes critical starts after 30 years, an enormous maintenance and rehabilitation effort is coming towards the road and bridge authorities. Regardless of root cause, functional deficiencies are present in civil infrastructure, and solutions to monitor and resolve these deficiencies are necessary. Vibration-based damage assessment of bridge structures and buildings is growing more and more in the last years. An increasing number of research studies have been carried out in the topics above. Technical challenges to develop in the future include:

  • Identification of the features sensitive to small damage levels
  • Ability to discriminate changes in these features caused by damage from those caused by changing environmental and/or test conditions
  • Development of statistical methods to discriminate features from undamaged and damaged structures
  • Development of methods to optimally define the number and location of the sensors
  • Implementation of smart structures
  • Use of new sensors such as PZT and Bragg grating-based fibre optic sensors
  • Performance of comparative studies of different damage identification methods.

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Retrofitting

Advanced composite materials are increasingly used in the strengthening of reinforced concrete (RC) structures. The use of externally bonded strips made of fiber-reinforced plastics (FRP) as strengthening method has gained widespread acceptance in recent years since it has many advantages over the traditional techniques, especially because of the high strength and modulus of elasticity, improved durability, and low weight of the composite material. FRP plates may be prefabricated or constructed on site in a wet lay-up process.
Although FRPs have been widely used for column strengthening by external wrapping, flexural and shear FRP externally bonded reinforcement (FRP EBR) to RC beams, constitute the larger body of current applications.
As a result of their growing application, some code proposals or recommendations have been published in different countries or continents for the design of reinforced concrete (RC) structures reinforced or strengthened with FRP.
However, there are several issues which remain unresolved during detailed design of such schemes. The following challenges should be considered in the future:

  • Transparency of failure mechanisms and checks
  • Safety factors
  • Behaviour under extreme loading (including impact, blast and vandalism)
  • Near-surface mounted (NSM) reinforcement
  • Prestressed FRP
  • Strengthening under live load
  • Anchorage
  • Redistribution of bending moments
  • Rectangular wrapped columns
  • Size effect in shear strengthening
  • Implementation of non-destructive methods to detect hidden disbonds between the composite and the concrete structure

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CONTACT

Ricardo Perera, Tel: 34-913363278, Fax: 34-913363004, E-mail: perera@etsii.upm.es

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