A feasibility study of building monitoring and forensic engineering with Interferometric Synthetic Aperture Radar

A feasibility study of building monitoring and forensic engineering with Interferometric Synthetic Aperture Radar

Van Waning, H.W.

Hanssen, R.F. (mentor)
Terwel, K.C. (mentor)
Hordijk, D.A. (mentor)

Civil Engineering and Geosciences

Structural Engineering

Structural Design

2014-10-30

The last years have seen a few severe cases of structural damage to buildings in the Netherlands. A recent case was the shopping mall ‘t Loon in Heerlen. It would be beneficial if structural failures could be avoided, or at least be predicted. New satellite technology, Interferometric Synthetic Aperture Radar (InSAR), proves that it is possible to detect structural deformation in buildings at the level of millimeters and to receive weekly updates. TU Delft has shown that for the Heerlen case, the deformation could already be detected years before the collapse. The InSAR data was also used for forensic research at Heerlen. The previously discussed developments resulted in the main research question of this thesis: How can InSAR data contribute to forensic engineering and building monitoring in general? The objective is to determine in which cases data provided by radar interferometry can be used, and how this data should be interpreted for building monitoring and forensic engineering. A literature review is conducted to identify the general properties and limitations of InSAR. To research the potential contribution to forensic engineering, an analysis of a damage database is made to determine InSAR’s potential as a forensic engineering tool. The database is assessed according to the guiding principles of forensic engineering using InSAR as laid out by this thesis: opportunistic character, large deformations and no sudden deformations. A research methodology for forensic engineering with InSAR is proposed and tested with a couple of case studies. Building monitoring is subdivided into object-driven building monitoring and data-driven building monitoring. Conventional building monitoring techniques are analysed to research the potential of InSAR as a building monitoring tool. To research object-driven building monitoring, a literature study is conducted to examine the different variables that cause building movement that influence the InSAR data. One dominant variable is analysed to research the relation between a variable and the InSAR data. To research data-driven buildings monitoring, general building limits for deformations are discussed. InSAR data of Delft, provided by the TerraSAR-x satellite, is used to analyse the potential of InSAR as a data-driven building monitoring tool. Deformation areas with very high deformation rates are examined to find out how to work with InSAR as a data-driven building monitoring tool. ? The development of the movements caused by torsion, inelastic deformation, fracture, second order effects and buckling are hard to detect with InSAR. Deformation caused by failure needs to be visible on the outer shell of the structure. Damage on the outer shell is visible to InSAR, as are damages that influence the supporting structure of the building. Deformations of the supporting structure can be damped in the outer shell; this is caused by the structural integrity. One fifth of the damage cases of the damage database have potential to be researched with InSAR. Only failures caused by aging and structural errors were suitable for research. Deformation measurements for buildings is one of the building monitoring fields in which InSAR can compete. Competitors in this field are Lidar, photogrammetry, levelling, and tachymetry. One of the main advantages of monitoring with InSAR is that large areas can be monitored with one measurement, and no one needs to be present at the site. Object-driven monitoring of buildings can be done by monitoring a building and identifying explanations for building movements. The movement of a Persistent Scatter point (PS-point) is caused by forces that work on a building and by the resistance of the building. Forces that do not change over time will not make the building move, unless there is degradation of the building elements. InSAR measurements are most suitable for vertical deflection monitoring because of the sensitivity of the satellite measurements. Factors that are suitable to monitor with InSAR are temperature, settlement and groundwater change. Data-driven monitoring is most suitable for monitoring foundation problems. The movements are often gradual over time, and large deformations limits are allowed. Attention should be paid to the translation of the top structure of the movement. Movements of 3 mm/year of a PS-point in vertical direction, or 1.5 mm/year relative to another PS-point on a building, are alarming. InSAR can become an addition to conventional monitoring techniques for building research. For forensic engineering InSAR can indicate which parts of building elements were influenced by the failure, and when deformation started to develop. InSAR can support evidence for the possible cause of the failure, when the failure is expressed in deformation. For building monitoring InSAR may support the indication of the development of deformation that may cause damage. The monitoring of vertical deformations is limited by the sensitivity and the phase ambiguity. These boundaries make InSAR most suitable for monitoring gradual deformations, often found in deformations of foundations.

InSAR
monitoring
deformation monitoring
building failure
structural failure
forensic
deformation

http://resolver.tudelft.nl/uuid:89d652f8-39c1-4100-86a8-2c975e02ab5d

Student theses

master thesis

(c) 2014 Van Waning, H.W.