IMAGE-BASED DEFORMATION MONITORING OF STATICALLY AND DYNAMICALLY LOADED BEAMS
I. Detchev
a,
, A. Habib
a
, M. El-Badry
b a
Department of Geomatics Engineering
b
Department of Civil Engineering University of Calgary, 2500 University Drive NW,
Calgary, Alberta, T2N 1N4 Canada - i.detchev, ahabib, melbadryucalgary.ca
Commission I, WG I3
KEY WORDS: close range, digital, photogrammetry, camera, image, acquisition, three-dimensional, precision, reconstruction ABSTRACT:
Structural health monitoring of civil infrastructure systems is an important procedure in terms of both safety and serviceability. Traditionally, large structures have been monitored using surveying techniques, while fine-scale monitoring of structural components
has been done with instrumentation for civil engineering purposes. As a remote sensing technique, photogrammetry does not need any contact with the object being monitored, and this can be a great advantage when it comes to the deformation monitoring of
inaccessible structures. The paper shows a low-cost setup of multiple off-the-shelf digital cameras and projectors used for three- dimensional photogrammetric reconstruction for the purpose of deformation monitoring of structural elements. This
photogrammetric system setup was used in an experiment, where a concrete beam was being deformed by a hydraulic actuator. Both static and dynamic loading conditions were tested. The system did not require any physical targets other than to establish the relative
orientation between the involved cameras. The experiment proved that it was possible to detect sub-millimetre level deflections given the used equipment and the geometry of the setup.
Corresponding author.
1. INTRODUCTION
Deformation monitoring of civil infrastructure systems, or structural health monitoring in general, is an important
procedure in terms of both the public safety and the serviceability of the structure. In order to avoid potential
structural failure, the maximum loading capacity of the system must be known before its completion, and regularly scheduled
maintenance checks must be performed after its completion Park
et al.
, 2007. Traditionally, large structures have been monitored using surveying techniques Ebeling
et al.
, 2011; González-Aguilera
et al.
, 2008, while fine-scale monitoring of smaller
structural components
has been
done with
instrumentation for civil engineering purposes such as strain gauges as explained in González-Aguilera
et al.
, 2008; Maas and Hampel, 2006. Both methods have two downsides
– deformation could only be detected at specific point locations,
and in the case of failure during the time of monitoring, the area around the object of interest can become hazardous. Thus, this
paper will explore the remote sensing technique of photogrammetry for the purpose of fine-scale deformation
monitoring of concrete beams.
2. PREVIOUS RESEARCH
As a remote sensing technique, photogrammetry can provide high-precision non-contact measurements of objects or
surfaces of interest with no risk of injury to the operators or damage to the equipment used. Here are some examples from
the photogrammetric literature: Mills
et al.
2001 used a single small format digital camera attached to a moving crane in order to map a
test bed in a pavement rolling facility. Given the used geometry, the experiment resembled near vertical
airborne mapping. Despite the undesirable base-to- height ratio, the overall reconstruction root mean
square error RMSE for the performed experiments was about 2-3 mm;
Fraser and Riedel 2000 performed near real-time multi-epoch deformation monitoring of heated steel
beams while cooling off in a thermal test facility. Three digital cameras positioned at convergent
geometry, and specially designed targets for a such high temperature environment were used to obtain a
final precision for the reconstructed object space coordinates of 1 mm;
Jáuregui
et al.
2003 used double sided targets and measured deflections in steel beams at an RMSE of
0.5-1.3 mm in an indoor laboratory. In addition, they also managed to measure the vertical deflections in
bridge girders on a highway at an RMSE of 0.5-1.5 mm;
Lin
et al.
2008 monitored the deformations of membrane roofs with a precision of 1.3-1.6 mm. Their
system consisted of two machine vision cameras and one data projector, and it could operate without the
use of traditional signalized targets. They achieved targetless relative orientation by defining the scale
XXII ISPRS Congress, 25 August – 01 September 2012, Melbourne, Australia
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through imaging the footprint of a reflectorless total station. Also, they managed to generate a point cloud
without any physical targets by the means of projecting a pattern onto the surface of interest during
the data collection. As stated in their article, the precision could have been significantly improved if
more cameras were available.
The next sections of this paper show how a low-cost photogrammetric setup can be used for precise three
dimensional 3D objectsurface reconstruction, which could be useful for the deformation monitoring of structural elements in
both static and dynamic loading conditions.
3. PROPOSED METHODOLOGY
