Mamdouh El-Badry

Structural Deflection Measurement with a Range Camera

AbstractRange cameras offer great potential for the measurement of structural deformations because of their ability to directly measure video sequences of three-dimensional coordinates of entire surfaces, their compactness, and their relatively low cost compared with other active imaging technologies such as terrestrial laser scanners. Identified limitations of range cameras for high-precision metrology applications such as deformation measurement include the high (centimeter level) noise level and scene-dependent errors. This paper proposes models and methodologies to overcome these limitations and reports on the use of a SwissRanger SR4000 range camera for the measurement of deflections in concrete beams subjected to flexural load-testing. Results from three separate tests show that submillimeter precision and accuracy—assessed by comparison with estimates derived from terrestrial laser scanner data—can be achieved. The high-accuracy range camera results were realized by eliminating the systematic, scen...

Precise Photogrammetric Reconstruction Using Model-Based Image Fitting for 3D Beam Deformation Monitoring

Periodic structural health monitoring of infrastructure systems is important to avoid economic losses and human casualties. Traditionally, deformation monitoring has been done through surveying techniques. Recently, with the increased availability of inexpensive off-the-shelf cameras, photogrammetry has become a viable noncontact alternative for complete three-dimensional reconstruction of the object or surface of interest. This paper aims at combining two methodologies of photogrammetric reconstruction—image-matching-based reconstruction and model-based image fitting—to achieve submillimeter precision for the estimation of both vertical deflections and horizontal displacements. The proposed methodology was tested with data collected using a photogrammetric system at a structures laboratory where a concrete beam was subjected to different loading conditions by a hydraulic actuator. The experimental results showed that the photogrammetric system was capable of monitoring both static and dynamic deformations. The methodology used exhibited a high level of automation and the final results yielded a root-mean-square error (RMSE) of half a millimeter.

CONTROL OF THERMAL CRACKING OF CONCRETE STRUCTURES

Studies have proven that tensile stresses due to temperature can be high enough to produce cracking in concrete structures, and that thermal stresses are substantially alleviated when cracking occurs, causing a drop in stiffness. The authors review the Analysis of thermal stresses in statically determinate and indeterminate concrete structures and describe an analytical model for determining the effects of progressive reduction in stiffness as cracks form on thermal stresses and internal forces in continuous structures. Design criteria and equations are presented for determining the minimum amount of reinforcement necessary to control cracking due to temperature.

Control of cracking due to temperature in structural concrete reinforced with CFRP bars

The effects of thermal incompatibility of carbon fibre reinforced polymers (CFRP) and concrete on the behaviour of reinforced concrete members are investigated. Concrete beams reinforced with CFRP rebars are tested under the effects of temperature gradients while the rotations at the beam ends are prevented. The bending moments and cracking developed by the temperature gradients are monitored. The results are compared with those obtained from tests on beams of the same dimensions but reinforced with steel bars. Reduction of thermal moments due to progressive stiffness degradation with crack formation is investigated analytically and compared with the moment values recorded in the tests. The test series includes beams with variable amounts of CFRP reinforcement to study their effects on thermal moments and on crack widths and spacing. Design charts are presented for determining the minimum amount of CFRP reinforcement necessary for control of cracking due to temperature.

Vertical Dynamic Deflection Measurement in Concrete Beams with the Microsoft Kinect

The Microsoft Kinect is arguably the most popular RGB-D camera currently on the market, partially due to its low cost. It offers many advantages for the measurement of dynamic phenomena since it can directly measure three-dimensional coordinates of objects at video frame rate using a single sensor. This paper presents the results of an investigation into the development of a Microsoft Kinect-based system for measuring the deflection of reinforced concrete beams subjected to cyclic loads. New segmentation methods for object extraction from the Kinects depth imagery and vertical displacement reconstruction algorithms have been developed and implemented to reconstruct the time-dependent displacement of concrete beams tested in laboratory conditions. The results demonstrate that the amplitude and frequency of the vertical displacements can be reconstructed with submillimetre and milliHz-level precision and accuracy, respectively.

Deflection Control of Prestressed Box Girder Bridges

The models for prediction of creep in codes and design guides are mainly based on tests in which the load is sustained for a number of years, rarely exceeding 10; however, most models predict that creep reaches its extreme after approximately 30 years. An exception is the frequently accepted Model B3; it predicts indefinite increase of creep with the logarithm of the number of days of sustained loading. Analysis of deflection using Model B3 of a large number of bridges agrees with measured deflection in terms of magnitude and continued increasing tendency. Modern design requires satisfactory serviceability sustainable for a long life span. The absolute value of camber or deflection must not be excessive. This paper shows that by adopting Model B3, combined with appropriate prestressing, it is possible to satisfy this requirement for 125 years.

EXPERIMENTAL STUDY ON THERMAL CRACKING IN REINFORCED CONCRETE MEMBERS

Reinforced concrete beams, with and without prestressing, are subjected to thermal gradient while the rotations of the beam ends are prevented. The bending moments and the cracking developed by the temperature gradient are monitored. Alleviation of the thermal bending moments due to creep of concrete and due to progressive stiffness reduction with crack formation is studied analytically and compared with the moment values recorded in the experiments. The test series includes beams with variable amounts of non-prestressed and prestressed reinforcements to study their effects on the thermal moments, the crack widths, and the crack spacings. The experimental and the analytical research presented is intended to help structural designers in realistic prediction if the thermal bending moments and to give guidance on the amounts of the prestressed or the nonprestressed reinforcement required to control cracking.

Measurement of Deflection in Concrete Beams During Fatigue Loading Test Using the Microsoft Kinect 2.0

Abstract This study focuses on 3 Hz fatigue load testing of a reinforced concrete beam in laboratory conditions. Three-dimensional (3D) image time series of the beam’s top surface were captured with the Microsoft time-of-flight Kinect 2.0 sensor. To estimate the beam deflection, the imagery was first segmented to extract the top surface of the beam. The centre line was then modeled using third-order B-splines. The deflection of the beam as a function of time was estimated from the modeled centre line and, following past practice, also at several witness plates attached to the side of the beam. Subsequent correlation of the peak displacement with the applied loading cycles permitted estimation of fatigue in the beam. The accuracy of the deflections was evaluated by comparison with the measurements obtained using a Keyence LK-G407 laser displacement sensors. The results indicate that the deflections can be recovered with sub-millimetre accuracy using the centreline profile modelling method.

Alternative Reinforcing Details in Dapped Ends of Precast Concrete Bridge Girders : Experimental Investigation

The ends of precast girders often have a reduced depth over short lengths in the form of dapped ends. Girders with dapped ends normally are used in parking structures and pedestrian bridges. Because of the reduced depth at the girder ends, the shear stresses are high, and, therefore, the design of dapped ends requires special consideration. Dapped ends typically are reinforced with conventional stirrups and longitudinal reinforcing bars, which require hooks and bends and even welded plates to ensure sufficient anchorage. The efficiency of use of studs with single or double heads for reinforcing dapped ends is investigated. Strut-and-tie models are used to develop different layouts of the reinforcement. Two analytical methods based on the shear friction and diagonal bending theories are used to determine the location of the critical crack at failure and to examine the effectiveness of the reinforcement layouts. An experimental program is conducted on a series of dapped-end beams to corroborate the analytical study. The use of studs in dapped-end zones is shown to provide an efficient and reliable solution that prevents premature failure caused by inadequate anchorage of conventional reinforcement.

Evaluating the capability of time-of-flight cameras for accurately imaging a cyclically loaded beam

Time-of-flight cameras are used for diverse applications ranging from human-machine interfaces and gaming to robotics and earth topography. This paper aims at evaluating the capability of the Mesa Imaging SR4000 and the Microsoft Kinect 2.0 time-of-flight cameras for accurately imaging the top surface of a concrete beam subjected to fatigue loading in laboratory conditions. Whereas previous work has demonstrated the success of such sensors for measuring the response at point locations, the aim here is to measure the entire beam surface in support of the overall objective of evaluating the effectiveness of concrete beam reinforcement with steel fibre reinforced polymer sheets. After applying corrections for lens distortions to the data and differencing images over time to remove systematic errors due to internal scattering, the periodic deflections experienced by the beam have been estimated for the entire top surface of the beam and at witness plates attached. The results have been assessed by comparison with measurements from highly-accurate laser displacement transducers. This study concludes that both the Microsoft Kinect 2.0 and the Mesa Imaging SR4000s are capable of sensing a moving surface with sub-millimeter accuracy once the image distortions have been modeled and removed.