Image analysis of the deformation behaviors of artificially damaged rc slab under moving wheel load

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Image analysis of the deformation behaviors of artificially damaged rc slab under moving wheel load

Takamasa Nagai, Takashi Matsumoto

Sapporo, Japan

Abstract

This study analyzes the deformation behaviors of artificially damaged RC slab under moving wheel load by using image analysis. First, moving wheel load test was conducted on an artificially damaged RC slab and pictures were captured at every 9000 cycles. Next, those pictures were analyzed by image analysis. Analytical results indicate that the slab develops the built-up-beam behaviors as the fatigue deterioration accumulates.

Keywords: RC slab, artificial damage, moving wheel load test, image analysis

Абстракт

Анализ деформационного поведения искусственно поврежденной плиты под нагрузкой движущегося колеса

Такамаса Нагай, Такаши Матсумото

Университет Хоккайдо, Саппоро, Япония

В этой статье исследуется поведение деформации искусственно поврежденной плиты RC под нагрузкой движущегося колеса, при помощи анализа изображений. Во-первых, испытание нагрузки на подвижное колесо было проведено на искусственно поврежденной плите RC, и снимки были сделаны при каждом из 9000 циклов. Затем эти фотографии были проанализированы. Аналитические результаты показывают, что деформация плиты развивает поведение нарастающих лучей по мере накопления усталостного износа.

Ключевые слова: железобетонная плита, искусственное повреждение, нагрузочное испытание движущегося колеса, анализ изображения.

Introduction

Recently, the combined deterioration of RC slab is a problem in Japan. That deterioration is caused by frost attack and repetitive loadings from heavy traffic. In cold snowy regions, horizontal cracks occurred in RC slab due to frost attack and those cracks affect fatigue deterioration processes. This paper discusses the deformation behaviors of artificially damaged RC slab under moving wheel load fatigue.

1. Moving wheel load test

The tested RC slab (hereinafter called Specimen D; D standing for dry condition.) has a span of 1112.5mm and measuring 1500mm in the longitudinal direction, 600mm in the transverse direction and 180mm in the thickness direction. The slab is reinforced with D19@150mm in the transverse direction and D19@260mm in the longitudinal direction on the top side. On the bottom side, it is reinforced with D19@150mm. Specimen D has horizontal artificial crack at 40mm from top surface by using horizontal agent (Figure 1).

Fig. 1. The cross section of Spacimen D

Moving wheel load test was executed on Specimen D and W (W standing for wet condition) until the damage reaches about 40mm from top surface. The load of 100kN was moved on the blocks that were 500mm in the longitudinal direction and 200mm in the transverse direction. The load was moved on these two specimens and moving length was 2000mm in the longitudinal direction. At every 9000 cycles, moving loading test was interrupted and static loading was applied on LP1, LP2 and LP3 (Figure 2) to take pictures for analysis. Finally, the test was ended after 45000 cycles of loading.

Fig. 2. Loading points and picture area

2. Image analysis

An image is converted to a grayscale image, and furthermore to a binary image. Measurement points for image correlation are set as follows. Figure 2 shows the area of image analysis where measurement points are allocated. Measurement points of 166 points in the horizontal direction and 35 points in the vertical direction are placed at the interval of 25 pixels. Mask image (128*128 pixels) is clipped out around a measurement point of the image which is captured before loading, and region image (256*700 pixels) is similarly clipped out from the image which is captured during loading. The rectangular region image takes a long side in the vertical displacement direction so as to include the displaced measurement point. A value outside the clipped region was set to 0 (black), and an image (700 * 700 pixels) including clipped image was created. The cross correlation is calculated for the two images of the measurement point before and after deformation, and the position with the maximum cross correlation value is regarded as the measurement point after deformation. The displacement vector can be obtained by the positions of the measurement point before and after deformation.

3. Analytical results

0 cycle loading. Figure 3 and Figure 4 show displacement map of 0 cycle loading. In X direction, focusing the right half part, the displacement value is not continuous near horizontal crack. Bending behavior is shown right half. However, the part above horizontal crack does not appear to be bended clearly. In Y direction, the continuous of displacement slightly exist. In addition, the maximum displacement area is different in upper and lower layer of horizontal crack. That area appears just below loading point in upper layer. About the lower layer, the maximum area appears at span center.

9000 cycles loading. Figure 5 and Figure 6 show displacement map of 9000 cycles. At this situation, the behavior of built-up-beam appears in right half of the slab. The value of displacement is not continuous near horizontal crack in X and Y direction. The gradual changing of displacement in X direction appear in the upper layer. This fact means the bending behavior appears in that layer. On the other hand, left half part of the slab shows negative bending behavior.

4. Discussions

The most important change from 0 cycle to 45000 cycles is the division of the slab due to horizontal crack. Horizontal crack gradually progresses by repetitive loading. This phenomenon is confirmed from the fact that the discontinuous displacement area extended from the right. After growing horizontal crack, the slab behavior has the feature of built-up-beam.

Conclusion

The deformation behaviors of artificially damaged RC slab under moving wheel load is investigated with image analysis. The results indicate that the slab shows the built-up-beam behaviors in the accumulation of fatigue deteriorations. Artificial crack progresses horizontally and the discontinuity of deformation appear near the crack. In X direction displacement map, the slab was divided due to horizontal crack in right half and bending behavior appeared in top part after 9000 cycles. In Y direction displacement map, the discontinuous displacement area appeared near the horizontal crack after 9000 cycles. In addition, the maximum displacement area was different between the upper layer and lower layer. In the upper layer, the maximum displacement area appears just below the loading point. On the other hand, in the lower layer, the maximum displacement area appears at the center of span. This supports the fact that the slab has built-up-beam behavior and the deformation behavior is different between the upper layer and lower layer.

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