Sumitomo Mitsui Construction Co., Ltd., (hereinafter “Sumitomo Mitsui Construction”) has developed an automatic inspection measurement system for as-built structures with the FARO FocusS 350 Laser Scanner for inspection measurements of the end section of concrete bridges under construction and for point cloud data-based inspection of bridge girder dimensions. As a result, the measurement time per profile has been significantly reduced by approximately half as compared to previous measurements. The following introduces Sumitomo Mitsui Construction’s method of work execution management that takes advantage of the merits of the compact, lightweight FocusS 350.
“Now we can automatically create as-built profile drawings and reports of bridge girders just by loading point cloud data of bridge girder end faces measured with the FocusS 350,” says Mr. Taisuke Fujioka, the section chief of the Civil Structural Engineering Group, Structural Engineering Service Department, and Technical & Engineering Service Division of Sumitomo Mitsui Construction.
In the construction of prestressed concrete bridges (PC bridges), which is one of Sumitomo Mitsui Construction’s specialties, a construction method known as the balanced cantilever method is often used to extend bridge girders from each end of the pier supporting the bridge.
Bridge girder erection work is performed in blocks with each normally 3 to 5 meters long by operating a form traveler to cast concrete. The bridge girder thickness gradually decreases with the distance from the pier. Hence, “as-built management” is important, wherein measurements are taken block-by-block to ensure that the cross-sectional geometry matches the design.
“Conventionally, two measuring persons, a photographing person, a recording person, and an inspector worked on a team of five people to measure the dimensions of each block using a measuring tape. This method required approximately 45 minutes of man-hours per profile. Our newly developed system has reduced on-site measurement time by as much as 20 minutes of man-hours per profile,” says Mr. Taketoshi Mizuta, the section chief of the ICT/CIM Promotion Group, Civil Engineering Administration Department, Civil Engineering Division of Sumitomo Mitsui Construction.
(Left) Geometry of a bridge girder end face to be measured
(Right) Concrete bridge under construction by the overhang erection method.
Measurement of a bridge girder end face takes place after removal of the end-face formwork from the hardened cast concrete.
The FARO® FocusS 350 is mounted sequentially at four locations in front of the bridge girder at the upper left, lower left and right sides, and point cloud measurements will be made on the end face of the bridge girder block. The challenge here is how to take measurements from the top left and right corners. With the scanner mounted on a conventional tripod, the bottom section of the bridge girder will fall into the blind area.
FocusS 350 during point cloud measurement of the bridge girder end face visible on the far side. Mounted sideways to prevent any blind area from occurring during measurement.
“Then, we hit on the idea of taking measurements with the FocusS 350’s axis turned sideways by 90 degrees. With the gravity sensor switched off, the FocusS 350 allows us to take measurements easily even in a sideways position. This is something only possible with the compact, lightweight FocusS 350,” explains Ms. Rei Takaoka, a senior staff member of the Civil Structural Engineering Group, Structural Engineering Service Department, and Technical & Engineering Service Division of Sumitomo Mitsui Construction.
Install FocusS 350 at the upper and lower 1 to 4 locations on the front of the bridge girder to perform point cloud measurement.
Point cloud measurement from the top of the bridge girder. FocusS 350 is mounted sideways and target spheres set-up to merge point clouds.
Point cloud measurement from the top of the bridge girder. FocusS 350 mounted on a conventional tripod for measurement.
Even if mounted in a difficult-to-access corner, FocusS 350 can be operated remotely from a tablet terminal.
Measured and merged point cloud data.
For use as datums for merging point cloud measurements from four spots into one, target spheres are installed on several spots on the surrounding a bridge girder. To perform scanning at an optimal angle, the FocusS 350 must be mounted sideways on the top section of the traveler’s member. Even where there is no nearby scaffolding available, the scanner can be safely operated via remote access from a tablet terminal.
The reason Sumitomo Mitsui Construction selected the FARO FocusS 350 from among numerous 3D laser scanners is explained by Ms. Takaoka as follows: “The 3D laser scanner we used before was so bulky and heavy it could not be switched back and forth from the vertical to horizontal positions in a narrow space. Conversely, the FocusS 350 is compact, lightweight, and reasonably priced and hence provides a tool easy to use on-site. Another reason for its selection is that while being able to measure up to a distance of 350 meters ahead, it achieves a high measuring precision of ±2 mm at a distance of 10 meters.”
After point cloud acquisition, what matters in achieving the objective is point cloud data processing through a software. To process and convert point cloud measurement data into drawings, Sumitomo Mitsui Construction uses InfiPoints, Elysium Co., Ltd.’s software for large-scale point cloud processing. This software features flexible easy-to-use functions, such as seamless interfacing with building information modeling (BIM) or construction information modeling (CIM) software or automatic external calling and running of specific processes, in addition to high-speed, high-accuracy automatic merging of multiple point cloud data.
In as-built management of a bridge girder, the vertices and edges of the bridge girder end face are used as datums for length measurement. Hence, Sumitomo Mitsui Construction has developed SMC-Smart Measure™ as an optional add-on for InfiPoints that enables length measurements based on point cloud data obtained with a laser scanner.
InfiPoints has a function for automatically recognizing planes and other elements from point cloud data and automatically converting them into 3D models of surfaces. With this function, bridge girder end faces can be turned into shape of models that can be processed on a purpose-developed program for automatic determination of intersection point coordinates on surfaces or point-to-point distances.
A software developer kit (SDK) is publicly available for developing apps compatible with the FARO® FocusS series 3D laser scanners, including the FocusS 350; thus, users can easily develop their own apps.
The SMC-Smart Measure™ functionality for extracting the contour lines of bridge girders from point cloud data for automatic calculation of distances to specified points.
Automatic documentation up to report creation based on loaded point cloud data.
Among other methods of point cloud data acquisition are solutions that analyze and generate images stereoscopically photographed with digital cameras.
“As in the current case, however, where there are many obstacles protruding from a bridge girder end face, such as numerous rebars or sheaths for passing prestressing steels through, photographic measurement would require several hundreds of photographs. With a 3D laser scanner such as the FocusS 350, we only have to take measurements at several spots for one-time acquisition of a large amount of high-accuracy point cloud data,” says Mr. Mizuta regarding the advantages of 3D laser scanners. He tells future prospects as follows: “Point cloud data acquisition from on-site measurements taken with 3D laser scanners allows us to archive information about bridge girders, such as the number of rebars or geometries of recessed portions, thereby providing the advantage of post checking of various as-built portions. In the near future, we may even be able to further reform working practices, say, by performing witnessed inspections through viewing of point cloud data on-site via virtual reality goggles.”
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