Laser scanning and masonry construction may seem like an odd combination. Laser scanning is a relatively new technology (less than ten years) while masonry has been around for centuries; however, scanning and masonry construction are in reality a natural combination.
While laser scanning can be used to verify new building tolerances, the real advantage is realized for existing construction. Older buildings suffer the effects of time, especially in freeze/thaw climates, unstable soils, or seismic areas. Eventually, masonry construction cracks, moves, or bulges. Masonry walls in this condition can suddenly topple to the street below, possibly with deadly effects.
In addition, masonry modifications, repairs, or other changes may not be reflected in the original design documents. Laser scanning records all movements as well as modifications.
Laser scanning consists of three main components: scanner, software, and computer. The scanner produces a laser beam of pulsed or phase shift energy from the unit to the area being checked. This pulse (point) of energy is reflected and returned to the unit where it is incorporated into the master point cloud. The returned point has all the correct spatial data, such as X, Y, and Z (elevation) coordinates of the area.
Individual scanner set-ups and resultant point clouds can be registered together to act as one giant scan cloud. After scanning, the results can be immediately displayed on a computer screen.
This process utilizes a low energy system that does not present any danger to the operator or bystanders. Scanners using low power do not have the ability to penetrate the surface of the structure. No data can be gathered from the internals of the masonry wall or surrounding soils. Only data from the exterior wall is captured.
Software controls the process and captures the image into a series of 3D points, typically called a “point cloud.” Each returned point is the equivalent to a manual survey point. The resultant data is then imported into CAD software used to analyze the surface of the existing masonry. The point cloud data is immediately ready for analysis and is a complete 3D representation of the area scanned. Depending on the type of laser used, the range of data collected can be upwards of 450 ft.
Imagine surveying masonry construction to a 1-in. sampling frequency with an accuracy of 3/8 in. or greater, without scaffolding, plumb bobs, or time consuming measurements. It would take an inordinate amount of time to survey the exterior with a total station to the same degree of accuracy. A laser scanning system quickly and accurately captures the exterior condition of a masonry system, analyzes the information, and places the data into easily read CAD drawings.
Scanning has many virtues, but some limitations exist. The scope of work and the capability of the scanner should be thoroughly understood. The scanner is a line of sight device that only captures data that is not obstructed. Objects between the scanner and building, such as trees, shrubs, signs, and banners, prevent the data from being captured.
While this may not present a major problem with trees that shed their leaves in the fall, the resultant branches will block some of the scan. Evergreens and trees in full foliage are problematic.
Another problem is rain. Moisture on the surface absorbs the laser energy and results in no or partial data collection.
Certain levels of detail, such as cracked or missing mortar, cannot be readily determined from the point cloud. It would require a very dense scan (super high resolution) to gather data for missing mortar within the joints. This type of scan may become prohibitive as the time component to gather data every 1/8 in. at a distance of hundreds of feet would be very high.
Also, the nature of the joint, with the mortar being recessed by 3/8 in., may block the scan beam at extreme oblique angles. Again, the data can be captured, but requires a higher effort than normal scans for construction tolerance and displacement.
The cost of hardware and software may be prohibitive to the occasional user. However, laser scanning is available in almost any part of the country. Look in the yellow pages or online for “Laser Scanner Services,” also known as “Laser Scanner Providers.”
If this approach does not produce results, major laser scanner manufacturers can provide a supplier in your area. A well-trained team will capture huge amounts of accurate, useful data at a very reasonable cost, when compared to other conventional methods.
Most of this article has been devoted to exterior masonry walls. However, with laser scanning, data collected for the buildings entire exterior and interior can be utilized to create a full 3D model or building information model (BIM), complete with piping and ductwork.
Laser scanning allows confirmation of critical areas in an existing building that may involve interference issues for new structural, mechanical, and electrical construction work.
Laser in action
Giffels Inc., Southfield, Mich., was one of the first architectural/engineering firms in North America to utilize a laser scanning system that maps and models large complex building sites and facilities in 3D, with an unprecedented level of detail, speed, and accuracy.
This technology was used on an existing 80-yr old building in the Northern-Midwest portion of the country. The structure is entirely brick veneer, with stone accent pieces and coping. The building has a trapezoidal plan (5 exterior walls), stands about 85-ft tall, and is approximately 300 ft on a side. Typical of this area, freeze/thaw conditions existed, which required periodic maintenance of the brickwork.
With a new exterior façade being planned, the plumbness of the brick was very important. The scanned data was imported into AutoCAD and the architect utilized this information to position the new façade to miss the existing brick.
The point cloud showed many cases of cracking and displaced brickwork. In one case, an upper corner of the building showed a separation and displacement of brick by over 2 in. from the adjacent brickwork. The stone coping exhibited a reverse bulge of over 6 in. from start to finish. None of this information was apparent with the eye from ground level. The displacement/cracks could be seen with binoculars, but impossible to measure without scaffolding.
The data for three sides of the building (higher walls) were scanned in one day. It took approximately one week to cut the proper exterior sections (approximately one for every 10 ft of wall) that were required by the architect.
Paul Palleschi, a 30+-year employee at Giffels Inc., supervises a team that captures all forms of laser data, not limited to construction verification, complex industrial buildings, and intricate tooling. His team produces highly detailed 3D models from the point clouds, which are used during the design and construction phases for interference correction, as well as model simulations for assembly processes.
Giffels Inc. is a multi-disciplined, full service architectural, engineering, and planning firm. Since 1925, Giffels has provided professional consulting services for a wide range of challenging projects across North America and internationally in 16 different market sectors.