The technology using laser scanners is an improvement for field surveys. In classical topography, using angles and displacements in three-dimensional surveys, the final objective is to determine coordinate points. Initially, terrestrial surveys used theodolites and the technique was efficient when introducing electronic measurements of displacement and directions. The integration between both techniques led to total stations, employing reflective prisms to determine three-dimensional coordinate points on terrestrial surfaces. Subsequently, the evolution of laser measurement allowed finding three-dimensional coordinate points without prisms. These points are calculated remotely, which is useful mainly in places with difficult access or risk to the operator’s safety. These factors led to the development robotic total stations, where coordinates can be measured without operators (Wutke, 2006).
This characteristic makes TLS a versatile technique, with various applications, such as engineering, architecture and geology. Besides that, the equipment has high data acquisition rates (thousands or millions of points per second), which can provide high agility at construction sites. Moreover, the high acquisition generates a large quantity of data on the structural feature of interest. This is a noninvasive and nondestructive technique, where there is no contact between the equipment and the object of analysis (Pavi et al, 2014).
Reinforced concrete structures in general develop pathologies due to external factors, such as weather and human actions. In Brazil, analysis of the structural integrity of concrete structures is deficient, leading to precarious conservation due to the failure to detect pathologies and avoid disasters such as building collapses. In this context, the use TLS for semi-automatic detection and classification of pathologies can be a relevant advance to prevent disasters.
In recent years, several applications of the Terrestrial Laser Scanning (TLS) and the point cloud generated from it have been studied by countless authors, aided in large part by the intense technological development of the last two decades. Among the application areas of TLS, they stand out in engineering and architecture, infrastructure, in industry, in mining and geology, archeology, ecology, medicine and in the forensic and agricultural sectors. In engineering and architecture, the generation of as-built and 2D plans, interior design, 3D modeling (Pu and Vosselman, 2009) and integration with BIM (Building Information Modeling) technology, structure monitoring (Godycka et al.,2014) and interventions in existing structures.
As mentioned by Pavi et al. (2014, p. 8-10) and Lubowiecka et al. (2009), used the laser scanner in the dimensional and structural analysis of a spanish bridge. Pesci et al. (2011) analyzed deformations and deviations of structures from TLS data. González-Jorge et al. (2012) used the terrestrial laser scanning to detect the presence of biofilm and moss proliferation in reinforced concrete structures.
Teza et al. (2009) developed a computational method to identify surface damage caused by loss of mass in reinforced concrete structures. Rabah et al. (2013) used the TLS to detect and automatically map cracks in concrete surfaces. Brandão (1998) studied its application to buildings.
In topography, it has great utility in planialtimetric topographic surveys, calculation of volumes, maps and generation of topographic profiles and Digital Elevation Models – DEM (Meouche et al., 2013).
In this case, the objective was to determine areas at risk of flooding in urban zone. Wutke (2006, p. 15) mentions applications in geotechnics and geophysical modeling. It also mentions studies in reverse engineering, prototyping, aeronautical, vehicles, vessels and large objects in general modeling. It is also used in the documentation of industrial plants, in mining, with calculation of ore volume, in studies of natural risks and verification of underbreak and overbreak during tunnel excavation (Gonçales, 2007). Fekete et al. (2010) used the TLS to scan tunnels in the process of excavation and drilling. There are also studies on the documentation and preservation of historical heritage. In the forensic sector, it is used to reconstruct crime scenes.
According to Giongo et al. (2010, p. 231), the TLS can be used in coastal planning, flood risk assessment, telecommunications and energy transmission networks. It is also possible to use it in agriculture and in the oil sector, transportation and urban planning. In medicine, Dalmolin and Santos (2004, p. 89) mention the design and manufacture of prostheses and comparative studies of volume and surface textures before and after surgeries.
Mugnai et al. (2019) presented a research study designed to assess the health status of a medieval bridge built on 1500 under the Medici dynasty over the river Sieve, close to Florence, using Terrestrial Laser Scanning (TLS) to identify anomalies and deformations. Marzouk et al. (2019) proposed a framework with TLS data and BIM models in order to overcome the weaknesses of the traditional methods in Egyptian Heritage called Tosson Palace. Takhirov et al. (2019) used the high-definition laser scanning technology in an extensive structural assessment of historic monuments in Uzbekistan.
Shafikani et al. (2019) showed an application of TLS technology for assessing the performance of bridge infrastructures, including highway embankments, bridge decks, approach slabs, abutments, and columns supported on drilled shafts. This application also studied the ground movements. Cha et al. (2019) introduced a practical feasibility study of a shape information model to monitor deformation or deflection of bridge structures using TLS. Finally, Carvalho (2019) presented a case study of the application of the terrestrial laser scanning in the identification of structural pathologies in an viaduct.
Armesto et al. (2010) developed a methodology using TLS to estimate the deformation of arches or vaults based on the symmetry of sections obtained along the vault guideline. TLS technology applied to register as-built projects can be found in Tang et al. (2010), Brilakis et al. (2010) and Bosché (2010). Armesto-González et al. (2010) presented a methodology to combine the technology of the terrestrial laser scanner with the techniques of digital image processing in order to study damages on stony materials that constitute historical buildings.
In addition to the Civil Engineering field, the are several another applications of TLS technology as described below among others:
• architectural restoration of iconic buildings, such as the Glass House, built in the 1950s, as well as the MASP Structure Conservation Plan, both in the city of São Paulo;
• documentation and renovation of the Malé Hukuru Miskiy, located at Malé city in the Republic of Maldives
• based on the fire that almost destroyed Notre Dame Cathedral in Paris a lot of other Museums, Heritages, Opera Houses and other iconic buildings are investing in this scope of work.
• volumetric measurement of chemicals products in storage sheds;
• elaboration of three-dimensional electronic model and architectural plans on a large scale map;
• planialtimetric mine survey for mining planning and track of tunnels; and
• new experiences and services for real estate market: accurate floorplans for customers to know exactly what they are paying for.
So, the general objective of this work is to study the applicability of terrestrial laser scanning for identification of pathologies in reinforced concrete structures, to demonstrate how remote sensing can be used in civil engineering in complementation with visual inspection to improve detection of pathologies and thus conservation of structures.
This article is divided into three more sections. Section 2 outlines the results of the evaluations of the normalized point cloud of the São Cristóvão Viaduct, as well as the three-dimensional model prepared from it and the classification made. Section 3 presents in greater detail the normalized point cloud and the three-dimensional surface generated for the São Cristóvão Viaduct. Finally, Section 4 presents our concluding remarks.