## 5 Application Domain
### Maintenance Inspection  
Operation and maintenance of a building cost about 50-70% of the total life-cycle cost of a project [138]. Structures deteriorate due to aging and extreme weather [139]. Regular maintenance increases the useful life of the building [138]. It is crucial to identify defects before they get worse and cause building failure [140]. Periodic monitoring of a structure after it has been constructed for maintenance purposes is also known as structural health monitoring (SHM) [141]. SHM is critical to ensure the safety and integrity of the structures [142]. Visual inspection has long been used to uncover structural flaws in order to guide building rehabilitation [143]. Current practices involve regular and manual inspection of the structure for any structural defects, which is slow and costly [138; 140]. Robots can regularly monitor the structural elements for any signs of damage and alert humans if further analysis is required [144]. Maintenance inspection also involves measuring the rate of deterioration for predictive analysis [145]. Images captured using robots are more consistent in their perspective, which is more useful in noticing the rate of change as compared to images captured manually [145]. Robotic inspection also provides a safer alternative to manual inspection. High-rise towers with glass facades, which are a common sight in most cities, require regular maintenance [107]. The classical approach to the maintenance of high-rise buildings poses a high risk to human workers due to high winds [107]. UAVs and wall-climbing robots provide a safer alternative for performing maintenance inspections of high-rise buildings [108; 146]. Inspection of tall cylindrical structures such as storage tanks and silos also poses a similar risk to human inspectors [147], and so do roof inspections, since manually inspecting roofs can be difficult due to access difficulties [56]. Old structures may also become unsafe for humans to inspect, especially after sustaining damage from a natural disaster [11; 148]. Many historical buildings are abandoned because of numerous structural defects that make them hazardous for manual inspection [149]. Robots equipped with special sensors can be used to diagnose structural integrity before a human can perform a detailed inspection [150]. [PERSON] et al. [151] trained a convolutional neural network (CNN) model with images captured from UAVs for assessing the extent of damage in disaster-affected structures. Sometimes, a single type of sensor is not adequate to identify all types of defects; therefore, multi-robot systems with different types of sensors are also deployed to monitor the structure [152]. One such sensor used is an infrared thermal camera to collect thermal images of the building [153]. Thermal  
Figure 4: Application domains of using robots for inspection and monitoring. images may reveal special defects such as material degradation and air leakage that might not be detectable using the naked eye or simple RGB images [153]. The monitoring of bridges is often undertaken as a manual inspection task. However, it involves a human inspector being exposed to high-speed traffic and fall hazards from going under the bridge deck [154]. It also involves the bridge being closed and the use of lifting equipment to reach the hard-to-reach places under the bridge [152]. Due to these challenges, bridges may suffer from poor maintenance, which has been the reason for many collapses [154]. UAVs can be used for regular structural health monitoring of bridge decks where it is riskier for humans to reach frequently [32]. [PERSON] [155] used a climbing robot for the inspection and testing of high bridge pillars. [PERSON] et al. [156] studied the use of a teleoperated robot for the inspection of hard-to-reach parts of a bridge. Robots are also used for measuring building performance. Thermal leakages in a building may cause up to 40% energy loss, thereby decreasing building performance [22].