# Structural Health Monitoring for Prefabricated Building Envelope under Stress Tests
## 2 Materials and Methods
### Method
#### 2.1.1 Analysis of Facade Structural Stress  
The analysis of structuring components to be monitored is investigated with the objective of examining the stress conditions and the range of operations, consequently deriving the sensing solution needed. The comprehensive evaluation of these components to be monitored addresses the final structural health monitoring sensing technologies to be included in an SHM configuration. Given their exposure to various environmental stressors, such as wind, temperature fluctuations, moisture, accidental impact, and seismic activity, facades are susceptible to degradation and structural issues over time. Consequently, defining the components and parameters relevant to facade monitoring becomes important for effective maintenance, timely detection of defects, solution replicability, and proactive mitigation of risks. Indeed, during the research, a list of possible facade defects to be monitored and relative parameters based on structural analysis and an internal key stakeholders' interview was defined. Table 1 presents the facade parameters, their description, and the range of value acceptable for the facade structural health together with the selected monitoring sensors. Therefore, Table 1 summarizes the most relevant parameters in terms of facade safety, scheduled for monitoring, accompanied by a selection of the suitability of employing FBG technology and conventional sensors for each defined objective. Alongside FBG, conventional sensors will also be applied in the facade system with the aim of defining a complete kit of sensors for building envelope SHM. Therefore, the kit of sensors selected for the facade monitoring, based on possible facade defects, are described as follows:  
* FBGs--Previous applications demonstrated the effectiveness of these technologies in the building and infrastructure sectors, such as bridges [29; 30; 31], concrete, wood [32], and steel structures, where strain and temperature have so far been the dominating measurands of interest. Utilizing conventional FBG sensors for SHM in building facades offers significant advantages over electrical strain gauges. Unlike electrical strain gauges, which require multiple wires per sensor point, leading to scalability issues, FBG sensors allow for multiplexing multiple sensors into a single fiber. This feature makes FBG sensors highly suitable for environments requiring numerous sensor points, such as the building envelope sector. The main advantages are their lightweight characteristics, single-ended connections, water and corrosion resistance,and absence of electric current in the measurement array, making them suitable for embedding within or attaching to a structure [33], which make them suitable for embedding within or attaching to a structure. In addition, research on integrating FBG cables into the facade system involved examining critical factors to determine the optimal configuration. Key considerations included the FBG cable's bending radius, path within facade components towards the monitoring system for efficiency and aesthetics, sensor position, cable dimensions, lengths, thickness, and material properties for fixing method (e.g., glue, silicone). In this research, the use of FBG for temperature monitoring is integrated into the InComEss architecture. Given that the MonadGator can monitor only one FBG at a time, it was connected to the FBG for temperature, which requires punctual monitoring. The integration of FGB for temperature in the glazed facade design should prevent thermal shock episodes in vision and spandrel parts caused by solar radiation and light converting to IR. Installing temperature sensors can prevent damage and provide data for future thermal shock designs. Conversely, conventional FBGs for strain were selected to investigate further applications and to compare their results to those of conventional sensors such as accelerometers. In this case, FBGs for strain are connected to a conventional switchgator, allowing for measuring multiple FBGs and powered by commercial energy.