# Intelligent Safety Assessment of Prestressed Steel Structures Based on Digital Twins
## 3 Construction of Multidimensional DTs Model
### Information Capture in Physical Space  
In the process of constructing a multidimensional DTs model, the information capture of physical space is the first step to realize the safety assessment. The dynamic information of the construction site can be sensed in real-time through sensing equipment such as RFID. This realizes the one-to-one mapping between the real space and the virtual model [27]. The main analysis objects of the safety assessment of building structures are structural response and environmental loads [28]. Hence, this study divides the information of physical space into two aspects, namely component information (_CI_) and environmental information (_EI_). (1) Component information capture  
There are many kinds of components involved in the construction process of pre-stressed steel structures, and the construction sequence of each component is complicated. Therefore, the information capture of various components in the construction process is of great significance to the safety performance assessment. In the process of component information capture, the main information is divided into the component symbol (_CS_), basic information (_BI_), construction information (_CI_*), and mechanical information  
Figure 2: Construction safety assessment method. (_M_I). The mathematical language for information capture of components is expressed in Equations (1)-(4):  
\[Cl_{i}=(CS_{i},\ BI_{i},\ CI_{i}^{*}\ C_{i},\ MI_{i}) \tag{1}\]  
\[Bl_{i}=(CD_{i},\ CL_{i},\ CM_{i},\ Unit_{i},\ Data_{i}) \tag{2}\]  
\[Cl_{i}^{*}=(CP_{i},\ CT_{i},\ QR_{i},\ T_{i}) \tag{3}\]  
\[MI_{i}=(E_{i},\ C_{\beta},\ \varepsilon_{i},\ V_{di}) \tag{4}\]  
In the equations, \(Cl_{i}\) represents the component information for the \(i\)th component, \(CS_{i}\) means the unique identifiable ID bound by the \(i\)th component, and \(Bl_{i}\) is the basic attribute set of the \(i\)th component. \(Bl_{i}\) contains the dimension information (\(CD_{i}\)), the locating information (\(CL_{i}\)), the material information (\(CM_{i}\)), the production unit (\(Unit_{i}\)), and the date of production (\(Data_{i}\)). \(Cl_{i}^{*}\) is the construction information of the \(i\)th component. \(Cl_{i}^{*}\) contains the construction process (\(CP_{i}\)), construction technology (\(CT_{i}\)), construction quality requirements (\(QR_{i}\)), and the time (\(T_{i}\)) used in this step. \(MI_{i}\) means the mechanical information of the \(i\)th component in the construction process. \(MI_{i}\) involves the elastic modulus (\(E_{i}\)), cable force (\(C_{\beta}\)), stress (\(\varepsilon_{i}\)), vertical displacement (\(V_{di}\)), and other mechanical properties. In the process of capturing component information, the symbol, basic information, and construction information of the component are filled in the active RFID tag. For structural components, the relevant information is updated through the RFID tag at all times to realize the dynamic perception of the information. For the information change of the construction process component, the editability of the label can be used to modify it through the reader. As a result, the basic information and construction information of the component can be viewed in real-time in the mobile terminal device. For the capture of mechanical information of components, the mechanical parameters of components are collected by sensors for each construction step. Cable force is the key information collected in the study and the basis for evaluating the safety performance of the structure. This type of information is collected in real-time by the column tension-compression sensor in the test. By arranging sensing devices on the components, the efficiency of information collection and update is improved. Therefore, the self-perception, self-decision, and self-execution of the components can be realized to a certain extent. The real-time information is captured by the sensing equipment at each construction step. Structure information of the scene is collected and has interactive feedback with the virtual model.