# Knowledge-Based Fuzzy Expert System to the Condition Assessment of Historic Road Bridges
###### Abstract  
A systematic methodology for condition assessment of the historic road bridges was needed because of the poor and inadequate condition of bridges which cannot satisfy everyday dynamic loads and deteriorations due to the aging process. Thus in this study, a new expert system based on the knowledge approach has been proposed to develop a systematic procedure for condition assessment of these bridges using fuzzy logic and sets of \(\alpha\)-cuts. Each bridge is divided into three components: superstructure, substructure, and equipment, and each component is divided into relevant elements. These elements are evaluated by an expert and their ratings are fuzzified according to defined fuzzy sets, their membership functions, and linguistic values. Furthermore, fuzzy structural importance is given to ratings of each element. Combinations of these two values are calculated to obtain a fuzzy rating of the component using the Fuzzy Weighted Geometric Mean (FWGM). Finally, for the defuzzification of the component rating, the centroid method is proposed. The Analytic Hierarchy Process (AHP) is used for comparison of the components. The bridge condition rating is achieved by summering all the components ratings multiplied by their relative importance, and it is presented as a value of the Historic Road Bridge Condition Assessment Index (HRBCAI). The validation is conducted on the bridges built until the end of the Austro-Hungarian Monarchy in Split-Dalmatia County, Croatia. h +
Footnote †: journal: Applied  
1  
h +
Footnote †: journal: Applied  
1
Footnote 1: Received: 23 December 2020  
20 January 2021  
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**Cob**  
ensure the basic values of the building (mechanical resistance and stability, safety in use, etc.) such as renovation, adaptation, and reconstruction to enable safety and usability of the bridge [2]. Inspection and maintenance of road bridges is a very sensitive and complex task due to the increased volume of traffic, degradation and various damages of existing bridges. The management of road bridges is entrusted to public institutions and is shaped by technical, political, environmental, and historical aspects. It deals with all activities during the life of the bridge from construction to replacement, intending to ensure its safety and functionality. It also provides the necessary protection, maintenance planning, and minimization of bridge life cycle costs [5]. The lifespan of a bridge can be divided into four different phases [6]: design and construction, slight deterioration, obvious damage, and the occurrence of extensive degradation. The most effective way to select an adequate maintenance strategy, including replacement, repair, restoration, and preventive maintenance, is to apply mathematical modelling of computer systems [7]. With the advancement of technology, the combination of bridge inspection and maintenance or restoration methods has been controlled by a computer-assisted Bridge Management System (BMS) used worldwide to address the complexity of bridge management decision-making [5]. However, each BMS differs from state to state because of the use of different ways of inspecting bridges and strategies for maintaining, rebuilding, and repairing bridges within a distributed budget [8]. Road bridge management in Croatia began to be studied more intensively in the 1980s, when the first systematic inspections of road network bridges were conducted [9]. The main activities of the bridge management system are: database module, condition assessment and decision-making process [10]. The database module consists of bridge documentation and a computer database. One of the basic requirements of a bridge management system is a comprehensive and accessible list of bridge data.