With the increase in population, surface transportation has significantly increased, highlighting the need to maintain reliable and safe civil infrastructures. Bridges can be considered the most critical element in transportation infrastructure. Accordingly, they require periodic inspection to prevent any failure caused by aging and environmental impacts. Over the years, visual inspection has been practiced the most due to its simplicity. However, detection of small and internal cracks and defects requires more advanced techniques. To address this, various non-destructive testing (NDT) methods have been developed and implemented in recent decades. With the advance of technology, opportunities for developing more advanced and effective NDT methods have been created. To achieve the development of such advanced techniques, the knowledge of available methods and their future trends becomes necessary. This paper gathers in one place all the relevant information regarding existing non-destructive testing for steel bridges. Furthermore, the future direction and recent innovations in this field, including the application of robots, sensors, and drones for fast and efficient evaluation of steel bridges are discussed. The parameters for selecting the most appropriate NDT method for specific cases are explored. The methodology, and pros and cons of each technique are also presented. It is expected that the results of this study pave the way for development of new methods and improvement of currently practiced NDT techniques for steel bridges.
