Design, construction and testing of a smart under-deck cable-stayed footbridge prototype

Under-deck cable-stayed systems are commonly employed to enhance the structural performance of footbridges. However, their ability to withstand live loads is most effective only for a particular load distribution, thereby limiting opportunities for material savings. To overcome this challenge, the authors previously introduced the concept of smart cable-stayed footbridges, demonstrating its theoretical feasibility and potential for substantial material savings. This paper drives forward this idea and presents the first experimental proof-of-concept of a smart under deck cable-stayed footbridge. The smart behavior is achieved through the use of a linear electric actuator that replaces the midspan strut of a conventional under-deck cable-stayed footbridge. The smart system is completed by a sensor and a control system that interprets displacement data and communicates with the actuator, which elongates and contracts depending on the acting live load. This paper aims to experimentally validate the concept of smart under-deck cable-stayed footbridges. To achieve this goal, a 6-meter-span prototype was designed, constructed, and subjected to a comprehensive testing campaign, including static, quasi-static, and dynamic load scenarios. The experimental response under static loads closely matches the analytical and numerical models, with differences ranging from 4%-8%. In addition, dynamic analysis revealed that the smart control significantly increases the stiffness related to the bending vibration mode, reducing vibrations by up to 20% compared to a conventional structure. In summary, this investigation provides the first successful physical validation of the theoretical concepts and offers insights into the structural response of smart under-deck cable-stayed footbridges, demonstrating their potential for a more efficient and sustainable footbridge design.