Flutter is one of the key issues threatening long-span bridge safety. Aerodynamic flaps have been examined for flutter suppression by altering bridge aerodynamic characteristics through active control. Traditional control strategies are based on system models, and the control effectiveness heavily depends on model accuracy. Due to the complexity involved in bluff-body aerodynamics, however, an accurate model for girder-flap aerodynamics is not available. System models are often simplified by assuming the main girder and the flap are ideal flat plates, leading to non-optimal control. Therefore, this study employs a control method that does not rely on system models. Specifically, the active control problem of bridge flutter is solved by reinforcement learning, using the proximal policy optimization (PPO) algorithm. Accordingly, the flap vibration is adjusted based on the monitored bridge-wind field state enabling the main girder-flap system to generate aerodynamic forces that are favorable for suppressing bridge flutter. To avoid the abrupt changes of the controlled flap displacement, the mode control rather than instantaneous angle control is utilized here. The numerical example demonstrated that the PPO-based deep reinforcement learning developed in this study can effectively control bridge flutter under different wind speeds and angles of attack.

In the process of designing long span bridges, runability analysis plays an important role. In fact, it deals with the assessment of the impact on the structure’s response and train running safety of external factors such as environmental actions, like wind and earthquake, or catastrophic events like ship impact. Runability analysis involves a combination of local aspects (e.g. wheel–rail interaction) with global and local bridge dynamic response. In this respect, runability analysis represents a complex task to be tackled and requires adequate modelling. The present work proposes a runability study to be performed on the New Storstrøm Bridge, which is currently under construction in Denmark connecting Zealand with Falster. In this numerical analysis. two scenarios have been considered separately: ship impact on the bridge’s superstructure and wind action on a rail vehicle, using both the “Chinese hat” and stochastic turbulent wind formulations. The outcomes of this study clearly show that, even when threshold values were locally reached in terms of train running safety, a close examination of the local wheel–rail contact condition helps in defining the expected evolution of the dynamics of the train and thus documenting a higher safety level than indicated by the basic requirements.

In Japan, timber has been used for not only traditional building but also bridge construction since olden times. At least until the 1950s, various types of bridge were in service, including trestle, truss, suspension, etc. for forest railways. However such timber bridges were replaced with concrete or steel bridges, which were thought to be, and were called, “permanent bridges” in those days. Government policy represented by the Five-Year Plan for Road Construction in 1954 facilitated the replacements, and a large percentage of timber bridges disappeared from Japan. Since the late 1980s, new types of timber bridge, so-called “modern timber bridges”, began to be constructed in Japan. The development of materials such as glulam (glue-laminated timber) with a large section, curved glulam, etc. treated with preservative made it possible to construct roadway bridges with several ten-metre spans. The longest span bridge in Japan is Karikobozu Bridge, which was completed in 2003 and has three king post truss spans (the longest span being 48 m). Construction of modern timber bridges reached its peak around 2000 and decreased significantly after that. As budget allocations for public works projects were decreasing, it became difficult to construct symbolic timber road bridges with higher costs. From the 2010s onwards, new approaches have been tried for timber bridges, utilizing the lightweight properties and easy workability of timber but avoiding high-specification road bridge requiring higher costs. Typical examples are illustrated and recent directions discussed.

In Transit-Oriented Development (TOD), over-track buildings (built over railways) are increasingly popular in Japan for effective use of urban space. However, it is generally not permitted to construct an underground structure directly under a railway while the railway is in operation. This article discusses the structural design of a mid-story isolated high-rise building constructed over railways in Ikebukuro, Tokyo. It covers the philosophy of the system, the structural design, full-scale experiments, and an evaluation of the performance of each structural element. The authors believe that this structural design will provide an effective solution for over-track buildings.