Kazutaka Shirai

A passive resettable stiffness damper is presented for controlling vibrations in seismically excited structures. The damper generates forces in proportion to the piston displacement, making it effective over a wide range of vibration amplitudes and frequencies. Energy dissipation occurs by resetting the damper force to zero at each change in piston direction. This is achieved using a special resetting mechanism that is integrated with the damper body. A model of the resetting mechanism was developed that considers the detailed geometry of its components, and the model was validated using CAD software. The model was used to investigate the influence of the mechanism geometry on its performance, leading to a design methodology that ensures the mechanism operates properly and without interruption during a dynamic event. A prototype was constructed and subjected to multiple cycles of sinusoidal loading at different amplitudes and frequencies. The results showed that the damper force increased with input amplitude but was independent of input frequency. However, the energy dissipation capacity of the damper was found to be frequency dependent. The damper hysteresis loops showed stable force–displacement characteristics over several hundred cycles of motion, thereby validating the damper concept and demonstrating the reliability of the resetting mechanism.

The present study developed a method for evaluating the response, damage, and repair cost of super high‐rise reinforced concrete (RC) buildings subjected to large‐amplitude earthquakes. The response was numerically assessed using three‐dimensional 40‐story RC frame models under the predicted seismic motions of earthquakes along the Sagami Trough and Nankai Trough considering the effects of slip behavior, slab cooperative width, and stud‐type dampers. Even when the RC mainframe exhibited slip, the peak response deformation was effectively reduced by the friction dampers incorporated into each story. A probabilistic approach based on fragility was used to evaluate the damage and repair cost of the building models. The distributions of the damage states and repair cost for each story under the predicted seismic motions of earthquakes along the Sagami Trough and Nankai Trough were determined, and the total repair cost in relation to the total construction cost was evaluated. The occurrence of damage state 1 had a relatively large effect on the evaluated total repair cost under the evaluation conditions used in this study. A nonlinear relationship was observed between the input magnification and the total repair cost. The friction dampers reduced the damage and total repair cost.

Geopolymers are emerging low-carbon cement-free binders that offer a sustainable and environmentally friendly alternative to ordinary Portland cement (OPC)

The challenges of handling user-hostile alkaline solutions in the conventional alkali-activated binders (AAB) have initiated the development of “just add water” or one-part solid-based AAB systems. This paper aims to present a preliminary investigation on the development of one-part ambient-cured alkali-activated binders produced by synthesising high-calcium fly ash (HCFA) and ground granulated blast furnace slag (GGBS) using sodium metasilicate anhydrous. Three test series were conducted in this study to investigate the effects of GGBS/binder, activator/binder and water/binder ratios on the fresh and hardened properties of the one-part synthesis AAB system. It was found that the SiO₂/Al₂O₃ molar ratio plays an important role in the attainment of compressive strength and limits the amounts of solid activators effective in contributing to the alkali-activation reaction process. The optimum SiO₂/Al₂O₃ molar ratio was found between 3.20 and 3.30. The test results revealed that the optimum proportion between HCFA and GGBS was discovered at a GGBS/binder ratio of 0.50. The optimum activator/binder ratio was between 0.08 and 0.12, and it is recommended that the water/binder ratio should not exceed 0.50. This study demonstrated the potential of the one-part synthesis method in the production of alkali-activated binder for practical structural applications.