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During the last decades, great progress has been made in the research and application of high strength concrete (HSC). Due to its high strength, low dilation and brittle nature, substantial more transverse reinforcement is needed for HSC columns to obtain ductile behavior, especially for columns with large axial load ratio and/or located in seismic zones. In this paper, a novel HSC concrete column with double high-strength stirrups is proposed, which features two concentric transverse stirrups. The concrete in the cross section are divided into three parts under different confinement level, namely unconfined concrete, singly and doubly confined concrete. This structural form possesses many advantages over traditional HSC with single stirrup and steel-concrete composite columns, including enhanced strength and ductility, easy to construction and easy to connection with RC beams. Three demonstrative circular HSC columns with double spirals were prepared and tested under concentric axial compression. A current stress-strain model for steel confined HSC was modified and found suitable to predict the behavior of present HSC column with double spirals. A parametric study was then conducted to investigate the influence of several key parameters on load-strain response of HSC column with double spirals, including concrete strength, transverse reinforcement ratio, yield strength of transverse reinforcement and center to center diameter of inner spiral.

Low-frequency noise radiated from bridge vibrations has been reported as an environmental noise problem in many countries. In order to investigate the mechanism of low-frequency noise radiated from bridge vibration, a steel bridge with a double-box is adopted for study. Modal parameters of the bridge, including natural frequency, damping ratio and mode shape, are identified from field tests by a combination of Eigensystem Realization Algorithm and Fast Fourier Transformation. Then the grillage model of the bridge is established and physics parameters of the model are updated by genetic algorithm according to identified natural frequencies. The dynamic response of the bridge by the action of a moving vehicle is calculated and assumed as the sound source of low-frequency noise. Then low-frequency noise due to bridge vibration is estimated according to sound wave propagation theories. The validity of the numerical method is verified through comparison with experimental results. Furthermore, noise reduction methods are proposed and corresponding effects are discussed. Results show that numerical simulation is feasible in assessing low-frequency noise due to traffic induced vibration of a bridge, which offers a possible way for environmental assessment as well as being a good reference for noise reduction design of bridges. The deck plate of the bridge is the primary source of low-frequency noise. Hence, increasing the stiffness of a deck plate is effective for noise control. Improving the road roughness can also reduce low-frequency noise.

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Reinforced concrete column confined using two layers of stirrups is a new kind of column form recently proposed by the authors. The concrete of the column is under three different levels of confinement, namely unconfined concrete cover, singly confined, and doubly confined concrete core. This column form provides a simple but effective solution for reinforced concrete columns located in seismic hazard zones and/or reinforced concrete columns with large axial load ratio, where large amount of transverse reinforcement is necessary to achieve a ductile response. This study aims to investigate the axial compressive behavior of square reinforced concrete columns confined using two layers of stirrups. In total, 15 columns were prepared and tested under axial compression. Two different stirrup configurations were investigated. The axial responses and the failure modes of the columns were examined in detail, and the average stress–strain curve of the singly confined and doubly confined concrete core was derived. A stress–strain model with satisfactory accuracy was proposed based on the interpretation of test results.