No abstract

UR50 ultra-early-strength cement-based self-compacting high-strength material is a special cement-based material. Compared with traditional high-strength concrete, its ultra-high strength, ultra-high toughness, ultra-impact resistance, and ultra-high durability have received great attention in the field of protection engineering, but the dynamic mechanical properties of impact compression at high strain rates are not well known, and the dynamic compressive properties of materials are the basis for related numerical simulation studies. In order to study its dynamic compressive mechanical properties, three sets of specimens with a size of Φ100 × 50 mm were designed and produced, and a large-diameter split Hopkinson pressure bar (SHPB) with a diameter of 100 mm was used to carry out impact tests at different speeds. The specimens were mainly brittle failures. With the increase in impact speed, the failure mode of the specimens gradually transits from larger fragments to small fragments and a large amount of powder. The experimental results show that the ultra-early-strength cement-based material has a greater impact compression brittleness, and overall rupture occurs at low strain rates. Its dynamic compressive strength increases with the increase of strain rates and has an obvious strain rate strengthening effect. According to the test results, the relationship curve between the dynamic enhancement factor and the strain rate is fitted. As the impact speed increases, the peak stress rises, the energy absorption density increases, and its growth rate accelerates. Afterward, based on the stress–strain curve, the damage variables under different strain rates were fitted, and the results show that the increase of strain rate has a hindering effect on the increase of damage variables and the increase rate.

For river crossing bridges, the vehicle-induced vibration can be transmitted to the bridge tower and foundation system. This vibration induced low frequency underwater noise radiation can cause great harm to aquatic organisms. A river crossing suspension bridge was selected to study the sound contribution and spatial distribution of the underwater noise. A bridge-sediment coupling finite element model was developed, and the vehicle-bridge-sediment interaction analysis was conducted to investigate the dynamic response of the coupling system. An acoustic finite element model was built to predict the underwater noise radiated from the tower and sediment, and the noise contribution of these two sound sources was compared. The research shows that the noise radiated from the bridge tower and the sediment is below 6.3 Hz, and the peak frequency is around 3.15 Hz. The noise radiated from bridge tower only has a larger contribution to the total noise level in its vicinity than the sediment, especially around the water surface. In other space, the noise generated through the sediment vibration plays a dominant role in the total noise. The radiated noise from the tower has lateral directivity, and the directivity of the sediment radiation is similar to the point sound source.

The stiffness degeneration of small to medium span bridges has been increasingly observed in recent years, and it has become a major concern of government and bridge owners. A quantitative evaluation method for the bridge performance with strengthening measures is highly desired. Due to the advantages of uninterrupted traffic and long-term tracking capability, a temperature-driven approach for characterization of the correlation pattern between bridge temperature-induced strains and bridge status was proposed in the present study by using structural health monitoring data. First, a theoretical solution of the simplified bridge model was derived to establish the correlation between the stress and deterioration extent under temperature gradient load. After a numerical simulation that combines the thermal–structural interaction analysis and the vehicle–bridge interaction analysis, the strain range was proposed as an assessment index to ensure the stability and effectiveness of the evaluation results. Next, the Generalized Extreme Studentized Deviate method was used for detecting the outliers. The statistical results of the assessment index for different strengthening methods were compared to evaluate the associated strengthening efficiency, and the associated equivalent section height was calculated for visualizing the bridge condition after strengthening measures were taken. The results demonstrated that the proposed temperature-driven method was able to quantitatively evaluate the bridge strengthening effects with a high efficiency.