Nanosilica (NS) may be obtained as a by-product in several industrial processes and is associated with high availability and affordability among other nanoadditives. NS has been used for asphalt modification, and improvement in high-temperature performance and several other physical properties has been reported. However, due to the wide varieties and intrinsic variability of asphalt materials, concerns have been raised about the reproducibility of some conclusions, and therefore, a review was conducted. According to the results, NS additives with a purity of over 99% were usually used for modification and the specific surface area was over 100 m ² /g, leading to the superior absorption of asphalt and thus improvement in rutting resistance of the mixtures. Due to a lack of guidance for the blending procedures, inconsistency exists among studies in the shear speed, blending duration, and temperature, leading to possible excessive blending and unnecessary energy and time consumption. Rises in NS concentration would cause higher softening point and rotational viscosity, and therefore elevated temperatures for mixing and paving, but penetration would be reduced. According to rheological evaluations, with the rise of NS concentration, the rutting parameter would increase, indicating an improvement in the high-temperature performance, but the low-temperature performance may deteriorate.

Prefabricated beam–column connections are the most vulnerable components of prefabricated buildings during earthquake events. The seismic performance of the beam–column connection is functional as the critical component plays a key role in structural safety. This study aimed to develop a novel hybrid prefabricated concrete (HPC) connection, combining with wet and dry connection techniques, to enhance the seismic performance of prefabricated concrete frames. A quasi-static experimental investigation was carried out to examine the seismic performance of the proposed connection. Two full-scale prefabricated connection specimens utilizing the proposed HPC connection and another code-defined monolithic prefabricated concrete (PC) connection were tested under cyclic loading, keeping the axial load on the column constant. The ductility, stiffness degradation, energy dissipation capacity, post-tensioned force, and residual displacement were obtained based on the experimental output. The results indicated that the HPC connection developed had high construction efficiency and better seismic performance than the conventional PC connection. The strength and energy dissipation capacity were significantly improved by up to 52% and 10%, respectively. The cracking and stiffness degradation were well-controlled.

To investigate the effect of nano carbon-fiber-reinforced polymer (nano CFRP) on retrofitting reinforced concrete (RC) structures, this article presented the progressive collapse performance of two half-scale four-bay RC frames including one control specimen S1 and specimen S2 with nano CFRP retrofitting beam ends. The progressive collapse performance was discussed by comparing crack patterns, failure mode, load–displacement curves, horizontal displacement, strains, and rotational and energy dissipation capacity. The test results demonstrated that nano CFRP did not change the ductile beam-hinge failure mode, but improved the load-bearing capacity and ductility efficiently, and postpone shear failure of the joint core region obviously. Due to the insufficient development of plastic hinges limited by nano CFRP, S2 failed to enter catenary action, which revealed its own defects in anti-progressive collapse. It was shown that the retrofitting strategy using nano CFRP can substantially improve the mechanical characteristics and implement the strong column-weak beam failure mode.

To study the seismic strengthening of damaged reinforced concrete (RC) frames using CFRP sheets, this study designed and tested the scaled 2-bay and 2-storey RC frame specimens. After applying a low cyclic horizontal load to simulate the initial damage to the specimen in an earthquake disaster, CFRP was used to strengthen the joints of the damaged RC frame. Pseudo-static tests of strengthened specimens and counterpart specimens were then carried out. Seismic performance, including stiffness, load capacity, ductility and energy dissipation were further analyzed. The failure mode of strengthened RC frame structures showed excellent ductility. The results demonstrated that the strengthening method involving wrapping CFRP can significantly improve the maximum horizontal bearing capacity, initial stiffness and energy dissipation capacity of the non-ductile reinforced concrete frame structure. The average displacement ductility coefficient of strengthened specimen can be enhanced to 3.41 compared with that of counterpart specimen (3.00). The pushover analysis based on the OpenSees model determined that the prototype frame with CFRP strengthening can maintain structural integrity and safety, with its maximum interstorey displacement angle below the limit of seismic specification (i.e., 1/50 in a severe earthquake). This study can contribute to the development of practical and efficient methods for restoring and improving the performance of damaged RC frames in seismic-prone regions.

Elastically mounted flexible membrane roofs exposed to flows are prone to vortex-induced vibrations and even aero-instability due to the strong fluid–structure interaction (FSI). This study is to investigate the FSI mechanism in the saddle-shaped membrane structure over a range of Reynolds numbers and wind directions in laminar flows, by bridging structural vibration responses and flow dynamics. The aeroelastic characteristics of membrane structures, including statistics of displacement responses, oscillation frequency, and oscillation damping ratios, were identified from the perspective of time and frequency domains. Simultaneously, the particle image velocimetry system was employed to visualize the flow features, including velocity vector, turbulence intensity, and vortex evolution in both space and time. The flow modes were further decomposed by proper orthogonal decomposition (POD) to capture the salient aspects of the flow. Three patterns of POD modes are identified, and the first mode plays the dominant role in POD modes. It showed that as the wind Reynolds number increases, the space between the shear layer and membrane surface would be narrowed, and resultantly the vortices turn out smaller in scale and closer in space. This trend leads to an increase in the frequency of vortex shedding and a stronger FSI effect. When the frequency of vortex shedding approaches the fundamental frequency of structures, the vibration of the membrane would be shifted from turbulent buffeting to vortex-induced resonance, featured with lock-in frequency, significant amplified displacement, and negative aerodynamic damping ratio.

The dynamic behavior of flexible membrane roofs in surrounding fluid flows involves complex fluid−structure interactions (FSIs), which would lead to vortex resonance and even aeroelastic instability. In this paper, the FSI effects of saddle-shaped membrane roofs in laminar flows over a range of wind velocities and wind directions are investigated, by simultaneously applying a high-resolution particle image velocimetry (PIV) system and laser displacement sensor in wind tunnels. The flow field is visualized by the PIV system and analyzed in the view of the spatiotemporal evolution of flow velocity and vorticity, as well as the proper orthogonal decomposition analysis. Then, the structural dynamic response is investigated in terms of displacement statistics and dynamic characteristics, and finally the FSI mechanisms are revealed. The results show that both wind velocity and wind direction have a significant effect on the leading-edge separation, especially in the case of larger wind velocity and 45° wind direction. The increasing wind velocity would result in the unstable leading-edge separated shear layer, reduced vortex diameter, and increased vortex shedding frequency. Consequently, the leading-edge separation intensifies the vibration of the membrane roof, which could increase the vibration frequency, the average and maximum displacement by a factor of 3 to 4, and the standard deviation value by a factor of 3 to 5. The vortex-induced resonance appears at the wind velocity of 20 m/s and wind direction of 0°, featuring the sharp increase in displacement, negative aerodynamic damping, and frequency lock-in.