Narrow Results

Structural dynamic properties like frequencies and mode shapes have been widely adopted for bridge condition assessment and damage identification. One of the main challenges lies in environmental factors, particularly the varying temperature, which significantly influences the bridge’s natural frequencies. In some cases, the effect of temperature changes can be comparable to, or even exceed, the effect caused by damage, rendering the damage identification methods ineffective. This study investigates the influence of the cross-sectional non-uniform temperature distribution, as a result of surrounding environmental factors, on the frequency of concrete girder bridges. A theoretical analysis is conducted to derive the bridge’s frequencies considering the cross-sectional non-uniform temperature distribution. The upper and lower bounds of the frequencies are developed by using only the environmental temperature and the largest temperature gradient defined by codes. More importantly, the damage to the bridge can be detected if the frequencies exceed the bounds for a certain period. This approach is convenient and practical in real applications without embedding thermocouples in the main girder. Numerical simulations, laboratory experimental tests, and field measurements are carried out to validate the derived frequency considering the cross-sectional non-uniform temperature distribution as well as the upper and lower bounds of the frequency. In particular, the results of the Z24 bridge show that when the bridge is damaged, the measured frequency exceeds the bound continuously, verifying the capability of the developed upper and lower bounds to evaluate bridge conditions.

The blast-resistant performance of protective structures is very important for the protection of human life. In this study, blast experiments were performed on the composite arches strengthened with polyurea with different thicknesses. The failure modes of the polyurea-strengthened arches, such as the spalling of concrete and the debonding of polyurea, were identified through the experiments. The test results indicate that polyurea-strengthening can change the internal stress distribution of the arch structure, prevent cracks from developing, and maintain structural integrity efficiently, even when exposed to repeated blast loads. A simplified theoretical model is developed for analyzing the strengthening mechanism of polyurea and the loading state of the arch. The damage situation of the composite arch predicted by the theoretical model is in high agreement with the test results. According to the study, it is possible to construct a composite protective arch structure with strong integrity and outstanding anti-blast performance by employing polyurea as reinforcement.

To study the dynamic response of curved polymer sandwich panels under contact explosion loads, three deformation stages of curved polymer sandwich panels were analyzed. A single degree of freedom rigid plastic dynamic model was established. The bending moment and membrane force effects of the panel and sandwich on deformation were considered in the model. The dynamic response of curved polymer sandwich panels with different panel and sandwich thicknesses under contact explosion loads was calculated through numerical simulation. The mid-span displacement of the panel calculated based on the dynamic model is in good agreement with the numerical calculation results. On this basis, the deformation and velocity changes of the panels were further analyzed, and the force and motion of the panels and sandwich at each stage in the dynamic model were verified. Research has shown that increasing the thickness of panels and sandwich panels can enhance the blast resistance of curved polymer sandwich panels, and increasing the front thickness has a more significant effect on improving the blast resistance of sandwich panels, which can provide a reference for future structural design and engineering applications.

Ordinary nonlinear differential equations with classical and fractional derivatives are used to simulate several real-world problems. Nonetheless, numerical approaches are used to acquire their solutions. While various have been proposed, they are susceptible to both disadvantages and advantages. In this paper, we propose a more accurate numerical system for solving nonlinear differential equations with classical and Caputo–Fabrizio derivatives by combining two concepts: the parametrized method and the predictor–corrector method. We gave theoretical analyses to demonstrate the method’s correctness, as well as several illustrated examples for both scenarios.

We have here an insight into the features of molecular structures of bio-polymers with α-helix structure using infrared spectrum and elucidated theoretically, its relationship with bio-functions. In this case, we analyzed first the features of molecular structure of collagen and collected further the infrared spectrum of absorption of collagen and bovine serum albumin containing α-helix conformation in 400–4000 cm^-1 as well as their changes of strength of infrared absorption with varying temperatures using Fourier Transform–Infrared (FT-IR) spectrometers in the region of 15–95°C. The results show that there is a new band of 1650 cm^-1 close to the amide-I band of 1666 cm^-1 or 1670 cm^-1 in these bio-polymers, its strength decreases exponentially with increasing temperature of the systems, which can be expressed by exp[-(0.437 + 8.987 × 10^-6 T²)], but 1666 cm^-1 band increases linearly with increasing temperature. We calculated the energy spectrum of the protein molecules with α-helix conformation using the Soliton Theory of bio-energy transport, which are basically same with the experimental results measured by us. From these results and soliton theory we can conclude that the nonlinear soliton excitation, corresponding to 1650 cm^-1 band and the exciton excitation, is related to 1666 cm^-1 band, exists in the collagen and bovine serum albumin. In the meanwhile, these results also verified that the soliton theory of bio-energy transport along α-helix bio-polymers is appropriate to the protein molecules with α-helix conformation. Therefore, the studied results are helpful to elucidate the relationship between the molecular structure and bio-function of these bio-polymers.

To develop large-span but ultralight lattice truss columns, a hierarchical IsoTruss column (HITC) was proposed. The multi-buckling behavior of the axially compressed HITC was analyzed by the finite element method (FEM) using a parametric approach in the framework of ANSYS parametric design language (APDL). It was demonstrated that the program enables efficient generation of the finite element (FE) model, while facilitating the parametric design of the HITC. Using this program, the effects of helical angles and brace angles on the buckling behavior of the HITC were investigated. Depending on the helical angles and brace angles, the HITCs mainly have three buckling modes: the global buckling, the first-order local buckling and the second-order local buckling. Theoretical multi-buckling models were established to predict the critical buckling loads. Buckling failure maps based on the theoretical analyses were also developed, which can be useful in preliminary design of such structures.

A study is made to investigate the compression behavior of different nested tube systems made of mild steel under lateral compression. The nested tube systems including stacked groups of circular, rectangular and square tubes are built for application in narrow compressive zones. The deformation mode of these systems is observed and their lateral compression behavior are identified. The desirable stepwise energy absorption is obtained by designing the nested tube system. The load response revealed that there is no appearance of the peak compressive load in the case of a circular-circular tube (CCT) system, while a circular-rectangular tube (CRT) system offers bigger peak compressive load compared with that of a circular-square tube (CST). The energy absorptions of CCT and CRT systems are smallest and greatest, respectively. This study also estimates the energy absorption capacity of these system. By implementing the “plastic hinge line” concept of the modified simplified super folding element (MSSFE) theory and superposition principle, the analytical models predicting compressive load of the nested tube systems are introduced. The analytical investigations are compared with the data obtained from tests on these systems. Excellent correlation is observed between the theoretical and experimental data.

To improve the calculation accuracy of the horizontal-to-vertical spectral ratio (HVSR) method, this study theoretically analyzed the influencing factors of Rayleigh wave polarizability. The phase difference of the horizontal component and the phase difference of the vertical component are found to play a key role in calculating the polarizability. The influence mechanism of the superposition of body waves and different Rayleigh waves on the polarizability of the Rayleigh wave is derived. The effects of the body wave, amplitude, frequency and Rayleigh wave superposition of different sources on the polarizability are verified by numerical simulation. The results show that the body wave significantly interferes with the polarizability of the Rayleigh wave. When a signal contains more than one set of Rayleigh waves, the superposition of the same-source Rayleigh waves does not affect the ratio. However, the superposition of Rayleigh waves from different sources significantly interferes with the calculation of the polarizability. This provides a technical method and a theoretical basis for accurately extracting the Rayleigh wave polarizability dispersion curve from a seismic record signal. This would help improve the detection accuracy of the HVSR method for ground pulse signals.

The single pile foundation of offshore wind turbine is currently the most common form, but the huge loads and the overturning moment make characteristics of foundation is different from offshore oil platforms. Using elastic-plastic element of ABAQUS simulation of pile foundation in bearing stress and failure modes in soil layers. The results show that the single pile foundation subjected to vertical ultimate load in soil layers, no plastic strain. Under the horizontal ultimate load, pile shows plastic strain. Under limit bending moment load, the plastic zone in the soil is mainly distributed in the surface soil in front of pile.