Although orthotropic steel decks (OSDs) have been widely used in the construction of long-span bridges, there are frequently reported fatigue cracks after years of operation, and the bridge deck overlay also presents severe damage due to OSD crack-induced stiffness reduction. Ultra-high performance concrete (UHPC), recognized as the most innovative cementitious composites and the next generation of high-performance materials, shows high strength, ductility, toughness, and good performance on durability. After its first application to the OSD bridge in the early 2000s, the orthotropic steel–UHPC composite deck has been comprehensively studied worldwide. This review will summarize some important studies and findings on the behavior and fatigue performance of the orthotropic steel–UHPC composite deck. The existing studies and engineering applications indicate that such a deck system presents good bending behavior and high fatigue performance. The failure mode of shear studs in the UHPC layer is dominated by shear fractures. The cracking of the UHPC layer shall consider the superposition effect of stress from both the whole bridge structure and local decks. While some reasonable structural details in the traditional OSD may not work for the orthotropic steel–UHPC composite deck, this paper has shown that the steel–UHPC composite deck has excellent performance in bearing capacity, stiffness, and fatigue resistance. However, the fatigue performance of the steel–UHPC composite deck and its evaluation method still need validation from engineering applications. It is recommended to evaluate the stress behavior and structural parameters, as well as fatigue life by conducting the field test under in-service traffic conditions.

The application of cast-in-situ phosphogypsum as the wall material of building structures can greatly reduce the environmental pollution caused by phosphogypsum. Through the uniaxial compression test of cast-in-situ phosphogypsum specimens, the compressive strength of cast-in-situ phosphogypsum is determined, the constitutive relationship of the material is drawn up, and the elastic modulus and Poisson’s ratio of the material are determined. The results show that when the strain of the specimen is close to the peak strain, the cast-in-situ phosphogypsum has brittle properties and rapidly fails, where the failure state is mainly splitting failure. The retarder has a great influence on the peak stress. When the content of the retarder is about 0.3%, the peak stress is 8.6 MPa and the ultimate strain is 2.54 × 10⁻³, while the peak stress is 2.8 MPa and the ultimate strain is 2.01 × 10⁻³. The three segment constitutive fitted equations reflect all the characteristics of the compression specimen. When the strength of the cast-in-situ phosphogypsum is high, the elastic modulus is also high. When the content of the retarder is about 0.3%, the elastic modulus is 5300 MPa, and when the content of retarder is far greater than 0.3%, the elastic modulus is 2000 MPa. The Poisson’s ratio of material is recommended as 0.19.

Although the Orthotropic steel decks (OSDs) have been widely used in the construction of long-span bridges, there are frequently reported fatigue cracks after years of operation, and the bridge deck overlay also presents severe damage due to OSD crack-induced stiffness reduction. The ultra-high performance concrete (UHPC), recognized as the most innovative cementitious composites and the next generation of high-performance materials, shows high strength, ductility, toughness and well performance on durability. After its first application to the OSD bridge in early 2000s, the orthotropic Steel-UHPC composite deck has been comprehensively studied worldwide. This review will summarize some important studies and findings on behavior and fatigue performance of orthotropic steel-UHPC composite deck. The existing studies and engineering application indicate that such deck system presents good bending behavior and high fatigue performance. The failure mode of shear studs in UHPC layer is dominated by shear fractures. The cracking of UHPC layer shall consider the superposition effect of stress from both the whole bridge structure and local decks. While some reasonable structural details in the traditional OSD may not work for the orthotropic steel-UHPC composite deck. It is recommended to evaluate the stress behavior and structural parameters, as well as fatigue life by conducting the field test under in-service traffic conditions.

Accurate and scalable estimation of rock shear strength parameters is essential for remote-sensing-supported geological hazard assessment, slope stability evaluation, and engineering geological mapping. However, determining cohesion and internal friction angle requires multiple triaxial tests under different confining pressures, which are time-consuming, costly, and difficult to apply widely. To support remote-sensing-oriented geoscience and civil engineering applications, this study develops a hybrid machine learning framework for estimating cohesion and internal friction angle from geophysical and mechanical indicators. A cross-source database was compiled from published rock records collected from the Jinchuan mining area in China and the Luhri area in India. After completeness screening and unit harmonization, 213 mixed-lithology cases were retained for modeling, with P-wave velocity, density, uniaxial compressive strength, and tensile strength used as input variables. An Equilibrium Optimizer was coupled with a multilayer perceptron to optimize the network weights and biases, and model performance was evaluated using five-fold cross-validation, independent testing, repeated runs, and comparisons with conventional MLP and several typical machine learning models. The proposed EO–MLP model achieved high prediction accuracy, with test-set coefficient of determination values of 0.946 for internal friction angle and 0.983 for cohesion and corresponding RMSE values of 1.072 and 0.671, respectively. Robust scaler normalization produced the best performance among the three tested normalization strategies. SHapley Additive exPlanations analysis indicated that density was the dominant predictor of cohesion, whereas uniaxial compressive strength and P-wave velocity made the largest contributions to internal friction angle prediction. The proposed framework provides an indirect data-driven tool for estimating shear strength parameters and can complement engineering-geological investigation and rock engineering design.