Previous studies have shown that coal-based solid waste can be utilized in combination with cement, silica fume, and other modified materials to create a cemented backfill material. However, traditional cemented backfill materials have poor mechanical properties, which may induce the emergence of mining pressure and trigger dynamic disaster under complex mining conditions. In this study, the nanocomposite fiber was used to modify the traditional cemented backfill materials and a new cemented backfill material was developed using coal-based solid waste, nanocomposite fiber and other materials. Specifically, coal gangue, fly ash, cement, and glass fibers were used as the basic materials, different mass fractions of nano-SiO₂ were used to prepare cemented backfill materials, and the mechanical enhancement effect of the compressive strength, tensile strength, and shear strength of the modified materials was analyzed. The results show that when the nano-SiO₂ dosage is 1%, the optimal compressive strength of the specimens at the curing age of 7 d can be obtained compared with cemented materials without nano-SiO₂, and the compressive strength of the modified specimens raises by 84%; when the nano-SiO₂ dosage is 1%, the optimal tensile strength and shear strengths of the modified specimens can be obtained at the curing age of 28 d, increasing by 82% and 142%. The results reveal that nanocomposite fibers can be used as additives to change the mechanical properties of cemented backfill materials made using coal-based solid waste. This study provides a reference for the disposal of coal-based solid waste and the enhancement of the mechanical properties of cemented backfill materials.

The mechanical properties and microstructure of the cemented paste backfill (CPB) in dry–wet cycle environments are particularly critical in backfill mining. In this study, coal gangue, fly ash, cement, glass fiber, and nano-SiO₂ were used to prepare CPB, and dry–wet cycle tests on CPB specimens with different curing ages were conducted. The compressive, tensile, and shear strength of CPB specimens with different curing ages under different dry–wet cycles were analyzed, and the microstructural damage of the specimens was observed by scanning electron microscopy (SEM). The results show that compared with the specimens without dry–wet cycles, the uniaxial compressive strength, tensile strength, and shear strength of the specimens with a curing age of 7 d after seven dry–wet cycles were the smallest, being reduced by 40.22%, 58.25%, and 66.8%, respectively. After seven dry–wet cycles, the compressive, tensile, and shear strength of the specimens with the curing age of 28 d decreased slightly. The SEM results show that with the increasing number of dry–wet cycles, the internal structure of the specimen becomes more and more loose and fragile, and the damage degree of the structural skeleton gradually increases, leading to the poor mechanical properties of CPB specimens. The number of cracks and pores on the specimen surface is relatively limited after a curing age of 28 d, while the occurrence of internal structural damage within the specimen remains insignificant. Therefore, the dry–wet cycle has an important influence on the both mechanical properties and microstructure of CPB. This study provides a reference for the treatment of coal-based solid waste and facilitates the understanding of the mechanical properties of backfill materials under dry–wet cycling conditions.

With the development of blind bolts that can be installed from the outer side of a section, the application of steel pipe hollow sections in prefabricated structures has become possible. The novel one-side bolt with a flip-top collapsible washer (FTW-OSB) is proposed, which can fold the washer at the end of the bolt to achieve a simple and efficient installation. Firstly, the components and installation process of the FTW-OSB are introduced. Additionally, axial tensile tests were carried out on three types of new bolts, and the failure mode, load–displacement curve, and ultimate capacity were analyzed. Based on this, the finite element model was verified, and through a series of finite element parameter analyses, the influence of washer size and construction, the friction coefficient, and the contact surface size on the new bolt were analyzed and optimized. The results show that the L-shaped washer can prevent washer rotation and has better anchoring performance than the I-shaped washer. The washer thickness, height, and upper contact surface size are the key factors affecting the anchoring performance of the FTW-OSB bolt. Among these factors, when the washer thickness increases from 0.1 d₀ to 0.3 d₀, the ultimate capacity and initial stiffness of the FTW-OSB bolt increase by 136.5% and 100.3%, respectively. The lower contact surface size and friction coefficient can be ignored. The failure model of the FTW-OSB is mainly washer shear failure and bolt tension failure. By effectively adjusting the washer thickness, side wall height, and upper contact surface size, shear failure of the washer can be avoided and an anchoring performance can be achieved that is the same as that of the same type of 10.9-grade ordinary high-strength bolt.

Based on the newly developed sinking headframe for the deep and large shaft, the finite element model of the full‐scale headframe was established by using SAP2000. Through the calculation, the theoretical stress of the headframe at sinking depths of 40 m, 143 m, 223 m, 518 m, 762 m, 1000 m, 1250 m, and 1503 m was obtained and then compared with the field measured stress. The results show that with the increase of shaft sinking depth, the theoretical stress of finite element simulation and the field measured stress of each member of the sheave wheel platform and the headframe increase linearly, and for the maximum member stress in the upper, middle, and lower layers of the headframe, the numerical simulation value is greater than the field measured value and less than the designed steel strength. In other words, under normal working conditions, headframe members are in the elastic stress stage and meet the design requirements, and instability failure of headframe members will not occur. The end‐restraint mode of the supporting bars has a great influence on the force of the top member. The reasonable selection of the restraint mode in the simulation is the key to the accuracy of the calculation results. The simulation results well reflect the actual stress of the headframe and provide a reliable guarantee for the follow‐up work of the project.

Modular steel buildings that employed off-site prefabricated volumetric units offered advantages in construction speed and sustainability. The highly integrated buildings assembled by only column-to-column connections were prone to a global collapse, and beam-to-beam connections could greatly promote the overall mechanical performance. However, cooperative bending performance has not been fully understood from a theoretical perspective, and therefore, a performance-based structural design cannot be conducted in practical engineering. In the present study, the laminated double beams in modular steel buildings were theoretically and experimentally investigated. Theoretical models for interfacial slip strain and slippage were established based on differential equations, accounting for both frictional and bolted connection types. In addition, mathematical expressions for bending curvature incorporating interfacial slip were derived, leading to a theoretical procedure for calculating the equivalent initial bending stiffness. In this way, the mechanical performance of laminated beams was analyzed, and the superimposed bending effect was further evaluated. The results demonstrated that bolted connections improved bending capacity by approximately 8% and increased initial bending stiffness by 17–28% compared to friction-only connections. The proposed stiffness prediction models showed significant agreement with experimental data, providing a theoretical basis for the structural design of laminated beams in modular steel buildings.

Modular steel buildings were characterized by the off-site prefabrication of standardized volumetric units, offering the significant advantages in construction speed, environmental sustainability, and on-site safety. It was well-known that the highly integrated buildings was prone to the global collapse assembled by only column-to-column connections and the beam-to-beam connections could greatly promote the overall mechanical performance. However, the cooperative bending performance have not been fully understood in a theoretical prospective, thereby unable to conduct the performance-based structural design in practical engineering. In present study, the superimposed bending performance of laminated double beams in modular steel buildings were theoretically and experimentally investigated. The theoretical analysis was performed on the modular laminated beams with friction and point connection of high-strength bolts. The analytical expressions for interfacial slipping strain were established based on the fundamental differential equation. The theoretical models of interfacial slippage were derived for the laminated steel beams with different connections. Then, the mathematical expressions were established for the bending curvature of laminated beams, considering interfacial slippages. In this way, the theoretical procedure to calculate the equivalent initial bending stiffness were ultimately developed. By this way, the mechanical performance of laminated beams was analyzed and the superimposed bending effect was further evaluated. It was indicated that the bending capacities of laminated beams with bolt connections were approximately improved by 8% compared to specimens with only friction restraints. In addition, the enhancement of initial bending stiffness reached 17% to 28%. Finally, the prediction models of the initial bending stiffness were greatly validated by the experimental data, which could provide the theoretical foundations for the structural design of laminated beams in modular steel buildings.