Research on Influence Factors of Bearing Capacity of Concrete-Filled Steel Tubular Arch for Traffic Tunnel

When a traffic tunnel passes through special strata such as soft rock with high geo-stress, expansive rock, and fault fracture zones, the traditional supporting structure is often destroyed due to complicated loads, which threatens the construction and operation safety of tunnel engineering. Concrete-filled steel tubular (CFST) structure gives full play to the respective advantages of steel and concrete and has better bearing capacity and economic benefits than traditional support structure, which has achieved good results in some underground engineering applications. In order to promote the application of CFST in the construction of traffic tunnels with complex geological conditions and improve the bearing capacity of the initial supporting structure of tunnels, the influencing factors of the bearing capacity of CFST arch were studied by numerical simulation. The main achievements are as follows: (1) The load-displacement curves of CFST members under different material parameters are basically consistent. CFST members have significant restrictions on displacement in the elastic stage and have high ultimate bearing capacity. Although the bearing capacity decreases obviously after reaching the peak, it shows good extension performance. (2) The height of the steel tube section, the thickness of the steel tube wall and the grade of the core concrete have an approximately linear positive correlation with the bearing capacity of CFST arch, but the influence of these three factors on the bearing capacity of CFST arch decreases in turn, and when the grade of core concrete increases above C50, it has no significant effect on the bearing capacity of members.

Study on synergistic system of energy-absorbing yielding anti-impact supporting structure and surrounding rock

Through the improvement of supporting structure and the utilization of the interaction between surrounding rock and supporting structure, the synergistic system of energy-absorbing yielding anti-impact supporting structure and surrounding rock is established. The process of energy absorption device, energy-absorbing yielding anti-impact supporting structure and synergistic system under impact is simulated to analyze the properties of them. The following conclusions could be drawn. The deformation and yielding process under compression of energy absorption device is divided into five stages. Compared with the traditional supporting structure, the energy-absorbing yielding anti-impact supporting structure has the reaction force with lower value and smaller fluctuation range before the deformation of the energy absorption device reaches the third ascending section. The synergy between surrounding rock and supporting structure plays an important role in roadway support. Compared with the supporting structure without surrounding rock, the reaction force of the supporting structure in the synergistic system is lower, and a stationary stage is added in the early stage of the reaction force curve.

Research on the Method and Model for Calculating Impact Load in the Rockburst Tunnel

Among several design methods of tunnel supporting structure, the load-structure method is widely used in different countries, but the determination of load is essential in this design method. The problem of rockburst is becoming more prominent as tunnel engineering enters the deep underground space. However, the research on the impact load on the supporting structure is insufficient in relevant fields. Therefore, from the perspective of energy, this paper deduces the method and model for calculating the impact load of the rockburst tunnel acting on the supporting structure by using the method of structural mechanics first, after the location effect of impact load is determined under different section types and different section sizes. The results indicated that: dynamic load factor K is related to the stiffness EI and supporting size coefficient K0 of the supporting structure, also the difference of impact load in different sections is proved. Tunnel rockburst-prone location is related to lateral pressure coefficient, thus when λ = 1, the probability of rockburst in the whole circular tunnel is the same, while side wall and vault are prone to rockburst in single-track horseshoe tunnel, and the side wall is prone to rockburst in double-track horseshoe tunnel; furthermore when λ > 1, the vault and the inverted arch are prone to rockburst; additionally, when λ < 1, the rockburst is most likely to occur in the arch waist of the circular tunnel and the side walls and the arch waist of the horseshoe tunnel. Finally, the rockburst tunnel’s local load-structure calculation model and the calculation process based on the model are provided.

In Vitro Fatigue and Fracture Load of Monolithic Ceramic Crowns Supported by Hybrid Abutment

Objective: This study evaluated the performance of zirconia and lithium disilicate crowns supported by implants or cemented to epoxy resin dies. Methods: Eigthy zirconia and lithium disilicate crowns each were prepared and assigned in four groups according to the crown material and supporting structure combinations (implant-supported zirconia, die-supported zirconia, implant-supported lithium disilicate, and die-supported lithium disilicate). Ten crowns in each group acted as control while the rest (n=10) underwent thermocycling and fatigue with 100 N loading force for 1.5 million cycles. Specimens were then loaded to fracture in a universal testing machine. Data were analysed using one-way ANOVA and Tukey multiple comparison test with a 95% level of significance. Results: No implants or crown failure occurred during fatigue. The mean fracture load values (control, fatigued) in newton were as follows: (4054, 3344) for implant-supported zirconia, (3783, 3477) for die-supported zirconia, (2506, 2207) for implant-supported lithium disilicate, and (2159, 1806) for die-supported lithium disilicate. Comparing the control with the corresponding fatigued subgroup showed a significantly higher fracture load mean of the control group in all cases. Zirconia showed a significantly higher fracture load mean than lithium disilicate (P=0.001, P<0.001). However, comparing crowns made from the same material according to the supporting structure showed no significant difference (P=0.923, P=0.337). Conclusion: Zirconia and lithium disilicate posterior crowns have adequate fatigue and fracture resistance required for posterior crowns. However, when heavy fatigue forces are expected, zirconia material is preferable over lithium disilicate. Zirconia and lithium disilicate implant-supported crowns cemented to hybrid abutments should have satisfactory clinical performance.

Study on Failure Characteristics and Rock Burst Mechanism of Roadway Roof under Cyclic Dynamic Load

Rock burst is a catastrophic phenomenon that often occurs in underground rock mass engineering. In order to reveal the essence of rock burst of a hard roof in the process of roadway excavation, the particle discrete element method is used to establish a roadway model and simulate the disturbance of harmonic dynamic load based on the analysis of a rock burst accident in a deep mine. The crack field, stress field, displacement field, and kinetic energy of roadway surrounding rock disturbed by cyclic dynamic load were analyzed, and the disaster mechanism of roadway impacting roof instability was discussed. The results show that, compared with the roadway support structure under static load that can give full play to its control function of surrounding rock, the roadway surrounding rock will collapse and lose stability in a large area under the roof cyclic dynamic load, and the ordinary supporting structure cannot give full play to its control function of surrounding rock, resulting in the surrounding rock destruction and supporting structure failure. In addition, the essence of rock burst in a hard thick roof is due to the instantaneous superposition of static stress and dynamic load, leading to the instantaneous instability and collapse of roadway roof in a large area. The research is of great significance to further understand the deformation and failure mechanism of roadway surrounding rock under strong impact load, to guide the safe production and prevent the occurrence of rock burst hazard in underground rock mass engineering.

Cutting Edge Fabrication: Investigating Timber Sheet Materials with Robotic Fabrication

<p>Timber sheet materials have been used in the same manner for decades despite having a vital role in the construction industry. This often results in indistinguishable surfaces with no identity. The research developed in this thesis is the creation of a workflow to create a self-supporting structure from sheet materials using robotic fabrication and computational tools. Timber sheet materials is the key focus for this research, as timber is a material that can be altered in a variety of ways. Japanese timber connections were a strong influence for this research, due to its prolonged life span and sustainable advantages. In the past, timber fabrication techniques have been limited due to design limitations. Current technology, specifically parametric software combined with the robotic arm was explored to find how it can create timber connections to connect sheet materials at different angles. This method was utilised to repurpose the concept of sheet materials towards a complex structure, which adopted the idea of mass customisation over mass production. Prototypes of timber connections were created to develop an outcome that will structurally support itself. The outcome of each prototype was evaluated and compared with one another to establish which connection would be most suited to bring forward to the self-supporting structure. Computational simulations were used to explore individual structures which created panels that were automatically flattened in the software. This allowed the digital file to be transferred to the robotic arm to be milled. Using the robotic arm was an advantage, as it can rotate around six-axis giving multiple degrees of design freedom which broadened the range of construction techniques that can be used with sheet materials. There is a high chance of human error with manual labour, therefore precision is a positive attribute of the robotic arm. The precision helped minimise waste compared to manual labour. This thesis presented an opportunity for the design/construction industry to adopt a new workflow to bring leading-edge technology to focus on sustainable materials and to steer away from the repetitions evident in buildings today.</p>

Cutting Edge Fabrication: Investigating Timber Sheet Materials with Robotic Fabrication

<p>Timber sheet materials have been used in the same manner for decades despite having a vital role in the construction industry. This often results in indistinguishable surfaces with no identity. The research developed in this thesis is the creation of a workflow to create a self-supporting structure from sheet materials using robotic fabrication and computational tools. Timber sheet materials is the key focus for this research, as timber is a material that can be altered in a variety of ways. Japanese timber connections were a strong influence for this research, due to its prolonged life span and sustainable advantages. In the past, timber fabrication techniques have been limited due to design limitations. Current technology, specifically parametric software combined with the robotic arm was explored to find how it can create timber connections to connect sheet materials at different angles. This method was utilised to repurpose the concept of sheet materials towards a complex structure, which adopted the idea of mass customisation over mass production. Prototypes of timber connections were created to develop an outcome that will structurally support itself. The outcome of each prototype was evaluated and compared with one another to establish which connection would be most suited to bring forward to the self-supporting structure. Computational simulations were used to explore individual structures which created panels that were automatically flattened in the software. This allowed the digital file to be transferred to the robotic arm to be milled. Using the robotic arm was an advantage, as it can rotate around six-axis giving multiple degrees of design freedom which broadened the range of construction techniques that can be used with sheet materials. There is a high chance of human error with manual labour, therefore precision is a positive attribute of the robotic arm. The precision helped minimise waste compared to manual labour. This thesis presented an opportunity for the design/construction industry to adopt a new workflow to bring leading-edge technology to focus on sustainable materials and to steer away from the repetitions evident in buildings today.</p>