Yes / Finite element (FE) analysis of fiber-reinforced polymer (FRP) reinforced concrete beams cast in U-shaped ultra-high performance concrete (UHPC) permanent formworks is presented in this paper. Concrete damage plasticity (CDP) and FRP brittle damage models were used to simulate the damage behavior of concrete and FRP bars. The results of FE simulation are in good agreement with the experimental results. Furthermore, parametric studies were conducted to investigate the effect of concrete and UHPC strengths, yield strength of steel bars, elastic modulus of FRP bars, ultimate tensile strength of FRP bars, types of UHPC normal strength concrete (NSC) interface and thickness of UHPC under different reinforcement conditions. Flexural performances, in terms of cracking, yield, ultimate loads and corresponding deflections, failure mode, energy dissipation and ductility, were investigated. Traction-separation model was used to describe the bonding degradation and the maximum slip of two types of bonding interfaces (smooth surface and medium-rough surface). Both flexural capacity and resistance to deformation of composite beams are significantly improved by the utilization of hybrid FRP/steel reinforcement. The UHPC formwork can also delay the occurrence and development of cracks. By appropriately increasing the strength of UHPC or elastic modulus of FRP bar, the flexural capacity of composite beams is effectively improved. It is expected that the results presented in this paper can guide the design and construction of U-shaped UHPC permanent formwork-concrete composite beams reinforced with FRP bars.

Better understanding and control of crack growth direction during hydraulic fracturing are essential for enhancing productivity of geothermal and petroleum reservoirs. Structural analysis of fracture propagation and impact on fluid flow is a challenging issue because of the complexity of rock properties and physical aspects of rock failure and fracture growth. Realistic interpretation of the complex interactions between rock deformation, fluid flow, heat transfer, and fracture propagation induced by fluid injection is important for fracture network design. In this work, numerical models are developed to simulate rock failure and hydraulic fracture propagation. The influences of rock deformation, fluid flow, and heat transfer on fracturing processes are studied using a coupled thermo-hydro-mechanical (THM) analysis. The models are used to simulate microscopic and macroscopic fracture behaviors of laboratory-scale uniaxial and triaxial experiments on rock using an elastic/brittle damage model considering a stochastic heterogeneity distribution. The constitutive modeling by the energy release rate-based damage evolution allows characterizing brittle rock failure and strength degradation. This approach is then used to simulate the sequential process of heterogeneous rock failures from the initiation of microcracks to the growth of macrocracks. The hydraulic fracturing path, especially for fractures emanating from inclined wellbores and closed natural fractures, often involves mixed mode fracture propagation. Especially, when the fracture is inclined in a 3D stress field, the propagation cannot be modeled using 2D fracture models. Hence, 2D/3D mixed-modes fracture growth from an initially embedded circular crack is studied using the damage mechanics approach implemented in a finite element method. As a practical problem, hydraulic fracturing stimulation often involves fluid pressure change caused by injected fracturing fluid, fluid leakoff, and fracture propagation with brittle rock behavior and stress heterogeneities. In this dissertation, hydraulic fracture propagation is simulated using a coupled fluid flow/diffusion and rock deformation analysis. Later THM analysis is also carried out. The hydraulic forces in extended fractures are solved using a lubrication equation. Using a new moving-boundary element partition methodology (EPM), fracture propagation through heterogeneous media is predicted simply and efficiently. The method allows coupling fluid flow and rock deformation, and fracture propagation using the lubrication equation to solve for the fluid pressure through newly propagating crack paths. Using the proposed model, the 2D/3D hydraulic fracturing simulations are performed to investigate the role of material and rock heterogeneity. Furthermore, in geothermal and petroleum reservoir design, engineers can take advantage of thermal fracturing that occurs when heat transfers between injected flow and the rock matrix to create reservoir permeability. These thermal stresses are calculated using coupled THM analysis and their influence on crack propagation during reservoir stimulation are investigated using damage mechanics and thermal loading algorithms for newly fractured surfaces.