An analytical investigation focusing on the concrete damage progress of the PBL shear connector under the influence of various lateral pressures, employing a coupled RBSM and solid FEM model was carried out. The analytical model succeeded in simulating the test shear capacities and the failure modes adequately. The internal failure process was also clarified; the two horizontal cracks occurred near the top of the concrete dowels through the hole of the perforated steel plate, and afterward, the two vertical cracks also initiated and propagated along with the shear surface. In a low lateral pressure case, the shear strength was determined by the vertical cracks propagated along the shear surface. While as the amount of applied lateral pressure increased, the shear strength of the two vertical cracked surfaces was enhanced, and the shear strength of the PBL was characterized by the occurrence of the splitting cracks and caused the splitting failure into the side concrete blocks. Moreover, the combined effects of lateral pressure and hole diameters were also evaluated numerically, and it was found that the increase in shear strength was more in a large diameter case subjected to high lateral pressure because of the wide compressive regions generated around the concrete dowel.
The research manuscript deals with the brief introduction to the development and the validation of the new coupled numerical formulation, comprised of the Rigid Body Spring Model (RBSM) and the solid Finite Element Method (FEM) evaluating the bond behavior and failure mechanism of the actively confined and unconfined RC specimens loaded under pull-out test. The RBSM has been referred as an effective numerical framework for the evaluation of nonlinear mechanical response of concrete, quantitatively. However, the modeling of the reinforcing steel in RBSM has difficulty for simulating the complex behavior of steel such as elastoplasticity. Therefore, this limitation refers towards the development of new numerical formulation, i.e., coupled RBSM-FEM. In coupled RBSM-FEM, steel embedded in concrete is modeled using eight noded nonlinear solid finite elements considering the actual geometrical features e.g., rib height, shape and lug spacing, etc. In the coupled numerical formulation, concrete is modeled using RBSM. The boundary interfaces between concrete and steel (Solid FEM) has been accomplished through link element. The link element on the interface between RBSM element and solid FEM element consists of two shear springs and one normal spring. The proposed model is validated through the experimental investigations on RC specimens loaded under pull-out test with and without externally applied normal pressure. The proposed model has capability to simulate the internal fracture mechanism of concrete and elastoplastic behavior of the steel.
The National Research Universal (NRU) reactor at Canadian Nuclear Laboratories (CNL) operated safely for over 60 years and supported a wide range of applications including, testing of fuels and materials under typical power reactor conditions in two experimental loops (U-1 and U-2). Both experimental loops had been taken out of service to address seismic deficiencies. CNL applied a graded approach to successfully return one of these loops, the U-2 Loop to service. The graded approach, without compromising safety, applied a risk informed methodology commensurate to the potential risk posed by the operation of the U-2 Loop. The work enabled the U-2 Loop to resume operation until the NRU reactor was permanently shut down in Mar. 31, 2018, generating valuable data that will be used in the development of advanced nuclear fuels and materials. This paper describes the graded approach employed by CNL that supported U-2 loop return to service (RTS). The use of graded approach is articulated to support development of safety and licensing cases for small modular reactor projects.
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