Browsing by Author "Van der Voet, Adrian Frank"
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- ItemOpen AccessFinite element modelling of load transfer through articular cartilage(1992) Van der Voet, Adrian Frank; Shrive, Nigel G.Articular cartilage is a hydrated connective tissue lining apposing bones in synovial joints. Articular cartilage is essential for load transmission of joint forces and joint lubrication. Mechanical factors are implicated in joint diseases, such as osteoarthritis, therefore knowledge of mechanical function and properties is necessary in prevention and treatment of joint diseases. Indentation testing of intact cartilage is one method of evaluating the mechanical function and properties of articular cartilage. The first hypothesis is that indentation stiffness is affected by structural heterogeneity and mechanical anisotropy. Numerical finite element models revealed that indentation stiffness was insensitive to variations of anisotropy in the plane of the surface layer of articular cartilage. Cartilage was modelled as a poroelastic material, consisting of separate fluid and solid phases, to simulate viscoelastic mechanical behaviours due to expression of water from the matrix upon loading. A poroelastic finite element model successfully replicated mechanical behaviours of cartilage in confined compression and indentation. Also demonstrated was sensitivity of indentation stiffness to indentor roughness and permeability, cartilage layer geometry and the displacement rate of the indentor. A plane strain poroelastic finite element model of a typical whole joint tested the hypothesis that whole joints are affected by hydraulic boundary conditions which exist along the contact surface. This model simulated a displacement controlled relaxation test Results showed that hydraulically sealed boundaries at the contacting interface of apposing cartilages are a mechanically admissible condition for transmission of joint forces developed during stress relaxation. Observation of transient tensile stresses in cartilage revealed that collagen appears to function as tissue reinforcement. Vertical stress distribution in the cartilage layer was similar in shape and behaviour to that found in numerical simulations of idealized indentation tests. This suggests that indentation testing is a valid means to simulate cartilage compression behaviours in vivo. The full joint model was modified to model joint articulation. Tensile stresses, developed near the contacting interface, demonstrated that superficial collagen has a function in joint articulation. The methods used in this dissertation show promise in further investigations of mechanical behaviours of joints and mechanisms of joint disease and repair.
- ItemEmbargoThe shear strength of slabs with mechanically anchored shear reinforcement(1980) Van der Voet, Adrian Frank; Dilger, Walter H.The use of reinforced concrete flat plates (slabs) in floor construction is often limited by the punching shear strength of the slab-column connection. The purpose of this study is to investigate the use of shear reinforcement, consisting of thin vertical bars with square anchor plates welded at both ends, as a means of improving shear strength and ductility of slabs. Eight specimens were tested, including one without shear reinforcement. Slab dimensions were 1900 x 1900 mm and 150 mm deep (effective depth d = 113 mm) and the column dimensions were 250 x 250 mm. Only axial forces were applied to the centrally located column. Test variables consisted of the number of shear reinforcement elements, the area of each element and the distribution of the elements within the slab. Two types of shear failure are possible; failure by yielding of the shear reinforcement adjacent to the column (under-reinforced for shear) or failure by exhaustion of the shear strength of the slab concrete on a section to the outside of the shear reinforcement, with little or no yielding of the shear reinforcement (over-reinforced for shear). The nominal concrete shear stress which allows the latter failure condition to occur was calculated using a design perimeter extending 'd/2' beyond the outer row of shear reinforcement and was found to be inversely proportional to the length of the design perimeter. The former failure condition depends on the yield force developed by the shear reinforcement within a distance 'd' of the column. Of the seven shear reinforced slabs, one failed after the shear reinforcement yielded; the remainder failed by punching along a section outside the shear reinforcement. A procedure for the design of a slab under-reinforced for shear is presented. The concrete shear strength is calculated using the current Canadian CSA Code equation for the nominal slab punching strength. The contribution by the shear reinforcement to the shear strength of a slab is determined by the elements located within 'd' of the column face, using the truss analogy to account for the effects of spacing and inclination of the failure surface. The ultimate shear strength of a thin slab can be increased by at least 33 percent over the current Code provisions for slabs containing mechanically anchored shear reinforcement so long as the shear reinforcement is suitably detailed. While slab ductility was improved by including shear reinforcement, full yield lines were not observed for any test.