Browsing by Author "Trafford, Nicholas John"

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    A parametric study of the cable positioning of Tensairity beam members using experimental and finite element methods
    (Stellenbosch : Stellenbosch University, 2023-03) Trafford, Nicholas John; Venter, M. P.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH SUMMARY: A parametric study into the arrangement of reinforcing cables of a Tensairity beam girder was conducted. A 1500mm long, 140mm diameter beam was constructed with low-cost and freely available materials and fabrication methods. Three-point bending tests were performed to find cable arrangement parameters responsible for decreasing the central deflection of the beam. The reference test used in the study contained one pair of cables, with each cable forming a helical shape of one revolution around the bladder in a symmetrical orientation. Comparisons with the reference test were confirmed with two-tailed, pooled, statistical t-tests based on a 95% confidence interval. In comparison to the reference test, using one pair of cables with two or three revolutions decreased the stiffness of the beam by 49.7% and 55%, respectively. Adding a second pair of cables with either two or three revolutions statistically increased the stiffness of the beam by 8.5% in the worst case and by 18.6% in the best case scenario. The shortening of each pair of cables by 0%, 1%, 2% and 3%, respectively, was also investigated. The increase in stiffness was found for cables shortened by at least 1%. However, there was no added stiffness past a 1% decrease in length. The cable shortening affected the beam's shape more significantly than the stiffness. A non-linear Finite Element (FE) model of the Tensairity beam was also produced with linear-elastic material models derived from material testing of two components of the beam. The beam deflection calculated by the FE model, agreed within 5% of the experimental testing. The model concluded that a no-slip, no-roll assumption between the bladder and cables is viable for future simulation of Tensairity beams with shorted cables. Experimental testing also demonstrated viable use of a proportional method for maintaining air-pressure, which can be tested on full-scale models in future studies.