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13:30   Design of new sports surfaces Chair: Paul Flemming 13:30 20 mins MODELLING AND ANALYSIS OF ALTERNATIVE “TILE TO TILE” ATTACHMENT MECHANISM DESIGNS, FOR A MODULAR PLASTIC TILE SPORTS FLOOR USING FINITE ELEMENT MODELLING Alexander Walker Abstract: Main Research Question(s) A sports surface that encourages elastic deformation during contact in combined anterior-posterior and medial-lateral directions through a process of horizontal deformation and displacement, may result in reduced foot and lower limb loading. Research concluded that a modular plastic tile surface which permits a limited amount of horizontal displacement via the tile connections has the potential to attenuate more braking force in comparison to a typical homogenous sports surface and therefore reduce the risk of tissue overloading and potential injury. A system whereby a modular plastic tile surface could encourage a limited amount of multi-lateral horizontal displacement via the tile attachment mechanisms was therefore developed. Research Method During rapid changes in direction or while landing on a sports surface, forces are transmitted from the athlete into the sports floor. Energy is preserved in the surface as the floor deforms, with a component of this energy being dissipated as a result of the dampening characteristics of the materials used to construct the sports surface. The sports tile development process therefore required the realisation of a retaining clip system to hold the tiles in firm engagement. Each tile also had to be able to be easily pulled apart for disassembly purposes. The tiles used in the surface had to be able to move independently from each other, in order for the surface to be able to dissipate energy. A design method was therefore adopted which saw the development of a number of alternative attachment approaches which were analysed via the Finite Element Analysis method. Results, Conclusions and General Significance A design solution was developed through a combination of iterative design and finite element simulation, with the final solution encouraging horizontal elastic deformation during athlete to surface contact, as a result of horizontal deformation and displacement. The “tile to tile” interface is the most critical aspect of the new modular tile surface that has been developed, as this feature in addition to its unique octagonal and square tessellated tile configuration, combine to allow multi-lateral horizontal displacement in the surface, and therefore the potential to reduce horizontal braking forces. 13:50 20 mins ROOT ZONE CONSTRUCTION AFFECTS HYBRID BERMUDAGRASS (C. DACTYLON X C. TRANSVAALENSIS) RESPONSES TO SIMULATED TRAFFIC Adam Thoms, James Brosnan, John Sorochan Abstract: Few studies have directly compared the types of root zones used for athletic fields. A two-year field study was conducted from 2012-2013 at the University of Tennessee Center for Athletic Field Safety (Knoxville, TN) to compare the performance of four root zones: a silt loam root zone, a sand-based root zone constructed to United States Golf Association (USGA) specifications, a sand-based root zone constructed to ASTM International (ASTM) specifications, and a sand-cap root zone (CAP) consisting of silt loam capped with 15 cm of sand that conformed to USGA particle size specifications. Hybrid bermudagrass (C. dactylon x C. transvaalensis, cv. ‘Tifway’) was established over all root zones. In addition to the bermudagrass treatments, two different synthetic turf surfaces varying in fiber type and infill ratio were included for comparison. All treatments were subjected to 30 simulated traffic events each autumn at rates of 0, 3 or 10 simulated traffic events per week in a split-plot design. Differences were only detected in percent green cover only for traffic rate in 2012. In 2013, bermudagrass on silt loam was reduced to 50% cover after ~10 simulated traffic events, compared to ~18 simulated traffic events on USGA and ASTM sand-based root zones. Surface hardness varied between treatments and years of the study; however, at no time did any surface exceed surface hardness thresholds associated with head injury (200 Gmax). Despite the loss of hybrid bermudagrass cover from the repeated simulated traffic events, few differences in surface hardness were detected between synthetic turf and hybrid bermudagrass plots in this study, regardless of root zone.   14:10 20 mins A 3D NUMERICAL MODEL FOR THE OPTIMIZATION OF RUNNING TRACKS PERFORMANCE Luca Andena, Serena Aleo, Stefano Mariani, Francesco Briatico-Vangosa, Andrea Pavan Abstract: In previous works, a finite element model of the shock absorbing characteristics of athletics tracks was developed, able to give sufficiently reliable predictions from laboratory tests performed on suitable material samples. The model proved to be effective in discriminating the effects of geometry (i.e. thickness) and material properties (essentially the elastic characteristics) on force reduction, thus allowing a first optimization of the tracks in view of their approval by the International Association of Athletics Federations (IAAF). This simplified 2D model neglected the real track structure, considering it as a single layer of material having homogenized properties. In the present study, a new 3D model was developed to accurately describe the structure of multi-layered tracks, with properties and geometrical construction (e.g. solid or honeycomb) differing from one layer to another. Several tracks having different combinations of top/bottom layers varying in both material formulation (i.e. chemical composition) and geometry were thus considered. Mechanical properties of the individual elements constituting the track were measured with small-scale laboratory tests, taking into account their strain-rate dependence. The 3D model allowed a complete representation of the loads acting on the track and it gave results which are in very good agreement with the experiments. This proves it to be a valuable tool for the purpose of optimizing the track in terms of material formulation as well as layer geometrical construction and arrangement: as an example, the effect of changing the cell size of the honeycomb pattern was investigated.