Design of floor structures for human induced vibrations

In recent years, the introduction of new structural materials and innovative construction processes, associated to architectural and space arrangement requirements, in multi-storey buildings construction have produced significantly more flexible floor structural systems. The design of these floor systems is usually controlled by serviceability criteria, deflections or vibrations. Recognizing a gap in the design codes, this report gives a procedure for the determination and assessment of floor response for human induced vibrations. First, the proposed procedure is presented, giving particular attention to the human induced loading characterization, dynamic properties and the comfort criteria for the verification of floor structural systems. Design charts are derived. Finally, it is presented a guidance manual to use the simplified procedure proposed for the design of building floors for human induced vibrations. Two worked examples of the proposed design procedure are given, namely a filigree slab with ACB-composite beams and a composite slab with steel beams.JRC.DG.G.5-European laboratory for structural assessmen

Biomass Increases Go under Cover: Woody Vegetation Dynamics in South African Rangelands

<div><p>Woody biomass dynamics are an expression of ecosystem function, yet biomass estimates do not provide information on the spatial distribution of woody vegetation within the vertical vegetation subcanopy. We demonstrate the ability of airborne light detection and ranging (LiDAR) to measure aboveground biomass and subcanopy structure, as an explanatory tool to unravel vegetation dynamics in structurally heterogeneous landscapes. We sampled three communal rangelands in Bushbuckridge, South Africa, utilised by rural communities for fuelwood harvesting. Woody biomass estimates ranged between 9 Mg ha^-1 on gabbro geology sites to 27 Mg ha^-1 on granitic geology sites. Despite predictions of woodland depletion due to unsustainable fuelwood extraction in previous studies, biomass in all the communal rangelands increased between 2008 and 2012. Annual biomass productivity estimates (10–14% p.a.) were higher than previous estimates of 4% and likely a significant contributor to the previous underestimations of modelled biomass supply. We show that biomass increases are attributable to growth of vegetation <5 m in height, and that, in the high wood extraction rangeland, 79% of the changes in the vertical vegetation subcanopy are gains in the 1-3m height class. The higher the wood extraction pressure on the rangelands, the greater the biomass increases in the low height classes within the subcanopy, likely a strong resprouting response to intensive harvesting. Yet, fuelwood shortages are still occurring, as evidenced by the losses in the tall tree height class in the high extraction rangeland. Loss of large trees and gain in subcanopy shrubs could result in a structurally simple landscape with reduced functional capacity. This research demonstrates that intensive harvesting can, paradoxically, increase biomass and this has implications for the sustainability of ecosystem service provision. The structural implications of biomass increases in communal rangelands could be misinterpreted as woodland recovery in the absence of three-dimensional, subcanopy information.</p></div