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Multi-objective optimal design of inerter-based vibration absorbers for earthquake protection of multi-storey building structures
In recent years different inerter - based vibration absorbers (IVAs) emerged for the earthquake protection of building structures coupling viscous and tuned - mass dampers with an inerter device . In the three most popular IVAs the inerter is functioning either as a motion amplifier [tuned - viscous - mass - damper (TVMD) configuration], mass amplifier [tuned - mass - damper - inerter (T MDI) configuration], or mass substitute [tuned - inerter - damper (TID) configuration]. Previous work has shown that through proper tuning , IVAs achieve enhanced earthquake - induced vibration suppression and/or weight reduction compared to conventional dampers/absorbers , but at the expense of increased control forces exerted from the IVA to the host building structure . These potentially large forces are typically not accounted for by current IVA tuning approaches. In this regard, a multi-objective IVA design approach is herein developed to identify the compromise between the competing objectives of (i) suppressing earthquake-induced vibrations in buildings, and (ii) avoiding development of excessive IVA (control) forces, while, simultaneously, assessing the appropriateness of different modeling assumptions for practical design of IVAs for earthquake engineering applications . The potential of the approach to pinpoint Pareto optimal IVA designs against the above objectives is illustrated for different IVA placements along the height of a benchmark 9-storey steel frame structure. Objective (i) is quantified according to current performanc e-based seismic design trends using first-passage reliability criteria associated with the probability of exceeding pre-specified thresholds of storey drifts and/or floor accelerations being the engineering demand parameters (EDPs) of interest . A variant, simpler, formulation is also considered using as performance quantification the sum of EDPs variances in accordance to traditional tuning methods for dynamic vibration absorbers. Objective (ii) is quantified through the variance of the IVA force. It is found that reduction of IVA control force of up to 3 times can be achieved with insignificant deterioration of building performance com pared to the extreme Pareto optimal IVA design targeting maximum vibration suppression , while TID and TMDI a chieve practically the same building performance and significantly outperform the TVMD. Moreover, it is shown that the simpler variant formulation may provide significantly suboptimal reliability performance . Lastly, it is verified that the efficacy of optimal IVA designs for stationary conditions is maintained for non-stationary stochastic excitation model capturing typical evolutionary features of earthquake excitations
Performance quantification of extensive green roof substrate blend: Expanded shale and biochar
Urban stormwater management practices often involve the redirection of runoff to local waterbodies. As such, the quality of runoff directly affects the condition of these receiving waters. Green roofs offer many benefits to the urban environment including attractive aesthetics, thermal insulation for buildings and stormwater runoff reduction. Unfortunately, in order to promote the spread of vegetation, fertilization is often practiced that can lead to elevated nutrient concentrations in runoff and, ultimately, nearby streams, rivers and bays. Different amounts of biochar, pyrolyzed biomass, were added to model green roof trays to test for the ability of this charcoal-like substance to prevent nitrate and phosphate leaching. Analysis of leachate from natural and simulated rain events showed statistically significant differences of average nitrate concentrations for two out of four rain events, though none for phosphate. Samples from the natural rain event exhibited a clear inverse relationship between nitrate concentration and biochar quantity. The second simulated rain event, however, produced nitrate concentrations that rose and subsequently fell as biochar quantity increased. Further research is needed on the method by which biochar attracts anions though different experimental designs and equipment may more conclusively reveal that biochar can play a role in green roofs as a soil amendment. More noteworthy, though, may be the consistently high nutrient concentrations in leachate originating from the fertilized model trays. The fertilizer application rate of 5 g N/m2 may not be suitable for the substrate and vegetation used in this study but nonetheless it is strongly recommended that controlled-release fertilizer types are used
Subject: Supervisors and Managers
Compiled by Susan LaCette.Supervisors.pdf: 1059 downloads, before Oct. 1, 2020
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