SummaryThis paper presents a wide parametric study aimed at elucidating the influence, on the computed seismic response of bridge piers, of two related aspects of the model: (1) the adoption of the classical hysteretic or the causal Biot's damping models for the soil and (2) the use of two different lumped parameter models of different complexity and accuracy to approximate the impedances of the pile foundation. A total of 2072 cases, including different superstructures, pile foundations, soil deposits, and seismic input signals, are studied. The results arepresented so that the influence of the different parameters involved in the analysis can be assessed. From an engineering point of view, both lumped parametermodels provide, in general, sufficiently low errors. The choice of the most adequate model for each case will depend not only on the configuration of the structure and the soil-foundation system but also on the assumed soil damping model, whose influence on the computed seismic responses is relevant in many cases. The nonphysical behaviour provided by the classical hysteretic damping model for the soil at zero frequency generates issues in the process of fitting the impedance functions. It is also found that larger deck displacements are predicted by Biot's model due to the higher damping at low frequencies provided by the classical hysteretic damping model. https://doi.org/10.1002/eqe.3137

Abstract Reverse osmosis efficiency depends on the precise prediction, among other factors, of membrane fouling. Although extensive research has been devoted to single foulants, rather less attention has been paid to simultaneous foulants which are more representative of real feed solutions. The main purpose of this research was therefore to characterize and quantify the fouling potential that results from the coexistence of simultaneous foulants. Silica and sodium alginate were used as respective models of inorganic and organic colloidal foulants. In order to understand the possible interactions, membrane fouling was first forced with a single foulant and the results compared to combined fouling. The experiments were carried out under constant pressure and employed synthetic seawater with 32 g/L of NaCl in a pilot-scale reverse osmosis unit. A standard commercial spiral-wound thin-film composite membrane was used. The results showed a more aggravated permeate flux decline in the combined fouling experiments. An exacerbated synergistic effect on membrane fouling was observed when the concentration of sodium alginate was equal to or higher than the concentration of silica. In these cases, the permeate flux decline of combined fouling was more severe than the sum of flux decline of individual foulants. https://doi.org/10.1016/j.desal.2018.03.032