Experimental tests on shallow foundations of onshore wind turbine towers

The current effort towards the progressive switch from carbon-based to renewable energy production is leading to a relevant spreading of both on- and off-shore wind turbine towers. Regarding reinforced concrete shallow foundations of onshore wind turbine steel towers, possible reductions of reinforcement may increase their sustainability, speed of erection, and competitiveness. The article presents the results of an experimental program carried out at Politecnico di Milano concerning both cyclic and monotonic loading, simulating extreme wind conditions on 1:15 scaled models of wind turbine steel towers connected by stud bolt adapters to reinforced concrete shallow foundations embedded in a sandy soil. Three couples of foundation specimens were tested with different reinforcement layouts: (a) similar to current praxis, (b) without shear reinforcement, and (c) without shear reinforcement and with 50% of ordinary steel rebars replaced by steel fibers. Additional vertical loads were added to the small-scale models in order to ensure similarity in terms of stresses. The test results allowed to (i) characterize the mechanical behavior of the foundation element considering soil-structure interaction under both service and ultimate load conditions, (ii) assess the foundation failure mode, (iii) highlight the role of each typology of reinforcing bars forming the cage, and (iv) provide hints for the optimization of these latter

Identificzione di strutture eccitate alla base e controllate con dispositivi non lineari

Per ridurre la risposta sismica esistono le tecniche del controllo strutturale che si classificano in: attivo, ibrido, semi attivo e passivo. Tra queste le tecniche del controllo passivo e semi attivo sono molto diffuse, e sono applicate in molte situazioni tipiche dell’ingegneria strutturale come mostrato nella Figura 1 nel caso dei: a) ponti, b e c) edifici, d) strutture adiacenti. Gli esempi mostrati hanno alcune caratteristiche comuni: sono utilizzati e posizionati opportunamente pochi dispositivi di controllo; è sempre possibile riconoscere due sottostrutture una a comportamento lineare e una a comportamento non lineare. In questi casi il problema della identificazione è diviso in una parte che riguarda la struttura a comportamento lineare (la struttura principale da proteggere), e dall’altra quella a comportamento non lineare (i dispositivi di controllo). Il lavoro focalizza l’attenzione sulla identificazione dei parametri modali e fisici della sottostruttura lineare eccitata dal sisma e dalle forze di controllo. Se sono misurati l’input sismico, le forze di controllo e le risposte sismiche, usando l’algoritmo ERA/OKID si identificano i parametri modali della struttura (frequenze, smorzamenti, autovettori non normalizzati e sismici). Se con le misure è stato realizzato almeno un grado di libertà collocato, allora è possibile normalizzare gli autovettori ed attenere, in alcuni casi, le matrici di massa, di rigidezza e di smorzamento. La metodologia di identificazione proposta è applicata al caso di due strutture adiacenti collegate mediante un dispositivo di controllo magnetoreologico utilizzando dati ottenuti con un modello numerico agli elementi finiti. I risultati ottenuti mostrano la validità della metodologia di identificazione proposta

Shaking table experimentation on adjacent structures controlled by passive and semi-active MR dampers

This paper presents the results of shaking table tests on adjacent structures controlled by passive and semi-active MR dampers. The aim was to demonstrate experimentally the effectiveness of passive and semi-active strategies in reducing structural vibrations due to seismic excitation. The physical model at issue was represented by two adjacent steel structures, respectively of 4 and 2 levels, connected at the second level by a MR damper. When the device operated in semi-active mode, an ON-OFF control algorithm, derived by the Lyapunov stability theory, was implemented and experimentally validated. Since the experimentation concerned adjacent structures, two control objectives have been reached: global and selective protection. In case of global protection, the attention was focused on protecting both structures, whereas, in case of selective protection, the attention was focused on protecting only one structure. For each objective the effectiveness of passive control has been compared with the situation of no control and then the effectiveness of semi-active control has been compared with the passive one. The quantities directly compared have been: measured displacements, accelerations and force-displacement of the MR damper, moreover some global response quantities have been estimated from experimental measures, which are the base share force and the base bending moment, the input energy and the energy dissipated by the device. In order to evaluate the effectiveness of the control action in both passive and semi-active case, an energy index EDI, previously defined and already often applied numerically, has been utilized. The aspects investigated in the experimentation have been: the implementation and validation of the control algorithm for selective and global protection, the MR damper input voltage influence, the kind of seismic input and its intensity. (C) 2013 Elsevier Ltd. All rights reserved

Feed frequency in a Sequencing Batch Reactor strongly affects the production of polyhydroxyalkanoates (PHAs) from volatile fatty acids

The production of polyhydroxyalkanoates (PHAs) by activated sludge selected in a sequencing batch reactor (SBR) has been investigated. Several SBR runs were performed at the same applied organic load rate (OLR), hydraulic retention time (HRT) and feed concentration (8.5 g COD L-1 of volatile fatty acids, VFAs) under aerobic conditions. The effect of the feeding time was only evaluated with a cycle length of 8 h; for this particular cycle length, an increase in the storage response was observed by increasing the rate at which the substrate was fed into the reactor (at a fixed feeding frequency). Furthermore, a significantly stronger effect was observed by decreasing the cycle length from 8 h to 6 h and then to 2 h, changing the feed frequency or changing the organic load given per cycle (all of the other conditions remained the same): the length of the feast phase decreased from 26 to 20.0 and then to 19.7% of the overall cycle length, respectively, due to an increase in the substrate removal rate. This removal rate was high and similar for the runs with cycle lengths of 2 h and 6 h in the SBR. This result was due to an increase in the selective pressure and the specific storage properties of the selected biomass. The highest polymer productivity after long-term accumulation batch tests was 1.7 g PHA L-1 d(-1), with PHA content in the biomass of approximately 50% on a COD basis under nitrogen limitation. The DGGE profiles showed that the good storage performance correlated to the development of Lampropedia hyalina, which was only observed in the SBR runs characterized by a shorter cycle length

Preliminary characterization of TCE- and TeCA-cometabolizing aerobic cultures under suspended and immobilized form

Chlorinated aliphatic hydrocarbons (CAHs) are toxic and environmental hazardous solvents increasingly detected in soil and groundwater for which new and most effective biormemdiation approaches are needed. In this context, the European project MINOTAURUS is aiming to develop groundwater bioremediation robust and reliable strategies based on the use of immobilized biocatalysts. This work was focused on the enrichment of aerobic trichloroethylene (TCE) and 1,1,2,2-tetrachloroethane (TeCA) co-metabolizing microbial cultures from a contaminated site in Rho (MI, Italy), their preliminary characterization both as freely suspended and immobilized biomass on different carrier materials (Biomax\uae, Biopearl\uae, Biomech\uae, Cerambios\uae) and the selection of the best performing culture to be employed in a continuous Packed Bed Reactor (PBR) process. The best performing culture was obtained through serial enrichment on filter sterilized site-water or a similar synthetic water in the presence of butane (2 mg/L) as carbon and energy source and TCE (10 mg/L) plus TeCA (3 mg/L). The structure and composition of the microbial population was carried out through denaturing gradient gel electrophoresis (DGGE) analysis of the 16S rRNA genes. The DGGE analysis outlined that the structure of the suspended microbial community changed remarkably throughout the enrichment with the exception of the most prominent phylotype. However, according to the Dice similarity coefficient, lower changes occurred during the last sub-culturing step, indicating a gradual stabilization of the community structure. When immobilized on different carriers, the most prominent phylotype previously detected represented a minor fraction of the immobilized community; conversely, several of the minor bands occurring in the suspended culture became dominant within the biofilm. Such a drastic change in the structure of the microbial community was evidenced by the separate clustering of the DGGE profiles from suspended cell cultures and biofilms. Furthermore, the high similarity indexes between the communities immobilized on different carriers (57.3% to 73.7%) suggest that the evolved consortium is quite stable and that the material and shape of the carrier do not affect remarkably its composition. Complementary information obtained from degradation kinetic tests showed that the selected culture immobilized on Biomax\uae retained the highest degrading activity. Identification of the community members via band sequencing and phylogenetic analysis is in progress and will allow to obtain key information on the potential TCE and TeCA co-metabolizing species both in the suspended and in the immobilized communities

A chemical-biological integrated approach for the valorization of olive mill wastewaters

An integrated chemical-biological process for the recovery of natural phenolic compounds from an olive mill wastewater (OMW) and for the anaerobic production of volatile fatty acids (VFAs) from the pre-treated OMW was developed in this work. The recovery of OMW polyphenols was carried out through solid phase extraction (SPE) by using Amberlite XAD16 resin as the adsorbent and ethanol as the biocompatible desorbing phase. Thereafter, the acidogenic digestion of the dephenolized OMW was performed in a mesophilic packed-bed biofilm reactor filled with ceramic cubes, who was operated at an OLR of about 5.9 g L-1 day-1. As a result of the integrated process, more than 60% of polyphenols were recovered and 19 gCOD L-1 of VFAs were obtained, representing more than 70% of the anaerobic effluent COD

Repeated batch approach as a feasible procedure for the acclimatization of anaerobic consortia capable of an effective biomethanization of mechanically-sorted organic fraction of municipal solid waste

The acclimatization of anaerobic consortia capable of an effective biomethanization of a mechanically sorted-organic fraction of municipal solid waste (MS-OFMSW) was achieved in this study by following a repeated batch co-digestion approach. Mixtures of MS-OFMSW and cattle manure were processed in successive batch anaerobic digestion processes. Such an approach generally allowed a significantly increasing of the methane production when the MS-OFMSW represented the 30 and 40 % (v/v) of the initial mixture. On the other hand, the acclimated inocula did not adapt efficiently to higher concentration of the target waste MS-OFMSW. The acclimatization of the anaerobic consortia was demonstrated by means of molecular biology tools, by which a high diversity among populations occurring in the experimental matrices and after anaerobic processes was observed