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

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

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

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

Acclimation of an anaerobic consortium capable of an effective biomethanization of mechanically-sorted organic fraction of municipal solid waste through a semi-continuous enrichment procedure

Aneffective mesophilic continuous anaerobic digestion process fed only with amechanically sorted organic fraction of municipal solid waste (MS-OFMSW) was developed. During a preliminary 3-month experimental phase, the microbial consortium was acclimated toward MS-OFMSW by initially filling the reactor with cattle manure and then continuously feeding it with MS-OFMSW. The Hydraulic Retention Time (HRT) and Organic Loading Rate (OLR) were 23 days and 2.5 g/L/day, respectively. After 4 weeks, the reactor reached stationary performances (84% COD removal yield, 0.15 LCH4 /gCODremoved methane production yield). The acclimated consortiumwasthen employed in a second run in which the reactorwasoperated under steady state conditions at the previous HRT and OLR for 73 days. The COD removal and the methane production yield increased up to 87% and 0.25 LCH4 /gCODremoved, respectively. The capability of the acclimated consortium to biomethanize MS-OFMSW was further studied via batch digestion experiments, carried out by inoculating the target waste with reactor effluents collected at the beginning of first run and at the end of the first and second run. The best normalized methane production (0.39 LCH4 /ginitial COD) was obtained with the inoculum collected at the end of the second run. Molecular analysis of the microbial community occurring in the reactor during the two sequential runs indicated that the progressive improvement of the process performances was closely related to the selection and enrichment of specific hydrolytic and acidogenic bacteria in the reactor

Prove dinamiche su strutture controllate con dispositivi magnetoreologici (MR)

In this paper a shaking table experimentation is presented, which refers to a coupled adjacent structures configuration, that may be used in civil and industrial applications. The physical model is a 1:5 scaled coupled structures. The first structure is a 4-story model, while the second structure is a 2-story model. The introduction of the magnetorheological (MR) device between the adjacent structures is shown to be able a viable method to protect the structures from seismic excitation. The MR damper is applied as passive and semiactive device. The results confirm good performance of the passive and semiactive control system in reducing the response of both structures. Finally a mathematical model of the structures and the device has also been identified and validate

Role of numerical modelling choices on the structural response of onshore wind turbine shallow foundations

Structural modelling of wind turbine shallow foundations on granular soil strata deals with combined complex phenomena, such as soil-structure interaction, material nonlinearities, local stress concentration in both reinforced concrete foundation and soil. Numerical finite element analyses are performed employing three-dimensional elements for both concrete foundation and soil and one-dimensional elements for reinforcement. The results of the nonlinear static simulations are validated with experimental results of recent tests carried out on 1:15 scaled models having reinforcement ratios and stress conditions similar to the prototype foundations designed according to current codes. The validated modelling strategies are also applied to investigate the role of nonlinearities in both soil and concrete foundation, emphasizing the parameters and the nonlinear constitutive laws that significantly affect the foundation response. Three different reinforcement layouts are considered in both testing and simulations of the prototype: (a) complete prototype reinforcement, (b) prototype without shear reinforcement and (c) prototype without shear reinforcement and with 50% of remaining reinforcement replaced by steel fibres. A critical comparison is also made with models employing elastic two-dimensional shell finite elements lying over elastic supports, typically adopted for design purposes