Excessive Strand End Slip in Prestressed Piles

This paper presents the results of a research project that investigated excessive strand end slip observed recently in some prestressed piles. From measurements taken in the field, it is apparent that the problem o excessive initial strand slip is independent of pile shape and size. Strand end slip is evident in piles of different manufacturers in different states in the Southeast. Excessive strand end slip was found in both the top and bottom of the cross section of the piles, although the top portion of the cross section generally exhibited much higher initial slip. Several preventive measures can be adopted to reduce the excessive strand end slip. These preventive measures include: a) proper concrete mixture proportioning to reduce top bar effect; b) use of higher-strength concrete with the lowest possible slump and setting time; c) assessment of the condition of the strands prior to installation to insure excellent bond characteristics; d) gradual release of prestress, with an optimal release sequence; and e) use of adequate vibration to ensure consolidation. The strand end slip measured at five prestressing plants in the Southeast is considerably higher than the allowable end slip and is expected to affect the pile performance. If the strand slip theory is adopted, the strand development length increases substantially due to the excessive strand end slip. A top bar effect factor similar to the one used in reinforced concrete design is recommended. To maintain the excellent quality of precast and prestressed concrete products, manufacturers should adopt a dynamic quality control process that follows the rapid changes in the industry. More tests are necessary to ensure excellent quality, such as the Moustafa or an equivalent test, to assess the bond capabilities of the strands, end slip measurements, and direct measurement of the transfer length. Installation of piles should proceed in a manner to alleviate the top bar effects by placing piles alternately in their best and worst directions

Modelling the Influence of Layout On Overheating Risk of London Flats

An analysis of overheating levels corresponding to building morphology yielded the modelling uncertainty due to the geometry and layout of two-bedroom flats in London, England. A new method is introduced, which collates information on various flat layouts in the current London housing stock. To ensure an unbiased sample was selected, dwellings were chosen randomly, yielding twelve flats in and around inner London. Dynamic thermal simulations were performed using EnergyPlus to determine individual dwellings’ overheating risk. The results described the influence of geometry and layout configuration on overheating risk, which has rarely been analysed in previous studies. Irregular façades led to higher overheating levels in the set-back part of the building. Default configurations were used to model basecase archetypes, with further simulations performed to study the effects of orientation, ceiling heights and window glazing fractions. Compared with these factors, bigger differences between mean operative temperatures of flats were due to layout, with 3.5 °C in bedrooms, 1.5 °C in living rooms and 2.2 °C in kitchens

A case study on the impact of fixed input parameter values in the modelling of indoor overheating

Global efforts to reduce greenhouse gas emissions from buildings while also improving their environmental resilience have intensified. These efforts are often supported by building stock models which can inform policymakers on the impact of policies on energy consumption, greenhouse gas emissions and the indoor environment. The input values of such models are commonly informed by reference tables, which can result in inaccurate specification and incomplete representation of the distribution of possible values. In this modelling case study of a semi-detached dwelling archetype, the influence of using a reference U-value (2.1 W/(m2K)) for solid walls in England on heat-related mortality rate is compared to a probabilistic specification based on empirical evidence (median = 1.7W/(m2K)). Using the theoretical reference U-value generally resulted in a lower indoor overheating risk compared to the use of the empirically derived U-values pre-retrofit, but a larger increase in heat-related mortality rate following internal wall insulation (1.20%) than the use of the empirical median (0.94%, 95 % Confidence Interval = 0.87–0.99 %). This highlights the potentially significant implications of using fixed reference values. Future work will employ this probabilistic framework on multiple influential parameters

Internal Transitions of Two-Dimensional Charged Magneto-Excitons X-: Theory and Experiment

Internal spin-singlet and spin-triplet transitions of charged excitons X- in magnetic fields in quantum wells have been studied experimentally and theoretically. The allowed X- transitions are photoionizing and exhibit a characteristic double-peak structure, which reflects the rich structure of the magnetoexciton continua in higher Landau levels (LL's). We discuss a novel exact selection rule, a hidden manifestation of translational invariance, that governs transitions of charged mobile complexes in a magnetic field.Comment: 4 pages, 2 figures, submitted to Physica

Toward a joint catalogue of recent seismicity in western Greece: preliminary results

Οι κατάλογοι με δεδομένα πρώτων αφίξεων των σεισμικών κυμάτων που συντάσσονται από τα τρία μόνιμα σεισμολογικά δίκτυα της Ελλάδας ενοποιήθηκαν και υπέστησαν κοινή επεξεργασία προκειμένου να επαναπροσδιοριστούν οι θέσεις των σεισμικών επικέντρου στη Δυτική Ελλάδα. Τα αποτελέσματα της κοινής επεξεργασίας, που παρουσιάζονται στην παρούσα εργασία, αφορούν στην εξαετία 2000 - 2005 και τη γεωγραφική περιοχή μεταξύ 35-42°Β και 19-22°Α. Μετά τη διαδικασία της ενοποίησης των φάσεων των διάφορων κέντρων, ο αριθμός των σεισμικών γεγονότων στον κατάλογο που προέκυψε αυξήθηκε κατά 3000 περίπου σε σχέση με τους προϋπάρχοντες, επιμέρους καταλόγους. Τα επίκεντρα των σεισμών του ενιαίου καταλόγου επαναπροσδιορίστηκαν με τη χρήση του αλγόριθμου Hypoinverse και διάφορους συνδυασμούς μονοδιάστατων μοντέλων ταχυτήτων που έχουν προταθεί για τον ελλαδικό χώρο και συντελεστές βαρύτητας για τα δεδομένα των φάσεων. Από τους διάφορους συνδυασμούς που δοκιμάστηκαν προέκυψε ότι η βαρύτητα που δίνεται στις φάσεις των S κυμάτων επηρεάζει δραστικότερα τα αποτελέσματα του επανα-προσδιορισμού των επικέντρων. Οι μικρότερες τιμές σφαλμάτων στους χρόνους γένεσης των σεισμών και τη χωροθέτηση των επικέντρων τους κατά την οριζόντια και την κατακόρυφη διεύθυνση προκύπτουν όταν οι φάσεις των S κυμάτων δε χρησιμοποιηθούν. Τα επανα προσδιορισμένα επίκεντρα εμφανίζουν περισσότερο διακριτές συγκεντρώσεις και διαγράφουν με μεγαλύτερη σαφήνεια τις τεκτονικές δομές της περιοχής μελέτης.Routine catalogue phase data of three Greek permanent seismic networks are merged and jointly used to relocate earthquakes in western Greece. Processed data refer to the time period from 2000 to 2005 and to the geographical area between 35- 42°N and 19-22Έ. After the merging procedure, the number of events in the joint catalogue is increased by more than 3000 compared to the individual pre-existing catalogues. Earthquakes are relocated using the Hypoinverse algorithm and several different combinations of ID velocity models and phase weighting schemes. Among these two tested factors, S-phase weights are found to affect the relocation results more drastically. In fact, minimum mean rms, erh and erz values (0.28 sees, 3.6 km and 5.8 km, respectively) are found when S-phases are neglected. Relocated epicenters appear more clustered and illuminate well-known, as well as obscure, seismotectonic structures of the are

Pneumococcal disease : a systematic review of health utilities, resource use, costs, and economic evaluations of interventions

Background Pneumococcal diseases cause substantial mortality, morbidity, and economic burden. Evidence on data inputs for economic evaluations of interventions targeting pneumococcal disease is critical. Objectives To summarize evidence on resource use, costs, health utilities, and cost-effectiveness for pneumococcal disease and associated interventions to inform future economic analyses. Methods We searched MEDLINE, Embase, Web of Science, CINAHL, PsycINFO, EconLit, and Cochrane databases for peer-reviewed studies in English on pneumococcal disease that reported health utilities using direct or indirect valuation methods, resource use, costs, or cost-effectiveness of intervention programs, and summarized the evidence descriptively. Results We included 383 studies: 9 reporting health utilities, 131 resource use, 160 economic costs of pneumococcal disease, 95 both resource use and costs, and 178 economic evaluations of pneumococcal intervention programs. Health state utility values ranged from 0 to 1 for both meningitis and otitis media and from 0.3 to 0.7 for both pneumonia and sepsis. Hospitalization was shortest for otitis media (range: 0.1-5 days) and longest for sepsis/septicemia (6-48). The main categories of costs reported were drugs, hospitalization, and household or employer costs. Resource use was reported in hospital length of stay and number of contacts with general practitioners. Costs and resource use significantly varied among population ages, disease conditions, and settings. Current vaccination programs for both adults and children, antibiotic use and outreach programs to promote vaccination, early disease detection, and educational programs are cost-effective in most countries. Conclusion This study has generated a comprehensive repository of health economic evidence on pneumococcal disease that can be used to inform future economic evaluations of pneumococcal disease intervention programs