24 research outputs found
Dynamical behaviour of an under-deck cablestayed footbridge under the action of pedestrian transit
In recent years, the new trends in the construction of footbridges have led to the design of
innovative bridge types, such as under-deck cable-stayed bridges, with slender and lighter decks. This
tendency has made the serviceability limit state of vibrations relevant in the design of footbridges.
The natural frequencies of these bridge types, in many occasions, fall within the range of the
frequencies of the dynamic forces induced by pedestrians. Therefore, the accelerations induced by
pedestrian transit are not admissible when the usersâ comfort has to be guaranteed. In this paper, the
dynamical behaviour of an under-deck cable-stayed footbridge under pedestrian action is presented.
Both vertical and lateral components of the pedestrian action have been considered. For the analysis
of the vertical component, the under-deck cable-stayed footbridge is loaded with groups of
pedestrians moving across the footbridge with two different velocities. For the analysis of the lateral
component, the frequencies of the lateral forces induced by the pedestrians are taken from the range
0.7-1.2Hz. (Bachmann, 2002). The verification criteria for the serviceability limit state of vibrations
established by Eurocode are considered, and the response of the under-deck cable-stayed footbridge
was compare with these design standards.Results of the analyses carried out shows the acceleration
values of the footbridge in both horizontal and vertical direction. The important of the application of a
bracing system on the horizontal acceleration due to laterally induced pedestriansâ action. The effect
of density on the vertical and horizontal acceleration values of the footbridge due to induced
pedestriansâ action. Finally, the result of the effect of speed and different phase time in the induced
pedestriansâ action is shown
Research achievements in under-deck and combined cable-stayed bridges
Under-deck cable-stayed bridges and combined cable-stayed bridges constitute two
innovative bridge types that have been designed and built on only a few occasions over the last thirty
years by outstanding structural engineers, such as Leonhardt, Schlaich, Menn, Virlogeux, Manterola,
and Cremer. In these bridge types, the stay cables have unconventional layouts: below the deck, in the
case of under-deck cable-stayed bridges, and above and below the deck, in the case of combined
cable-stayed bridges. Over the last few years, major research advances related to these bridge types
have been made to the point that now research dictates the development of these new bridge
typologies. In this communication, a general overview of the current state-of-art will be set out;
addressing issues related to built bridges, research developments, structural behaviour, design criteria
and potential applications for these innovative bridge types. Major attention will be paid to their
highly-efficient structural behaviour, that allows a significant reduction in the amounts of materials in
comparison with conventional bridges, leading to sustainable design. Other advantages of these
structural types, such as the numerous construction possibilities, aesthetical properties, and broad
range of potential applications, will also be stressed
Shear behaviour of steel-fibre-reinforced concrete simply supported beams
The structural behaviour of steel-fibre-reinforced concrete beams was studied using non-linear finite-element analysis
and existing experimental data. The work aim was to examine the potential of using steel fibres to reduce the
amount of conventional transverse steel reinforcement without compromising ductility and strength requirements set
out in design codes. To achieve this, the spacing between shear links was increased while steel fibres were added as a
substitute. Parametric studies were subsequently carried out and comparisons were also made with BS EN 1992-1-1
predictions. It was concluded that the addition of steel fibres enhanced the load-carrying capacity and also altered
the failure mode from a brittle shear mode to a flexural ductile one. The provision of fibres also improved ductility.
However, interestingly it was found that adding excessive amounts of fibres led to a less-ductile response. Overall,
the study confirmed the potential for fibres to compensate for a reduction in conventional shear reinforcement
State-of-the-art of spatial arch bridges
The paper describes a new form of bridge called a spatial arch bridge. This bridge type was developed in response to the demand for landmark structures, which have started to appear in the modern urban landscape to provide a symbol of originality, innovation and progress. Spatial arch bridges are defined as bridges in which the vertical deck loads produce bending moments and shear forces not contained in the arch plane, owing to their geometrical and structural configuration. Moreover, the arch itself may not be contained in a plane. The different variables and geometries that create such a structural configuration have been studied and classified. A wide compilation of examples of this bridge type has been made in chronological order, according to their construction date, from Maillarts first concrete spatial arch bridges to the latest designs and materials
Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU
Contains fulltext :
172380.pdf (publisher's version ) (Open Access
Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study
Summary
Background Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally.
Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies
have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of
the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income
countries globally, and identified factors associated with mortality.
Methods We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to
hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis,
exomphalos, anorectal malformation, and Hirschsprungâs disease. Recruitment was of consecutive patients for a
minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical
status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary
intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause,
in-hospital mortality for all conditions combined and each condition individually, stratified by country income status.
We did a complete case analysis.
Findings We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital
diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal
malformation, and 517 with Hirschsprungâs disease) from 264 hospitals (89 in high-income countries, 166 in middleincome
countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male.
Median gestational age at birth was 38 weeks (IQR 36â39) and median bodyweight at presentation was 2·8 kg (2·3â3·3).
Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income
countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups).
Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in lowincome
countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries;
pâ€0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients
combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88â4·11],
p<0·0001; middle-income vs high-income countries, 2·11 [1·59â2·79], p<0·0001), sepsis at presentation (1·20
[1·04â1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention
(ASA 4â5 vs ASA 1â2, 1·82 [1·40â2·35], p<0·0001; ASA 3 vs ASA 1â2, 1·58, [1·30â1·92], p<0·0001]), surgical safety
checklist not used (1·39 [1·02â1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed
(ventilation 1·96, [1·41â2·71], p=0·0001; parenteral nutrition 1·35, [1·05â1·74], p=0·018). Administration of
parenteral nutrition (0·61, [0·47â0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65
[0·50â0·86], p=0·0024) or percutaneous central line (0·69 [0·48â1·00], p=0·049) were associated with lower mortality.
Interpretation Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between lowincome,
middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will
be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger
than 5 years by 2030
Non-linear Analysis of Statically Indeterminate SFRC Columns
The structural behaviour of steel fibre-reinforced concrete (SFRC) has been studied using non-linear finite element analysis (NLFEA) and ABAQUS software. An interesting feature of this work is the consideration of statically indeterminate SFRC columns. Most of the SFRC specimens studied in the literature are simply supported beams, and information on statically indeterminate columns is sparse. In addition, both axial and lateral loads were considered in order to allow for compression and flexural effects on the columns. The aim of the work was to examine the potential for using steel fibres to reduce the amount of conventional transverse steel reinforcement without compromising ductility and strength requirements. To achieve this, the spacing between shear links was increased while steel fibres were added as a substitute (spacing between shear links increased by 50 and 100 % with fibre volume fraction Vf increased to Vf = 1, 1.5, 2 and 2.5 %). The numerical model was carefully calibrated against existing experimental data to ensure the reliability of its predictions. Parametric studies were subsequently carried out, which provided insight into how the steel fibres can help reduce the number of conventional shear links