State of the art on Timber Concrete Composite floor

Interest in timber-concrete composite (TCC) floors has increased over the last 20-30 years. Since the 1990âs, TCC solution is seen as a viable and effective alternative to conventional reinforced concrete and/or traditional timber floors in multistorey buildings. In TCC technology, a timber beam, either solid wood, glued laminated or laminated veneer lumber (LVL), is connected to a concrete slab using a connection system that resists shear forces and impedes slip between the members of the composite section. The strength, stiffness, location and number of connectors play a crucial role for the composite action and determine the structural and serviceability performance of the floor system. This paper discusses the state of the art of TCC structures. It presents a comprehensive review of the literature about the development and structural behaviour of TCC structures. The review addresses construction aspects and shear connection concepts. It evaluates experimental tests, finite element and numerical models. It discusses the influence of concrete elements. As recommendations, the best types of shear connection for cast in-situ and prefabricated TCC floors are put forward and assessed for criteria such as strength, stiffness, ductility and ease of manufacturing. Furthermore the most relevant numerical models are introduced. These models can be used to further the experimental results in parameters such as connections, configurations, geometrical and material properties

Structural behaviour of timber concrete composite connections and floors utilising screw connectors

University of Technology, Sydney. Faculty of Engineering and Information Technology.The traditional materials such as reinforced concrete and structural steel have been widely used in the construction market. These construction materials produce a large quantity of greenhouse gases as a by-product. An environmentally sustainable solution to decrease the production of greenhouse gases is creation of composites with other materials such as timber to reduce the amount of steel and concrete used in construction. Timber-concrete composites (TCC) structures, extends upon this by combining timber and concrete in order to form a composite structural member that utilises the properties of both materials. Since the 1990s, Timber Concrete Composite (TCC) floors have been gaining wider recognition as being a viable and effective alternative to both reinforced concrete and traditional timber floors. TCCs are a structural form whereby a concrete slab is fixed to a timber joist at the interface using a suitable shear connector which transfers shear forces and impedes slip between concrete and timber. Hence, the strength, stiffness, location and number of shear connectors used at the composite interface are the key factors in determining the composite action, the strength and stiffness of a TCC system. TCC exploits the mechanical properties of each material favourably with the concrete in compression and the timber in tension. TCCs have several advantages over full timber construction, including improved strength (double), stiffness (triple), vibration control, fire performance and thermal and sound insulation. TCCs also have advantages compared to full concrete construction, including a much higher load capacity per unit of self-weight and a lower embodied energy. Mechanical fasteners for example screw and dowel TCC connectors are relatively simple and easy to install, cost effective and structurally efficient connectors with lower labour requirement. With these considerations, mechanical fasteners can be preassembled in prefabrication or cast in situ TCC solutions. Hence, application of mechanical fasteners in TCCs overcomes the drawbacks of alternative connection such as notch type connection and reduces the time required to construct a TCC system. This research investigates the experimental parametric study on the effect of different types of high-performance concrete on mechanical properties of TCC connections and floors using locally available materials in Australia to evaluate their potential for use in the construction market. A parametric study of mechanical fasteners such as crossed SFS VB, crossed SPAX and coach screws connections in different lengths (short and long SFS VB), angles (±30°, ±45° and ±60°) to the connection face and a number of crossed SFS VB and SPAX at 45° series utilising 17mm plywood formwork interlayer and different types of concrete was carried out. Hence, the effects of connector type, inclination angle and length of screw and existence of plywood interlayer on mechanical properties of the TCC connections were investigated. Moreover, two innovative TCC shear connection systems were put forward and assessed for their suitability as a substitute or replacement for existing connection systems using push-out test. The application of high-performance concrete such as light-weight concrete and self-consolidating concrete provides a great deal of benefits in TCC technology to minimize the dead-load on the timber component or increase the concrete workability and accelerate the process of pouring. Such weight reduction and increased workability may be favourable in the renovation of old timber floors. The use of TCC technology is also advantageous in new multi-storey buildings for aspects such as prefabrication and mitigation of excess dead load – leading to saving on foundation and walls and/or column sizes. This research investigates the effect of different types of high-performance concrete on the mechanical properties of TCC connections and floors using locally available materials in Australia to evaluate their potential for use in construction market. Push-out test was used to determine the mechanical properties and failure modes of shear connections and once the mechanical properties of connection type were identified, full-scale TCC modules utilising different types of shear connector and concrete properties were subjected to four-point bending tests. Hence, the predictions of full beam behaviour using the connection properties were validated and the effect of shear connection and concrete type on structural behaviour of an entire floor was investigated. Literature reports a significant lack of information on analytical closed-form equations to predict the strength and stiffness of TCC connections utilising vertical and inclined fasteners to be used in the design of timber composite beams. This study reviewed the methodology of available analytical models for prediction of the strength and serviceability stiffness of vertically inserted single timber to timber and TCC shear connections and validated their accuracy using the experimental push-out test results. Moreover, an analytical strength model based on some adjustment to EYM to predict the strength of TCC connections utilising single and crossed screws inclined to the timber grain was proposed. This research also presented a model for the stiffness of TCC connections using crossed inclined screws. The Winkler theory of beam on elastic foundation proposed was extended to derive the serviceability slip modulus of TCC connections with inclined screws which were loaded in tension and compression. In addition, a 3-D FE model has been put forward to simulate different TCC connections such as single and multiple wood screws and inclined coach screw utilising the commercial FE analysis software ANSYS. The findings of this part demonstrate that by using a simple numerical model, the behaviour of TCC connections can be accurately modelled and can therefore be used for parametric study of changes in end distance, edge distance, member thickness, screw diameter, screw length and number of screws

Enhancing Industry Exposure, Discovery-Based and Cooperative Learning in Mechanics of Solids

BACKGROUND Mechanics of Solids is a second year undergraduate subject, undertaken by both Civil and Mechanical engineering students at the University of Technology, Sydney (UTS). Mechanics of Solids has been delivered for many years in a traditional format with lectures and problem solving tutorials. As part of a national Australian project “Enhancing Industry Exposure in Engineering Degrees”, UTS in partnership with other universities and industry partners in Australia has sought industry involvement to engage students with the real-world challenges of engineering practice. PURPOSE The main objective of this project is to design, develop and implement learning modules in Mechanis of Solids that integrate industry exposure to provide context for the concepts included in this subject. DESIGN The project consisted of six guest lectures by industry representatives on topics related to typical Mechanics of Solids subject matter and two seminars on using MDSolids software. Students completed a collaborative assignment aligned with one of the industry presentations. Their reports and presentations were assessed on assessment criteria which included contextual understanding, judgement, effective collaboration and creativity, and their perceptions were captured to evaluate the impact of industry engagement in this subject. RESULTS One of the major benefits of this project was students’ better understanding of engineering practice. There were also positive effects on students’ motivation for learning engineering. CONCLUSIONS This paper reports the major findings, outcomes and challenges for implementing enhancing industry exposure approach in Mechanics of Solids subject at UTS. The main finding of this research concluded that this project is very valuable to both students as it promotes exposure to real-world engineering challenges. The students’ exposure to real and substantive challenges improves their contextual understanding, plus their judgement, practice based planning, teamwork, and initiative learning skills

The predictive model for strength of inclined screws as shear connection in timber-concrete composite floor

Interest in timber-concrete composite (TCC) floors has increased over the last 30 years. TCC technology relies on timber and concrete members acting compositely together. Both timber and concrete exhibit a quite brittle behaviour in bending/tension and compression respectively whilst the shear connection is identified as the only contributor of ductile behaviour. Therefore, the strength, stiffness and arrangement of the shear connection play a crucial role in the structural design of TCC. There are only few investigations on analytical closed-form equation to predict the stiffness and strength of TCC joints as input values to design a partially composite floor. For example, Johansen's yield theory was adopted as European yield model in Eurocode 5. However, the equations are limited to vertically inserted dowels or screws and Eurocode 5 recommends that the strength and stiffness of unconventional joints should be determined by push-out tests. Previous investigations reported that the inclined shear connector significantly increase the initial stiffness and ultimate strength of the TCC joints and consequently composite floor. This paper presents a model for the strength ofTCC joint using crossed (±45°) proprietary screws (SFS Intec). The Johansen yield theory is extended to derive the strenght model of TCC joint with crossed (±45°) screws which are loaded in tension and compression. The model is an upper bound plastic collapse model that assumes the behaviour of timber and screw perfectly plastic with undamaged concrete. The failure modes considers of yield of screw, in tension or shear, and some combined modes assuming screw withdrawal, lateral crushing of the timber and the development of plastic hinges in the screw. The experimental aspect of the research consists of push-out tests and aims to verify the strength model of TCC joints with inclined screws. The failure modes are also investigated. The model seems to be reasonably accurate in predicting both the characteristic strength and failure mode. This research suggests the model to facilitate the design of inclined screw shear connections for TCC construction. © 2013 Taylor & Francis Group

Variability in gene cassette patterns of class 1 and 2 integrons associated with multi drug resistance patterns in Staphylococcus aureus clinical isolates in Tehran-Iran

Background: To investigate antibiotic resistance, the occurrence and distribution of class 1 and 2 integrons in multidrug- resistant Staphylococcus aureus isolates from hospitals in Tehran, Iran. The isolates were examined for susceptibility to antimicrobial agents. The mecA gene, class 1 and 2 integrons were detected by PCR. Integrase positive strains were further analysed for the presence of resistance gene cassettes using specific primers and were sequenced. Results: Among 139S.aureus isolates, 109 (78.4 ) and 112 (80.5 ) strains were considered as multidrug resistant and mecA positive, respectively. Class 1 integrons and internal variable regions were found in 72.6 (101/139) and 97 (98/101) and class 2 integrons and variable regions also in 35.2 (49/139) and 65.3 (32/49) of S.aureus clinical isolates, respectively. Twelve distinct cassette arrays were found, containing genes encoding resistance to β-lactams, aminoglycosides, streptothricin, trimethoprim, chloramphenicol,a putative glucose dehydrogenase precursor and a protein with unknown function. Gene cassette arrays aadB, aadA2 and dhfrA1-sat2-aadA1 were common in S.aureus isolates. We detected a completely new gene cassettes which contained aadB, oxa2, aacA4, orfD-aacA4-catB8, aadB-catB3, orfD-aacA4 and aadB-aadA1-cmlA6 of class 1 and dhfrA1-sat2-aadA1, dhfrA11, dhfrA1-sat2 of class 2 integrons. Conclusions: This is the first study to report carriage of class 1 and 2 integrons and associated gene cassettes among in S.aureus isolates from Iran. © 2015 Mostafa et al

Preparation and Evaluation of a New Lipopolysaccharide-based Conjugate as a Vaccine Candidate for Brucellosis

Objectives: Development of an efficacious vaccine against brucellosis has been a challenge for scientists for many years. At present, there is no licensed vaccine against human brucellosis. To overcome this problem, currently, antigenic determinants of Brucella cell wall such as Lipopolysaccharide (LPS) are considered as potential candidates to develop subunit vaccines. Methods: In this study, Brucella abortus LPS was used for conjugation to Neisseria meningitidis serogroup B outer membrane vesicle (OMV) as carrier protein using carbodiimide and adipic acid-mediated coupling and linking, respectively. Groups of eight BALB/c mice were injected subcutaneously with 10μg LPS alone, combined LPS+OMV and conjugated LPS-OMV on 0 days, 14 days, 28 days and 42 days. Anti-LPS IgG was measured in serum. Results: The yield of LPS to OMV in LPS-OMV conjugate was 46.55, on the basis of carbohydrate content. The ratio for LPS to OMV was 4.07. The LPS-OMV conjugate was the most immunogenic compound that stimulated following the first injection with increased IgG titer of ~5-fold and ~1.3-fold higher than that produced against LPS and LPS in noncovalent complex to OMV (LPS+OMV), respectively. The highest anti-LPS IgG titer was detected 2 weeks after the third injection (Day 42) of LPS-OMV conjugate. The conjugated compound elicited higher titers of IgG than LPS+OMV, that showed a 100-120-fold rise of anti-LPS IgG in mice. Conclusion: These results indicate that our conjugated LPS-OMV can be used as a brucellosis vaccine, but further investigation is required. © 2014

Biallelic UBE4A loss-of-function variants cause intellectual disability and global developmental delay

Purpose: To identify novel genes associated with intellectual disability (ID) in four unrelated families. Methods: Here, through exome sequencing and international collaboration, we report eight individuals from four unrelated families of diverse geographic origin with biallelic loss-of-function variants in UBE4A. Results: Eight evaluated individuals presented with syndromic intellectual disability and global developmental delay. Other clinical features included hypotonia, short stature, seizures, and behavior disorder. Characteristic features were appreciated in some individuals but not all; in some cases, features became more apparent with age. We demonstrated that UBE4A loss-of-function variants reduced RNA expression and protein levels in clinical samples. Mice generated to mimic patient-specific Ube4a loss-of-function variant exhibited muscular and neurological/behavioral abnormalities, some of which are suggestive of the clinical abnormalities seen in the affected individuals. Conclusion: These data indicate that biallelic loss-of-function variants in UBE4A cause a novel intellectual disability syndrome, suggesting that UBE4A enzyme activity is required for normal development and neurological function

Erratum: Author Correction: Identification of genes required for eye development by high-throughput screening of mouse knockouts.

[This corrects the article DOI: 10.1038/s42003-018-0226-0.]

The molecular epidemiology of multiple zoonotic origins of SARS-CoV-2

Understanding the circumstances that lead to pandemics is important for their prevention. Here, we analyze the genomic diversity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) early in the coronavirus disease 2019 (COVID-19) pandemic. We show that SARS-CoV-2 genomic diversity before February 2020 likely comprised only two distinct viral lineages, denoted A and B. Phylodynamic rooting methods, coupled with epidemic simulations, reveal that these lineages were the result of at least two separate cross-species transmission events into humans. The first zoonotic transmission likely involved lineage B viruses around 18 November 2019 (23 October–8 December), while the separate introduction of lineage A likely occurred within weeks of this event. These findings indicate that it is unlikely that SARS-CoV-2 circulated widely in humans prior to November 2019 and define the narrow window between when SARS-CoV-2 first jumped into humans and when the first cases of COVID-19 were reported. As with other coronaviruses, SARS-CoV-2 emergence likely resulted from multiple zoonotic events