Improved modelling and design of portal frame building systems

The traditional approach for the design of steel portal frame building systems is based on the idealised two-dimensional behaviour of a bare internal frame in the system. This approach totally ignores the integral action of other structural components in the system. In order to design the portal frame building system based on its 'true' threedimensional behaviour, it is necessary that other structural components such as steel roof and wall cladding systems and end frames (or their effects) are included in the analysis. In the UK and USA, this has been achieved using the principles of stressedskin (diaphragm) action. However their design is limited to valley-fixed cladding systems and therefore, their results can not be used for crest-fixed cladding systems used in Australia. This thesis describes an improved three dimensional modelling using an equivalent truss member method to simulate steel cladding systems and an improved design method which includes the shear strength of crest-fixed cladding system. It also includes the development of essential cladding data for this process. In the first stage of this research program, a total of 19 shear/racking experiments was carried out on large- scale profiled steel claddings and sandwich panel systems up to a size of 6 m x 6 m. These experiments produced the shear strength and flexibility data required for the improved three dimensional modelling. Despite the use of crest fixing with screw fasteners, the conventional profiled thin steel claddings provided reasonably good shear capacit\~s. The failure was ductile in the case of conventional cladding systems whereas it was brittle and the capacity was the same in the case of stronger sandwich panel systems. Therefore, an improved fastening system was developed which resulted in approximately 2.5 times larger shear strength and improved ductility. The new system had sufficient shear capacity that eliminated the conventional cross bracing members used in portal frame buildings: Analytical formulae were developed to predict the shear strength of these cladding systems and the simple connection tests to obtain the basic tearing loads are described. The results obtained using these formulae agreed well with the corresponding experimental results. The shear strengths of the cladding systems not considered in this investigation can be predicted using these analytical formulae, and the basic tearing loads of connections using the simple connection tests. An improved three-dimensional computer modelling was developed by considering columns, rafters, purlins and girts as beam elements and roof and wall claddings as equivalent truss (tension only) members. Shear flexibility values found experimentally for the steel cladding and sandwich panel systems were used to determine the equivalent truss member sizes required in the improved three dimensional analysis using 'MicroStran'. This model was validated using available full-scale experimental data of a typical portal frame building. This investigation clearly indicated that there are considerable differences between the design actions obtained from the two and three-dimensional modelling and analyses. It revealed the reduction in design action effects when the latter method was used. An improved design method was developed considering the design action effects from the improved three-dimensional computer modelling and the shear strength of the wall and roof cladding system in the bracing design. A typical medium size portal frame building with conventional steel cladding systems was designed using the improved method which showed that reduction in member sizes was small and that cost saving in building was only 4 %. This is mainly because the shear strength and stiffness of the profiled steel cladding systems are not large enough; however, they will be adequate for smaller buildings such as garage and farm sheds. Finally, an innovative port~l frame system incorporating the conventional steel frames, sandwich panels as roof and wall claddings and steel rectangular hollow sections as purlins and girts at wider spacing was developed. The conventional roof and wall cross bracing members were eliminated because of the greater shear capacity of sandwich panel systems. The portal column size was also reduced. The use of improved modelling and design methods thus led to a cost saving of approx. 8 % for the new system. The new system appears to be very efficient and has the potential of becoming the future portal frame system

Shear strength and stiffness of crest-fixed steel claddings

Diaphragm action of crest-fixed profiled steel claddings is present in low-rise buildings whether the designer acknowledges it or not. For the designers to take advantage of the diaphragm strength of the crest-fixed steel claddings in the design of low-rise buildings in a similar manner to valley-fixed claddings, and to design the buildings based on the true behaviour rather than the assumed behaviour, shear/racking behaviour of the three trapezoidal and corrugated steel claddings commonly used at present was investigated using large scale experiments. Crest-fixed claddings (up to a maximum size of 6 x 6.2m) with different aspect ratio and fastening systems were tested to failure, based on which suitable shear strength and stiffness values have been proposed for these claddings as they are used at present. A simple analytical model combined with basic connection data from small scale experiments was used to predict the shear strength of tested panels. Currently attempts are being made to develop general design formulae to determine shear strength and stiffness of crest-fixed steel claddings..

Shear Strength of Sandwich Panel Systems

The use of sandwich panels as roof and wall claddings has increased considerably in recent times. For the designers to take advantage of the diaphragm action of stronger sandwich panel systems under in-plane shear forces due to wind loading, appropriate data on shear strength and stiffness of these systems is required. An experimental investigation was therefore conducted to investigate the shear behaviour of commonly used crest-fixed sandwich panel systems. An improved fastening system was developed which resulted in approximately 2.5 times greater shear strength, and improved ductility. Shear strength and stiffness data were developed for sandwich panel systems with the improved fastening system for varying aspect ratio. Analytical formulae were also developed to predict the shear strength of sandwich panel systems using the basic tearing loads obtained from simple connection tests. This paper presents the details of both experimental and analytical studies on the shear behaviour of sandwich panel systems and the results

Development of a multi-locus sequence typing scheme for avian isolates of Pasteurella multocida

A total of 63 isolates of Pasteurella multocida from Australian poultry, all associated with fowl cholera outbreaks, and three international reference strains, representing the three subspecies within P. multocida were used to develop a multi-locus sequence typing scheme. Primers were designed for conserved regions of seven house-keeping enzymes - adk, est, gdh, mdh, pgi, pmi and zwf - and internal fragments of 570-784 bp were sequenced for all isolates and strains. The number of alleles at the different loci ranged from 11 to 20 and a total of 29 allelic profiles or sequence types were recognised amongst the 66 strains. There was a strong concordance between the MLST data and the existing multi-locus enzyme electrophoresis and ribotyping data. When used to study a sub-set of isolates with a known detailed epidemiological history, the MLST data matched the results given by restriction endonuclease analysis, pulsed-field gel electrophoresis, ribotyping and REP-PCR. The MLST scheme provides a high level of resolution and is an excellent tool for studying the population structure and epidemiology of P. multocida. Crown Copyrigh

Multilocus Sequence Typing of Total-Genome-Sequenced Bacteria

Accurate strain identification is essential for anyone working with bacteria. For many species, multilocus sequence typing (MLST) is considered the “gold standard” of typing, but it is traditionally performed in an expensive and time-consuming manner. As the costs of whole-genome sequencing (WGS) continue to decline, it becomes increasingly available to scientists and routine diagnostic laboratories. Currently, the cost is below that of traditional MLST. The new challenges will be how to extract the relevant information from the large amount of data so as to allow for comparison over time and between laboratories. Ideally, this information should also allow for comparison to historical data. We developed a Web-based method for MLST of 66 bacterial species based on WGS data. As input, the method uses short sequence reads from four sequencing platforms or preassembled genomes. Updates from the MLST databases are downloaded monthly, and the best-matching MLST alleles of the specified MLST scheme are found using a BLAST-based ranking method. The sequence type is then determined by the combination of alleles identified. The method was tested on preassembled genomes from 336 isolates covering 56 MLST schemes, on short sequence reads from 387 isolates covering 10 schemes, and on a small test set of short sequence reads from 29 isolates for which the sequence type had been determined by traditional methods. The method presented here enables investigators to determine the sequence types of their isolates on the basis of WGS data. This method is publicly available at www.cbs.dtu.dk/services/MLST