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Composite construction is a method whereby a concrete floor slab is utilised as part of the beam system. The slab acts as a concrete flange to the beam. As the beam and slab are of different materials, the size of the concrete flange is scaled down using a modular ratio where the young's modulus of steel is divided by the young's modulus of concrete. When these two elements bend, the top of each element is in compression and the bottom in tension. Because the bottom of the concrete is in tension of the top of steel is in compression this causes shear along the interface of the two materials. To overcome this a steel stud is welded through the metal deck. The stud is designed to take the shear force.
The composite system consists of a concrete slab cast on profiled steel decking acting compositely with glue-laminated timber beams. Composite action is achieved with coach screw shear connectors between the beams and slab. The connectors have been tested in 'push out' shear tests and a three-point bend test of a full-scale floor slab has been completed. The composite system is more than three times as stiff and almost twice as strong as the same beam/slab configuration without composite action. Richard Persaud, Dr Digby Symons The Structural Engineer - 21 February 2006
Euro codes are a full set of structural design codes for building and civil engineering that used across Europe to open up trade boundaries allowing designers, and manufacturers to supply designs and products to other countries across the continent. Conceived over 30 years ago, the Eurocodes are now landing on the desks of engineers, and are expected to be fully adopted in 2010. For this reason, the Eurocodes were used for the design comparisons.
In 2004, The Steel Construction Institute published a study comparing the costs and construction programme of various methods of steelwork and concrete framing solutions that reflect modern construction techniques to determine which is the most cost effective. The study looked at two types of buildings, costing and programming each of them. The study also looked at other aspects of the building, which can be affected by the choice of framing solution such as foundations, external elevation treatments and mechanical/electrical services. The study was motivated by the Egan report, which looked at the construction industry and how to lower costs. The report encourages offsite construction to improve speed and quality on site.
People are starting to use tree planting as a way of offsetting carbon emissions. This is because of trees absorbing carbon dioxide from the atmosphere. One of the problems is that once a tree reaches maturity it stops absorbing CO2, then the next problem is when it dies and decays it starts to release CO2 back into the atmosphere. One solution round this is to store the carbon in materials, by using the timber as a construction material.
The way in which timber is used us also key in reducing CO2 emissions. Timber should be dried before it can be used as a material, and it must be. One method is by kiln drying. Kiln drying is an artificial method of drying the timber by heating it up and in turn using fossil fuels, emitting CO2. This defeats the point of the object. The sustainable alternative is to allow the timber to dry naturally under cover.
The ideal situation would be for people to use natural unaltered timber and design buildings within its limitations. However, due to human nature and the endeavour to improve, we are going to build higher and wider buildings that are filled with more objects and fewer supports. For this reason, we must come up with more innovative and sustainable solutions to overcome these challenges. We must harness timbers ability to lock CO2 into its structure and adopt methods to manipulate its properties. One of these engineered lumbers is Glue Laminated Timber, commonly abbreviated to Glulam in the industry.
Timber in the UK as a building material is widely used, but not so much as for major building components such as beams and columns. In our history, we used to use great oak timbers for roofs and beams, but due to time it takes to grow these massive timbers, it was not long until demand outstripped supply. Moving into the 21st Century with the use of high strength glues, we are able to utilise fast growing tree species and mechanically bonded the timbers to form sizes and strengths that rival the oak timbers. These mechanically glued timbers are referred to as Glued Laminated Timber, which has been abbreviated to Glulam.
In sustainability, the social impact on an area cannot be discussed without also discussing the environment and economics. The introduction of an industry can create an economic wealth for the local population that can lift certain areas out of poverty. This can be balanced against the environmental impact on the are by such industries. Industries can create noise and vibration, dust, local climate, ecology, soils, heritage, and archaeology as a by-product of the manufacturing process.
Initially I thought that the timber would have a great depth of construction as compared to steel. The depth of steel beams were indeed shallower than the timber beams but because the steel beams require a concrete slab needs to span from beam to beam, the overall construction depth of the steel beam plus the slab is only marginally shallower than the overall timber floor construction. The shallowest overall floor construction is of the concrete flat slab because you do not require a beam as such; the slabs span directly to the columns.