TASK DESCRIPTION| Question 1: Compare and contrast the use of timber frame with concrete frame in construction, clearly comparing the use of each material by their individual characteristics and properties, advantages and disadvantages, costs, durability, climatic resistance and ease of assembly and adaptation. Concrete is “a building material made from a mixture of broken stone or gravel, sand, cement, and water, which can be spread or poured into moulds and forms a stone-like mass on hardening” (http:// (www. oxforddictionaries. om/definition/english/concrete) Timber is described “as wood prepared for use in building and carpentry” (http://oxforddictionaries. com/definition/english/timber). Concrete is known to be one of the most durable building products. As you can see from the above description, the ingredients of concrete are mineral based. When you combine these minerals with water, the particles chemically bind to produce a mixture with great compressive strength. This creates the concretes durability. The placing and curing of concrete is detrimental in determining a better durability.
The combining of minerals and water, as stated above, as long as it is adequately mixed ensures good compressive strength. Yet the tensile strength of concrete isn’t as advantageous. Although tensile strength increases after curing, it is still only at an average of 15% of the compressive strength. This is why some companies use post tensioning methods whilst building a concrete frame structure. Steel strands are run through the concrete via tubes so that they don’t directly connect with the concrete. This allows flexibility and movement in the concrete. Steel is strong in tension and so putting the two together creates a stronger structure.
The strength of timber is considered to be lower than that of concrete. This can be due to a number of factors, the main one being the direction of the grain in the timber. Timber is also known not to be as durable as concrete because it is more susceptible to deficiencies. Moisture is needed to form concrete to construct concrete frames, yet moisture can cause massive defects in timber frames. It can cause mechano-sorptive creep; this can also be a storage problem for timber as it cannot be left out in extreme weathers. Timber also has a lot of natural defects that can limit ts use as a construction building material, some examples are; Knots – caused by the trunk enclosing the branch during growth. Knots can decrease the strength of wood but in contrast can be very aesthetic for a building, due to the knot effect being visible. Sloping grain – this is when the grain changes direction, usually caused by the above knots. Again this decreases the strength of the wood. Porteaux en terre (insect damage) – Insects tunnel through wood. Apart from the holes left from this decreasing the strength of the timber, they also decrease the timbers value as it is not as aesthetic.
Porteaux du sole (fungal decay) – can come in many different forms. Some causes decay, some not. Although it doesn’t have an effect on the strength, the same as insect damage it an effect its attractiveness. This requires timber to have preservative treatments, that are a cost. Wood preservatives are classified in BS 1282. However, there are species of rot that can pass through concrete and cause cracks, therefore reducing the strength of the concrete. Also if you used timber internally, this rot could pass through the concrete and damage any internal timber structure. Different materials react differently in different weather climates.
There are 4 main different types of climate: Cold – acute heat loss for the majority of the year, with the minimum temperatures being described as -15 degrees. Temperature – Where there is excessive and heat loss and gain throughout the calendar year. With temperatures varying from -30 to 30 degrees. Raining seasons can occur throughout the year. Hot – Temperatures reach 45 degrees. There is very little rain and high radiation levels. Humid – The temperature usually falls over 20 degrees, there is high moisture levels due to the high rainfall at certain times of the year. There is very little cooling because of the humidity levels.
The climate usually affects the ground conditions of the site as well; there can also have a massive impact on the selection of what material to use for constructing a frame. The foundations for a timber frame house have to be very accurate to place the frame on top. There is very little room for movement or changes. However with insitu-concrete, the design can be changed up to the last minute and alterations are easily made if the foundations are inaccurate. Many timber frames are built off site, therefore are less labour intensive, with only a general need for carpenters onsite during installation, and extremely quick o erect. Reinforced concrete frames are built up onsite. They are very labour-intensive, with multiple trades having to work onsite at any one time, and the programme of works is generally a lot longer as the workers onsite have to wait for the concrete to cure. Because the timber frame e is built off site, there doesn’t need to be as much storage space onsite. This can be a massive factor, depending on the area you have got to work in, and can be an impeding factor on what frame you decide to use to construct your frame.
There is also likely to be more downtime onsite with a concrete frame, due to not being able to our concrete in the rain. The addition of extra water to a concrete mix can weaken the concrete and therefore it may not meet the strength it requires to take the load of the building. Timber is a poor conductor of heat and therefore a timber frame would retain the heat better, this then goes on to mean lower heating bills in the future, but also using less energy. Concrete is a conductor of heat and therefore releases heat out of the building. Although timber is not as efficient as a sound insulator.
Concrete is a non-combustible material and therefore has better fire-resistance. With a reinforced concrete frame, extreme heat can sometimes cause the rebar to lose its bond with the concrete. Timber can also be very good in the incident of a fire, due to its slow combustion rate. “although its structural properties are good, timber, being an organic material .. will spread fire over its surface” (Advanced Construction Technology, Fourth Edition, Roy Chudley & Roger Greeno, 2006) Building a concrete frame can be one of the biggest contributors to CO2 emissions in the building industry.
This is due to a number of reasons including the transport of materials, the extensive use of plant and machinery and the amount of workers on site (therefore higher levels of transport etc to site). However, the majority of concrete can be recycled or re-used after serving its initial purpose. Timber is seen as probably the most sustainable and environmentally friendly building product; when timber grows, it takes in carbon dioxide from the atmosphere, in then acts as a carbon store and once it has served its purpose it can be recycled or used as a biofuel – therefore reducing energy levels this way.
The European Commission estimates “that on average, substituting one cubic metre of wood for other building materials results in 0. 8 tonnes of CO2 savings. ” Both frames have advantages and disadvantages. Deciding on what frame is more suitable for your construction project depends on what your main aims and objectives are for the project. If you have a very tight budget, it would seem that a timber frame would be more suitable, although a concrete frame would generally be better for cash flow as it is a longer term project and slower release payments.
A timber frame would also save costs on heating in the long run. However, it would appear that a concrete frame would need less maintenance and would last longer; it is less susceptible to weather and environmental damage. This could save costs long term. A timber frame is more economical to build and is less damaging to the environment. However concrete has a better sound insulation and therefore your building would be less disruptive, and again wouldn’t have to spend as much money on sound insulation. However a concrete frame would require more heat insulation as it is a conductor of heat. Approx. 1500 – 1800 words) (50 marks) Question 2: 3. 27kg of a piece of dry timber was immersed in water for 7 days. The timber was removed from the water, wiped carefully and found to weight 3. 87kg. a) What is the percentage of moisture content of the timber? (5 marks) The formula to work out moisture content is the following: Initial wet weight – dry weight x100 Dry weight Therefore, the following is accurate: 3. 87kg – 3. 27kg x100 3. 27kg = 18. 348624% moisture content or 18. 35% (2dp) moisture content b) Fully explain the term ‘hygroscopic material’ (5 marks) . “Hygroscopic materials can absorb moisture from the air during moisture load periods and transfer it back to the air during low humidity periods,” (Research in Building Physics: Proceedings of the 2nd International, T. Ojanen & M. Salonvaara). Timber is a hygroscopic material, if it becomes too wet it will swell, if it becomes to dry it will warp. When wood is processed, they try to eliminate this characteristic, so that it can be a more durable construction material. c) Fully explain why timber for internal use requires specific moisture content. 4 marks) The British Standard – BS EN 942 Timber in joinery defines the physical characteristics of the timber. It states that the joinery timber is required to have specific moisture content at all times, until the project is handed back to the client. d) What are the visual and olfactory signs of dry rot and what sequence of actions would you take to totally eradicate an outbreak? (6 marks) There are many warning signs to show that there may be dry rot present. These are as follows: * The wood shrinks and becomes darker in colour There is visible cracking in the wood when it is bent a little * There can be a multi-coloured silk overskin * A white fluffy substance can be visible * There can be a damp odour from the wood To get rid of dry rot, you have to eliminate the source of water that is creating it. This can be done by visually inspecting likely areas, such as roof spaces, joints. It can be sourced by looking for any obvious signs of leaking, such as condensation or damp through the walls. The next step to be taken is getting rid of any damaged wood. Any new wood put in place should be treated.
And any ends of cut off wood should also be treated to prevent dry rot spreading. Question 3: The following particle size distribution was obtained from a sieve analysis on an aggregate of sample size of 1400g (sample 2). Sieve Size (mm)| Mass(g)| % on sieve| % Passing| 125| 0| 0| 100| 75| 0| 0| 100| 63| 88| | | 37. 5| 55| | | 20| 87| | | 10| 98| | | 6. 3| 95| | | 3. 35| 102| | | 2| 129| | | 1. 18| 89| | | 0. 6| 85| | | 0. 3| 90| | | 0. 212| 92| | | 0. 15| 84| | | 0. 063| 90| | | a) On a separate sheet, reproduce and complete the table to obtain ‘percentage on’ and ‘percentage passing’ each sieve. 14 marks) b) Plot the particle size distribution on the attached graph. (8 marks) c) Comment on this sample aggregates particle size distribution and (8 marks) it’s suitability for direct use as an aggregate when compared to Sample 1 from a different location (already plotted). Approximately 15% of sample 2 is almost dust like and therefore isn’t suitable to be used as an aggregate. Sample 1 shows to have 10% more available material that is suitable to use as an aggregate. Bibliography DHIR, N. J. &. R. K. Civil Engineering Materials, Fifth Edition. [S. l. ]: [s. . ], 1996. GREENO, R. C. &. R. Advanced Construction Technology, Fourth Edition. [S. l. ]: [s. n. ], 2006. SALONVAARA, T. O. &. M. Research in Building Physics: Proceedings of the 2nd International. [S. l. ]: [s. n. ]. WWW. OXFORDDICTIONARIES. COM/DEFINITION/ENGLISH/CONCRETE).. www. oxforddictionaries. com. Acesso em: January 2013. WWW. OXFORDDICTIONARIES. COM/DEFINITION/ENGLISH/TIMBER. www. oxforddictionaries. com. Acesso em: January 2013. The European Commission The British Standard – BS EN 942 Timber in joinery The British Standard – BS 1282 Code of practice for preservation of timber