Suitability to Construct the Building - Coursework Example

Report on our Suitability to Construct the Building Name: Subject: Instructor: March 11th, 2014. ТHЕ SСIЕNСЕ АND МАTЕRIАLS FОR СОNSTRUСTIОN АND THЕ BUILT ЕNVIRОNMЕNT Introduction This report outlines the science and a range of construction material available for application in the construction of the development of estate housing project to underline the suitability of our company for this housing project that satisfies the Code for Sustainable Homes Standards. And in order to achieve this, the report will in detail describe and assess the properties of various available constructions materials, explore the impacts of loading structural materials, compare the behavior of reinforced concrete, steel and timber structural members under load, link scientific standards to human comfort, assess methods deployed to integrate building services into the overall design of the building and finally establish the thermal performance of buildings in relation to heat losses and gains. 1. Property of Construction Materials Examples of metals and alloys include lead, zinc, steel, iron, aluminum and brass. Timber and timber products are trusses, composite boards, softwoods and hardwood. Clay products include drainage, tiles and bricks. Concrete products include concrete, block-work and pre-cast units. Concrete has a relatively poor tension but very in compression: Timber is very strong along (parallel) the grain, however perpendicular to the grain it is weak. Timber can withstand high bending strengths Steel is an alloy of carbon and iron and is good in shear, compression and tension; however it requires protection over fire. In construction steel is perhaps the most significant ferrous structural material. Block-work and brickwork is quite strong in compression (Cain 2001). But they both depend on the mortar and the ties to offer the lateral resistance to avoid being pressed over. Glass also has good compression; nonetheless in its normal uses it needs support to repel shattering. Its production process can be changed to create a toughened product. 2. Assessing the Properties and Applications of Construction Materials a) Concrete Strength: According to BS1881 strength normally refers to comprehensive strength and is the most significant property of concrete. Strength of a concrete can be affected by the ration of water to cement, aggregate properties and type of cement. With increase of water ratio, on hydration the volume of pores increase. Usually crushed aggregates offer greater strength as opposed to uncrushed once, shapes which are irregular offer better key. Faster cement hardening create high early strength, however the same as OPC in the long run. Just like strength, durability reflects the ration of water to cement. For greater durability at given workability we specify a minimum cement content/m3. Principally, concrete mixes are systems of establishing batch quantities of water, aggregates, and cement per a specific concrete volume. Concrete usually fails due to physical attack such as damage caused by frost, and chemical attack; for instance ion formation due to water presence. The suitable applications of concrete include; mass and blinding concrete fill, trench fill foundations, strip footing, mass concrete foundation, drainage surrounds and unreinforced floors as well. b) Steel: Steel is ductile and without damage can undergo plastic flow. Various metals have different properties. Stronger steel has greater tensile and stiffness, they are not porous and their versatility can be increased by manufacturing alloys. Bonds can be created through welding, brazing and soldering (Markus and Morris 1990). Applications: Steel is viewed to be perfect structural material. They are used in pre-stressing and reinforcement for concrete, cavity ties, various fixings and lintels. c) Timber The density of timber is about 7% to that of steel. It has a lower compressive strength, and its fibres usually crumble. Timber can withstand high bending strengths, and this is especially important if structural member self –weight is added to the dead load (Cain 2001). Application: Timber can be used in suspended flooring and roof works. 3. Justification of the specification of development materials Timber: We visually inspect every piece of timber and then graded as follows; SS (Special Structural), these once have about 50-60% strength of an ideal timber. GS (General Structural) has approximately 30-50% strength of an ideal timber and we reject the use of timber of below 30% strength of perfect timber. The timber that has been graded is then marked based on TRADA rules. Computer systems are used to examine sections of each member for possible deflection when under load. This operation is also supported by visual examination because usually computer testing result is less rejects. A lot of roof trusses are constructed using computer examined timber sections. BS 5268 assists our engineers to categorizing various stress and species grades together. This enables our designers to utilize alterative species that achieve similar strength requirements (BS 5760, 1986). Concrete The standard mixes include (ST1, ST2 …ST5): These engineered mixes enable us to obtain a mix which is absolutely correct for the use, to produce suitable and consistent properties and are pperfect for huge volume as well as high strength uses. Steel BS EN 10025 steel grades have superseded BS 4360. For instance in S 275 J2 H implies S means Structural steel, J2 means impact performance, 275 refers to minimum yield strength (275n/mm2) and finally H means hollow section (BS 5760, 1986). 2. Effects of Loading Structural Materials In general we have four kinds of loads and they include Shear, Bending, Compression and Tension. When force is exerted on an individual member stress is produced. Tension force develops vertical cracks adjacent to concrete midspan, because it makes the concrete to crack so as to allow the reinforcing steel to repel the tension force. Such cracking will be monitored within the damaged structure to determine to possibility of collapsing. Hairline, stable cracks are a normal phenomenon, however if cracks widen is an indication of looming failure. Reinforced concrete and structural steel experience compression and tension forces on opposite faces, and these forces may reverse during high winds and earthquake. Tension stress can stretch members of timber or steel. A steel bar lengthens when a considerable tension stress is applied, and reverts to its original length when the stress if lifted. Compression stresses push on the structural members and might result into material crushing if members are relatively fat and short, especially at the surface bearings between concrete or wood columns and beams (ASHRAE handbook 2001). Failures of crushing usually give warning for instance concrete splitting and slow and noisy compression wood fibres. When slender and long structural members are loaded in compression, there possibility of failure can be abrupt by bowing (buckling). Comparison of the behaviour of reinforced concrete, steel and timber under load: Steel is formable, ductile, strong and tough but must be fireproofed. It has a magical ductility property, meaning it can be stressed over and above its elastic threshold and relentlessly bent, yet still has adequate strength to repel failure (Cain 2001). It is strong in shear, compression, and tension. Structures of steel frame have to be perfectly proportioned to escape column overloading. Wood on the other hand is fibrous, tough and fire supporting. It has defects such as knots. The bearing walls of light framed steel and wood are constructed using columns which are closely spaced, (about 16-41” o.c), which has to be interconnected with a skin so as to offer lateral strength which will enable each member to be loaded in compression with no buckling. Masonry and concrete bearing walls are properly proportioned to bear huge vertical loads based on their ration of height to thickness. Normally individual columns carry huge compression forces and can be constructed with reinforced concrete, steel or wood. For any member the load capacity is dependent upon the individual’s ratio of slenderness (I/r, I/d) and also the connection adequacy between the horizontal system and column (Building Performance Group 2001). There are a number wood trusses failures as a result of seasoning defects. Wood splits may occur adjacent to the edges of tension members has caused a lot of failures in bolted connections. Overloads because of snow or rain can result to abrupt collapse, because of failure on tension connection or compression member buckling. Steel trusses are quite reliable; however they are also vulnerable to abrupt compression failures as a result of a momentary overload. 3. Human Comfort Conditions Within the buildings you require air movement to make sure that fresh air is provided to occupants, odour is removed, excessive moisture is removed, and condensation is prevented. Good illumination will ensure that natural daylight assist offer a feel good factor, and to prevent disorders for instance seasonal affective disorder (SAD) (Koenigsberger, Ingersoll, Mayhew and Szokolay 2008). The building has to have the right temperature. This is because the human body upholds a core temperature of about 370C, and just a slim variation on this temperature can lead to death of illness (Nayak and Francis 2002). Humans are comfy with a 40-60% relative humidity. Any increase of that causes discomfort, and we can remedy this by increasing ventilation to get the right humidity (BS5760, 1986). Methods applied to integrate building services into the overall building design a) Reactive Building Elements These are building elements that help maintain a desirable balance between the environmental performance and optimum interior conditions through reacting in an integrated and dynamic matter to changes in internal or external conditions as well as occupant intervention and by vigorously communicating with technical processes. Examples will include façade systems; such as green facades, shading devices, adaptable facades, double skin facades, and ventilation openings; Roofing systems such as green roofs systems; concept of whole room, storages, core activation (heating and cooling) and earth coupling foundation systems (Nayak and Francis 2002) Concept of whole building: This entails integrated engineering solutions whereby the building components alongside service functions are incorporate into one common system so as to attain optimal cost and environmental performance as illustrated in the diagram below. While environmental performance encompasses energy performance together with its associated ecological loadings, resource consumption as well as interior environmental quality. . Integration illustration between building elements, controls, outdoor and indoor conditions and performance (Building Performance Group 2001). Building’s Thermal Performance concerning Heat Loss and Gain A building’s thermal performance is described as the process of modelling transfer of energy between the building and it’s environ. In case of a conditioned building it measures the cooling and heating load, and this the selection and sizing of HVAC machine can be properly made. In the case of non-conditioned building, it measures the variation of temperature within the building over a given period of time and assists us to approximate the duration of uncomfortable spans. Fig 2 Exchange of heat between the building and external surrounding As shown in the above diagram, thermal performance relies on various elements (Nayak and Francis 2002). We can summarize them as a) material properties (specific heat, density, thermal conductivity e.tc), b) design variables such as roof, window, walls, shading devices and orientation, c) weather data such as wind speed, solar radiation, humidity) and finally usage data of the building for instance the internal gains because of the occupants, equipment and lighting. The assumed values for the internal load density parameter comprises the gains associated with people, equipment and lighting. The sum gain of the lighting system would be taken as W//m2 whereas the value for people would be taken as m2 /people depending on the sum heat dissipation of the total occupants. The orientation of the building is defined as East-West or North-South and is based on the largest façade. This parameter would allow the heat gain via opaque objects and its effect on the entire building consumption of energy to be assessed. Parameter Value assumed Air conditioning system Split-COP of 3.20 (w/) Orientation of the building (o True North) East-West; North South Roof absorptance 0.2; 0.5; 0.8 Use patterns (hours/day) 11;14 External wall aborptance of solar radiation 0.2; 0.5; 0.8 ACH (air changes per hour) 0.5; 3 Coefficient of solar heat gain 0.87; 0.81; 0.76; 0.59; 0.49; 0.25 Ratio of wind to wall % 5, 15, 30, 45, 60 Internal load density (W/m2 ) 20, 35, 40, 70 Roof thermal resistance (W//(m2 .K)) 0.62;1.03;1.18;1.75;1.92; 4.56 External wall thermal resistance (W//(m2 .K)) 0.66;1.61;2.02;2.28;2.24; 3.7 Vertical shading 35;45 Horizontal shading 45 References Building Performance Group. 2001, Building Services – Component Life Manual, Blackwell Science, UK. ISBN: 0 6320 5887 0 Cain, C. 2001, A guide to Best Practice in Construction Procurement, Construction Best Practice Programme, UK. CIBSE, 2000. Guide to ownership, operation and maintenance of building services, Black Bear Press, UK. ISBN: 1 9032 8705 7 BS 5760, 1986. Reliability of Systems, Equipment and Components. Koenigsberger O.H., Ingersoll T.G., Mayhew A. and Szokolay S.V., 2008. Manual of tropical housing and building, part 1- climatic design, Orient Longman, Madras. Markus T.A. and Morris E.N., 1990. Buildings, climate and energy, Pitman Publishing Limited, London. ASHRAE handbook: 2001. Fundamentals, American Society of Heating, Refrigerating and Air- conditioning Engineers, Inc., Atlanta, GA, USA. Nayak J.K. and Francis S, 2002. Tools for architectural design and simulation of building (TADSIM), SESI Journal 12, pp. 81 – 91. Read More