However, the fill material is still necessary to support the curing concrete and its reinforcement. A one-way reinforced slab may be stronger than a two-way non-reinforced slab, depending on the type of load. Thermal conductivity l [8] This is a disadvantage when rooms are heated intermittently and require a quick response, as it takes longer to warm the entire building, including the slab. If the slab is to be reinforced, the rebars, or metal bars, are positioned within the formwork before the concrete is poured in. {\displaystyle l_{y}} [11], For ground-bearing slabs, it is important to design the slab around the type of soil, since some soils such as clay are too dynamic to support a slab consistently across its entire area. [4] The R-value does not consider thermal mass, since it is tested under constant temperature conditions. This is usually aided by a membrane, either plastic (temporary) or a liquid compound (permanent).[13]. Energy efficiency has become a primary concern for the construction of new buildings, and the prevalence of concrete slabs calls for careful consideration of its thermal properties in order to minimise wasted energy. As a result, any stress induced by a load, static or dynamic, must be within the limit of the concrete's flexural strength to prevent cracking. A two-way slab has moment resisting reinforcement in both directions. Since these slabs are inevitably poured on-site (rather than precast as some suspended slabs are), it can be difficult to control conditions to optimize the curing process. Ground-bearing slabs, also known as "on-ground" or "slab-on-grade", are commonly used for ground floors on domestic and some commercial applications. 27/$ï¶z.ÉÀÉÔ q "—57æa`°™2‚u2dàj»æ20 :ã4P As shown below, the thermal mass and thermal conductivity establish the thermal inertia, which causes a damping and time lag of the temperature peaks. Ground-bearing slabs are usually supplemented with some form of reinforcement, often steel rebar. In some cases formwork is not necessary - for instance, a ground slab surrounded by brick or block foundation walls, where the walls act as the sides of the tray and hardcore (rubble) acts as the base. A common type of insulated slab is the beam and block system (mentioned above) which is modified by replacing concrete blocks with expanded polystyrene blocks. x 47. In this case, the fill material is less important structurally as the dead weight of the slab is supported by the piers. Typically concrete slabs perform better than implied by their R-value. Concrete has low thermal diffusivity, high heat capacity, and its thermal mass is negatively affected by insulation (e.g. is the long dimension, then moment in both directions should be considered in design. Initial test results have shown that For a suspended slab, the formwork is shaped like a tray, often supported by a temporary scaffold until the concrete sets. [4] The primary influences on conductivity are moisture content, type of aggregate, type of cement, constituent proportions, and temperature. By reducing the concrete block density by volume and producing a lower-weight block, manufacturers increase the heat-insulating properties of the blocks. [7] This is relatively high when compared to other materials, for example the conductivity of wood may be as low as 0.04 W m−1 K−1. ÄWÒæh²ÜyXzòL¾Á~†ÔU) FÂR’rJÅ®ÉuÌg³ÜÔwƒÅ'ƒÁ£ƒA¢%¬££ADt4x4 êY¶•Ú@šˆ…AŒþ‚ʍ™ø4X]òáTº+£Ñ¨á䂪® A concrete slab may be prefabricated (precast), or constructed on site. In many domestic and industrial buildings, a thick concrete slab supported on foundations or directly on the subsoil, is used to construct the ground floor. A slab is ground-bearing if it rests directly on the foundation, otherwise the slab is suspended. Mud slabs, also known as rat slabs, are thinner than the more common suspended or ground-bearing slabs (usually 50 to 150 mm), and usually contain no reinforcement. As shown below, the thermal mass and thermal conductivity establish the thermal inertia, which causes a damping and time lag of the temperature peaks. New York: Van Nostrand Reinhold, 1992. is the short dimension and For a suspended slab, there are a number of designs to improve the strength-to-weight ratio. : Thermal conductivity of a concrete slab indicates the rate of heat transfer through the solid mass by conduction, usually in regard to heat transfer to or from the ground. For a ground-bearing slab, the formwork may consist only of side walls pushed into the ground. 1242 0 obj <>/Filter/FlateDecode/ID[<63E73177C6342E4BA0710C1B4FBDE5EB><67BE2D50D1AD7B478AF1256AB7B72198>]/Index[1225 45]/Info 1224 0 R/Length 94/Prev 690534/Root 1226 0 R/Size 1270/Type/XRef/W[1 3 1]>>stream Print. The calculation of One Way Slab Reinforcement Details Design is extremely tedious and time-consuming and after give more time is not 100% sure that design is best or not and also if some minor change comes in design if force to calculate full design step again and again, Also, there are so many factor work as silent during structure design of one way slab as belove they are supported in one axis). Effective Span. The actual value of k varies significantly in practice, and is usually between 0.8 and 2.0 W m−1 K−1. hÞÜXëoÛ6ÿWìK‹5£(¾"@M`M&kú Új"ÀÀVÚæ¿ßݑT$DZݠ]‡A I‘wäïwYäJ²Œ‰\)¦sì5˝Áa:38°Ìh‹ÇŒ¡g–htƜBn-˜È®á&‚vҒ )hUÁ(§‘fB)b…­]Ft–åÞ¯cRx…#ϤuF&cÒÓF0%rÀRÄk$SZã~F1e Êk4S>'^TÁ¯í¼~Íß/Æõ¢™]¿8׳¶iï_òõu³l÷/ÆóOõK~qw{;©§°Ì²ý}à9XŽðÅyÁ¾\_5ãö†©Lð£êö´n®oZf¼äÇu Û˅á'“êzÉdÎOæ³öðpþ­ØÓ ®±Ž’OšIZI&ù@SçÕ´æ—Í´^þ–gçõWøý0ŸV3Z¼ slab" or simply "r.c.". Without insulation, concrete slabs cast directly on the ground can cause a significant amount of extraneous energy transfer by conduction, resulting in either lost heat or unwanted heat. A non-reinforced slab is two-way if it is supported in both horizontal axes. [18] Since unreinforced concrete is relatively very weak in tension, it is important to consider the effects of tensile stress caused by reactive soil, wind uplift, thermal expansion, and cracking. Garber, G. Design and Construction of Concrete Floors. %%EOF To simplify this, particles of aggregate may be considered to be suspended in the homogeneous cement. Non-reinforced slabs may also be considered one-way if they are supported on only two opposite sides (i.e. [21] In general, they may be used for any application which requires a flat, clean surface. 2 This property is determined by the mass and thermal conductivity of the building material. If the block layer or section is solid, and made of concrete, its thermal resistance can be obtained by equation (3), R. C = L k. C. A. C. ϑ(3) where. Sometimes a mud slab may be a substitute for coarse aggregate. [25] Plastic-tipped metal or plastic bar chairs, are used to hold the rebar away from the bottom and sides of the form-work, so that when the concrete sets it completely envelops the reinforcement. For multi-storey buildings, there are several common slab designs (see § Design for more types): On technical drawings, reinforced concrete slabs are often abbreviated to "r.c.c. Sensitivity of wall thermal transmittance to changes in block configuration, con crete thermal conductivity, and fill thermal conductivity is discussed. Prefabricated concrete slabs are built in a factory and transported to the site, ready to be lowered into place between steel or concrete beams. Subsequently, Valore (1980) developed another formula in terms of overall density. Steel-reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ceilings, while thinner mud slabs may be used for exterior paving (see below).[1][2]. èÂPãl)lè|¡³ŒÅVJSØ. %PDF-1.6 %âãÏÓ y The second consideration is the high thermal mass of concrete slabs, which applies similarly to walls and floors, or wherever concrete is used within the thermal envelope. In these cases, casting the slab directly onto a substrate of aggregate will maintain the slab near the temperature of the substrate throughout the year, and can prevent both freezing and overheating. 'ª,ãgm5iF³ëIÍ2þg]A1¦rþ®ú¤„ûSü¢­§_ÞßÖ´ŠºhnÛù‚ÿ5 ³îï²@óJ)K! Thermal mass is also related to thermal diffusivity, heat capacity and insulation. In some cases, a naturally sloping site may be levelled simply by removing soil from the uphill site. They may be pre-stressed (in the factory), post-stressed (on site), or unstressed. On uneven or steep surfaces, this preparatory measure is necessary to provide a flat surface on which to install rebar and waterproofing membranes. 1983 Annual Book of ASTM Standards ( Philadelphia : American Society for Testing and Materials , 1983 ). However, the high thermal mass is an advantage in climates with large daily temperature swings, where the slab acts as a regulator, keeping the building cool by day and warm by night. Duncan, Chester I. Soils and Foundations for Architects and Engineers. Energy efficiency has become a primary concern for the construction of new buildings, and the prevalence of concrete slabs calls for careful consideration of its thermal properties in order to minimise wasted energy.