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All About Headers

Posted by on 14/ 11/ 15

Подпись: A SOLID HEADER IN A LOAD-BEARING 2x4 WALLAll About HeadersПодпись: A SOLID HEADER IN A NONLOAD-BEARING 2x4 WALLПодпись:All About HeadersAll About Headers

SPANNING THE DISTANCE above window and door openings, headers transfer the weight of the roof down through the trimmers, making it pos­sible to have openings in a wall with­out compromising its strength. There are three things you need to know about headers: length, cross-sectional dimensions, and construction details.

Header Lengths

Window and door manufacturers typically provide recommended rough opening sizes for the prehung units thev sell. To determine the length of a header, you can simply add 3 in. to the rough opening size; this is the combined thickness of the trimmers that support the ends of the header.

a – The length of a door header is usu­ally 5 in. greater than the width of the door. Therefore, a 3/0 door (36 in. wide) needs a 41-in. header. The extra 5 in. includes 3 in...

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Traffic Loading

Posted by on 14/ 11/ 15

Perhaps the most important step in designing a pavement is the estimation of the design traffic. Overestimation of the design traffic results in a thicker pavement than necessary with associated higher costs. Underestimation of traffic results in a thin pavement that will fail prematurely, resulting in higher maintenance and user costs. If the proposed pavement will be used to replace an existing pavement, the design traffic could be a projection of the existing traffic. If the proposed pavement is a new loca­tion, the design traffic will have to be estimated on the basis of the proposed use of the pavement. For design purposes, all traffic is equated to an equivalent 18-kip (80-kN) single-axle load, or ESAL...

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Thermal Diffusivity, a

Posted by on 14/ 11/ 15

The thermal diffusivity, a (m2/s), is the ratio between thermal conductivity (X) and thermal capacity (c):

a = X/c (4.3)

It, thus, measures the ability of a material to conduct thermal energy relative to its ability to store thermal energy. Soils of large a will respond quickly to changes in their thermal environment, while materials of small a will respond more sluggishly. From a physical point of view the thermal diffusion of a medium is indicative of the speed of propagation of the heat into the body during temperature changes. The higher the value of a, the faster propagation of heat within the medium.

For example, during sunny days the pavement surface temperature will show strong daily oscillation and in soils and pavement materials with a high thermal diffusivity this oscillation pe...

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PARAMETERS FOR AASHTO PAVEMENT DESIGN

Posted by on 14/ 11/ 15

The AASHTO pavement design equations have some variables that are common to both rigid and flexible pavements, including serviceability, traffic loading, reliability, overall standard deviation, and roadbed soil resilient modulus. These parameters are discussed in the following articles. Subsequently, the design procedure is presented for rigid pavements in Art. 3.6 and for flexible pavements in Art. 3.7.

3.3.1 Serviceability

The AASHTO design equations are developed around the concept of serviceability, which serves as the pavement performance parameter by which a pavement’s condition is valued. Present serviceability is defined as the momentary ability of a pavement to serve traffic. The present serviceability rating (PSR) was developed to measure service­ability...

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Mechanistic-Empirical Pavement Design

Posted by on 14/ 11/ 15

AASHTO has given interim approval for a new approach to pavement design as described in the AASHTO Interim Mechanistic-Empirical Pavement Design Guide Manual of Practice. Several years in development, this M-E pavement design guide and the accompanying software should provide a significant advancement in pavement performance prediction. As its title implies, mechanistic-empirical models are used to analyze input data for traffic, climate, materials, and the proposed pavement structure, and then to estimate pavement service life damage. The distress prediction models have been calibrated to national averages based on data gathered by the Long-Term Pavement Performance program...

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Thermal Capacity, c

Posted by on 14/ 11/ 15

Thermal capacity characterises the ability of a material to store or release heat. It is the important property that relates to the delay in heat transfer. The thermal capacity of water is approximately twice as high as that for most minerals and for ice, while the thermal capacity of air is negligible.

Thermal Capacity, c

Temperature (°С)

Thermal Capacity, c

Volumetric water content, в

Fig. 4.2 Typical relationships between thermal conductivity and ice content (top) and between thermal conductivity and water content (bottom) (Hansson et al., 2004). Credit: the Vadose Zone Journal, published by the Soil Science Society of America

The thermal capacity of saturated soils ranges between 800 and 1000 J/(kg°C) – that is between 2000 and 2400 J/(m3°C) – while dry soils exhibit values of between 300 and 1600 J/(m3°C)...

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Step 16-Plumb & Line (continued)

Posted by on 14/ 11/ 15

Racking Brace

 

Do not let brace protrude above double plate.

 

Two 16d nails in top plate.

 

One 16d nail in center if it is a bearing wall or exterior wall.

 

Step 16-Plumb & Line (continued)

Подпись: Two 16d nails into bottom plate once the wall is plumbed.Step 16-Plumb & Line (continued)

Use crowbar to rack brace and wall. Turn brace around if wall

needs to be racked in other direction.

Racking a wall is moving the top of the wall with the bottom secure until the wall is plumb.

One framer racks the wall with a brace and crowbar, while the second framer checks for plumb.

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Porosity, n

Posted by on 14/ 11/ 15

Because the thermal conductivity of minerals is much higher than that of water and air, thermal conductivity of soil decreases with increasing porosity.

4.3.2 Degree of Water Saturation, Sr

The thermal conductivity of air in a soil or aggregate’s pores is negligible but the conductivity increases with increasing degree of water saturation.

Fine soils generally have a high porosity and a low quartz content and, conse­quently, the thermal conductivity of dry clay and silt is low. However, the fine pores of these soils more easily hold a higher amount of water and fine soils typically deliver thermal conductivities in the same range as other soils.

4.3.3 Temperature, T

The thermal conductivity of ice is four times higher than that of water and con­sequently the thermal conductivity of soil...

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Designing an Aggregate Mix Less than 2 мм

Posted by on 14/ 11/ 15

When designing the gradation of aggregate smaller than 2 mm (filler and fine aggre­gate), it should be kept in mind that the excellent properties that allow SMA to resist permanent deformation are connected mainly with a coarse aggregate skeleton. Mastic made of filler, fine aggregate, and binder should play the role of bonding and sealing the coarse aggregate, while its quantity cannot be greater than the free space left among the compacted active grains. See Chapter 7 for a discussion of the Dutch method of designing the volume of mastic in SMA.

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Conclusions Concerning Heat Transfer

Posted by on 14/ 11/ 15

For pavements, conduction of heat is the most important factor for heat transfer. During warm and sunny summer days though, the temperature of a pavement base layer under a thin asphalt concrete, may reach high values and natural convection in a fairly permeable base layer should not, then, be neglected.

4.3 Thermal Conductivity, X

Mineral content, porosity, degree of water saturation and temperature affect the ther­mal conductivity of soils. The total conductivity is a function of the conductivity of each soil phase, solid grains, water and gas. Various equations for these mixtures have been proposed by Keey (1992) and Krischer (1963). Thermal conductivity values range between 1 and 4 W/m°C for saturated soils, and from 0.2 to 0.4 W/m°C for dry soils.

4.3.1 Mineral Content

Because ther...

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