Blog Archives

Structural and Nonstructural Panels

Posted by on 12/ 11/ 15

Plywood and OSB are the structural panels most often specified to sheathe wood framing and increase its shear strength. For example, a 20-ft. wall sheathed with %6-in. plywood can withstand more than a ton of lateral force pushing against the top of the wall.

PLYWOOD

Structural plywood is made by laminating soft­wood plies. Each panel is stamped to indicate veneer grade, species group or span rating, thick­ness, exposure durability, mill number, and certi­fying agency.

Veneer grades. Veneer grades range from A to D, with letters appearing in pairs to indicate the front and back veneers of the panel. "A/B Exterior,” for example, has a grade A front veneer, a grade B back veneer, and grade C inner plies...

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Vertical Alignment

Posted by on 12/ 11/ 15

The design of the vertical alignment of a roadway also has a direct effect on the safety and comfort of the driver. Steep grades can slow down large, heavy vehicles in the traffic stream in the uphill direction and can adversely affect stopping ability in the downhill direction. Grades that are flat or nearly flat over extended distances will slow down the rate at which the pavement surface drains. Vertical curves provide a smooth change between two tangent grades, but must be designed to provide adequate stopping sight distance.

Tangent Grades. The maximum percent grade for a given roadway is determined by its functional classification, surrounding terrain, and design speed. Table 2.16 shows how the maximum grade can vary under different circumstances...

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Horizontal Alignment and Superelevation

Posted by on 12/ 11/ 15

The horizontal alignment of a roadway should be designed to provide motorists with a facility for driving in a safe and comfortable manner. Adequate stopping sight distance should be furnished. Also, changes in direction should be accompanied by the use of curves and superelevation when appropriate in accordance with established guidelines. Some changes in alignment are slight and may not require curvature. Table 2.5 lists the maximum deflection angle which may be permitted without the use of a horizontal curve for each design speed shown. It is assumed that a motorist can easily negotiate the change in direction and maintain control over the vehicle without leaving the lane.

TABLE 2.4 Decision Sight Distance (DSD) for Design Speeds from 30 to 70 mi/h (48 to 113 km/h)

Decision sight dista...

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Statistical Properties of Random Variables

Posted by on 12/ 11/ 15

In statistics, the term population is synonymous with the sample space, which describes the complete assemblage of all the values representative of a partic­ular random process. A sample is any subset of the population. Furthermore, parameters in a statistical model are quantities that are descriptive of the pop­ulation. In this book, Greek letters are used to denote statistical parameters. Sample statistics, or simply statistics, are quantities calculated on the basis of sample observations.

2.1.3 Statistical moments of random variables

In practical statistical applications, descriptors commonly used to show the sta­tistical properties of a random variable are those indicative of (1) the central tendency, (2) the dispersion, and (3) the asymmetry of a distribution...

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Framing with Steel

Posted by on 12/ 11/ 15

The use of steel framing in residential renovation is increasing, but it’s still rare and generally not advised for novice builders unless working with a builder experienced with it.

Подпись:LIGHT STEEL FRAMING

Light steel framing consists primarily of C – shaped metal studs set into U-shaped top and bottom plates, joined with self-drilling pan-head screws. Fast and relatively cheap to install, light steel framing (20 gauge to 25 gauge) is most often used to create non-load-bearing interior partitions in commercial work.

Its advocates argue that more residential con­tractors would use it if they were familiar with it...

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Darcy’s Law

Posted by on 12/ 11/ 15

Water flows though porous media from a point to which a given amount of energy can be associated to another point at which the energy will be lower (Cedergren, 1974, 1977). The energy involved is the kinetic energy plus the potential energy. The kinetic energy depends on the fluid velocity but the potential energy is linked to the datum as well as the fluid pressure. As the water flows between the two points a certain head loss takes place.

From an experimental setup as shown in Fig. 2.6, the total energy of the system between points A and B is given from Bernoulli equation as

Подпись: (2.13)UA V A uB vB

— + TT + ZA = — + ^ + ZB + Ah Pwg 2g Pwg 2g

where u and v are the fluid pressure and velocity respectively, z is elevation above the datum line and h is head loss between point A and B that is genera...

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United States

Posted by on 12/ 11/ 15

U. S. requirements for aggregates constitute a compromise between high quality con­ditions and the necessity of taking into account the economics of manufacturing asphalt mixtures. The number of properties specified are limited, while the require­ments themselves are somewhat broad (see Table 5.5), compared with the European standards. The requirements also vary from state to state. Similar requirements are used in the United States for SMA airfield surfacing (ETL 04-8).

Additionally, the possibility of using reclaimed dusts (baghouse fines) from an asphalt mixing plant is a fine example of the pragmatic approach to the selection of aggregates for asphalt mixtures.

Dusts, mineral powders, hydrated lime, and pulverized fly ashes are allowed, while lumps and organic impurities are excluded...

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Sight Distance

Posted by on 12/ 11/ 15

A primary feature in the design of any roadway is the availability of adequate sight distance for the driver to make decisions while driving. In the articles that follow, the text contains conclusions based on information contained in Ref. 1. Derivation of for­mulas and references to supporting research are contained in that document and will not be repeated here. The reader is encouraged to consult that document for more detailed background information. The following paragraphs discuss various sight distances and the role they play in the design of highways.

Stopping Sight Distance. Stopping sight distance is the distance ahead that a motorist should be able to see so that the vehicle can be brought safely to a stop short of an obstruction or foreign object on the road...

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Requirements According to European Standard EN 13043

Posted by on 12/ 11/ 15

In the Comite Europeen de Normalisation, or European Committee for Standardi­zation (CEN), the member states’ requirements for aggregates designed for asphalt mixtures have been unified in the EN 13043 standard entitled Aggregates for Bituminous Mixtures and Surface Treatments for Roads, Airfields, and Other Trafficked Areas. It provides a set of aggregate properties and a series of requirement levels (categories) for each property.

Each CEN member state adopting this standard has defined its own national requirements, considering such issues as local climatic conditions and experience of engineering, from among the alternative properties and categories provided in the standard.

The requirements for SMA aggregates according to the EN 13043 standard are displayed in Tables 5.1 and 5.2...

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ENGINEERED BEAMS

Posted by on 12/ 11/ 15

The most daunting part of using engineered beams may be the wide selection. Fortunately, lumberyard staff can usually explain the merits of each type and help you determine correct size.

Glulams, or glue-laminated timbers, are the granddaddy of engineered beams. They’ve been used in Europe since the early 1900s. In North America, they’re fabricated from relatively short pieces of dimension lumber (often Douglas fir or southern pine), which is overlapped or finger – jointed, glued, and pressure clamped. Glulams come in stock widths 3% in. to 6% in., but you can obtain them in almost any size or shape, includ­ing curves and arches, as well as pressure treated.

Glulams are expensive, but their stability and strength make them suitable for high loads in clear spans as great as 60 ft...

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