Blog Archives

Coatings Improve Performance

Posted by on 18/ 11/ 15

Energy-efficient windows were developed during the previous energy crisis. When Jimmy Carter was installing solar panels on the White House and making conserva­tion a priority, the Department of Energy’s Lawrence Berkeley National Laboratory was charged with finding ways to conserve energy. Windows were among their targets. The insulating windows of that era allowed an inordinate amount of heat to escape. The lab’s scientists concluded that by using exist­ing technologies to deposit a virtually invis­ible metal or metal-oxide coating on the glass, insulating windows could be dramati­cally more efficient. This coating is trans­parent to visible light, but blocks long – and short-wave radiation by reflecting it...

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STRUCTURAL DESIGN OF DRAINAGE PIPES

Posted by on 18/ 11/ 15

5.8.1 General Considerations

The structural capacity of an underground structure and the methods of determining that capacity are dependent upon the material properties of the structure and its physical configuration. In this context, the structure is the composite structure comprised of the pipe and the surrounding soil. The surrounding soil is generally referred to as the soil envelope, and buried structures rely upon the soil envelope for their ability to with­stand loads.

Under load, the pipe will deflect laterally and mobilize the passive resistance of the surrounding soil. Also, the pipe and surrounding soil will settle and the pipe will deflect to varying degrees...

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Sampling of Soil and Soil Water

Posted by on 18/ 11/ 15

Having entered the soil environment near roads, contaminants will either be retained in the soil or transported through the soil. Depending on soil characteristics and other environmental conditions, different contaminants are transported with the soil
water through the soil at varying rate. Mobile compounds (such as chloride) move rapidly whereas many heavy metals and organic contaminants move much slower. Often, contaminant concentrations are much higher in the upper soil layers than further down the soil profile.

Sampling of soil water gives a picture of the rate of transportation of contami­nants down a soil profile whereas sampling of soil gives a picture of the contaminant quantities having accumulated in the various soil layers over a long period of time.

Seepage and soil water (por...

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Seasoning the Timbers

Posted by on 18/ 11/ 15

How long to air-dry or season the timbers before use is a much-debated question. The best answer I have encountered is from contemporary timber framer and colleague Steve Chappell in his book A Timber Framers Workshop, listed in the Bibliography. Steve uses the term “curing” to describe the early stages of the seasoning process. He describes this initial phase:

Once the tree dies and is milled, the wood fibers begin to relax and take on their natural shape. There is usually an immediate reaction to being milled in the form of crowning, warping, or twisting, resulting from the inherent tension in the wood, but no shrinkage will occur until all of the free water (moisture in the cell cavities), and the bound water (moisture in the cell walls) begins to leave. (Chappell, 1998, p. 139)

Cha...

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Thermal Protection

Posted by on 18/ 11/ 15

Moisture Problems Associated with Building Insulation

The addition of thermal insulation into wall cavities has had a major impact on moisture control in buildings. As buildings have become tighter and better insulated, the opportunity for water vapor to dry out from wall and roof

assemblies has been reduced. Trapped water leads to wall assembly failures.

Buildings in cold winter climates will tend to dry to the outside since moisture flows from the warm interior towards the cold exterior. Under these conditions, water vapor passing through insulated building assemblies will reach a temperature where it will begin to condense. If this condensation occurs before the vapor reaches the exterior of the building, the insulation will become wet...

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HOISTING MATERIALS TO THE ROOF

Posted by on 18/ 11/ 15

HOISTING MATERIALS TO THE ROOFHere in the West, we try to order shingles the day before they will be installed. Suppliers arrive with a hoist and stack both shingles and felt paper directly onto the roof. An experienced delivery per­son knows to stack bundles of shingles about 6 ft. apart on both sides of the roof.

The other way to get shingles onto the roof is the hard way— hoisting one bundle at a time. If you must haul roofing shingles up to the roof yourself, make sure you have a secure ladder that is positioned properly and is 2 ft. to 3 ft. taller than the roof. It’s a good idea to nail a temporary 2x tread at the spot on the roof where you will step off the ladder. This tread provides a solid foothold where you need it most.

BUST THE BUNDLE. Shingles are much easier to carry if you “bust" the bundle first...

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WALLS AN! CE I..IN SS

Posted by on 18/ 11/ 15

The first house I helped build was in 1948, on the high plains of western Nebraska. It was a precut house, shipped by rail and brought to the job site on a large wagon pulled by a team of horses. Every piece of wood—wall plates, studs, headers, cripple studs, sills, braces, and joists—was wrapped and labeled in color-coded bundles. Putting the house together was like putting together a three-dimensional jigsaw puzzle.

Houses are still puzzles. All the different pieces have to be laid out, cut, and nailed together to create the frame. The sheathed floor or concrete slab acts as the "table" on which all the puzzle pieces are assembled. But puzzles go together easier when you have an idea of what the finished product will look like...

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Guidelines for Culvert Selection

Posted by on 18/ 11/ 15

The following general guidelines from the Federal Lands Highway (FLH) manual should assist in determining appropriate culvert material types and necessary coatings. Other methods are available. Many state departments of transportation and local governmental agencies have published durability criteria, and this information should be used where available. A materials engineer should be consulted for important applications. Of course, the final selection must provide for structural requirements as discussed in Art. 5.8.

Concrete Pipe. Where the pH is less than 3.0 and the resistivity is less than 300 U • cm, reinforced concrete pipe should not be specified. If the sulfate concentration exceeds 0.2 percent in the soil or water, type V cement should be specified...

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Circular Stairs

Posted by on 18/ 11/ 15

Circular stairs are not as difficult as they seem the first time you think about doing them. They do, however, take some planning and careful work. There is no one way that curved stairs need to be built, as long as they are strong enough to bear the traffic. The method that follows is commonly used.

First of all, unlike straight stairs, we will not use stringers. Instead, each tread will be supported independently, by either a wall or a header. The header method allows for space to be usable under the stairs. The system outlined here uses a header to create what are called tread walls.

• It is not uncommon for a set of plans to be drawn up with the stair headroom less than the 6′-8" that the code requires...

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Abrasion

Posted by on 18/ 11/ 15

Abrasion causes a loss of section thickness due to impacts by the aggregate carried by stream flow. Protection from abrasion generally takes the form of providing a sacrifi­cial thickness of the structural material, whether it be a thicker sheet of steel or con­crete paved invert for metal pipe, or more concrete cover over the reinforcement for reinforced concrete pipe. Alternatives to providing for a thicker section include using debris control structures to prevent the abrasive material from reaching the culvert, and providing metal planking longitudinally along the invert as a separation between the bed load and the bottom of the culvert.

Abrasion can be considered in four levels of severity as categorized by streambed velocity and general aggregate size...

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