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All Natural

Posted by on 17/ 11/ 15

What the subtractive process requires, more than anything else, is a firm understanding of necessity. Knowledge of universal human needs and the archetypal forms that satisfy them is a prerequisite for the practice of good design. This knowledge is available to anyone willing to pay attention.

A vernacular architect who has come across a photo of a Kirghizian yurt and encountered a Japanese unitized bathroom and a termite mound while traveling does not set out to build a yurt with a unitized bathroom and termite inspired air conditioning just to show what he has learned. He retains the forms for a time when necessity demands their use.

Vernacular architects do not strive to produce novel designs for novelty’s sake. Necessity must be allowed to dictate form...

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Reactions Between Oxidizers and Reducers (Electron Exchange)

Posted by on 17/ 11/ 15

Many chemical reactions imply the transfer of electrons from one chemical species to another. These reactions are called redox reactions and they are usually rather slow. In soil and water, redox reactions involve hydrogen ions and are thus greatly pH dependent. The most important redox reactions involve oxygen, carbon, nitro­gen, sulphur, manganese and iron. In polluted soils, arsenic and mercury can also participate.

The redox potential, and changes thereof, play a crucial role in the behaviour of metals in soils. For instance, iron oxides are formed at high redox potentials. Iron oxides and hydroxides are capable of adsorbing heavy metals onto their surfaces, which will greatly reduce the mobility of the heavy metals...

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Critical Flow Depth

Posted by on 17/ 11/ 15

When the depth of flow is plotted against the specific energy, the specific energy diagram may be obtained and the critical depth found as illustrated in Fig. 5.5. The critical depth is defined as that depth where the specific energy is minimum. The flow velocity at the

Critical Flow DepthCritical Flow DepthШШїші

HTDKAUlic graoe LINE

channel bottom

DATUM LINE

FIGURE 5.4 Flow characteristics for uniform open-channel flow. (From F. S. Merritt, ed., Standard Handbook for Civil Engineers, McGraw-Hill, 2004, with permission)

Supercritical

range

(critical

depth)

Подпись:(Specific energy)

FIGURE 5.5 Specific energy diagram. (From Highway Design Manual, California Department of Transportation, with permission)

critical depth is called the critical velocity...

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Exchange Reactions

Posted by on 17/ 11/ 15

Exchange reactions take place between two reactants, usually meaning that both are in the liquid phase (although some surface complexation reactions may involve an exchange reaction, too). They include electron exchanges (reactions between ox­idizers and reducers), proton exchanges (reactions between acids and bases) and
“particle”[13] exchanges (formation of complexes from ions or molecules) (Stumm & Morgan 1996).

On its way from the road surface downwards, the infiltrating seepage (carry­ing chemicals accumulated during rainfall and runoff) will encounter and interact with varying redox-potential and acidity conditions in the various layers of the road construction and soil layers beneath. The resulting more or less steady conditions will govern the equilibria of chemical reactions...

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Extra joists and headouts

Posted by on 17/ 11/ 15

Extra joists are needed under parallel walls (walls that aren’t perpendicular to the floor joists) to carry the added weight that gets transferred down through these walls. Move the extra joists away from the center of each
parallel wall about 3 in. to allow room for pipes and conduit to be run up into the walls from below (see the draw­ing above).

Sometimes joists must be cut to allow room for a stairway, access to an attic, a place to install a skylight, or even for a heater vent in a wall or a tub trap in a bathroom. Carpenters call these open­ings headouts (see the drawing on p. 98). Regular 2x joists (not I-joists) can be cut as long as they are sup­ported by a header joist and fastened to parallel joists. Here are some basic rules for headouts:

• If more than one joist is cut, doub...

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SIZING WATER HEATERS

Posted by on 17/ 11/ 15

S

izing water heaters is not a complicated process. It is, however, an im­portant part of most plumbing jobs. Local code requirements call for minimum standards. The minimum facility requirements can be found in any major codebook or local code enforcement office. Since plumbing codes are regional, you will have to check your local code for exact requirements. But, the math that I’m about to show you will work in any location. Some of the numbers might be different, depending on code requirements, but the mathematical procedure will be the same.

When you figure the size of a water heater, remember that the codes of­fer suggestions and regulations for minimum requirements...

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The water delivery system of Pergamon: the first large forced main

Posted by on 17/ 11/ 15

Lysimachus, who had received Thrace in the partition of Alexander the Great’s empire, imprudently left part of his war spoils in the custody of Philetairos, in the Asia Minor citadel of Pergamon. This citadel occupied a rocky spire that overlooked the plain from 300 m above it, and about 30 km from the sea. After the secession of Philetairos, in 282 BC, Pergamon rapidly became the capital of a kingdom, then an intellectual center that sought to rival Alexandria with a great Library (some 200,000 rolls of papyrus) and a School of original thought.

The provision of a supply of water to these citadels perched on hills always posed a problem in Antiquity. Initially, cisterns were built to store rainwater...

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Energy Equation

Posted by on 17/ 11/ 15

The energy equation is based on the principle that energy must be conserved; that is, the energy at any one cross-section on a stream is equivalent to the energy at any other section plus any intervening energy losses. This relationship, a form of the Bernoulli equation, may be used wherever there is a change in the size, shape, or slope of the channel and is useful in determining the depth of flow.

Подпись: FIGURE 5.3 Nomograph for solution of Manning equation. (From Highway Design Manual, California Department of Transportation, with permission)
Energy Equation

/ V2 І V2

z1 + d1 + у j = z2 + d2 + у ^Lg j + hL (5.13)

where zn = distance above some datum, ft (m) dn = depth of flow, ft (m)

Vn = flow velocity, ft/s (m/s) g = acceleration of gravity, 32.2 ft/s2 (9.8 m/s2) hL = head loss between the two sections, ft (m)

TABLE 5.6 Values of the Roughness Coefficient n for Use in the Manning’s Equation

Min

Avg

Max

A...

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Plumb and brace the trusses

Posted by on 17/ 11/ 15

When bracing trusses, take time to read and follow the directions from the engineering com­pany. These, along with local building codes, must be followed to guarantee that the house will have a strong and stable roof. Most simple gable-truss roofs are easy to brace.

After four to six trusses have been installed, plumb the gable-end truss and begin bracing the roof. Use a level to plumb the end truss, then install a diagonal 2×4 sway brace from the double top (cap) plate of the exterior wall (where the gable-end truss is installed) to an inboard truss (see the photo on p. 124). The brace should extend at a 45-degree angle from the top plate and be nailed to the top chord (or rafter) or the webbing of an inboard truss.

Plumb and brace the trussesПодпись: ATTACHING TRUSS CLIPSPlumb and brace the trussesПодпись:If the gable-end rafter is plumb, the rafters tied to it at 24 in. o. c...

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Other Methods

Posted by on 17/ 11/ 15

Various methods of testing for an increase in the softening point are used in many countries. For example, in Germany, two methods are applied: the R&B method and Wilhelmi’s method. According to an U. S. review of fillers (Harris and Stuart, 1995), in Germany an acceptable range of AR&B of 10-20°C has been adopted for the R&B method, with components selected at the filler-binder content ratio (F:B) equal to 65:35, % (v/v). Mortars with AR&B greater than 20°C are too stiff and are not accepted. Similarly, mortars with AR&B less than 10°C are not accepted due to their excessive plasticity.

Another interesting test applied in Germany is the determination of a stiffen­ing factor (in Germany Stabilisierungindex) (Schellenberger, 2002)...

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