Blog Archives

Metal Plate-Connected Wood Trusses

Posted by on 19/ 11/ 15

Metal plate-connected (MPC) wood trusses were first used in the early 1950s. Today they are used in more than 75% of all new residential roofs. Basically they are dimension lumber engineered and connected with metal plates. Less expensive than alternative roof systems, these trusses can also span longer distances. The “Pitched Truss Parts" illustration shows the parts of a single pitched truss on the next page.

Because MPC trusses are engineered products, they should never be cut, notched, spliced, or drilled without first checking with the designing engineer.

Building codes require that a truss design drawing be delivered to the job site. The drawings must show, among other things, the layout locations and bracing details...

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Compaction Factor as a Quotient of the Bulk and Maximum Densities

Posted by on 19/ 11/ 15

Calculating the quotient of the bulk and maximum (the so-called theoretical maxi­mum density [TMD] or the Rice density after ASTM 2041) densities is a popular method of determining the compaction factor. The requirement for compaction of an SMA layer is a minimum 94% (of the maximum density) according to the NAPA SMA Guidelines QIS 122; that makes upto 6% (v/v) of air voids allowable after compaction. In this case the reference density does not depend on conditions for preparing laboratory specimens. As in the previous method, densities obtained in a laboratory during mix design are not taken into account; results from testing the den­sity of a mixture taken from an asphalt plant during trial production are recorded.

The essential strength of that method is making the compaction factor f...

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Tips for Installing Glu-Lam Beams

Posted by on 19/ 11/ 15

• For glu-lam beams that are installed at a pitch and need to have the bottom cut to be level, make sure that the end of the bottom cut closest to the bearing edge receives full bearing. (See “Cut Edge Full Beaning" illustration.)

• Ends of beams should not be notched unless approved by the engineer. (See “No Notching End of Glu-Lam Beam" illustration.)

• Glu-lam beams will shrink as they dry out.

If the top of the beam is connected in a way that doesn’t allow for shrinkage, the glu-lam beam will split. (See “Glu-Iam Beam Shrinkage" illustration.)

• When a lateral support plate is used to connect two glu-lam beams, the holes should be slotted horizontally to prevent splitting. (See “Lateral Support Plate" illustration).

• Glu-lams are also used for posts...

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Water Content Variations in Pavements

Posted by on 19/ 11/ 15

In the last ten years, significant progress has been made in the measurement of in-situ water contents in pavements, using in particular TDR probes (see Chapter 3, Section 3.2.2). These measurements have shown that, often, significant amounts of water infiltrate in to pavements through the pavement surface and from the shoulders.

Low traffic pavements are particularly exposed to water infiltration. Examples of moisture measurements on a typical flexible pavement (6 cm thick bituminous surfacing and granular base) are shown in Figs. 8.3 and 8.4. Figure 8.3 shows that the daily variations of water content in the granular base and in the clayey sub­grade (near the pavement edge) are important and strongly related with the rainfall. Figure 8...

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Influence of Water Infiltration on Pavement Deterioration and Mechanical Degradation

Posted by on 19/ 11/ 15

Changes in water content, especially excess moisture, in pavement layers com­bined with traffic loads and freezing and thawing can significantly reduce pavement service life. Failures associated with moisture are detected on roads all over the Europe. There is some evidence to suggest that water has less impact on thick and well-construced pavements than it does on thinner ones (Hall & Crovetti, 2007). It appears that in thicker pavements the effect of water may be more indirect than in thinner ones, reducing material stiffness leading to later distress.

To minimize the negative effects of moisture on pavement performance, first we have to identify the sources of infiltration of water. There are many different possible sources of water infiltration in pavement systems...

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Development of the water mill in the Roman Empire

Posted by on 19/ 11/ 15

About fifty years after Vitruvius, under the reign of Vespasian and Titus, Pliny the Elder[255] wrote in his book, The Natural History:

“All the grains are not easily broken. [….] Throughout the greater part of Italy, however, they employ a pestle that is only rough at the end, and wheels turned by water, by means of which the corn is gradually ground.”[256]

The Roman development of the water mill has been consistently underestimated; but new archaeological findings are becoming more and more numerous.[257] One can find remains of simple mills on small rivers near Hadrian’s Wall at the Scottish border.[258] In eastern Tunisia, at Chemtou (the Roman Simitthus) the remains of an installation com­prising three horizontal wheels set side by side have been found near a dam constructed by ...

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Acceptance-rejection methods

Posted by on 19/ 11/ 15

Consider a problem for which random variates are to be generated from a specified probability density function (PDF) fx(x). The basic idea of the

TABLE 6.3 List of Distributions the Cumulative Distribution Function (CDF) Inverses of which Are Analytically Expressible

Distribution

Fx (x) =

x = Fx fiu)

Exponential

1 — exp(-вx), x > 0

—в ln(1 — F)

Uniform

(x — a)/(b — a)

a + ( b – a) F

Gumbel

exp{ exp[ (x — %)/в)]}

% — в ln[ ln(F)]

Weibull

1 — exp{—[(x — % )/в ]a}

% + в[— ln( 1 — F )]1/a

Pareto

1 — x—a

(1 — F)—(1/a)

Wakeby

Not explicitly defined

% + (a/в)[1 — (1 — F )в ] — (y/m — (1 — F )—s ]

Kappa

{1 — h[1 — a(x — % )/в]1/а }1/ h

% + (e/a){1 — [(1 — Fh)/h]a}...

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About Metal Fasteners

Posted by on 19/ 11/ 15

Several companies manufacture metal fasteners for a variety of wood-to-wood and wood-to-foundation applications. Since 1975, I have done a lot of timber framing without using these fasteners (except for truss plates), and I will share my techniques in these pages. But manufactured metal fasteners can make life easier, the building inspector happier, and improve the strength of the structure, so they are a valuable option. There are hundreds of different connectors available, and, while reading this book is a good introduction, I cannot cover all of the products in this relatively small volume. Therefore, you should also 1) go to your local hardware or building supply store and look at what’s readily available in your area (see Fig. 4...

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Classifications of Random Variates Generation Algorithms

Posted by on 19/ 11/ 15

6.1.1 CDF-inverse method

Let a random variable X have the cumulative distribution function (CDF) Fx(x). From Sec. 2.3.1, Fx(x) is a nondecreasing function with respect to the value of x, and 0 < Fx(x) < 1. Therefore, F-1(u) may be defined for any value of u between 0 and 1 as F-1(u) is the smallest x satisfying Fx(x) > u.

For the majority of continuous probability distributions applied in hydrosys­tems engineering and analysis, Fx(x) is a strictly increasing function of x. Hence a unique relationship exists between Fx (x) and u; that is, u = Fx (x), as shown in Fig. 6.1. Furthermore, it can be shown that if U is a standard uniform ran­dom variable defined over the unit interval [0, 1], denoted by U ~ U(0,1), the following relationship holds:

X = Fx-1(U) (6.6)

Note that X is a random vari...

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INSTALLING CUT-IN BOXES

Posted by on 19/ 11/ 15

Cut-in boxes have special mounting devices that enable you to mount them directly to finish sur­faces. But first you’ve got to cut a hole for them. Hold the new box at the same height as other outlet boxes in the room, lightly pencil trace around the box, and then drill a small exploratory hole to locate studs or wood lath behind. Insert an offset screwdriver or a bent coat hanger in the hole and twirl it. If the tool hits a stud, move the box till it’s clear. If you hit wood lath, keep drilling small holes within the opening till you find the edges of the lath. If you position the box

correctly, you should need to remove only one section of lath. Cut-in box ears (also called plaster ears) mount to the lath top and bottom, so you may need to adjust the box height to make that happen.

Onc...

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