Edge Sealing

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In regard to edge sealing, the following reasonable solution definitely extends the durability of a pavement and has been adopted in German practice (Milster et al., 2004):

• An extra layer of tack coat (of hot binder) is placed on the edges of pavement (between the layers), minimum 10 cm wide.

• A binder layer, minimum 2 mm thick, on a side surface of all layers, is applied (to achieve such a layer of binder, the tack coating usually needs to be repeated, or a hot sealant 2 mm thick needs to be applied in one work­ing cycle).

This sealing is aimed at protecting the pavement against water infiltration between layers and inside them.

10.6 OPENING TO TRAFFIC

Before opening up a road section with a new SMA layer to traffic, one should be sure that it has sufficiently cooled. Letting traffic go on an SMA layer while it is still warm may cause its premature rutting and the squeezing-out of the mastic. Some regulations stipulate that the opening to traffic may happen no sooner than 24 hours after finishing the placement, or at least, when the temperature in the middle of a layer drops to 30°C. The common practice is to delay the opening to traffic until the moment that the layer temperature drops to the air temperature. When an earlier opening to traffic is necessary, only light vehicle traffic should be allowed.

Edge Sealing

Tool Talk TOOLS FOR VINYL SIDING

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Tool Talk TOOLS FOR VINYL SIDINGA LONG, FLAT work surface is essential for vinyl siding and sheet-metal work. A couple of 2×12 boards on sawhorses work fine. For precise 90-degree-angle cuts and angled rake cuts, I suggest making a cutting jig for a circular saw (see the photo at bottom left). The jig, which sits on a long worktable, is essentially a wooden cradle that guides the base of the circular saw. The cradle can be positioned at a right angle, or at

Tool Talk TOOLS FOR VINYL SIDINGother angles, to the siding.

Use both right – and left-handed aviation snips to make straight and curved cutouts (see the photo at top right); tinsnips are also helpful. Other specialty tools you’ll need include a slot-punch, to make nailing slots in siding (see the photo at center right); a snap-lock punch, to create crimps or tabs that lock into the finish trim (see the photo at bottom right); and a zip tool, in case you need to remove a damaged panel from a wall.

the siding. Its also smart to check with builders in your area for any local wisdom. This is the best way to avoid the bulges, buck­les, and tears that can result from incorrect installation. Most vinyl siding should not be nailed firmly against sheathing. The installa­tion slots in the siding, starter strips, and other vinyl components are there for a reason. Keep the nail heads proud of the vinyl so that the vinyl can move.

The tools you need to install vinyl siding are mostly tools you probably already own, but there are a few others you’ll need to either buy or make (see the sidebar above). These tools are also handy for the sheet-metal work we’ll tackle later in the chapter.

Starter strips

The installation of vinyl siding begins with different trim elements: starter strips, inside corners, outside corners, J-channel, and so on. The various trim details are designed to hide or interlock with siding ends and edges (see the illustration on p. 159). As with other homebuilding phases, if you get started right, the next steps follow more smoothly. The crit­ical first step is to put on a straight and level starter strip right above the top of the con­crete foundation wall or slab (see the top photo on the facing page). This strip can usu­ally be installed by nailing through the sheath­ing and into the bottom of the mudsill or sole plate. The strip’s bottom edge can then extend about 1 in. over the concrete.

Tool Talk TOOLS FOR VINYL SIDINGINSTALL VINYL TRIM. Attached along edges and corners, vinyl molding helps secure siding panels and contributes to a nice, finished appearance. Starter strips are installed along the bottom edge of the wall (left). To allow for heat-induced expan­sion, the end of a starter strip should be at least 1 in. away from the out­side corner trim (below).

Tool Talk TOOLS FOR VINYL SIDING

If the house is covered with housewrap, it is not always easy to see where to nail the starter strip. One way to establish the exact height of the strip is to measure down from the underside of the joist chords on the roof trusses and mark the proper height at various points around the house. This will ensure that the starter strip is level and equidistant from the top plates. Connect these points with a chalkline all around the house. On long walls, keep the line from sagging in the middle by having someone hold the line to a height mark near the middle of the wall, then snap the chalkline from the center to both corners.

To secure the starter strip, drive nails in the center of the installation slots, spacing them every 12 in. to 14 in. Leave at least / in. to ‘/ in. of expansion room between sections of starter strip as you install it around the building, and drive your first nail in each piece no less than 4 in. from an end. Remember: The strip must be able to move beneath the nail heads. At a walls outside corner, the starter strip must be 1 in. or more from the vinyl corner trim, as shown in the photo at right. Keep the strip

I. in. to 2 in. from the inside corners.

Gritting Execution

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Grit is spread on an hot SMA mixture using one of the two following techniques:

• With a gritter installed on a roller, during the first pass of the roller there is no gritting, but during the second pass the gritting is turned on. One should remember to grit in one direction of roller movement, and to not grit when returning; when using that technique, grit particles are pressed into the hot SMA mixture (Figure 10.15).

• With a self-propelled gritter, gritting starts after rolling the layer down with the rollers, when the SMA is still hot enough and prior to the last pass of the roller. This method is seldom used.

Remember that the quantity of grit per square meter has been established for a given machine (a gritter) and for a specific passing speed. Any change to the speed

image106

FIGURE 10.15 SMA gritters installed on rollers—the gap gritter. (Photo courtesy of Bartosz Wojczakowski.)

image107

FIGURE 10.16 Movement traces of a roller after gritting a freshly made SMA layer. (Photo courtesy of Krzysztof Blazejowski.)

results in a change in the quantity of grit applied to the layer. The minimum tempera­ture of a layer being gritted is 110°C; below that temperature the grit is unlikely to stick to the SMA (Jacobs and Fafie, 2004).

Figure 10.16 shows movement traces of a roller fitted with a gritter. Spots where the roller has changed direction before the gritter was fully disengaged are visible. This is not a substantial mistake of execution; at most it is likely to spoil the aesthetic impressions of some road users. After gritting and cooling of the layer, excess grit aggregate or unbonded grit should be removed, (e. g., by sweeping).

Research has proved that gritting makes sense since it enhances SMA antiskid­ding performance in the initial period after pavement construction. When gritting is not used, better coefficients of friction are available with SMA 0/8 mm than with SMA 0/11 mm (more contact points between SMA and tire). It should be mentioned additionally that the application of gritting influences the macrotexture during the first period after construction. Grains and crushed particles of grit occupy spaces between coarse grains and decrease the macrotexture depth.

Finally, it should be clearly stated that gritting is not a way to cover or hide fat spots occurring on SMA surfaces during placement. In some cases, even gritting is not likely to conceal a fat spot, since gritting would be “drowned” in an excess of mastic (Figure 10.17).

image108

FIGURE 10.17 Gritting of chippings 2/5 mm applied over a fat spot of mastic. (Photo cour­tesy of Krzysztof Blazejowski.)

Hold-Downs

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Hold-downs are connections commonly used for foundations, wall-to-wall connections, wall-to – concrete connections, and wall or floor-to-drag strut. Hold-downs are also called anchor downs and tie-downs. They can be difficult to install, but if you plan ahead and install as you go, the job is more manageable. Hold-downs that attach walls to the concrete foundation are typically attached to bolts already in the concrete. These bolts are generally set in place by the foundation crew. Sometimes they won’t be set in the right place.

You will want to locate the hold-down as close to the end of the shear wall as possible. If the bolt is already in the concrete, you will have to locate a hold-down on either side of the bolt. When considering the location, be aware of how it relates to what is on the floor above it; you don’t want, for example, the hold-down coming up in a door or window.

You should also allow enough space to install and tighten nuts and bolts.

When to Install Hold-Downs

Although it is common to wait until the building is framed to install the hold-downs, waiting can also present problems, such as studs that are already nailed in place where you want to install the hold­downs, sheathing that is hard to nail because it may be on the exterior of a second or higher floor, and possible pipes or wires running in the stud cavity.

It is helpful to install the hold-down studs as you build the walls. The layout framer should detail the hold-down studs while detailing the wall plates, and should also drill the plates for the anchor bolt or the threaded rods. If an upper floor is involved, the framer should also drill down through the subfloor sheathing and the top and double plate of the wall on the floor below. The wall builder should drill the

studs before nailing them into the wall. When the wall sheathing is installed, make sure it is nailed to the hold-down studs using the same nailing pattern that was used for edge nailing. (See “Hold-Down Nailing" illustration.)

Install the hold-downs and bolts, and washers and nuts, as soon as possible. Note, too, that when installing hold-downs after the walls are built, it is more productive to do an entire floor at one time. If the anchor bolts in the concrete do not extend high enough, a coupler nut can be used to extend the length. (See “Coupler Nuts Can Extend Anchor Bolts" illustration.)

As noted previously, the holes drilled for the bolts attaching the hold-down to the studs should not be more than!/іб” bigger than the bolts. However, it is acceptable to oversize the holes you drill for the threaded rod that passes between the floors. This will make installation easier without affecting
strength. (See “Drill Hole Size for Hold-Downs" illustration.)

With all nail-on connection hardware, it is important to use the right size nail. Hardware manufacturer’s catalogs indicate nail size appropriate for each piece of hardware. Most catalogs also give some options for nail use.

Hold-downs

Drill Hole Size for Hold-Downs

Drill holes no more than /16" bigger than bolts to maintain strength.

Fastening the Girt to the Top of the Posts

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Before attempting to lift a heavy girt (or girding beam) to the top of posts, make sure that the posts are vertically plumb — check two adjacent sides with the plumbing bubble on your level — and that all the posts are supported with sturdy bracing, as already discussed. Make sure that the posts are all the same — and the correct — height (see Post Height earlier in this chapter), and that their tops are square, which, in this case, translates to flat.

Based on your plan, the girts might be supported by two, three, or even more posts. A post at each end supports the 16-foot-long (4.9-meter-long) eight-by – eight girts in our garage, with a third post supporting the middle. The posts need to be the same height so that the girt will rest nicely on all three.

Russell Pray, a contractor friend, actually erected our entire garage framework for us while we were conducting workshops in British Columbia. He used a beam-cutting saw (very expensive!) to get nice square cuts on the eight-by-eight and four-by-eight posts and the eight-by-eight girts. To fasten the girts to the top of the posts, he used a heavy-duty electric drill to install ten-inch TimberLok™[7] screws down through the eight-inch girt and into the tops of the posts, two screws at each post. Lots of temporary diagonal bracing protected the entire frame against racking and provided stability while the 30-foot-long (9.1-meter-long) trusses were installed over the girts. Where two girts butt together over the post halfway along the sidewalls, shorter toe screws at the tops of the girts help tie one to the other.

Fastening the Girt to the Top of the Posts

Fig. 4.21: Install toe-nails (or screws) at about a 60-degree angle. As it is driven in, the toenail on the right will drive the post to the left. See sidebar text entitled Toe-nailing and Toe-screwing on the following page.

 

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Gamma distribution

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The gamma distribution is used frequently in the statistical analysis of hydro­logic data. For example, Pearson type III and log-Pearson type III distributions used in the flood frequency analysis are members of the gamma distribution family. It is a very versatile distribution the PDF of which can take many forms (see Fig. 2.20). The PDF of a two-parameter gamma random variable, denoted by X ~ GAM(a, в), is given by Eq. (2.72). The standard gamma PDF involving one-parameter a can be derived using variable transformation by letting

Y = X/в. The PDF of the standard gamma random variable Y, denoted by

Y ~ GAM(a), is shown in Eq. (2.78). The standard gamma distribution is used in all algorithms to generate gamma random variate Y s from which random variates from a two-parameter gamma distribution are obtained from X = вY.

The simplest case in generating gamma random variates is when the shape parameter a is a positive integer (Erlang distribution). In such a case, the random variable Y ~ GAM(a) is a sum of a independent and identical standard exponential random variables with parameter в = 1. The random variates from

Y ~ GAM(a), then, can be obtained as

a

Y = £- ln(U) (6.21)

i = 1

To avoid large numbers oflogarithmic evaluations (when a is large), Eq. (6.21) alternatively can be expressed as

Y = -1п^П Uij (6.22)

Although simplicity is the idea, this algorithm for generating gamma random variates has three disadvantages: (1) It is only applicable to integer-valued shape parameter a, (2) the algorithm becomes extremely slow when a is large, and (3) for a large a, numerical underflow on a computer could occur.

Several algorithms have been developed for generating standard gamma ran­dom variates for a real-valued a. The algorithms can be classified into those which are applicable for the full range (a > 0), 0 < a < 1, and a > 1. Dagpunar (1988) showed that through a numerical experiment, algorithms developed for a full range of a are not efficient in comparison with those especially tailored for subregions. The two efficient AR-based algorithms are presented in Dagpunar (1988).

Placement of Crash Cushions

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For proper performance, crash cushions should be placed on level terrain with a clear path between the roadway and the attenuator so the vehicle can strike at normal height, with the suspension system in a neutral state. Avoid curbs or slopes in front of the device. Install the attenuator on a smooth surface (usually concrete) so it can com­press uniformly. Conspicuous, well-delineated crash cushions are less likely to be hit than those that blend into the background. If the system is not reflective, install stan­dard object markers to improve visibility at night and during inclement weather.

Lognormal distribution

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Consider a random variable X having a lognormal distribution with a mean H-x and standard deviation ox, that is, X ~ LN(^x, ox). For a lognormal random variable X, its logarithmic transform Y = ln(X) leads to a normal distribution for Y. The PDF of X is given in Eq. (2.65). In the log-transformed space, the mean and standard deviation of ln(X) can be computed, in terms of цx and ox, by Eqs. (2.67a) and (2.67b). Since Y = ln(X) is normally distributed, the generation of lognormal random variates from X ~ LN(^x, ox) can be obtained by the following steps:

1. Calculate the mean ^ln x and standard deviation oin x of log-transformed vari­able ln(X) by Eqs. (2.67a) and (2.67b), respectively.

2. Generate the standard normal variate г from N(0,1).

3. Compute y = ,u. lnx + olnxZ.

4. Compute the lognormal random variate x = ey.

6.1.3 Exponential distribution

The exponential distribution is used frequently in reliability computation in the framework of time-to-failure analysis. It is often used to describe the stochastic behavior of time to failure and time-to-repair of a system or component. A ran­dom variable X having an exponential distribution with parameter в, denoted by X ~ EXP(e), is described by Eq. (2.79). By the CDF-inverse method,

u = Fx (x) = 1 – e-x/e (6.18)

so that

Подпись: (6.19)X = – в ln( 1 – U)

Since 1 – U is distributed in the same way as U, Eq. (6.19) is reduced to

X = – в ln(U) (6.20)

Equation (6.20) is also valid for random variables with the standard exponential distribution, that is, V ~ exp(e = 1). The algorithm for generating exponential variates is

1. Generate uniform random variate u from U(0,1).

2. Compute the standard exponential random variate v = – ln(u).

3. Calculate x = vft.

GUTTERS AND GUTTER GUARDS

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Gutters are sometimes required by code. When com­bined with downspouts and their associated fittings, gutters help keep water away from the foundation, pre­venting serious erosion and reducing water accumula­tion under the house. Gutters, downspouts, attachment hardware, and other components are available at most building-supply outlets. Also, consider buying and

installing gutter guards, especially if there are large trees nearby. Different types of gutter guards are avail­able, but they all perform the same function of keeping leaves, seedpods, and other debris out of the gutter while allowing water in. This eliminates the annual (or more frequent) chore of having to climb up on a ladder or onto the roof to clean out the gutters.

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GUTTERS AND GUTTER GUARDS

Diaphragm Framing Tasks of Particular Concern

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• Nail spacing—The nailing pattern for nailing the sheathing to the intermediate framing members is usually the standard 12" O. C. It is the edge nailing that changes to increase the strength.

• Penetration—The nail must not penetrate the sheathing’s outside veneer.

Nail Penetration

3/8" minimum from nail to edge of sheathing

/8" minimum gap

• Nail size—The nail sizes will vary based on the engineer’s design, or code requirements. Check the specified thickness and length.

• Blocking—It is common to have blocking in the joist space that runs parallel to the exterior walls. It will be detailed on the plans if it is required. Blocking can also be used on the edges of the sheathing.

Connections

“Connectors" can refer to beams or other construction elements, but in most cases, connectors are hardware specifically designed for common framing connections. As part of the load path, connections have to be strong enough to transfer the forces of nature.

In the prescriptive code, the connections are made with anchor bolts to the foundation, and with nails to connect floor joists to the plates below them, wall bottom plates to floors, and rafters or trusses to wall plates.

In non-prescriptive design, there are many ways to achieve the required force transfer between the shear walls, diaphragms, and foundation. The most common method involves metal connectors, which are produced by many companies. The Simpson Strong-Tie Company, because of its work in developing, testing, and cataloging connectors, is often referenced in building plans. Simpson Strong – Tie connector catalog numbers will be used in the balance of this book. Please note that substitutes with equivalent strength are available.

There are connectors made for just about every type of connection you can think of. As the framer in charge, however, it is not your job to decide on the type of connector, but rather to use correctly the connector that is specified. The best way to do this is to read the specifications in the connector catalog. Following is an illustration from a Simpson Strong-Tie Catalog, and a good example of instructions for installing hold-downs. You can reference the connectors at www. strongtie. com.

There are different connectors for the variety of different framing details, but only four common areas of connection:

• Foundation

• Wall-to-wall

• Roof-to-wall

• Foundation-to-top-of-the-top-wall

Important Points for Connection Framing

• Install all connectors per catalog instructions.

• Drill holes no more than VW bigger than bolts.

• Use washers next to wood.

• Fill all nail holes unless using catalog specifications.

• Know that the connection is only as strong as the weakest side. Make sure to space and nail each side the same. (See “Equal Nailing" illustration later in this chapter.)

• Be aware that some connectors have different-shaped nail holes. The different­shaped holes have different meaning, as illustrated in “Nail Hole Shapes" later in this chapter.