Blog Archives

DEFLECTION AND EXPANSION JOINTS

Posted by on 16/ 11/ 15

Joints in bridges fall into two categories: deflection joints and expansion joints.

4.14.1 Deflection Joints

Contrary to what the name implies, deflection joints, when placed in concrete barriers and parapets, are used primarily to minimize the vertical shrinkage cracking that would otherwise occur in long, unjointed panels. Some states permit a longitudinal spacing of joints as great as 30 ft (9.1 m) in simple spans. Over piers of continuous bridges, the spacing is generally less, 7.5 ft (2.3 m) or closer. Preformed joint filler is used to form the joints and is left in place. Sometimes the placement of parapet concrete is required to be done in two stages, with placement of alternate panels only in the first stage, to facilitate placement of the joint filler.

When barriers are permitted ...

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LEVELING CEILINGS

Posted by on 16/ 11/ 15

The older the house, the more likely its ceiling joists are sagging. If you’re gutting the old finish ceiling, the easiest way to create a flat, level plane for the drywall that will follow is to fasten light­weight steel studs to the old joists at a uniform height below the lowest joist (see p. 168).

With the aid of a helper, stretch a taut, level stringline perpendicular to existing joists at each end of the room and position each string lower than the bottom of the lowest joist so the studs won’t deflect it as you work. Here’s how:

1. Use a self-leveling laser level to establish a level line around the room that is % in. below the lowest point of your ceiling joists.

Подпись: bracing FOR A LOAD In addition to providing something solid to nail stud wall plates to, blocking also braces a floor, distributing loads between joists so that individual joists can carry roughly 10 percent to 15 percent more than unbraced joists. If you don't need solid blocking to nail wall plates to but still want to brace joists, consider installing bridging, which is metal or 1x4 wood pieces installed diagonally between joists. Bridging is generally easier and quicker to retrofit than solid blocking and interferes less with pipes and wires running in the joist bays. Where Walls Meet

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Where a new partition abuts an existing wall, cut back finish surfaces to the centers of the ne...

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Independent Tests Yield Clear Performance Comparisons

Posted by on 16/ 11/ 15

Fisette conducted independent testing of housewrap not to establish quantifiable data that mimicked real-world performance, but rather to subject the products to a set of sim­ple laboratory conditions to see how they compared. For more on Fisette’s testing, see www. umass. edu/bmatwt/publications.

According to Fisette’s research, the best housewraps (those that resist water infiltra­tion and also permit water vapor to evapo­rate) include Tyvek HomeWrap, R-Wrap by Berry Plastics™ Corporation, Typar® (manu­factured in 2003 or later), and—believe it or not—traditional #15 felt paper (see the side­bar on p. 75).

I prefer Tyvek, which scored well for resisting water penetration in the Massachu­setts study while also having one of the industry’s highest perm ratings for water- vapor ...

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Irish Method

Posted by on 16/ 11/ 15

In the publication by Brennan et al. (2000) is proposed another method of SMA design developed in Ireland. This method allows for a required discontinuous grada­tion of an asphalt mix between 0.6 mm and 5.0 mm sieves (for SMA 0/14) to create a strong skeleton of coarse grains. The determination of the properties of the coarse aggregate fraction (greater than 2 mm), screened out of the aggregate mix, has been recognized as the key issue, as in other methods. The density of the compacted coarse aggregate fraction is determined by vibration; a sample is tested under low pressure in the mold used during the California Bearing Ratio (CBR) test by placing it on a vibration table commonly used for compacting samples of ready-mix concrete...

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OTHER METHODS OF DESIGN

Posted by on 16/ 11/ 15

7.5.1 Dilation Point Method

The dilation point method, which was devised by the American National Center for Asphalt Technology (NCAT) and then adopted in Australia (Stephenson and Bullen, 2002), serves to determine the maximum content of aggregate less than 4.75 mm (i. e., the passive fraction), which still does not cause the dilation of the coarse aggregate (i. e., the active fraction). The method consists of preparing a series of samples with various contents of fine aggregate. The samples are compacted in a gyratory com­pactor with a constant content of binder and stabilizer. According to the rule, voids among the coarse aggregate are gradually filled with passive particles...

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Limitations of Hydrologic Frequency Analysis

Posted by on 16/ 11/ 15

3.9.1 Distribution Selection: Practical Considerations

Many different probability distributions have been proposed for application to hydrologic data. Some of them were proposed because the underlying concept of the distribution matched the goal of hydrologic frequency analysis. For ex­ample, the extremal distributions discussed in Sec. 2.6.4 have very favorable properties for hydrologic frequency analysis. Ang and Tang (1984, p. 206) noted that the asymptotic distributions of extremes in several cases tend to converge on certain limiting forms for large sample sizes n, specifically to the double­exponential form or to two single-exponential forms...

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The Board Foot

Posted by on 16/ 11/ 15

Whether you are dealing with the local sawmill or buying salvage, you need to be familiar with the term board foot, because that is the unit by which timber is sold.

A board foot (BF) is a square foot of wood one inch thick, or 144 cubic inches (2,360 cubic centimeters) of material. Every linear foot (LF) of a full one-by-twelve board is a board foot, but every linear foot of a full two-by-six is also a BF, because it also contains 144 cubic inches of wood (2 x 6 x 12=144). A linear foot (LF) is also called a running foot at many sawmills.

This lumber scale gives the number of board feet with virtually every size of rough-cut lumber you are likely to want, in lengths from eight feet (2.44 meters) to twenty feet (6 meters).

Lumber scale, in board feet (BF)

Size Length (feet)

8

10
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RISER DIAGRAMS

Posted by on 16/ 11/ 15

Riser diagrams are often required by code officers prior to any plumbing be­ing installed. Supplying a detailed riser diagram (Fig. 5.44 and Fig. 5.45) is usu­ally a standard part of a permit applica­tion. You can also use riser diagrams to help you when sizing a vent system. If

RISER DIAGRAMS

FIGURE 5.45 ■ DWV riser diagram, with size and location of pipes. (Courtesy of TAB Books, Home Plumbing Illustrated, by R. Dodge Woodson, p. 50)

RISER DIAGRAMS

FIGURE 5.46 ■ Poorly designed DWV layouts. (Courtesy of TAB Books, Home Plumbing Illustrated, by R. Dodge Woodson, p. 55)

RISER DIAGRAMS
you draw a riser for the job you are working with, the diagram will make it easier for you to label the fixture-unit loads and the sizes of the vents re­quired. Another good use of a riser diagram is to minimize wasted piping...

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A Side-by-Side Comparison Is Often Pointless

Posted by on 16/ 11/ 15

Nowadays, any approved weather-resistive barrier, from #15 felt to high-tech house – wrap, touts the dual benefit of being a weather-resistive drainage plane that also allows the passage of water vapor. But not every product balances these two features equally. To add to this confusion, house – wraps are now available in dozens of variet­ies, so how do you choose? Unfortunately, there’s no easy answer.

The American Society for Testing and Materials (ASTM) is working to standardize the tests used to evaluate weather-resistive barriers. For now, when trying to gain code approval, manufacturers can choose from at least two dozen different tests. Even if two manufacturers choose the same test, though, there is nothing to regulate the way in which the test materials are set up...

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WEATHERING STEEL

Posted by on 16/ 11/ 15

The cost of initial painting and periodic repainting of structural steel bridges can often be eliminated by the use of bare weathering steel. From an economic standpoint, the use of multicoat high-technology paint systems should be reserved to those bridges that are not suitable candidates for weathering steel.

To ensure successful long-term performance, the Federal Highway Administration

(FHWA) has published “Guidelines for the Use of Unpainted Weathering Steel.”

Principal considerations are as follows:

• Consider with caution use in marine coastal areas; in areas of frequent high rainfall, high humidity, or persistent fog or condensing conditions; at grade separations in “tunnel-like” conditions; and at low-level water crossings...

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