Blog Archives

CORROSION PROTECTION OF NEW STEEL BRIDGES

Posted by on 16/ 11/ 15

The application of protective coatings to steel bridges, and the maintenance reapplication of coatings, is costly and so alternatives to the use of coated steel should be sought. Where appropriate, unpainted weathering steel should be used instead (see Art. 4.13). If a coated bridge is still the best candidate for the particular location, a long-lasting coating system should be applied.

Modern Paint Systems. The development of high-performance paint systems for new bridges has resulted mostly in two – or three-coat systems involving combinations of various materials including organic and inorganic zinc, epoxy, and urethane...

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Road Equipment

Posted by on 16/ 11/ 15

Road equipment comprises crash barriers, road signs, sign-posts, lamp-posts, etc. Many of these structures are made of galvanized steel. Corrosion of these surfaces releases zinc to the environment (Barbosa & Hvitved-Jacobsen, 1999). Corrosion is promoted under moist conditions often prevailing as a result of splashing from the traf­fic during and after precipitation. Soiling and the use of de-icing salt further enhance the corrosion. Re-painting is usually preceded by the removal of old paint. The old paint may contain heavy metals. Regular washing of road equipment may contribute pollutants to the environment in cases where detergents are used (Folkeson, 2005).

6.2.2 Maintenance and Operation

Many measures taken within road maintenance and operation introduce pollutants into the highway...

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Application of the Method during Production Control

Posted by on 16/ 11/ 15

Subsequent to the design of the recipe and its approval, it is time for the pro­duction of an SMA mix. Production control using the Dutch method takes into account the same factors that have been used during SMA design (job mix for­mula [JMF]).

The properties of some elements are naturally changeable; this particularly applies to the aggregate gradation, particle shape, and resistance to crushing.

As noted earlier, designing an SMA using the Dutch method is based on optimiz­ing the coarse-aggregate content in order to obtain the selected air void content in compacted samples of the SMA. So if the gradation of the supplied coarse aggregate changes during production of the SMA in an asphalt plant, then the SMA volumet­ric parameters change accordingly...

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Procuring the Timbers

Posted by on 16/ 11/ 15

W

HEN I WAS A YOUNG MASONS LABORER IN SCOTLAND BACK IN THE 1970 S, master stone mason Hughie Mathieson would say to me, “You cannae build without the stones, Robbie, you cannae build without the stones!” It was his way of telling me to get the lead out and provide him with more building stones on his scaffold.

With timber framing, you cannae build without the timbers! Now, where are they going to come from?

Recycled Timbers

Years ago, there used to be more old timber frame barns available for salvage than there are now. Jaki and 1 used lots of recycled barn beams at Log End Cottage, Log End Cave, and Earthwood. But, recently, a large barn became available. We heard about it through a friend...

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Traffic and Cargo

Posted by on 16/ 11/ 15

Road traffic and cargo produce a range of compounds that pollute the environment. Corrosion of vehicle compartments is a source of heavy metals. Tyre wear gives rise to particles containing zinc, cadmium and iron (literature cited by Fergusson, 1990 [p. 420]; Landner & Lindestrom, 1998; Sarkar, 2002). Brake pads and brake linings emit copper, zinc and lead (Weckwerth, 2001). Fuel, fuel additives and lubricants are sources of hydrocarbons. Lead (Pb) is no longer allowed in the EU states but in countries where leaded petrol is still used, e. g. many African countries, this metal is emitted in the exhausts. Wear of catalytic converters gives rise to emission of plat­inum, palladium and rhodium, though in minor amounts...

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SUPPORTING A VENT SYSTEM

Posted by on 16/ 11/ 15

Подпись: ✓ fast code fact If a vent is run up the outside wall of a building and is exposed to weather, the pipe must be protected from freezing. One way of doing this that is generally accepted is to enlarge the diameter of the vent to prevent condensation from freezing and ultimately sealing the vent pipe with ice.

SUPPORTING A VENT SYSTEM Подпись: Support material Maximum distance between supports (ft)

Supporting a vent system is another element of a system design. The spac­ing allowed for support varies from code to code and with the type of pipe being used in the vent system. The tables below will show you some examples of recommended minimums for support spacing.

SUPPORTING A VENT SYSTEM
Подпись: Lead pipe Cast iron Galvanized Copper PVC ABS Подпись: Type of vent pipe Maximum distance between supports

FIGURE 5.38 ■ Horizontal pipe-support intervals in Zone Two. [Courtesy of McGraw-Hill)

FIGURE 5.39 ■ Vertical pipe-support intervals in Zone One. [Courtesy of McGraw-Hill)

SUPPORTING A VENT SYSTEM

Type of vent pipe Maximum distance between supports (ft)

 

ABS

Cast iron

Galvanized

PVC

Copper (2 in and larger) Copper (ІУ2 in and smaller)

 
SUPPORTING A VENT SYSTEM

Maximum distance between supports (ft)

 

Lead pipe

4

Cast iron

At each storyt

Galvanized

At each storyt

Copper (ІУ4 in)...

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Cantilever

Posted by on 16/ 11/ 15

A cantilever, as in Fig. 2.4, can be thought of as an upside down beam, supported at just one end. It is “upside down” in the sense that its top surface is in tension while its bottom surface is in compression. Note that the unsupported part of the cantilever tends to impart the same kind of upside-down stresses as the supported part. I think of it as being a bit like a first-class lever: the downward pressure of

the overhanging load pivots at the wall (which acts like a fulcrum) and causes an uplifting pressure on the supported portion.

Подпись: building to exceed the one-thirdimage25During my researches, I have found writers (some of them engineers) who say that the over-hanging part should be one-third of the supported apart. Others say 40 percent. Some say 50 percent is the absolute limit...

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Tools

Posted by on 16/ 11/ 15

My tools are pictured on the facing page. They are pretty much all I have needed to build a dozen small houses. Folks I’ve worked with tell me I’m a fool for not using a table saw, too. You might want to add one to your list.

1. skill saw, 2. jig saw, 3. plyers, 4. files, 5. miter saw, 6. hammer, 7. wrench, 8.goggles, 9. tape measure, 10. drill & drill bits, 11. pencil, 12. box cutter, 13. level, 14. chisel.

image40

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Selection of Distribution Model

Posted by on 16/ 11/ 15

Based on a given sample of finite observations, procedures are needed to help identify the underlying distribution from which the random samples are drawn. Several statistical goodness-of-fit procedures have been developed (D’Agostino and Stephens, 1986). The insensitivity to the tail portion of the distribution of the conventional chi-square test and Kolmogorov-Smirnov test has been well known. Other more powerful goodness-of-fit criteria such as the probability plot correlation coefficient (Filliben, 1975) have been investigated and advocated (Vogel and McMartin, 1991). This and other criteria are described herein.

3.7.1 Probability plot correlation coefficients

Подпись: PPCC = Подпись: X^m=1(x(m) x)(ym y) [£ m=1( x(m) — x)2£ m=1( ym — y)2]0'5 Подпись: (3.17)

The probability plot is a graphic representation of the mth-order statistic of the sample x(m) as a function of a ...

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SELECTION OF MATERIALS FOR MAIN SUPERSTRUCTURE MEMBERS

Posted by on 16/ 11/ 15

For the primary superstructure members of a bridge (not including the deck), concrete (reinforced and prestressed) and structural steel are the principal candidates. Concrete and steel both have desirable attributes and shortcomings as bridge materials. In general, bridges of both materials can be designed, constructed, and maintained to ensure long life.

Claims of both steel and concrete industry associations, including references to national bridge inventory data used to support contentions of superiority of one material over the other, must be critically considered. One can find examples of both concrete and steel bridges that are old and in good condition, and conversely, relatively new and in poor condition. The trade associations do a service in countering each other’s claims.

Some...

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