Blog Archives

Steel-Beam Bridge

Posted by on 16/ 11/ 15

The steel-beam bridge uses rolled steel beams as shown in Fig. 4.8. Beam depths of 44, 40, and 36 in (1118, 1016, and 914 mm) are available, as well as shallower sections. Check with producers on current availability of the deeper sections from domestic sources because federal law applicable to federally aided projects, as well as many state laws, prohibits the use of foreign steel.

Steel beams may be made continuous by welding or bolting sections in the field. In the past, some states made welded connections at the piers, and currently at least

Steel-Beam Bridge

FIGURE 4.8 Cross-section of bridge with rolled steel beams. Conversions: 1 in = 25.4 mm, 1 ft = 0.305 m.

one state makes welded connections at contraflexure points, supporting the field sections temporarily and providing enclosures to shield...

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Prestressed-Concrete I-Beam Bridge

Posted by on 16/ 11/ 15

Prestressed-concrete beams of the basic I-shape, but with variations, can be used over approximately the same range of spans as steel beams. The deepest AASHTO standard prestressed beams (72 in or 1828 mm) have a somewhat greater simple-span capacity than 36-in-deep (914-mm) rolled steel beams, although deeper rolled beams are avail­able. This type of bridge is illustrated in Fig. 4.7.

Подпись: Prestressed I-beam

Prestressed-concrete beams are heavier to transport and erect than steel beams, and require more care in handling. A prestressed-concrete beam can be destroyed if it is not maintained in an upright position.

I-beams may be standard AASHTO-PCI sections or conform to individual state standards...

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Preparing Samples with the Use of the Marshall Hammer

Posted by on 16/ 11/ 15

The procedure of preparing samples using the Marshall method is common. It is currently available in EN 12697-30 and ASTM D 6926-04.

The biggest drawback of this method is the incompatibility of laboratory con­ditions and the realism of a construction site. This type of laboratory compaction consists of tamping a mix down with strokes of a predetermined compaction effort defined by the number of impacts on the face of a cylindrical sample.[47] The Marshall method was created several decades ago for designing an optimal content of binder in fine- and medium-graded mixes with continuous grading. Despite progress in technology, the impact method of compaction is still being widely used.

Besides the gap between the lab and the construction site, the most important issue is the energy used for...

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Engineering projects developed in Greece by the Persians during the Median wars

Posted by on 16/ 11/ 15

Herodotus’ history of the Median wars is interesting for its representation of the first confrontation between the classical Greek world and the Orient. Certain elements of Herodotus’ writings show the technical and cultural abyss that separated the two civiliza­tions, both in their relationships to the sea and their practice of fluvial engineering.

During the first Median war, the Persian fleet suffered major losses during its pas­sage around Mount Athos, a cape that extends quite far into the northern portion of the Aegean Sea (see Figure 4.6). Anticipating the second war, king Xerxes spent three years, according to Herodotus, digging a canal to get around the mountain on the land side of the isthmus...

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Prestressed-Concrete Box-Beam Bridges

Posted by on 16/ 11/ 15

The span range of a shallow bridge may be extended beyond the limits of a slab bridge by using precast prestressed-concrete box beams as illustrated in Fig. 4.6. The beams are prefabricated off-site. They are rectangular and, except for very shallow beams [12 in (305 mm)], which may be solid, have from one to three rectangular or circular voids. The void forms are either waterproofed cardboard or solid polystyrene foam and are left in the beams. Void drains must be provided to prevent entrapment of water. Prestressing strands are located on the bottom and in the sidewalls of the box, and may include debonded or deflected strands. The selection depends upon owner preference or, where the designer and owner allow the option, fabricator preference.

Wearing surface

This type of bridge can be c...

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Install foam sheathing

Posted by on 16/ 11/ 15

There are many areas in the country where ply­wood or OSB sheathing is required only at exte­rior corners and every 25 ft. along exterior walls. This allows you to install nonstructural sheathing material everywhere else. On this house, we used /fi-in. foam sheathing. The foam board is light and easy to handle, though it can be damaged by a stray hammer blow or by someone stepping on it. Attach foam sheathing with l’/Tin. roofing nails. Sheathe right over window openings, then go inside the house with a handsaw and cut out the foam from the openings (see the right photo on p. 109).

If you’ve come this far, congratulations!

Install foam sheathingПодпись: It's exciting to see an entire wall nailed together on the subfloor. We line up and grab part of the top plate to get ready to l ift. Then up it goes. At first, we're not worried about making sure the walls are plumb or straight—we just keep them up with diagonal braces. Then we start finding the exact positions with a level. As soon as the exterior walls are up, we start on the inside. It's amazing to think that just a short while ago we had only piles of lumber and a bare floor. This is going to be a great house! Make sure you spend some time cleaning up the job site at this point in your project...

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Analyses and Laboratory Tests

Posted by on 16/ 11/ 15

The components of stone matrix asphalt (SMA) and methods of SMA design have been discussed in the previous chapters of this book. In addition to the basic mix design processes, however, there are additional laboratory tests and procedures that are recommended to supplement the mix design work. Some unique tests focus on special properties of SMA mixes that may be encountered from time to time. Therefore it is necessary to undertake a short review of some selected tests. Some guidance is also offered on the interpretation of test results to avoid misunderstand­ings caused by inaccurately defined properties or incorrect test parameters. Such cases are also described in this chapter.

8.1 PREPARING SAMPLES IN A LABORATORY

At present, two methods of preparing samples in a laboratory are common...

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Method of Successive Iterations

Posted by on 16/ 11/ 15

This method, also called the method of iteration, is known chiefly by those who have practiced ready-mix concrete design in a laboratory. It is a laborious procedure because numerous tests need to be conducted (so now it is rarely used). It involves selection of consecutive aggregate fractions so that smaller particles can fit in among bigger ones with no increase in the mix volume (i. e., so that no larger particles are shoved aside by smaller ones).

We start by fixing the proportion of the coarsest aggregate (N1) with a finer frac­tion (N2). Having found such proportions for which we have a minimum of air voids with an unchanged volume of the mix, we mark the acquired mixture as aggregate N1,2...

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Bailey’s Method

Posted by on 16/ 11/ 15

The Bailey method was created in the United States in the early 1980s by Robert Bailey of the Illinois Department of Transportation. It enables the selection of an aggregate gradation that guarantees the best interlocking of aggregate particles, a suitable amount of VMA, and proper voids in the final asphalt mix. It was primarily intended for designing continuously graded mixtures with high deformation resis­tance, but it may also be applied to designing SMA gradation.

The method for gradation selection is based on the principle of the packing char­acteristics of aggregates and finally allows designing mixtures with expected aggre­gate interlocking. The complete method is used only for aggregate gradation design, not for full SMA (with binder) recipe design.

Those who are interested in ...

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MATERIALS

Posted by on 16/ 11/ 15

Work is not complete when the house frame is standing or when all of the trim and siding are nailed in place. From sandpaper to tape, from adhesive to caulk, other important materials are available to help carpenters put the fin­ishing touches on our work.

Sandpaper

The simplest thing to do when buying sandpaper is to pay attention to the grit. Look on the back of the sheet for the number of the grit. The higher the num­ber, the finer the sandpaper grit, and the smoother the finished surface will be.

So, for example, 40 grit is coarse paper, 80 grit is medium, and 120 grit is fine. I try to buy sandpaper in bulk rather than in expensive precut pieces. Cut larger sheets of sandpaper grit-side down using a straightedge and a utility knife.

Tape

The two tapes I keep in my tool bucket are du...

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