Blog Archives

Mass Transport in Unsaturated Soil

Posted by on 16/ 11/ 15

Mass transport in the unsaturated part of the road construction (the sub-base and upper part of the subgrade) strongly depends on the soil moisture distribution inside the pores. Where the mass transport is principally by advection then the water move­ment direction will control the contaminant flux direction. As the principal fluxes in the vadose zone are those due to evaporation and percolation, it follows that the
direction of the mass transport will then be essentially vertical, upwards or towards the lower part of the subgrade.

Soil moisture travelling through the unsaturated part of the road construction moves at different velocities in different pores due to the fact that saturated pores through which the moisture moves have different-sized pore throats and differ­ent thickness of t...

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SAGGING STAIRS

Posted by on 16/ 11/ 15

If the staircase has several of the ailments described in preceding sections, it may also have major troubles underneath. Investigate further. If the stairs tilt to one side, the carriage on the low side is having difficulty: That is, nails or screws holding it to the wall may be pulling out, the wood may be rotting or splitting, or the carriage may be pulling free from the stringer. Sagging on the open side of a stairway is common, for there’s no wall to bolt its carriage to. If there are large cracks or gaps at the top and bottom of the stairs, you’re seeing symptoms of a falling carriage.

To learn more, remove the finish surfaces from the underside of the staircase...

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Timbers from Your Own Land

Posted by on 16/ 11/ 15

Some owner-builders may harvest tall straight trees on their own property to make their own timbers for their frame. Hardwoods, in general, are stronger than softwoods, but its best to compare individual species, as there is considerable overlap in strength characteristics between a list of hardwoods and softwoods. Being generally harder, the hardwoods are more difficult to nail into. You may have to drill holes and use screws to make connections. Also, hardwoods tend to shrink quite a bit more than softwoods. Here are some common woods, beginning with so-called hardwoods — which are actually deciduous or broad – leafed trees.

Hardwoods

• Ash. Quite strong and usually straight, without a lot of knots. A favorite for baseball bats and hockey sticks. Can develop large checks...

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Mass Transport in Saturated Media

Posted by on 16/ 11/ 15

Transport in saturated soil takes place in that part of soil where pores are completely saturated by water. In the road construction, this usually occurs in the subgrade but rarely in the sub-base. Three principal transport processes are defined:

• Diffusion – pollutants move from compartments with higher concentrations to compartments with lower concentrations, even if the fluid is not moving;

• Advection – pollutants are carried with the flow of the water;

• Dispersion – the pollutants are locally redistributed due to local variations in fluid flow in the pores of the soil or pavement material.

Diffusion

Diffusion will occur as long as a concentration gradient exists...

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Beam and Girder Spacing for Steel Beam and Plate Girder Bridge

Posted by on 16/ 11/ 15

In regard to efficiency in the number of lines of girders in bridges consisting of multiple girders connected by cross frames, cursory cost comparisons almost always conclude that the widest spacing of girders is the most economical. Savings result not only from the reduced number of main members but also from the reduced number of secondary elements (shear connectors, cross frames, stiffeners, and bearings). However, other costs must be considered. Wide girder spacing will generally be accompanied by a wide slab overhang over the outside girders, for a balance of load on interior and exterior girders. This may necessitate extra reinforcing steel in the top of the deck slab beyond the amount required for the slab span between girders, and may require a thicker slab...

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CUTTING, MARKING, AND DRILLING SILL PLATES

Posted by on 16/ 11/ 15

Just as you must follow rules when play­ing sports, there are rules—or building codes—to follow when building a house. Most codes require that every sill plate have a bolt about 1 ft. from each end and every 4 ft to б ft. between to connect the house frame securely to the foundation. So the edges of the founda­tion and the location of the bolts let you know where cuts in the sill plates should be made.

These cuts can be made by eye if you’re feeling confident in your ability to make a square cut with a power saw.

Remember, sill plates must be placed on the foundation accurately, not perfectly. This is frame carpentry, not finish work.

Sill plates normally are bolted flush to the outside of the foundation...

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Composite Construction for Steel Beam and Plate Girder Bridge

Posted by on 16/ 11/ 15

The concrete deck for steel beam and girder bridges may be designed and constructed on the basis of either composite or noncomposite behavior. With composite construction, the effective area of the slab can be calculated and used in determining the moment resistance of the section in positive moment regions. In negative moment regions, ten­sile stresses can be resisted by the reinforcing steel. The required number of shear connectors must be calculated and furnished. These are generally headed studs that are welded to the top flange (Fig. 4.9). Overall economy depends upon the cost of the installed shear connectors and the reduction in steel weight that can be obtained. However, composite construction is frequently the economical choice.

4.16...

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Evaluating Recycled Timbers

Posted by on 16/ 11/ 15

Recycled timbers should be carefully evaluated before you buy them or agree to dismantle a building, so carry your wish list (more correctly called a timber schedule) with you to the procurement site. Firstly, timbers have to be of sufficient sectional size and length to do the job. Use actual usable length,
allowing for damaged ends or unusable ends due to mortise and tenon joints.

Подпись: Fig. 3.1: The author uses a knife to probe an old timber for soft or deteriorated wood. This one was a reject. Once you’ve established that you’ve got something potentially worthwhile, you need to look at each piece carefully for defects that might compromise their use on your project. With barn beams especially, all deterioration is not necessarily obvious: use a sharp knife to poke all four sides to check for soft wood. Reject any soft or “punky” pieces...

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Greek philosophers and thinkers of the classical era

Posted by on 16/ 11/ 15

The hydraulic works of Greece during the classical era do not measure up to those of the Mycenaen era. The few extracts cited above also show that in Greece, hydraulic know-how lags behind that of the Orient. And yet this classical Greece is known to us as the privileged cradle of development of philosophical and mathematical thought. Two facts are important in this regard. First, Greek science at this period took it as a point of honor to be disconnected from engineering, i. e. not to be associated with prac­tical applications. Second, and it is here that one can effectively and for perhaps the first time refer to science, the “sages” sought to apply reasoning to the explanation of great natural phenomena.

Such explanations of natural phenomena are often incomplete, and sometimes fal...

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Physical Processes

Posted by on 16/ 11/ 15

Many physical processes in the pavement, the embankment and the road environ­ment influence the flow of water away from the road surface. Pollution transport is heavily influenced by the physical and chemical characteristics of the specific pollutants. It is also strongly influenced by the interaction between pollutants, and with materials making up the pavement and embankment. During their transport, pollutants interact with materials in the solid, liquid and gaseous form.

The physical processes of the movement of pollutants in and by fluids in roads and their environment can be described in terms of pollutant mass transport. Mass transport can take place in solution, in suspension or in the form of particulate mat­ter...

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