SAINT - VENANT PRINCIPLE BASICS AND CIVIL ENGINEERING TUTORIALS

SAINT - VENANT PRINCIPLE BASIC INFORMATION
What Is The Saint - Venant Principle?


Saint-Venant’s principle states that in a body under the action of a system of forces which are applied in a limited region of its boundary, the stresses and strains induced by those forces in another region of the body, located at a large distance from the region where the forces are applied, do not depend on the particular way the forces are applied, but only on their resultant.

This “large distance” may be considered, in most cases, as the largest dimension of the region where the forces are applied.

This principle does not have a formal, general and exact demonstration as yet, but it has been verified in so many cases, both experimentally and numerically, that it is accepted as valid by the generality of authors on this subject.

It is a very useful principle, since complex force systems may be reduced to their resultants, which substantially simplifies and reduces the computation effort in practical problems. Besides, it is a very helpful tool in the theoretical development of solutions for problems in Theory of Elasticity and Strength of Materials.

As an example, let us consider the prismatic bar represented in Fig. 56 under the action of three systems of forces with equal resultants: the stresses at a grater distance than the transversal dimension 2b from the upper end of the bar may be accepted as equal in the three cases.

This principle is also valid in the cases of non-isotropic materials, nonlinear material behaviour, plastic and viscous deformations and material heterogeneity. Furthermore, the validity of this principle is not limited to small deformations.

ORGANISMS THAT DEGRADE WOOD USED IN CIVIL ENGINEERING CONSTRUCTION BASIC ENGINEERING TUTORIALS

ORGANISMS THAT DEGRADE WOOD USED IN CIVIL ENGINEERING CONSTRUCTION
What Are The Organism That Degrade Wood Used In Civil Engineering Construction?


Wood can experience degradation due to attack of fungi, bacteria, insects, or marine organisms.

Fungi
Most forms of decay and sap stains are the result of fungal growth. Fungi need four essential conditions to exist: food, proper range of temperature, moisture, and oxygen.

Fungi feed on either the cell structure or the cell contents of woody plants, depending on the fungus type. The temperature range conducive for fungal growth is from 5°C to 40°C (40°F to 100°F). Moisture content above the fiber saturation point is required for fungal growth. Fungi are plants and, as such, require oxygen for respiration.

Fungi attack produces stains and/or decay damage. To protect against fungal attack, one of the four essential conditions for growth needs be removed. The most effective protection measure is to keep the wood dry by correct placement during storage and in the structure.

Fungi growth can also be prevented by treating the wood fibers with chemical poisons through a pressure treatment process.Construction procedures that limit decay in buildings include the following:

1. Building with dry lumber that is free of incipient decay and excessive amounts of stains and molds
2. Using designs that keep the wood components dry
3. Using a heartwood from decay-resistant species or pressure-treated wood in sections exposed to above-ground decay hazards
4. Using pressure-treated wood for components in contact with the ground.

Insects
Beetles and termites are the most common wood-attacking insects. Several types of beetles, such as bark beetles, attack and destroy wood. Storage of the logs in water or a water spray prevents the parent beetle from boring.

Quick drying or early removal of the bark also prevents beetle attack. Damage can be prevented by proper cutting practices and dipping or spraying with an appropriate chemical solution.

Termites are one of the most destructive insect that attacks wood. The annual damage attributed to termites exceeds losses due to fires. Termites enter structures through wood that is close to the ground and is poorly ventilated or wet.

Prevention is partially achieved by using pressure-treated wood and otherwise prohibiting insect entry into areas of unprotected wood through the use of screening, sill plates, and sealing compounds.

Marine Organisms
Damage by marine boring organisms in the United States and surrounding oceans is principally caused by shipworms, pholads, Limnoria, and Sphaeroma. These organisms are almost totally confined to salt or brackish waters.

Bacteria
Bacteria cause “wet wood” and “black heartwood” in living trees and a general degradation of lumber. Wet wood is a water-soaked condition that occupies the stem centers of living trees and is most common in poplar, willows, and elms.

Black heartwood has characteristics similar to those of wet wood, in addition to causing the center of the stem to turn dark brown or black. Bacterial growth is sometimes fostered by prolonged storage in contact with soils.

This type of bacteria activity produces a softening of the outer wood layers, which results in excessive shrinkage when redried. Bacterial attack does not pose a significant problem to common structural wood species.