In IBC 2000, the following basic information is required to determine the seismic loads:

1. Seismic Use Group According to the nature of Building Occupancy, each structure is assigned a Seismic Use Group (I, II, or III) and a corresponding Occupancy Importance (I) factor (I = 1.0, 1.25, or 1.5).

Seismic Use Group I structures are those not assigned to either Seismic Use Group II or III. Seismic Use Group II are structures whose failure would result in a substantial public hazard due to occupancy or use.

Seismic Use Group III is assigned to structures for which failure would result in loss of essential facilities required for post-earthquake recovery and those containing substantial quantities of hazardous substances.

2. Site Class Based on the soil properties, the site of building is classified as A, B, C, D, E, or F to reflect the soil-structure interaction. Refer to IBC 2000 for Site Class definition.

3. Spectral Response Accelerations SS and S1 The spectral response seismic design maps reflect seismic hazards on the basis of contours. They provide the maximum considered earthquake spectral response acceleration at short period SS and at 1-second period S1. They are for Site Class B, with 5% of critical damping. Refer to the maps in IBC 2000.

4. Basic Seismic-Force-Resisting System Different types of structural system have different energy-absorbing characteristic. A response modification coefficient R is used to account for these characteristics.

Systems with higher ductility have higher R values. With the above basic parameters available, the following design and analysis criteria can be determined.


In the criterion presented by Murray, an acceptable steel floor system is predicted, with respect to vibration levels due to walking excitation, if the dynamic criterion below is met.

This criterion is applicable to offices and residences with fundamental natural frequencies below 10 Hz.

Murray criterion:
D > 35Aoƒ + 2.5

where D = damping in floor system, expressed as a percent of critical

Ao = maximum initial amplitude of the floor system due to a heel-drop excitation, in

ƒ = first natural frequency of the floor system, Hz

This criterion is only applicable for the units specified. The reader is cautioned against using other units.


External loads on a structure may be classified in several different ways. In one classification, they may be considered as static or dynamic.

Static loads are forces that are applied slowly and then remain nearly constant. One example is the weight, or dead load, of a floor or roof system.

Dynamic loads vary with time. They include repeated and impact loads.

Repeated loads are forces that are applied a number of times, causing a variation in the magnitude, and sometimes also in the sense, of the internal forces. A good example is an off-balance motor.

Impact loads are forces that require a structure or its components to absorb energy in a short interval of time. An example is the dropping of a heavy weight on a floor slab, or the shock wave from an explosion striking the walls and roof of a building.

External forces may also be classified as distributed and concentrated.

Uniformly distributed loads are forces that are, or for practical purposes may be considered, constant over a surface area of the supporting member. Dead weight of a rolled-steel I beam is a good example.

Concentrated loads are forces that have such a small contact area as to be negligible compared with the entire surface area of the supporting member. A beam supported on a girder, for example, may be considered, for all practical purposes, a concentrated load on the girder.

Another common classification for external forces labels them axial, eccentric, and torsional.

An axial load is a force whose resultant passes through the centroid of a section under consideration and is perpendicular to the plane of the section.

An eccentric load is a force perpendicular to the plane of the section under consideration but not passing through the centroid of the section, thus bending the supporting member.

Torsional loads are forces that are offset from the shear center of the section under consideration and are inclined to or in the plane of the section, thus twisting the supporting member.

Also, building codes classify loads in accordance with the nature of the source. For example:

Dead loads include materials, equipment, constructions, or other elements of weight supported in, on, or by a building, including its own weight, that are intended to remain permanently in place.

Live loads include all occupants, materials, equipment, constructions, or other elements of weight supported in, on, or by a building and that will or are likely to be moved or relocated during the expected life of the building.

Impact loads are a fraction of the live loads used to account for additional stresses and deflections resulting from movement of the live loads.

Wind loads are maximum forces that may be applied to a building by wind in a mean recurrence interval, or a set of forces that will produce equivalent stresses.

Snow loads are maximum forces that may be applied by snow accumulation in a mean recurrence interval.

Seismic loads are forces that produce maximum stresses or deformations in a building during an earthquake.


The notion that human beings can design incredible processes such as ecosystems has been described as the height of hubris by some; ecosystems are too complex, the argument goes, and our knowledge too incomplete. In reality, we design ecosystems every time we start a bulldozer or tractor, every time we change land use or reroute stream flow.

We just do not design explicitly, and the consequences are apparent. Designing ecosystem services should be approached with a deep sense of humility and respect for what we do not know.

In order to ensure that this philosophy is embodied in the practice of ecological design, we propose the following three axioms of ecological engineering:

1. Everything is connected
2. Everything is changing
3. We are all in this together

The first two axioms are fundamental principles of systems ecology described by H. T. Odum (1988) and are the foundation of ecological design. They are critical for understanding and conceptualizing solutions to the challenges of developing sustainable design strategies.

The interconnectedness of all biotic and abiotic processes throughout the biosphere is demonstrated by the effects of urban land use on almost every aspect of ecosystem function, from climate to hydrology to biodiversity. Everything is changing, and the rate of change is increasing.

Changes in the biosphere are being driven by changes in global climate, land use, and human population, among other factors.

The third axiom, embodied by the Cherokee cultural ideal gadugi, roughly translated as “we are all in this together,” is a normative claim that connects ecosystem theory with sustainability. This is the essence of the ecological engineering ethics.


Fundamental Precepts

Experience has taught us the following fundamental precepts in process selection (MWH, 2005):

1. The raw water quality of every source is different.

2. Raw water quality is variable.

3. There is no standard water treatment plant design that is applicable to all sources.

4. For every source, a number of treatment process alternatives are available.

5. Site conditions often limit the types of treatment process that can be used.

6. Retrofitting and upgrading of existing plants requires creative solutions that are not presented in standard textbooks such as this one.

7. Pilot plant testing is highly recommended in the selection of retrofit and upgrade alternatives.

8. Pilot plant testing requires careful planning and execution to obtain useful design and operating criteria.

9. It is essential that the multibarrier concept be a feature of all designs.

10. Operator experience is invaluable in developing a design.


What Are The Characteristics Of Concrete?

Characteristics of Concrete
1) Convenient for use: the new mixtures have good plasticity that can be cast into components and structures in various shapes and sizes.

2) Cheap: raw materials are abundant and available. More than 80% of them are sand and stone whose resources are rich, energy consumption is low, according with the economic principle.

3) High-strength and durable: the strength of ordinary concrete is 20 - 55MPa with good durability.

4) Easy to be adjusted: the concrete with different functions can be made just by changing the varieties and quantities of composing materials to meet various demands of projects; steel bar can be added to concrete to improve its strength, and this kind of concrete is a composite material (reinforced concrete) which can improve its low tensile and bending strength in order to meet the needs of various structural engineering.

5 ) Environment-friendly: concrete can make full use of industrial wastes, such as slag, fly ash and others to reduce environmental pollution. Its major shortcomings are high dead weight, low tensile strength, brittle and easy to crack.


How To Prevent Corrosion Of Cement Paste?

The corrosion of cement paste occurs because chemical reaction can happen between its external environment and internal environment. The corrosive compound must be the solution with a certain concentration, such as high temperature, proper humidity, fast flow, and the corrosion of steel bar.

Thus, the following measures can be adopted in the use of cement:

1) Select the cement varieties reasonably based on the features of the erosive environment. For example, the cement whose hydrates contains a little calcium hydroxide has high capacity to resist erosive effects of soft water and others; the anti-sulfate cement whose content of tri-calcium aluminate is less than 5% can resist the sulfate erosion.

2) Raise the Density of Cement Paste. The amount of mixing water for Portland cement should be strictly controlled in order to reduce the pore space.

The water theoretically needed in hydration of Portland cement is only 23% but much more mixing water (accounting for about 40%-70% of the cement mass) is needed in practical projects, and the pores connect to each other after the excessive water evaporates, so the erosive media go through the inner part of cement easily to accelerate the corrosion of cement.

The mix proportion should be designed reasonably in order to improve the compactness of cement concrete. Low water-cement ratio and the best construction method should be adopted as much as possible.

In addition, the insoluble calcium carbonate shell or calcium fluoride and thin silica gel film generated by conducting carbonization or fluosilicic acid treatment on the surface of concrete and mortar can increase the compactness of the surface and decrease the infiltration of erosive media.

3) Add a Protective Layer. The resistant stone, ceramic, plastic, and waterproof material are covered on the surface of cement paste, forming a impermeable layer for protection, to prevent the corrosion media contacting with cement paste directly.


Who Is Siméon Denis Poisson?

Siméon Denis Poisson is mathematician famous and responsible for an important mathematical expression known as Poisson's Ratio.

He was born on 21-Jun-1781 at Pithiviers, France.

Siméon Poisson was a protégé of Laplace. Poisson was an extremely prolific researcher and also an excellent teacher. In addition to important advances in several areas of physics, Poisson made important contributions to Fourier analysis, definite integrals, path integrals, statistics, partial differential equations, calculus of variations and other fields of mathematics.

The Poisson Distribution is a discrete distribution is also named after Poisson. He published its essentials in a paper in 1837. The Poisson distribution and the binomial distribution have some similarities, but also several differences.

Among the books he authored:

Traité de Mécanique (1811, science)
Théorie Nouvelle de l'Action Capillaire (1831, science)
Théorie Mathématique de la Chaleur (1835, science)
Recherches sur la Probabilité des Jugements en Matière Criminelle et en Matière Civile (1837)


What Is Poisson's Ratio? Sample Problem And Solution Using Poisson's Ratio

When a homogeneous slender bar is axially loaded, the resulting stress and strain satisfy Hooke’s law, as long as the elastic limit of the material is not exceeded.

In all engineering materials, the elongation produced by an axial tensile force P in the direction of the force is accompanied by a contraction in any transverse direction (Fig. 2.36).† In this section and the following sections (Secs. 2.12 through 2.15), all materials considered will be assumed to be both homogeneous and isotropic, i.e., their mechanical properties will be assumed independent of both position and direction.

It follows that the strain must have the same value for any transverse direction.\ Therefore, for the loading shown in Fig. 2.35 we must have Py 5 Pz. This common value is referred to as the lateral strain.

An important constant for a given material is its Poisson’s ratio, named after the French mathematician Siméon Denis Poisson (1781–1840) and denoted by the Greek letter n (nu). It is defined as

v = - lateral strain / lateral stress.

Sample Problem:

A 500-mm-long, 16-mm-diameter rod made of a homogenous, isotropic material is observed to increase in length by 300 mm, and to decrease in diameter by 2.4 mm when subjected to an axial 12-kN load. Determine the modulus of elasticity and Poisson’s ratio of the material.


Click on the image to enlarge and see the solution.


What Are Fly Ashes?

Fly ash meeting the requirements of ASTM C618, ‘‘Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete,’’ is generally used as a cementitious material as well as an admixture.

Natural pozzolans are derived from some diatomaceous earths, opaline cherts and shales, and other materials. While part of a common ASTM designation with fly ash, they are not as readily available as fly ashes and thus do not generate the same level of interest or research.

Fly ashes are produced by coal combustion, generally in an electrical generating station. The ash that would normally be released through the chimney is captured by various means, such as electrostatic precipitators. The fly ash may be sized prior to shipment to concrete suppliers.

All fly ashes possess pozzolanic properties, the ability to react with calcium hydroxide at ordinary temperatures to form compounds with cementitious properties. When cement is mixed with water, a chemical reaction (hydration) occurs.

The product of this reaction is calcium silicate hydrate (CSH) and calcium hydroxide [Ca(OH)2]. Fly ashes have high percentages of silicon dioxide (SiO2). In the presence of moisture, the Ca(OH)2 will react with the SiO2 to form another CSH.

Type F ashes are the result of burning anthracite or bituminous coals and possess pozzolanic properties. They have been shown by research and practice to provide usually increased sulfate resistance and to reduce alkali-aggregate expansions.

Type C fly ashes result from burning lignite or subbituminous coals. Because of the chemical properties of the coal, the Type C fly ashes have some cementitious properties in addition to their pozzolanic properties. Type C fly ashes may reduce the durability of concretes into which they are incorporated.


What Are Porcelain Enamel On Metals?

Low-temperature softening glasses must be employed, especially with sheet metal, to avoid the warping and distortion that would occur at high temperatures. To obtain lower softening temperatures than would be attainable with high-silica glasses, boron is commonly added.

Fluorine may replace some of the oxygen, and lead may also be added to produce easy-flowing brilliant enamels; but lead presents an occupational health hazard.

Composition of the enamel is carefully controlled to provide a coefficient of thermal expansion as near that of the base metal as possible. If the coefficient of the enamel is greater than that of the metal, cracking and crazing are likely to occur, but if the coefficient of the enamel is slightly less, it is lightly compressed upon cooling, a desirable condition because glass is strong in compression.

To obtain good adhesion between enamel and metal, one of the so-called transition elements used in glass formulation must be employed. Cobalt is favored.

Apparently, the transition elements promote growth of iron crystals from base metal into the enamel, encourage formation of an adherent oxide coating on the iron, which fuses to the enamel, or develop polar chemical bonds between metal and glass.

Usually, white or colored opaque enamels are desired. Opacity is promoted by mixing in, but not dissolving, finely divided materials possessing refractive indexes widely different from the glass. Tin oxide, formerly widely used, has been largely displaced by less expensive and more effective titanium and zirconium compounds.

Clay adds to opacity. Various oxides are included to impart color. Most enameling consists of a ground coat and one or two cover coats fired on at slightly lower temperatures; but one-coat enameling of somewhat inferior quality can be accomplished by first treating the iron surface with soluble nickel salts.

The usual high-soda glasses used to obtain low-temperature softening enamels are not highly acid-resistant and therefore stain readily and deeply when ironcontaining water drips on them.

Enamels highly resistant to severe staining conditions must be considerably harder; i.e., have higher softening temperatures and therefore require special techniques to avoid warping and distorting of the metal base.

Interiors of refrigerators are often made of porcelain-enameled steel sheets for resistance to staining by spilled foods, whereas the exteriors are commonly bakedon synthetic-resin finishes.


What Is The Purpose Of Zoning Codes In Construction?

Like building codes, zoning codes are established under the police powers of the state, to protect the health, welfare, and safety of the public. Zoning, however, primarily regulates land use by controlling types of occupancy of buildings, building height, and density and activity of population in specific parts of a jurisdiction.

Zoning codes are usually developed by a planning commission and administered by the commission or a building department. Land-use controls adopted by the local planning commission for current application are indicated on a zoning map.

It divides the jurisdiction into districts, shows the type of occupancy, such as commercial, industrial, or residential, permitted in each district, and notes limitations on building height and bulk and on population density in each district.

The planning commission usually also prepares a master plan as a guide to the growth of the jurisdiction. A future land-use plan is an important part of the master plan.

The commission’s objective is to steer changes in the zoning map in the direction of the future land-use plan. The commission, however, is not required to adhere rigidly to the plans for the future. As conditions warrant, the commission may grant variances from any of the regulations.

In addition, the planning commission may establish land subdivision regulations, to control development of large parcels of land. While the local zoning map specifies minimum lot area for a building and minimum frontage a lot may have along a street, subdivision regulations, in contrast, specify the level of improvements to be installed in new land-development projects.

These regulations contain criteria for location, grade, width, and type of pavement of streets, length of blocks, open spaces to be provided, and right of way for utilities.

A jurisdiction may also be divided into fire zones in accordance with population density and probable degree of danger from fire. The fire-zone map indicates the\ limitations on types of construction that the zoning map would otherwise permit.

In the vicinity of airports, zoning may be applied to maintain obstruction-free approach zones for aircraft and to provide noise-attenuating distances around the airports. Airport zoning limits building heights in accordance with distance from the airport.


What Are Synthetic Fibers?

The fi rst synthetic fi bre was a polyamide, generally known as nylon, which started to be marketed in 1938 and found applications in wartime technical uses. Its tenacity was in the region of 0.5 N/tex and the modulus 2.5 N/tex.

Another synthetic fibre that followed was the polyester fi bre (polyethylene terephthalate), which had a similar tenacity but a higher modulus of around 10 N/tex. Varieties of these fibres developed for industrial \ applications, such as ropes and tyre cords, exhibit tenacities over 0.8 N/tex for both nylon and polyester and moduli of 9 N/ tex for nylon and 12 N/tex for polyester.

Another fi bre of increasing interest in technical applications is polypropylene. Its tenacity is in the region of 0.65 N/tex with a modulus of 7.1 N/tex and a specifi c gravity of 0.91.

Nylons, but especially polypropylene and polyester, are widely used in geosynthetics, and polyester is very much used for tensile surface structures, particularly in Europe. Other applications of polypropylene include anti-crack building products for wall surfaces.

High-performance fi bres were developed in the latter part of the twentieth century and inhibit a step change in strength and stiffness, compared to previous ones.

Advances in the 1960s led DuPont scientists in the USA to spin para-aramid fi bres from liquid-crystal solutions. These highly oriented fi bres achieved tenacities in excess of 2 N/tex and moduli reaching 80 N/tex. More-recent developments enabled some polymer fi bres to attain tenacities above 3.5 N/tex and moduli exceeding 150 N/tex.

Other interesting characteristics of para-aramids include fl ame resistance (selfextinguishing), low electrical conductivity, high chemical resistance, excellent dimensional stability, low thermal shrinkage, high toughness (work of rupture) and high cut resistance. Apart from their use in the reinforcement of composite materials, para-aramids are also of interest for ropes and cables and as a replacement for asbestos materials.

The first high-strength carbon fi bres were developed at the Royal Aircraft Establishment in the UK, and were produced by high-temperature processing of acrylic fi bres under tension. This resulted in tenacities of up to 3 N/tex and moduli of over 400 N/tex.

Carbon fibre is engineered for strength and stiffness, but variations differ in electrical conductivity, thermal, and chemical properties. The primary factors governing the physical properties are the degree of carbonization, the orientation of the layered carbon planes, and the degree of crystallization.

They have lower thermal expansion coeffi cients than both the glass and aramid fi bres, and the material has a very high fatigue and creep resistance. Much research is also now being done using carbon fi bre-reinforced plastic (CFRP) as internal reinforcement in concrete structures, such as beams and bridge decks.

The material has many advantages over conventional steel, especially in that it is much stiffer and corrosion resistant. CFRP has become of prominent importance in structural engineering, due to its cost-effectiveness in the repair of old bridges, many of which were designed to tolerate far lower service loads than they are subject to today.

Reinforcing with CFRP is a much cheaper alternative when compared with the cost of replacing the bridge. Due to the very high stiffness of CFRP, it can be used underneath spans to help prevent excessive deflections, or wrapped around beams to limit shear stresses.

Glass fi bres are used widely as reinforcements in order to increase the stiffness of composite materials. The tenacity of glass fibres may reach 1.6 N/tex and their moduli 35 N/tex, which are lower than those of aramids (on a weight basis).

The development of ceramic fi bres is primarily related to their high-temperature performance in metal and ceramic matrix composites to use in engines. However, because of their structure they exhibit high moduli, which may reach 100 N/tex, with tenacities of up to 1 N/tex, which may not be considered particularly high (on a weight basis).

Glass fi bres are divided into three classes, i.e. E-glass, S-glass and C-glass. The E-glass is designated for electrical use, and the S-glass for high strength. The C-glass is for high corrosion resistance, and it is not of common use in civil engineering applications. Of the three fibres, the E-glass is the most common reinforcement material used in civil engineering structures.

Glass fibres are also used for fi re-protective walls, fl oors and ceiling panels, as well as fi reproof curtains and partitions for indoors and outdoors. They are used for heat insulation in heating systems, power generation and incinerators.

Basalt fibres have similar applications to carbon and glass fi bres in the reinforcement of composite materials, having better physical-mechanical properties than glass and being much cheaper than carbon fibre. Basalt fibre products include: chemically resistant chopped strands for concrete reinforcement; high-strength rovings for pultruded load-bearing parts and concrete reinforcing bars; basalt woven fabrics for heat, sound insulation, and fire protection; geogrids for road and land reinforcement; and stucco nets for wall reinforcing and renovation.


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.


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.

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.

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 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.


What Are The Different Heat Treatment Of Steel?

Heat Treatment of Steel
Properties of steel can be altered by applying a variety of heat treatments. For example, steel can be hardened or softened by using heat treatment; the response of steel to heat treatment depends upon its alloy composition.

Common heat treatments employed for steel include annealing, normalizing, hardening, and tempering. The basic process is to heat the steel to a specific temperature, hold the temperature for a specified period of\ time, then cool the material at a specified rate.

The objectives of annealing are to refine the grain, soften the steel, remove internal stresses, remove gases, increase ductility and toughness, and change electrical and magnetic properties. Four types of annealing can be performed, depending on the desired results of the heat treatment:

Full annealing requires heating the steel to about 50°C above the austenitic temperature line and holding the temperature until all the steel transforms into either austenite or austenite–cementite, depending on the carbon content.

The steel is then cooled at a rate of about 20°C per hour in a furnace to a temperature of about 680°C, followed by natural convection cooling to room temperature. Due to the slow cooling rate, the grain structure is a coarse pearlite with ferrite or cementite, depending on the carbon content.

The slow cooling rate ensures uniform properties of the treated steel. The steel is soft and ductile. Process annealing is used to treat work-hardened parts made with low carbon steel (i.e., less than 0.25 percent carbon). The material is heated to about 700°C and held long enough to allow recrystallization of the ferrite phase.

By keeping the temperature below 727°C, there is not a phase shift between ferrite and austenite, as occurs during full annealing. Hence, the only change that occurs is refinement of the size, shape, and distribution of the grain structure.

Stress relief annealing is used to reduce residual stresses in cast, welded, and cold-worked parts and cold formed parts. The material is heated to 600 to 650°C, held at temperature for about one hour, and then slowly cooled in still air.

Spheroidization is an annealing process used to improve the ability of high carbon (i.e., more than 0.6 percent carbon) steel to be machined or cold worked. It also improves abrasion resistance. The cementite is formed into globules (spheroids) dispersed throughout the ferrite matrix.

3.3.2 Normalizing
Normalizing is similar to annealing, with a slight difference in the temperature and
the rate of cooling. Steel is normalized by heating to about 60°C (110°F) above the
austenite line and then cooling under natural convection. The material is then
air cooled. Normalizing produces a uniform, fine-grained microstructure. However,
since the rate of cooling is faster than that used for full annealing, shapes with varying thicknesses results in the normalized parts having less uniformity than could
be achieved with annealing. Since structural plate has a uniform thickness, normalizing
is an effective process and results in high fracture toughness of the material.

Steel is hardened by heating it to a temperature above the transformation range and holding it until austenite is formed. The steel is then quenched (cooled rapidly) by plunging it into, or spraying it with, water, brine, or oil. The rapid cooling “locks” the iron into a BCC structure, martensite, rather than allowing the transformation to the ferrite FCC structure.

Martensite has a very hard and brittle structure. Since the cooling occurs more rapidly at the surface of the material being hardened, the surface of the material is harder and more brittle than the interior of the element, creating nonhomogeneous characteristics.

Due to the rapid cooling, hardening puts the steel in a state of strain. This strain sometimes causes steel pieces with sharp angles or grooves to crack immediately after hardening. Thus, hardening must be followed by tempering.

The predominance of martensite in quench-hardened steel results in an undesirable brittleness. Tempering is performed to improve ductility and toughness. Martensite is a somewhat unstable structure.

Heating causes carbon atoms to diffuse from martensite to produce a carbide precipitate and formation of ferrite and cementite. After quenching, the steel is cooled to about 40°C then reheated by immersion in either oil or nitrate salts. The steel is maintained at the elevated temperature for about two hours and then cooled in still air.

Example of Heat Treatment
In the quest to produce high-strength low-alloy steels economically, the industry has developed specifications for several new steel products, such as A913. This steel is available with yield stresses ranging from 50,000 to 75,000 psi.

The superior properties of A913 steel are obtained by a quench self-tempering process. Following the last hot rolling pass for shaping, for which the temperature is typically 850°C (1600°F), an intense water-cooling spray is applied to the surface of the beam to quench (rapidly cool) the skin.

Cooling is interrupted before the core on the material is affected. The outer layers are then tempered as the internal heat of the beam flows to the surface. After the short cooling phase, the self-tempering temperature is 600°C (1100°F).


What Are The Types Of Civil Engineering Project Construction Companies?

The principles of construction project management, as outlined in this article, apply equally to those engaged in subcontracting and those engaged in general contracting.

Small Renovation Contractors. These companies generally work on jobs requiring small amounts of capital and the type of work that does not require much estimating or a large construction organization. They usually perform home alterations or small commercial and office work.

Many small renovation contractors have their offices in their homes and perform the ‘‘paper work’’ at night or on weekends after working with the tools of their trade during the day. The ability to grow from this type of contractor to a general contractor depends mainly on the training and business ability of the individual.

Generally, if one is intelligent enough to be a good small renovation contractor, that person may be expected to eventually move into the field of larger work.

General Contractors. These companies often are experts in either new buildings or alteration work. Many building contractors subcontract a major portion of their work, while alteration contractors generally perform many of the trades with their own forces.

Some general contractors specialize in public works. Others deal mainly with private and commercial work. Although a crossing of the lines by many general contractors is common, it is often in one or another of these fields that many general contractors find their niche.

Owner-Builder. The company that acts as an owner-builder is not a contractor in the strict sense of the word. Such a company builds buildings only for its own ownership, either to sell on completion, or to rent and operate. Examples of this type of company include giants in the industry, and many of them are listed on the various stock exchanges.

Many owner-builders, on occasion, act in the capacity of general contractor or as construction manager (see below) as a sideline to their main business of building for their own account.

Real Estate Developer. This is a type of owner-builder who, in addition to building for personal ownership, may also build to sell before or after completion of the project. One- and two-family home builders are included in this category.

Professional Construction Manager. A professional construction manager may be defined as a company, an individual, or a group of individuals who perform the functions required in building a project as the agent of an owner, but do so as if the job was being performed with the owner’s own employees.

The construction management organization usually supplies all the personnel required. Such personnel include construction superintendents, expediters, project managers, and accounting personnel.

The manager sublets the various portions of the construction work in the name of the owner and does all the necessary office administration, field supervision, requisitioning, paying of subcontractors, payroll reports, and other work on the owner’s behalf, for a fee.

Generally, construction management is performed without any risk of capital to the construction manager. All the financial obligations are contracted in the name of the owner by the construction manager.

Program Manager. A general contractor or construction manager may expand services by undertaking program management.

Such services will include: demolition of existing buildings on the site; devising and providing financial analyses of new buildings or a program to replace what was there, or for the acquisition of a new site; hiring an architect and other design professionals on behalf of the owner and supervising their services; performing preconstruction services during the planning stage; advertising for and receiving bids from contractors for the new work; consulting on financing and methods of payment for the work; supervising the contractor; obtaining tenants, whether commercial, residential, or industrial for the completed project; helping to administer and manage the complete project.

Obviously, the comprehensive services outlined above will require that the general contractor or construction manager augment his staff with trained architects, accountants, real estate professionals, and management and leasing experts.

Package (Turnkey) Builders. Such companies take on a contract for both design and construction of a building. Often these services, in addition, include acquisition of land and financing of the project. Firms that engage in package building usually are able to show prospective clients prototypes of similar buildings completed by them for previous owners.

From an inspection of the prototype and discussion of possible variations or features to be included, an approximate idea is gained by the prospective owner of the cost and function of the proposed building.

Package builders often employ their own staff of architects and engineers, as well as construction personnel. Some package builders subcontract the design portion to independent architects or engineers.

It is important to note that, when a package builder undertakes design as part of the order for a design-construction contract, the builder must possess the necessary professional license for engineering or architecture, which is required in most states for those performing that function.

Sponsor-Builder. In the field of government-aided or subsidized building, particularly in the field of housing, a sponsor-builder may be given the responsibility for planning design, construction, rental, management, and maintenance. A sponsor guides a project through the government processing and design stages.

The sponsor employs attorneys to deal with the various government agencies, financial institutions, and real estate consultants, to provide the know-how in land acquisition and appraisal. On signing the contract for construction of the building, the sponsor assumes the builder’s role, and in this sense functions very much as an owner builder would in building for its own account.


What Is The Composition Of Civil Engineering Project Cost?

The total price of a construction project is the sum of direct costs, contingency costs, and margin. Direct costs are the labor, material, and equipment costs of project construction.

For example, the direct cost of a foundation of a building includes the following:

Costs of formwork, reinforcing steel, and concrete
Cost of labor to build and later strip the formwork, and place and finish the concrete
Cost of equipment associated with foundation activities, such as a concrete mixer

Contingency costs are those that should be added to the costs initially calculated to take into account events, such as rain or snow, that are likely to occur during the course of the project and affect overall project cost.

Although the effects and probability of occurrence of each contingency event cannot be accurately predicted, the total effect of all contingencies on project cost can be estimated with acceptable accuracy.

Margin (sometimes called markup) has three components: indirect, or distributable, costs; company-wide, or general and administrative, costs; and profit.

Indirect costs are project-specific costs that are not associated with a specific physical item. They include such items as the cost of project management, payroll preparation, receiving, accounts payable, waste disposal, and building permits.

Company-wide costs include the following:

(1) Costs that are incurred during the course of a project but are not project related; for example, costs of some portions of company salaries and rentals.

(2) Costs that are incurred before or after a project; for example, cost of proposal preparation and cost of outside auditing.

Profit is the amount of money that remains from the funds collected from the client after all costs have been paid.


Document A United Kingdom Building Regulations

Use of Guidance
a. Eurocodes: an announcement is given  regarding the forthcoming introduction  of the Structural Eurocodes and their   National Annexes.

b. House construction: reference is made to the intended publication of guidance  by industry of alternative forms of house  construction to that of traditional masonry. A1 and A2 Traditional dwellings

c. The guidance on the sizing of timber floors  and roofs for traditional house construction  has been removed as the Timber Tables  are now published by TRADA. However,  the TRADA Tables are referenced under Section 2B.

d. A revised map of basic wind speeds in  accordance with BS6399:Part 2 replaces  the superseded map which was based on  BS CP3 Chapter V.

e. Stainless steel cavity wall ties have  been specified to all houses regardless  of their location.

f. The guidance on masonry walls to dwellings  has been extended to enable the rules to be  applicable when using either the appropriate  British Standards or the emerging BS EN CEN  Standards.

g. The guidance on concrete foundations to  houses has been revised to align with the  recommendations given in the British  Standards and other authoritative guidance.  Recommendations on minimum foundation depths have also been included to counter   the impact of predicted climate changes.

h. The guidance on the design and construction  of domestic garages has been extensively  updated to reflect modern practice.

The following documents have been approved  and issued by the First Secretary of State for the   purpose of providing practical guidance with  respect to the requirements of the Building  Regulations 2010.

Approved Document A: Structure  2004 edition incorporating 2010 amendments

Approved Document B (Fire safety) – Volume   1: Dwellinghouses 2006 edition incorporating 2010 amendments

Approved Document B (Fire safety) – Volume  2: Buildings other than dwellinghouses  2006 edition incorporating 2007 and 2010  amendments

Approved Document C: Site preparation and  resistance to contaminants and moisture  2004 edition incorporating 2010 amendments

Approved Document D: Toxic substances  1992 edition incorporating 2002 and 2010 amendments

Approved Document E: Resistance to the  passage of sound  2003 edition incorporating 2004 and 2010 amendments



National Building Code Of The Philippines

SECTION 1.01.01: Title
(a) This Act shall be known as the "National Building Code of the Philippines" and shall hereinafter be referred to as the "Code". 
SECTION 1.01.02: Declaration of Policy 
(a) It is hereby declared to be the policy of the State to safeguard life, health, property, and public welfare, consistent with the principles of environmental management and control; and to this end, make it the purpose of this Code to provide for all buildings and structured, a framework of minimum standards and requirements by guiding, regulating, and controlling their location, siting, design, quality of materials, construction, use, occupancy, and maintenance, including their environment, utilities, fixtures, equipment, and mechanical electrical, and other systems and installations. 
SECTION 1.01.03: Scope 
(a) The provisions of this Code shall apply to the design, location, siting, construction, alteration, repair, conversion, use, occupancy, maintenance, moving, and demolition of, and addition to, public and private buildings and structures. 
(b) Additions, alterations, repairs, and changes of use or occupancy in all buildings and structures shall comply with requirements for new buildings and structures except as otherwise herein provided. Only such portion or portions of the existing building or structure which have to be altered to effect the addition, alteration, or repair shall be made to conform to the requirements for new buildings or structures. Alterations should preserve the aesthetic value of the building to be altered. 
(c) Where, in any specific case, different section of this Code specify different materials, methods of construction, or other requirements, the most restrictive shall govern. 
SECTION 1.01.04: Application 
(a) This Code shall apply to all buildings and structures constructed and any change or repair made thereon after the approval of said Code. Buildings or structures constructed before the approval of this Code shall not be affected thereby; Except, where their continued use or occupancy is dangerous to life or limb; or where alterations, additions, conversions, or repairs are to be made thereon, this Code shall apply only to such portions of the buildings or structure which have to be altered in order to effect such damages or repairs. 
(b) This Code shall apply to chartered cities, poblaciones of municipalities and municipal districts with a population of at least two thousand (2,000) inhabitants, and to barrios of urban areas with a population of at least two thousand (2,000) inhabitants. This Code shall also apply to any area where there are fifty (50) or more families per hectare. 
(c) This Code shall likewise apply to any area proposed for or being developed into a new town site, residential subdivision, commercial or residential site, school site, housing project, and similar construction projects where five or more buildings not covered by paragraph (d) of this Section will be constructed even if the poblacion or barrio population is less than two thousand (2,000) or the density of population is less than fifty (50) families per hectare. 
(d) The design and construction requirements of this Code shall not apply to any traditional indigenous family dwelling costing not more than five thousand pesos (P5,000.00) and intended for use and occupancy of the family of the owner only. The traditional type of family dwellings are those that are constructed of native materials such as bamboo, nipa, logs, or lumber, wherein the distance between vertical supports or suportales does not exceed 3.00 meters (10 feet); and if masonry walls or socalos are used, such shall not be more than 1.00 meter (3 feet, 3 inches) from the ground: Provided, however, That such traditional indigenous family dwelling will not constitute a danger to life or limb of its occupants or of the public; will not be fire hazard or an eyesore to the community; and does not contravene any fire zoning regulation of the city or municipality in which it is located. chan robles virtual law library
(e) Notwithstanding paragraph (d) of this Section, this Code shall apply to Group A dwellings produced on a commercial scale and intended for use by the general public. 


What Is The Provision In The California Building Code On Emergency Escape Windows?


Section 310.4

Basements in dwelling units and every sleeping room below the fourth story shall have at least  one operable window or door approved for emergency escape or rescue that shall open directly into a public  street, public alley, yard or exit court.

The door or window shall be operable from the inside to provide a full clear  opening without the use of separate tools.

All escape or rescue windows shall have a minimum net clear openable area of 5.7 square feet.  The minimum net clear openable height dimension shall be twenty-four inches.

The minimum net clear openable width  dimension shall be twenty inches.  When windows are provided as a means of escape or rescue they shall  have a finished sill height not more than forty-four inches above the floor.

This measurement is taken from the  floor to the clear opening of the window, not the lower, wooden, plaster or sheetrock window stool.

Bars, grilles, grates or similar devices may be installed on an emergency escape or rescue windows or doors, provided:

1. Such devices are equipped with approved release mechanisms which are openable from the inside without the use of a key or special knowledge or effort; and

2. The building is equipped with smoke detectors installed in accordance with section 310.9.


What Are Mock Ups And Wind Model Tests?

In addition to tests that are performed in the field, certain assemblies of buildings are mocked up at full scale and fully tested. This would be true for the assembles that are associated with curtain wall construction.

These mock-ups are required because it is extremely difficult to test in situ (on site when constructed). Also, it is more cost effective to check the assembly in the laboratory rather than finding a failure when the assembly is installed.

In addition, in the urban environment, wind loads on a building are impacted by other structures in the area. To account for this variable, a model of the building is created, along with models of the surrounding buildings.

These models are then tested in a wind tunnel. Sensors are placed on the building being tested and readings are taken of the pounds per square foot (psf) that would be imposed on the total outside surface of the building.

The wind tunnel loads that are used for testing are based on historical wind data of the area in question and requirements from the local code.

When a mock-up of the curtain wall is constructed (full scale) in a laboratory setting, it usually consists of a typical two-story curtain wall section of the building. Any unusual condition may have to be mocked-up for testing as well.

The mock-up assembly is tested to determine:

1. Amount of air and water infiltration observed
2. Drainage of the system
3. Structural capability of the mullions and glass
4. Expansion and contraction of the assemblies
5. Deflection of materials

Corrections are made to the mock-up, if required, so that all the assemblies are performing according to specified criteria. The components are then fabricated based on the results of the test.

Thus, the installation of the curtain wall should perform according to the standards established by the organizations. This eliminates the potential for failure that could have occurred and the consequence of replacement of the curtain wall if the mock-up was not tested in the laboratory.


What Are Field Fabrication Of Structural Components?

Structural components that are fabricated on site by trades people constitute the greatest risk for a catastrophic failure. This is due to the fact that control of putting parts together in the field is not done with the same diligence and controlled environment as a factory-made component.

Thus, great care must be taken to ensure that proper testing is performed so that a failure will not occur. The erection of a concrete structure is an excellent example where the use of a mixed type material must have adequate testing.

Concrete is a very viable construction material if placed according to the standards established by the organizations. However, due to the complexity of mixing the ingredients at the plant and transporting it to the site, placing the concrete at the site requires numerous controls to obtain an excellent final product.

The testing of concrete should include:

1. A trial concrete mix approved by the owner’s engineer
2. Proper mixing procedures at the concrete plant
3. Timing for the transportation of the concrete mix
4. Designed and properly installed form work and shoring so that they will not collapse or deflect
5. Temperature monitoring of the concrete at the site (to make sure that flash setting will not occur)
6. Ambient temperature monitoring (too hot for flash setting and too cold for freezing)
7. Slump test to confirm water/cement ratio of the concrete
8. Supervision for concrete vibration and dropping height for the actual placement of the concrete
9. Monitoring the thickness of a concrete slab
10. Assurance that all the concrete encapsulates the reinforcing bars, especially when
pouring columns
11. Placement of a sample of the concrete into concrete cylinders to determine the compressive strength of the concrete at 7, 14, and 28 days (via testing in the laboratory). This will be accomplished for design strength conformance and to know when the forms can be stripped
12. Checking the number and location of the reinforcing bars required for the pour
13. Proper curing of the concrete
14. Assurance that reinforcing bars are properly lapped
15. Assurance that all exterior exposed concrete is covered by 3 inches of concrete
(2 inches for interior concrete) over the reinforcing steel

Even though steel sections are fabricated in a controlled environment at a plant, the steel members must be connected in the field by iron workers with bolts and/or welding.

Thus, stringent testing is also required for a steel structure. Some of the tests that would have to be considered when erecting steel are the following:
1. Proper bolts are being utilized.
2. Required tightening (torque) of the bolts needs to be accomplished by code standards.
3. Steel sections as indicated on the approved shop drawings are in fact being installed.
4. Welds have to be checked for proper thickness and continuity.
5. All welders have to be certified.
6. Shear stud connectors have to be attached to the steel with proper spacing and welds.
7. The steel has to be fireproofed with approved material that will have proper thickness, adhesion, and density.
8. All columns are perfectly aligned (plumbed).
9. Correct steel is being used (i.e., A36).
10. Proper steel camber has been placed on the steel as specified by the consultants.
11. Splice plates must be of the approved thickness.
12. Inspection at the fabricator’s shop would be helpful for checking beam camber and obtaining coupons.


How To Do The Methods Of Joint Truss Members Analysis?

This method for finding the forces in the members of a truss consists of satisfying the conditions of equilibrium for the forces acting on the connecting pin of each joint. The method therefore deals with the equilibrium of concurrent forces, and only two independent equilibrium equations are involved.

We begin the analysis with any joint where at least one known load exists and where not more than two unknown forces are present. The solution may be started with the pin at the left end. Its free-body diagram is shown in Fig. 4/7.

With the joints indicated by letters, we usually designate the force in each member by the two letters defining the ends of the member. The proper directions of the forces should be evident by inspection for this simple case.

The free-body diagrams of portions of members AF and AB are also shown to clearly indicate the mechanism of the action and reaction. The member AB actually makes contact on the left side of the pin, although the force AB is drawn from the right side and is shown acting away from the pin.

Thus, if we consistently draw the force arrows on the same side of the pin as the member, then tension (such as AB) will always be indicated by an arrow away from the pin, and compression (such as AF) will always be indicated by an arrow toward the pin.

The magnitude of AF is obtained from the equation ΣFy = 0 and AB is then found from ΣFx = 0. Joint F may be analyzed next, since it now contains only two unknowns, EF and BF. Proceeding to the next joint having no more than two unknowns, we subsequently analyze joints B, C, E, and D in that order.

Figure 4/8 shows the free-body diagram of each joint and its corresponding force polygon, which represents graphically the two equilibrium conditions ΣFx = 0 and ΣFy = 0. The numbers indicate the order in which the joints are analyzed.

We note that, when joint D is finally reached, the computed reaction R2 must be in equilibrium with the forces in members CD and ED, which were determined previously from the two neighboring joints. This requirement provides a check on the correctness of our work.

Note that isolation of joint C shows that the force in CE is zero when the equation ΣFy = 0 is applied. The force in this member would not be zero, of course, if an external vertical load were applied at C.

It is often convenient to indicate the tension T and compression C of the various members directly on the original truss diagram by drawing arrows away from the pins for tension and toward the pins for compression.

This designation is illustrated at the bottom of Fig. 4/8. Sometimes we cannot initially assign the correct direction of one or both of the unknown forces acting on a given pin. If so, we may make an arbitrary assignment. A negative computed force value indicates that the initially assumed direction is incorrect.


What Are The Equilibrium Categories?

The categories of force systems acting on bodies in two-dimensional equilibrium are summarized in Fig. 3/3 and are explained further as follows.

Category 1, equilibrium of collinear forces, clearly requires only the one force equation in the direction of the forces (x-direction), since all other equations are automatically satisfied.

Category 2, equilibrium of forces which lie in a plane (x-y plane) and are concurrent at a point O, requires the two force equations only, since the moment sum about O, that is, about a z-axis through O, is necessarily zero.

Included in this category is the case of the equilibrium of a particle.

Category 3, equilibrium of parallel forces in a plane, requires the one force equation in the direction of the forces (x-direction) and one moment equation about an axis (z-axis) normal to the plane of the forces.

Category 4, equilibrium of a general system of forces in a plane (x-y), requires the two force equations in the plane and one moment equation about an axis (z-axis) normal to the plane.


Construction of Free-Body Diagrams Tutorials

The full procedure for drawing a free-body diagram which isolates a body or system consists of the following steps.

Step 1. Decide which system to isolate. The system chosen should usually involve one or more of the desired unknown quantities.

Step 2. Next isolate the chosen system by drawing a diagram which represents its complete external boundary. This boundary defines the isolation of the system from all other attracting or contacting bodies, which are considered removed. 

This step is often the most crucial of all. Make certain that you have completely isolated the system before proceeding with the next step.

Step 3. Identify all forces which act on the isolated system as applied by the removed contacting and attracting bodies, and represent them in their proper positions on the diagram of the isolated system. Make a systematic traverse of the entire boundary to identify all contact forces. 

Include body forces such as weights, where appreciable. Represent all known forces by vector arrows, each with its proper magnitude, direction, and sense indicated. Each unknown force should be represented by a vector arrow with the unknown magnitude or direction indicated by symbol. 

If the sense of the vector is also unknown, you must arbitrarily assign a sense. The subsequent calculations with the equilibrium equations will yield a positive quantity if the correct sense was assumed and a negative quantity if the incorrect sense was assumed. 

It is necessary to be consistent with the assigned characteristics of unknown forces throughout all of the calculations. If you are consistent, the solution of the equilibrium equations will reveal the correct senses.

Step 4. Show the choice of coordinate axes directly on the diagram. Pertinent dimensions may also be represented for convenience. 

Note, however, that the free-body diagram serves the purpose of focusing attention on the action of the external forces, and therefore the diagram should not be cluttered with excessive extraneous information. 

Clearly distinguish force arrows from arrows representing quantities other than forces. For this purpose a colored pencil may be used.


What Are The Type Of Steels Used In Constructing Bridges?

Steels for application in bridges are covered by A709, which includes steel in several of the categories mentioned above. Under this specification, grades 36, 50, 70, and 100 are steels with yield strengths of 36, 50, 70, and 100 ksi, respectively.

The grade designation is followed by the letter W, indicating whether ordinary or high atmospheric corrosion resistance is required. An additional letter, T or F, indicates that Charpy V-notch impact tests must be conducted on the steel.

The T designation indicates that the material is to be used in a non-fracture-critical application as defined by AASHTO; the F indicates use in a fracture-critical application.

A trailing numeral, 1, 2, or 3, indicates the testing zone, which relates to the lowest ambient temperature expected at the bridge site. (see Table Below)

As indicated by the first footnote in the table, the service temperature for each zone is considerably less than the Charpy V-notch impact-test temperature.

This accounts for the fact that the dynamic loading rate in the impact test is more severe than that to which the structure is subjected.

The toughness requirements depend on fracture criticality, grade, thickness, and method of connection. A709-HPS70W, designated as a High Performance Steel (HPS), is also now available for highway bridge construction.

This is a weathering plate steel, designated HPS because it possesses superior weldability and toughness as compared to conventional steels of similar strength.

For example, for welded construction with plates over 21⁄2 in thick, A709-70W must have a minimum average Charpy V-notch toughness of 35 ft lb at 10 F in Zone III, the most severe climate.

Toughness values reported for some heats of A709-HPS70W have been much higher, in the range of 120 to 240 ft lb at 10 F. Such extra toughness provides a very high resistance to brittle fracture.

(R. L. Brockenbrough, Sec. 9 in Standard Handbook for Civil Engineers, 4th ed., F. S.
Merritt, ed., McGraw-Hill, Inc., New York.)


What Are Space Trusses?

A space truss is the three-dimensional counterpart of the plane truss described in the three previous articles. The idealized space truss consists of rigid links connected at their ends by ball-and-socket joints.

Whereas a triangle of pin-connected bars forms the basic noncollapsible unit for the plane truss, a space truss, on the other hand, requires six bars joined at their ends to form the edges of a tetrahedron as the basic noncollapsible unit.

In Fig. 4/13a the two bars AD and BD joined at D require a third support CD to keep the triangle ADB from rotating about AB. In Fig. 4/13b the supporting base is replaced by three more bars AB, BC, and AC to form a tetrahedron not dependent on the foundation for its own rigidity.

We may form a new rigid unit to extend the structure with three additional concurrent bars whose ends are attached to three fixed joints on the existing structure. Thus, in Fig. 4/13c the bars AF, BF, and CF are attached to the foundation and therefore fix point F in space.

Likewise point H is fixed in space by the bars AH, DH, and CH. The three additional bars CG, FG, and HG are attached to the three fixed points C, F, and H and therefore fix G in space. The fixed point E is similarly created.

We see now that the structure is entirely rigid. The two applied loads shown will result in forces in all of the members. A space truss formed in this way is called a simple space truss.

Ideally there must be point support, such as that given by a balland- socket joint, at the connections of a space truss to prevent bending in the members.

As in riveted and welded connections for plane trusses, if the center lines of joined members intersect at a point, we\ can justify the assumption of two-force members under simple tension and compression.


What Are Simple Trusses?

The basic element of a plane truss is the triangle. Three bars joined by pins at their ends, Fig. 4/3a, constitute a rigid frame. The term rigid is used to mean noncollapsible and also to mean that deformation of the members due to induced internal strains is negligible.

On the other hand, four or more bars pin-jointed to form a polygon of as many sides constitute a nonrigid frame. We can make the nonrigid frame in Fig. 4/3b rigid, or stable, by adding a diagonal bar joining A and D or B and C and thereby forming two triangles.

We can extend the structure by adding additional units of two end-connected bars, such as DE and CE or AF and DF, Fig. 4/3c, which are pinned to two fixed joints. In this way the entire structure will remain rigid.

Structures built from a basic triangle in the manner described are known as simple trusses. When more members are present than are needed to prevent collapse, the truss is statically indeterminate.

A statically indeterminate truss cannot be analyzed by the equations of equilibrium alone. Additional members or supports which are not necessary for maintaining the equilibrium configuration are called redundant.

To design a truss we must first determine the forces in the various members and then select appropriate sizes and structural shapes to withstand the forces. Several assumptions are made in the force analysis of simple trusses.

First, we assume all members to be two-force members. A two-force member is one in equilibrium under the action of two forces only, as defined in general terms with Fig. 3/4 in Art. 3/3.

Each member of a truss is normally a straight link joining the two points of application of force. The two forces are applied at the ends of the member and are necessarily equal, opposite, and collinear for equilibrium.

The member may be in tension or compression, as shown in Fig. 4/4. When we represent the equilibrium of a portion of a two-force member, the tension T or compression C acting on the cut section is the same for all sections.

We assume here that the weight of the member is small compared with the force it supports. If it is not, or if we must account for the small effect of the weight, we can replace the weight W of the member by two forces, each W/2 if the member is uniform, with one force acting at each end of the member.

These forces, in effect, are treated as loads externally applied to the pin connections. Accounting for the weight of a member in this way gives the correct result for the\ average tension or compression along the member but will not account for the effect of bending of the member.


Tutorials On Center of Gravity and Mass Moment of Inertia of Homogeneous Solids

This is a reference on the center of gravity and mass moment of inertia for typical homogeneous solids. These are helpful reference in solution of civil engineering problems.










What Are Subsoil Drainage System?

Subsoil Drainage ~ Building Regulation C2 requires that subsoil drainage shall be provided if it is needed to avoid:-

a) the passage of ground moisture into the interior of the building or
b) damage to the fabric of the building.

Subsoil drainage can also be used to improve the stability of the ground, lower the humidity of the site and enhance its horticultural properties. Subsoil drains consist of porous or perforated pipes laid dry jointed in a rubble filled trench.

Porous pipes allow the subsoil water to pass through the body of the pipe whereas perforated pipes which have a series of holes in the lower half allow the subsoil water to rise into the pipe.

This form of ground water control is only economic up to a depth of 1„500, if the water table needs to be lowered to a greater depth other methods of ground water control should be considered.

The water collected by a subsoil drainage system has to be conveyed to a suitable outfall such as a river, lake or surface water drain or sewer.

In all cases permission to discharge the subsoil water will be required from the authority or owner and in the case of streams, rivers and lakes, bank protection at the outfall may be required to prevent erosion.

Subsoil Drainage Systems ~ the lay out of subsoil drains will depend on whether it is necessary to drain the whole site or if it is only the substructure of the building which needs to be protected.

The latter is carried out by installing a cut off drain around the substructure to intercept the flow of water and divert it away from the site of the building. Junctions in a subsoil drainage system can be made using standard fittings or by placing the end of the branch drain onto the crown of the main drain.

NB. connections to surface water sewer can be made at inspection chamber or direct to the sewer using a saddle connector † it may be necessary to have a catchpit to trap any silt.


What Are Structural Column Curves?

Curves obtained by plotting the critical stress for various values of the slenderness ratio are called column curves. For axially loaded, initially straight columns, the column curve consists of two parts: (1) the Euler critical values, and (2) the Engesser, or tangent-modulus critical values.

Column curves: (a) stress-strain curve for a material that does not have a sharply defined yield pont: (b) column curve for this material; (c) stress-strain curve for a material with a sharply defined yield point; (d ) column curve for that material.

The latter are greatly affected by the shape of the stress-strain curve for the material of which the column is made, as shown in Fig. 5.44.

The stress-strain curve for a material, such as an aluminum alloy or high-strength steel, which does not have a sharply defined yield point, is shown in Fig. 5.44a.

The corresponding column curve is drawn in Fig. 5.44b.

In contrast, Fig. 5.44c presents the stress strain curve for structural steel, with a sharply defined point, and Fig. 5.44d the related column curve.

This curve becomes horizontal as the critical stress approaches the yield strength of the material and the tangent modulus becomes zero, whereas the column curve in Fig. 5.44b continues to rise with decreasing values of the slenderness ratio.

Examination of Fig. 44d also indicates that slender columns, which fall in the elastic range, where the column curve has a large slope, are very sensitive to variations in the factor k, which represents the effect of end conditions.

On the other hand, in the inelastic range, where the column curve is relatively flat, the critical stress is relatively insensitive to changes in k.

Hence the effect of end conditions on the stability of a column is of much greater significance for long columns than for short columns.


What Are The Forms Of Silica Fumes?

Silica fume is available commercially in several forms in both North America and Europe:

• As-produced silica fume is silica fume collected in dedusting systems known as bag houses. In this form, the material is very fine and has a bulk density of about 200 to 300 kg/m3, compared with 1500 kg/m3 for Portland cement (Malhotra et al., 1987).

As-produced silica fume is available in bags or in bulk. Because of its extreme fineness, this form poses handling problems; in spite of this, the material can be and has been transported and handled like Portland cement.

• Compacted silica fume has a bulk density ranging from 500 to 700 kg/m3 and is considerably easier to handle than as-produced silica fume.

To produce the compacted form, the as-produced silica fume is placed in a silo, and compressed air is blown in from the bottom of the silo. This causes the particles to tumble, and in doing so they agglomerate.

The heavier agglomerates fall to the bottom of the silo and are removed at intervals. The air compaction of the asproduced silica fume is designed so the agglomerates produced are rather weak and quickly break down during concrete mixing.

Mechanical means have also been used to produce compacted silica fume.

• Water-based silica fume slurry overcomes the handling and transporting problems associated with as-produced silica fume; the slurry contains about 40 to 60% solid particles. Typically, these slurries have a density of about 1300 kg/m3.

Some slurries may contain chemical admixtures such as superplasticizers, water reducers, and retarders. One such product (known as Force 10,000®) has been successfully marketed in North America.