POISSON’S RATIO BASIC INFORMATION AND TUTORIAL

POISSON'S RATIO TUTORIALS AND SAMPLE PROBLEM
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.

Solution:

Click on the image to enlarge and see the solution.

SYNTHETIC FIBERS USED IN CIVIL ENGINEERING BASICS AND TUTORIALS

SYNTHETIC FIBERS USED IN CIVIL ENGINEERING BASIC INFORMATION
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.

HEAT TREATMENT OF STEEL BASICS AND CIVIL ENGINEERING TUTORIALS

DIFFERENT HEAT TREATMENT OF STEEL BASIC INFORMATION
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.

Annealing
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.

Hardening
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.

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).

FIELD FABRICATION OF STRUCTURAL COMPONENTS (MIXTURE AND COMPONENTS) BASIC AND CIVIL ENGINEERING TUTORIALS

FIELD FABRICATION OF STRUCTURAL COMPONENTS (MIXTURE AND COMPONENTS) BASIC INFORMATION
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.

SPACE TRUSSES BASICS AND CIVIL ENGINEERING TUTORIALS

SPACE TRUSSES BASIC INFORMATION
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.

SIMPLE TRUSSES CIVIL ENGINEERING TUTORIALS

SIMPLE TRUSSES BASIC INFORMATION
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.

SUBSOIL DRAINAGE BASIC AND CIVIL ENGINEERINGTUTORIALS

SUBSOIL DRAINAGE BASIC INFORMATION
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.

STRUCTURAL COLUMN CURVES REFERENCE AND CIVIL ENGINEERING TUTORIALS

STRUCTURAL COLUMN CURVES BASIC REFERENCE
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.

WISS AND PARMELEE RATING FACTOR FOR TRANSIENT VIBRATIONS BASICS AND TUTORIALS

WISS AND PARMELEE RATING FACTOR FOR TRANSIENT VIBRATIONS BASIC INFORMATION
What Is The Wiss And Parmelee Rating Factor?


Wiss and Parmelee also conducted research to refine the findings of Lenzen’s research. In particular, they attempted to quantify, in a more scientifically rigorous manner, human perception to transient floor motion.

They subjected 40 persons, standing on a vibrating platform, to transient vibration episodes with different combinations of frequency (2.5 to 25 Hz), peak displacements (0.0001 to 0.10 in), and damping (0.1 to 0.16, expressed as a ratio of critical).

After each episode, the subject was asked to rate the vibration on a scale of 1 to 5 with the following definitions: (1) imperceptible, (2) barely perceptible, (3) distinctly perceptible, (4) strongly perceptible, and (5) severe. Using regression analysis, an equation was perception ratings.

This equation is presented below. Wiss and Parmelee rating factor:

R= 5.08 (FA/ D^0.217)^0.265

where
R= response rating; 1= imperceptible; 2= barely perceptible; 3= distinctly perceptible; 4= strongly perceptible; 5= severe.
F= frequency of the vibration episode, Hz
A= maximum displacement amplitude, in
D= damping ratio, expressed as a ratio of critical

A graph of this subjective rating system is shown in Fig. 5.115. It should be noted that the lines represent a mean for that particular rating. The authors suggest that the boundaries for each rating lie halfway between the mean lines.

The boundaries defining R= 1 and R= 5 are not identified by the authors. These ratings are unbounded; therefore, a mean line cannot be computed.

IRON CARBON EQUILIBRIUM DIAGRAM BASICS AND TUTORIALS

IRON CARBON EQUILIBRIUM DIAGRAM BASIC INFORMATION
What Is Iron-Carbon Equilibrium Diagram?


The iron-carbon equilibrium diagram in Figure below shows that, under equilibrium conditions (slow cooling) if not more than 2.0% carbon is present, a solid solution of carbon in gamma iron exists at elevated temperatures.

This is called austenite. If the carbon content is less than 0.8%, cooling below the A3 temperature line causes transformation of some of the austenite to ferrite, which is substantially pure alpha iron (containing less than 0.01% carbon in solution).

Still further cooling to below the A1 line causes the remaining austenite to transform to pearlite—the eutectoid mixture of fine plates, or lamellas, of ferrite and cementite (iron carbide) whose iridescent appearance under the microscope gives it its name.

If the carbon content is 0.8%, no transformation on cooling the austenite occurs until the A1 temperature is reached.

At that point, all the austenite transforms to pearlite, with its typical ‘‘thumbprint’’ microstructure.

At carbon contents between 0.80 and 2.0%, cooling below the Acm temperature line causes iron carbide, or cementite, to form in the temperature range between Acm and A1,3. Below A1,3, the remaining austenite transforms to pearlite.

FLOOD PROOFING CIVIL ENGINEERING DESIGN BASIC AND TUTORIALS

FLOOD PROOFING CIVIL ENGINEERING DESIGN BASIC INFORMATION
What Is Flood Proofing? Civil Engineering In Flood Proof


A flood occurs when a river rises above an elevation, called flood stage, and is not prevented by enclosures from causing damage beyond its banks. Buildings constructed in a flood plain, an area that can be inundated by a flood, should be protected against a flood with a mean recurrence interval of 100 years.

Maps showing flood-hazard areas in the United States can be obtained from the Federal Insurance Administrator, Department of Housing and Urban Development, who administers the National Flood Insurance Program. Minimum criteria for floodproofing are given in National Flood Insurance Rules and Regulations (Federal Register, vol. 41, no. 207, Oct. 26, 1976).

Major objectives of floodproofing are to protect fully building and contents from damage from a l00-year flood, reduce losses from more devastating floods, and lower flood insurance premiums. Floodproofing, however, would be unnecessary if buildings were not constructed in flood prone areas.

Building in flood prone areas should be avoided unless the risk to life is acceptable and construction there can be economically and socially justified.

Some sites in flood prone areas possess some ground high enough to avoid flood damage. If such sites must be used, buildings should be clustered on the high areas.

Where such areas are not available, it may be feasible to build up an earth fill, with embankments protected against erosion by water, to raise structures above flood levels. Preferably, such structures should not have basements, because they would require costly protection against water pressure.

An alternative to elevating a building on fill is raising it on stilts (columns in an unenclosed space). In that case, utilities and other services should be protected against damage from flood flows. The space at ground level between the stilts may be used for parking automobiles, if the risk of water damage to them is acceptable or if they will be removed before flood waters reach the site.

Buildings that cannot be elevated above flood stage should be furnished with an impervious exterior. Windows should be above flood stage, and doors should seal tightly against their frames. Doors and other openings may also be protected with a flood shield, such as a wall.

Openings in the wall for access to the building may be protected with a movable flood shield, which for normal conditions can be stored out of sight and then positioned in the wall opening when a flood is imminent.

To prevent water damage to essential services for buildings in flood plains, important mechanical and electrical equipment should be located above flood level. Also, auxiliary electric generators to provide some emergency power are desirable.

In addition, pumps should be installed to eject water that leaks into the building. Furthermore, unless a building is to be evacuated in case of flood, an emergency water supply should be stored in a tank above flood level, and sewerage should be provided with cutoff valves to prevent backflow.

FOUNDATION CLASSIFICATIONS AND SELECT DEFINITION BASICS AND TUTORIALS

FOUNDATION CLASSIFICATIONS AND SELECT DEFINITION BASIC INFORMATION
What Are Structure Foundations?


Foundations may be classified based on where the load is carried by the ground, producing:

Shallow foundations—termed bases, footings, spread footings, or mats. The depth is generally D/B < 1 but may be somewhat more. Refer to Fig. 1-la.

Deep foundations—piles, drilled piers, or drilled caissons. Lp/B > 4+ with a pile illustrated
in Fig. l-\b.

Figure 1-1 illustrates general cases of the three basic foundation types considered in this text and provides some definitions commonly used in this type of work. Because all the definitions and symbols shown will be used throughout the text, the reader should give this figure careful study.

The superstructure brings loads to the soil interface using column-type members. The loadcarrying columns are usually of steel or concrete with allowable design compressive stresses on the order of 14O+ MPa (steel) to 1O+ MPa (concrete) and therefore are of relatively small cross-sectional area. The supporting capacity of the soil, from either strength or deformation considerations, is seldom over 1000 kPa but more often on the order of 200 to 250 kPa.

This means the foundation is interfacing two materials with a strength ratio on the order of several hundred. As a consequence the loads must be "spread" to the soil in a manner such that its limiting strength is not exceeded and resulting deformations are tolerable. Shallow foundations accomplish this by spreading the loads laterally, hence the term spread footing.

Where a spread footing (or simply footing) supports a single column, a mat is a special footing used to support several randomly spaced columns or to support several rows of parallel columns and may underlie a portion of or the entire building. The mat may also be supported, in turn, by piles or drilled piers.

Foundations supporting machinery and such are sometimes termed bases. Machinery and the like can produce a substantial load intensity over a small area, so the base is used as a load-spreading device similar to the footing.

Deep foundations are analogous to spread footings but distribute the load vertically rather than horizontally. A qualitative load distribution over depth for a pile is shown in Fig. 1-1 b. The terms drilled pier and drilled caisson are for the pile type member that is constructed by drilling a 0.76+-m diameter hole in the soil, adding reinforcing as necessary, and backfilling the cavity with concrete.

A major consideration for both spread footings (and mats) and piles is the distribution of stresses in the stress influence zone beneath the foundation [footing or pile tip (or point)].

The theoretical distribution of vertical stress beneath a square footing on the ground surface is shown in Fig. IAa. It is evident that below a critical depth of about 5B the soil has a negligible increase in stress (about 0.02qo) from the footing load.

This influence depth depends on B, however. For example, if B = 0.3 m, the critical stress zone is 5 X 0.3 = 1.5 m, and if B = 3 m, the zone is 15 m for a zonal influence depth ratio of 1 : 10. Because these B values are in a possible range beneath a large building, any poor soils below a depth of 2 m would have a considerable influence on the design of the wider footings.

Any structure used to retain soil or other material (see Fig. 1-lc) in a geometric shape other than that naturally occurring under the influence of gravity is a retaining structure.

Retaining structures may be constructed of a large number of materials including geotextiles, wood and metal sheeting, plain or reinforced concrete, reinforced earth, precast concrete elements, closely spaced pilings, interlocking wood or metal elements (crib walls), and so on. Sometimes the retaining structure is permanent and in other cases it is removed when it is no longer needed.

The foundations selected for study in this text are so numerous that their specialized study is appropriate. Every building in existence rests on a foundation whether formally designed or not. Every basement wall in any building is a retaining structure, whether formally designed or not.

Major buildings in areas underlain with thick cohesive soil deposits nearly always use piles or drilled caissons to carry the loads vertically to more competent strata, primarily to control settlement. Note that nearly every major city is underlain by clay or has zones where clay is present and requires piles or caissons.

Numerous bridges have retaining structures at the abutments and spread foundations carrying the intermediate spans. Usually the abutment end reactions are carried into the ground by piles. Harbor and offshore structures (used primarily for oil production) use piles extensively and for both vertical and lateral loads.

HANDBOOK OF STRUCTURAL STEEL CONNECTION DESIGN AND DETAILS FREE EBOOK DOWNLOAD LINK

HANDBOOK OF STRUCTURAL STEEL CONNECTION DESIGN AND DETAILS FREE EBOOK
Free E-Book Download Link: Handbook of Structural Steel Connection Design and Details

Handbook of Structural Steel Connection Design and Details Editorial Reviews


This book not not only gives you the best and latest methods in connection design, it supplies fabricated examples on the CD-ROM that you can use for instant application and configuration of your own designs.

Featuring a broad range of design methods and details, the Handbook demonstrates the newest techniques and materials in welded joint design and production...seismically resistant connnections...partially restrained connections...steel decks...inspection and quality control...and more.

You get the newest connection designs based on load and resistance factor AISC design methods; special methods for seismic connection design; new material on fracture and fatigue design; improved methods of connection force analysis for various structures; 400 illustrations that show you how to do the job right; and much more.

Book Description
Publication Date: April 15, 1999 | ISBN-10: 0070614970 | ISBN-13: 978-0070614970 | Edition: 1

About the Author
Akbar R. Tamboli is a senior project engineer with CUH2A in Princeton, New Jersey. He was previously vice president and project manager with Irwin G. Cantor, P.E., Consulting Engineers in New York City. A Fellow of the American Society of Civil Engineers, Mr. Tamboli is the editor of Steel Design Handbook: LRFD Method, published by McGraw-Hill.

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SEISMIC LOAD ON ROOFS DESIGN AND CALCULATION BASIC AND TUTORIALS

SEISMIC LOAD ON ROOFS DESIGN AND CALCULATION BASIC INFORMATION
How To Make Seismic Load On Roofs Design and Calculation?


Seismic Loads Calculations
The engineering approach to seismic design differs from that for other load types. For live, wind or snow loads, the intent of a structural design is to preclude structural damage. However, to achieve an economical seismic design, codes and standards permit local yielding of a structure during a major earthquake.

Local yielding absorbs energy but results in permanent deformations of structures. Thus seismic design incorporates not only application of anticipated seismic forces but also use of structural details that ensure adequate ductility to absorb the seismic forces without compromising the stability of structures.

Provisions for this are included in the AISC specifications for structural steel for buildings. The forces transmitted by an earthquake to a structure result from vibratory excitation of the ground. The vibration has both vertical and horizontal components.

However, it is customary for building design to neglect the vertical component because most structures have reserve strength in the vertical direction due to gravity-load design requirements. Seismic requirements in building codes and standards attempt to translate the complicated dynamic phenomenon of earthquake force into a simplified equivalent static force to be applied to a structure for design purposes.

For example, ASCE 7-95 stipulates that the total lateral force, or base shear, V (kips) acting in the direction of each of the principal axes of the main structural system should be computed from
V = CsW(9.139)

where Cs seismic response coefficient
W total dead load and applicable portions of other loads

The seismic coefficient, Cs, is determined by the following equation:
Cs = 1.2Cv /RT^2/3(9.140)

where Cv seismic coefficient for acceleration dependent (short period) structures
R response modification factor
T fundamental period, s

Alternatively, Cs need not be greater than
Cs = 2.5Ca/R(9.141)

where Ca seismic coefficient for velocity dependent (intermediate and long period) structures.

A rigorous evaluation of the fundamental elastic period, T, requires consideration of the intensity of loading and the response of the structure to the loading. To expedite design computations, T may be determined by the following:
Ta = CThn^3/4(9.142)

where CT 0.035 for steel frames
CT 0.030 for reinforced concrete frames
CT 0.030 steel eccentrically braced frames
CT 0.020 all other buildings
hn height above the basic to the highest level of the building, ft

For vertical distribution of seismic forces, the lateral force, V, should be distributed over the height of the structure as concentrated loads at each floor level or story. The lateral seismic force, Fx, at any floor level is determined by the following equation:
Fx = CuxV(9.143)

where the vertical distribution factor is given by

(9.144)

where wx and wi height from the base to level x or i
k 1 for building having period of 0.5 s or less 2 for building having period of 2.5 s or more  use linear interpolation for building periods between 0.5 and 2.5 s


For horizontal shear distribution, the seismic design story shear in any story, Vx, is determined by the following:

 (9.145)

where Fi the portion of the seismic base shear induced at level i. The seismic design story shear is to be distributed to the various elements of the force resisting system in a story based on the relative lateral stiffness of the vertical resisting elements and the diaphragm. Provision also should be made in design of structural framing for horizontal torsion, overturning effects, and the building drift.

RELATIVE COST OF STRUCTURAL STEEL BASICS AND TUTORIALS

RELATIVE COST OF STRUCTURAL STEEL BASIC INFORMATION
How To Compute Relative Cost Of Structural Steel?

Because of the many strength levels and grades now available, designers usually must investigate several steels to determine the most economical one for each application. As a guide, relative material costs of several structural steels used as tension members, beams, and columns are discussed below.

The comparisons are based on cost of steel to fabricators (steel producer’s price) because, in most applications, cost of a steel design is closely related to material costs. However, the total fabricated and erected cost of the structure should be considered in a final cost analysis.

Thus the relationships shown should be considered as only a general guide.

Tension Members. Assume that two tension members of different-strength steels have the same length. Then, their material-cost ratio C2 /C1 is

C2/C1 = A2P2/A1P1

where A1 and A2 are the cross-sectional areas and p1 and p2 are the material prices per unit weight. If the members are designed to carry the same load at a stress that is a fixed percentage of the yield point, the cross-sectional areas are inversely proportional to the yield stresses. Therefore, their relative material cost can be expressed as

C2/C1 = Fy1p2/Fy2p1  (1.2)

where Fy1 and Fy2 are the yield stresses of the two steels. The ratio p2 /p1 is the relative price factor. Values of this factor for several steels are given in Table 1.4, with A36 steel as the base.

The table indicates that the relative price factor is always less than the corresponding yield-stress ratio. Thus the relative cost of tension members calculated from Eq. (1.2) favors the use of high-strength steels.

Civil Engineering Design And Construct - A Guide To Integrating Design Into The Construction Process Free E-Book Download Link

Free E-Book Download Link of Civil Engineering Design And Construct - A Guide To Integrating Design Into The Construction Process

This publication is a guide to best practice in managing the project process in civil engineering design and construct (D&C) projects. It discusses the issues to be addressed when managing design and explains the attitudes and practices that are recommended to enable projects to succeed. 

It is intended to increase awareness and understanding of the issues involved, identifying what decisions need to be made, when and why. Differences between D&C and traditional procurement routes are highlighted along with contractual issues.

"Design and construct" is taken to be a generic term encompassing the whole family of design, construct, finance, own, operate and transfer procurement strategies, in which one party is responsible for both designing and constructing a facility. 

This includes projects procured under the Private Finance Initiative (PFI). Considerable emphasis is placed on imparting awareness of the importance of the designer-constructor interface as, in a D&C project, the most critical lines of communication are at this interface. 

As well as describing contractual frameworks, this guide also contains management toolboxes for reference. It is a working document that will assist those at a senior level (clients, contractors and consultants alike) who have to make crucial decisions affecting the outcome of a project.

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