What Are The Considerations During Floor Framing Design?

Selection of a suitable and economical floor system for a steel-frame building involves many considerations: load-carrying capacity, durability, fire resistance, dead weight, overall depth, facility for installing power, light, and telephones, facility for installing aid conditioning, sound transmission, appearance, maintenance, and construction time.

Building codes specify minimum design live loads for floor and roof systems. In the absence of a code regulation, one may use ‘‘Minimum Design Loads in Buildings and Other Structures,’’ ASCE 7-93, American Society of Civil Engineers.

Floors should be designed to support the actual loading or these minimum loads, whichever is larger. Most floors can be designed to carry any given load. However, in some instances, a building code may place a maximum load limit on particular floor systems without regard to calculated capacity.

Resistance to lateral forces should not be disregarded, especially in areas of seismic disturbances or for perimeter wind bents. In designs for such conditions, floors may be employed as horizontal diaphragms to distribute lateral forces to walls or vertical framing; those elements then transmit the lateral forces to the

When using lightweight floor systems, special reinforcement in the floor slab may be necessary at those points where the floor diaphragm transfers the horizontal forces to the frame elements. Durability becomes a major consideration when a floor is subject to loads other than static or moderately kinetic types of forces.

For example, a light joist system may be just the floor for an apartment or an office building but may be questionable for a manufacturing establishment where a floor must resist heavy impact and severe

Shallow floor systems deflect more than deep floors; the system selected should not permit excessive or objectionable deflections.

Fire resistance and fire rating are very important factors, because building codes in the interest of public safety, specify the degree of resistance that must be provided. Many floor systems are rated by the codes or by fire underwriters for purposes of satisfying code requirements or basing insurance rates.

The dead weight of the floor system, including the framing, is an important factor affecting economy of construction. For one thing, substantial saving in the weight and cost of a steel frame may result with lightweight floor systems.

In addition, low dead weight may also reduce foundation costs. Joist systems, either steel or concrete, require no immediate support, since they are obtainable in lengths to meet normal bay dimensions in tier building construction.

On the other hand, concrete arch and cellular-steel floors are usually designed with one or two intermediate beams within the panel. The elimination of secondary beams does not necessarily mean overall economy just because the structural-steel contract is less.

These beams are simple to fabricate and erect and allow much duplication. An analysis of contract price shows that the cost per ton of secondary beams will average 20% under the cost per ton for the whole steel structure; or viewed another way, the omission of secondary beams increases the price per ton on the balance of the steelwork by 31⁄2% on the average. This fact should be taken into account when making a cost analysis of several systems.

Sometimes, the depth of a floor system is important. For example, the height of a building may be limited for a particular type of fire-resistant construction or by zoning laws. The thickness of the floor system may well be the determining factor limiting the number of stories that can be built. Also, the economy of a deep floor
is partly offset by the increase in height of walls, columns, pipes, etc.

Another important consideration, particularly for office buildings and similar type occupancies, is the need for furnishing an economical and flexible electrical wiring system. With the accent on movable partitions and ever-changing office arrangements, the readiness and ease with which telephones, desk lights, computers, and other electric-powered business machines can be relocated are of major importance.

Therefore, the floor system that by its makeup provides large void spaces or cells for concealing wiring possesses a distinct advantage over competitive types of solid construction. Likewise, accommodation of recessed lighting in ceilings may disclose an advantage for one system over another. Furthermore, for economical air conditioning and ventilation, location of ducts and method of support warrant study of several floor systems.

Sound transmission and acoustical treatments are other factors that need to be evaluated. A wealth of data are available in reports of the National Institute of Standards and Technology. In general, floor systems of sandwich type with air spaces between layers afford better resistance to sound transmission than solid systems, which do not interrupt sound waves.

Although the ideal soundproof floor is impractical, because of cost, several reasonably satisfactory systems are available. Much depends on type of occupancy, floor coverings, and ceiling finish—acoustical plaster or tile.

Appearance and maintenance also should be weighed by the designer and the owner. A smooth, neat ceiling is usually a prerequisite for residential occupancy; a less expensive finish may be deemed satisfactory for an institutional building.

Speed of construction is essential. Contractors prefer systems that enable the follow-up trades to work immediately behind the erector and with unimpeded efficiency.

In general, either rolled beams or open-web joists are used to support the floor elements. The most common types of flooring are (a) concrete fill on metal deck, (b) pre-cast concrete plank, and (c) cast-in-place concrete floors with integral joist.

Metal decks may be cellular or plain and are usually stud-welded to the supporting elements to provide composite action. Cast-in-place concrete floors, or concrete pan floors, are becoming less common than in the past. In addition to the systems described, there are several adaptations of these as well as other proprietary systems.


How Steel and Concrete Framing Works?

In another type of framing system, different from those described, a partial use of structural steel has an important role, namely, composite framing of reinforced concrete and structural steel.framing in carrying loads. The term composite, however, often is used for the specific cases in which concrete slabs act together with flexural members.

Reinforced-concrete columns of conventional materials when employed in tall buildings and for large spans become excessively large. One method of avoiding this objectionable condition is to use high-strength concrete and high-strength reinforcing bars.

Another is to use a structural-steel column core. In principle, the column load is carried by both the steel column and the concrete that surrounds the steel shape. Building codes usually contain an appropriate formula for this condition.

A number of systems employ a combination of concrete and steel in various ways. One method features steel columns supporting a concrete floor system by means of a steel shearhead connected to the columns at each floor level.

The shallow grillage is embedded in the floor slab, thus obtaining a smooth ceiling without drops or capitals.

Another combination system is the lift-slab method. In this system, the floor slabs are cast one on top of another at ground level. Jacks, placed on the permanent steel columns, raise the slabs, one by one, to their final elevation, where they are made secure to the columns.

When fireproofing is required, the columns may be boxed in with any one of many noncombustible materials available for that purpose. The merit of this system is the elimination of form work and shoring that are essential in conventional reinforced-concrete construction.

For high-rise buildings, structural-steel framing often is used around a central, load-bearing, concrete core, which contains elevators, stairways, and services. The thick walls of the core, whose tubular configuration may be circular, square, or rectangular, are designed as shear walls to resist all the wind forces as well as
gravity loads.

Sometimes, the surrounding steel framing is cantilivered from the core, or the perimeter members are hung from trusses or girders atop the core and possibly also, in very tall buildings, at midheight of the core.


What Are the Different Types of Trusses In Construction?

Trusses. When depth limits permit, a more economical way of spanning long distances is with trusses, for both floor and roof construction. Because of their greater depth, trusses usually provide greater stiffness against deflection when compared pound for pound with the corresponding rolled beam or plate girder that
otherwise would be required.
Six general types of trusses frequently used in building frames are shown in Fig. 7.11 together with modifications that can be made to suit particular conditions.

Trusses in Fig. 7.11a to d and k may be used as the principal supporting members in floor and roof framing. Types e to j serve a similar function in the framing of symmetrical roofs having a pronounced pitch. As shown, types a to d have a top chord that is not quite parallel to the bottom chord. Such an arrangement is
used to provide for drainage of flat roofs.

Most of the connections of the roof beams (purlins), which these trusses support, can be identical, which would not be the case if the top chord were dead level and the elevation of the purlins varied. When used in floors, truss types a to d have parallel chords.

Properly proportioned, bow string trusses (Fig. 7.11j) have the unique characteristic that the stress in their web members is relatively small. The top chord, which usually is formed in the arc of a circle, is stressed in compression, and the bottom chord is stressed in tension. In spite of the relatively expensive operation of forming the top chord, this type of truss has proved very popular in roof framing on spans of moderate lengths up to about 100 ft.

The Vierendeel truss (Fig. 7.11k) generally is shop welded to the extent possible to develop full rigidity of connections between the verticals and chords. It is useful where absence of diagonals is desirable to permit passage between the verticals.

Trusses also may be used for long spans, as three-dimensional trusses (space frames) or as grids. In two-way girds, one set of parallel lines of trusses is intersected at 90 by another set of trusses so that the verticals are common to both sets.

Because of the rigid connections at the intersections, loads are distributed nearly equally to all trusses. Reduced truss depth and weight savings are among the apparent advantages of such grids.

Long-span joists are light trusses closely spaced to support floors and flat roofs. They conform to standard specifications (Table 7.1) and to standard loading. Both Pratt and Warren types are used, the shape of chords and webs varying with the fabricator.

Yet, all joists with the same designation have the same guaranteed load supporting capacity. The standard loading tables list allowable loads for joists up to 72 in deep and with clear span up to 144 ft. The joists may have parallel or sloping chords or other configuration.


What Are Girders In Construction?

Girders are the usual choice where depths are limited, as over large unobstructed areas in the lower floors of tall buildings, where column loads from floors above must be carried across the clear area.

Sometimes, when greater strength is required than is available in rolled beams, cover plates are added to the flanges (Fig. 7.10a) to provide the additional strength.
When depths exceed the limit for rolled beams, i.e., for spans exceeding about 67 ft (based on the assumption of a depth-span ratio of 1:22 with 36-in-deep Ws), the girder must be built up from plates and shapes.

Welded girders are used instead of the old-type conventional riveted girds (Fig. 7.10b), composed of web plate, angles, and cover plates.Welded girders generally are composed of three plates (Fig. 7.10c). This
type offers the most opportunity for simple fabrication, efficient use of material, and least weight.

Top and bottom flange plates may be of different size (Fig. 7.10d), an arrangement advantageous in
composite construction, which integrates a concrete floor slab with the girder flange, to function together.

Heavy girders may use cover-plated tee sections (Fig. 7.10e). Where lateral loads are a factor, as in the case of girders supporting cranes, a channel may be fastened to the top flange (Fig. 7.10ƒ).

In exceptionally heavy construction, it is not unusual to use a pair of girders diaphragmed together to share the load (Fig. 7.10g).

The availability of high-strength, weldable steels resulted in development of hybrid girders. For example, a high strength steel, say A572 Grade 50, whose yield stress is 50 ksi, may be used in a girder for the most highly stressed flanges, and the lower-priced A36 steel, whose yield stress is 36 ksi, may be used for lightly stressed flanges and web plate and detail material.

The AISC specification for allowable-stress design requires that the top and bottom flanges at any cross section have the same cross-sectional area, and that the steel in these flanges be of the same grade.

The allowable bending stress may be slightly less than that for conventional homogeneous girders of the high strength steel, to compensate for possible overs tress in the web at the junction with the flanges.

Hybrid girders are efficient and economical for heavy loading and long spans and, consequently, are frequently employed in bridgework.


What Is Skeleton Framing?

In skeleton framing all the gravity loadings of the structure, including the walls are supported by the steel framework. Such walls are termed non bearing or curtain walls. This system made the skyscraper possible.

Steel, being so much stronger than all forms of masonry, is capable of sustaining far greater load in a given space, thus obstructing less of the floor area in performing its function. With columns properly spaced to provide support for the beams spanning between them, there is no limit to the floor and roof area that can be constructed with this type of framing, merely by duplicating the details for a single bay.

Erected tier upon tier, this type of framing can be built to any desired height. Fabricators refer to this type of construction as ‘‘beam and column.’’ A typical arrangement is illustrated in Fig. 7.8.
The spandrel beams, marked B1 in Fig. 7.8, are located in or under the wall so as to reduce eccentricity caused by wall loads. Figure 7.9 shows two methods for connecting to the spandrel beam the shelf angle that supports the outer course of masonry over window openings 6 ft or more in width.
In order that the masonry contractor may proceed expeditiously with the work, these shelf angles must be in
alignment with the face of the building and at the proper elevation to match a masonry joint. The connection of the angles to the spandrel beams is made by bolting; shims are provided to make the adjustments for line and elevation.

Figure 7.9a illustrates a typical connection arrangement when the outstanding leg of the shelf angle is about 3 in or less below the bottom flange of the spandrel beam; Fig. 7.9b illustrates the corresponding arrangement when the outstanding leg of the shelf angle is more than about 3 in below the bottom flange of the spandrel

In the cases represented by Fig. 7.9b, the shelf angles are usually shipped attached to the spandrel beam. If the distance from the bottom flange to the horizontal leg of the shelf angle is greater than 10 in, a hanger may be required.

In some cases, as over door openings, the accurate adjustment features provided by Fig. 7.9a and b may not be needed. It may then be more economical to simplify the detail, as shown in Fig. 7.9c. The elevation and alignment will then conform to the permissible tolerances associated with the steel framework.


What Is Wall Bearing Framing Method?

Probably the oldest and commonest type of framing, wall-bearing (not to be confused with bearing-wall construction), occurs whenever a wall of a building, interior or exterior, is used to support ends of main structural elements carrying roof or floor loads.

The walls must be strong enough to carry the reaction from the supported members and thick enough to ensure stability against any horizontal forces that may be imposed. Such construction often is limited to relatively low structures, because load-bearing walls become massive in tall structures. Nevertheless, a wall bearing system may be advantageous for tall buildings when designed with reinforcing steel.

A common application of wall-bearing construction may be found in many single-family homes. A steel beam, usually 8 or 10 in deep, is used to carry the interior walls and floor loads across the basement with no intermediate supports, the ends of the beam being supported on the foundation walls. The relatively shallow
beam depth affords maximum headroom for the span. In some cases, the spans may be so large that an intermediate support becomes necessary to minimize deflection.

Usually a steel pipe column serves this purpose. Another example of wall-bearing framing is the member used to support masonry over windows, doors, and other openings in a wall. Such members, called lintels, may be a steel angle section (commonly used for brick walls in residences) or, on longer spans and for heavier walls, a fabricated assembly.

A variety of frequently used types is shown in Fig. 7.6. In types b, c, and e, a continuous plate is used to close the bottom, or soffit, of the lintel, and to join the load-carrying beams and channels into a single shipping unit.
The gap between the toes of the channel flanges in type d may be covered by a door frame or window trim, to be installed later. Pipe and bolt separators are used to hold the two channels together to form a single member for handling.

Bearing Plates. Because of low allowable pressures on masonry, bearing plates (sometimes called masonry plates) are usually required under the ends of all beams that rest on masonry walls, as illustrated in Fig. 7.7.
Even when the pressure on the wall under a member is such that an area no greater than the contact portion
of the member itself is required, wall plates are sometimes prescribed, if the member is of such weight that it must be set by the steel erector. The plates, shipped loose and in advance of steel erection, are then set by the mason to provide a satisfactory seat at the proper elevation.

Anchors. The beams are usually anchored to the masonry. Government anchors, as illustrated in Fig. 7.7, are generally preferred.

Nonresidential Uses. Another common application for the wall-bearing system is in one-story commercial and light industrial-type construction. The masonry side walls support the roof system, which may be rolled beams, open-web joists, or light trusses.

Clear spans of moderate size are usually economical, but for longer spans (probably over 40 ft), wall thickness and size of buttresses (pilasters) must be built to certain specified minimum proportions commensurate with the span—a requirement of building codes to assure stability. Therefore, the economical aspect should be carefully investigated.

It may cost less to introduce steel columns and keep wall size to the minimum permissable. On the other hand, it may be feasible to reduce the span by introducing intermediate columns and still retain the wall-bearing system for the outer end reactions.

Planning for Erection. One disadvantage of wall-bearing construction needs emphasizing: Before steel can be set by the iron workers, the masonry must be built up to the proper elevation to receive it. When these elevations vary, as is the case at the end of a pitched or arched roof, then it may be necessary to proceed in alternate stages, progress of erection being interrupted by the work that must be performed by the masons, and vice versa.

The necessary timing to avoid delays is seldom obtained. A few columns or an additional rigid frame at the end of a building may cost less than using trades to fit an intermittent and expensive schedule. Remember, too, that labor-union regulations may prevent the trades from handling any material other than that belonging to their own craft.

An economical rule may well be: Lay out the work so that the erector and iron workers can place and connect all the steel work in one continuous operation.


What Are Unfinished Bolts?

Known in construction circles by several names—ordinary, common, machine, or rough—unfinished bolts are characterized chiefly by the rough appearance of the shank. They are covered by ASTM A307. They fit into holes 1⁄16 in larger in diameter than the nominal bolt diameter.

Unfinished bolts have relatively low load-carrying capacity. This results from the possibility that threads might lie in shear planes. Thus, it is unnecessary to extend the bolt body by use of washers.

One advantage of unfinished bolts is the ease of making a connection; only a wrench is required. On large jobs, however, erectors find they can tighten bolts more economically with a pneumatic-powered impact wrench. Power tightening generally yields greater uniformity of tension in the bolts and makes for a better balanced connection.

While some old building codes restrict unfinished bolts to minor applications, such as small, secondary (or intermediate) beams in floor panels and in certain parts of one-story, shed-type buildings, the AISC specifications for structural steel buildings, with a basis of many years of experience, permit A307 bolts for main connections on structures of substantial size.

For example, these bolts may be used for beam and girder connections to columns in buildings up to 125 ft in height. There is an economic relation between the strength of a fastener and that of the base material.

So while A307 may be economical for connecting steel with a 36- ksi yield point, this type of bolt may not be economical with 50-ksi yield-point steel. The number of fasteners to develop the latter becomes excessive and perhaps impractical due to size of detail material.

A307 bolts should always be considered for use, even in an otherwise all-welded building, for minimum-type connections, such as for purlins, girts, and struts.

Locking Devices for Bolts. Unfinished bolts (ASTM A307) and interference body-type bolts usually come with American Standard threads and nuts. Properly tightened, connections with these bolts give satisfactory service under static loads.

But when the connections are subjected to vibration or heavy dynamic loads, a locking device is desirable to prevent the nut from loosening. Locking devices may be classified according to the method employed: special threads, special nuts, special washers, and what may be described as field methods.

Instead of conventional threads, bolt may be supplied with a patented self-locking thread called Dardelet. Sometimes, locking features are built into the nuts. Patented devices, the Automatic-Nut, Union-Nut, and Pal-Nut, are among the common ones.

Washers may be split rings or specially touched. Field methods generally used include checking, or distorting, the threads by jamming them with a chisel or locking by tack welding the nuts.


What Are the Different Steel Structural Shapes?

Steel mills have a standard classification for the many products they make, one of which is structural shapes (heavy). By definition this classification takes in all shapes having at least one cross-sectional dimension of 3 in or more. Shapes of lesser size are classified as structural shapes (light) or, more specifically, bars.

Shapes are identified by their cross-sectional characteristics—angles, channels, beams, columns, tees, pipe, tubing, and piles. For convenience, structural shapes are simply identified by letter symbols as indicated in Table 7.3.
The industry recommended standard (adopted 1970) for indicating a specific size of beam or column-type shape on designs, purchase orders, shop drawings, etc., specifies listing of symbol, depth, and weight, in that order.

For example, W14 30 identifies a wide-flange shape with nominal depth of 14 in and weight of 30 lb / lin ft. The , read as ‘‘by,’’ is merely a separation.

Each shape has its particular functional use, but the workhorse of building construction is the wide-flange W section. For all practical purposes, W shapes have parallel flange surfaces.

The profile of a W shape of a given nominal depth and weight available from different producers is essentially the same, except for the size of fillets between web and flanges.


What Are the Types of Arc Welding?

Shielded metal arc welding (SMAW): 
Shielded metal arc welding, which is also known as stick welding, is the most widely used process. The arc is struck between the metal to be welded and a flux coated consumable electrode.

The fluxes are mostly made from mineral components and cover the hot weld deposit and protect it from the environment. The solidified glassy product, slag should be removed by chipping or with a wire brush.

Gas metal arc welding (GMAW):
This process is also referred to as metal inert-gas (MIG) welding uses an uncoated continuous wire. The weld area is shielded from contamination by the gas that is fed through the welding torch.

The mode of metal transfer (spray, globular, short-circuiting, pulsed-arc) is varied by adjusting the amperage and the shielding gases used depending on the welding position and the type of joint.

Flux-cored arc welding (FCAW):
The shielding gases and slag are provided by the decomposing flux that is contained within the electrode. Auxiliary shielding is also used in certain instances where deeper penetration is needed.

Gas tungsten arc welding (GTAW): 
Also known as tungsten inert-gas (TIG), the process uses a non-consumable electrode. The shielding gas is again fed through the welding torch.

Welding may be accomplished without the addition of filler metal, which is advantageous especially for thin walled parts.


What Are the Types of Stones Used in Civil Engineering Construction?

The following are the some of commonly used stones:

(i) Basalt and trap (ii) Granite
(iii) Sand stone (iv) Slate
(v) Laterite (vi) Marble
(vii) Gneiss (viii) Quartzite.

Their qualities and uses are explained below:

(i) Basalt and Trap:
The structure is medium to fine grained and compact. Their colour varies from dark gray to black. Fractures and joints are common. Their weight varies from 18 kN/m3 to 29 kN/m3. The compressive strength varies from 200 to 350 N/mm2. These are igneous rocks. They are used as road metals, aggregates for concrete. They are also used for rubble masonry works for bridge piers, river walls and dams. They are used as pavement.

(ii) Granite:
Granites are also igneous rocks. The colour varies from light gray to pink. The structure is crystalline, fine to coarse grained. They take polish well. They are hard durable. Specific gravity is from 2.6 to 2.7 and compressive strength is 100 to 250 N/mm2. They are used primarily for bridge piers, river walls, and for dams. They are used as kerbs and pedestals. The use of granite for monumental and institutional buildings is common. Polished granites are used as table tops, cladding for columns and wall. They are used as coarse aggregates in concrete.

(iii) Sand stone: These are sedimentary rocks, and hence stratified. They consist of quartz and feldspar. They are found in various colours like white, grey, red, buff, brown, yellow and even dark gray. The specific gravity varies from 1.85 to 2.7 and compressive strength varies from 20 to 170 N/mm2. Its porosity varies from 5 to 25 per cent. Weathering of rocks renders it unsuitable as building stone. It is desirable to use sand stones with silica cement for heavy structures, if necessary. They are used for masonry work, for dams, bridge piers and river walls.

(iv) Slate: 
These are metamorphic rocks. They are composed of quartz, mica and clay minerals. The structure is fine grained. They split along the planes of original bedding easily. The colour varies from dark gray, greenish gray, purple gray to black. The specific gravity is 2.6 to 2.7. Compressive strength varies from 100 to 200 N/mm2. They are used as roofing tiles, slabs, pavements etc.

(v) Laterite:
It is a metamorphic rock. It is having porous and sponges structure. It contains high percentage of iron oxide. Its colour may be brownish, red, yellow, brown and grey. Its specific gravity is 1.85 and compressive strength varies from 1.9 to 2.3 N/mm2. It can be easily quarried in blocks. With seasoning it gains strength. When used as building stone, its outer surface should be plastered.

(vi) Marble:
This is a metamorphic rock. It can take good polish. It is available in different pleasing colours like white and pink. Its specific gravity is 2.65 and compressive strength is 70–75 N/mm2. It is used for facing and ornamental works. It is used for columns, flooring, steps etc.

(vii) Gneiss:
It is a metamorphic rock. It is having fine to coarse grains. Alternative dark and white bands are common. Light grey, pink, purple, greenish gray and dark grey coloured varieties are available. These stones are not preferred because of deleterious constituents present in it. They may be used in minor constructions. However hard varieties may be used for buildings. The specific gravity varies from 2.5 to 3.0 and crushing strength varies from 50 to 200 N/mm2.

(viii) Quartzite:
Quartzites are metamorphic rocks. The structure is fine to coarse grained and often granular and branded. They are available in different colours like white, gray, yellowish. Quartz is the chief constituent with feldspar and mica in small quantities. The specific gravity varies from 2.55 to 2.65. Crushing strength varies from 50 to 300 N/mm2. They are used as building blocks and slabs. They are also used as aggregates for concrete.


What Are The Requirements for Good Stones Used In Civil Engineering?

The following are the requirements of good building stones:
(i) Strength: The stone should be able to resist the load coming on it. Ordinarilly this is not of primary concern since all stones are having good strength. However in case of large structure, it may be necessary to check the strength.

(ii) Durability: Stones selected should be capable of resisting adverse effects of natural forces like wind, rain and heat.

(iii) Hardness: The stone used in floors and pavements should be able to resist abrasive forces caused by movement of men and materials over them.

(iv) Toughness: Building stones should be tough enough to sustain stresses developed due to vibrations. The vibrations may be due to the machinery mounted over them or due to the loads moving over them. The stone aggregates used in the road constructions should be tough.

(v) Specific Gravity: Heavier variety of stones should be used for the construction of dams, retaining walls, docks and harbours. The specific gravity of good building stone is between 2.4 and 2.8.

(vi) Porosity and Absorption: Building stone should not be porous. If it is porous rain water enters into the pour and reacts with stone and crumbles it. In higher altitudes, the freezing of water in pores takes place and it results into the disintegration of the stone.

(vii) Dressing: Giving required shape to the stone is called dressing. It should be easy to dress so that the cost of dressing is reduced. However the care should be taken so that, this is not be at the cost of the required strength and the durability.

(viii) Appearance: In case of the stones to be used for face works, where appearance is a primary requirement, its colour and ability to receive polish is an important factor.(ix) Seasoning: Good stones should be free from the quarry sap. Laterite stones should not be used for 6 to 12 months after quarrying. They are allowed to get rid of quarry sap by the action of nature. This process of removing quarry sap is called seasoning.

(x) Cost: Cost is an important consideration in selecting a building material. Proximity of the quarry to building site brings down the cost of transportation and hence the cost of stones comes down.

However it may be noted that not a single stone can satisfy all the requirements of a good building stones, since one requirement may contradict another. For example, strength and durability requirement contradicts ease of dressing requirement.

Hence it is necessary that site engineer looks into the properties required for the intended work and selects the stone.


Why Conduct Feasibility Study on Civil Engineering Projects?

Feasibility studies of an engineering nature are needed for most construction projects. It can be an advantage to a promoter if he employs an independent consulting engineer to check the technical feasibility and cost of the project.

The consulting engineer should be able to bring extensive design and construction experience in the type of work the promoter needs, and be able to offer economic solutions to problems his experience tells him are likely to arise. The value of an independent consultant is that he uses only his professional judgement in deciding what will serve the promoter’s interests best.

Such a consultant should have no relationship with any commercial or other firm which could
have an interest in favouring any particular kind of development.

In the initial stages, the studies usually concentrate on various options for the location, design and layout of the project. The studies may include different methods for producing the required results, such as the alternatives of building a dam or river intake or sinking boreholes or buying water from an adjacent company to produce a new supply of water.

Accompanying this work there will be data gathering and analysis, followed by the development and costing of alternative layouts and designs, so the promoter can be assisted to choose the scheme which seems most suitable.

Site investigations are particularly important, and sufficient time and money should be spent on them. Although they cannot reveal everything below ground, inadequate site investigations are one of the most widespread causes of construction costs greatly exceeding the estimate.

On large or specialist projects, trial constructions or pilot plant studies may be necessary such as,
trial construction of earthworks, sinking of test borings for water, setting up pilot plant to investigate intended process plant, or commissioning model tests of hydraulic structures.

The feasibility studies should include a close examination of the data on which the need for the project is based. Many instances could be quoted where large sums of money have been saved on a project by carrying out, at an early stage, a critical examination of the basic data the promoter has relied upon. This data has to be tested for accuracy, reliability, and correctness of interpretation.


What Is the Proper Way Of Installing Nuts and Bolts?

Washer requirements for high-strength bolted assemblies depend on the method of installation and type of bolt holes in the connected elements. These requirements are summarized in Table 7.5.

Bolt Tightening. Specifications require that all high-strength bolts be tightened to 70% of their specified minimum tensile strength, which is nearly equal to the proof load (specified lower bound to the proportional limit) for A325 bolts, and within 10% of the proof load for A490 bolts.

Tightening above these minimum tensile values does not damage the bolts, but it is prudent to avoid excessive uncontrolled tightening. The required minimum tension, kips, for A325 and A490 bolts is given in Table 7.6.

There are three methods for tightening bolts to assure the prescribed tensioning:

By means of a manual or powered wrench, the head or nut is turned from an initial snug-tight position. The amount of rotation, varying from one-third to a full turn, depends on the ratio of bolt length (underside of heat to end of point) to bolt diameter and on the disposition of the outer surfaces of bolted parts (normal or sloped not more than 1:20 with respect to the bolt axis). Required rotations aretabulated in the ‘‘Specification for Structural Steel Joints Using A325 of A490 Bolts.’’

Calibrated Wrench.
By means of a powered wrench with automatic cutoff and calibration on the job. Control and test are accomplished with a hydraulic device equipped with a gage that registers the tensile stress developed.

Direct Tension Indicator.
Special indicators are permitted on satisfactory demonstration of performance. One example is a hardened steel washer with protrusions on one face. The flattening that occurs on bolt tightening is measured and correlated with the induced tension.


What Are the Different Grades of Steel?

Structural steel grades are referred to by their corresponding ASTM designation. For example, the most commonly used grade of structural steel is A36, which is produced to meet the requirements of the ASTM A36 specification.

This grade offers a good mix of strength, weldability, and cost. In many designs, this specification alone will satisfy designers’ needs. Other specifications, such as A53 for pipe, provide an equivalent grade of steel for that type of product. However, as loads on the structural elements becomes larger, other grades of steel may become more economical because of dimensional limitations or simpler fabrication.

These grades provide greater strength levels at somewhat higher costs per unit weight. AISC recommends certain grades of steel, all of which have desirable characteristics, such as weldability and cost-effectiveness, for use where higher strength levels are required.

The specifications covering these grades are listed in Table 7.2.

Several steels have more than one level of tensile strength and yield stress, the levels being dependent on thickness of material. The listed thicknesses are precise for plates and nearly correct for shapes. To obtain the precise value for shapes, refer to an AISC ‘‘Manual of Steel Construction’’ (ASD or LRFD) or to mill catalogs.

Weathering Steels. The A242 and A588 grades of steel offer enhanced corrosion resistance relative to A36 material. These steels, called weathering steels, form a thin oxidation film on the surfaces that inhibits further corrosion in ordinary atmospheric conditions. However, special treatment of construction details is required.

Because of such constraints, and because these grades are more expensive, utilization of weathering steels in building construction is limited. These grades are more commonly used in bridge construction.

Steel Grade Identification. Because of the several grades of steel in use, ASTM specifications require that each piece of hot-rolled steel be properly identified with vital information, including the heat number. The AISC specifications for structural steel buildings require fabricators to be prepared to demonstrate, by written procedure and by actual practice, the visible identification of all main stress-carrying elements at least through shop assembly.

Steel identification include ASTM designation, heat number (if required), and mill test reports when specifically ordered.

Availability. Because structural steel is produced in a batch process, the less commonly used shapes and the higher-strength grades are produced less frequently than commonly used A36 shapes. Furthermore, steel service centers stock the smaller A36 shapes. As a result, availability of steels can affect construction schedules.

Consequently, steel designers should be aware of the impact of specifying less commonly used materials and shapes if the project has a tight schedule. Fabricator representatives can provide needed information.



Structural engineering, being considered a field of specialty within the realm of civil engineering, is the application of math and science to the design of structures, including buildings, bridges, storage tanks, transmission towers, roller coasters, aircraft, space vehicles, and much more, in such a way that the resulting product will safely resist all loads imposed upon it.

The design of structures has always involved theory, buttressed by testing and direct observation, and a professional engineer is able to make wise use of intuition and experience to bring theoretical truths into reality.

In order to develop an adequate understanding of structures that are designed, an engineer must make justifiable approximations and assumptions in regards to materials used and loading imposed and must also simplify the problem in order to develop a workable mathematical model.


What Are Foundation Analysis Computer Programs?

A large number of foundation engineering problems can be efficiently analyzed and/or designed using a digital computer. Particular advantages of using a computer accrue from these features:

1. One is able to try a range of problem variables to obtain a feel for the effect of specifying, or using, a particular set of soil parameters.

2. One can avoid having to use tabulated data or plotted curves, which usually require interpolation and excessive simplification of the foundation model.

3. One can minimize computational errors from these sources:
a. Erroneous key entry when using a calculator. The bad entry is (or should be) output to paper using a computer so the input can be checked.

b. Omission of computational steps. A working computer program usually includes all the design steps. A set of hand computations may not include every step for any number of reasons (forget, not be aware of, carelessness, etc.).

c. Calculator chip malfunction not readily detected except by using two calculators. Computer chips are often internally checked on power-up, or output is so bad that chip errors are visually detected.

4. With output to a printer one has a paper record of the problem for office files without the necessity of transcribing data from intermediate steps. This avoids copy errors such as 83 for 38 and the like.

The major disadvantage of using a computer program is that it is difficult to write a first generation, error-free program of real use in a design office. Program usability tends to increase with each revision (or history) level.

With the current wide availability of computer programs—many, such as those on the included diskette, having a "history"—the advantages gained from program use far exceed any perceived disadvantages.

The author suggests that both geotechnical and foundation engineers should use computer programs whenever possible—and certainly be aware of what computer program(s) each is likely to use for the given project.

This statement is made with full awareness of the possibility of program errors (or "bugs"). Fortunately, most geotechnical software is task-specific so that the possibility of program errors or their not being detected is not so likely as for some of the large finite-element or structural analysis programs that purport to solve a wide range of tasks.

In any case, the author cannot recall a single reported foundation design failure that can be attributed to a bad4 computer program. It should be evident that computer programs vary widely in perceived quality, perceived quality being defined here as problem limitations and "ease of use." Both users and programmers should be aware that it is difficult to predefine the full range of problem parameters likely to be encountered in practice, so nearly any geotechnical program of significant value is likely to have some built-in limitations.

Ease of use is highly subjective and depends more on user familiarity with a program than how easy it really is to use—many users like pulldown menus and graphics whereas others are quite content without these features. As a final comment on computer programs, be aware that although business applications and games usually have a market in the hundreds of thousands, geotechnical programs have a potential market of only a few thousand.

This small market means geotechnical software is likely to be more expensive than other software and, to minimize development costs, it is not likely to have many so-called user-friendly features.

One should routinely check the output from any computer program used for design or analysis. The user is responsible for his or her design since it is impossible to write a computer program with any usefulness that cannot be misused in some manner. Primarily for this reason most computer programs are sold or licensed with a disclaimer making the user responsible.

Fortunately, most computer programs can be written to be somewhat self-checking, either by writing back the input data or by providing output that can be readily identified as correct (or incorrect) if the user understands or knows how to use the program. It should go without saying that, if you do not know much about the specific problem being designed or analyzed, you should first do some preliminary study before using a computer program on it.


What Is Foundation Engineering

The title foundation engineer is given to that person who by reason of training and experience is sufficiently versed in scientific principles and engineering judgment (often termed "art") to design a foundation. We might say engineering judgment is the creative part of this design process.

The necessary scientific principles are acquired through formal educational courses in geotechnical (soil mechanics, geology, foundation engineering) and structural (analysis, de-sign in reinforced concrete and steel, etc.) engineering and continued self-study via short courses, professional conferences, journal reading, and the like.

Because of the heterogeneous nature of soil and rock masses, two foundations—even on adjacent construction sites—will seldom be the same except by coincidence. Since every foundation represents at least partly a venture into the unknown, it is of great value to have access to others' solutions obtained from conference presentations, journal papers, and textbook condensations of appropriate literature.

The amalgamation of experience, study of what others have done in somewhat similar situations, and the site-specific geotechnical information to produce an economical, practical, and safe substructure design is application of engineering judgment.

The following steps are the minimum required for designing a foundation:
1.       Locate the site and the position of load. A rough estimate of the foundation load(s) is usually provided by the client or made in-house. Depending on the site or load system complexity, a literature survey may be started to see how others have approached similar problems.

2.       Physically inspect the site for any geological or other evidence that may indicate a potential design problem that will have to be taken into account when making the design or giving a design recommendation. Supplement this inspection with any previously obtained soil data.

3.       Establish the field exploration program and, on the basis of discovery (or what is found in the initial phase), set up the necessary supplemental field testing and any laboratory test program.

4.       Determine the necessary soil design parameters based on integration of test data, scientific principles, and engineering judgment. Simple or complex computer analyses may be involved. For complex problems, compare the recommended data with published literature or engage another geotechnical consultant to give an outside perspective to the results.

5.       Design the foundation using the soil parameters from step 4. The foundation should be economical and be able to be built by the available construction personnel. Take into account practical construction tolerances and local construction practices. Interact closely with all concerned (client, engineers, architect, contractor) so that the substructure system is not excessively overdesigned and risk is kept within acceptable levels. A computer may be used extensively (or not at all) in this step.

The foundation engineer should be experienced in and have participation in all five of the preceding steps. In practice this often is not the case. An independent geotechnical firm specializing in soil exploration, soil testing, design of landfills, embankments, water pollution control, etc. often assigns one of its geotechnical engineers to do steps 1 through 4.

The output of step 4 is given to the client—often a foundation engineer who specializes in the design of the structural elements making up the substructure system. The principal deficiency in this approach is the tendency to treat the design soil parameters—obtained from soil tests of variable quality, heavily supplemented with engineering judgment—as precise numbers whose magnitude is totally inviolable.

Thus, the foundation engineer and geotechnical consultant must work closely together, or at least have frequent conferences as the design progresses. It should be evident that both parties need to appreciate the problems of each other and, particularly, that the foundation design engineer must be aware of the approximate methods used to obtain the soil parameters being used. This understanding can be obtained by each having training in the other's specialty.

To this end, the primary focus of this text will be on analysis and design of the interfacing elements for buildings, machines, and retaining structures and on those soil mechanics principles used to obtain the necessary soil parameters required to accomplish the design. Specific foundation elements to be considered include shallow elements such as footings and mats and deep elements such as piles and drilled piers.


What is Stress - Strain Relations?

Materials deform in response to loads or forces. In 1678, Robert Hooke published the first findings that documented a linear relationship between the amount of force applied to a member and its deformation.

The amount of deformation is proportional to the properties of the material and its dimensions. The effect of the dimensions can be normalized. Dividing the force by the cross-sectional area of the specimen normalizes the effect of the loaded area.

The force per unit area is defined as the stress in the specimen (i.e., ). Dividing the deformation by the original length is defined as strain of the specimen (i.e., length/original length). Much useful information about the material can be determined by plotting the stress–strain diagram.

Figure 1.2 shows typical uniaxial tensile or compressive stress–strain curves for several engineering materials. Figure 1.2(a) shows a linear stress–strain relationship up to the point where the material fails. Glass and chalk are typical of materials exhibiting this tensile behavior.

Figure 1.2(b) shows the behavior of steel in tension. Here, a linear relationship is obtained up to a certain point (proportional limit), after which the material deforms without much increase in stress.

On the other hand, aluminum alloys in tension exhibit a linear stress–strain relation up to the proportional\ limit, after which a nonlinear relation follows, as illustrated in Figure 1.2(c).

Figure 1.2(d) shows a nonlinear relation throughout the whole range. Concrete and other materials exhibit this relationship, although the first portion of the curve for concrete is very close to being linear.

Soft rubber in tension differs from most materials in such a way that it shows an almost linear stress–strain relationship followed by a reverse curve, as shown in Figure 1.2(e).