Methods of Piling

Other Methods of Piling

1. Jetting Piles - water jetting may be used to aid penetration of a pile into a sand gravel stratum. It is ineffective infirm to stiff clay or soils containing much coarse gravel, cobbles or boulders.

2. Pile Driving by Vibration - vibratory methods of driving sheet piles or bearing piles best suited to sandy or gravelly soils. Pile driving vibrators consist of pair or exciters mounted on the vibrator unit, the motors of each pair rotating in opposite directions. The amplitude of vibrations is sufficient to break down the skin friction on the sides of the pile. Vibrators will drive steel piles through loose to medium dense sands and gravel with comparative ease, but there are likely to be difficulties with dense sands, where energy may be insufficient to displace the material to permit entry of the pile. Vibrators can also be used for extracting piles and are frequently used connection with large diameter bored and cast-in-place piling work for sinking and extracting pile casings.

3. Pile Driving over Water - piles for jetty or wharf structures built over can be driven from specially designed pile frames cantilevered out from the permanent piles already driven, from ordinary pile frames operating from temporary piled trestles, from jack-up barges or from floating plant.

4. Pile Driving through difficult ground - these methods include boring a hole sufficient diameter through the difficult ground to receive the pile. In loose ground, the hole may have to be cased which sometimes leads to difficulties with extraction of the casing. Another method is to drive a heavy steel spud or joist section through the ground and to drive the pile through the loosened soil left after withdrawing the spud. Another is through the use of diamond core drills.

5. Test Piling - whenever possible, test piles should be of the same type and dimensions as the permanent piles which are intended to be used. This is the only way to ensure that the designed penetration will be attained and that the designer's estimate of the safe working load can be checked when the piles are subjected to test loading.

Read more »

Pile Driving Equipment

Pile Driving Equipment

1. Piling Rigs. Piling Rigs consist of a set of leaders mounted on a standard crane base. The leaders consist of a stiff box or tubular member which carries and guides the hammer and the pile as it is driven into the ground. The leaders can be raked backwards and forwards by screw or hydraulic adjustment of the back stay and lower attachment to the base machine.

2. Piling Winches. Winches operating with pile frames mounted on barges or fixed stagings may be powered hydraulically or by steam, diesel pr petrol engines, or electric motor. Steam powered winches are commonly used where steam is also used for the piling hammer. Light winches may only have a single drum, but double and triple drum winches which can raise hammer and pile separately are more useful where speed of handling and driving is desirable. The winches may be fitted with reversing gears so that in addtion to their main purpose of lifting hammer and pile, they can also carry out the auxiliary function of the operating the raking, rotating and travelling gear.

3. Hanging Leaders. Hanging leaders are designed for suspension from the jib of a crane or excavator. A steel strut, capable of adjustment in lengths, forms a rigid attachment from the foot of the leaders to the bed-frame of the machine.

4. Hammer Leaders. In situation where it is desirable to dispense wholly with piling frames or hanging leader, hammer guides or rope-suspended leaders can be attached to the piles and the latter are guided by timber or steel frameworks.

5. Piling Hammers. The selection of suitable hammer for a piling project depends on a number of factors including the size and weight of the pile. The driving resistance which has to be overcome to achieve the design penetration, the available space and headroom on the site and the availability of the cranes and the noise restrictions which may be in force in the locality.

6. Helmet, driving cap, dolly and packing

A steel helmet is placed over the top of the concrete pile in order to hold the resilient dolly packing which are interposed between the hammer and the pile to prevent shattering of the latter at the head.

The dolly is placed in a square recess in the top of the helmet. It is square at the base and rounded at the top. Elm dollies are used for easy to moderate driving and for hard driving a hardwood. Plastic dollies car, withstand much heavier driving than timber dollies.

Packing is placed between the helmet and the top of the pile to cushion the blow between the two. Various types of material are used such as hessian and paper sacking, thin timber sheets, coconut matting, saw dusts in bags and wall  board.

Driving caps are used to protect the heads of steel bearing piles. They are especially shaped to receive the particular type of pile to be driven and are fitted with recess for a hardwood or plastic dolly and with steel wedges to keep the caps tight on the pile. A cheap from of cushioning consists of scrap wire rope in coils or in the form of short pieces of laid cross-wise in two layers.

Read more »

Piles

Piles

Piles are used to transmit foundation loads through strata of low bearing capacity to deeper soil or rock strata having a high bearing capacity. Piled are also used in normal ground condition to resist heavy uplift forces or in poor soil condition to resist horizontal loads. Piles are convenient method of foundation construction works over water such as bridge piers or jetties.

Classification of Piles

Piles are classsified according to their carrying capacity,

1. End-bearing Piles - carrying capacity derived from toe of the piles.

2. Friction Piles - are piles which derive their carrying capacity by skin friction or adhesion. the piles do not reach an impenetrable stratum but are driven for some distance into a penetrable soil.

Types of Piles

1. Driven Piles - preformed units such as timber, concrete, steel, driven into the soil by the blows of a hammer.

2. Driven and Cast-in-place Piles - formed by driving a tube with a closed end into the soil and filling ethe tube with concrete. The tube may or may not be withdrawn.

3. Jacked Piles - steel or concrete units jacked into the soil.

4. Bored and Cast-in-place Piles - piles formed by boring hole into the soil and filling it with concrete.

5.  Composite Piles - combination of two or more of the preceding types, or a combination of different materials in the same type of pile.

Considerations in the Selection of Piles

1. Location and type of structure
2. Ground conditions
3. Durability
4. Final selection is made from considerations of overall cost.

Read more »

Preparation of Foundation

Site Investigation

A site investigation is required for any engineering or building structure. The investigation may range in scope from a simple examination of the surface soils with or without a few shallow trial pits to a detailed study of the soil and ground water conditions to a considerable depth below the surface.

Three Geotechnical Categories

1. Category 1 - light structures such as buildings with column loads up to 250 KN or walls loaded to 100 KN/m, low retaining walls, single and or two-storey houses.

2. Category 2 - structures for which quantitative geotechnical studies are required with the involvement of qualified engineers with relevant experience. Conventional substructures such as shallow spread footing, rafts and piles, retaining walls, bridge piers and abutments, excavations and excavation supports and embankments. A two-stage investigation is required for this category. The first stage includes boreholes, in-situ tests, and laboratory tests. The second stage is a detailed study of the ground-water conditions is required.

3. Category 3 - structures include buildings with exceptional loads, multi-storey  basement, dams, large bridges and tunnels, heavy machinery foundations and offshore platforms. Structures located on expansive or collapsing soils or in areas of exceptionally high seismic activity.

Subsurface Soil Exploration Methods

1. Trial Pits. Trial pits are generally used for category 1 investigations. They are useful for examining the quality of weathered rocks for shallow foundations.

2. Hand & Mechanical Auger Borings. Hand & mechanical auger borings are also used for category 1 investigations in soils which remain stable in an unlimited hole. When  carefully done augering causes the least disturbance of any boring method.

3. Light Cable Percussion Borings. Light cable percussion borings are used in British practice. It is well suited to the widely varying soil conditions in Britain, including the very stiff or dense stony glacial soils and weathered rocks of soil-like  consistency.

4. Rotary Open Hole Drilling. Rotary Open Hole drilling is generally used in the USA, Middle East and Far Eastern Countries. The rotary drills are usually tractor or skid-mounted and are capable of rock drillings as well as drilling in soils. Hole diameters are usually smaller than percussion drilled holes and sample sizes are usually limited to 50 mm diameter.

5. Wash Borings. Wash borings are small holes 65 mm in diameter drilled by water flush aided by chiselling.

6. Wash Probings. Wash probings are used in over-water soil investigations. They consist of a small-diameter pipe jetted down and are used to locate rock head or a strong layer overlain by loose or soft soils, i.e., investigations for dredging.

Types of Foundations

1. Pad Foundations. Pad foundations are used to support structural columns. They may consist of a simple circular, square, or rectangular slab of uniform thickness or they may be stepped or haunched to distribute the load from a heavy column. Pad foundations to heavily loaded structural steel columns are sometimes provided with a steel grillage.

Types of Pad Foundations

a. Mass concrete for steel column
b. Reinforced concrete with s/loping upper surface
c. Plain reinforced concrete.
d. Stepped reinforced concrete.

2. Strip Foundations. Strip Foundations are normally provided for load-bearing walls and for rows of columns which are spaced so closely that pad foundations would nearly touch each other.

3. Wide Strip Foundation. Wide strip foundations are necessary where the bearing capacity of the soils is slow enough to necessitate a strip so wide that transverse bending occurs in the projecting portions of the foundation beam and reinforcement is required to prevent cracking.

4. Raft Foundations. Raft foundations are required on soils of low bearing capacity, or where structural columns or other loaded areas are so closed in both directions that individual pads would nearly touch each other. raft foundations are useful in reducing differential settlement on variable soils or where there is a wide variation in loading between adjacent columns or other applied loads.

5. Bearing Piles. bearing piles  are required where the soil at normal foundation level cannot support ordinary pad, strip or raft foundations or where structures are cited for deep filling which is compressible and settling under its own weight. Piled foundations are a convenient method of supporting structures built over water or where uplift loads must be settled.

Read more »

Architect or Civil Engineer??

Well? This is an issue between the architecture and engineers but seems there are no clear conversations about this. What should be the responsibilities and tasks by the two profession when it comes to planning of a certain structure? 


Anyway, what is architecture? According to Wikipedia, Architecture is both the process and product of planning, designing and construction. Architectural works, in the material form of buildings, are often perceived as cultural and political symbols and as works of art. Let's study the words "planning, designing and construction", planning is the foundation of a proposed project, this is were the layout and placing of the different part of the structure is being planned, designing consist of the aesthetic part of the building and how about the construction, construction is the actual practice of performing the plan. Architects are not taking an important role in the construction, since in order to be successful in a certain project, we need skilled laborers for the construction.


What is Civil Engineering? Again, according to Wikipedia, Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings. A civil engineer takes an important role in the design of the project, for an engineer is responsible in the allocation of materials to be used in the design of the structure, the availability and cost of the materials used in the building of the structure. Maintenance is also a task to be made by the engineer since engineer plans the internal reactions of the columns, slabs, floors etc, for the safety of the people who will use the structure.


Architects and Civil Engineers both play an important role to accomplish a certain project. It doesn't matter whether both of the profession takes bigger responsibility, important is they should be concern of the good result of the project. ^^

Read more »

Loaders

Types of Loaders

1. Crawler-tractor Loader

2. Wheel Tractor-mounted Loader

Read more »

Rippers

Rippers

Rippers are equipment attached to a tractor used to break rocks.

Types of Rippers

1. Tractor-mounted hydraulically operated type
2. Towed Type

Types of Rippers according to Linkage

1. Parallel-type linkage
2. Hinge-type linkage

Rippability of Rocks

Rippability of most types of rocks is related to the speed of sound to which it travels through the rock. Geo-physical equipment is measured sound wave in rocks. Rocks which propagate sound waves at low velocities are rippable. The number of shanks used depends on the following:

1. size of the tractor used
2. the depth of penetration desired
3. the resistance of the material being ripped
4. the degree of breakage of the material desired.

Prior to selecting the method of excavating and hauling rock, it is desirable to determine if the rock can be ripped or if it will be necessary to drill and blast.

Read more »

Clearing Lands

Clearing Lands

Clearing lands may be divided into several operations, depending on the type of vegetation, the condition of the soil and topography, the amount of clearing required, and the purpose for which the clearing is done, as listed below,

1. Removing all tress and stumps, including roots.
2. Removing all vegetation above the surface of the ground only, leaving stumps and roots in the  ground.
3. Disposing of vegetation by stacking and burning it.
4. Knocking all vegetation down, then chopping or crushing it or onto the surface of the ground or burning it later.
5. Killing or retarding the growth of brush by cutting the roots below the surface of the ground.

Types of Equipment used for Clearing Operations

1. Tractor-mounted Bulldozer

2. Tractor-mounted Special Blades

3. Tractor-mounted Rakes

4. Tractor-pulled Chains and Cables

Read more »

Bulldozers

Bulldozers

A bulldozer is a crawler equipped with a substantial metal plate (known as a blade) used to push large quantities of soil, sand, rubble, etc., during construction work and typically equipped at the rear with a claw-like device (known as a ripper) to loosen densely-compacted materials.
--Wikipedia


Bulldozers are classified according to the type of mounting.


1. Crawler Mounted Bulldozer

2. Wheel Mounted Bulldozer


Bulldozers are classified according to the method of raising and lowering the blade.


1. Cable-controlled Bulldozer
2. Hydraulically-controlled Bulldozer




Uses of Bulldozer


1. Clearing land of timber and stumps.
2. Opening up pilots roads through mountains and rocky terrain.
3. Moving earth from haul distances up to approximately 100 meters.
4. Helping load tractor-pulled scrapers.
5. Spreading earth fill.
6. Backfilling trenches.
7. Clearing construction sites of debris.
8. Maintaining haul roads.
9. Clearing the floors of borrow and quarry pits.


Advantages claimed for the Crawler-Mounted Bulldozer


1. Ability to deliver greater tractive effort, especially in operating on soft footing, such as loose or muddy soil.
2. Ability to travel over muddy surfaces.
3. Ability to operate over rocky formations, where rubber ties might be seriously damaged.
4. Ability to travel over rough surfaces, which may reduce the cost of maintaining haul roads.
5. Greater flotation because of the lower pressures under the tracks.
6. Greater use versatility on  jobs.


Advantages claimed for Wheel-Mounted Bulldozers


1. Higher travel speeds on the job or from one job to another.
2. Elimination of hauling equipment to transport the bulldozer to a job.
3. Greater output, especially when considerable travelling is necessary.
4. Less operator fatigue.
5. Ability to travel on paved highways without damaging the surface.

Read more »

Tractors

Tractor


A type of equipment used to pull or push loads. It is also used as a mount for many types of accessories such as front end shovels, rippers, bulldozers blades, side-booms, hoes, trenchers and many others. The sizes and types fit almost any job for which they are usable.

Types of Tractors

1. Crawler Tractor

2. Wheel Tractor

a. Two-Wheeled

b. Four-Wheeled

Factors to be considered in selecting a Tractor


1. The size required for a given job.
2. The kind of job for which it will be used-bulldozing, pulling a scraper, ripping, clearing land, etc.
3. The type of footing over which it will operate, i.e. high tractive or low tractive efficiency
4. The firmness of the haul road.
5. the smoothness of the haul road.
6. The slope of the haul road.
7. The length of the haul road.
8. The type of work it will do after this job is completed.

Read more »

Methods of Erection

Methods of Erection

-       methods depend upon the ff. sites condition:

a.       size and shape of the members

b.      the relatuve quantities of precast and cast-in-place work.

c.       availablity of equipment

d.      etc.

-       ingenuity of the engineer in charge of wthe project plays an important role.

Examples of these in practice are the following:

a.       Choisy-le-Roi Bridge, France (Architect Jacques Ferrier of Paris)

-       Built by cantilever principle with precast hollow-box section were placed on a mobile frame running inside the structure joints by epoxy resin.

-       Post tensioning of each section through its opposite number then followed.

-       70 meters long

  

b.      King’s Avenue Bridge,  Canberra

-       2 independent bridges, 7 spans of 272 meters.

-       Span lengths are 28.5 from the abutments to 47 meters at the center.

-       The deck system comprises of 4 longitudinal prestressed T-Beams, connected by reinforced concrete deck slabs cast in situ.

-       Beams were precast in sections and stressed in full length behind the abutmen; they were then rolled out by trolleys to a launching truss, which itself was previously launched by cantilevering across the span to be erected.

-       This truss had overhead trolley gear with hydraultick jacks, which enabled the beam to be picked up one end and run out to the next pier; the truss could also traverse sideways across the bridge width to cover all girder positions.

c.       Woolloomooloo Viaduct, Sydney

-       a post-tensioned precast box girder bridge of 10 spans, 11 m wide, with a total length of 425 meters, part of which is on a 400 meters radius curve.

-       the precast segments, 2.36 meters long and the full width of the bridge, were erected by travelling gantry into falsewor, and stressed together in lengths of about 45 meters using the VSL system, each length bbeing stressed back to its predecessor, so that the completed bridge is continuously prestressed between abutments.

 

The conception of any structure in prestressed concrete requires the closest possible cooperation between the designer and the contstructor in order to acieve the best method s of erection to suits the economics of each individual project.

Read more »

Prestressing Systems and Techniques

Prestressing Systems

Prestressed concrete construction has been applied to many types of structures including bridges, buildings, dams, tunnels, elevated reservoirs, aircraft runways, floors, roofs, piles and whole variety of precast products. These are the list of prestressing systems that was adopted:

1.       Pre-tensioned Wire/Strands

-       may be either in individual molds or in a long pre-tensioning bed; stretched tendons are held by special grips until the stress is transferred to the concrete where it is maintained by bond.

2.       Macalloy System/ Stresssteel System

-       high tensile steel wires/strands are pre-tensioned and are anchored by means of nut or by wedge grips.

3.       Freyssinet System

-       high tensile steel wires/strands  assembled into cables are pre-tensioned and are secured in special anchorage cones.

4.       PSC and CCL Systems

-       High tensile steel wires/strands are stretched one at a time, and held by special grips against an anchorage plate or in an anchorage tube assembly.

5.       Magnel-Blaron System

-       High tensile steel wires/starnds are pretensioned by pairs and secured by steel wedges in special anchorage plates.

6.       BBR System

-       Fixed lengths of high tensile steel wires or strands are prefixed in common anchorage head by upsetting their ends or by wedging, and are then simultaneously pre-tensioned and anchored by nuts and shins.

7.       VSL System

-       High tensile steel strands are pretensioned and anchored individually by wedge grips in a common anchor block.

8.       Preload System for circular structures

**Each system requires a suitable jack for stretching the cables, wires, strands, or rods; and all post-tensioning systems require that the duct in which the high tensile steel tendon is carried be subsequently grouted up to prevent future corrosion.

Prestressing Techniques

-       post tensioning rods and anchorages are supplied fabricated to detail by the manufacturer, and therefore require no further work on the site except their erection in the forms.

-       post tensioning cables of all types are usually fabricated on the site by passing the wires through a spacer and binding the finished cable with tie wire or plastic tape at suitable intervals. The wwire is supplied from the manufacturer in coils 1.5 to 2 meters in diameter, from which it may be wound off directly.

-        strands are likewise supplied in coils, or on reels, from which it pays off reasonably straight. Tendons of strands may be assmebled into cables, or they may be used individually, depending upon the system of prestressing adopted.

-       tensioning of tendons are carried out with hydraulic jacks, and may be either one or both ends of a tendon.

-       trushing of test cylinders to determine the strength of the concrete before pre-stressing.

-       after prestressing, grouting of the holes from which the tendons pass through is necessary.

-       when the tendons has been stressed and grouted , lengths are cut off the ends.

-       the whole ancchorage is covered with mortar or concrete to protect it and leave a neat external appearance.

Read more »

Pre-Stressed Concrete Construction

Types of Prestressed Concrete Construction

1.       Precast complete

-       pre-tensioned factory products and post-tensioned members.

-       manufacture may take place on or off the site, and the units are lifted into place with suitable tackle. In either case the actual prestressed cannot be applied to the concrete until sufficient strength has been developed, but economy in formwork is usually possible, particularly if steam curing is applicable.

2.       Precast in sections

-       a prestressed member may be composed of a series of sections united by prestressed. This allows precasting of units which may then be transported to the site for assembly.

-       the joints between the segments are most important. In order to minimize delays in assembling the member, they may be made with Ciment Fondu, but usually epoxy mortar or cement mortar or concrete using high early strength Portland cement is satisfactory. segments must of course be precisely aligned before jointing, to permit exact location of tendons.

3.       Cast in situ

-       construction is similar to reinforced concrete work, the usual falsework and formwork being employed. To enable early stripping, the concrete is usually made with high early strength cement. With bridges a methods for saving falsework is to cast one girder at a time across the gap; after stressing, either the falsework or the girder is moved sideways to the next position.

-        

4.       Composite construction

-       Prestressed concrete elements and plain or conventionally reinforced concrete elements, interconnected structurally so that the two act integrally, may be adopted in cases where such composite construction provides an economical structure.

-       The prestressed elements may be pre-tensioned or post-tensioned,a nd may be precast or cast-in-place; the plain or reinforced concrete elements are usually cast in place.

5.       Circular structures

-       Reservoirs and similar structures may be economically built in prestressed concrete. The latter may be either wrapped round the wall with a special wire winding machine which tensions the wire as it is applied; or tendons may be laid round the wall or cast into the wall sheaths, and subsequently stressed with jacks. When tendons are on the outside of the wall, subsequent protection is obtained with a dense Gunite coating. When the tendons are buried inside the concrete they emerge  through special anchor blocks spaced uniformly round the periphery, and are protected by grouting.

Read more »

Production of High Strength Concrete

Production of High strength concrete

-       the development of the technique of making and placing high quality concrete.

Five Division of High Strength Concretes

1.       A minimum crushing strength of from 35 to 50 Mpa at 28 days for concrete subjected to normal to medium to high stresses.

2.       A minimum strength of 35 to 70 Mpa at 28 days for particularly highly stressed concrete.

3.       A minimum strength of 30 Mpa at 3 or 4 days for concrete that is to be post tensioned at an early age or precast and pre-tensioned when several days’ curing can be tolerated.

4.       A  minimum strength of 30 Mpa at 12 to 24 hours for post-tensioned concrete when earlier application of stress is required, or precast and pre-tensioned when the moulds are used once per day.

5.       A minimum strength of 30 Mpa at 4 hours or less for precast a nd pre-tensioned concrete when moulds are used twice a day.

Important points in designing a mix concretes for high strength.

1.       Don’t consider/count the lowest single test as the minimum strength for this may be because of errors in making the test. Permit a small perscentage of the test results to fall below the specified nominal strength of the test results to fall below the specified nominal minimum strength.

2.       Make the specimens in groups of three from the same mix sample in order to reduce the risks of errors in making and in testing.

3.       It is easier to work with a single graded coarse aggregate , but it may be necessary to use more than one sand, in order to maintain uniformity of grading from batch to batch, and to avoid segregation in handling prior to mixing.

4.       A sand with an appreciably higher bulk density than the coarse is more satisfactory.

5.       The maximum particle size of the sand should be less than the void size of the coarse aggregates so that the whole sand volume may be absorbed in the coarse aggregate without bulking.

6.       Cement and water-cement ratio should me the minimum that will give the desired workabilityand strength; the result will be minimum shrinkage, low permeability and high durability.

7.       The use of a water-reducing admixture is usually beneficial, but it is most important that calcium chloride admixtures shall not be used in  prestressed concrete because of the resulting corrosion of the tendons.

8.       Adequate high frequency and curing is essential for high strength concretes.

Read more »

Group A Dwellings

Minimum Requirements for Group A Dwellings

a. Dwelling Location and Lot of Occupancy

The dwelling shall occupy not more than ninety percent of a corner lot and eighty percent of an inside lot, and subject to the provisions on Easements of Light and View of the Civil Code of Phillipines, shall be at least 2 meters from the property line.

b. Light and Ventilation

Every dwelling shall be so constructed and arranged as to provide adequate light and ventilation as provided under Section 806 to Section 811 of the national Building Code.

c. Sanitation 

Every dwelling shall be provided with at least one sanitary toilet and adequate washing and drainage facilities.

d. Foundation

Footings shall be of sufficient size and strength to support the load of the dwelling and shall be at least 250 millimeters below the surface of the ground.

e. Post

The dimensions of wooden posts shall be those found in the Table 708-A: Dimensions of Wooden Posts (Annex B-1). Each post shall be anchored to such footing by straps and bolts of adequate size.

f. Floor

The live load of the first floor shall be at least 200 kilograms per square meter and for the second floor, at least 150 kilograms per square meter.

g. Roof

The wind load for roofs shall be at least 120 kilograms per square meter for vertical projections.

h. Stairs

Stairs shall be at least 750 millimeters in clear width, with a rise of 200 millimeters and a minimum run of 200 millimeters.

i. Entrance and Exit

There shall be at least one entrance and another one for exit.

j. Electrical Requirements 

An electrical installation shall conform to the requirements of the Philippine Electrical Code.

k. Mechanical Requirements

Mechanical Systems and/or equipment installation shall be subject to the requirement of the Philippine Mechanical Engineering Code.

Read more »

Metal Reinforcement

Metal Reinforcement

ACI Code on Metal Reinforcement for Prestressed Concrete

-       ASTM A416 – Uncoated Seven-Wire Stress-Relieved Strand For Prestressed Concrete

-       ASTM A421 – Uncoated Stress Relieved Wire for Prestressed Concrete

-       Alloy Steel Bars shall be 85% proof stressed, heat treated for prescribed properties, shall conform with the ff. properties:

a.       Yield Strength (0.2 % offset) 0.085%

b.      Elongation at Rupture in 20 diameters 4%

c.       Reduction of Area at Rupture 20%

Minimum Bonded reinforcement

-       Bonded reinforcement as in beams and one way slabs shall be:

As = Nc/0.5fv   or    As = 0.004A

                                where:

As = area in between the flexural tension face and the center of gravity               

                of the cross section

Nc = tensile force in the concrete ≤ 60,000 psi

End regions

-       reinforcement shall be provided on the anchorage to resist bursting, splitting and spalling.

End Blocks

-       shall be provided for end bearing or for distribution of concentrated prestressing forces.

Continous Beams

-       shall be designed for adequate strength and satisfactory behavior.

Compression members (Combine axial load and bending)

-       Shall be proportioned by the strength design method s for members without prestressing.

Lateral reinforcement

-       prestressing steel shall be enclosed by spirals ate least 10 mm diameter.

-       spacing of the ties shall not exceed 48 times the diameter or dimension of the column.

-       beams or brackets provide enclosure on all sides of the columns, the ties may be terminated not more than 7 cmbelow the lowest reinforcement.

Corrosion protection for  unbonded tendons.

-       wrapping must be continous over the entire zone to be unbonded and shall prevent intrusions of cement paste or the loss of coating materials during casting operations.

ACI Code on Post Tensioning Anchorages

-       shall develop the specified ultimate capacity of the tendons without exceeding anticipated set.

-       shall develop at least 90% of the specified ultimate capacity of the tendons.

-       anchor fitting shall be capable of transferring to the concrete a load equal to the capacity of the tendon under both static and cyclic loading conditions.

ACI Code on Grout for bonded Tendons

-       shall consist of prtland cement, sand and portable water. Admixtures may be used. Avoid using Calcium Chloride.

-       Sand if used shall conform to Specifications for Aggregate for Masonry Mortar.

-       Proportioning of the grout shall be based on the results of the tests on fresh and hardened grout prior to beginning work.

-       Ducts for grouted or unbonded tendons shall be mortar tight and nonreactive with concrete.

Shape of Prestresse Structure

1.       Double Tee

-        1.20-2.40 meter wide, thickness depends on the requirement, span extend up to 18 meters.

2.       Single Tee

-       longer span up to 36 meters with heavier loads.

3.       Channel  Slab

-       Used for floors in the intermediate span.

4.       Box Girder

-       Used on bridges of intermediate and major span.

5.       Inverted Tee Section

-       Provides a bearing ledge to carry the precast deck members having perpendicular direction of span.

Read more »