Sunday, May 13, 2007

THE SPUN PRESTRESSED CONCRETE PRODUCT

The spun concrete products (poles and piles) offers an improved technology that combines the benefits of centrifugal casting with those of prestressing and high strength concrete in the manufacturing process. Spinning is the highlight of the manufacturing process. During spinning the fresh concrete is subjected to very high centrifugal forces that compact the material against the interior of the steel mold and expel excess water in the mix. The overall porosity of the material is therefore reduced, and as a result the hardened concrete is exceptionally dense and is high strength. The higher strength is attributed mainly due to the lower w/c and the higher density of the concrete after spinning.

MATERIAL

The Poles are designed as member subjected primarily to flexure. Axial load effects should be considered since large considered since large secondary moments may occur due to the deflection of the pole. In the case of guyed poles, the axial loads may be large enough that the pole should be treated as a compression member. Shear and torsion may be significant in some cases but seldom control the design.
The piles are designed as member subjected to axial and flexure. Both axial load and flexure should be considered together because this component is used as part of the foundation, and they support the gravity load as well as the lateral loads which cause bending and shear action on it (earthquake). The codes used as the standard design are JIS A 5335, ACI 543, and Indonesian Concrete Codes (PBI).
Currently concrete design strength range from 50 to 65 MPa. In many cases; however, spun cylinders are made to take advantage of the increased compressive strength due to spinning. The reinforcing steel cage is composed of main and secondary steel. High strength, wire prestressing strand or prestressing wire oriented in the longitudinal direction comprise the main steel reinforcement. Closely spaced spiral steel wire wrapped around the strands provides the necessary secondary reinforcement. The spiral reinforcement, which is normally 5-mm diameter, with yield strength up to 400 MPa, is needed to resist temperature stresses, transfer forces at end parts, and contribute to the torsion and shear strength of the member.

The spun prestressed concrete pole and pile.

they are made in the similar procedure and process of production. The difference between pole and pile is only in the physical dimension and their function/ application. The pole usually has different diameter on the top and the bottom part (conical shape), while the pile has the same diameter for the whole part (cylindrical shape). The pole is an upper ground structure, while the pile is an underground structure. The applications of the pole include decorative street lighting, distribution poles, rail electrification, support for high voltage transmission poles, communication towers, and wind turbine support structure. The pile is used as a deep foundation.

DELIVERY

Truck transportation is the most common method used to haul the concrete poles and piles to the jobsite. Rail and barge are also utilized when feasible or necessary. At the jobsite a crane removes them from the truck using a spread yoke or spreader bar. Typically a two-point pickup are provided to handle poles and piles by crane in horizontal position; however, during erection they are usually handled from one-point pickup at or the center of gravity.
Segmental construction is also used and preferred where it is difficult to transport the full length member or when the poles are to be erected in the congested areas. The poles and piles are made of shorter segments and then assembled at the site using one of several splicing methods.

PRECAST CONCRETE WALL PANELS

Precast wall panels, particularly architectural precast panels, enjoy widespread popularity because of their construction efficiency and esthetic possibilities through the use of aggregates, veneer facing materials, varying shapes, size and texture. The comprehensive report prepared by ACI Committee 533, Precast Panels, focuses on precast concrete wall panels that are produced in established precasting plants, although site precasting is an alternative fabrication method. The ACI 533R-93 should be used together wit ACI 318 "building Code Requirements for Reinforced Concrete", which may be legally binding. The guide covers both load-bearing and non-load-bearing panels. These can be fabricated of either normal weight or lightweight concrete, and may be solid, insulated, ribbed, hollow core, or sculptured. Any of panels can be reinforced with deformed bars, or welded wire fabric, or prestressing tendons.

MATERIAL

Precast concrete panels are fabricated and erected using the same basic materials as for all concrete construction: Portland cement, fine and corse aggregates, admixtures, inserts, insulating materials, and specialty coatings to enhance esthetic appearance.

Architectural precast panels are often made of two types of concrete because of the cost of decorative aggregates and white cement. A backup, or structural, concrete is used for most of the panel thickness, and the concrete for the exposed face of the panel thickness, and the concrete for the exposed face of the panel is selected for its architectural appearance.

DESIGN

Non-load-bearing panels, often called cladding, are in general not significantly different from load bearing wall panels. For design purposes, non-load-bearing panels are assumed to transfer negligible load from other elements. Handling, storage, transportation, and erection consideration are identical for all precast panels. Thermal movement and other volume change effects of the panels are likewise identical for both classes. The codes adopted for designing precast concrete panels are ACI 553R-93 and ACI 318-94.

FABRICATION AND DELIVERY

Concrete mix proportioning is generally the same as cast-in-place concrete, but greater emphasis is placed on the ability of the mix to produce the desired finish and durability of the concrete surface. Factors to be considered in the concrete mix are:
- Finish, size and shape of the precast units.
- Method of consolidation.
- Maximum size of coarse aggregate.
- Required comprehensive strength.
- Required surface finish.
- Exposure to severe and the other condition.
Handling and storage procedures should not cause structure damage, detrimental cracking, architectural impairment, or permanent distortion when a panel is being lifted or stripped from the mold, moved to various location for finishing or storage, stored, or loaded or unloaded for delivery and erection. Structural calculation should verify that the panel can be handled in the desired manner, otherwise it should be braced during stripping, handling, transportation and delivery operation.

PRECAST CONCRETE PRODUCTS

There are several reasons why precast concrete is particularly suitable for an intensive building components. Precast construction is a I building process ideally suited for the future. Materials are relatively inexpensive and the method of construction, involving factory manufacture of components and rapid site erection, lends itself to innovation in design and construction.

Advanced technology, including robotics and the use of computer aided manufacture, will lead to more efficient erection procedures. The potential for significant reductions in building cost is apparent. The high technology or low labor content aspect make it suitable for any conditions and technological strengths, without necessarily losing the flexibility of construction form that has resulted from mass produced "system building" developed in countries that are technological less advanced.

The advantages of using precast concrete products as building components:

Quality control:

High precision machinery and mould impose a schedule and a discipline. Higher tolerances, more accurate measurements, with less maintenance (because of high performance concrete), and material waste and greater consistency of finishing and results.

Production Control:

Programmed production, time delivery, and/or erection lessen the need for large stock inventoried left in the factory or on the site. Construction is faster on the site where a more efficient order of building components sequences can be maintained.

Inventory Control:

The thight inventory controls possible in a factory setting, over small-piece building material and components virtually eliminates the high rates of theft and vandalism on the site.

Labor Control:

More extensive use of unskilled labor is possible in the factory because of improved supervision (one foreman can adequately supervise more men) and because of the quality control inherent in the machinery or in the factory.


Climate Control:

Factory conditions release certain areas from the "building session" limitation imposed by their climate conditions. A permanent labor force that can be employed when days lost bad weather are minimized also reduces cost of training and initiation to jobs.


Problem Control:

the detailed appraisal of constructional problems before work begins results in fewer delays in construction after commencement on the site.

PRECAST CONCRETE FOR LOW COST HOUSING PROJECT

Recently, some conrete product manufactures propose Low Cost Housing model of structure. The five stories building for Low Cost Housing provides general facility room on the first floor and apartments on the upper floors. The building is designed as a bearing wall type of structures using prefabricated concrete panels. All gravity load and lateral loads are supported wall two-way wall system, which is tightened vertically and horizontally together. The lateral loads are transmitted from one wall to another wall by a rigid diaphragm floor slab. Other structural components, like: foundation, tie beam and stairs are prefabricated products. All components jointed vertically using "wet joint type of connection ”(grouting) and horizontally using "dry type of connection" (welded).

MARINE STRUCTURES

There are some projects recognized as a state-of-the-art of using precast concrete used in their construction method. It can be mentioned some of them; for examples: The Ocean Going and the Inter-island Harbors in Surabaya, and the Breakwater/Pier Structure at U.S. Naval Station Everett in Washington which received the 1998 PCI Design for the best Miscellaneous Structure. Precast/prestressed concrete provided a cost-effective solution that is both functional and aesthetic for marine/naval facility situated in a difficult and environmentally sensitive coastal area. It can be adapted to similar structural applications in aggressive marine environments. Another important reason for the success of those projects is that high quality precast/prestressed concrete products, manufactured under controlled "factory conditions", were delivered by the producers/contractors to the site on schedule.

The use of precast/prestressed concrete for the marine structures provided for the following benefits:

  1. Giving an aesthetically pleasing structure
  2. Low in maintenance for highly functional structure
  3. Limited environmental impact
  4. Durability in an aggressive marine environment
  5. A fast track construction schedule
  6. A cost effective in an integrated structural system.

FRAME AND SHEAR WALL BUILDING

People always ask how about the use of the precast/prestressed concrete components in the high seismic region. It can be informed in this occasion that on August 9, 1999, The University of California - San Diego had an experimental program for their PRESS Research (Precast Seismic Structural Systems). It is to view the seismic testing of a five-story precast, prestressed concrete frame and shear wall building. The preliminary result is that in general the seismic frames performed very well with the base shear continuing to increase even at a maximum drift. The performance of the prestressed frame was particularly good. Damage to beam-column connections was minimal in all frames. The results obtained from this research will be used to develop design guidelines that emphasize the inherent advantages of precast, prestressed concrete system in various seismic zones. These guidelines can then be incorporated into various building codes.

CONCRETE CORRUGATED SHEET PILE (CCSP)

Prestressed Concrete Corrugated Sheet Piles (CCSP) can be used for port structures, river rieetment, sewerage, earth retaining walls and many other uses and were developed as a substitute for steel sheet piles. Because of there corrugated cross section, CCSP have better capabilities and are cheaper than conventional steel sheet piles. In particular, corrugated sheet piles perform at their best when being driven in; they can be placed with greater accuracy. Many users are already using CCSP and their excellent performance has been highly appreciated. These piles will satisfy for all structural demands.

Materials.

Currently, the specified concrete strength used is 60 Mpa. Prestressing steel used for pretensioned member is either 15.2 or 12.7 mm diameter low relaxation strand with ultimate strength of 1900 MPa. Because the high performance concrete is protected against penetration of oxygen and chloride, durability against corrosion is very high under soil and water condition. High quality of vinyl chloride material is used for expansion joints and water stops, and this can protect spilling sand, leakage of dirty water and grass growing.

Design.

The CCSP is designed based on JIS A 5354-1993

BRIDGE GIRDER

Nearly 50 years have elapsed since precast, prestressed concrete was the first introduced in the construction industry. During this period, precast, prestressed members have been utilized mainly in bridge system. The high quality of precast, prestressed concrete makes it the material choice for short to medium span bridges. Of the system described here, only post tensioned I girders are used with structural "half-slab system" to produce a composite deck system.

PRODUCTION

Bridge girders can be produced segmentally or unsegmentally. The segmental precast girder, or shortened as segmental bridge girder, is a development of the precast system by exploitation of the prestressed implementation system in the manner of the post tensioning. The main purpose of this segmental system is to facilitate the transportation of the members from the plant/ production location to the jobsite. The segmental part length is limited to the maximum of 6 m and the maximum weight of 8 tons so that it can be handled and transported by using light trucks to reach the remote location.

MATERIALS

Selection of the concrete strength and type of prestressing steel is influenced by the type of girder and construction procedure adopted. A concrete compressive strength of 50 MPa is used for the girders since a high degree of quality control is maintained at the precasting plant. Precast concrete slab and diaprragm have a concrete strength in the 30 MPa. Prestressing steel used here is 12.7-mm diameter low relaxation strand with an ultimate strength of 1900 MPa.

DESIGN CONCEPT

Flexural design of prestressed concrete girders is primarily based on the working stress method with the flexural strength checked, similar to the approach taken by American Association of State Highway and Transportation Officials (AASHTO) Specification. Design for shear and diagonal tension involves both working stress and strength design calculation. The formulas are somewhat similar to those used in the United States. If the section requires shear reinforcement, it may provide in the form of mild steel reinforcement. Some codes are adopted as the basic design, such as: SKBI-1.3.28.87, Indonesian BMS 1992, Indonesian Concrete Code, ACI 343-77, AASHTO, CP 110-1972.

ADVANTAGES OF CONCRETE CORRUGATED SHEET PILE (CCSP)

High Strength and high quality

CCSP are manufactured using the highest production techniques in plants where quality control is strictly enforced.

High performance and economics

High strength material is used. At the same time, the use of corrugated cross section makes them mechanically efficient while reducing weight. This allows PC Corrugated Sheet Piles to be produced very economically.

CCSP have no front or back making handling easier

Since a PC Corrugated Sheet Pile has no front or back, they can be used in various applications. No special instructions are needed for carrying, temporarily placing or lifting. This makes handling easy and reduces placement errors.

Large CCSP can be manufactured

Large or long CCSP can be manufactured from prestressed concrete (PC) without problems.

Completely free from rust and corrosion; make them useable even in marine structures

Since the piles are prestressed, there is no cracking. Also, they can be used for ocean structures in accordance with Standard Concrete Specification requirement, especially sever corrosive environment.

Can be made watertight

Using newly developed highly elastic vinyl chloride sealing materials, sheet piles can be sealed to prevent sand being sucked out, discoloration from water leaks and growth of weeds joints.

Excellent workability

Sheet piles can withstand a high tensile force, allowing them to be pulled out after driving; and are suited to mechanical construction work involving many kinds of machines, even vibro hammer, because they are made of prestressed concrete.

High driving accuracy

Because of corrugated cross section of the sheet piles, resisting planes are large in the lateral direction and the normal direction so that there is less tilting or overturning.

Small displacement (deflection) at the head of sheet piles

Even in case of self-standing sheet pile retaining walls, the displacement at the head portions is smaller than for other types, because the moment of inertia is large since the cross section is a wave form. This makes higher retaining walls possible.

Saturday, May 12, 2007

PRESLAB : QUALITY CERTIFICATE

Type & Dimension :

Width : 1.00 m up to 2.485 m

Length : 1.00 m up to 6.00 m

Spesification of Material :

  1. Portland Cement Type I according ASTM C150
  2. Aggregate according ASTM C33
  3. Water according ASTM C94
  4. Fly Ash according ASTM C618
  5. PC Single Wire according JIS G3536 4 phase Indented Low Relaxation
  6. Concrete strength according ACI 318
Concrete Mix Design Data
  1. Slump on site 16 +/-2 cm
  2. Water cement ratio 0.38
  3. Free water required +/- 6.75%
  4. Cement +/- 15%
  5. Fly Ash +/- 2.625%
  6. Additive F Type +/- 3 litres/m3

PRELAB : TECHNICAL DATAS

Thickness :

  • 60 up to 120 mmConcrete Strength :

K-350 up to K-450Scope of Work :

  • Design, Production, ErectionType Of Product :

Square and FlexibleType of Project :

  • Building, Housing, Jetty and Harbour, Deck SlabPretension System & Non-Prestressed Expose Bottom Surface

PC I GIRDER

Technical Datas :
Type of Girder - Prestressed Concrete I Girder
Prestressing System - Post-tension and Pre-tension
Post-tension System - VSL System, DSI System, etc
Production System - Segmental and Monolith
Concrete Strength - K500 up to K600
Dimension :
Height - 0.9 m : Width - 0.65 m
Height - 1.25 m : Width - 0.65 m
Height - 1.6 m : Width - 0.65 m
Height - 1.7 m : Width - 0.7 m
Height - 1.85 m : Width - 0.7 m
Height - 2.1 m : Width - 0.7 m
Center to center girder depends requested on design

PRESLAB | PRETENSION HALF SLAB

APPLICATION
PC preslab is used in every conceiveable type of building and can be utilized with any wall bearing or framing system
SOUND PROOF
PC preslab concrete floor slab is resistant to air borne noise and transmission of impact noise and provides qualities of a solid concrete slab for quieter building and more privacy.
FINISHED CEILINGS
PC preslab has an excellent appearance, due to the form smooth concrete minor caulking of the joint and a coat of paint achieve and attractive ceiling.
EARTHQUAKE RESISTANCE
The place of steel in both directions and the addition of connecting muss allow the PC preslab to be erected in seismic areas and for the construction of high rise building.
ECONOMY
The use of PC precast preslab will result in a lower total construction cost for any project. This economy can be found in the reduction of steel and concrete and elimination of formwork at the job site. The strength of the PC preslab section allows minimal temporary supports and the preplanning of their location below the stay-in place PC preslab forms enables the work of other trades to proceed immediately and with safety. Field operation is highly simplified.
PRODUCTION FACILITIES
The PC preslab is produced on automated beds either indoors or outdoors. When it appears necessary, the beds can be moved from site to site.FIRE RESISTANCEPC preslab has one and two hour tire ratings and three to four ratings can be obtained with additional coating