Precast Prestressed Hollow Core Slab

Introduction

A precast prestressed hollow core slab is a factory fabricated slab consisting typically of tubular voids which extend throughout the length of the slab. Hollow core slabs were invented in the 1950's and has gain rapid popularity and usage in temperate countries where labour is expensive and constrained working hours due to factors such as short hours of day light and other environmental factors that are unsuitable and undesirable for concrete casting . Precast prestressed hollow core slabs can be used for a wide range of applications requiring floor or roof systems. This system can be ideally used in schools, office buildings, condominiums, hotels, apartments, commercial buildings, residential dwellings, houses of worship, nursing homes, educational facilities or repetitive construction projects. a precast prestressed hollow system is also economical. Modular precast concrete floor and roof slabs are machine manufactured under controlled conditions in modern precast plants

Why Hollow Core?

The present concrete industry is constantly searching for revolutionary products and buildings system that can satisfy the future challenges posed by modern society : shortage of ; and costly labor force, structural efficiency , fire resistance, sound proofing, rate of speed of construction, execution quality and also most importantly , sustainability. Concrete structures in general and prefabrication in particular have characteristics to meet the posed challenges and also future environmental demands. However the most remarkable and successful developments in this context is the precast prestressed hollow core slab. The precast prestressed hollow core slab provides a solution to the current and future market demand for the building industry.

Precast prestressed hollow core slabs provide maximum structural efficiency with the utilization of high strength concrete, yet at the same time requiring low material consumption. With its structural efficiency, it is possible to obtain slender floor thickness. It is also possible for the slab to be reuse and recycling at the end of the life cycle. Moreover, there is less material wastage in the process of manufacturing as precast elements are produced in an automated and environmentally friendly manner. With factory production, the wellbeing and safety of the workers is safeguarded as the environment for the workers is easily controlled. Also recycling of all materials is comparatively simple to achieve in a closed factory environment as opposed to in-situ processes.

Precast prestressed hollow core floors are produced using extruders or slipformers on either a smooth concrete bed or over steel bed and completely do without any formwork compared to conventional in-situ casting. Precast prestressed hollow core system can provide the most economical and sustainable flooring solution for a wide variety of situations that may arise in masonry, steel and concrete structures, providing maximum benefits of construction speed.

Concrete is a versatile building material and has properties that at the outset are ecologically advantageous.It is durable, and requires no toxic preservatives in order to prevent its deterioration. In industrialized countries corrosion of steel is costing about 4% of the gross national product, and half of the annual steel production in the world is used to replace corroded structures.

In addition, the energy consumption of concrete is extremely low, compared to other construction materials. The utilization of the thermal mass of the concrete will save up to 35% of the energy required to heat or cool buildings. Furthermore, the mass of concrete provides excellent sound insulating properties.

Prestressed Hollow core floor units are normally 1200mm wide and up to 20m long. Hollow core units are mainly used in buildings with larger spans or loadings such as office buildings, hospitals, schools, retail developments, hotels, student accommodation, industrial buildings and sports arenas. Prestressed Hollow core units are the optimum form of floor construction in multi-occupancy apartment buildings and social housing, hollow core floors are the favored form of floor construction in individual houses, both at ground and intermediate levels. Hollow core floors are used because of their favorable cost rate and fast erection offering significant benefits to specifier and contractor.

Benefits and Advantage

Prestressed Hollow core Floors are highly engineered structural products manufactured under factory controlled conditions.
The top-15 advantages as mentioned but the International prestressed hollow core association of the product are:
• Reduced self-weight
• Provides versatility for designers
• Wide range of applications — suitable for the residential, healthcare, education, industrial and commercial markets
• Long spans without intermediate supports
• High load capacity
• Efficient span/depth-ratio leading to reduced storey heights
• Provision of a safe working platform
• Excellent fire resistance
• Excellent acoustic insulation and thermal properties
• Green product – reduced use of raw material
• Economical solution
• Reduction in number of site personnel
• High speed of erection
• Easily modified to enable heating and cooling of a building even without burning fossil fuels
• Easily modified to be highly efficient in distributing fresh and warm air, electrical wiring, plumbing and sprinkler services through a building

Speed of Construction

Fast construction can be achieved because casting of slabs does not rely on other critical-path activities to begin, precast elements can be produced as soon as drawings are approved, ensuring units are ready for assembly as foundation work and other site preparations is completed. Moreover, slabs are continuously manufactured in high efficiency plants while site construction is still underway, hence reducing any delays in material delivery on traditional site construction.

Precast prestressed hollow core slabs can be delivered to the construction site to meet a client’s schedule regardless of weather conditions. Besides that, the speed of assembly of precast elements allows it to be erected in all kinds of weather, benefiting the entire construction team. These advantages allow the building’s shell, whether load-bearing or cladding, to be enclosed quickly and provides a working platform for other trades. This, in turn, lets interior trades begin work earlier and reduces overall construction time. Faster completion reduces interim financing costs, results in earlier cash flows, and produces other economic benefits. This ultimately lowers the building’s long-term overall cost and can make the use of precast concrete more economical than other materials.

The combination of hollow core with a structural precast concrete frame and/or precast concrete bearing walls will speed construction even more if the entire building shell is supplied and installed under a single contract.

Other inherent benefits

Reduced Cost

Prestressed Hollow core slabs have longitudinal cores of which the main purpose is to reduce the weight of the floor. When hollow core slabs are used in floor applications, it acts as a load-bearing panel which can reduce the cost of framing by providing a column-free perimeter. Layout flexibility can be greatly increased depending on floor planning as there is potential for reducing the number and/or size of interior columns. However, if there is a desire to reduce interior columns, there are elements available in different depths in order to satisfy the various performance needs for greater spans and loading. This results in a more efficient and less costly construction. Cost savings are greatest for low-to mid-rise structures of three to 10 stories with a large ratio of wall-to-floor area.

Fire Resistance

Precast concrete is non-combustible with inherent fire-resistant capability that helps protect personnel, equipment and the building itself. It also eliminates the need and cost of additional fireproofing measures.

Environmentally Friendly

Precast concrete is an environmentally sound material. It is produced from natural materials and no toxic substances are produced in its production or use. Besides that, Concrete requires only small amounts of energy to produce. Temperature swings are reduced thanks to the thermal mass of concrete which results in great saves in energy year-round.

Sustainable

When expansion work on buildings is to be carried out, precast sections can be typically reused. Nonload-bearing panels on the end simply are disconnected from the framing and additional panels and framing are added on each side. The end panels can be replaced with the new additions in place. Concrete strikes a perfect balance between meeting today’s needs and natural resources for tomorrow , hence regarding up well to sustainability.

Single Source Provider

As a single unit, precast panels provide one source for supplying the entire exterior wall system. When load-bearing precast structural floors along with panels are specified, it concentrates the complete shell with one certified and reliable producer. This approach ensures complete responsibility and accuracy for meeting design specifications with only one supplier, reducing the number of subcontractors and minimizes trade coordination. In turn, it minimizes errors and miscommunication. Also, the producer’s competent staff of plant engineers is available to assist the design team.

Application

Residential


Commercial


Figure 1: Flooring Solution

Figure 2: Roofing Solution

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