9 Introduction to Precast Construction
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Questions and Answers

What is a characteristic of large-panel systems?

  • They enclose spaces for rooms within a building. (correct)
  • They are made solely from linear beam elements.
  • They primarily rely on shear walls.
  • They do not connect panels in vertical and horizontal directions.

Frame systems use linear elements to construct the precast frames most of the time.

True (A)

What type of loads do slab-column systems primarily resist?

gravity loads

In large-panel systems, both vertical and horizontal panels resist ________ load.

<p>gravity</p> Signup and view all the answers

Match the precast system types with their characteristics:

<p>Large-panel systems = Box-like structure with panels enclosing rooms Frame systems = Constructed with linear elements Slab-column systems = Relies on shear walls for lateral loads Mixed systems = Combination of different precast elements</p> Signup and view all the answers

Which system is known for its ability to transfer lateral loads to walls?

<p>Large-panel systems (B)</p> Signup and view all the answers

What is the primary advantage of using plant-cast precast concrete over site-cast concrete?

<p>Higher quality control (B)</p> Signup and view all the answers

In a lift-slab system with walls, slabs are poured in place on the site.

<p>False (B)</p> Signup and view all the answers

What do beam-column joints in frame systems typically use?

<p>hinged connections or rigid connections</p> Signup and view all the answers

Precast concrete elements can be cast and cured in as little as 24 hours.

<p>True (A)</p> Signup and view all the answers

What type of steel is commonly used to reinforce structural elements in plant-cast precast concrete?

<p>Pretension steel strands</p> Signup and view all the answers

The ___ lifting device is used to lift and place precast concrete planks.

<p>vacuum</p> Signup and view all the answers

Match the Precast Concrete components with their usage:

<p>Precast Columns = Two stories high Precast Slabs = Floor and roof decks Plant-Cast Process = Higher efficiency and quality control Vacuum Lifting Device = Lifting precast elements</p> Signup and view all the answers

What structure supports precast concrete slabs until they are connected?

<p>Temporary supports (D)</p> Signup and view all the answers

Precast concrete erection is more affected by adverse weather conditions compared to site-cast concrete.

<p>False (B)</p> Signup and view all the answers

What is used to ensure better surface finishes in precast concrete components?

<p>Durable steel forms</p> Signup and view all the answers

What is a key advantage of precast construction compared to site-cast concrete?

<p>Faster erection time (A)</p> Signup and view all the answers

Precast construction methods allow for greater flexibility in production under a closed system.

<p>False (B)</p> Signup and view all the answers

What is the main characteristic of open system precast construction?

<p>Production of building units without knowledge of the specific project.</p> Signup and view all the answers

Precast construction is also known as __________ construction.

<p>prefabricated</p> Signup and view all the answers

Match the following features with their descriptions:

<p>Division of workforce = Specialization of tasks Automated tools = Increased efficiency in production High quality control = Greater control on finishes Faster erection = Less affected by weather conditions</p> Signup and view all the answers

What is a primary feature of precast construction?

<p>Production of interchangeable parts (B)</p> Signup and view all the answers

The production of housing units using open systems is generally considered uneconomical.

<p>True (A)</p> Signup and view all the answers

What is a significant challenge of using closed system precast construction?

<p>Limited flexibility for different projects.</p> Signup and view all the answers

What is the primary function of precast concrete beams and girders?

<p>To provide support for slabs (A)</p> Signup and view all the answers

Precast concrete columns and wall panels primarily carry bending forces rather than axial loads.

<p>False (B)</p> Signup and view all the answers

What are the types of precast concrete wall panels mentioned?

<p>Solid, hollow, or sandwiched</p> Signup and view all the answers

Precast concrete ___ are uniquely shaped structural elements commonly used in sports stadiums.

<p>stairs</p> Signup and view all the answers

Match the following precast concrete elements with their functions:

<p>Precast Beams = Support for slabs Precast Columns = Support for beams and slabs Precast Wall Panels = Vertical support and insulation Precast Stairs = Access between different levels</p> Signup and view all the answers

Which of the following describes how precast concrete columns may be designed for certain applications?

<p>They may be conventionally reinforced or prestressed. (D)</p> Signup and view all the answers

Precast concrete elements are manufactured on site to minimize transportation issues.

<p>False (B)</p> Signup and view all the answers

What is the advantage of using ribbed precast concrete wall panels?

<p>Increases vertical span capacity while minimizing weight</p> Signup and view all the answers

What is the primary purpose of prestressing strands in precast concrete elements?

<p>To resist tensile forces (A)</p> Signup and view all the answers

Untensioned prestressing strands are used more effectively than tensioned strands in some applications.

<p>False (B)</p> Signup and view all the answers

What process is used to form low-slump concrete over tensioned strands in hollow core slabs?

<p>Extrusion process</p> Signup and view all the answers

Once the concrete has cured, the sections are lifted from the casting bed and __________ for shipping.

<p>stockpiled</p> Signup and view all the answers

Match the precast concrete elements with their functions:

<p>Prestressing Strands = Resisting tensile forces Conventional Reinforcing = Providing shear resistance Casting Bed = Forming concrete shapes Transverse Bulkheads = Dividing casting sections</p> Signup and view all the answers

Flashcards

Precast Construction

A type of construction where major building parts are made in a factory, transported to the site, and assembled. This method utilizes standard designs and mass production for faster and more cost-effective construction.

Closed System

Precast construction systems where components are designed specifically for a single project and are not reusable for other projects.

Open System

Precast construction systems where components are standardized and can be used in various projects, offering flexibility and potential cost savings.

Faster Erection

A key advantage of precast construction over site-cast concrete that allows for quicker construction and less interruption from weather conditions.

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High Quality Control

A major advantage of precast construction that allows for precise control over quality and appearances of building elements.

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Industrialized Methods

A process that involves the use of tools and machinery in factories for mass production of standardized building components.

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Workforce Specialization

Construction methods benefit from division of labor and specialization, enabling increased efficiency and productivity.

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Off-site Manufacturing

The core concept behind precast construction: manufacturing building elements in a factory before transporting them to the construction site.

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Large Panel Systems

Building systems made of large concrete panels that form walls and floors, connected vertically and horizontally to create box-like structures. Panels resist gravity loads, and horizontal elements act as diaphragms to transfer lateral loads to the walls.

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Frame Systems

Precast systems using linear elements (beams and columns) or spatial beam-column sub-assemblages to create the building frame. Linear elements are more common due to ease of handling and erection.

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Slab-Column Systems with Shear Walls

These systems rely on shear walls to resist lateral loads, while the slab-column structure primarily supports gravity loads.

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Lift-Slab System

A type of slab-column system where precast concrete slabs are poured on the ground, one on top of the other. These slabs are lifted and placed in position, creating the floors.

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Prestressed Slab-Column System

A type of slab-column system that uses precast concrete slabs and columns where the slabs are prestressed, meaning they are tensioned to increase their strength and reduce deflection.

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Plant-Cast Precast Concrete

Precast concrete elements are made in a factory, allowing for greater quality control and faster construction.

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Pretension Steel

Precast concrete elements are often strengthened with high-tension steel wires that provide increased structural efficiency.

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Thermal Stress Reinforcement

Steel reinforcement is added to precast concrete elements to resist stresses caused by temperature changes.

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Precast Concrete Erection

Precast concrete elements are lifted and assembled on site, providing faster and more weather-resistant construction compared to traditional methods.

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Precast Concrete Slabs

Used for floor and roof decks, these precast slabs can span long distances depending on their depth. Hollow core slabs offer reduced weight and increased span.

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Precast Concrete Framing

Precast concrete elements are typically cast and cured in a factory, creating a durable and long-lasting structure.

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Plant Casting

The process of casting and curing concrete elements in a factory under controlled conditions, ensuring high quality and efficiency.

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Prestressing Strands

High-strength steel wires used to add compressive strength to concrete structures. They are commonly used in precast elements to improve load-bearing capacity.

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Conventional Reinforcing

Steel bars used in concrete to reinforce and resist tensile forces. Unlike prestressing strands, they are not tensioned.

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Extrusion Process for Hollow Core Slabs

A method of producing precast concrete elements with hollow cores. This technique uses tensioned prestressing strands and extrusion to create the desired shape.

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Transverse Bulkheads

Vertical barriers used in casting beds to separate sections of concrete elements. They are particularly useful when creating precast hollow core slabs.

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Curing (Precast Concrete)

The stage in manufacturing precast concrete elements where the concrete gains enough strength to be lifted and handled.

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Precast Concrete Beams and Girders

Precast concrete beams and girders are used to support slabs. They have reinforcing bars that bond with concrete cast on-site.

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Precast Concrete Columns and Wall Panels

Precast concrete columns and wall panels provide support for beams and slabs. They often use conventional reinforcement for axial loads, but can be prestressed for greater strength in slender elements.

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Precast Concrete Wall Panels

Precast wall panels can be solid, hollow, or sandwiched for insulation. They can also have ribs for strength and be shaped for architectural designs.

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Other Precast Concrete Elements

Precast concrete is used for a wide variety of elements, including stairs, unique structural shapes, and more.

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Assembly Concepts for Precast Concrete Buildings

Precast concrete buildings can be assembled using columns, beams, and wall panels in various combinations.

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Assembly Concepts for Precast Concrete Buildings (Examples)

Different types of precast concrete slabs and wall panels are used to create diverse structures like warehouses, carparks, and more.

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Manufacturing Process for Precast Concrete Elements

Precast concrete elements are manufactured in casting beds, which can be very long (up to 800 ft). High-strength steel strands are tensioned to create pre-stressed concrete.

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Casting Hollow Core Planks

Hollow core planks are a specific type of precast element used in construction. They are typically manufactured in long beds with tensioned steel strands running through them.

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Study Notes

Precast Introduction

  • Precast construction involves pre-fabricating structural components in a factory and transporting them to the site for assembly.
  • This method utilizes standardized components for mass production, speeding up construction and potentially lowering costs.
  • Precast components are typically manufactured using industrial methods and standardized designs, leading to efficiency and control in the construction process.

Precast Construction Systems

  • Closed System: Building units are non-standardized and used only once per project, resulting in high waste and less economical construction. A large number of building units can produce economically feasible results. Molding the units is uneconomical.
  • Open System: Building units can be produced without knowledge of the project and are versatile in their application across various types of projects. The method allows for flexibility in design and application, but standardization may be lacking.

Main Features of Precast Construction

  • Division and Specialization of Labor: Tasks are divided and specialized among trained workers enhancing efficiency and precision.
  • Use of Machinery and Tools: Tool and machinery use, often automated, aids in the standardisation of components and speedens production.
  • Interchangeable Parts and Products: Standardized parts can be easily replaced and fitted, enabling faster construction.
  • Faster and Less Affected by Weather: Precast erection is generally quicker and less impacted by weather conditions compared to conventional concrete.
  • Increased Efficiency and High Quality Control: Control over casting and finishing processes boosts efficiency and improves quality greatly.

Types of Precast Systems

  • Large-Panel Systems: Multi-story buildings constructed using large precast wall and floor panels. Panel connections are planned vertically and horizontally to create an encased or box-like structure.
  • Frame Systems: Frames may use linear elements or sub-assemblages. Linear elements are simpler to form, handle, and erect, and may be seated on beams using corbels. Joinery connections may be hinged, though in some cases may be designed for rigidity and continuity.
  • Slab-Column Systems with Shear Walls: Precast elements assembled using special joints. Slabs are lifted vertically to required heights. Temporary supports keep slabs positioned until joints to columns are achieved.
  • Mixed Systems: A combination of different precast techniques.

Plant-Cast Precast Concrete

  • Cast in plants for consistency in strength, quality, and to limit waste.
  • Plant casting allows for more efficient construction, superior quality control, and reduces formwork costs compared to site-cast concrete.
  • High-quality forms allow for consistent surface finishes.
  • High-strength and high-early strength concrete enable casting and curing processes in a much shorter timeframe.

Precast Concrete Structural Elements

  • Slabs: Used for flooring and roofing, varying in depth. Hollow core slabs are commonly employed and are stacked at the manufacturing plant.
  • Beams and Girders: Provide load support for slabs, with reinforcing bars bonded with site-cast concrete. Beam supports may include inverted T-beams.
  • Columns and Wall Panels: Support beam and slab loads, and may be reinforced with prestressing elements to handle potential bending forces during erection. Ribbed or hollow designs are used for weight efficiency.
  • Stairs and Other Elements: Specialized precast parts often include stairs and structures for specific purposes like sports stadiums.

Assembly Concepts

  • Vertical Support: Support columns and beams, or a combination of methods may be used.
  • Span Requirements: Chosen for roof and floor slab components primarily based on span requirements.
  • Combined Systems: Precast can be combined with other construction methods such as site-cast concrete, reinforced masonry, or steel systems for further functionality.

Manufacturing of Precast Concrete Elements

  • Hollow Core Planks: Precast elements are cast and designed at their manufacturing plant and transported. These may also utilize high-strength steel strands stretched along the bed during manufacturing. Various elements like weld plates are added for functionality.
  • Prestressing/Reinforcing: These help bolster design strength and resilience by preventing tensile forces from impacting the core structure. Prestressing strands are often inserted into shallow v-shape grooves to facilitate efficient resistance to forces.
  • Casting/Curing/Sections/Transportation: The precast system involves the process of sectional casting, concrete curing, and element movement. Casting occurs at factories and sections are often stockpiled until the time for transport and site-erection.

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Description

Explore the concepts of precast construction, including the definition, advantages, and the differences between closed and open precast systems. Understand how these systems impact efficiency, costs, and design flexibility in construction projects.

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