Precast Concrete by Northeastern School of Architecture

FALL 2009

PRECAST CONCRETE Northeastern University School of Architecture ARCH G691 Graduate Degree Project Studio

FALL 2009

PRECAST CONCRETE Northeastern University School of Architecture ARCH G691 Graduate Degree Project Studio

TRANSPORTX+XASSEMBLY

MANUFACTURE

DESIGN

INTRODUCTION

TRANSPORTX+XASSEMBLY

Precast Concrete MANUFACTURE

DESIGN

INTRODUCTION

Table of Contents

DESIGN

1.1 1.2 1.3 1.4

Component Relationships Slabs Beams Columns

MANUFACTURE

2.1 2.2 2.3 2.4

Plant Logics Mixtures Reinforcement Molds

TRANSPORT + ASSEMBLY

3.1 Shipping Logics 3.2 Crane and Site Logics 3.3 Joinery and Detail Connections

Precast Concrete

DESIGN

INTRODUCTION

MANUFACTURE

Definition of Precast Organization

TRANSPORTX+XASSEMBLY

INTRODUCTION

Introduction

INTRODUCTION Conclusions

This book looks at the structural system of

In an effort to create an in depth model of the

precast concrete through a discerning lens.

precast system, the content of this book is limited

construction is driven by economics and time.

While tons of books exist on the subject, none

to structural members. More specifically we have

Being a material known for its quick on-site

distill relevant information down for architectural

focused on panel construction rather than

construction, every step of precast construction

practice. Moreover, we have decided to examine

masonry units. Despite this fact, many of the

is geared towards improving cost and schedule.

the processes inherent to this building material

insights uncovered in the following analysis can

Consequently, the system has developed the

instead of creating a survey of precast concrete

be applied to the expanded scope of precast

reputation of being the low-grade building

use. The chapters are organized by design,

construction.

material of developers. The content of this book

all

have

discovered

that

precast

manufacture, and transport and assembly. We

attempts to reconnect the profession with this

are hoping that this approach better unites the

undervalued structural system.

architectural design process with the realities of

DESIGN

Scope

MANUFACTURE

Approach

building construction, revealing the inner logics

Precast Concrete

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and latent opportunities.

Design

This chapter focuses on the design of precast components in a site-less condition. Specifically, the sections are divided

INTRODUCTION

Design

1.0 Introduction

into the parts that make up the structural system: columns, beams and slabs. Through this investigation, the varying depths of each piece are diagramed, along with their corre-

DESIGN

sponding spans, that are determined by the number of steel reinforcement bars. Along with these span graphs, each piece has a graph that compares the safe service load, when considering the depth of the piece and the span. In addition, a typical arrangement of these parts is shown in an axon, along with standard dimensions and an explanation of the

MANUFACTURE

logic of these sizes and distances.

The standard used to develop these charts assumed no topping on precast components. The logic carried through this section was due to the fact that not all components have toppings and for the sake of clarity and consistency, these additional variables were not included in the chart. In instances where more information could be found about toppings, the

Precast Concrete

TRANSPORTX+XASSEMBLY

section instructs you where to find these calculations.

INTRODUCTION

Design

1.0 Component Relationships

MANUFACTURE

DESIGN

10ft typ. 8ft typ.

TRANSPORTX+XASSEMBLY

60ft typ.

30ft typ.

Typical Dimensions The above diagram illustrates the tyical dimensions of a single bay of parking, and the logic behind those measurements. The span of 60ft allows for two rows of 18 foot deep parking, with 24 feet of car circulation space. The space of 30 feet between the columns in the lateral direction allows for three adjacent parking spots of 9 feet, uninterupted by columns.

The use of 10 foot width double tee members allows for only three pieces to be used to make the 30 foot dimension between the columns. If the double tee width were to change to be 8 feet, the distance between the two columns could change into 32 feet to still accomodate three parking spots, but four double tee members are used instead of three. The 8 foot tall dimension of the column allows for the minimum height clearance of the parking garage ceiling.

In this particular example, the seams of the double tee line up with the center of the column, so the dimension of three 10 foot double tees creates the 30 foot distance between the columns. If the beam was rectangular instead of L shaped, the double tees would rest on top and cause the floor thickness to be greater. In other causes, the double tee members donâ&#x20AC;&#x2122;t have to line up with the center of the column. The double tees can continue uninterrupted as long as the legs of the double tee fall onto a beam.

Precast Concrete

TRANSPORTX+XASSEMBLY

MANUFACTURE

DESIGN

INTRODUCTION

Design

1.0 Design Relationships

TRANSPORTX+XASSEMBLY

MANUFACTURE

DESIGN

INTRODUCTION

1 Design

1.1 Components: Slabs

Slabs These pieces come in four different shapes: double tees, single tees, solid slab and hollow core slab. The span of each of these can vary greatly and is only limited by how much service load is desired. The width, however, has a much smaller range, and is determined by the width of the transporting vehicle. Widths are also determined by how many pieces are going to be used and the spacing of the columns.

Precast Concrete

TRANSPORTX+XASSEMBLY

MANUFACTURE

DESIGN

INTRODUCTION

Design

1.1 Components: Slabs

These are the most commonly manufactured shape of precast slab. They can span longer distances than a solid slab or hollow core, and can easily be stacked and transported. Although they can span a long distance, a large number of pieces are necessary to complete a specific width. Also, in order to span a larger distance, the pieces need to have a greater depth.

8’-0” wide

12” 14” 16” 18” 20” 24” 28” 32” 36”

MANUFACTURE

1.1 Components: Double Tees

depth (in.)

INTRODUCTION DESIGN

Design

Double Tees

Spans and Service Loads

TRANSPORTX+XASSEMBLY

In the diagrams to the right and on the opposite page, varying depths correspond to span lengths and capacity to support certain levels of service load. The deeper the double tee component, the higher the constructible span. In the lower diagram, each polyline boundary designates the possible safe service loads, depending on depth of the double tee, and the span. Typically, the longer the span, the lower amount of service load the member is able to support. Additionally, the higher the number of reinforcement steel bars used in the precast member, the higher the capability to hold a higher service load. These reinforcement bars also allow the double tees to span farther distances, but as a result of the spans being greater, less service load can be supported.

Increasing Safe Service Loads PLEASE NOTE: The load chart on the opposite page represents a double tee with no additional topping. By adding either a 2 inch or 4 inch topping of reinforced concrete, the span and safe service loads can greatly increase. This is more commonly used when a member needs to be able to support a certain amount of service load, but it cannot increase its span. The amount of depth at which the component increases is very small, so this is a more viable option than producing a piece of much greater depth and span. For measurements of safe serviceable loads when using additional topping, please reference the PCI handbook.

DESIGN

INTRODUCTION

Design

1.1 Components: Double Tees

100 104

MANUFACTURE

span (ft.) 250 240 230 220 210 200 190 180 garages (trucks /buses) 170 160 library stacks 150 140 light manufacturing / 130 light storage 120 gym /restaurant 110 office 100 90 retail /hotel / 80 multifamily housing 70 60 garages (cars) one / two family housing 50 40 30

safe service loads (psf)

heavy manufacturing / heavy storage

span (ft.)

Precast Concrete

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INTRODUCTION DESIGN

Design

Double Tees These are the most commonly manufactured shape of precast slab. They can span longer distances than a solid slab or hollow core, and can easily be stacked and transported. Although they can span a long distance, a large number of pieces are necessary to complete a specific width. Also, in order to span a larger distance, the pieces need to have a greater depth.

1.1 Components: Double Tees 10’-0” wide

depth (in.)

12” 16” 20” 24” 28” 32”

MANUFACTURE

36”

Spans and Service Loads

TRANSPORTX+XASSEMBLY

span (ft.)

240 230 220 210 200 190 180 garages (trucks /buses) 170 160 library stacks 150 140 light manufacturing / 130 light storage 120 gym /restaurant 110 office 100 90 retail /hotel / 80 multifamily housing 70 garages (cars) 60 one / two family housing 50 40 30 20

50 span (ft.)

Precast Concrete

MANUFACTURE

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safe service loads (psf)

DESIGN

INTRODUCTION

Design

1.1 Components: Double Tees

INTRODUCTION DESIGN

Design

1.1 Components: Double Tees

depth (in.)

12’-0” wide

32”

MANUFACTURE

Spans and Service Loads

TRANSPORTX+XASSEMBLY

span (ft.)

200 190 180 garages (trucks /buses) 170 160 library stacks 150 140 light manufacturing / 130 light storage 120 gym /restaurant 110 office 100 90 retail /hotel / 80 multifamily housing 70 60 garages (cars) one / two family housing 50 40 30

span (ft.)

Precast Concrete

MANUFACTURE

TRANSPORTX+XASSEMBLY

safe service loads (psf)

DESIGN

INTRODUCTION

Design

1.1 Components: Double Tees

1.1 Components: Single Tees 8’-0” wide

Single Tee Many existing buildings utilize single tees, however as precast technologies have improved, manufacturers have realized that double tees are easier to produce, easier to transport because additional bracing is not necessary to hold them up, and the same distance can be spanned, with a shallower depth of the member. In fact, in the newest versions of the PCI Handbook, single tees are not included.

depth (in.)

INTRODUCTION

Design

36”

MANUFACTURE

DESIGN

Spans and Service Loads

TRANSPORTX+XASSEMBLY

In the diagrams to the right and on the opposite page, varying depths correspond to span lengths and capacity to support certain levels of service load. The deeper the single tee component, the higher the constructible span. In the lower diagram, each polyline boundary designates the possible safe service loads, depending on depth of the single tee, and the span. Typically, the longer the span, the lower amount of service load the member is able to support. Additionally, the higher the number of reinforcement steel bars used in the precast member, the higher the capability to hold a higher service load. These reinforcement bars also allow the single tees to span farther distances, but as a result of the spans being greater, less service load can be supported.

Increasing Safe Service Loads PLEASE NOTE: The load chart on the opposite page represents a double tee with no additional topping. By adding either a 2 inch or 4 inch topping of reinforced concrete, the span and safe service loads can greatly increase. This is more commonly used when a member needs to be able to support a certain amount of service load, but it cannot increase its span. The amount depth at which the component increases is very small, so this is a more viable option than producing a piece of much greater depth and span. For measurements of safe serviceable loads when using additional topping, please reference the PCI handbook.

100

span (ft.)

190 180 garages (trucks /buses) 170 160 library stacks 150 140 light manufacturing / 130 light storage 120 gym /restaurant 110 office 100 90 retail /hotel / 80 multifamily housing 70 garages (cars) 60 one / two family housing 50 40

span (ft.)

Precast Concrete

MANUFACTURE

TRANSPORTX+XASSEMBLY

safe service loads (psf)

DESIGN

INTRODUCTION

Design

1.1 Components: Single Tees

Design

1.1 Components: Single Tees 10’-0” wide

depth (in.)

INTRODUCTION DESIGN

MANUFACTURE

48”

Spans and Service Loads

TRANSPORTX+XASSEMBLY

Increasing Safe Service Loads PLEASE NOTE: The load chart on the opposite page represents a double tee with no additional topping. By adding either a 2 inch or 4 inch topping of reinforced concrete, the span and safe service loads can greatly increase. This is more commonly used when a member needs to be able to support a certain amount of service load, but it cannot increase its span. The amount depth at which the component increases is very small, so this is a more viable option than producing a piece of much greater depth and span. For measurements of safe serviceable loads when using additional topping, please reference the PCI handbook.

100

110

100

110

span (ft.)

MANUFACTURE

garages (trucks /buses)

170 160 library stacks 150 140 light manufacturing / 130 light storage 120 gym /restaurant 110 office 100 90 retail /hotel / 80 multifamily housing 70 garages (cars) 60 one / two family housing 50 40

span (ft.)

Precast Concrete

TRANSPORTX+XASSEMBLY

safe service loads (psf)

DESIGN

INTRODUCTION

Design

1.1 Components: Single Tees

Design

1.1 Components: Solid Slabs

Solid Slab This type of slab can vary in width, but has the smallest distance it can span. However, it does have the highest safe service load, especially at the shortest spans. These components are also much shallower than the double and single tees, so this allows for a much larger floor to ceiling height. In addition, the pieces are lighter, easily stacked for transportation, and much more can fit on the transportation vehicle.

(width varies) 4” 6” 8”

Spans and Service Loads In the diagrams to the right and on the opposite page, varying depths correspond to span lengths and capacity to support certain levels of service load. The deeper the solid slab, the higher the constructible span. Although the solid slab cannot span as far as the single and double tees, it can carry a larger service load.

TRANSPORTX+XASSEMBLY

depth (in.)

INTRODUCTION DESIGN MANUFACTURE

In the lower diagram, each polyline boundary designates the possible safe service loads, depending on depth of the solid slab, and the span. Typically, the longer the span, the lower amount of service load the member is able to support. Additionally, the higher the number of reinforcement steel bars used in the precast member, the higher the capability to hold a higher service load. These reinforcement bars also allow the hollow core to span farther distances, but as a result of the spans being greater, less service load can be supported.

Increasing Safe Service Loads PLEASE NOTE: The load chart on the opposite page represents a double tee with no additional topping. By adding either a 2 inch or 4 inch topping of reinforced concrete, the span and safe service loads can greatly increase. This is more commonly used when a member needs to be able to support a certain amount of service load, but it cannot increase its span. The amount depth at which the component increases is very small, so this is a more viable option than producing a piece of much greater depth and span. For measurements of safe serviceable loads when using additional topping, please reference the PCI handbook.

DESIGN

span (ft.)

MANUFACTURE

300 290 280 270 260 heavy manufacturing / 250 heavy storage 240 230 220 210 200 190 180 garages (trucks /buses) 170 160 library stacks 150 140 light manufacturing / 130 light storage 120 gym /restaurant 110 office 100 90 retail /hotel / 80 multifamily housing 70 60 garages (cars) one / two family housing 50

span (ft.)

Precast Concrete

TRANSPORTX+XASSEMBLY

safe service loads (psf)

INTRODUCTION

Design

1.1 Components: Solid Slabs

Design

1.1 Components: Hollow Core Slabs

Hollow Core This type of slab can vary in width, but has a much smaller span distance than the double or single tee. The biggest advantage of this type is the fact that it weights much less than the tees, and even less than the solid slab. These components are also much shallower than the double and single tees, so this allows for a much larger floor to ceiling height. In addition, the pieces are lighter, easily stacked for transportation, and much more can fit on the transportation vehicle. Through the hollow core, it is possible to run wiring or other mechanical equipment through the spaces.

4’-0” wide 6” 8” 10” 12”

Increasing Safe Service Loads Spans and Service Loads In the diagrams to the right and on the opposite page, varying depths correspond to span lengths and capacity to support certain levels of service load. The deeper the hollow core component, the higher the constructible span. Although the hollow core cannot span as far as the single and double tees, it can carry a larger service load.

TRANSPORTX+XASSEMBLY

depth (in.)

INTRODUCTION DESIGN MANUFACTURE

In the lower diagram, each polyline boundary designates the possible safe service loads, depending on depth of the hollow core, and the span. Typically, the longer the span, the lower amount of service load the member is able to support. Additionally, the higher the number of reinforcement steel bars used in the precast member, the higher the capability to hold a higher service load. These reinforcement bars also allow the hollow core to span farther distances, but as a result of the spans being greater, less service load can be supported.

PLEASE NOTE: The load chart on the opposite page represents a double tee with no additional topping. By adding either a 2 inch or 4 inch topping of reinforced concrete, the span and safe service loads can greatly increase. This is more commonly used when a member needs to be able to support a certain amount of service load, but it cannot increase its span. The amount depth at which the component increases is very small, so this is a more viable option than producing a piece of much greater depth and span. For measurements of safe serviceable loads when using additional topping, please reference the PCI handbook. Unique to the hollow core, there is a huge variety of shapes, numbers and sizes of holes in the various types of hollowcore. These variables affect the depth, reinforcement, span and service loads. To explore these possibilities please reference the PCI handbook.

DESIGN

span (ft.)

MANUFACTURE

290 280 270 260 heavy manufacturing / 250 heavy storage 240 230 220 210 200 190 180 garages (trucks /buses) 170 160 library stacks 150 140 light manufacturing / 130 light storage 120 gym /restaurant 110 office 100 90 retail /hotel / multifamily housing 80 70 garages (cars) 60 one / two family housing 50 40

span (ft.)

Precast Concrete

TRANSPORTX+XASSEMBLY

safe service loads (psf)

INTRODUCTION

Design

1.1 Components: Hollow Core Slabs

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MANUFACTURE

DESIGN

INTRODUCTION

1 Design

1.2 Components: Beams

Beams There are three different types of beams: rectangular, L shaped and inverted T. These components rest on top of the columns and must support the weight of the slabs that rest on top of them. In each example, the width stays constant, but the depth and spans have a very large range. Steel reinforcement is not a variable when calculating safe service loads.

Precast Concrete

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MANUFACTURE

DESIGN

INTRODUCTION

Design

1.2 Components: Beams

Design

1.2 Components: Rectangular Beams

12” wide

depth (in.)

DESIGN

INTRODUCTION

16” 20” 24” 28” 32”

TRANSPORTX+XASSEMBLY

MANUFACTURE

36”

Spans and Service Loads

Rectangular Beams

In the diagrams to the right and on the opposite page, varying depths correspond to span lengths and capacity to support certain levels of service load. The deeper the beam, the higher the constructible span.

This type of beam allows the slab to rest on top of it, creating larger depth per floor. Because it is of uniform shape, it can be placed anywhere in the building, whether it resting on the exterior columns or the interior columns. Typically these types of beams do not hold as much load as an L shaped or inverted T beam, but they are shallower in depth.

In the lower diagram, each polyline boundary designates the possible safe service loads, depending on depth of the beam, and the span. Typically, the longer the span, the lower amount of service load the member is able to support. The required level of safe service load is very high, because it is supporting the weight of the slabs that rest on top of it, and the weight that the slabs support.

DESIGN

INTRODUCTION

Design

1.2 Components: Rectangular Beams

MANUFACTURE

10,000 9,500 9,000 8,500 8,000 7,500 7,000 6,500 6,000 5,500 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000

span (ft.)

Precast Concrete

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safe service loads (psf)

span (ft.)

Design

1.2 Components: Rectangular Beams

16” wide

depth (in.)

DESIGN

INTRODUCTION

24” 28” 32” 36”

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MANUFACTURE

40”

Spans and Service Loads

Rectangular Beams

DESIGN

INTRODUCTION

Design

1.2 Components: Rectangular Beams

MANUFACTURE

10,000 9,500 9,000 8,500 8,000 7,500 7,000 6,500 6,000 5,500 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000

span (ft.)

Precast Concrete

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safe service loads (psf)

span (ft.)

INTRODUCTION

Design

1.2 Components: L Shaped Beams

12” wide

20”

DESIGN

28”

24”

32” 36” 40” 44” 48” 52” 56”

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MANUFACTURE

60”

18” wide

depth (in.)

Spans and Service Loads

L Shaped Beams

This type of beam allows the slab to rest on grooves located on one side, causing this type to be best utilized as beam places on the perimeter of the building. Although this type can range to a depth greater than the rectangular beam, the shape allows for the slab to rest of the grooves, therefore reducing the thickness of the floor. In addition, this type can support a greater service load than the rectangular beams.

safe service loads (psf)

span (ft.) 10,000 9,500 9,000 8,500 8,000 7,500 7,000 6,500 6,000 5,500 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000

span (ft.)

Precast Concrete

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MANUFACTURE

DESIGN

INTRODUCTION

Design

1.2 Components: L Shaped Beams

INTRODUCTION

Design

1.2 Components: Inverted T Beams

12” wide

20”

DESIGN

28”

24”

32” 36” 40” 44” 48” 52” 56”

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MANUFACTURE

60”

24” wide

depth (in.)

Spans and Service Loads

Inverted T Beams

This type of beam allows the slab to rest on grooves located on both sides, causing this type to be best utilized as an interior beam. Although this type can range to a depth greater than the rectangular beam, the shape allows for the slab to rest of the grooves, therefore reducing the thickness of the floor. In addition, this type can support a greater service load than the rectangular beams.

safe service loads (psf)

span (ft.) 10,000 9,500 9,000 8,500 8,000 7,500 7,000 6,500 6,000 5,500 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000

span (ft.)

Precast Concrete

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MANUFACTURE

DESIGN

INTRODUCTION

Design

1.2 Components: Inverted T Beams

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MANUFACTURE

DESIGN

INTRODUCTION

1 Design

1.3 Components: Columns

Columns Although there are a few different types of columns, this book focuses on square columns, because it is more commonly used due to the assembly process being easier than if a round column was used. Columns need to support the largest abount of service load because they hold up the beams and the slabs.

Precast Concrete

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MANUFACTURE

DESIGN

INTRODUCTION

Design

1.3 Components: Columns

Design

1.3 Components: Square Column 8” 10” 12” 14” 16” 18” 20” 22” 24” 26” 28”

width (in.)

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MANUFACTURE

DESIGN

INTRODUCTION

Heights and Service Loads

Square Columns

In the diagrams to the right and on the opposite page, varying column widths correspond to column heights and capacity to support certain levels of service load. The wider the column, the tallerer the constructible height.

These members are not categorized by depth and span, instead they are measured by width and height. Columns have additional extrusions that act as a shelf to support the beams. The spacing between columns is determined by the span of the slabs that rest on top of the beams, and in the other direction, it is determined by the width of the slabs.

In the lower diagram, each polyline boundary designates the possible safe service loads, depending on width of the column, and the height. Typically, the taller the height, the lower amount of service load the member is able to support. The required level of safe service load is very high, because it is supporting the weight of the beams and slabs that rest on top of it, and the weight that those members support.

20 30 height (ft.)

DESIGN

INTRODUCTION

Design 1

1.3 Components: Square Column

27,000 26,000 25,000

MANUFACTURE

24,000 23,000

18,000 17,000 16,000 15,000 14,000 13,000 12,000 11,000 10,000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000

Precast Concrete

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safe service loads (psf)

22,000 21,000 20,000 19,000

Manufacture

2.0 Introduction

INTRODUCTION

Manufacture

Precast concrete can be cast using wet or dry methods. Wet casting is the typical method used

DESIGN

in precast concrete and therefore the focus of this chapter. It utilizes workable, fluid mixes of air, aggregates, cement, pigments, and water. While there are thousands of mix combinations, the main variables relevant to precast are compressive

MANUFACTURE

strength and weight. Tensile strength is determined through reinforcing. All structural concrete members are reinforced and most precast shapes are prestressed as well. In addition to these design basics, one must consider a molding strategy. The repition and economy of materials are huge influences on the design of custom shapes. Even basic shapes have some variables like curing time. Once the construction site. Overall this chapter navigates the logics and goals of the manufacturing process.

Precast Concrete

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product is cured, it is shipped off to the

INTRODUCTION

Manufacture

2.1 Plant Logics

Location In looking at the location of precast plants in the

DESIGN

North Eastern corner of the United States, a couple of trends become apparent. For the most part plants are evenly spaced out due to price competition. A manufacturer’s price is always dependent on how far they are shipping. If another plant is closer to a job site, their price will

MANUFACTURE MANUFACTURE

be lower. Within the state of Pennsylvania the radius of competition for suburban manufacturer’s is around 50 miles. Once plants enter a city’s zone of development, this radius of competition becomes smaller, around 30 miles. Therefore, the location of precast plants is evenly spaced and loosely clustered around metropolitian

TRANSPORTX+XASSEMBLY

areas.

Architectural Precast Plant Structural Precast Plant Large Metropolitan Area

MANUFACTURE

DESIGN

2.1 Plant Logics

Precast Concrete

INTRODUCTION

TRANSPORTX+XASSEMBLY

Manufacture

INTRODUCTION

Manufacture 2.1 Plant Logics

Plant Layout + Work Flow Most plants are layed out using four main

DESIGN

components: a mixing station, steel shop, main facility, and stock yard. Once a batch is mixed, trucks or special concrete transporters carry it through the main facility to the casting beds. Meanwhile, any reinforcement is constructed in the steel shop and brought over in cages as

MANUFACTURE MANUFACTURE

needed. The pieces are cured in the main bay and then carried out to the stock yard where they are stamped and stored until delivery to the site. Concrete Mix Station

Steel Shop

Main Facility

Stock Yard

The Main Facility The main facility is organized into a series of rows that alternate between molds and flex

TRANSPORTX+XASSEMBLY

space. Pouring and moving trucks use this space to service curing molds. Equipment and products are transported by overhead skips and rollers fixed to the casting bed rails. Such equipment includes: concrete transporters, vibrating sleds, slip formers, extruders, and cleaning devices. This use of space allows the largest efficiency of manufacture.

MANUFACTURE

DESIGN

2.1 Plant Logics

Precast Concrete

INTRODUCTION

TRANSPORTX+XASSEMBLY

Manufacture

INTRODUCTION

Manufacture 2.1 Plant Logics

Production Sequence The average plant casts one mold per day. At 7

DESIGN

am the mold is emptied and cleaned. Then the reinforcing for the next cast is put in place. By around 2 pm the concrete can be poured in, and the form vibrated for curing. Curing time can take up to two days, but is generally shortened through

TRANSPORTX+XASSEMBLY

MANUFACTURE MANUFACTURE

heating systems.

7 am

2 pm

Demolding

Concrete Pouring

Cleaning

Vibration

Placing the Reinforcement

Curing

2.1 Plant Logics

Curing Systems

INTRODUCTION

Manufacture

Without any external influences a precast to reach the strength required to remove it from a mold. This time is quite impractical and a number of measures have been created to shorten this time. The fastest curing method is high pressure

DESIGN

concrete member takes approximately 48 hours

steam curing, or autoclaving. However, the cost

48 Hour Stand Cure

around time of six hours. Most plants employ thermal tarps and a hydro-thermal system under the casting form. The form material is very important in this approach since steel is several hundred times more conductive than wood.

MANUFACTURE

of this process is not currently justified by a turn

6 Hour Steam Cure

Precast Concrete

TRANSPORTX+XASSEMBLY

14-18 Hour Tarp + Hydrothermal Heating

INTRODUCTION

Manufacture 2.1 Plant Logics

Casting Sequence Precast plants organize their casting sequence

DESIGN

by what parts are assembled first. Accordingly, elevator and stair cores are cast first, then columns, beams, slabs, moving up in level. This creates the greatest economy of time by allowing manufacture

and

assembly

Slabs X 12

occur

MANUFACTURE MANUFACTURE

simultaneously.

Beams X 17

TRANSPORTX+XASSEMBLY

Cores X 2

Columns X 12

2.1 Plant Logics

INTRODUCTION

Manufacture

Week 28

Mold Fabrication Panel Fabrication Slabs X 12

Panel Assembly

DESIGN

MANUFACTURE

Panel Fabrication and Production Schedule

Beams X 17

Panels X 20

Precast Concrete

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Columns X 12

INTRODUCTION

4 3 5

5 3

5 4

Manufacture 2.2 Mixtures5

The Basics The basic ingredients of concrete are portland

DESIGN

cement, water, air, and a mix of fine and course aggregates. Admixtures are often added to alter the behavior of the concrete mix. Most precast plants have computer controlled mixing stations right next to the main facility, making changes

TRANSPORTX+XASSEMBLY

MANUFACTURE MANUFACTURE

seemless.

1 Water 2

2 1 3 Portland Cement

3 1

3 2 4 Air

4 2

4 3 5 Fine Aggregates

5 3

5 Course Aggregates 4 4 5

Concrete Mix Station

2.2 Mixtures

1 2

Normal Mix

High Strength

Lightweight

The typical concrete mix represents the most

High strength concrete has a low water to

The proportions of lightweight concrete appear

economical balance of ingredients. The water to

cementing material ratio, around .30. The

to be the same as normal weight, but the

cementing material ratio is around .70. These

increased cement content is what increases the

aggregates are up to 50% less dense than those

days most concrete is air entrained to better

compressive strength. Both normal and light

typically

freeze-thaw conditions, accordingly the mixes

weight concrete mixes can be made high

shown below reflect a higher air content.

strength.

4 5

used.

Such

aggregates

lamexpanded ron clay and shale.

50% less dense

include

DESIGN

Manufacture

INTRODUCTION

lamron*

1 2

MANUFACTURE

htgnerts hgih

3 1

3 4

lamron*

htgnerts hgih

Ingredient Proportions by Volume

1 1

Precast Concrete

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ocal

INTRODUCTION

Manufacture 2.2 Mixtures

Densities + Strengths

15000

As mentioned the strength of a concrete mix is

DESIGN

not dependent on its density. However, there are slight differences between normal weight and light weight concrete. The strength of light weight

12000

is always a little less than the typical mix. Otherwise, the two behave similarly when more

MANUFACTURE MANUFACTURE

cement is added to increase strength.

9000

Multiple 6000

High TRANSPORTX+XASSEMBLY

stant

regates

White 3000

Single

Low

Gray

Admixtures

Pigments

Cement

Density Normal Mix

High Strength

Light weight

2.2 Mixtures

15000

Economy

INTRODUCTION

Manufacture

From looking at the economic impact of adjusting

Better

mix variables, one starts to wonder whether the

Distant

benefits gained by lightweight concrete are 12000

outweight by the high cost of specific aggregates. As shown by the chart to the left, the farther an aggregate has to travel, cost increases. On the

DESIGN

High

other hand, cement is not as costly, making high strenth concrete feasible.

MANUFACTURE

Costs

9000

Multiple 6000

White 3000

Low

Worse

Local

Single

Low

Gray

Uniformity

Aggregates

Admixtures

Pigments

Cement

Density Normal Mix

Precast Concrete

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High

High Stren

INTRODUCTION

Manufacture 2.3 Reinforcement

Types of Reinforcement There are two basic types of reinforcement used and reinforcing bars (rebar). Welded wire is used for thin shapes like slabs and rebar is formed into self supporting cages for more three dimensional shapes.

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MANUFACTURE MANUFACTURE

DESIGN

in precast construction, welded wire reinforcement

Reinforcing of Typical Bay

2.3 Reinforcement

Typical Shapes

INTRODUCTION

Manufacture

Flat slabs almost always use welded wire enough they sometimes utilize rebar cages and tensioning cables. Due to the three dimensional quality of columns and beams, they generally use rebar cages.

MANUFACTURE

Flat Slab

DESIGN

reinforcement while if double tees get large

Double Tee

Precast Concrete

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Beam or Column

Manufacture 2.3 Reinforcement

Prestressing

24’

18’

12’

6’

It is very common for precast members to be

DESIGN

prestressed. This type of reinforcement allows for longer spans and thinner sections than can be achieved with regular reinforcing. Most slabs, double tees, and beams are prestressed, but wall

18’

panels and columns vary. Prestressing can be done before or after the concrete is poured and

MANUFACTURE MANUFACTURE

cured. While pretensioning strands are generally laid flat across the casting bed, post tensioning is done through a monostrand.

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Prestressed

Regular Reinforcing

Height of Panel

INTRODUCTION

6’

3”

Prestressing Regular Reinforcing

3”

6”

9”

12”

Depth

6”

9” 3”

12” 6”

9”

12”

DESIGN

2.3 Reinforcement

INTRODUCTION

Manufacture

Before Pouring

Post Tensioned Monostrand

After Curing

Precast Concrete

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Cross Strands

MANUFACTURE

Pre Tensioned

INTRODUCTION

Manufacture

2.4 Molds

Mold Design Understanding and applying the concepts behind

DESIGN

mold design can really help make a project economical. With precast systems the number of uses per mold really counts towards justifying the manufacturing plant strategy.

MANUFACTURE MANUFACTURE

Total Mold

Basic Mold Types There are an infinite number of possible mold designs, but by looking at the envelope molds one can

start

discern

workable

types.

Conventional Mold

demonstrated to the right, mold approaches can be broken down into four basic types. There are total molds, conventional molds, back forming molds,

and

molds

with

haunches.

Simple

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conventional are the most preferred. They utilize a basic design that can be altered with removeable bulkheads. While the total mold appears to be the

Back Mold

most simplistic, it only yields one shape. Particle settling and extra cost make back forming molds uncommon. Haunches can be a reductive approach to this design strategy. Haunch Mold

2.4 Molds

Typical Shapes

INTRODUCTION

Manufacture

Shapes typically cast for precast construction always constructed out of steel because of the high reuse rate. The beds can last as long as 20 years, while a custom bed only lasts at most 100 casts.

DESIGN

have standard mold forms. These forms are

Double Tee can all be cast on conventional casting beds. The tailored shape is achieved through a slipformer or extruder. These machines set the shape and Flat Slab

MANUFACTURE

Compact shapes, beams and hollow core slabs,

Slipformer

Piles

Precast Concrete

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Beam

INTRODUCTION

Manufacture 2.4 Molds

Master Mold Concept The master mold strategy is the number one rule

DESIGN

of mold design. Born from the basic modified mold, a master mold is a manufacturers main tool for gaming costs. Through simple, inexpensive modifications one mold can be used to generate a number of shapes. With all precast design, the economics of each modification should be con-

MANUFACTURE MANUFACTURE

sidered. In the example shown to the right, one mold designed with two removeable bulkheads is used to create an assortment of six shapes.

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Mold Configurations

Cast, with side variations

Resultant Shapes

MANUFACTURE

DESIGN

2.4 Molds

1 2

2,3 4,5

Precast Concrete

INTRODUCTION

TRANSPORTX+XASSEMBLY

Manufacture

INTRODUCTION

Manufacture 2.4 Molds

Adjustable Molds Adjustable molds are more expensive, but under

DESIGN

certain circumstances they can make precasting a reasonable choice. They can be constructed of wood or steel and are fixed into position by clamps or laminatation. Due to the high reuse factor of steel, it is a more logical candidate for adjustable

molds.

with

most

precast

MANUFACTURE MANUFACTURE

methodology, it is more effecient to cast one shape as much as possible before reconfiguring the mold for further use.

1 4

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1. Mold Face

5. Wood Block

2. Wood Side Rail

6. Wood End Gate

3. Adjustable Clamps

7. Wood Wedges

4. Casting Deck

8. Wood Wedge Rail

2.4 Molds

U = Mold Cost per Sq Ft

Materials + Economy Everytime a mold is used, its cost efficiency used 25-30 times, and steel 50-100. This obsolescence provides an opportunity to create a new part when a new mold is needed

MANUFACTURE

anyways.

DESIGN

increases. However, wood molds can only be

Wood Steel

Uses

Precast Concrete

TRANSPORTX+XASSEMBLY

Cost per Sq Ft

( $f )

INTRODUCTION

Manufacture

Transport + Assembly

3.0 Introduction

Some of structural precast concreteâ&#x20AC;&#x2122;s greatest

INTRODUCTION

Transport + Assembly

advantages become apparent during its transportation and assembly sequences.

DESIGN

After the pieces have been manufactured according to their order of assembly, they are transported and assembled while other members are being cast in the plant. Large pieces of the building, in some cases even whole spaces, can be transported in one trip by several trucks and

MANUFACTURE

assembled expeditiously in much the same manner as structural steel. There are also much fewer details to fastened and connected by builders during the process, so the construction can be much faster and more predictable. Unlike site-cast concrete, construction phases can occur during poor weather conditions. Because the concrete has already cured, little damage will be incurred. This section will detail the transport of precast by trucking, the logic of its movements on site, and together and stabilize them through the finishing process and lifecycle of the building. While an inventive architect can create a wide variety of parts, connections, and details using precast methods, this section will focus on the simpler and more commonly used techniques.

Precast Concrete

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the joinery and detailing that secures the pieces

INTRODUCTION

Transport + Assembly 3.1 Shipping Logics

13’6” o.a. DESIGN

height

standard load

max gross vehicle weight:

≈ 8’6”

80,000 lbs

allowable overhang:

15 ft or 1/3 of

MANUFACTURE

total bed length

oversized load

≈ 14’

Highway Regulation

General Cost Note

Height and width are determined by federal hghway regulation. Length of trailer is unregulated by highway, but is subject to manufacturer standards.

While shipping costs vary, in most cases they tend to be cheaper than costs for welding crews. The fewer welds you make, the cheaper it will be. In order to make fewer welds, you must make larger pieces. In general the larger and fewer pieces, the better.

TRANSPORTX+XASSEMBLY

Average Single Vehicle Transportation Costs*: $6.99 /mile $11.29 /mile

Standard Load Size Oversized (Permit) Load Size

*Figures are derived from a Pittsfield-Hartford trip carrying 91 pieces over 78 loads on flatbed trucks. 36 of these were permit loads, and the permit cost for transporting an oversized load in the state of Massachusetts (2009, $350). Transportation and permitting costs will fluctuate based on state and current market prices.

3.1 Shipping Logics

8’6” load

INTRODUCTION

Transport + Assembly

60’ standard bed length FLATDECK TRAILER

The various deck sizes for carrying precast loads are usually chosen to facilitate carrying either long loads effienctly, in which case the flatdeck would be most logical, or taller loads, at which point the choice comes to efficiency versus heigh requirement of individual members. Flatdeck Trailers beds sit 60” above the ground.

DESIGN

Decks

height

Double-Drop Trailers sit as low as 20” above the ground.

10’2” load height

MANUFACTURE

Stepdeck Trailers sit 40' above the ground.

43’ standard bed length

11’10” load height

30’ standard bed length DOUBLE-DROP TRAILER Precast Concrete

TRANSPORTX+XASSEMBLY

STEPDECK TRAILER

Transport + Assembly 3.1 Shipping Logics

Attachments for Movement During manufacter, attachments are imbedded to allow for loops or hooks to be attached to the tops of the concrete members. These allow for cranes to lift the pieces into place on site and can be removed after installation before the finishing and grouting takes place. After detaching the loops and carrying apparatus, attention must be paid to make sure that the material left does not become corrosive or detract from material stability. (A) Imbedded in concrete (B) For crane to attach to, can be removed after installation.

TRANSPORTX+XASSEMBLY

MANUFACTURE

DESIGN

3.1 Shipping Logics

INTRODUCTION

Transport + Assembly

Carrying Precast Above, loads must be stacked on trucks in particular ways. Beams (A) and other horizontal members can overhang truckbeds because of their tensioning and intended load distribution. Slabs can be stacked on top of each other, which may also facilitate an easier installation from the truck bed. Vertical members (C) such as columns and panels must be kept upright to maintain their structural integrity. Here a stepdeck truck is used to allow a taller panel to be carried.

Precast Concrete

TRANSPORTX+XASSEMBLY

INTRODUCTION

Transport + Assembly 3.2 Crane and Site Logics

TRANSPORTX+XASSEMBLY

MANUFACTURE

DESIGN

Crawler Crane

Tower Crane

Derrick

Widest range of applications and sizes. Can range from small trucks outfitted with cranes to larg units that can rival tower cranes in height. Have the most manueverability but also the most intense operation. Unlike tower crane, range and height of movement are inversely proportional. Range will decrease with added height of the crane. Range: 280 ft max Weight Lift: 250 ton max Height Lift: 260 ft

Used to move pieces in a stable manner around site and for raising members. Used primarily in steel construction as well as pre-cast concrete. Range: 290 ft max Weight Lift: 19 ton max Height Lift: 270 ft

The derrick can range from small single units to large derrick systems consisting of multiple cranes. They are meant to lift vertically in an efficient manner and do not have much range. Typical application: installation of heavy precast panels, especially in facade construction, movement of large members and sections for road construction

3.2 Crane and Site Logics

generic street a

derrick

building foundation

tower crane

MANUFACTURE

generic street c

crawler

DESIGN

generic street a

INTRODUCTION

Transport + Assembly

offloading

generic street b

Transport and Site Logic Each type of transport has a specific logic on site that aids in the assembly of precast buildings. The site is commonly allocated so that multiple trucks can move and deliver pieces simultaneously as well as to allow for crawler movement.

Precast Concrete

TRANSPORTX+XASSEMBLY

freight truck

TRANSPORTX+XASSEMBLY MANUFACTURE

DESIGN

INTRODUCTION

3 Transport + Assembly

3.3 Joinery and Details

Assembly Sequence This urban condition has a grade that requires the trucking ramp to be built within the foundation walls at the edges of the site. Here (far left), you can see multiple loads of materials delivered by truck and ordered by their use and placement order. The crane then lifts these members into their corresponding location with the aid of workers on site (left and above).

Precast Concrete

TRANSPORTX+XASSEMBLY

MANUFACTURE

DESIGN

3.3 Joinery and Details

INTRODUCTION

Transport + Assembly

Transport + Assembly 3.3 Joinery and Details

TRANSPORTX+XASSEMBLY

Key of Details and Joints

Horizontal to Horizontal Transfer

Transport + Assembly 3.3 Joinery and Details

3.35

MANUFACTURE

DESIGN

Slab to Beam Connections

Horizontal to Vertical Transfer

3.33

Beam to Column Connections

Vertical to Vertical Transfer

INTRODUCTION

3.34

Beam to Beam Connections

3.32

Foundation to Column/Panel, Column/Panel to Column/Panel Connections

Precast Concrete

TRANSPORTX+XASSEMBLY

Horizontal to Horizontal Transfer

INTRODUCTION

Transport + Assembly 3.31 Joinery and Details

From the Ground Up: The pieces are manufactured, transported, and

DESIGN

assembled in an ascending order from the ground up. The pieces are then welded to each other through steel plates embedded in each piece. This ensures for seismic stability and to create a more rigid lateral bracing. However, the pieces

abide by much the same stacking logic of building

MANUFACTURE

blocks and the primary component holding them together, in the standard applications, is gravity. To create habitable space, the columns and beams create a framework (A) which allows the floor slabs (B) to sit inside. There are allowances

within this frame for the next level of columns and beams (C) to adhere to and rest in. The attachment of corresponding members is intrinsic to each piece of the framework. Each course of frame work allows for the easy assembly of the next level of framework as well as the addition of

TRANSPORTX+XASSEMBLY

floor levels and non structural panelling within the frame to create habitable space. Of course, as any child with building blocks will quickly learn from wind and the occasional bully, gravity alone will not do. The holding properties of gravity must be aided by fastening and attachments in order to ensure the stability and longevity of a structure.

While they appear to be independent members resting on each other, each piece is connected via steel apertures to corresponding members for greater stability.

MANUFACTURE

Detail Key 1. Precast concrete 2. Grout 3. Steel Contact Weld 4. Grouted Steel Tension Connection Steel contacts are welded together on site to finally bond the pre-cast members. these contacts are imbedded during the manufacturing process pre-cast elements. Contacts imbedded in foundation are done during the site casting process.

Precast Concrete

TRANSPORTX+XASSEMBLY

In this drawing, you can see the beams linked together by steel chords that connect through holes pre-drilled or cast in the vertical column (A). There are welds that occur at steel plates imbedded in the beam and column where the plates are linked by a steel angle welded between the two members (B). After the welds are complete, the steel chords are grouted over (C).

INTRODUCTION

3.31 Joinery and Details

DESIGN

Transport + Assembly

Transport + Assembly 3.32 Joinery and Details

Vertical to Foundation Transfer Foundation to Column, Foundation to Panel Connections

MANUFACTURE

DESIGN

INTRODUCTION

welded and bolted

welded plate

cast- in anchor

grouted dowel

Vertical to Vertical Transfer

TRANSPORTX+XASSEMBLY

Column/Panel to Column/Panel Connections

bolted and welded

welded plate

Horizontal to Vertical Transfer Beam to Column/Panel Connections

Precast Concrete

TRANSPORTX+XASSEMBLY

MANUFACTURE

DESIGN

3.33 Joinery and Details

INTRODUCTION

Transport + Assembly

INTRODUCTION

Transport + Assembly 3.34 Joinery and Details

TRANSPORTX+XASSEMBLY

MANUFACTURE

DESIGN

Horizontal to Vertical Transfer

Horizontal to Horizontal Transfer

Slab to Column/Panel Connections

Beam to Beam Connections

these connections can be varriated to include rectangular beams, t- beams, notch

Horizontal to Horizontal Transfer Slab to Beam Connections

Precast Concrete

TRANSPORTX+XASSEMBLY

MANUFACTURE

details in slabs and different slab types

INTRODUCTION

3.35 Joinery and Details

DESIGN

Transport + Assembly

TRANSPORTX+XASSEMBLY

MANUFACTURE

DESIGN

INTRODUCTION

Sources Allen, Edward, and Joseph Iano. The Architect’s and Sons, 2002 American Institute of Architects. Architectural Graphic Standards. Hoboken, NJ: John Wiley

DESIGN

Studio Companion. Hoboken, NJ: John Wiley

Breen, Timothy. Personal Interview. 28 Oct. 2009. Bruggeling, A.S.G. Prefabrication with Concrete. 1st ed. Taylor & Francis, 1991. Print.

MANUFACTURE

and Sons, 2007

Kind-Barkauskas, Friedbert et al. Concrete Construction Manual (Construction Manuals. 1st ed. Birkhäuser Basel, 2002. Print. Martin, Leslie D., and Christopher J. Perry. PCI Concrete, Sixth Edition, 2004. 6th ed. Precast/ Prestressed Concrete Institute, 2004. Print. Morris, A. E. J. Precast concrete in architecture. 1st ed. Whitney Library of Design, 1978. Print.

Precast Concrete

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Design Handbook: Precast and Prestressed

PRECAST CONCRETE ARCH G691 GRADUATE DEGREE PROJECT STUDIO FALL 2009 This publication has been prepared as part of a five week graduate thesis studio assignment in the Northeastern University School of Architecture for the Fall 2009 Architecture G691 course. Other publications in this series include urban retail, office, and parking garage typologies, all produced by graduate students in the Northeastern University architecture program.