1. precast concrete introduction_ravi

Precast Concrete

International Institute of Information Technology HyderabadGachibowli, Hyderabad 500 032, India

IIIT- HYDRavikanth CH, Build India

1. Introduction

2. Why precast?

Contents of the presentation:

3. Design process

4. Architectural design aspects

6. MEP services aspects

7. Manufacturing aspects

8. Construction aspects

5. Structural design aspects


Why precast?


Factors to be considered when deciding to implement precast concrete construction:

Quality

Building site

Unique capabilities with precast Speed of construction

Construction aspects Costing


Quality in Precast

High strength concrete (M40 to M60)

High quality precast products

Skilled labor force

Ordinary reinforcement and prestressing steel Specialized design engineers

Controlled environment

Less wastage


Examples : high quality finishing

IIIT- HYD

Decision making why precast?

Ravikanth CH, Build India


Examples : high quality finishing


Unique capabilities with precast

Colored concrete and Graphic concrete

Prestressing

Natural stone / marble / tiling / bricks Sandwich panels with insulation

Mechanization mass production Customization small production

Fair faced concrete (exposed)



Examples : mass production of standard elements



Examples : customization



Examples : exposed aggregates



Examples : polished concrete samples




Examples : formliners



Examples : graphic concrete



Examples : sandwich panels


Speed of construction

Long lead time Longer design process Planning and logistics are crucial Overall shorter construction time

Very short erection time


Small team for execution



Examples : planning and logistics



Examples : small team for execution


Building site

Just in time delivery of precast elements Site casting vs factory casting Possible crane positions

Size of the construction site


Availability of nearby land Access for transportation

Clean and neat construction site



Examples : small site in urban areas



Examples : clean and neat construction site


Construction aspects

Health and safety standards Ease of construction Project management

Availability of labor


Availability of precast equipments



Examples : Small team / health and safety


Cost of precast

Time = Money

Long term strategy

Price vs Quality Think precast from the start

Consider total costs


Simplicity = cost saving



Examples : Simplicity in precast design


Major advantages of precast concrete

Reduction in manpower Less wastage Large floor spans possible

High Quality


Fast construction

Good health and safety standards Durable construction material


Major disadvantages of precast concrete

Limited flexibility Transportation problems Taxation

Large initial investment required


Heavy lifting equipment Longer preparation time required


Why precast? key decision making aspects

Availability of labor Price vs Quality Building site constraints

Total building cost


Time = money

Building design constraints Government initiatives

Unique capabilities with precast


Design process

for precast buildings


Aspects

Team

Design process

Tasks and responsibilities Design brief

Design process of precast buildings

Challenges


Architectural

Structural Services

Manufacturing Erection

Precast concrete

building



Team

Structural engineer

Precast manufacturer

Services consultant General contractor

Client Architect


Precast contractor Precast design engineer


Tasks and responsibilities

Strict planning has to be followed

Avoid last minute changes

MEP design required at early stage Early completion of detailed design

Decisions have to be made early One party has to coordinate


Work closely together


Design brief

Aesthetics finishing and joint locations

Manufacturing limitations

Design Codes Structural connections

Precast systemMaximum weight and size of pc elements


Tolerances of the precast componentsIIIT- HYDRavikanth CH, Build India


Design brief

Concept design

Final design

Shop drawings

Erection drawings

Architect sketch plan


Challenges during design phase

Coordination Lack of experience

Time pressure Lack of information



Architectural

design aspects

of precast buildings


Architectural design aspects

Design approach:

Modular design Design with larger floor spans

Not everything has to be precast concrete

Integration with MEP services

Minimize joints Restrict maximum weight of pc elements

No conversion of cast in-situ design Integration with structure


Layout

Simple and symmetrical layouts Alignment of load bearing elements Strategic location of shafts for services

Floor to floor height

Transportation restrictions height of panelsMinimum required clear heightMinimum space for services

Minimize cantilevers and offsets



Simple layout



Simple precast villas



Modular system is guided by the standard slabs

Modular design system

Grid size: multiple of 300mmMultiple of 1200mm for standard precast slabs


Important for standardized production methods

Alignment of other precast elementsWalls and columns are more flexible than slabs


Depending on design requirements

Repetition of precast elements

Small project minimize number of moulds

Evaluate per project Depending on production methods


Outer size of mould can be fixed (basic mould) Positions of windows and doors can vary Use symmetrical precast elements



Repetition in large scale precast project


Tolerances between elements

Detailing

Building should be water proof

Integration of architectural features inthe precast concrete elements.

Location of panel joints and false joints Deep recesses under 10 angle

Standard concept with simple customization


Chamfering at cornersIIIT- HYDRavikanth CH, Build India

False joints in precast panel


Chamfering


False joints in precast panels



Structural design aspects

of precast buildings


Seismic design of precast concrete structures

Precast structure has to withstand earthquake forces.

Structural integrity and connections between the precast elements are important.

Ductile behavior and detailing.

Structural system:



Frame structures Wall structures

- Moment resisting frame- Gravity frame with core

- Shear walls- Coupled shear walls



Low rise precast frame structures

Low rise frames with columns fixed in the foundation.



Possible arrangements of connections for precast concrete moment resisting frames in seismic zones.

Multistoried precast frames



Precast beams between columns



Precast T or cruciform units



Example of precast T units



Large panel systems Lift and staircase core

Precast floor slabs

External wall panelsInternal wall panels

Precast balcony



Erection of wall panels



Large wall panels

Design criteria


Advantages precast wall structure compared to rcc frame structure:

No brickwork infill walls required

Saves time and reduces manpower

Precast has superior quality of finishing No plastering is required

Thin walls increase the carpet area Precast concrete is more durable than clay brick Better health and safety standards




Structural design aspects:

Vertical load path

Lateral load path

Structural connections

Structural integrity

Configuration of the building


Configuration of the building:

Simple and symmetrical layout is required forearthquakes

Structures with precast shear walls are stiff whichresults in less damage during heavy earthquakes.

Avoid soft stories.

Avoid torsion.



Vertical load path:

Achieve proper transfer of vertical loads.

Grouted joints.

Corrugated steel sleeves filled with grout.

Welded and bolted connections



Wall to wall connection with grouting

Vertical load path:

High strength non-shrink grout

Reinforcement bar


Corrugated steel sleeve filled with grout.



Dowel bars in wall panels:


corbel

No disturbance in vertical load path. Direct load transfer between walls.

Enough bearing length for floor slab.

Enough space for tie reinforcement and wall to floor connection.

Vertical load path:



Vertical load path Grouting of the connections



Lateral load path:

Shear walls required in two directions

Floor diaphragm action

Structural integrity

Wind loads and Earthquake loads



Shear walls are cantilevered from the foundation.

Bottom walls are will develop yielding areas during heavy earthquake.

In the yielding areas ductile reinforcement detailing is required.

Shear walls structure:



Monolithic wall to wall connection:

Only use at critical locations

Preferred for inner wall panels because of finishing



Wall panels with reinforcement connection



shear shear

tensiontension

tensiontension

Connection can take load in both directions

Double wire loop connection



Embedded steel plates with site welding



Overlapping corner wall connections:

Simple connection

Suitable for inner walls

Not suitable for outer walls because of exposed joints

Ongoing research about structural behavior.



Floor diaphragm:

Tying the individual floor slabs.

Tie reinforcement at the edges.

Connection of floor diaphragm to shear walls.

Adequate connections to transfer diaphragmforces and adequate support of the pc floor

units are the basic requirements.



Floor diaphragm

hollow core slabs



Connections to achieve diaphragm action

Side connection

End connection



Hollow core connections



RCC topping on hollow core slabs:

Tying the individual members. Improve the waterproofing.Minimum 60mm thick Rough top surface of hollow core required



Casting rcc topping



Precast plank floor with lattice girder and rcc topping




Design of propping



MEP Services


MEP services

Services consultant and vendors have to bepart of the design team.

Some important points:

Coordination between the various consultants is very important.

Integration of services in the precast elements.


MEP services

Conduits inside RCC topping on slabs.

Electrical wiring:

Conduits inside precast wall panels


MEP services

Electricity conduit and electricity box in mould


MEP services

Electrical conduiting

Ducting

Plumbing

Conduits in toppingIIIT- HYDRavikanth CH, Build India

MEP services

Location of shafts

Provisions for air-conditioning

Openings in walls and beams

Hanging support for ac system


MEP services

Shaft opening


MEP services

Multiple openings in wall panels


MEP services

Precast beams with openings


MEP services

Typical hangers for hollow core slabs


MEP services

Special hollow core with space for ducts


MEP services

Exposed plumbing

Plumbing

Plumbing in recess in walls

Ledge wall

Plumbing inside topping


MEP services

Vertical grooves in precast walls


MEP services

Plumbing within rcc topping of plank floor


Manufacturing aspects



Different precast plants:

Permanent plant

Ordinary reinforced concrete elements

Site plant (casting yard)

Prestressed concrete elements

Different precast elements:



Site plantIIIT- HYDRavikanth CH, Build India


Permanent plant for hollow core slabsIIIT- HYDRavikanth CH, Build India


The design team has to understand the capabilities of the manufacturing unit.

Type of precast factories:

Semi Automated precast factory. Fully Automated precast factory.

Conventional precast factory.

Hollow core slab manufacturing process Precast plank floor manufacturing process



Flat moulds:

Vertical moulds:

Stationary flat moulds Circulating pallet system Tilting tables

Battery mould Column mould

Prestressing beds

Generally precast members are made as flat 2D elements.


Vertical battery moulds



Battery mould

(vertical)



Circulating pallet system

(flat moulds)



Tilting table



Design aspects regarding moulds:

- Size of mould

- Type of shuttering

- Finishing methods

- Curing methods

- Stripping methods

- Details like: chamfering, drip holes,

block outs, water proofing etc.


Fixed side shuttering at one side Steel angle

with magnets




Standard steel side shuttering with magnets:

Chamfer at edgesIIIT- HYDRavikanth CH, Build India


Steel flat mould with corbelIIIT- HYDRavikanth CH, Build India


Wooden moulds:

- Custom made wooden moulds

- Highly skilled carpentry work

- High flexibility

- Time consuming



Custom made wooden mould



Special machinery



Highly skilled carpentry work



Embedded parts in precast:

Standard products

Avoid penetrations through the mouldMinimum variation in embedded parts

Reinforcement:

Use prefab reinforcement Detailing check if reinforcement fits



Corrugated steel ducts



Standard coupler bars



Steel anchors in mould



Steel angle connected to embedded anchors



Reinforcement cages



Reinforcement cage placed in mould



Maximum size and weight of the elements?

Floor slabs:

Wall panels:

Depends on maximum span Generally slabs are lighter than walls

Depends on vertical transport on road Depends on crane capacity Depends on size of mould


Execution / Erection


Execution / erection aspects

Design aspects:

Easy access to connections Clean connections Tolerances Easy and fast erection

Crane position and lifting capacities

Casting of rcc topping Position of props and supports

Transportation restrictions



Just in time delivery



Mobile crane



Crawler crane



Lifting with two cranesIIIT- HYDRavikanth CH, Build India

Introduction

Tower cranes outside the buildingIIIT- HYDRavikanth CH, Build India

Introduction

Tower cranes inside the buildingIIIT- HYDRavikanth CH, Build India

Introduction

Position of temporary shoringIIIT- HYDRavikanth CH, Build India

Filling of horizontal joints with grout:

1. Place in mortar bed

2. Fill joint by hand placement

3. Pump grout in joint

4. Fill joint with flowable grout


Good joint filling has to be achieved.

Proper execution and quality control is required Grouting procedure has to be specified.

Easy access to the joint should be possible


Problem:

Mortar is coming out of joint.


This has to be cleaned.



Place grout by hand



Pouring grout in tubesIIIT- HYDRavikanth CH, Build India


Grouting pump


THE END


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1. precast concrete introduction_ravi

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