Introduction to Concrete Structures

8/6/2019 Introduction to Concrete Structures

1/41

Concrete StructuresConcrete Structures

! Introduction to design methods in reinforced

concrete

! Sustainable construction is concrete green?

! Possibilities in concrete structure

!Technical concepts: Bending moment diagrams

Reinforced vs. prestressed concrete

Strut and tie method of design


2/41

OutlineOutline

! Introduction to concrete as a material

! Stresses in bending

! Reinforced concrete vs. prestressed

concrete

! Design methods

! Environmental issues

! Design possibilities

! Conclusions


3/41

UnreinforcedUnreinforced ConcreteConcrete

! Same as masonry: it must act in compression

(no resistance to tension)

Roman Pantheon, 126 AD


4/41


5/41


6/41


7/41

Design Basis for Reinforced ConcreteDesign Basis for Reinforced Concrete

Concrete must crack in order for the

reinforcing steel to carry load


8/41

Reinforced vs.Reinforced vs. PrestressedPrestressed ConcreteConcrete


9/41


10/41

Two design methods for concreteTwo design methods for concrete! Conventional design:

Determine moment diagram

Specify steel in areas of tension

! Strut and tie models:

Define internal forces in tension and

compression (ties and struts)

Specify steel in areas of tension


11/41

Strut and Tie ModelingStrut and Tie Modeling


12/41


Tie (tension)

Struts(compression)


13/41


T T

T

C C

C

C C


14/41



15/41

What is concrete?What is concrete?


16/41

Is concrete a green material?Is concrete a green material?


17/41

Construction and the EnvironmentConstruction and the Environment

In the United States, buildings account for:

36% of total energy use

(65% of electricity consumption)

30% of greenhouse gas emissions30% of raw materials use

30% of waste output (136 million tons/year)

12% of potable water consumption

-US Green Building Council (2001)


18/41

Construction WasteConstruction Waste

! US Environmental

Protection Agency (EPA)

estimates that 136 million

tons of waste is generated

by construction each year

! Most results from

demolition/renovationand nearly half the

weight is concrete

New construction:8%

Demolition:

48%Renovation:

44%


19/41

Embodied Energy per StiffnessEmbodied Energy per Stiffness

Wood Brick Concrete Steel Aluminum

(kJ/MN-

m)

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Source: Biggs (1991)


20/41

Energy required for concreteEnergy required for concrete

0%

6%

2%

92%

Energy %

6%Water

48%Crushed

stone

34%Sand

12%Portland

cement

Percent by

weight

Component

Each ton of cement produces one ton of CO2


21/41

! Concrete is in tune with the environment. From an environmentalstandpoint, concrete has a lot to offer.

!

The ingredients of concrete (water, aggregate, and cement) are abundant.Concrete can be made from local resources and processed near a jobsite.

! Concrete is an ideal medium for recycling waste or industrial byproducts.Many materials that would end up in landfills can be used instead to makeconcrete.

! Concrete is modest in its energy needs and generous in its payback. Theonly energy intensive demand is in the manufacture of portland cement,typically a 10-15% component of concrete.

! Concrete offers significant energy savings over the lifetime of a buildingor pavement. Concretes high thermal mass moderates temperatureswings by storing and releasing energy needed for heating and cooling.And concrete is a durable material that conserves resources by reducingmaintenance and the need for reconstruction.

! A reliable and versatile product for centuries, concrete paves the way

toward an environmentally secure future for successive generations.


22/41

Corrosion of Reinforced ConcreteCorrosion of Reinforced Concrete


23/41

Reinforced Concrete CorrosionReinforced Concrete Corrosion


24/41

Corrosion of RCCorrosion of RC

!

In the United States, the overall costsof reinforcing steel corrosion havebeen estimated at more than $150

billion per year.

! A particular problem for highwaybridges due to de-icing salts


25/41

Corrosion Prevention of RCCorrosion Prevention of RC

! Simplest method: Maintain concrete incompression and provide greater cover ofconcrete over rebar

! More complicated and more expensive: Protect steel (with epoxy coating) or by using

stainless steel rebar Use non-metallic reinforcing, such as carbon

or kevlar, but these materials are expensiveand energy-intensive


26/41

Structural Design in RCStructural Design in RC

! Maintain concrete in compression as much as

possible

! Follow moment diagram to minimize material use

! Detailed design Prevent water infiltration

Protect steel

Specify use of fly ash

Recycle old concrete


27/41

Fly Ash in ConcreteFly Ash in Concrete

! Fly ash is a byproduct of coal burning:

600 million tons are produced per yearand over 80% goes to the landfill

! Up to 50% of cement (by volume) can bereplaced with fly ash (15-35% is typical)

! Today only about 10% of available fly ashis used in concrete


28/41

Why use fly ash in concrete?Why use fly ash in concrete?

!

Reduce environmental impact

!

Improve workability (better finish)

! Increase corrosion resistance

! Improve long term concrete strength


29/41

Good practice in concrete designGood practice in concrete design

Reduce waste through design by eliminating unnecessary

concrete (i.e. use smaller transfer beams in the Stata

Center)

Use concrete waste as fill whenever possible around

buildings or as aggregate under parking lots and

driveways.

Specify fly ash, which can improve workability and

strength, as well as help to recycle waste.

Consider pre-cast concrete systems which can use

considerably less concrete.


30/41

PrecastPrecast Planks in ConcretePlanks in Concrete


31/41

TiltTilt--Up Concrete ConstructionUp Concrete Construction


32/41

Hanging Model by HeinzHanging Model by Heinz IslerIsler


33/41

Tension Model by HeinzTension Model by Heinz IslerIsler


34/41

Compression Model by HeinzCompression Model by Heinz IslerIsler


35/41


36/41


37/41

ConclusionsConclusions

! Concrete will continue to be a dominant

construction material! Reinforced concrete must crack in order for

reinforcing to work" lower durability becausesteel can corrode

! Prestressed concrete prevents cracking

!

Two powerful design methods: momentdiagrams or strut and tie models

! Environmental impact can be reduced through

design


38/41


39/41


40/41

Material PropertiesMaterial Properties

269180238000270070000Al

271597430007800210000Steel

117388300240027000Concrete

171682800180030000Brick

2253117050011000Wood

Energy/stiffnessEnergy

kJ/kgDensitykg/m3

StiffnessMN/m2


41/41

17010000Al

49029000Steel

1503000Concrete

1303100Brick

3011000Wood

Densitylb/ft3

Stiffnessksi

Material PropertiesMaterial Properties

Date post:	08-Apr-2018
Category:	Documents
Upload:	joseph-cloyd-l-lamberte
View:	224 times
Download:	0 times

Introduction to Concrete Structures

Documents