Structure Codes and the Design Basis of RC Structures

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Department of Civil Engineering, University of Engineering and Technology Peshawar

Structure Codes and the Design Basis of
RC Structures

By: Prof Dr. Qaisar Ali

Civil Engineering Department

UET Peshawar

drqaisarali.com

drqaisarali@nwfpuet.edu.pk


Department of Civil Engineering, University of Engineering and Technology Peshawar

Topics Addressed


Building

Codes

and

the

ACI

Code



Objectives

of

Design


Design

Process


Limit

States

and

the

Design

of

Reinforced

Concrete


Basic

Design

Relationship


Structural

Safety




Department of Civil Engineering, University of Engineering and Technology Peshawar

Topics Addressed


Design

Procedure

Specified

in

the

ACI

Code


Design

Loads

for

Buildings

and

other

Structures


Customary

Dimensions

and

Construction

Tolerances


Admixtures


Factors Affecting Strength of Concrete


High Strength Concrete







Department of Civil Engineering, University of Engineering and Technology Peshawar

Topics Addressed


Durability
of Concrete


Concrete Subjected to High
Temperatures


Reinforcing
Steel


Chapter

3

:

Materials


Chapter

4

:

Durability

of

Concrete


Chapter

5

:

Concrete

Quality,

Mixing

and

Placing





Department of Civil Engineering, University of Engineering and Technology Peshawar

Building Codes and the ACI Code


General

Building

Codes


Cover

all

aspects

of

building

design

and

construction

from

architecture

to

structural

to

mechanical

and

electrical
---
.

UBC,

IBC

and

Euro
-
code

are

general

building

codes
.


Seismic

Codes


Cover

only

seismic

provisions

of

buildings

such

as

SEAOC

and

NEHRP

of

USA,

BCP
-
SP

07

of

Pakistan
.




Department of Civil Engineering, University of Engineering and Technology Peshawar


Material

Specific

Codes


Cover

design

and

construction

of

structures

using

a

specific

material

or

type

of

structure

such

as

ACI,

AISC,

AASHTO

etc
.


Others

such

as

ASCE


Cover

minimum

design

load

requirement,

Minimum

Design

Loads

for

Buildings

and

other

Structures

(ASCE
7
-
02
)
.




Building Codes and the ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar


General Building Codes in USA


The

National

Building

Code

(NBC),



The

Standard

Building

Code

(SBC),


The

Uniform

Building

Code

(UBC),


Building Codes and the ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar


General Building Codes in USA


The

International

Building

Code

IBC,



Published

by

International

Code

Council

ICC

for

the

first

time

in

2000
,

revised

every

three

years
.


The

IBC

has

been

developed

to

form

a

consensus

single

code

for

USA
.


Currently

IBC

2012

is

available
.


UBC

97

is

the

last

UBC

code

and

is

still

existing

but

will

not

be

updated
.

Similarly

NBC,

SBC

will

also

be

not

updated
.


In

future

only

IBC

will

exist
.


Building Codes and the ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar


Seismic Codes in USA


NEHRP

(National

Earthquake

Hazards

Reduction

Program)

Recommended

Provisions

for

the

Development

of

Seismic

Regulations

for

New

Buildings

developed

by

FEMA

(Federal

Emergency

Management

Agency)
.


The

NBC,

SBC

and

IBC

have

adopted

NEHRP

for

seismic

design
.


SEAOC

“Blue

Book

Structural

Engineers

Association

of

California

(SEAOC),

has

its

seismic

provisions

based

on

the

Recommended

Lateral

Force

Requirements

and

Commentary

(the

SEAOC

“Blue

Book”)

published

by

the

Seismology

Committee

of

SEAOC
.


The

UBC

has

adopted

SEAOC

for

seismic

design
.



Building Codes and the ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar


Building

Code

of

Pakistan


Building

Code

of

Pakistan,

Seismic

Provision

BCP

SP
-
07

has

adopted

the

seismic

provisions

of

UBC

97

for

seismic

design

of

buildings
.


IBC

2000

could

not

be

adopted

because

some

basic

input

data

required

by

IBC

for

seismic

design

does

not

exist

in

Pakistan
.



Building Codes and the ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar


The

ACI

MCP


ACI

MCP

(American

Concrete

Institute

Manual

of

Concrete

Practice)

contains

150

ACI

committee

reports
;

revised

every

three

years
.


ACI

318
:

Building

Code

Requirements

for

Structural

Concrete
.


ACI

315
:

The

ACI

Detailing

Manual
.


ACI

349
:

Code

Requirement

for

Nuclear

Safety

Related

Concrete

Structures
.


Many

others
.









Building Codes and the ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar


The

ACI

318

Code


The

American

Concrete

Institute

“Building

Code

Requirements

for

Structural

Concrete

(ACI

318
),”

referred

to

as

the

ACI

code,

provides

minimum

requirements

for

structural

concrete

design

or

construction
.


The

term

“structural

concrete”

is

used

to

refer

to

all

plain

or

reinforced

concrete

used

for

structural

purposes
.


Prestressed

concrete

is

included

under

the

definition

of

reinforced

concrete
.




Building Codes and the ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar


The

ACI

318

Code


7

parts,

22

chapters

and

6

Appendices
.


Brief

visit

of

the

code



Building Codes and the ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar


Legal

Status

of

The

ACI

318

Code


The

ACI

318

code

has

no

legal

status

unless

adopted

by

a

state

or

local

jurisdiction
.


It

is

also

recognized

that

when

the

ACI

code

is

made

part

of

a

legally

adopted

general

building

code,

that

general

building

code

may

modify

some

provisions

of

ACI

318

to

reflect

local

conditions

and

requirements
.




Building Codes and the ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar


The

Compatibility

Issue

in

BCP

SP
-
2007


Building

Code

of

Pakistan,

Seismic

Provision

BCP

SP
-
07

has

adopted

the

seismic

provisions

of

UBC

97

for

seismic

design

of

buildings
.


As

the

UBC

97

has

reproduced

ACI

318
-
95

in

Chapter

19

on

concrete,

the

load

combinations

and

strength

reduction

factors

of

ACI

318
-
02

and

later

codes

are

not

compatible

with

UBC

97

and

hence

BCP

SP
-
07
.

Therefore

ACI

318
-
02

and

later

codes

cannot

be

used

directly

for

design

of

a

system

analyzed

according

to

the

seismic

provisions

of

UBC

97
.



Building Codes and the ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar


The Compatibility Issue in BCP SP
-
2007


To

resolve

this

issue,

BCP

SP
-
2007

recommends

using

ACI

318
-
05

code

for

design

except

that

load

combinations

and

strength

reduction

factors

are

to

be

used

as

per

UBC

97
.


The

IBC

adopts

the

latest

ACI

code

by

reference

whenever

it

is

revised

and

hence

are

fully

compatible
.



Building Codes and the ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar

The Design & Design Team


General
:


The

design

covers

all

aspects

of

structure,

not

only

the

structural

design
.


The

structural

engineer

is

a

member

of

a

team

whose

members

work

together

to

design

a

building,

bridge,

or

other

structure
.

Department of Civil Engineering, University of Engineering and Technology Peshawar

Objectives of Design


Four

Major

Objectives

of

Design

1.
Appropriateness
:

This

include,


Functionality,

to

suit

the

requirements
.


Aesthetics,

to

suit

the

environment
.

2.
Economy


The

overall

cost

of

the

structure

should

not

exceed

the

client’s

budget
.

Department of Civil Engineering, University of Engineering and Technology Peshawar

Objectives of Design


Four

Major

Objectives

of

Design

3.
Structural

Adequacy

(safety)


Strength
.


Serviceability
.

4.
Maintainability


The

structure

should

be

simple

so

that

it

is

maintained

easily
.

Department of Civil Engineering, University of Engineering and Technology Peshawar

The Design Process


Three

Major

Phases

of

Design


1.
The

client’s

needs

and

priorities
.

2.
Development

of

project

concept
.

3.
Design

of

Individual

systems
.


Department of Civil Engineering, University of Engineering and Technology Peshawar

Basic Design Relationship


Limit

State

Design

approach


Capacity

is

reduced

and

demand

is

increased

based

on

scientific

rationale
.

In

LSD

approach,

we

have


f

M
n



M
u

(
α

M
s

)


f

V
n



V
u

(
α

V
s

)


f

P
n



P
u

(
α

P
s

)


f

T
n



T
u

(
α

T
s

)


f

=

strength

reduction

factor


α

=

load

amplification

factor



Department of Civil Engineering, University of Engineering and Technology Peshawar


Variability in Resistance


Effects of simplifying
assumptions


The

fig

shows

Comparison

of

measured

(M
test
)

and

computed

(M
n
)

failure

moments

for

112

similar

RC

beams

Structural Safety

Department of Civil Engineering, University of Engineering and Technology Peshawar


Variability

in

Loads


Fig

shows

variation

of

Live

loads

in

a

family

of

151
sft

offices
.


The

average

(for

50

%

buildings)

sustained

live

load

was

around

13

psf

in

this

sample
.


1
%

of

measured

loads

exceeded

44

psf
.


Building

code

specify

50

psf

for

such

buildings

(
ASCE

7
-
02
)


Structural Safety

Department of Civil Engineering, University of Engineering and Technology Peshawar

Structural Safety

Conclusion


Due

to

the

variability

of

resistances

and

load

effects,

there

is

definite

chance

that

a

weaker
-
than
-
average

structure

will

be

subjected

to

a

higher
-

than
-
average

load
.



In

extreme

cases,

failure

may

occur
.


The

load

factors

and

resistance

factors

are

selected

to

reduce

the

probability

of

failure

to

a

very

small

level
.


Department of Civil Engineering, University of Engineering and Technology Peshawar

Design Procedures Specified in the
ACI Code


The

Design

Philosophy

of

the

ACI

Code


9
.
1
.
1
-

structures

and

structural

members

shall

be

designed

to

have

design

strengths

at

all

sections

at

least

equal

to

the

required

strength

calculated

for

the

factored

loads

and

forces

in

such

combinations

as

are

stipulated

in

this

code
.


9
.
1
.
2
-

members

also

shall

meet

all

other

requirements

of

this

code

to

ensure

adequate

performance

at

service

load

levels
.



Department of Civil Engineering, University of Engineering and Technology Peshawar


The

Design

Philosophy

of

the

ACI

Code


This

process

is

called

strength

design

in

the

ACI

code
.



In

the

AISC

Specifications

for

steel

design,

the

same

design

process

is

known

as

LRFD

(Load

and

Resistance

Factor

Design)
.



Strength

design

and

LRFD

are

methods

of

limit
-
state

design,

except

that

primary

attention

is

always

placed

on

the

ultimate

limit

states,

with

the

serviceability

limit

states

being

checked

after

the

original

design

is

completed
.


Design Procedures Specified in the
ACI Code

Department of Civil Engineering, University of Engineering and Technology Peshawar


ACI

318
-
02
,

Section

8
.
2
-
LOADING
:


8
.
2
.
2
:

Service

loads

shall

be

in

accordance

with

the

general

building

code

of

which

this

code

forms

a

part,

with

such

live

load

reductions

as

are

permitted

in

the

general

building

code
.


Section

R
8
.
2

:
The

provisions

in

the

code

are

for

live,

wind,

and

earthquake

loads

such

as

those

recommended

in

“Minimum

Design

Loads

for

Buildings

and

Other

Structures,”
(ASCE

7
)
.



If

the

service

loads

specified

by

the

general

building

code

(of

which

ACI

318

forms

a

part)

differ

from

those

of

ASCE

7
,

the

general

building

code

governs
.

However,

if

the

nature

of

the

loads

contained

in

a

general

building

code

differs

considerably

from

ASCE

7

loads,

some

provisions

of

this

code

may

need

modification

to

reflect

the

difference
.


A

Design Loads for Buildings and Other
Structures

Department of Civil Engineering, University of Engineering and Technology Peshawar


ASCE

Recommendations

on

Loads
:



ASCE

7
-
02

sections

1

to

10

are

related

to

design

loads

for

buildings

and

other

structures
.


The

sections

are

named

as
:

general,

load

combinations,

dead,

live,

soil,

wind,

snow,

rain,

earthquake

and

ice

loads
.


Brief

visit

of

ASCE

7
-
02
,

Section

1

to

10




Design Loads for Buildings and Other
Structures

Department of Civil Engineering, University of Engineering and Technology Peshawar

Design Loads for Buildings and Other
Structures


Loads

on

Structure

During

Construction


During

the

construction

of

concrete

buildings,

the

weight

of

the

fresh

concrete

is

supported

by

formwork,

which

frequently

rests

on

floors

lower

down

in

the

structure
.


ACI

section

6
.
2
.
2

states

the

following
:


No

construction

loads

exceeding

the

combination

of

superimposed

dead

load

plus

specified

live

load

(un
-
factored)

shall

be

supported

on

any

un
-
shored

portion

of

the

structure

under

construction,

unless

analysis

indicates

adequate

strength

to

support

such

additional

loads




Department of Civil Engineering, University of Engineering and Technology Peshawar

Customary Dimensions and
Construction Tolerance


Difference

in

Working

and

As
-
Built

Drawings’

Dimensions


The

actual

as
-
built

dimensions

will

differ

slightly

from

those

shown

on

the

drawings,

due

to

construction

inaccuracies
.



ACI

Committee

117

has

published

a

comprehensive

list

of

tolerance

for

concrete

construction

and

materials
.


As

an

example,

tolerances

for

footings

are

+
2

inches

and



½

inch

on

plan

dimensions

and



5

percent

of

the

specified

thickness
.



Department of Civil Engineering, University of Engineering and Technology Peshawar

Admixtures


A

material

(usually

in

liquid

form)

other

than

cement,

water

and

aggregates,

that

is

used

as

an

ingredient

of

concrete

and

is

added

to

the

batch

immediately

before

or

during

mixing

to

change

properties

of

fresh

or

hardened

concrete
.

Department of Civil Engineering, University of Engineering and Technology Peshawar

Admixtures


Uses

Admixtures

are

used

to
:


achieve

certain

properties

in

concrete

more

effectively

than

by

other

means
.


maintain

the

quality

of

concrete

during

the

stages

of

mixing,

transporting,

placing,

and

curing

in

adverse

weather

conditions
.



reduce

the

cost

of

concrete

construction
.


Department of Civil Engineering, University of Engineering and Technology Peshawar

Admixtures


Types


As

per

ACI

Committee

212
,

admixtures

have

been

classified

into

following

groups
:


Air
-
entraining

Admixtures
:

causes

the

development

of

a

system

of

microscopic

air

bubbles

in

concrete,

mortar,

or

cement

paste

during

mixing
.

Air
-
entrained

concrete

should

be

used

wherever

water

saturated

concrete

may

be

exposed

to

freezing

and

thawing
.

Air

entrainment

also

improves

the

workability

of

concrete
.

Department of Civil Engineering, University of Engineering and Technology Peshawar

Admixtures


Types


Accelerating

Admixtures
:

causes

an

increase

in

the

rate

of

hydration

of

the

hydraulic

cement

and

thus

shortens

the

time

of

setting,

increases

the

rate

of

strength

development,

or

both
.


Water

Reducing

and

Set
-
Controlling

Admixtures
:

Reduce

the

water

requirements

of

a

concrete

mixture

for

a

given

slump,

modify

the

time

of

setting,

or

both
.


Department of Civil Engineering, University of Engineering and Technology Peshawar

Admixtures


Types


Admixtures

for

Flowing

Concrete
:

Flowing

Concrete

is

concrete

that

is

characterized

as

having

a

slump

greater

than

190

mm

(
7
-
1
/
2

in
.
)

while

maintaining

a

cohesive

nature
.


Miscellaneous


Freeze

Resistant,

Pigments,

Bonding,

Grouting

etc
.

(Refer

ACI

212

for

details

and

more

types

of

miscellaneous

admixtures)

Department of Civil Engineering, University of Engineering and Technology Peshawar


Factors

Affecting

Concrete

Strength


In

addition

to

mixing,

conveying,

placing

and

compaction,

the

strength

of

concrete

primarily

depends

on
:



Water

Cement

Ratio
:

Decrease

in

water

cement

ratio

increases

the

strength
.


Aggregate

Cement

Ratio
:

Decrease

in

aggregate

cement

ratio

increases

the

strength

up

to

a

value

of

around

2
.
0
.

Further

decrease

may

cause

decrease

in

strength
.

Properties of Concrete

Department of Civil Engineering, University of Engineering and Technology Peshawar


Factors

Affecting

Concrete

Strength


Aggregate
:

The

concrete

strength

is

affected

by

the

aggregate

strength,

its

surface

texture,

its

grading

and

maximum

size

of

the

aggregate
.


Curing
:

Prolonged

moist

curing

leads

to

the

highest

concrete

strength

Properties of Concrete

Department of Civil Engineering, University of Engineering and Technology Peshawar


Rate of Strength Gain


ACI

Committee

209

[
3
-
21
]

has

proposed

the

following

equation

to

represent

the

rate

of

strength

gain

for

concrete

made

from

Type

1

cement

and

moist
-
cured

at

70
°
F
.


f


c(t)
= f


c(28)

{t/(4 + 0.85t)}


Where

f


c(t)

=

is

the

compressive

strength

at

age

t

in

days
.



Properties of Concrete

Department of Civil Engineering, University of Engineering and Technology Peshawar


Rate

of

Strength

Gain

and

Cement

Types


Figure

shows

the

effect

of

type

of

cement

on

strength

gain

of

concrete

(moist

cured
;

w/c

=

0
.
49
)
.

I = Normal

II = Modified

III = High early strength

IV = Low heat

V = Sulfate resisting


Properties of Concrete

Department of Civil Engineering, University of Engineering and Technology Peshawar

High Strength Concrete


Concretes

with

strengths

in

excess

of

6000

psi

are

referred

to

as

high

strength

concrete
.



The

resulting

concrete

has

a

low

void

ratio
.


Only

the

amount

of

water

needed

to

hydrate

the

cement

in

the

mix

is

provided
.

Department of Civil Engineering, University of Engineering and Technology Peshawar

High Strength Concrete


UET

Lab

Results

for

Producing

High

Strength

Concrete


Mix

design

results

for

6000

and

8000

psi

concrete
.







Admixture

used
:

Sikament

520
BA


Table
-
A


Trial Test

Proportion

No.

of

cylinders

Date

of

preparation

Date

of

Testing

Slump
(in)

Avg.

Strength
(psi)

6000 psi

(1:1:2)

w/c (0.36)

6

25/6/2010

22/7/2010

2.5

6100


8000 psi

(1:0.8:1.5)

w/c (0.31)

6

28/6/2010

25/7/2010

2

8000

Department of Civil Engineering, University of Engineering and Technology Peshawar

Durability of Concrete


Three

most

common

durability

problems

in

concrete

are
:


Corrosion

of

steel

in

concrete
.


Breakdown

of

the

structure

of

concrete

due

to

freezing

and

thawing
.



Breakdown

of

the

structure

of

concrete

due

to

chemical

action
.


Department of Civil Engineering, University of Engineering and Technology Peshawar

Concrete Subjected to High
Temperatures


Compressive

Strength

of

Concrete

at

High

Temperatures


Department of Civil Engineering, University of Engineering and Technology Peshawar


ASTM

A

615
,

Specification

for

Deformed

and

Plain

Carbon
-
Steel

Bars

for

Concrete

Reinforcement
.


ASTM

A

706
,

Specification

for

Low
-
Alloy

Steel

Deformed

and

Plain

Bars

for

Concrete

Reinforcement
.


ASTM

A

996
,

Specification

for

Rail
-
Steel

and

Axle
-
Steel

Deformed

Bars

for

Concrete

Reinforcement
.

Deformed Bar Reinforcement

Department of Civil Engineering, University of Engineering and Technology Peshawar

Deformed Bar Reinforcement


Variation

in

Yield

Strength


Distribution

of

mill

test

yield

strength

for

grade

60

steel
.


Department of Civil Engineering, University of Engineering and Technology Peshawar

Deformed Bar Reinforcement


Strength

of

Reinforcing

Steel

at

High

temperatures


Deformed

reinforcement

subjected

to

high

temperatures

in

fires

tends

to

lose

its

strength
.


Department of Civil Engineering, University of Engineering and Technology Peshawar

ACI Chapter 3: Materials


Tests

of

Materials


A

complete

record

of

tests

of

materials

and

of

concrete

shall

be

retained

by

the

inspector

for

2

years

after

completion

of

the

project,

and

made

available

for

inspection

during

the

progress

of

the

work
.


Water


Water

used

in

mixing

concrete

shall

be

clean

and

free

from

injurious

amounts

of

oils,

acids,

alkalis,

salts,

organic

materials,

or

other

substances

deleterious

to

concrete

or

reinforcement
.

Department of Civil Engineering, University of Engineering and Technology Peshawar

ACI Chapter 3: Materials


Steel

Reinforcement


Reinforcement

shall

be

deformed

reinforcement,

except

that

plain

reinforcement

shall

be

permitted

for

spirals

or

pre
-
stressing

steel
;

and

reinforcement

consisting

of

structural

steel,

steel

pipe,

or

steel

tubing

shall

be

permitted

as

specified

in

this

code
.

Department of Civil Engineering, University of Engineering and Technology Peshawar

ACI Chapter 4: Durability of Concrete


Sulfate

exposures


Concrete

to

be

exposed

to

sulfate
-
containing

solutions

or

soils

shall

conform

to

requirements

of

Table

4
.
3
.
1

or

shall

be

concrete

made

with

a

cement

that

provides

sulfate

resistance

and

that

has

a

maximum

water
-
cementitious

materials

ratio

and

minimum

compressive

strength

from

Table

4
.
3
.
1
.


Department of Civil Engineering, University of Engineering and Technology Peshawar

ACI Chapter 5: Concrete Quality, Mixing
and Placing


Average

Strength

of

Concrete

Produced

in

the

Field


It

is

emphasized

in

this

chapter

that

the

average

strength

of

concrete

produced

in

the

filed

should

always

exceed

the

specified

value

of

fc


used

in

the

structural

design

calculations
.



This

is

based

on

probabilistic

concepts,

and

is

intended

to

ensure

that

adequate

concrete

strength

will

be

developed

in

the

structure
.




Department of Civil Engineering, University of Engineering and Technology Peshawar


Average

Strength

of

Concrete

Produced

in

the

Field


Variation

in

Strength


Variations

in

the

properties

or

proportions

of

constituents

of

concrete,

as

well

as

variations

in

transporting,

placing,

and

compaction

of

the

concrete,

lead

to

variations

in

the

strength

of

the

finished

concrete
.

In

addition,

discrepancies

in

the

tests

will

lead

to

apparent

differences

in

strength
.

ACI Chapter 5: Concrete Quality,
Mixing and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


Average

Strength

of

Concrete

Produced

in

the

Field


Variation

in

Strength


Figure

shows

the

distribution

of

strengths

in

a

sample

of

176

concrete

cylinder

tests

for

the

concrete

having

nominal

strength

of

3000

psi



Strength

less

than

nominal

=

9


Strength

more

than

nominal

=

167


ACI Chapter 5: Concrete Quality,
Mixing and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


ACI

recommendations

for

achieving

specified

strength

in

the

field


The

ACI

code

recommends

that

selection

of

concrete

proportions

for

achieving

a

specified

concrete

strength

in

the

field

shall

be

based

on

the

required

average

compressive

strength

of

concrete

f

cr



and

not

on

the

specified

strength
.



ACI

table

5
.
2
.
2
.


ACI Chapter 5: Concrete Quality, Mixing
and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


Selection

of

Concrete

Proportions


Proportions

of

materials

for

concrete

shall

be

established

to

provide
:


Workability

and

consistency

to

permit

concrete

to

be

worked

readily

into

forms

and

around

reinforcement

under

conditions

of

placement

to

be

employed,

without

segregation

or

excessive

bleeding
;


Resistance

to

special

exposures

as

required

by

Chapter

4

of

ACI
;


Conformance

with

strength

test

requirements

of

ACI

5
.
6
.


ACI Chapter 5: Concrete Quality, Mixing
and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


Selection

of

Concrete

Proportions


Recommendations

for

selecting

proportions

for

concrete

are

given

in

detail

in

“Standard

Practice

for

Selecting

Proportions

for

Normal,

Heavyweight,

and

Mass

Concrete”

(ACI

211
.
1
)
.


ACI Chapter 5: Concrete Quality, Mixing
and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


Sampling

Frequency

for

Strength

Tests


ACI

R
5
.
6
.
2
.
1
:

As

a

measure

of

quality

control,

the

code

recommends

following

criteria

for

collecting

samples

of

concrete

cylinders

from

a

given

class

of

concrete
:


Once

each

day

a

given

class

is

placed,

nor

less

than



Once

for

each

150

yd
3

of

each

class

placed

each

day,

nor

less

than


Once

for

each

5000

ft
2

of

slab

or

wall

surface

area

placed

each

day
.


In

calculating

surface

area,

only

one

side

of

the

slab

or

wall

should

be

considered
.






ACI Chapter 5: Concrete Quality, Mixing
and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


Strength

Test


A

strength

test

shall

be

the

average

of

the

strengths

of

two

cylinders

made

from

the

same

sample

of

concrete

and

tested

at

28

days

or

at

test

age

designated

for

determination

of

f
c

.





ACI Chapter 5: Concrete Quality, Mixing
and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


Criterion

for

Satisfactory

Concrete

Strength


ACI

5
.
6
.
3
.
3
:

Strength

level

of

an

individual

class

of

concrete

shall

be

considered

satisfactory

if

both

of

the

following

requirements

are

met
:


(a)

Every

arithmetic

average

of

any

three

consecutive

strength

tests

equals

or

exceeds

f
c

;


(b)

No

individual

strength

test

(average

of

two

cylinders)

falls

below

f
c


by

more

than

500

psi

when

f
c


is

5000

psi

or

less
;

or

by

more

than

0
.
10
fc


when

f
c


is

more

than

5000

psi
.





ACI Chapter 5: Concrete Quality, Mixing
and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


The

steps

taken

to

increase

the

average

level

of

test

results
:



It

will

depend

on

the

particular

circumstances,

but

could

include

one

or

more

of

the

following
:


An increase in
cementitious

materials content


Changes in mixture proportions


Reductions in or better control of levels of slump supplied


Closer control of air content


An improvement in the quality of the testing, including strict
compliance with standard test procedures





ACI Chapter 5: Concrete Quality, Mixing
and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


Investigation

of

Low

Strength

Test

Results


If

any

strength

test

of

laboratory
-
cured

cylinders

falls

below

specified

value

of

f
c


by

more

than

the

values

given

in

5
.
6
.
3
.
3
(b),

steps

shall

be

taken

to

assure

that

load
-
carrying

capacity

of

the

structure

is

not

jeopardized
.



ACI Chapter 5: Concrete Quality, Mixing
and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


Investigation

of

Low

Strength

Test

Results


If

the

likelihood

of

low
-
strength

concrete

is

confirmed

and

calculations

indicate

that

load
-
carrying

capacity

is

significantly

reduced,

tests

of

cores

drilled

from

the

area

in

question

in

accordance

with

“Method

of

Obtaining

and

Testing

Drilled

Cores

and

Sawed

Beams

of

Concrete”

(ASTM

C

42
)

shall

be

permitted
.



In

such

cases,

three

cores

shall

be

taken

for

each

strength

test

that

falls

below

the

values

given

in

5
.
6
.
3
.
3
(b)
.





ACI Chapter 5: Concrete Quality, Mixing
and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


Investigation

of

Low

Strength

Test

Results


According

to

ACI

5
.
6
.
5
.
4
,

concrete

in

an

area

represented

by

core

tests

shall

be

considered

structurally

adequate

if

the

average

of

three

cores

is

equal

to

at

least

85

percent

of

f
c


and

if

no

single

core

is

less

than

75

percent

of

f
c

.


ACI Chapter 5: Concrete Quality, Mixing
and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


Investigation

of

Low

Strength

Test

Results


If

criteria

of

ACI

5
.
6
.
5
.
4

are

not

met

and

if

the

structural

adequacy

remains

in

doubt,

the

responsible

authority

shall

be

permitted

to

order

a

strength

evaluation

in

accordance

with

Chapter

20

for

the

questionable

portion

of

the

structure,

or

take

other

appropriate

action
.



ACI Chapter 5: Concrete Quality, Mixing
and Placing

Department of Civil Engineering, University of Engineering and Technology Peshawar


Regular refresher courses for field staff at least twice a year


Code implementation in full letter and spirit


Provision for structural design cost in PC
-
1


Field execution check lists to be developed


Certification courses for contractors, fabricators and masons


Dissemination of FPM and the like material


Retrofitting of vulnerable structures


Strong link with Universities.

Some Humble Suggestions

Department of Civil Engineering, University of Engineering and Technology Peshawar








The End



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