DESIGN OF MULTI-STORY PRECAST CONCRETE …DESIGN OF MULTI-STORY PRECAST CONCRETE BUILDING STUDENT’S NAME 1. Ahmed Kreem Mohammed 2. Hussein Shuai Shamran 3. Karar Latef Naji SUPERVISOR

DESIGN OF MULTI-STORY PRECAST

CONCRETE BUILDING

STUDENT’S NAME

1. Ahmed Kreem Mohammed

2. Hussein Shuai Shamran

3. Karar Latef Naji

SUPERVISOR

Asst.Prof. Dr.Sa'ad F.Resan

A project report submitted in partial fulfilment of the

requirements for the award of the degree of

Bachelor of Civil Engineering

Civil Engineering Department

Engineering College

University of Misan

Iraq

2017-2018

i

DECLARATION

I hereby declare that this project report is based on my original work except for

citations and quotations which have been duly acknowledged.

Signature : _________________________

Name : _________________________

Date : _________________________

ii

APPROVAL FOR SUBMISSION

I certify that this project report "DESIGN OF MULTI-STORY PRECAST

CONCRETE BUILDING"

was prepared by KRAR LATEF , AHMED KREAM and HUSSEIN SHUAI has

met the required standard for submission in partial fulfilment of the requirements for

the award of Bachelor of Civil Engineering at University of Misan.

Approved by,

Signature : _________________________

Supervisor : _________________________

Date : _________________________

iii

Specially dedicated to

my beloved mother

to my deceased father.

to my brothers

to my best freind Hussein Ali

to my teachers

iv

ACKNOWLEDGEMENTS

I would like to thank everyone who had contributed to the successful completion of

this project.I would like to express my gratitude to my research supervisor,

Asst.Prof. Dr.Sa'ad F.Resan for his invaluable advice, guidance and his enormous

patience throughout the development of the research.

In addition, I would also like to express my gratitud to my loving brother and

friends who had helped and given me encouragement......

v

DESIGN OF MULTI-STORY PRECAST CONCRETE BUILDING

ABSTRACT

The project consists of three-story classroom building of precast

structures element and this building consist of wall and hollow core

slab prestress that design with specification requirement

for load and safety according to ACI code for design wall

and PCI for design hollow core slab Iraqi Code of Loads and Powers.

vi

TABLE OF CONTENTS

DECLARATION i

APPROVAL FOR SUBMISSION ii

ACKNOWLEDGEMENTS iv

ABSTRACT v

LIST OF SYMBOLS / ABBREVIATIONS viii

CHAPTER ONE

1 INTRODUCTION 1

1.1 Background 1

1.2 Advantages of Precast Concrete Construction 3

1.3 Disadvantages of Precast Concrete 5

1.4 Applications 5

1.5 Literature Review 9

CHAPTER TWO

2 METHODOLOGY 12

2.1 prestressed hollow core slabs 12

2.2 precast wall 17

2.3 Connection 20

2.3.1 Connection details for hollow core slab system 20

2.3.2 connection wall to wall 24

2.4 Case Study 29

CHAPTER THREE

3.1 Design Prestressed hollow core slabs 40

3.2 Design of wall 48

3.3 Design of wall as deep beam 49

vii

CHAPTER FOUR

CONCLUSION AND RECOMMENDATIONS 52

REFERENCES 55

viii

LIST OF SYMBOLS / ABBREVIATIONS

A = Cross-sectional area

a = Depth of equivalent compression stress block

Aps = Area of prestressed reinforcement

bw = Net web width of hollow core slab

C = Factor for calculating steel relaxation

losses

CR = Prestress loss due to concrete creep

DL = Dead load

db = Nominal diameter of reinforcement

dp = Distance from extreme compression fiber to centroid of prestressed

reinforcement

e = Distance from neutral axis to centroid of prestressed reinforcement

Ec = Modulus of elasticity of concrete

Eci = Modulus of elasticity of concrete at the time of initial prestress

ES = Prestress loss due to elastic shortening of concrete

Es = Modulus of elasticity of steel reinforcement

f'c = Specified design compressive strength of

concrete

fci = Compressive strength of concrete at the time of initial prestress

fcir = Net compressive stress in concrete at centroid of prestressed reinforcement at

time of initial prestress

fcds = Stress in concrete at centroid of prestressed reinforcement due to superimposed

dead load

fd = Stress at extreme tension fiber due to unfactored member self weight

fpe = Compressive stress in concrete at extreme

fiber where external loads cause tension due to the effective prestress only

fps = Stress in prestressed reinforcement at nominal strength

fpu = Specified tensile strength of prestressing steel

fse = Effective stress in prestressing steel after all losses

fsi = Stress in prestressing steel at initial prestress

ix

J = Factor for calculating steel relaxation losses

k = Fraction of total load in a horizontal joint in a grout column

Kcir = Factor for calculating elastic shortening prestress losses

Kcr = Factor for calculating prestress losses due to concrete creep

Kes = Factor for calculating prestress losses dueto elastic shortening

Kre = Factor for calculating prestress losses dueto steel relaxation

Ksh = Factor for calculating prestress losses due to concrete shrinkage

LL = Live load

Mcr = Cracking moment

Md = Unfactored dead load moment

Mg = Unfactored self-weight moment

Mn = Nominal flexural strength

Msd = Unfactored moment due to superimposed dead load

P = Effective force in prestressing steel after all losses

Po = Effective prestress force at release prior to long term losses

Pi = Initial prestress force after seating losses

RE = Prestress loss due to steel relaxation

yb = Distance from neutral axis to extreme bottom fiber

yt = Used as either distance to top fiber or tension fiber from neutral axis

Chapter one introduction

10


1

Chapter One

Introduction

1.1 Background

The concept of precast (also known as “prefabricated”) construction

includes those buildings where the majority of structural components

are standardized and produced in plants in a location away from the

building, and then transported to the site for assembly. These

components are manufactured by industrial methods based on mass

production in order to build a large number of buildings in a short

time at low cost.

The main features of this construction process are as follows:

• The division and specialization of the human workforce

• The use of tools, machinery, and other equipment, usually

automated, in the production of standard, interchangeable parts and

products This type of construction requires a restructuring of the

entire conventional construction process to enable interaction

between the design phase and production planning in order to

improve and speed up the construction. One of the key premises for

achieving that objective is to design buildings with a regular

configuration in plan and elevation. In general, precast building

systems are more economical when compared to conventional

multifamily residential construction (apartment buildings) in many

countries.


2


3

1.2 Advantages of Precast Concrete Construction

a) Reduced Construction Time

Precast concrete construction will save valuable time and helps to

reduce the risk of project delay and possible monetary losses.

Precast design and production of elements can be started while the

construction site is under survey or earthworks. Production are

also unaffected by weather conditions due to the controlled

environment of the casting area. Also, the usage of large precast panels

will reduce the time taken to complete the structural works. Therefore, other

trades such as painting and electrical wiring can begin work sooner.

b) High quality and aesthetical value of products

Precast products are manufactured in a casting area where critical

factors including temperature, mix design and stripping time can

be closely checked and controlled and this will ensure that the

quality of precast products are better than cast-in-situ concrete. A

huge sum of money will be saved by not having to do rectification

works. Also due to factory-controlled prefabrication environment,

many combinations of colours and textures can be applied easily

to the architectural or structural pieces. A vast range of sizes and

shapes of precast components can be produced, providing a great

deal of flexibility and offer fresher looks to the structures.

c) Greater unobstructed span

The usage of prestressed precast solutions such as the Hollow

Core slabs and Double-T beams offer greater unobstructed span


4

than the conventional reinforced concrete elements. Having lesser

beams and columns, will provide larger open space. It is very ideal

for the construction of places of worship, warehouses, halls, car

parks, shops and offices

d) Cleaner and safer construction sites

Usage of precast elements eliminates or greatly reduces

conventional formworks and props. Precast construction also

lessens the problem of site wastages and the related environmental

problems. The prefabricated products also provide a safe working

platform for workers to work on.

e) Increased Quality of Structural Elements

Precast concrete elements produced in plants using modern

techniques and machineries. Raw materials such as concrete, sand,

and reinforcement bars are under high level of quality control.

Formworks used are of higher quality than those used at

construction sites. This allows truer shapes and better finishes in

precast components. Precast components have higher density and

better crack control, offering better protection from harsh weathers

and sound insulation.

f) Increased Durability and Load Capacity of Structural

Elements Prestressed precast concrete components have high

structural strength and rigidity, which are important to support

heavy loads. This allows shallow construction depth and long span

in structural components. Fewer supporting columns or walls

result in larger floor space, which allow more flexibility in interior

design.


5

1.3 Disadvantages of Precast Concrete

a) The precast method of construction becomes uneconomical for

small residential construction.

b) While transportation of the precast units to larger distance it may

subject to get damage

c) Sophisticated Connection Works

The behaviour of connections determines the performance of

precast concrete structures. When assembling of precast concrete

structures, connections between precast components must be

supervised and done properly.

1.4 Applications

1.4.1 Building Structures


6

1.4.2 Residential Buildings

1.3.1 Office Buildings


7

1.3.2 Warehouses and Industrial Buildings

1.3.3 Parking Structures


8

1.3.4 Stadiums/Arenas

1.3.5 Bridges


9

1.4 Literature Review

Nowadays the precast concrete has been used extensively in many

residential and commercial construction projects. It is because of

the property of the precast concrete. It has higher durability,

thermal properties and very easy to handle and so on. Also the

quality of the precast concrete is higher as it is manufactured

under great control. But there is lack of awareness and knowledge

regarding the precast concrete in our country. This has to be

changed and more study has to be done regarding precast. The

connection details of the precast members also should be studied

well.

Sarakot Asaad Hasan, BEHAVIOUR OF DISCONTINUOUS

PRECAST CONCRETE BEAM-COLUMN CONNECTIONS,

University of Nottingham, 2011: The study investigates

experimentally and theoretically the behaviour of an internal

precast concrete beam-column connection, where both the column

and beam are discontinuous in construction terms. The aim was to

modify the behaviour mechanisms within the connection zone by

introducing a beam hogging moment resistance capacity under

dead loads and limiting the damage within the connection. This is

to offer permanent dead load hogging moments that could

counterbalance any temporary sagging moment generated under

sway loads, enhance the rotational stiffness, balance the design

requirements for the beam-end and beam mid-span moments,

provide efficient continuity across the column, and reduce the

deflection at the beam mid-span. Connection provides a hogging


10

moment capacity under dead loads as well as under live loads.

Connection could be dealt with as an equivalent monolithic

connection under gravity loading by using the strong connection

concept. The simplified semi-rigid analysis using short stubs with

appropriate stiffnesses, reflecting the connection flexibility, was

found to give the exact solution when the stub length approaches

zero.

Patrick Tiong Liq Yee, Azlan Bin Adnan, Abdul Karim Mirasa

and Ahmad Baharuddin Abdul Rahman , Performance of IBS

Precast Concrete Beam-Column Connections Under Earthquake

Effects: A Literature Review, American J. of Engineering and

Applied Sciences 4 (1): 93-101, 2011, ISSN 1941-7020,2010

Science Publications, 2011: The main objective of this study was

to identify the most appropriate type of beam-column connections

to be introduced to precast concrete industry, particularly for

regions of low to moderate seismicity. Hence, this study presented

a comprehensive literature overview of the findings from studies

conducted to analyze and investigate the behavior of precast

concrete systems assembled with typical connections or joints

under simulated earthquake loading. The seismic performance of

precast concrete structure very much depended on the ductility

capacity of the connectors jointing each precast components,

especially at critical joints such as the beam-tocolumn connections.

It was learnt from the review that (1) hybrid post-tensioned beam-

column connection and (2) Dywidag Ductile Connector were


11

among the most widely used connectors for precast construction in

seismic prone regions. Future refinement and research could be

carried out in order to optimize these connections to be used in

low seismicity regions. Proposed connection type should be

practical and well-accepted to avoid further impediment

of the precast system.

MULTILEVEL CAR PARK, INFOSYS, HINJEWADI, PUNE.

As per below photos, Concrete grade is M50. The precast column

are three floor height and the size is 900mm x 900mm and height

is 9.6m. Precast Beams are sitting on the corbel introduced in the

precast column. The dowel bar is embedded in the corbel while

production of column. There are sleeves provision in precast

beams. While installation of precast beams the dowel bars coming

from corbel are inserted in the beam sleeves. Elastomer pads are

used underneath of precast beams for lateral forces, rotation or

vertical movement in the columns due to seismic. These are

Dowel-pin connections

Chapter three Results and Discussion

12

Chapter Two

Methodology

2.1 DESIGN OF PRESTRESSED HOLLOW CORE

CONCRETE

2.1.1 Permissible stresses at transfer

a) Extreme fiber stress in compression ………. 0.6 f'c

b) Extreme fiber stress in tension except as permitted in (c)

…………………………………………… …………….3 √𝑓𝑐𝑖′

c) Extreme fiber stress in tension at ends of simply supported

members

……………...……………………………….. ………….6√𝑓𝑐𝑖′

2.1.2 Permissible stresses at service loads

a) Extreme fiber stress in compression due to prestress plus sustained

loads …….………………………………………….. ……...0.45f'c

b) Extreme fiber stress in compression due to prestress plus total

load ……………………………………………………… ..0.60f'c

c) Extreme fiber stress in tension in pre-compressed tensile

zone ……………………………………………………… 6 √𝑓𝑐′

d) Extreme fiber stress in tension in pre-compressed tensile zone

where deflections are calculated

considering bilinear moment-deflection

relationships………………………………………….. 12 √𝑓𝑐′


13

2.1.4 Stresses at Transfer

When the prestressing strands are cut to apply the prestressing

force to the concrete, only the slab self weight is present to

counteract the effects of eccentric prestress. A check of stresses is

required at this point to determine the concrete strength required to

preclude cracking on the tension side or crushing on the

compression side. The concrete strength at the time of transfer

may be only 50% to 60% of the 28 day design strength.

2.1.5 Prestress Losses

1) Elastic Shortening

ES = Kes ES

Eci fcir

Kes = 1.0 for pretensioned members

Fcir = Kcir (𝑃𝑖

𝐴+

𝑃𝑖𝑒2

𝐼) -

𝑀𝑔𝑒

I

Kcir = 0.9 for pretensioned members

2) Concrete Creep

CR = Kcr ES

Ec (fcir - fcds )

Kcr = 2.0 for normal weight pretensioned members

fcds = 𝑀𝑠𝑑 𝑒

I


14

3) Shrinkage of Concrete

SH = 8.2 x 10-6 KshEs x ( 1 − 0.06 V

S ) x (100 - RH)

Ksh = 1.0 for pretensioned members

4) Steel Relaxation

RE = [Kre - J (SH + CR + ES)]C

Total Loss = ES + CR + SH + RE

Table value J

Table Value of C


15

2.1.6 Service Load Stresses

Tensile stress limits of between 6 √𝑓′𝑐 and 7.5 √𝑓′𝑐 are

commonly used. In special circumstances where deflections will

not be a problem and where cracking will not be of concern, the

upper limit of 12√𝑓′𝑐 can be used.

2.1.7 Design Flexural Strength

φMn ≥ Mu

φMn ≥ 1.2 Mcr

Mcr = I

yb(

P

A +

Pe

Sb + 7.5√fc

′ )

φMn = φApsfps( dp - 𝑎

2 )

fps= fpu [1- 𝛾𝑝

𝛽1 ( ρp

fpu

𝑓𝑐′ )]

γp = 0.28

ρp = 𝐴𝑝𝑠

𝑏𝑑𝑝

ωp = ρpfps

fc′

Camber and Deflection

Camber : is the upward deflection of a prestressed member and results

from the prestressing force being eccentric from the center of gravity of

the cross-section Cambers and deflections will change with time due to

concrete creep, prestress loss and other factors.


16

Long term multipliers

Initial Camber

Camber = 𝑃𝑒𝑙2

8𝐸𝑐𝑖𝐼

Deflection = 5𝑊𝑙4

284𝐸𝑐𝑖𝐼


17

2.2 Design of walls

Design strength

(a) ϕPn ≥ Pu

(b) ϕMn ≥ Mu

(c) ϕVn ≥ Vu

Wall thickness

Design axial strength

ϕPn = ϕ0.55f'c*Ag*[1-( 𝑘𝑙𝑐

32ℎ)2]


18

Minimum reinforcement

Vertical reinforcement ratio

l 0.0015

Reduce to 0.0012 for bar sizes No. 16 and

fy 420 MPa

Horizontal reinforcement ratio

t 0.0025

Reduce to 0.0020 for bar sizes No. 16 and

fy 420 MP

Reinforcement detailing

For walls with h greater than 10 in., except basement walls and

cantilever retaining walls, distributed reinforcement for each direction

shall be placed in two layers parallel with wall faces in accordance with

(a) and (b):

(a) One layer consisting of at least one-half and not exceeding two-thirds

of total reinforcement required for each direction shall be placed at least

2 in., but not exceeding h/3, from the exterior surface.


19

(b) The other layer consisting of the balance of required reinforcement in

that direction, shall be placed at least 3/4 in., but not greater than h/3,

from the interior surface.

Spacing

Spacing s of longitudinal bars in precast walls shall not exceed the lesser

of (a) and (b):

(a) 5h

(b) 18 in. for exterior walls or 30 in. for interior walls

If shear reinforcement is required for in-plane strength , shall not exceed

the smallest of 3h, 18 in , and ℓw/3

Spacing s of transverse bars in precast walls shall

not exceed the lesser of (a) and (b):

(a) 5h

(b) 18 in. for exterior walls or 30 in. for interior walls

If shear reinforcement is required for in-plane strength, s

shall not exceed the least of 3h, 18 in., and ℓw/5

Reinforcement around openings

In addition to the minimum reinforcement required at least two No. 5

bars in walls having two layers of reinforcement in both directions and

one No. 5 bar

in walls having a single layer of reinforcement in both directions shall be

providedaround window, door, and similarly sized openings. Such bars

shall be anchored to develop fy in tension at the corners of the openings.


20

2.3 Connection

2.3.1 Connection details for hollow core slab system

Design considerations

Can transfer internal diaphragm forces

• Can be designed as structural

integrity tie Fabrication considerations

• Advantageous to have no hardware

in slab

• Beam embodiments’ must line up

with slab joints

• Accommodates variations in slab

Length Erection considerations


• Can transfer internal diaphragm

forces


integrity tie Fabrication considerations

• May increase beam reinforcement

For shallower beam

• Layout must have opposing slab

joints lined up Erection considerations

• Clean and simple


21



forces


integrity tie

Fabrication considerations

• May increase beam

reinforcement For shallower beam


joints lined up Erection.



forces


integrity tie


• May increase beam reinforcement

For shallower beam


joints lined up Erection

considerations


22



forces


integrity tie


• Clean and simple Erection

considerations

• Clean and simple


Can transfer diaphragm shear

Can provide lateral brace for beam

Potential to develop negative

moment in slabs

Erection considerations

Connection can be completed with

a follow-up crew

Lateral bracing for beam will not

be provided until keyway grout cures


Plates in beam must align with slab

joints allowing tolerance


23

Design considerations:


Can be designed as structural

integrity tie

Can provide lateral brace for

wall

Consider axial force path

through slab ends

Opposing slab joints must

line up

.Design considerations


Can be designed as structural

integrity tie

Can provide lateral brace for wall

Opposing slab joints must line up


Clean and simple for slabs

Erection considerations

Clean and simple

Wall is not braced until grout is

placed and cured


24

2.3.2 connection wall to wall


25


26


27


28


29

2.4 Case Study


30


31


32


33


34


35


36


37


38


39


40

Chapter Three

Results and Discussions

3.1 DESIGN OF PRESTRESSED HOLLOW CORE CONCRETE

f'c = 5000 psi

f'ci =2875 psi

fpu = 270,000 psi

Ec = 33*w1.5 *√𝑓𝑐′ = 33*(150)1.5*√5000

= 4300 ksi

Eci = 33*w1.5 *√𝑓𝑐′ = 33*(150)1.5*√2875

= 3250 ksi

Es = 28500 ksi

Properties of section

A = 259 in2

I = 3223 in4

yb = 5.00 in

yt = 5.00 in

Sb = 645 in3

St = 645 in3

wt = 270 lb/ft

DL = 68 lb/ft2

V/S = 2.23 in

bw = 10.5 in

e = 3.5 in

dp = 8.5 in

L = 7.2 m ( 23.6232 ft )

Lc = 7 m ( 22.967 ft )

D.L = 2 kn/m2 ( 41.77 psf )

L.L = 3 kn/m2 (62.65 psf )


41

Assume prestress steel 6- 1/2"

1) Transfer Stresses

Aps = 6(0.153) = 0.918 in2

assume 5% initial loss

Po = 0.7*Aps*fpu*(1- 0.05)

Po = 0.7*0.95*0.918*270 = 164.8 k

Prestress effect

σcp = P0

𝐴 ±

𝑃𝑜∗𝑒

𝑆

σcp = 164.8

259 ±

164.8∗3.5

645

= - 0.258 ksi for top fiber

= 1.53 for bottom

Self weight at transfer point

ℓt = 50db = 50(1/2) = 25 in

Md = ( 23.6232

2∗ 1.788 −

1.7882

2 ) = 10.03 ft-k

𝑀𝑑

𝑆 =

10.03

645

= 0.186 for top fiber

= - 0.186 for bottom

Net concrete stress at transfer point

= - 0.072 ksi top

= 1.344 ksi bottom

Self weight at midspan

Md = 𝑊∗𝑙2

8 =

0.068∗4∗23.62322

8

= 18.97 ft-k


42

𝑀𝑑

𝑆 =

18.97∗12

645

= 0.353 ksi top

= - 0.353 bottom

Net concrete stress at midspan

= - 0.095 ksi top

= 1.177 ksi bottom

Allowable stresses

Tension end = 6√𝑓𝑐𝑖′

f'ci = ( 72

6 )2 = 144 psi

tension at midspan = 3√𝑓𝑐𝑖′

does not control

compression = 0.6f'ci

f'ci = 1.344

0.6∗1000 = 2036 psi

concrete strength required at release = 2036 psi

Prestress Losses

1) Elastic Shortening

Pi = 0.7*6*0.153*270 = 173.5 k

fcir = 0.9(𝑃𝑖

𝐴+

𝑃𝑖∗𝑒2

𝐼−

𝑀𝑔

𝐼 )

= 0.9*(173.5

259+

173.5∗3.52

3223−

18.97∗3.5

3223 )

= 0.95 ksi

Es = 28500 ksi Eci= 3250 ksi

ES = 𝑘𝑒𝑠𝐸𝑠

𝐸𝑐𝑖∗ 𝑓𝑐𝑖𝑟 = 1*

28500

3250*0.95 = 8.33 ksi


43

2) Concrete Creep

CR = kcr* 𝐸𝑆

𝐸𝑐 *( fcir –fcds )

fcds= 𝑀𝑠𝑑 𝑒

𝐼

Msd = 0.04177∗4∗23.62322

8 = 11.65 ft-k = 140 in-k

fcds= 140∗3.5

3223 = 0.152 ksi

CR = 2*28500

4300∗ (0.95 − 0.152) = 10.58 ksi

3) Shrinkage of Concrete

𝑉

𝑆 = 2.23

Use RH = 70%

SH = 8.2 x 10-6KshEs(1 − 0.06*𝑉

𝑆 )

= 8.2 x 10-6*1*28500(1 − 0.06*2.23 ) = 6.07 ksi

4) Steel Relaxation

From Table

Kre = 5000, J = 0.04

From Table

C = 0.75 for fsi/fpu = 0.7

RE = [Kre – J*(SH + CR + ES)]C

= [5000/1000 − 0.04*(6.27 + 8.74 + 7.52)] 0.75

= 3 ksi

Total Loss = ES + CR + SH + RE

Total Loss = 10.58 + 8.33 + 6.07 + 3 = 27.98 ksi

Loss% = 27.98

0.7∗270*100 = 14.8 %


44

Service Load Stresses

Msustained = 22.9672

8*(0.068 + 0.04177)

= 7.24 ft.k/f = 86.88 in-k/ft

M Service = 22.9672

8 (0.068 + 0.04177 + 0.06265)

= 11.37 ft-k/ft = 136.44 in-k/ft

With losses = 14.8%

Apsfse = 0.7*6*0.153*270(1 – 0.148) = 147.8 k

Top fiber compression with sustained loads

ftop = 147.8

259−

147.8∗3.5

645+

86.88∗4

645 = 0.3 ksi

Permissible compression

= 0.45f′c

= 0.45(5000)

= 2.25 ksi > 0.3 ksi OK

Top fiber compression with total load

ftop = 147.8

259−

147.8∗3.5

645+

136.44∗4

645 = 0.614 ksi

Permissible compression

= 0.60f′c

= 0.60(5000)

= 3.00 ksi > 0.614 ksi OK

Bottom fiber tension

fbottom = 147.8

259+

147.8∗3.5

645−

136.44∗4

645 = 0.52 ksi


45

Permissible tension

= 7.5√𝑓𝑐′= 7.5√5000 = 0.53 ksi

= 0.530 ksi > 0.52 ksi OK

Design Flexural Strength

φMn = φApsfps( dp - 𝑎

2 )

fps= fpu [1- 𝛾𝑝

𝛽1 ( ρp

fpu

𝑓𝑐′ )]

γp = 0.28

𝛽1 = 0.85 - (5000 −4000

1000)*0.05 = 0.8

ρp = 𝐴𝑝𝑠

𝑏𝑑𝑝 =

6∗0.153

48∗8.5 = 0.00225

fps= 270 [1- 0.00225

0.8 ( 0.00225*

270

5 )] = 258.5 ksi

a = 𝐴𝑃𝑆𝑓𝑠𝑒

0.85 =

0.918∗258.5

0.85∗5∗48 = 1.16 in

φMn = 0.918*258.5( 8.5 - 1.16

2 ) = 140.95 ft-k/slab

Wu = 1.4*(0.068 + 0.04177) + 1.7*(0.06265) = 0.26 ksf

Mu = 𝑤𝑙2

8 =

0.26∗22.9672

8 = 17.14 ft-k/ft = 68.57 in.k/slab < 140.95 0k

Check minimum reinforcement

φMn ≥ 1.2 Mcr

Mcr = I

yb(

P

A +

Pe

Sb + 7.5√fc

′ )

Apsfse= 0.7*6*41.3*(1- 0.148) = 147.8 k

Bottom compression

fbottom = 147.8

259+

147.8∗3.5

645 = 1.37 ksi

Mcr = 3223

5∗(

147.8

259 +

147.8∗3.5

645 +

7.5∗√5000

1000 )

= 1224.95 in-k

φ𝑀𝑛

𝑀𝑐𝑟 =

140.95∗12

1224.95 = 1.32 > 1.2 ok


46

Camber and Deflection

Initial Camber

Po = 0.95*0.7*6*0.153*270 = 164.827 k

Camber = 𝑃𝑜𝑒𝑙2

8𝐸𝑐𝑖𝐼 =

164.827∗3.5∗(22.967)2

8∗3250∗3223 = 0.523"


284𝐸𝑐𝑖𝐼 =

5∗0.068∗4∗(22.967)4∗123

384∗3250∗3223 = 0.1626"

Net camber at release = 0.523 – 0.1626 = 0.36"

Long Term Camber

At erection,

initial camber = 0.36"

Erection camber = 0.523*(1.80) – 0.1626*(1.85)

= 0.64"

Final camber = 0.523*(2.45) – 0.1626*(2.70)

= 0.84″

Deflections

superimposed dead load instantaneous deflection


284𝐸𝑐𝐼 =

5∗0.04177∗4∗(22.967)4∗123

384∗4300∗3223 = 0.075"

Final deflection = 0.075* (3.0) = 0.225″

Instantaneous live load deflection

5𝑊𝑙4

284𝐸𝑐𝐼 =

5∗0.06865∗4∗(22.967)4∗123

384∗4300∗3223 = 0.124"

Final position

0.84 – 0.225 – 0.124 = 0.491"

Change in camber = 0.84 – 0.64 = 0.2

Sustained dead load = - 0.225


47

Instantaneous live loads = - 0.124

= -0.149"

0.149 < 22.967∗12

360= 0.765 " ok


48

Design of walls

Thickness of wall

h = 100 mm

Or

h ≥ 𝑙𝑐

25 =

3500

25= 140 𝑚𝑚

use h = 200 mm

1) Capacity of a Bearing Wall

ϕPn = ϕ0.55f'c*Ag*[1-( 𝑘𝑙𝑐

32ℎ)2]

ϕ = 0.65

=0.65*0.55*25000*6.2*0.2*[1-( 1∗3.5

32∗0.2)2]

= 7768 kn > 822.75 kn ok

2) Select Reinforcement

Vertical

As = (0.0012)(1000)(200) = 240 mm2/m

Horizontal spacing of vertical reinforcement

Sh,max = 𝐴𝑣

0.0012ℎ =

113.1

0.0012∗200= 470 𝑚𝑚

use 450 mm

Horizontal

As = (0.002)(1000)(200) = 400 mm2/m

Vertical spacing of horizontal reinforcement

Sv,max = 𝐴ℎ

0.0012ℎ =

113.1

0.002∗200= 282 𝑚𝑚

use 280 mm


49

Reinforcement around openings

Use one No. 5 (16 mm) bar in both directions around window, door

Design of walls as deep beam

Wbeam = 25*1*0.2*2.8 = 14 Kn

Pu = 822.75 kn


50

Pu = 1.2*(14/2)+(185.78)

= 194.2

RA=AD= 194.2 Kn

Max shear strength

Vu at A = RA=194.5 Kn

Assume d= 0.9 h=0.9*1000=

9000mm

Vn = 0.83* √25* 200*900= 747 Kn

ϕVn = 0.75 *747 = 560.25 Kn > 194.2 Kn

Strut BC

Fu BC = ϕFnc = ϕFce AC = ϕ(0.85 βC FC ) b Ws

βs = 1 horizontal strut

for tie AD

Fu AD = ϕ Fnt= ϕ FCe AC = ϕ(0.85 βn Fc) b Wt

βs= 0.8 (c- c - t)

Fu BC = F U AD

SO ;

Wt = 1.25 Ws

jd = 1000 - 𝑊𝑡

2 -

𝑊𝑡

2 = 1000 – 1.125Ws

Vu(1000) – Fu BC (jd) =0

194.2*1000*1000 – (0.85 βs fc )b Ws (1-125Ws)=0

Ws= 48 mm

Wt= 54 mm

Jd =1000 – 0.5*48 - 0.5*54 = 949 mm

AB = CD = √10002 + 9492 =1378.6 mm

tan θ = 949

1000

θ =43.5 > 25 ok

185.78 kn 185.78 kn


51

Fu BC =Fu AD=194.2( 1000

949 )= 204.6 Kn

Fu AB = Fu CD = 194.2

sin 43.5 = 282 Kn

Effect stress

Fce = 0.85 βs fc = 0.85 * 0.75 *25 =15.94 MPa

S= 𝑑

5 =

900

5 =180 mm

Av = Avh=0.0025 * 200 * 180 = 90 mm2 per 180 mm

As = 𝜋

4 (10)2=78.534 * 2 =157.9 two legs

Use ϕ10 mm @ 180 mm

angle between vertical bars and strut = 90 – 43.5 = 46.5

(𝐴𝑠𝑖

𝑏𝑠) sin γ =(

157

200∗180) sin 46.5 =0.00316

angle between horizontal bars and strut = 43.5

(𝐴𝑠𝑖

𝑏𝑠) sin γ =(

157

200∗180) sin 43.5=0.003

(𝐴𝑠𝑖

𝑏𝑠) sin γ = 0.00316 + 0.003 =0.00616 > 0.003 ok

Design tie reinforcement

Fu=ϕ As Fy

As= 204.6∗1000

0.75∗410 =665.366 mm2

Ab= 𝜋

4 = (25)2=490.87mm2

NO. = 1.35 USE 2 ϕ 25

As=2 (𝜋

4) 252 = 982 mm2

Chapter four Conclusion and Rexommendation

52

Chapter Four

Conclusion and Recommendations

The use of a relatively cheaper system of construction for building

construction instead of the widely used ones, will not only have

economical benefits but also avoids the dependence on usual systems,

thereby reducing the competition in the construction industry. Precast

prestressed hollow core slab system of construction is a system, which

does not need very heavy equipment for erection, and the component

members can be produced with locally abundant construction materials.

In addition it is a precast, prestressed concrete slab system with

continuous voids provided to reduce weight and, therefore, cost and, as a

side benefit, to use for concealed electrical or mechanical runs. Primarily

used as floor or roof deck systems, hollow core slabs also have

applications as wall panels, and bridge deck units. It should be

understood that the main objective of the present study is to investigate

the advantage of pre cast prestressed hollow core slab elements for floor

slab construction, by comparing with the precast beam-block slab system.

All construction projects are designed to end up with an optimum

economy and safety. To fulfill these criteria the construction method to

be adopted should be the one with minimum total cost that satisfies the

strength requirements.A cost comparison between the two systems of

construction the hollow core slab system and the precast beam slab

system was made by designing the floor slabs of a typical four-story

building, using both systems. Based on the cost comparison, the


53

theoretical investigation the following conclusions

and recommendations may be drawn

1. The cost comparison shown that the hollow core slab system of

construction is faster and less expensive than the precast beam-

block slab system. The total saving obtained from the use of

system is abut 6.04% of the total construction cost of a building

using the precast beam-block slab systems. In addition to the

economical benefits gained the application of this system is

believed to solve problems associated with delays in the

construction industry, since construction delays are one of the

main causes of disputes.

2. As it can be seen from the cost comparison the saving from

construction cost component is 44% of the total saving. Higher

value of construction cost saving and hence total saving could

have been obtained if the precast pre-stressed hollow core slab

elements are designed and produced more economically

3. For the production of the precast prestressed hollow core slab

elements. it is recommended to use a minimum concrete class

C-35 and the upper surface of the slab elements should be

sufficiently roughened to create a good bond with the floor finish

cement screed or structural topping and the lower surface slab

surface should be smooth enough for final painting. The top

surface is generally prepared to receive a screed or structural

topping. Because they are cast against a steel surface, the soffits

are smooth and ready to receive a decorating finish direct without

the need for plastering.


54

4. During handling, transporting and erecting the hollow core slab

elements great care should be taken not to impair some structural

properties. a minimum of two-point lifting mechanism is

recommended to use .

5. For a country like Iraq application of this system of construction

not only has economical benefits but also preserves the national

resource by avoiding excessive use of formwork and scaffolding.

6. Even though there are many advantages in precast construction

there is still non responsive in untries like iraq. They still opt for

the conventional construction and consider that to be safe as the

cost of precast is slightly higher than thatof the conventional

construction.

7. Finally, it is believed that the result of this study are encouraging

and has shade light into the introduction of precast pre-stressed

slab systems in the construction industry. However, it is suggested

that further research be carried out in this area for proper

utilization of the system. It is hoped that the present study serve as

an aid for further developments and other related studies

55

8. References Book [1] PCI DESIGN HANDBOOK PRECAST AND PRESTRESSED CONCRETE ,

9. 7TH EDITION (2010)

10. [2] Building Code Requirements for Structural Concrete(ACI 318-14)

11.

12. [3] Reinforced Concrete: Mechanics and Design (6th Edition) 6th Edition

13. by James K. Wight (Author), James G. MacGregor (Author)

14. [4] Design of Reinforced Concrete, 9th Edition

15. Jack C. McCormac, Russell H. Brown

Website

[5] http://www.google.com/

16. [6] http://www.scribd.com/

17. [7] http://www.springer.com/

18. [8] http://www.slideshare.net/

http://www.google.com/

http://www.scribd.com/

http://www.springer.com/

http://www.slideshare.net/

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DESIGN OF MULTI-STORY PRECAST CONCRETE …DESIGN OF MULTI-STORY PRECAST CONCRETE BUILDING STUDENT’S NAME 1. Ahmed Kreem Mohammed 2. Hussein Shuai Shamran 3. Karar Latef Naji SUPERVISOR