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DECLARATION OF THESIS / UNDERGRADUATE PROJECT PAPER AND COPYRIGHT
LEE SID HWAAuthor’s full name :
Date of birth : 26 / 10 / 1983
Title : FAILURE OF ROOF STRUCTUREDUE TO WIND LOAD
2007/2008Academic Session:
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OPEN ACCESS I agree that my thesis to be published as online open access
(full text)
831026-05-5155
9 APRIL 2008
P.M. DR. RAMLI ABDULLAH
“I hereby declare that I have read this thesis and in my
opinion this thesis is sufficient in terms of scope and quality for the
award of the Master of Civil Engineering (Civil – Structure)”
Signature : …………………………………...
Name of Supervisor : PM. DR. RAMLI ABDULLAH
Date : …………………………………….
FAILURE OF ROOF STRUCTURE DUE TO WIND LOAD
LEE SID HWA
A project report submitted in partial fulfilment of the
requirements for the award of the degree of
Master of Civil engineering (Civil – Structure)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
APRIL 2008
ii
I declare that this project report entitled “Failure of Roof Structure Due to Wind Load”
is the result of my own research except as citied in the references. The project report has
not been accepted for any degree and is not concurrently submitted in candidature of
any other degree.
Signature : …………………………………...
Name : LEE SID HWA
Date : ……………………………………
iv
ACKNOWLEDGMENT
First of all, I would like to thank my supervisor, Prof. Madya. Dr. Ramli
Abdullah, who had given guidance for my work and came up with some inspiring
suggestion, in the mean time, his patience and immeasurable contribution is the key to
generate this project. If Dr. Ramli didn’t spent his own valuable time to listen to my
problem and give advices, I would have not completing my project thesis.
Next, I would like to acknowledgement my thanks to the laboratory staff
especially Encik Zailani for his cooperation, hardwork and endless patience in my
laboratory testing. Their aid reduced my work load and also speed up the progress.
Last but not the least, I would like to express my deep appreciation to my family,
and people that I don’t mentioned their name for their support, suggestion and also
opinion.
v
ABSTRACT
There are reported roof failure due to uplifting of the roof structures or roof
sheeting during rainstorm has been causing damages to the buildings. Generally, failure
occurred at the two points, either at the roof truss’s sheeting or at the truss to roof beam
connections. There are 2 types of structure are to be analyzed; the different of these two
building will be the buildings dimension, meaning that one is a single storey houses and
other is a 20 storey apartment. The roof structure’s data is extracted from the reported
cases for simulation purposes. For a more conservative result, the wind speed is taken as
40 m/s. Due to different aspect for this 2 type of structure, the wind-uplifting force will
be determined. The calculated resulting forces transferred at different connection points
were compared with the experimental result obtained from laboratory testing. The result
of this, is that the connection of both houses and apartment is safe under the wind speed
of 40m/s. However, this happen when the proper used of selected material plus all the
material is in well condition. To improve the study of this project, the larger scale
testing like wind tunnel can provide the more accurate result due to the integrity of the
roof structure.
vi
ABSTRAK
Seperti yang dicatat dalam bahan bacaan seperti suratkhabar, kes-kes kepingan
atap yang dicabut oleh angin kuat dalam hujan lebat menyababkan kegagalan struktur
bumbung. Sebenarnya menurut kajian yang telah dilakukan, biasanya kegagalan
struktur bumbung berlaku di 2 tempat, iaitu di tempat sambungan pada komponen-
komponen kayu dan paku atau kepingan zink yang dipaku pada gulung gulung. Oleh itu,
2 jenis struktur akan dikaji untuk menyelidik bahawa faktor-faktor ketinggian, saiz, dan
lokasi akan menjadi sebab kegagalan struktur bumbung. Perhubungan antara bangunan
apartment yang setinggi 20 tingkat dan rumah biasa setinggi satu tingkat. Untuk
mendapatkan bacaan yang lebih selamat, halaju angin adalah 40 m/s. Selepas pengiraan
untuk kapasiti pada setiap sambungan, kapasiti yand dikaji akan selamat dalam halaju
angin 40 m/s. Tetapi keputusan ini adalah benar jikalau semua komponen dalam
struktur adalah baik. Pada akhirnya, kajian ini mencadangkan penggunaan Wind Tunnel
untuk mendapatkan keputusan yang lebih memuaskan.
vii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES x
LIST OF FIGURES xi
1 INTRODUCTION 1
1.1 Introduction 1
1.2 Problem Statement 3
1.3 Objective of Research 4
1.4 Scope of Research 5
1.5 The Contribution of the Research 5
2 LITERATURE REVIEW 6
2.1 Metal Roof Sheeting 6
2.2 Timber Roof Structure 10
2.3 Wind Action 12
2.4 Wind Tunnel Experimental done 15
2.4.1 Global roof failure testing 16
viii
2.4.2 Sheathing panels 16
2.4.3 Effects of dominant openings 17
2.4.4 Roof venting 17
2.5 Roof Structure Element 18
2.6 Supporting Structures 20
3 METHODOLOGY 22
3.1 Research Programme 22
3.2 Weather data 23
3.3 Materials 25
3.3.1 Zinc Roof Sheeting 25
3.3.2 Timber (Wood) 26
3.3.3 Caped Nail and Washer 26
3.3.4 Suitable Nails Used 27
3.4 Pre-assumption Involved in Calculation 27
3.4.1 Low Rise Ordinary Houses ( 1- storey high ) 28
3.4.2 High Rise Apartment ( 20-storey high ) 31
3.5 Laboratory Testing Process 34
3.5.1 Connection between Zinc Roof Sheeting and Purlin 34
3.5.2 Connection between Purlin and Rafter 36
3.5.3 Connection between Rafter and Beam 41
4 TEST RESULTS 42
4.1 Introduction 42
4.2 Experimental Result 42
4.2.1 Experimental Result – Zinc Sheeting and Purlin 43
4.2.2 Experimental Result – Purlin and Rafter 45
4.2.3 Experimental Result – Rafter and Beam 46
ix
5 ANALYSIS AND DISCUSSION 50
5.1 Analysis 50
5.1.1 Required Nail Pulling Resisting Force 50
5.1.2 Comparing Experimental Result 51
5.2 Reverse Calculation 52
5.2.1 Single Storey House 52
5.2.2 20 Storey Apartment 53
5.2.3 Total Roof Structure Failure 54
5.3 Discussion 55
6 CONCLUSION AND RECOMMENDATION 57
6.1 Conclusion 57
6.2 Recommendation 58
REFERENCES & BIBLIOGRAPHY 59
APPENDICES 60
x
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1: Types of metal roof sheeting and their properties 11
2.2: Roof systems materials consumed in homes 12
2.3: Maximum Bay Lengths of Rafters and Ceiling Ties(BS 5268 Table 3) 21
3.1: Weather data of Senai, Johor Bahru at January 2007 25
3.1(a): Legend of Table 3.1 26
3.2: Classification of timber due to strength 27
4.1: Failure load on the experimental testing – Zinc Sheeting and Purlin 44
4.2: Failure load on the experimental testing – Purlin and Rafter 46
4.3: Failure load on the experimental testing – Rafter and Beam 47
xi
LIST OF FIGURES
FIGURE NO. TITLE PAGE
1.1: Some of the common example roof failure 3
2.1: An example of outstation homestead of using zinc roof sheeting 8
2.2: Spandek Roof Sheeting 10
2.3: Custom Orb Roof Sheeting 10
2.4: Trimdek Roof Sheeting 10
2.5: Klip-Lok Roof Sheeting 10
2.6: Some of the common example truss shapes 12
2.7: Wind effect on a structure 13
2.8: Wind effect on a structure (2) 14
2.9: Wind action on corner of the roof structure 15
2.10: Winds create forces that attack the integrity of a structure inmultiple ways 16
2.11: Roof Structure parts and label 20
2.12: Battens (or Purlins) arrangement to avoid buckling 20
2.13: Truss and purlin spacing arrangement 20
2.14: Compression and Tension force along a normal truss 21
3.1: Flow chart of research planning 24
xii
LIST OF FIGURES (CON’T)
FIGURE NO. TITLE PAGE
3.2: Different condition of zinc roof sheeting 26
3.3: Caped nail and washer 27
3.4: Correct Nails Used (Simpson Ties Company) 28
3.5: Low Rise Structure Modeling Dimension 29
3.6: Wind Uplifting force for Pitched Roof (Low Rise) 31
3.7: High Rise Structure Modeling Dimension 32
3.8: Wind Uplifting force for Pitched Roof (High Rise) 34
3.9: Overall View of Roof Structure 35
3.10: Specimen Formed 36
3.11: Connection for the specimen 36
3.12: Testing Procedure using Rig Test 37
3.13: Testing specimens for connection between rafter and purlin 38
3.14: Setting of specimen 39
3.15: Specimen SP1 39
3.16: Specimen SP2 40
3.17: Isometric View and Side View of Connection between
Rafter and Beam 40
xiii
LIST OF FIGURES (CON’T)
FIGURE NO. TITLE PAGE
3.18: Specimen SP1 41
3.19: Specimen SP2 41
3.20: Connection between Rafter and Beam (Specimen SP1) 42
3.21: Connection between Rafter and Beam (Specimen SP2) 42
4.1: Testing result – Minor Rusted zinc sheeting teared off whilenail remains connected with the purlin 44
4.2: Testing result – Normal zinc sheeting tear off in the testing 45
4.3: Testing result – Rusted zinc sheeting tear off in the testing 45
4.4: Testing result for SP1– Purlin been pulling off 46
4.5: Testing result for SP2– Nail remain in rafter while the purlindetach from the connection 46
4.6: Testing result– Rafter is pulling up by testing machine 48
4.7: Testing result– The resistance of the nails has reached its limit 48
4.8: Testing result for SP1– Rafter detached from its position 49
4.9: Testing result for SP2– Nail being pulled out 49
4.10: Testing result for SP3– Nail being pulled out 50
CHAPTER 1
INTRODUCTION
1.1 Introduction
The roof is often the most expressive part of a house, symbolic of shelter and
functionally important for its capacity to protect the house from the element. However,
sometimes we tend to ignore the roof structure and put the concentration on the
structural member like beam and column. However, there is some real life report, wind
has cause of damage to buildings.
As printed on the newspaper or magazine, there is some cases that related to the
failure of roof structure due to the wind blow especially at rainstorm. Due to this
tragedy, there is something that can do to reduced or minimize through some study or
research to the wind load effect on the roof structure.
Wind damage in rainwater tends to occur progressively, usually starting with
damage to one of the components forming the building envelope (typically the roof,
cladding or unprotected windows), and which, if it progresses far enough, can lead to
failure of the complete structure. Even in cases where complete structural failure does
not occur failure of the building envelope often allows wind-driven rain to penetrate the
building leading to damage to the contents as well as loss of function. The loss of roof
sheeting is often attributed to the loss of roof sheeting is often attributed to either
inadequate nailing.
For roof pitches in the range commonly used for residential structures, wind
forces oriented normal to the ridge of the roof will cause wind uplifting forces.
Sometimes, there are weakness could extend the damage from wind; these weaknesses
involve the attachment of roofing to the roof sheathing. The sheathing attachment to the
roof framing, rake overhang details, and attachment of internal partitions to the external
walls contributes significantly to the extensive damage and to system failures.
For country that located at near the equator like Malaysia, the temperature is
high all year round (except at altitude). In many tropical regions people identify two
seasons: wet and dry. Unlike the foreign country, phenomenon like hurricane, snow fall
doesn’t happen on this area, but when the raining monsoon occurs: a large amount of
rainwater will fall, makes the withdrawal of water is crucial to avoid leaking or water
spill out. This is why pitched roof is so common compared to flat roof throughout the
country. Timber made roof truss has such advantages:
Lowest overall cost.
Fast to install.
Requires ordinary tools and
Doesn’t require skilled labour to install.
Virtually any roof and ceiling is possible.
Engineered product.
No job site waste.
1.2 Problem Statement
Throughout these years, there are some cases that related to the failure of roof
structure due to the wind blow especially at rainstorm. Due to this tragedy, there is
considered vital if there is a way that can do to reduced or minimize through some study
or research to the wind load effect on the roof structure.
For example, there are some real life cases like in the US, wind is the most
common, and the most costly cause of damage to buildings. Over a 7 year period from
1986 to 1993 extreme wind damage cost $41 billion in insured catastrophe losses as
compared to $6.8 billion for all other natural hazards combined. Reasons given for these
losses include: increased development in high risk areas, a lack of awareness of or
failure to follow recommended construction practices and the introduction of new and
unproven materials. Economic losses include repairing or replacing damaged homes
and their contents, while the loss of personal possessions and relocation during
reconstruction are common outcomes of residential damage.
Figure 1.1: Some of the common example of roof failure
Uplifting of the roof structures or roof sheeting during rainstorm has been
causing damages to the buildings. Generally, failure occurred at the two points, either at
the roof frame’s sheeting or at the frame to roof beam connections. There are 2 types of
structure are to be analyzed; the different of these two building will be the buildings
dimension and geographical locations.
Wind damage in rainwater tends to occur progressively, usually starting with
damage to one of the components forming the building envelope (typically the roof,
cladding or unprotected windows), and which, if it progresses far enough, can lead to
failure of the complete structure. Even in cases where complete structural failure does
not occur failure of the building envelope often allows wind-driven rain to penetrate the
building leading to damage to the contents as well as loss of function.
1.3 Objective of Research
Residential houses located in the countryside region (kampung houses) that were
relatively unsheltered from the full force of the storm incurred the decent damage. The
damage to these houses presented a unique opportunity to investigate the type and
extent of damage to this type of structure.
The objectives of this study are:
a) To investigate the roof structure elements and their tying down system
that frequently failed due to wind forces.
b) To determine the minimum wind speed required which causes the
uplifting of the roof of various construction and age.
c) To review the safety of the presently practiced construction of roof
structure.
1.4 Scope of Research
The scope of this research is to determine the ways to succeed the objectives.
One of these was the calculation of connection capacity. For those countryside housing
estates, it had presumed that all connection using nails rather than the metal connection
plate that used recently due to the age of the existing houses. And so, the weakness in
strength is the main focus of the research.
For the worst case environment performance, the experimental circumstances
practiced for extreme possibility, means the testing data based on the highest wind
speed that occurred before.
Moreover, this research will also determine the effect of the failure pattern of the
roof connection that due to strong wind blow condition. The connection part that
involved was connection between zinc roof sheeting and purlin; purlin and rafter; and
also the rafter and beam.
The result decided through the testing by laboratory equipment or through
certain calculation. And through that, the roof structures ultimate storm resistance can
be calculated. Data obtained through experiments will be analyzed and suggestions will
be given as necessary.
1.5 Significance of the Research
At the end of the research, the wind speed limit, ultimate resistance and effect
under severe weather will be provided, as an understanding and awareness to the
involved parties. With this, whenever the resident know about the current wind speed,
they will know the consequence of roof structure failure. To avoid the tragedy again,
repairing and strengthening of roof structure maybe needed.
CHAPTER 2
LITERATURE REVIEW
2.1 Metal Roof Sheeting
Metal roof sheeting is an old material, it has been made for about a century and
although it has had it's pro and cons in terms of popularity it has always been the best
roofing material for many people. A metal roof is a roofing system made from metal
pieces or tiles. They are components of the building envelope. Corrugated roof sheeting
or roofing iron has been around since the 1830's in England. It was and still is a
significant invention. The simple process or forming corrugations into a flat floppy
sheet of thin iron changed roofing for ever. Because of it's lightness and strength, easy
transportability, tons of it was shipped all over the world. Corrugated galvanised iron
describes the original product that was wrought iron plate coated with zinc and then roll
formed into corrugated sheets. However, the corrugated zinc roof sheeting now rare and
no longer manufactured in large amount. It has been replaced by some other else
material.
Figure 2.1: An example of outstation homestead of using zinc roof sheeting.
The main product that has replaced the old galvanised iron (zinc sheeting) is
called "Zincalume". This name being derived from the two main components of the
actual coating system, which consists of Zinc 55% / aluminium 43% / silicon 1.6% that
coat the steel base. The material is sent from the steel mill in large rolls of flat
sheet. The main difference in the coil products are:-
Zincalume - This is the natural colour of the sheet that looks similar to the
old galvanised iron. It weathers with times and loses it's bright shiny look.
Colorbond – Basically it is Zincalume with a paint surface added. It comes
in about 20 various colours. It has a plain painted finish to the underside.
Colorbond Metallic - A metallic sheen that changes under different light
conditions.
Colorbond Ultra - For severe coastal and industrial environments.
Stainless - For severe coastal and industrial environments.
Thickness - For the most part I think that for private house work the 0.42mm
thick is the most common. As you can see it is pretty thin stuff, less than
half a millimeter most of it.
Galvanised - Steel sheeting is still made, but in the thicknesses for roof
sheeting it most probably only done as special orders for heritage restoration
work. Where I do see it quite a lot is in the form of valley gutters, in thicker
gauges, say 2.0mm.
Various companies doing the different type of roll forming. They turn the coils
of flat into various standard profiles for which the engineering properties are
documented. The types of metal roofing will be as following:
Stainless steel. - Available for harsh conditions, rollformed and fixed similar to
corrugated steel profiles.
Aluminum - One of the longest lasting metals, but somewhat expensive.
Copper - Usually used for flashing or very small sections like covered
entryways. Expensive. If the building were ever to be dismantled the copper
would be reused because of its high value and variety of possible uses.
Stone Coated Steel - Stone Coated Steel shingle panels are made from pressure
formed, zinc/aluminum alloy coated steel with an acrylic, bonded, stone chip
finish, which resists fading and UV (Ultra-Violet) penetration. The panels are
lightweight (1.5 pounds per square foot) and walkable, and come in a variety of
earth-toned colors. They are fireproof and come with a 120-mile (190 km)-per-
hour wind rating and have a 50 yr to lifetime warranty against fading, cracking,
rusting, curling and de-granulation. Stone Coated Steel panels come in a wide
range of solid and Mediterranean blends and are vailable in both tile, shake,
slate and shingle style They withstand all extreme environmental elements
including Hail, Fire and Wind. Stone Coated Steel is ideal for flat to pitch
conversions and can even be installed over existing roofs without the need for
tear-off. Structural support is generally not required and can be walked on after
installation, too. Nails are installed horizontally to provide greater resistance
against vertical pullout due to high wind conditions.
Inverted Box Rib is a low-cost corrugated square-fluted iron roofing used
mainly in the South African market. It can be commonly seen all the way from
industrial sites to low-income shacks.
From the table shown below, that the shallower the roof sheeting pitch, the
deeper the ribs have to be, and also the thicker the material in most cases. There are a
handful of other profiles available but those are less common on typical house
construction. There are quite a few roof sheeting profiles available, but the main ones
for housing are as follows:-
Figure 2.2: Spandek Roof Sheeting.
Figure 2.3: Custom Orb Roof Sheeting.
Figure 2.4: Trimdek Roof Sheeting.
Figure 2.5: Klip-Lok Roof Sheeting.