Design of structural elements with tropical hardwoods

288 Pages·2018·9.08 MB·English

by  Olorunnisola

Abel O. Olorunnisola
Design of Structural
Elements with
Tropical Hardwoods
Design of Structural Elements with Tropical
Hardwoods
Abel O. Olorunnisola
Design of Structural
Elements with Tropical
Hardwoods
123
AbelO.Olorunnisola
Department ofWood ProductsEngineering
University of Ibadan
Ibadan, OyoState
Nigeria
ISBN978-3-319-65342-6 ISBN978-3-319-65343-3 (eBook)
DOI 10.1007/978-3-319-65343-3
LibraryofCongressControlNumber:2017948214
©SpringerInternationalPublishingAG2018
Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart
of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations,
recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission
orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar
methodologynowknownorhereafterdeveloped.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this
publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfrom
therelevantprotectivelawsandregulationsandthereforefreeforgeneraluse.
The publisher, the authors and the editors are safe to assume that the advice and information in this
book are believed to be true and accurate at the date of publication. Neither the publisher nor the
authorsortheeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinor
for any errors or omissions that may have been made. The publisher remains neutral with regard to
jurisdictionalclaimsinpublishedmapsandinstitutionalaffiliations.
Printedonacid-freepaper
ThisSpringerimprintispublishedbySpringerNature
TheregisteredcompanyisSpringerInternationalPublishingAG
Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland
With love to my late mum, Esther Tanimowo
Olorunnisola (1935–2005), a mother in a
million
Preface
The primary objective of writing this book is to provide basic information on the
design of structures with tropical woods. While this book is intended primarily for
teachinguniversity-andcollege-levelcoursesinstructuraldesign,itisalsosuitable
asareferencematerialforpractitioners.Thelanguageofthetexthasthereforebeen
tailored to suit the varied needs of these potential users. Although parts of the
background material relate specifically to West and East Africa, the design prin-
ciples apply to the whole of tropical Africa, Latin America and South Asia.
The most common wood products employed in structural applications in the
tropics remain roundwood in form of logs, poles and posts; sawn wood (lumber);
and to some extent glued laminated lumber (glulam). These wood products are,
therefore, the central focus of this book. Newer wood products such as laminated
veneer lumber (LVL), parallel strand lumber (PSL), laminated strand lumber
(LSL) and cross-laminated timber (CLT) are only mentioned in passing.
This book is laced with ample illustrations including photographs of real-life
wood structures and structural elements across Africa that make for interesting
reading. It has numerous manual and Excel spreadsheet worked examples and
reviewquestions that can properlyguide a first-time designer ofwoodenstructural
elements. A number of design problems were also solved using the FORTRAN
programming language. This was considered useful for readers who are already
familiarwiththatprogramminglanguageandcouldserveasaguideforthosewho
would prefer programming using other languages. Topics covered in the 13
chapters of this book include a brief introduction to this book, the anatomy and
physicalpropertiesoftropicalwoods;abriefreviewofthemechanicalpropertiesof
wood, timber seasoning and preservation, uses of wood and wood products in
construction; basictheoryofstructuresandstructuralloadcomputations; designof
woodenbeams,solidandbuilt-upwoodencolumns,woodconnectionsandwooden
trusses; as well as a brief introduction to the design of wooden bridges.
The writing of this book required consultation with numerous reference mate-
rials as indicated in the bibliography and critiques from several generations of
undergraduate and postgraduate students in the Departments of Agricultural and
Environmental Engineering as well as Wood Products Engineering at the
vii
viii Preface
UniversityofIbadan,Nigeria,whotookmyclassesinthedesignofwoodstructures
and who had access to the lecture notes that were later converted into the manu-
script for this book. The style of writing adopted for this book was positively
influencedbystudents’commentsandcriticisms.Thelanguagebecamesimplerand
more lucid. I am sincerely grateful to all the authors whose works I consulted and
my past and current students whose efforts made the writing much easier than it
would otherwise have been.
Ibadan, Nigeria Prof. Abel O. Olorunnisola
March 2017
Contents
1 Introduction... .... .... ..... .... .... .... .... .... ..... .... 1
References. .... .... .... ..... .... .... .... .... .... ..... .... 6
2 Anatomy and Physical Properties of Tropical Woods .. ..... .... 7
2.1 Anatomical and Gross Features of Hardwoods.... ..... .... 7
2.2 Physical Properties of Hardwoods.. .... .... .... ..... .... 18
2.2.1 Density . ..... .... .... .... .... .... ..... .... 18
2.2.2 Specific Gravity.... .... .... .... .... ..... .... 18
2.2.3 Moisture Content... .... .... .... .... ..... .... 19
2.2.4 Nail-Holding Ability .... .... .... .... ..... .... 20
2.2.5 Ease of Working ... .... .... .... .... ..... .... 21
2.2.6 Paint-Holding Ability.... .... .... .... ..... .... 21
2.2.7 Odour .. ..... .... .... .... .... .... ..... .... 21
2.2.8 Colour.. ..... .... .... .... .... .... ..... .... 23
2.2.9 Texture . ..... .... .... .... .... .... ..... .... 24
2.2.10 Figure .. ..... .... .... .... .... .... ..... .... 24
2.2.11 Luster .. ..... .... .... .... .... .... ..... .... 26
2.3 Concluding Remarks.... .... .... .... .... .... ..... .... 27
References. .... .... .... ..... .... .... .... .... .... ..... .... 29
3 Mechanical Properties of Wood.... .... .... .... .... ..... .... 31
3.1 Strength of Wood. ..... .... .... .... .... .... ..... .... 31
3.2 Strength Properties of Wood Typically Considered in
Structural Design . ..... .... .... .... .... .... ..... .... 37
3.3 Deformation of Wood Under Stress .... .... .... ..... .... 39
3.4 Modulus of Elasticity .. .... .... .... .... .... ..... .... 41
3.5 Modulus of Rupture .... .... .... .... .... .... ..... .... 43
3.6 Modulus of Rigidity.... .... .... .... .... .... ..... .... 44
3.7 Poisson’s Ratio... ..... .... .... .... .... .... ..... .... 44
3.8 Creep and Relaxation ... .... .... .... .... .... ..... .... 45
ix
x Contents
3.9 Hardness.... .... ..... .... .... .... .... .... ..... .... 45
3.10 Fatigue . .... .... ..... .... .... .... .... .... ..... .... 46
3.11 Toughness... .... ..... .... .... .... .... .... ..... .... 46
References. .... .... .... ..... .... .... .... .... .... ..... .... 47
4 Hardwood Timber Seasoning and Preservation ... .... ..... .... 49
4.1 Wood Moisture Content and Seasoning . .... .... ..... .... 49
4.2 Reasons for Human Intervention Timber Drying .. ..... .... 50
4.3 Basic Principles of Drying ... .... .... .... .... ..... .... 50
4.4 Seasoning Methods..... .... .... .... .... .... ..... .... 55
4.4.1 Air Seasoning . .... .... .... .... .... ..... .... 55
4.4.2 Artificial Seasoning (Kiln-Drying).. .... ..... .... 60
4.4.3 Milling and Seasoning Defects .... .... ..... .... 61
4.5 Hardwood Timber Preservation.... .... .... .... ..... .... 62
References. .... .... .... ..... .... .... .... .... .... ..... .... 68
5 Uses of Wood and Wood Products in Construction .... ..... .... 71
5.1 Emergence of Different Wood Products as Structural
Materials.... .... ..... .... .... .... .... .... ..... .... 71
5.2 Unprocessed and Semi-processed Solid Wood .... ..... .... 72
5.3 Sawn Wood . .... ..... .... .... .... .... .... ..... .... 76
5.4 Laminated Solid Wood Products... .... .... .... ..... .... 81
5.5 Wood-Based Panel Products.. .... .... .... .... ..... .... 84
5.6 Engineered Wood Products... .... .... .... .... ..... .... 86
5.7 A Glimpse into the Future ... .... .... .... .... ..... .... 90
References. .... .... .... ..... .... .... .... .... .... ..... .... 91
6 A Review of the Basic Theory of Structures.. .... .... ..... .... 93
6.1 Forces in Structures .... .... .... .... .... .... ..... .... 93
6.2 Basic Elements of a Framed Structure .. .... .... ..... .... 93
6.3 Types of Joints in a Framed Structure .. .... .... ..... .... 94
6.4 Types of Support in a Framed Structure. .... .... ..... .... 96
6.5 Equations of Equilibrium .... .... .... .... .... ..... .... 96
6.6 Basic Properties of Sections .. .... .... .... .... ..... .... 97
6.6.1 Moments of Area... .... .... .... .... ..... .... 97
6.6.2 Centroid of an Area. .... .... .... .... ..... .... 98
6.6.3 Moments of Inertia of Various Sections . ..... .... 98
6.6.4 Section Modulus ... .... .... .... .... ..... .... 99
6.6.5 Radius of Gyration . .... .... .... .... ..... .... 100
References. .... .... .... ..... .... .... .... .... .... ..... .... 105
7 Structural Load Computations. .... .... .... .... .... ..... .... 107
7.1 Types of Loads... ..... .... .... .... .... .... ..... .... 107
7.1.1 Dead Loads .. .... .... .... .... .... ..... .... 108
7.1.2 Live Loads.... .... .... .... .... .... ..... .... 110
Contents xi
7.1.3 Snow Loads... .... .... .... .... .... ..... .... 111
7.1.4 Lateral Forces . .... .... .... .... .... ..... .... 111
7.2 Controlling Loads for Design. .... .... .... .... ..... .... 112
7.3 The Concept of Tributary Loading. .... .... .... ..... .... 113
7.4 Structural Design Codes. .... .... .... .... .... ..... .... 114
References. .... .... .... ..... .... .... .... .... .... ..... .... 117
8 Design of Wooden Beams..... .... .... .... .... .... ..... .... 119
8.1 Stresses in Beams. ..... .... .... .... .... .... ..... .... 119
8.2 Bending Equation. ..... .... .... .... .... .... ..... .... 120
8.3 General Design Information for Designing Wooden
Beams.. .... .... ..... .... .... .... .... .... ..... .... 122
8.4 Actual Wooden Beam Design. .... .... .... .... ..... .... 122
8.4.1 Bending Stress Criterion . .... .... .... ..... .... 123
8.4.2 Shear Stress Criterion ... .... .... .... ..... .... 126
8.4.3 Deflection Criterion. .... .... .... .... ..... .... 128
8.4.4 Typical Cases of Wooden Beam Design . ..... .... 131
8.4.5 Design of Bearing Supports... .... .... ..... .... 132
8.4.6 Check for Lateral Stability.... .... .... ..... .... 134
8.4.7 Design for Combined Bending and Axial
Loading. ..... .... .... .... .... .... ..... .... 135
8.4.8 A Summary of the Procedures for Designing
a Wooden Beam ... .... .... .... .... ..... .... 135
8.5 Special Wooden Beams . .... .... .... .... .... ..... .... 136
8.5.1 Box Beams ... .... .... .... .... .... ..... .... 136
8.5.2 Composite Beams .. .... .... .... .... ..... .... 138
8.5.3 Lumber Decks. .... .... .... .... .... ..... .... 140
8.5.4 Stressed-Skin Panels .... .... .... .... ..... .... 141
References. .... .... .... ..... .... .... .... .... .... ..... .... 159
9 Design of Solid Wood Columns .... .... .... .... .... ..... .... 161
9.1 General Classification of Columns . .... .... .... ..... .... 161
9.2 End Conditions in Columns .. .... .... .... .... ..... .... 164
9.3 The Euler Column Buckling Equation .. .... .... ..... .... 166
9.4 The General Procedure for Designing a Wooden
Column. .... .... ..... .... .... .... .... .... ..... .... 172
9.4.1 The Rankin-Gordon Formula.. .... .... ..... .... 172
9.4.2 Perry Robertson Formula. .... .... .... ..... .... 173
9.4.3 The Madison Approach.. .... .... .... ..... .... 174
9.4.4 The FAO Formula.. .... .... .... .... ..... .... 175
9.4.5 The Revised Madison Approach ... .... ..... .... 176
9.5 Important Points to Note in the Design of Solid
Wooden Columns. ..... .... .... .... .... .... ..... .... 177
9.6 Design of Tapered Wooden Columns... .... .... ..... .... 177