# The design of simple roof trusses in wood and steel

THE DESIGN OF SIMPLE ROOF TRUSSES IN WOOD AND STEEL

WITH AN INTRODUCTION TO THE ELEMENTS OF GRAPHIC STATICS.

BY MALVERD A. HOWE, C.E.
Professor of Civil Engineering, Rose Polytechnic Institute; Member of American Society of Civil Engineers

NEW YORK: JOHN WILEY & SONS., 1915.

The design of simple roof trusses in wood and steel

PREFACE

Very little, if anything, new will be found in the following pages. The object in writing them has been to bring together in a small compass all the essentials required in properly designing ordinary roof-trusses in wood and steel.

At present this matter is widely scattered in the various comprehensive treatises on designing and in manufacturers' pocket-books. The student who desires to master the elements of designing simple structures is thus compelled to procure and refer to several more or less expensive books.

Students in mechanical and electrical engineering, as a rule, learn but little of the methods of designing employed by students in civil engineering. For this reason the writer has been called upon for several years to give a short course in roof-truss design to all students in the Junior class of the Rose Polytechnic Institute, and in order to do so he has been compelled to collect the data he has given in this book.

The tables giving the properties of standard shapes are based upon sections rolled by the Cambria Steel Company. Standard sections rolled by other manufacturers have practically the same dimensions.

CONTENTS

CHAPTER I. GENERAL PRINCIPLES AND METHODS
1. Equilibrium
2. The Force Polygon
3. Forces not in Equilibrium - Force Required to Produce Equilibrium as far as Motion of Translation is Concerned
4. Perfect Equilibrium
5. The Equilibrium Polygon
6. Application of the Equilibrium Polygon in Finding Reactions
7. Parallel Forces
8. The Direction of One Reaction Given, to Find the Magnitude and Direction of the Other
9. Application of the Equilibrium Polygon in Finding Centers of Gravity
10. Application of the Equilibrium Polygon in Finding Moments of Forces
11. Graphical Multiplication
12. To Draw an Equilibrium Polygon through Three Given Points

CHAPTER II. BEAMS AND TRUSSES
13. Vertical Loads on a Horizontal Beam, Reactions and Moments of the Outside Forces
14. Vertical Loads on a Simple Roof-truss - Structure considered as a Whole
15. Inclined Loads on a Simple Roof-truss - Structure considered as a Whole
16 Inclined Loads on a Simple Roof-truss, One Reaction Given in Direction Structure considered as a Whole
17. Relation between the Values of R in Arts. 15 and 16
18. Internal Equilibrium and Stresses
19. Inside Forces Treated as Outside Forces
20. More than Two Unknown Forces Meeting at a Point

CHAPTER III. STRENGTH OF MATERIALS.
21. Wood in Compression - Columns or Struts
22. Metal in Compression - Columns or Struts
23. End Bearing of Wood
24. Bearing of Steel
25. Bearing across the Fibers of Wood
26. Bearing across the Fibers of Steel
27. Longitudinal Shear of Wood
28. Longitudinal Shear of Steel
29. Transverse Strength of Wood
30. Transverse Strength of Steel Beams
31. Special Case of the Bending Strength of Metal Pins
32. Shearing Across the Grain of Bolts, Rivets, and Pins
33. Shearing Across the Grain of Wood
34. Wood in Direct Tension
35. Steel and Wrought Iron in Direct Tension

CHAPTER IV.  ROOF-TRUSSES AND THEIR DESIGN
36. Preliminary Remarks
37. Roof Coverings
39. Pitch of Roof
40. Transmission of Loads to Roof-trusses
41. Sizes of Timber
42. Steel Shapes
43. Round Rods
44. Bolts
45. Rivets
46. Local Conditions

CHAPTER V. DESIGN OF A WOODEN ROOF-TRUSS
47. Data
48. Allowable Unit Stresses
49. Rafters
50. Purlins
52. Stresses in Truss Members
53. Sizes of Compression Members of Wood
54. Sizes of Tension Members of Wood
55. Sizes of Steel Tension Members
56. Design of Joint with Bolts
56a. Design of Joint with Bolts and Metal Plates
57. Design of Joint with Nearly all Wood
58. Design of Joint with Steel Sturrup
59. Design of Joint with Steel Sturrup and Pin
60. Design of Joint with Plate Stirrup and Pin
61. Design of Joint with Steel Angle Block
62. Design of Joint with Cast-iron Angle Block
63. Design of Joint with Special
64. Design of Joint with Plank Members
65. Design of Wall Bearing
66. Remarks concerning the Design of Joint
67. Design of Joint U
68. Design of Joint U
69. Design of Joint L
70. Design of Joint L, and Hook Splice
71. Design of Joint L, Fish-plate Splice of Wood
72. Design of Joint, Fish-plate Splice of Metal
73. Metal Splices for Tension Members of Wood
74. General Remarks Concerning Splice
75. Design of Joint U
76. The Attachment of Purlins
77. The Complete Design

CHAPTER IV. DESIGN OF A STEEL ROOF-TRUSS.
78. Data
79. Allowable Stresses for Square Inch
80. Sizes of Compression Members
81. Sizes of Compression Tension Members
82. Design of Joint U
83. Design of Joint U
84. Design of Joint U
85. Design of Joint U
86. Splices
87. End Supports
88. Expansion
89. Frame Lines and Rivet Lines
90. Drawings

TABLES.

I. Weights of Various Substances
II. Roof Coverings - Weights of
III. Rivets - Standard Spacing and Sizes
IV. Rivets - Areas to be Deducted for
V. Round-headed Rivets and Bolts - Weights
VI. Bolt Heads and Nuts - Weights and Dimensions
VII. Upset Screw Ends for Round Bars - Dimensions
VIII. Right and Left Nuts - Dimensions and Weights
IX. Properties of Standard I Beams
X. Properties of Standard Channels
XI. Properties of Standard Angles with Equal Legs
XII. Properties of Standard Angles with Unequal Legs
XIII. Least Radii of Gyration for Two Angles Back to Back
XIV. Properties of T Bars
XV. Commercial Sizes and Relative Costs of Timbers
XVI. Average Safe Allowable Working Unit Stresses for Wood
XVIL Cast-iron Washers-Weights of

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