**This page includes notes related to the relevant Eurocodes EC5 ( BS EN 1995-1-1 ).
Elsewhere on the Roymech website there are notes on timber which relates to BS 5268 Timber Index this is now
superseded by the Eurocode. My information on the older standards is generally more detailed and much of the information is still relevant. **

Introduction....
Standards....
Symbols....
Timber properties....
Ultimate limit state design....
Serviceability limit state design....
Design strength values....
Service classes....

Actions....
Columns....
Design of Flexural Members....
Bending....
Buckling of beams....
Shear of Beams....
Compression....
Torsion....
Deflection....
Vibration....
Connections

** The building structures pages have been added the six months to Dec. 2012. They are very much work-in-progress and I will be updating them on a regular basis over the next six months.**

Introduction This page includes notes on design of timber structures and structural components in accordance with the relevant
Eurocode EC 5 (BS EN 1995-1-1: 2004). The notes are outline in nature suitable for enabling basic calculations. For detailed design
it is necessary to refer to the actual standard and all of the associated standards. Timber construction design to EuroCode 5 is based on limit state design with the two principal catergories being ultimate and seriviceability states. Ultimate limit state (ULS) = States associated with collapse or similar structural failure. The durability limit state also needs to be considered . This relates to the risk of
timber decay due to fungal or insect attack as well as the risk of corrosion of metal fasteners and connections. Included below are links to timber information pages which are useful but which are not necessarily in accordance witht the Eurocodes
Almost as important as the design of the timber members is the design of the method of connecting
the timber members. An example calculation with equations relating to most of the topics covered on this page is provided ..Example.. Relevant Standards .
symbols
Table of Timber Structural strength class according to BS EN 338 table 1Important Note; This table is equivalent to the table found in BS 5628 Timber Design however the strength values in this table are
characteristic strengths ( fifth percentile values derived directly from laboratory tests of five minutes ) whereas the equivalent values in
the BS 5628 table are grade stresses which have been reduced for long-term duration and already include a safety factor.
The characteristic value for strength as shown in the above table is based a reference depth in
bending and width in tension iof 150mm. For timber
with a depth in bending, or width in tension, less than 150mm the strength is increased in value by a factor k
Note: h = the beam depth in bending and the beam width in tension
Softwood Timber Sizes
Geometrical properties of sawn softwoods Based on timber with a 20% moisture content
Ultimate limit state design
The principle involved when considering a limit state of rupture or excessive deformation of a section or connection (STR ) is it shall be verified that : E E In simple English : the value of the product or the maximum expected forces or moments on a section
and the associated partial margins should be less than the characteristic value of the
strength of the sections divided by the relevant material partial safety margins.
Serviceability Limit State
Serviceability Limit state(SLS) is the design state such that the structure remains functional for its intended use subject to routine loading. This affects such situations as doors / windows failing to open due to structural deformation. It relates to factors others than the building strength that renders the buildings unusable. Serviceability limit state design of structures includes consideration of durability, overall stability, fire resistance, deflection, cracking and excessive vibration. This website only considers this limit state in outline. Verification for serviceability limit states in the ground or structional section or interface shall be such that E C In the notes below the sections on deflection and vibration relate to this limit state condition Design Strength values
The characteristic strengths, X Values for these factors are included in the tables below. k The eurocode , like BS 5268, allows the design strength determined using equation this be multiplied
by a number of other factors as appropriate such as k The design values for the stiffness are obtained as follows E Table for partial factor γ
table for k
examples of loading duration assignment are provided below
System strength Service Class
Moisture has a significant effect on the mechanical properties of timber and the British standard allocates service class
designations to allow for this
Service classes ( based on clause 2.3.1.3, BS EN 1995 ) Note: Design using timber sections greater than 100 thick or deep are generally based on service class 3 because of the difficulty in drying thicker sections. Design Resistance
The design value of a resistance ( load carrying capacity ) ,R
R Actions
The actions on a structure or a structural element comprise of permanent actions which are in principle unchanging through the life of the structure and variable actions which are not fixed. The prime example of a permanent action is the weight of the construction materials. Examples of variable actions include wind loading, occupancy loading, storage loading. As noted on the webpage Eurocodes Introduction,
the design value of an action (F F where ..F The general equation for the effect of actions should be The part of the equation inside the brackets represents the combination of permanent and variable actions In BS EN 1990 one of a number of equations for action (load ) combinations is equation 6,10 This is a quick, but conservative, method when compared to the alternative equations ( 6.10a and 6.10b )which are a little more complicated. 6.10b is generally the governing equation in the UK
Design of colums subject to compression or combined compression and bending.
Note: Basic information on columns and struts and the derivation of the buckling equations if found at Struts λ = Length ( Effective Length = L The relative slenderness ratios are obtained from Where both λ Combined bending and axial compression
for timber memebers ubject to combined bending and axial compression the following condiions should be satisfied Design of flexural members
The design of flexural members principally involves consideration of the following actions which are discussed next:
1. Bending σ As an example for a rectangular section beam of width b and height h M Lateral Buckling σ where
f Note: for softwoods with solid rectangular sections the following can be assumed where
Note; table only applies if compression load is on centre of gravity of section on torsionally restrained beams. SHEAR Reference Shear stress For shear with a stress component parallel to the grain as well as for shear with both components perpendicular to the grain. If flexural members are not to fail in shear, the following condition should be satisfied: τ where For a beam with a rectangular cross-section, the design shear stress occurs at the neutral axis and is given by: where
The design shear strength, f where Note: The shear strength for rolling shear is approximately twice the tensile strength perpendicular to the grain. For beams notched at their ends as shown in figure below the following condition should be checked k For beams notched at the opposite side to support k For beams of solid timber notched at the same side as support where σ where _{}
where The effective contact area, A k For beams on continuous supports and providing L For beams on discrete supports and providing L For beams subject to torsion the following expression shall be satisfied
where Note: Deflection and and vibration are generally most relevant for Design to serviceability limit states..
w Examples of limiting values of defelection based on BS EN1995-1-1 table 7,2
Specific limiting values for deflections of beams ( based on Table 4 of NA to EN 1995)
Eurocode 5 includes consideration for the load duration and moisture influences on deformations having time-dependent properties i.e creep. The final mean modulus of elasticity and shear modulus used to calculate deflections are obtained using the following equations. table for k
m = mass equal to the self weight of the floor
and other permanent actions per unit area in kg m For cases when the fundemental frequency of the floor exceeds 8 Hz the following additional requirements are imposed by the code.
ξ = modal damping coefficient, normally taken as 0.02 a = is the deflection of floor under a 1 kN point load .
a must not exceed 1,8mm for L <= 4 000mm b = is the velocity response constant .
b = 180 - 60.a if a <= 1mm ω may be estimated from the equation< below k
k
b is the floor width in m where (EI) |

- Introduction to Structural Timber design to The Eurocodes..Very important document to latest codes :75 page document
- Strength Graded Timber Mark..Download showing identification to be shown on strength graded timber
- Wood Handbook -- Wood as an Engineering Material..Downloads ..Comprehensive Document (American ) Excellent
- Canadian Wood Council ..Excellent site on Wood Engineering - my words
- Timber Trade Federation ..The Timber Trade Federation is the official voice of the UK timber trade.
- Scottish Timber Trade Association..Home page with links to useful information pages.
- In situ strength grade..Notes on visual strength grading of timber
- BSW Timber..Large UK Sawmill homepage
- Timber Size calculator ..Free on registration : In line with Eurocodes.