9.1. Material characteristics timber

This section contains tables with the material properties of the different timber strength classes. With the aid of a modification factor the characteristic values are adapted to the local environment and use.

Durability class

The upper table below can be used to judge whether wood species belonging to a particular durability class (D1-D5) is sufficiently durable or needs extra protection. The durability class of different wood species is depicted in the lower table below. The higher the durability class, the less durable a wood species 1.

Table 9.1 Durability classes timber.

Use class	D1	D2	D3	D4	D5
1	O	O	O	O	O
2	O	O	O	(O)	(O)
3	O	O	(O)	(O)-(X)	(O)-(X)
4	O	(O)	(X)	X	X
5	O	X	(X)	X	X

O: Natural durability is sufficient
(O): Natural durability in principle sufficient but some circumstances require wood treatment
(O)-(X): Natural durability can be sufficient
(X): Chemical treatment is advisable but for some applications the natural durability can suffice
X: Chemical treatment is necessary

Table 9.2 Durabilities per specimen.

Species	Natural durability
Spruce	D4
Pine	D3-D4
Oak (European)	D2
Oak (American)	D4
Larch	D3-D4
Azobe	D2
Robinia	D1-D2
Western Red Cedar	D2-D3

Use class

Table 9.3 Use classes for timber.

Class	Description	Example
1	Situations in which the wood or wood-based product is inside a construction, not exposed to the weather and wetting.	roof beam
2	Situations in which the wood or wood-based product is under cover and not exposed to the weather (particularly rain and driven rain) but where occasional, but not persistent, wetting can occur.	beam of open canopy
3	Situations in which the wood or wood-based product is above ground and exposed to the weather (particularly rain).	external column
4	A situation in which the wood or wood-based product is in direct contact with ground and/or fresh water.	foundation pile
5	A situation in which the wood or wood-based product is permanently or regularly submerged in salt water (i.e. sea water and brackish water).	sea lock gate

Service classes

Table 9.4 Service classes for timber.

Service class	Environment	R.H. in construction	Use class
1	Relative humidity exceeding 65% only a few weeks per year. Temperature 20°C	12% R.H.	1
2	Relative humidity exceeding 85% only a few weeks per year. Temperature 20°C	20% R.H.	1
2	If the component is in a situation where it could be subjected to prolonged wetting by liquid water e.g. condensation	20% R.H.	2
3	Climatic conditions leading to higher moisture contents than in service class 2	> 20% R.H.	3 or higher if used externally

Note

The relative humidity of in the material given in this column holds for most softwoods.

Load duration class

Table 9.5 Load duration class for timber.

Load duration class	Order of load duration	Example
Permanent	More than 10 years	Self weight
Long-term	6 months to 10 years	Storage
Medium-term	1 week to 6 months	Imposed floor load, snow
Short-term	Less than 1 week	Snow, wind
Instantaneous	-	Wind, accidental load

Modification factors \(k_{mod}\)

Table 9.6 Modification factors for timber.

Material	Service class	Permanent	Long-term	Medium-term	Short-term	Instantaneous
Solid Timber and Glued Laminated Timber	1	0.60	0.70	0.80	0.90	1.10
Solid Timber and Glued Laminated Timber	2	0.60	0.70	0.80	0.90	1.10
Solid Timber and Glued Laminated Timber	3	0.50	0.55	0.65	0.70	0.90

Note

Note that the modification factor needs to be chosen according to the load duration of the whole load combination.

Creep factors \(k_{def}\)

The creep factor is based on the service class.

Table 9.7 Creep factor for timber.

Material	1	2	3
Solid Timber and Glued Laminated Timber	0.60	0.80	2.00

Material properties: solid timber

Table 9.8 Material properties for solid timber.

Material property	C14	C16	C18	C20	C22	C24	C27	C30	C35
Bending \(f_{m;k}\) (N/mm²)	14	16	18	20	22	24	27	30	35
Tension \(f_{t;0;k}\) // (N/mm²)	8	10	11	12	13	14	16	18	21
Tension \(f_{t;90;k}\) ┴ (N/mm²)	0.4	0.4	0.4	0.4	0.4	0.4	0.4	0.4	0.4
Compression \(f_{c;0;k}\) // (N/mm²)	16	17	18	19	20	21	22	23	25
Compression \(f_{c;90;k}\) ┴ (N/mm²)	2.0	2.2	2.2	2.3	2.4	2.5	2.6	2.7	2.8
Shear \(f_{v;k}\) (N/mm²)	3.0	3.2	3.4	3.6	3.8	4.0	4.0	4.0	4.0
Mean MOE \(E_{0;\text{mean}}\) (N/mm²)	7000	8000	9000	9500	10000	11000	11500	12000	13000
5% MOE \(E_{0,05}\) (N/mm²)	4700	5400	6000	6400	6.7	7400	7700	8000	8700
Mean MOE \(E_{90;\text{mean}}\) (N/mm²)	230	270	300	320	0.33	370	380	400	430
Mean shear modulus \(G_{\text{mean}}\) (N/mm²)	440	500	560	590	630	690	720	750	810
Density \(\rho_k\) (kg/m³)	290	310	320	330	340	350	370	380	400
Mean density \(\rho_{\text{mean}}\) (kg/m³)	350	370	380	390	410	420	450	460	480

Note

1. MOE = modulus of elasticity or Young’s modulus.

2. Timber in strength classes C40 and C45 may not be readily available

Material properties: glued laminated timber

Table 9.9 Material properties for glued laminated timber.

Material property	GL24h	GL28h	GL32h
Bending \(f_{m;k}\) (N/mm²)	24	28	32
Tension \(f_{t;0;k}\) // (N/mm²)	16.5	19.5	22.5
Tension \(f_{t;90;k}\) ┴ (N/mm²)	0.4	0.45	0.5
Compression \(f_{c;0;k}\) // (N/mm²)	24	26.5	29
Compression \(f_{c;90;k}\) ┴ (N/mm²)	2.7	3.0	3.3
Shear \(f_{v;k}\) (N/mm²)	2.7	3.2	3.8
Mean MOE \(E_{0;\text{mean}}\) (N/mm²)	11600	12600	13700
5% MOE \(E_{0,05}\) (N/mm²)	9400	10200	11100
Mean MOE \(E_{90;\text{mean}}\) (N/mm²)	390	420	460
Mean shear modulus \(G_{\text{mean}}\) (N/mm²)	720	780	850
Density \(\rho_k\) (kg/m³)	380	410	430
Mean density \(\rho_{\text{mean}}\) (kg/m³)	420	450	470

Material properties continued: solid timber

Table 9.10 Material properties for solid timber.

	C40	C45	C50	D18	D24	D30	D35	D40	D50	D60	D70
\(f_{m;k}\)	40	45	50	18	24	30	35	40	50	60	70
\(f_{t;0;k}\) //	24	27	30	11	14	18	21	24	30	36	42
\(f_{t;90;k}\) ┴	0.4	0.4	0.4	0.6	0.6	0.6	0.6	0.6	0.6	0.6	0.6
\(f_{c;0;k}\) //	26	27	29	18	21	23	25	26	29	32	34
\(f_{c;90;k}\) ┴	2.9	3.1	3.2	7.5	7.8	8.0	8.1	8.3	9.3	10.5	13.5
\(f_{v;k}\)	4.0	4.0	4.0	3.4	4.0	4.0	4.0	4.0	4.0	4.5	5.0
\(E_{0;\text{mean}}\)	14000	15000	16000	9500	10000	11000	12000	13000	14000	17000	20000
\(E_{0,05}\)	9400	10000	10700	8000	8500	9200	10100	10900	11800	14300	16800
\(E_{90;\text{mean}}\)	470	500	530	630	670	730	800	860	930	1130	1330
\(G_{\text{mean}}\)	880	940	1000	590	620	690	750	810	880	1060	1250
\(\rho_k\)	420	440	460	475	485	530	540	550	620	700	900
\(\rho_{\text{mean}}\)	500	520	550	570	580	640	650	660	750	840	1080

Design values of material properties in ULS

The material properties given in the tables above are characteristic values. Depending on the local environment, use and load duration these values have to be adjusted to design values. The design value of the Young’s modulus is used to determine the force distribution in a statically indeterminate structure.

Strength properties:

\[\begin{gather*} X_d = k_{mod} \cdot \frac{X_k}{\gamma_M} \end{gather*}\]

Stiffness properties:

\[\begin{gather*} E_d = \frac{E_{mean}}{\gamma_M} G_d = \frac{G_{mean}}{\gamma_M} \end{gather*}\]

Where:
\(X_d\) = Design value of strength property
\(X_k\) = Characteristic value of strength property
\(E_d\) = Design value of Young’s modulus
\(E_{mean}\) = Characteristic value of Young’s modulus
\(k_{mod}\) = modification factor
\(\gamma_M\) = model factor; 1,25 for glued laminated timber, 1,3 for solid timber and connections

Final deflection

The final deflection in SLS including creep effects is defined as:

\[\begin{gather*} u_{fin} = u_{fin;G} + u_{fin;Q;1} + \Sigma u_{fin;Q;i}\\ u_{fin;G} = u_{inst;G} \cdot (1 + k_{def})\\ u_{fin;Q;1} = u_{inst;Q;1} \cdot (1 + \psi_{2,1} \cdot k_{def})\\ u_{fin;Q;i} = u_{inst;Q;i} \cdot (\psi_0 + \psi_{2,i} \cdot k_{def}) \end{gather*}\]

Where:
\(u_{fin}\) = final deflection
\(u_{inst}\) = instantaneous deflection
\(u_G\) = deflection under permanent load
\(u_{Q;1}\) = deflection under leading variable load
\(u_{Q;i}\) = deflection under other variable load
\(\Psi_0\) = load combination factor (see also general loads)
\(\Psi_2\) = factor for quasi permanent value of variable load i
\(k_{def}\) = creep factor

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