Introduction on Structural timber Design per BS 5268-3:2002
Strctural timber designing per BS 5268 is just a process of designing timber structures like trusses and timber houses using British Standard 5268 part 2 of the year 2002. it is not must that every persin who needs to design timber structure needs the BS 5268 to design timber structures, this may vary from one to another person depending the acceptable standards of his or her country.
General overview of checking sustainability of timber sections per BS5268-2:2002.
This is post is written typically for timber members facing compression stress, tension stress or both compression and tension stresses. Consider simple description below on how to check sustainabilty of timber member facing this stresses.
These simple descriptions are as follows;
i). When a member is facing only compressive stress.
A timber member facing only compression forces checking its sustainability is just by comparing two stresses on that timber member. Thsese stresses are applied compressive stress and permissible or admissible compressive stress. Here applied compressive should not exceed admissible cmpressive stress. Also being very small compared to admissible compressive stress may lead to overdesign of timber structure expected to be built.
ii). When a member is facing only tension stresse.
Now when you have given a timber member facing only tension stresses, checking its sustainability is not different to compresion members as explained above. This means that applied tension stress should not excveed admissible tension stress. Therefore you will need to calculate applied tension stress and calculating also admissible tension stress, then you compare their values.
Note, the above two paragraphs explain on how to check sustainability of a timber section when a member is facing only one kind of stresses either compression or tension stress. Now when you member is facing two stresses at the same time. This may be as follows;
iii). When a member is facing compression and bending stresses.
When your member is facing two stresses at the same time, it is facing compression and bending at the same time, checking its sustainability you will just use a formula, conside a formula in page 39 "page 14" in clause 2.11.6 of the BS 5268-2:2002 through that you can see that in order to check a sustainability of the timber section facing theses stresses you need to calculate the following;
- calculating applied bending moment of that section (using a formula Ma/Z).
- calculating applied compressive stress on that section (using a formula Fc/Anet).
- calculating admissible bending moment of that timber section.
- calculating admissible compressive stress on that section.
Therefoere after calculating above values in your timber scetion the you will plug a formula located on the BS 5268-2:2002 on page 39 "page 14", the formula is as shown in an image below.
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| Image by Mbedule design |
Now once you got the above values you will those data in that formula and then your value should be less or equal to one.
iv). when a member is facing tension and bending stresses at the same time.
Here you will need check a formula for a member facing tension and bending in page 44 of the BS 5268-2:2002 clause 2.12.3 "page 18". You can see that there are things to be considered when checking sustainability of the section over such stersses, same as in a member explained in iii above. Also here thaere are valus to be calculated first and plugging them in a formula thses are as follows,
- applied bending stress
- admissible bending stress
- applied tension stress
- admissible tension stress.
Consider an image below,
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| Image by Mbedule Design |
Generally this post can help someone check sustainability of the section on timber. But a person can use other alternatives than this listed in above paragraphs. Just try visiting Mbedule design for more updates about construction industry.
