Answers to FAQs
1. Figure G1 lacks some of the annotation. The correct version is shown below.
2.
3. The agreement between CEN (The European Standards Organisation on which BSI represents the UK) and the member states requires the conflicting national standards to be withdrawn in 2010. The Department for Communities and Local Government and BSI currently believe that this timetable should be adhered to.
Withdrawn standards will not be maintained by BSI but may still be used provided that clients are happy to accept them.
4. The selection of appropriate values for Nationally Determined Parameters in Eurocode 6 means that the overall economy in the use of masonry should remain the same as current design to BS 5628.
5. Thin layer mortars are fully covered by Eurocode 6 and the supporting BS EN standards. The equation used in Eurocode 6 to evaluate the Characteristic Compressive Strength of Masonry is modified when thin layer mortar is used and the supporting BS EN 771 group of standards provides requirements for the dimensional accuracy required of the units.
6. Residual standards are a particular form of NCCI (Non Contradictory Complimentary Information) intended to provide information not otherwise contained in the Eurocodes. In the case of masonry this is particularly necessary because custom and practice varies so much across Europe. Much of the extensive information contained in BS 5628 Part 3, for example, will be lost if it is not retained and maintained in some form. Unfortunately there is currently no funding available for this work.
7. Special Category of manufacturing control was replaced by the publication of the BS EN masonry standards and the revisions to BS 5628 which were published towards the end of 2005. Masonry units are now described either as Category I or Category II.
Category I masonry units are units with a declared compressive strength with a probability of failure to reach it not exceeding 5%. This may be determined via the mean or characteristic value.
Category II are masonry units not intended to comply with the level of confidence of Category 1 units.
8. Fire resistance is covered in BS EN 1996-1-2 and the corresponding National Annex. Information is provided on the passive fire resistance of masonry walls. Tabulated data covers loadbearing and non-loadbearing walls including cavity and separating walls.
9. The lateral load clauses in Eurocode 6 are based on those contained in BS 5628 and will therefore be familiar to UK engineers. The main difference is that the limiting dimensions for serviceability are now presented in graphical form. For some panel configurations there are some significant changes in these limiting dimensions.
10. The Eurocodes remain subservient to UK Building Regulations and Approved Document A will still be available for the design of masonry buildings. BS EN 1996-3 contains simplified calculation methods for unreinforced masonry based on the principles contained in BS EN 1996-1-1 and should not be confused with simple rules developed on the basis of experience. In general the rules in Part 3 are conservative and unlikely to result in the economy of solution to be found in Approved Document A.
11. There are no specific recommendations in Eurocode 6 for assessing existing buildings or structures. The situation remains that sensible engineering judgment needs to be applied when making such assessments. Remember that both the methods of test for masonry units and the test for determining the characteristic compressive strength of masonry changed with the introduction of the BS EN standards.
12. The structural design of low-rise buildings is covered by BS 8103 which has been updated to incorporate the BS EN material and test standards. This standard will continue to be used and is not affected by the introduction of Eurocode 6.
13. In Eurocode 6 the primary method of specifying mortar is by the strength grade. An M12 mortar should have a compressive strength at 28 days of 12 N/mm2. This strength is used in the relationship to determine the characteristic compressive strength of the masonry. The mortar manufacturer will provide information on the strength that a particular mortar will achieve and its expected durability when subjected to given exposure conditions.
Historically in the UK mortar is often specified as proportions by volume (i.e. prescribed proportions rather than designed to achieve a specified strength). The UK National Annexe indicates the following approximate equivalence:
Compressive strength class and equivalent Mortar designation
M12 .................(i)
M6 ...................(ii)
M4................... (iii)
M2................... (iv)
14. Shell bedded masonry is constructed so that the masonry units are bedded on two or more strips of mortar. Normally there are two strips which are at the outside edge of the bed face of the units. When shell bedding is used the procedure for determining the characteristic compressive strength of the masonry is modified.
15. The normalised compressive strength of masonry units is the compressive strength of the masonry units converted to the air dried compressive strength of an equivalent 100mm wide by 100mm high masonry unit. It is the normalised strength that is used to determine the characteristic compressive strength of the masonry. More detailed information may be found in BS EN 771-1,2,3,4,5&6 and BS EN 772-1.
16. Masonry units are designated Group 1,2,3 or 4 according to the the percentage, size and orientation of holes in the units when laid. This enables the properties of the unit to be characterised for structural design purposes.(For details see Table 3.1 of BS EN 1996-1-1)
17. There are five exposure classes recognised in Eurocode 6 which relate to the micro conditions of exposure of the completed masonry. The five conditions may be summarised as follows:
MX1 In a dry environment
MX2 Exposed to moisture or wetting
MX3 Exposed to wetting plus freeze/thaw cycling
MX4 Exposed to saturated salt air, seawater or de-icing salts
MX5 In an aggressive chemical environment.
More detailed information and examples are provided in Annex A of BS EN 1996-2. Annex B provides acceptable specifications of masonry units and mortar for durability but this is not applicable to the UK.
18. This is an error. Equation 8.1 of BS EN 1996-1-1 provides the straight anchorage length required for a reinforcing bar. The design strength and design anchorage strength of the reinforcing steel are used and the partial factor for material is not required.
19.Equation C.1 in Annex C of 1996-1-1 is incorrect. In the formula h3 and h4 should be changed to l3 and l4respectively.
20. A Normative Annex forms part of the Eurocode and therefore has to be followed. An example is Annex B of BS EN 1996-1-2. It is a matter of National Choice as to which of the Informative Annexes may be used in a particular country and the country's National Annex states which Informative Annexes may be used.
21. The designations P, M & S are used to specify the durability of mortar. Masonry mortar is specified for durability using the terms defined in BS EN 998-2. The designations provide a useful abbreviation as follows:
P - mortar for use in masonry subjected to passive exposure
M - mortar for use in masonry subjected to moderate exposure
S - mortar for use in masonry subjected to severe exposure
Table B.2 in Annex B of BS EN 1996-2 which relates these designations to the class of exposure is not applicable to the UK. Pending the development of suitable NCCI material designers in the UK should use BS 5628:Part 3: 2005.
22. Although recommendations for the corrosion protection required for different ancillary components, when subjected to a particular class of exposure, are provided in Annex C of BS EN 1996-2 this is not to be used in the UK. Pending the development of suitable NCCI material designers in the UK should use BS 5628:Part 3: 2005 and the corresponding BS EN 845 series standard appropriate to the ancillary component being used.
23.The title of Annex E of 1996-1-1 is incorrect. It should refer to α 2 and not α 1. The values in the tables are values for α 2.