Eurocode 6: Design of Masonry Structures

About Eurocode 6

Eurocode 6, or to use the more formal title, BS EN 1996, consists of four documents:
BS EN 1996-1-1: Rules for reinforced and unreinforced masonry 
BS EN 1996-1-2: Structural fire design
BS EN 1996-2: Selection and execution of masonry
BS EN 1996-3: Simplified calculation methods for unreinforced masonry structures
The four documents which make up BS EN 1996 were first published in 2005 and 2006. The supporting UK National Annexes were first published by BSI in June 2007. BS 5628 was withdrawn on 31st March 2010 leaving Eurocode 6 as the primary code for masonry design.

BS EN 1996-1-1: 2005 + A1: 2012 Rules for reinforced and unreinforced masonry
In developing Eurocode 6 a way had to be found to deal with the wide range of masonry units used across Europe. This range not only includes different material such as clay, concrete and stone, but also a variety of configurations based upon the proportion and direction of any holes or perforations, web thickness etc. This has resulted in four grouping of masonry units.

The characteristic compressive strength of masonry is presented in the form of an equation (3.1). This equation includes the normalised strength of the masonry and the strength of the mortar. The normalised strength is new to the UK and relates the compressive strength of the unit determined by test to a standardised shape and moisture content. The designation of mortars has also changed with the need for a declaration based on strength rather than mix proportions. Thus an M12 mortar may be expected to have a strength of 12N/mm2.
A key aspect of the standards supporting Eurocode 6 is that only masonry units are referred to leaving the various UK National Annexes to specify standard sizes for bricks and blocks and how to specify, using performance standards, such things as Engineering Bricks.

A further area of change for vertical load relates to the treatment of eccentricity where a capacity reduction factor needs to be calculated at the top and bottom and the mid height of the wall. The concept of an initial eccentricity to allow for any inaccuracies in the construction of the masonry is also introduced. Concentrated loads are also handled differently in Eurocode 6. Fortunately lateral load design is based on the BS 5628 approach and will be very familiar to UK designers. Ancillary components are now dealt with in a more coherent way and suitable values of partial safety factors have been introduced.

BS EN 1996-1-2:2005 Structural fire design 
Fire design will largely remain in the form of tables similar to those contained in BS 5628 Part 3. The fire resistance of a loadbearing wall now comprises two values depending upon how highly loaded the wall is and is further enhanced if the wall is plastered.

BS EN 1996-2:2006 Selection and execution of masonry
Part 2 of Eurocode 6 contains limited information of a very general nature on materials and execution. Five new exposure classifications MX1 to MX5 are defined. Part 2 is not, however, a replacement for the extensive guidance provided in BS 5628 which forms the basis of PD 6697 which is also published by BSI.

BS EN 1996-3:2006 Simplified calculation methods for unreinforced masonry structures
Part 3 deals with simplified calculation methods for unreinforced masonry but it is not anticipated that this will be widely used in the UK where other guidance, for example Approved Document A of the Building Regulations for England and Wales, produces more cost effective outcomes.

PD 6697:2010 Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2.
This Published Document is published by BSI and came into effect on 30 November 2010. It contains non-contradictory complementary information and additional gudance for use in the UK with BS EN 1996-1-1 and BS EN 1996-2. It does not specifically cover BS EN 1996-1-2 and BS EN 1996-3 but some of the information it contains may be relevant.

Key aspects of the Eurocodes

  • The Eurocodes support National Building Regulations and other National requirements for regulated work but remain subservient to them.
  • National regulations set the appropriate level of safety through Nationally Determined Parameters (NDP). Certain other parameters can be set by individual countries.
  • The clauses in the Eurocodes are divided into Principles and Application Rules. Principles are identified by (P) after the clause number and cover items for which no alternative is permitted. Application rules are recommended methods of achieving the Principles but alternative rules may also be used.
  • There are two types of Annex in the Eurocodes. Normative Annexes are part of the requirements of the code.
  • Informative annexes provide guidance which can be adopted or not on a country by country basis.
  • The National Annex is a special type of Informative Annex which contains the choices made by a particular country. Typically the National Annex will state values and classes applicable to that country, provide value where only a symbol is given in the Eurocode and provide country specific data. The National Annex also chooses when alternatives are given in the Eurocodes and indicates which Informative Annexes may be used. Finally it refers to Non-contradictory complementary information (NCCI).
  • An NCCI is a way of introducing additional guidance to supplement the Eurocodes without contradicting them.