Extension of the conditions for application of the simplified calculation methods according to DIN EN 1996‐3/NA for the design of unreinforced masonry walls

Dedicated to University Prof. Dr.‐Ing. Carl‐Alexander Graubner for his 60th birthday The simplified calculation methods for unreinforced masonry structures given in DIN EN 1996‐3/NA are an easily applicable design standard for an efficient and fast verification of the resistance of mainly vertically loaded masonry walls. However, the design rules are not based on mechanical models. Instead, they are empirical approaches for a simplified estimation of the load bearing capacity. For this reason, the range of application of DIN EN 1996‐3/NA is limited by several conditions to ensure a sufficient safety of this design procedure. With regard to extending the conditions for application, extensive comparative calculations were carried out. Thereby, considering clearly defined boundary conditions, the load bearing capacity according to DIN EN 1996‐3/NA was compared to that according to DIN EN 1996‐1‐1/NA. It was the aim of this comparison to identify load bearing reserves of the simplified calculation methods to point out potential for an extension regarding the maximum permissible clear wall height and the slab span. As a result, it can be stated, that an increase of the maximum wall height up to 6.0 m and the maximum slab span of 7.0 m is possible in certain cases.     

Veneer walls of masonry as specified in EC 6 (DIN EN 1996‐2/NA) / Zweischaliges Mauerwerk nach EC 6 (DIN EN 1996‐2/NA)

This article deals with the production of veneer walls as specified in DIN EN 1996‐2/NA [3]. Against this background of the extensive revision of the section for veneer walls an exposition in accordance with the previous requirements as specified in DIN 1053‐1 can hardly be recommended. The necessity for a basic revision of the section for veneer wall construction has already been discussed in detail and justified in several technical articles published in previous years, see [4] to [7]. With many changes and corrections in the section for veneer walls in the National Annex of DIN EN 1996‐2 [8] it is certainly not a question of new rules for this method of building, but an adjustment of the requirements in the previous standard on the basis of the practical experience gained over several years. The new requirements for the execution of cavity facing masonry enable a simple and economic implementation of this external wall construction.     

Tragfähigkeitstafeln für unbewehrtes Mauerwerk nach DIN EN 1996‐3/NA:2019‐12

Load‐bearing capacity tables for unreinforced masonry according to DIN EN 1996‐3/NA:2019‐12 Practical design aids are important tools in the day‐to‐day business of structural design. The design of primarily vertically loaded masonry walls in usual building construction can be carried out with the help of so‐called load‐bearing capacity tables. A table value is read off exclusively as a function of the geometric conditions, which – multiplied by the masonry compressive strength – results in the load‐bearing capacity of the wall for cold design and in case of fire. By comparing the acting and resisting force, the verification of structural design can be provided in a simple and yet economical form. The bearing capacity tables based on the simplified calculation methods according to DIN EN 1996‐3/NA:2019‐12 [1], [2] and DIN EN 1996‐1‐2/NA:2013‐06 [3], [4] are presented in this paper. Compared to the previous edition of Part 3 of Eurocode 6, the extended scope of application is taken into account, as well as the normative changes to the construction method with partially supported slabs.     

Extended conditions of application of DIN EN 1996‐3/NA for high walls

According to Eurocode 6, unreinforced masonry walls can be designed using different verification methods, whereby the simplified calculation methods are contained in Part 3 of DIN EN 1996 [1]. If the associated application limits and boundary conditions are fulfilled, a large part of the usual problems occurring in masonry construction can be dealt with without great effort. A limiting condition for the application of the simplified calculation methods is a maximum clear wall height of h = 2.75 m or h = 12 ? t. Changes in user requirements for modern buildings with masonry walls nowadays often require greater wall heights, wherefore a verification according to the general rules from DIN EN 1996‐1‐1/NA [2] is necessary. This means a considerably higher effort for the structural engineer. A considerable amount of calculations was done to verify whether the results of the simplified calculation methods are also valid for greater wall heights. The results were transferred into a consistent standardization proposal with regard to extended application limits of DIN EN 1996‐3/NA, which is contained in a new draft Amendment A3 for the National Application Document for Germany.     

Designing sound insulation in multi‐storey residential dwellings in accordance with E DIN 4109‐2 / Schallschutzplanung im Geschosswohnungsbau nach E DIN 4109‐2

The method for calculating airborne sound insulation between apartments as specified in DIN EN 12354‐1:2000 has been used for many years – and is increasingly being used – in architectural design. This article will give a short overview of the basic principles of this calculation method, highlighting some special aspects, and will then focus on its application in practice. In particular, the experience gained with the KS Schallschutzrechner software (calculator for the prediction of sound insulation between dwellings and terraced houses ), which has now been in use for twelve years, demonstrates that – in spite of the improved prognostic accuracy – the method is not more labour‐intensive than that of the previous procedure specified in DIN 4109 Supplement 1, provided suitable design aids are used.     

Practical application of a non‐linear earthquake analysis according to DIN EN 1998‐1 / Praktische Anwendung einer nichtlinearen Erdbebenanalyse nach DIN EN 1998‐1

Seismic safety verification can be performed by maintaining constructive rules or by calculation. Verification by calculation can be performed with a linear simplified or linear multi‐modal response spectrum analysis. Alternatively, a non‐linear quasi‐static verification is also possible according to DIN EN 1998‐1, which was not available in DIN 4149. In this article, the non‐linear quasi‐static earthquake verification according to DIN EN 1998‐1 is presented in practice, using the example of a building in Mittenwald/Germany. The verification has been checked and accepted by an independent building supervision report.     

Design tables for the utilisation factor α6,fi for the structural fire design of masonry according to DIN EN 1996‐1‐2/NA in the simplified calculation method

Easy‐to‐use verification equations are available for the verifications in the simplified calculation method. This applies also for the structural fire design of those masonry types for which a verification with the utilisation factor α_fi is given in the National Annex DIN EN 1996‐1‐2/NA. In specific applications, however, a classification can only be made applying the utilisation factor α_6,fi. In these cases, the verification for the structural fire design by calculation is considerably more complex than the mathematical verification of the structural design in the ”cold state“. The present paper shows how the design equation for α_6,fi can be made significantly easier with regard to its application by reference to the design value of the vertical load bearing resistance in the simplified method. Moreover, an upper limit value for the utilisation factor α_6,fi for the simplified method is summarised in tables.     

Reinforced masonry beams under shear load – Proposals for future designs / Bewehrte schubbeanspruchte Mauerwerksbalken – Vorschläge für zukünftige Bemessungen

This article is written against the backdrop of the work of the European standardisation committees on the amendment of EN 1996‐1‐1 [N 4] which will also exert an influence on the design of reinforced masonry in Germany. This paper focusses on the design approaches of DIN EN 1996‐1‐1 for untensioned reinforced masonry beams under shear load in the ultimate limit state (ULS). Proposals are made to discuss their revision. The contents of E DIN 1053‐3 [N 3] and of the final draft of the guideline ”Flat Lintels” [7] are taken into account.     

Verification of the fire resistance of clay brick masonry – hints for efficient design

In Germany, structural fire design of masonry is carried out in a simplified way using tabulated minimum wall thicknesses depending on the loading level in fire. Against this background the procedure of structural fire design is shown briefly before two approaches for a more efficient verification of the fire resistance are explained. The first possibility is to determine the reduction factor for the design value of the actions in fire more precisely and thereby reduce the loading level. Secondly, a design methodology is presented which can be applied in case of masonry walls with low vertical load but a large load eccentricity at mid‐height of the wall. Finally, the verification of the fire resistance of masonry according to national technical approval is discussed with an explanation how to obtain the same loading level in fire if the design is based on DIN EN 1996‐3/NA as when it is based on DIN EN 1996‐1‐1/NA.     

Design aids for unreinforced masonry under bending compression – Part 2: Application of design aids for structural design according to DIN EN 1996‐1‐1/NA

The semi‐probabilistic safety concept of divided safety factors for action and resistance of DIN EN 1990 [1] in combination with the structural design codes DIN EN 1996‐1‐1 [2] and DIN EN 1996‐1‐1/NA [3] include the requirement that acting normal forces N_Ed may not exceed the normal force resistances N_Rd for the structural design of masonry under bending compression. According to [3], fully plastic material behaviour can be assumed and the stress block used as the material law for masonry. Building on this, design aids and their theoretical basis were presented in Part 1 of this scientific paper [4], which are comparable with the ω tables (called the ? table here) and the general design diagram for massive construction. The application of the design aids is described in this second part of this scientific paper through calculation examples and the connection with the calculation approaches of [3] is made clear. The relation to the reduction factor ?_m, which covers effects of 2^nd order theory, is also obtained. With known values of the load eccentricities according to 1^st and 2^nd order theory, the design task becomes the analysis of the loadbearing capacity of the masonry section at half wall height. Knowing ?_m, the load eccentricity e₂ and the additional moment according to 2^nd order theory can subsequently be determined, which does not ensue from the calculation equations of [3]. With the general design diagram, the values of compression zone height and the assumed load eccentricities of the acting normal forces, which result from the reset rule for masonry sections with high load eccentricities, can be directly read off, greatly improving the clarity of this procedure.     

Wann kommt der EC 6 in Deutschland und was bedeutet das für die nationalen Bemessungsnormen?

Entsprechend der zwischen dem DIN und der europäischen Normungsorganisation CEN getroffenen Vereinbarungen sollen im Jahr 2010 alle europäischen Bemessungsnormen mit ihren nationalen Anhängen zur Verfügung stehen und diesen widersprechende nationale Normen zurückgezogen werden. Der Beitrag erläutert, wie der derzeitige Stand im Mauerwerksbau ist, ob und wie lange noch die deutschen Bemessungsnormen im Mauerwerksbau weiter angewendet werden können und was das für die überarbeitete DIN 1053‐1 bedeutet. Abschließend wird dem Wunsch der Praxis entsprechend zum Ausdruck gebracht, dass nur eine bauaufsichtliche Einführung als komplettes Dokument in der Liste der Technischen Baubestimmungen sinnvoll ist. When will be the EC 6 established for use in Germany and what means it for the national design codes? The European Design Codes with their National Annexes should be available in the year 2010 and contradictory national design standards withdrawn according to the agreement between DIN and the European Standardisation Organisation CEN. The contribution explains how the current state in masonry construction is, and how long the German design codes for masonry can be applied. Also the effect on the revised DIN 1053‐1 is described. Closing it will be expressed corresponding to the wish of practise that only a complete document should be introduced in the list of technically regulations for construction by the building authority.     

Spannungs‐Dehnungs‐Linien von Porenbeton bei hohen Temperaturen: ein erster Schritt zur versuchsbasierten Bemessung gemäß EN 1996‐1‐2

Stress‐strain curves of AAC at high temperatures: a first step toward the performance‐based design according to EN 1996‐1‐2 In this paper, the performance‐based approach for the design of autoclaved aerated concrete (AAC) masonry walls subjected to fire is presented. The problems associated with the calculation methods in the current version of EN 1996‐1‐2 for the assessment of AAC loadbearing walls are explained. The current version of EN 1996‐1‐2 offers only tabulated data as a reliable method for structural fire assessment. The content of current Annex C and D is generally considered as not being reliable for design because of the absence of an adequate validation by experimental tests. For this reason, a proposal is made for the improvement of the input parameters for mechanical models based on experimental tests on AAC masonry. On this basis, new stress‐strain curves as a function of temperature are proposed here and then compared with the stress‐strain curves currently included in the Annex D of EN 1996‐1‐2. The comparison results point out that the current curves do not correspond to the effective behaviour of AAC masonry under fire conditions. The proposed curves can be used as base to be implemented in the new version of EN 1996‐1‐2.     

Example calculation of the sound insulation of a floor slab between residential units according to DIN 4109‐2:2016 / Beispielhafte Berechnung der Luftschalldämmung einer Wohnungstrenndecke im Mauerwerkbau nach DIN 4109‐2:2016

The DIN 4109 series of standards has been revised in recent years and harmonised with European design codes. After the drafts of DIN 4109 were issued in November 2013, the documents shall now be finally published in summer 2016. The calculation procedure according to DIN 4109‐2 is based on the simplified procedure from EN 12354:2000, in which the noise transmission routes are calculated individually, similarly to the calculation for framed buildings according to supplement 1 to DIN 4109. The procedure according to DIN 4109‐2 is based on formulae, which are filled with figures from the building element catalogue of parts 3‐2 to 3‐6. This article shows examples of calculation steps for the determination of the weighted airborne sound reduction R'_w,Raccording to DIN 4109‐2:2016 for a floor slab between residential units.     

Out‐of‐plane bending moments in masonry walls – Analysis of different calculation methods

In the course of the revision of EN 1996‐1‐1, a new proposal has been made for the calculation of internal forces in frame‐type structures for the determination of bending moments due to slab rotation. In addition to a stiffness reduction for masonry walls in conjunction with the special features of partially supported slabs, which is already usual in Germany, the calculated ever‐present minimum loadbearing capacity of a wall is also increased due to a reduction of the maximum applied load eccentricity. Another major change is the direct implementation of wind loads in the method to determine the internal forces. To ensure that these changes do not lead to a safety deficit or an uneconomic reduction of the loadbearing capacity compared with the current situation, the results of extensive comparative calculations are presented. In addition, it is examined whether the proposal could conflict with further investigations to extend the conditions for application of the simplified design procedures according to EN 1996‐3. It is shown that the new draft provides similar results to the current method and that there are no concerns about its application. Also, the investigations to extend the conditions for application of the simplified calculation methods can be based on the new proposal without concerns.     

Development of a tool for the structural design of the vertical load‐bearing capacity of unreinforced masonry

Before the introduction of EC 6, simple codes permitted masonry to be designed manually. The simplified procedure according to EN 1996‐3 still allows manual design, but its application is restricted. Therefore, a more laborious design according to EN 1996‐1‐1 is often required. This article presents a newly developed software tool, which facilitates the structural design of the vertical load‐bearing capacity of unreinforced masonry according to EN 1996‐1‐1. The tool is intuitive to use and has been developed based on experience from working in the field. The tool assists the planner in making decisions during the masonry design process. This article describes and explains the implemented, theoretical assumptions as well as the software tool N_Rd‐Pro‐Tool itself. This software tool facilitates simple, clear und transparent structural design of the vertical load bearing capacity of unreinforced masonry.     

Proposal for the simplified design of basement walls under lateral earth pressure

This paper deals with the design of basement walls subjected to lateral earth pressure. The current simplified calculation method according to DIN EN 1996‐3/NA only covers active earth pressure, which is the lower limiting value of the earth pressure. Designing according to DIN EN 1996‐1‐1/NA, higher coefficients of earth pressure (like earth pressure at rest) can be considered, with an additional verification of the shear resistance being necessary. This paper presents a theoretical model, which forms the basis for an analytical derivation of the loadbearing capacity, and explains the required minimum values of the acting normal force to ensure sufficient resistance to cover bending and shear. Based on these results, a simplified equation is proposed for the determination of the required minimum normal force, based on the design according to DIN EN 1996‐3/NA and providing identical values in case of an earth pressure coefficient of 1/3. The required minimum load resulting from this approach fulfils the described requirement to cover bending and shear. The presented solution is verified and the conditions for application are defined. Finally, the minimum required normal forces are evaluated and tabulated for common cases relevant to building practice.     

Field report on application of the dimensioning procedure according to E DIN 4109‐2 / Erfahrungsbericht zur Anwendung des Bemessungsverfahrens nach E DIN 4109‐2

For several years, the sound insulation ratings for multi‐storey buildings have been in transition and are being brought into line with the European calculation method according to EN 12354:2000. The drafts of DIN 4109 have been available since November 2013. The forecasting procedure for the expected airborne sound insulation in solid buildings will change considerably by comparison to the regulations in Supplement 1 to DIN 4109:1989. In recent years, the building acoustics testing unit of Xella Technologie‐ und Forschungsgesellschaft mbH has carried out numerous quality tests to determine the acoustic insulation of apartment partitioning walls and apartment partitioning floors in apartment buildings. The exterior walls of the buildings reviewed consist exclusively of plastered, autoclaved aerated concrete block walls. The interior walls were made primarily of autoclaved aerated concrete or limestone blocks. In a few cases, dry constructed or reinforced concrete inner walls were present. A comparison is presented between the test results of these quality tests and the design values of the assessed sound reduction index R’w according to E DIN 4109‐2:2013. During these tests, a discussion took place on the uncertainty that must be incorporated in the calculation so as to achieve an adequately high level of planning assurance.     

Current developments in fire protection – Changeover to design and classification according to the Eurocode / Aktuelle Entwicklungen im Brandschutz – Umstellung auf die Bemessung und Klassifizierung nach europäischen Normen

The European requirements for fire safety design and testing of structural masonry members are already the governing requirements in many cases. In principle, both the European and the German classification may be used according to the Bauregelliste. However, the latter may only be used when European classification of a member or construction material is not possible because the appropriate European standards do not exist. The European standards do not differ fundamentally from the German standard DIN 4102‐2. One significant difference is that according to the DIN 4102‐2, it was required to carry out two tests with the most unfavourable result governing, while according to the European standard, only one test is required. According to the EN Standard, the tests for fire resistance and the reaction to fire are carried out separately. There are other differences related to the pressure in the furnace as well as the use of plate thermocouples instead of jacketed thermocouples. Fire safety design of masonry is carried out in accordance with EC 6‐1‐2 and the National Annex. Only the members not regulated in the EC 6‐1‐2, e.g. pre‐cast masonry members, non‐load‐bearing walls, lintels, connections and joints, should be designed and checked according to the revised DIN 4102‐4.     

Flexural tensile tests with vertically perforated clay unit masonry with thin layer mortar / Biegezugversuche an Planziegelmauerwerk

As part of the EU project, INSYSME – INnovative SYStems for earthquake resistant Masonry Enclosures in reinforced concrete buildings – to optimise infill masonry the German project partners carried out an initial part of the project on flexural strength testing of high‐tech clay block masonry in accordance with DIN EN 1052‐2. In this a wide range of modern products was considered which at present is regulated in Germany by means of general building authority approvals. The test results show that the specifications for flexural tensile strength of high‐tech clay block masonry in DIN EN 1996 are very conservative in most cases.