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.     

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.     

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.     

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.     

Load‐bearing capacity of slender unreinforced masonry compression members under biaxial bending

Dedicated to Prof. Dr.‐Ing. Carl‐Alexander Graubner on the occasion of his 60th birthday Masonry members have to resist vertical loads and bending moments about the weak axis due to rotation of adjacent slabs. If the compression member is part of the bracing system, there are also bending moments about the strong axis. This paper deals with the load‐bearing capacity of biaxially eccentrically compressed unreinforced compression members with rectangular cross‐sections. For linear‐elastic material, the principles of an analytical model is presented, which considers geometrical and physical (cracking) non‐linearity. The deflections of the wall can be determined by using moment‐curvature relations, making possible the analytical analysis of compression members considering the effects of 2nd order theory. For a non‐linear stress‐strain relation, the calculation of the load carrying capacity of rectangular compression members under biaxial bending is complex and has to be determined numerically. The good accordance of the results of the analytical model with the numeric calculations is also shown for various eccentricities. In addition, a simplified proposal for the calculation of the load‐bearing capacity of biaxially eccentrically compressed unreinforced compression members is shown. The proposal is based on the load‐bearing capacity of uniaxially eccentrically compressed unreinforced compression members. Therefore it is possible to use the proposal considering existing models, for example according to Eurocode 2 or 6.     

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.     

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.     

National Standards of the People’s Republic of China – Thoughts of revision on technical specification for application of autoclaved aerated concrete / Nationale Standards der Volksrepublik China – Gedanken zur Überarbeitung der technischen Spezifikationen für die Anwendung von dampfgehärtetem Porenbeton

The revision task on technical specification for application of autoclaved aerated concrete products JGJ/T17 is under way, which was assigned in November 2013.The framework, thoughts and contents of revision on the specification are presented in this paper.     

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.     

New approach for spacing of movement joints in reinforced and unreinforced masonry veneer walls. Part 1: Unreinforced masonry / Neue Bemessungsmethode für die Abstände von Dehnungsfugen in bewehrten und unbewehrten Verblendmauerwerksschalen. Teil 1: Unbewehrtes Mauerwerk

The spacing of movement joints has been subject of many discussions. The current methods for the determination of the spacing of movement joints are based on local traditions and bad experience with cracked veneer walls. This has resulted in various design rules throughout Europe with very stringent limits for spacing of movement joints. According to EC6, one of the solutions for increasing the spacing of movement joints is to introduce bed joint reinforcement, although unfortunately no specific design rules are given. Until now, most scientific research has been focused on numerical simulations without taking time‐dependent effects into account, which is a conservative approach. In this paper, a new approach is described. It is based on Peter Schubert's model and on practical experience with masonry buildings.