Establishment of an inter-university research and teaching group in the field of structural masonry

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Link zur deutschen Version: Einrichtung einer hochschulübergreifenden Gruppe für Forschung und Lehre im Bereich des konstruktiven Mauerwerkbaus.

Teaching and research in structural masonry have a long tradition at the Institute of Structural Engineering at ETHZ. Various pioneering works to describe the load-bearing behaviour of masonry and groundbreaking experimental investigations on masonry were carried out from the 1970s onwards under the direction of Prof. Dr. Bruno Thürlimann and his successor, Prof. Dr. Peter Marti. This work was widely accepted in the scientific community, and it provided the basis for today’s design code SIA 266 and was continued at ETHZ by Dr. Nebojsa Mojsilovic as well as Prof. Dr. Joseph Schwartz. The retirement of Prof. Schwartz at the beginning of 2023 and the upcoming retirement of Dr. Mojsilovic in 2025 prompted the Brick Industry Switzerland (Weblink) to seek a solution to ensure a continuation of the teaching and research activities in structural masonry.

Figure 1: Pioneering research at ETHZ in the field of structural masonry: (a) Biaxially loaded element tests with inclined bed joints (from  Ganz/Thürlimann, 1982); (b) Yield conditions for masonry under a plane stress state based on the theory of plasticity (from Ganz, 1985); (c) Development of ideal plastic stress fields (from Ganz, 1985).

Establishment of an inter-university masonry group

Prof. Dr. Walter Kaufmann (head of the Chair of Concrete Structures and Bridge Design) asked me whether I would like to take over the teaching and research activities in the field of structural masonry. In a few discussions with the Brick Industry Switzerland, the idea of an inter-university masonry group finally grew, which I will lead at the Chair of Concrete Structures and Bridge Design (Weblink) at ETHZ and the Institute for Civil Engineering (IBI) at Lucerne University of Applied Sciences and Arts (HSLU T&A). The masonry group is supported by a generous donation from the Brick Industry Switzerland, whereby the agreement – following our academic principles – guarantees our freedom of research and teaching at all times. Until his retirement, Dr. Mojsilovic will support the masonry group with his valuable expertise, ensuring continuity of the work and tradition.

The fascination of masonry – an ancient construction method in the modern world

Since my studies, masonry has accompanied me in various teaching and research activities, especially during my doctorate at the Institute of Construction Materials (IWB) at the University of Stuttgart (see list of publications here). In addition to numerous analytical and experimental investigations, I was fascinated by using state-of-the-art simulation tools in the analysis of the load-bearing behaviour of masonry and mixed systems (masonry/reinforced concrete) – or, in more technical terms, the development of mechanically consistent models and their implementation in numerical methods (e.g. linear/nonlinear finite elements → see blog post from 2022). In addition, I repeatedly had the pleasure of passing on knowledge through lecturing and co-supervising student projects.

Figure 2: Selected own research in the field of structural masonry: (a) Monotonic and semi-cyclic element tests with inclined bed joints (from Weber/Sharma/Hofmann, 2019); (b) Microplane modelling using MASA (from Weber/Hahn/Sharma, 2018); (c) Nonlinear material relationship (URM-Usermat) based on extended yield conditions from Ganz; (d) NLFE analysis of a masonry building using the URM-Usermat; (e) and (f) NLFE analysis of the experiments by Beyer et al, 2015 on mixed masonry and reinforced concrete structures by using the URM-Usermat for masonry and the CMM-Usermat for reinforced concrete (figures (c) to (f) from Weber, 2019).

Although masonry construction 1In the context of this blog post, masonry is used as a collective term for all types, combinations and arrangements of masonry blocks and mortar. has evolved over thousands of years, the basic principle (the stacking of stones 2Nowadays, however, a wide range of high-performance bricks are available, depending on the structural, building physics and aesthetic requirements.) has hardly changed over the cultural-historical civilisations – however, the way of analysis, investigation and calculation did so radically. While the Romans and Greeks had already recognized the self-supporting form of masonry vaults in ancient times, scholars in the Renaissance first systematically studied the question of an arch shape adapted to the force flow, from which the concept of the thrust line later developed – i.e. the theoretical line in a structure that represents the path of the compressive force resultant (see Figure 3 (a)). The related mechanical principle of the force transfer via compression struts is still used today for the analysis of masonry structures, for example when assessing masonry arch bridges using graphical statics or in the design of conventional masonry walls based on stress fields according to SIA code 266 (see Figure 3 (b)). However, the methodology for calculating the force flow and the ultimate loads has changed fundamentally due to the digital revolution in recent years. Computers efficiently take over complex computations and routines – however, the art and knowledge of structural and mechanical principles are not superfluous but indispensable for interpreting the results (and more demanding than ever!). Today, even conventional computers have sufficient power for the use of sophisticated (e.g. nonlinear) material models, which allows the force flow to be computed “automatically” 3“Automatically” refers to the computer’s calculation and optimization process. However, applying, interpreting, and verifying such refined models (notably the nonlinear finite element method) is highly time-consuming and requires in-depth expertise. (see Figure 3 (c)) and predictions can be made on the load-deformation behaviour, crack formation and the resulting redistribution of internal forces (e.g. with the URM-Usermat developed during my dissertation for the nonlinear finite element analysis of generally loaded 4Under a general stress state, it meant a shell loading. masonry structures). Given these developments, education and research in the field of structural masonry must not stop – the consistent application of the equilibrium and basic mechanical principles is, however, decisive (or rather mandatory) for their success.

Figure 3: Basic principle of force transfer in masonry by compression struts: (a) Section through the dome of St. Peter’s Basilica designed by Giacomo della Porta, Rome, 1547-1590 and analysis of the load-bearing behaviour by Giovanni Poleni using graphic statics and dual rope, 1748 (from Schwartz, 2011); (b) Design of masonry walls using ideal plastic stress fields according to SIA code 266; (c) Compressive stress field based on a FE analysis using the URM-Usermat (from Weber, 2019).

Combine research, teaching and practice

The main task of the masonry group is teaching and research in structural masonry, which are established simultaneously at the chair of Concrete Structures and Bridge Design at ETHZ and at IBI at HSLU T&A. The focus is mainly on promoting and developing numerical simulation tools for solving practical problems.

The research focus is on the development of mechanically consistent material models and their implementation in the software and analysis tools developed by the chair of Concrete Structures and Bridge Design – such as the open-source toolbox StrucEng Library, which is currently under development (more on this in the blog post from 2022). The tools aim at designing new structures more efficiently and identify existing structures’ load-bearing reserves to minimize strengthening without compromising structural safety and robustness. As a basis for developing and validating the material models, we conduct experimental investigations on the load-bearing behaviour of masonry. For this purpose, the unique Large Universal Shell Element Tester (LUSET) is available at the Chair of Concrete Structures and Bridge Design, which allows us to experimentally investigate the load-bearing behaviour of generally loaded shell elements made of masonry for the first time (see Figure 4 (b)).

Furthermore, we address open questions towards the mechanical load-bearing behaviour in structural masonry that have not yet been fully clarified. These include, for example, the question of the application limits of the lower bound theorem of limit analysis (a “sufficient” deformation capacity is assumed) to masonry with its well-known strongly limited deformation capacity or the load-bearing behaviour of hybrid masonry and reinforced concrete structures (e.g. load distribution through the reinforced concrete slabs, involvement of reinforced concrete walls, influence of lintel and parapet elements). To answer the related questions, we combine numerical tools and mechanical modelling with large-scale tests to derive appropriate design models and criteria with direct benefits for engineering practice. The focus is always on the consistent application of mechanically based models.

In the future, we will also increasingly focus on the application and integration of software tools in the digital planning, production and maintenance processes. We will develop new innovative solutions for digitally (pre)fabricated masonry components.

Figure 4: Open source toolbox StrucEng Library for the analysis of masonry and reinforced concrete (left) and Large Universal Shell Element Tester (LUSET) of the Chair of Concrete and Bridge Design (right).

A main concern of the masonry group is ensuring the transfer of research results and disseminating knowledge into engineering design and verification practice. On the one hand, this includes the future provision of the StrucEng Library as an open-source toolbox. On the other hand, we conduct lectures and courses at ETHZ and HSLU T&A, training civil engineers in designing and assessing masonry structures, including  the use of computer-aided analysis and design. Furthermore, we are involved in professional associations and code commissions, such as the SIA Group for Preservation of Structures (FEB) and the SIA 266 code commission (Weblink) and work closely with industry on sustainable solutions for construction practice.

Last but not least, the masonry group is intended to be a platform for exchange and discussion in structural masonry, and we invite you to collaborate on solutions for current and future challenges. We are pleased to be able to actively shape the future of masonry and thank the Brick Industry Switzerland for its valuable support. Let’s give masonry a new shine!

Marius Weber