Sustainable building for the future: Contemporary clay masonry – Resource‐saving building

Clay as a building material has a long tradition in Europe, largely losing its importance with industrialisation. Since the 1980s, clay building activity has steadily increased. Standard guidelines (Lehmbau‐Regeln) introduced in the 1990s, however, appear to be rather too cautious when examined in the light of current research findings on the load bearing capabilities of clay walls. Based on the evidence of historic clay buildings, on structural engineering calculations and building physics – the authors' research supports the assumption that masonry with modern unfired clay bricks has a much higher performance potential than previously assumed, which applies particularly to its sustainability. The biggest apprehension relates to the water‐sensitivity of this building material with regard to structural soundness. This can be countered however with the appropriate construction principles.     

High‐rise concrete and clay block masonry building in Brazil

Brazilian structural concrete and clay block masonry construction shares many common features with construction all over the world: blocks of a similar shape are bedded in mortar, vertical and horizontal reinforcement is placed in grouted cells, engineering analysis and design follows universal principles and local design codes mimic those adopted elsewhere. However, loadbearing masonry construction in Brazil has become one of the most preferred high‐rise building systems due to its cost‐effectiveness and ease of construction compared to normal reinforced concrete solutions. This paper provides an overview of loadbearing masonry building in Brazil, including case studies on notable high‐rise masonry structures, with an overview of how Brazilian materials, codes and practices differ from the rest of the world. Finally, the paper explains how the use of high‐strength units assists the growing demand for taller and taller buildings and provides insight into why owners and general contractors often prefer to use structural masonry.     

Bauakustische Bemessung von Mehrgeschossbauten mit monolithischen Ziegelaußenwänden

Acoustic design of multi‐storey buildings with external walls of monolithic clay masonry For masonry buildings with monolithic, highly insulated walls of clay units, no acoustic design according to standard was practically possible under Supplement 1 to DIN 4109:1989. Therefore a design procedure regulated by approvals was introduced in 2010, with which acoustic calculations for a building could be performed with a high security of forecasting. This procedure has been taken up in the completely revised series of standards DIN 4109:2016/2018 “Sound insulation in buildings”. The basis for the application of this method is knowledge of the individual sound insulation quantities and joint sound insulation quantities for the relevant clay masonry products or product combinations. In order to simplify performance of the verification for clay masonry buildings, the clay masonry industry provides the program “Modul Schall 4.0” (Acoustic module 4.0), in which the decisive acoustic parameters of external wall products from numerous clay masonry unit producers are stored in a database. In this report, experience of application of the design procedure for clay masonry buildings is presented. There is good agreement between forecasts and tests on completed buildings.     

Masonry and residential building in Germany: Status 2019 and forecast for 2021

About 80 % of all products of the masonry industry in Germany are used for new residential building. If products for the refurbishment of masonry buildings are added to this, then over 85 % of all masonry products are used in residential building. Regarding residential building activity, it can be stated that about 73 % of all residential buildings in Germany are of predominantly masonry construction, with a slightly increasing tendency. Table 1 shows the development of market shares of the various construction methods reinforced concrete, masonry and timber over the years 2012 to 2017.     

Solid and timber construction in residential buildings / Massiv‐ und Holzbau bei Wohngebäuden

In the context of a comprehensive analysis of the current situation in Germany’s residential sector as regards construction costs and developments in these, the Arbeitsgemeinschaft für zeitgemäßes Bauen e.V. (ARGE) undertook a specific study to investigate the use of the main materials for building walls (using both solid and timber construction methods) in residential buildings. In order to obtain comparable data, two buildings typical of the residential sector were modelled: an apartment block and a detached house. These reflect the current building situation in Germany. It should be noted that for both multi‐storey buildings and detached homes, if we look at the median cost, it is more economical to use masonry for the basic structure than timber. The cost advantage of the solid construction method over the timber method for detached houses is 4 %, and the median advantage for apartment blocks is between 4.7 and 6 %. The studies we used in our assessment of the sustainability of the building materials used (for example from TU Darmstadt) conclude that both construction methods (solid and timber) are comparable in terms of the ‘ecological balance sheet’ results achieved over their entire life cycles and occupancy phases.     

Massive versus lightweight construction in residential building

Masonry as the primary form of construction is currently the most economic option for the building of multi‐storey apartment blocks in Germany in order to provide affordable housing. It can however also be stated that there is definitely further rationalisation potential in masonry construction, in contrast to lightweight construction. In comparison to masonry construction, lightweight building methods show no apparent economic advantages, the ecological balance is objectively equivalent and the fire protection and sound insulation properties have to be provided technically and constructively at high cost in order to comply with the same requirements. Under consideration of a realistic and objective assessment, there is therefore no reason to promote the use of lightweight building methods, such as timber‐frame, from their current status as niche products, especially for residential building.     

Innovative insulation technology for the reduction of thermal transmission losses in cavity walls

The German energy‐saving regulations (EnEV) are continuously revised to make the statutory requirements for thermal insulation of new buildings more stringent, which results in an increased need for highly effective insulation systems. The objective of a research project being carried out at the TU Dresden, Faculty of Architecture, Chair of Structural Design is to solve the problem of reducing thermal losses from masonry buildings through the development of an innovative insulation and fixing system for cavity wall building. The newly developed insulation system should fulfil the essential requirements regarding geometry, loadbearing capacity, flexibility, lifetime and capability of dismantling as well as current requirements for energy saving to ensure the zero energy standard. The research project is mainly based on the use of vacuum panels (VIP vacuum insulated panels) as the central insulation layer in cavity masonry walls and the development of a linear tie system [1], [2].     

Masonry buildings at the borderline to high‐rise – Part 1 / Mauerwerksbauten an der Hochhausgrenze – Teil 1

The interaction of vertical and horizontal loads is the decisive combination of actions for multi‐storey buildings with masonry shear walls in most cases. This article presents a simple and clear method, which can be used with modern open floor plans to verify a favourable load transfer of the vertical actions for masonry walls. The method is extended in the second part of the article to be published in one of the coming issues of the journal Mauerwerk for horizontal actions and explained with an example.     

Einbruchhemmung mit Mauerwerk aus Leichtbeton

Burglary resistance with lightweight concrete masonry The product palette of lightweight concrete blocks ranges from heavy, high‐strength blocks for internal walls, cavity walls and externally insulated (ETICS) external walls to lightweight, highly insulating blocks with lower density and lower compressive strength for monolithic external walls. In the German National Annex to EN 1627, suitable wall constructions for the installation of burglary‐retarding building elements are given. Masonry walls made of heavy, high‐strength blocks fulfil all requirements up to the highest resistance class RC 6. The installation of burglary‐retarding building elements in modern, highly insulating blocks for monolithic masonry is therefore not covered by the standard yet. At the institute for window technology in Rosenheim (ift Rosenheim), testing has been undertaken of the burglary resistance of building elements installed in monolithic masonry made of highly insulating lightweight concrete blocks. For the usual 365 mm thick lightweight concrete masonry units of compressive strength class 2 and density class 0.40 with a lightweight plaster of Type I, the burglary resistance class RC 2 (recommended by the police in Germany) was verified in all the investigated variants of blocks. The results of the research project have been implemented in a proposed change of the German National annex to DIN EN 1627.     

Experimental‐numerical research on the seismic performance of URM buildings made of lightweight AAC blocks / Experimentell‐numerische Untersuchung zum seismischen Verhalten von unbewehrten Mauerwerksgebäuden aus Porenbetonblöcken

Masonry walls constructed with lightweight AAC blocks and thin‐layer mortar meet the increasingly strict requirements of energy efficiency and sustainability. In this sense, they represent an excellent solution for modern buildings, not only for external cladding but also as loadbearing elements. Despite the possible advantages of using lightweight AAC masonry, a specific assessment of its seismic performance is mandatory in order to set design recommendations allowing to reach safety levels consistent with those required for other masonry types complying with EN 1998 standard requirements. A comprehensive study on the seismic performance of unreinforced masonry buildings made of lightweight AAC was carried out in an integrated experimental‐numerical approach. The experimental campaign provided the necessary information to setup a reliable numerical model to be extensively used to assess the seismic performance of a number of prototype AAC masonry buildings with different characteristics, by means of both linear and nonlinear static (pushover) analysis. The results of this systematic numerical assessment were eventually used to draft design recommendations, to set parameters (behaviour factors) to be used in linear analysis and to calibrate rules for simple buildings.     

Investigation of the seismic out‐of‐plane behaviour of unreinforced masonry walls

The structural stability of unreinforced masonry (URM) walls has to be guaranteed not only under static (permanent and live) loads but also under earthquake loads. Loads transverse to the plane (out‐of‐plane) often have a decisive influence on the load‐bearing capacity. In practical applications, simplified methods from codes, guidelines and literature are often used to analyse and evaluate the out‐of‐plane capacity of load‐bearing and non‐load‐bearing URM walls. The results of these simplified methods can be significantly conservative and inaccurate since essential influencing effects are neglected. For many existing buildings, the simplified methods underestimate the capacity, which leads to cost‐intensive retrofitting and strengthening measures or complete replacement by other wall systems. In order to realistically estimate the out‐of‐plane capacity, parameters such as wall geometry, boundary conditions, vertical loads and especially dynamic effects (e.g. inertia forces) have to be taken into account. In this paper, non‐linear time history simulations are presented to investigate the influence of these effects. The numerically determined maximum acceptable earthquake acceleration is compared with results from simplified analysis models. The comparison shows that the out‐of‐plane capacity is significantly higher than the values predicted by simplified models. Finally, several initial experimental seismic tests conducted on the shaking table of the TU Kaiserslautern are presented, together with the planned extensive experimental test program on the out‐of‐plane capacity of masonry walls.     

Investigation of horizontal floor acceleration in historic masonry buildings

Earthquakes with comparatively low magnitudes can lead to serious damage to non‐structural components of historical masonry buildings, such as architectural facade elements. In order to assess the vulnerability of non‐structural components, the horizontal floor acceleration is used. This depends on the dynamic characteristics of the building, the ground acceleration and dissipative effects. In the present article comprehensive probabilistic FE time history analyses with different hazard levels have been carried out for selected masonry structures. In order to take induced non‐linearities into account, a macroscopic material model for historic masonry was calibrated and applied. It was shown that the chosen methodology enables the determination of the distribution of floor acceleration over the building height for historic masonry structures. In addition, due to the detailed scope, a robust comparison with the simplified design methods is possible. Finally, the applicability of the simplified design approach according to EN 1998‐1 [1] is discussed for the investigated case.     

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.     

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.     

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.     

Reinforced bending load‐stressed masonry – Suggestions for future designs / Bewehrtes biegedruckbeanspruchtes Mauerwerk – Vorschläge für zukünftige Bemessungen

European standardization bodies are currently working on the amendment to EN 1996‐1‐1, which will also affect the evaluation of reinforced masonry in Germany. For that reason, discussion suggestions are being made here for revisions to lay the groundwork for building materials evaluations and especially, evaluations of bending load‐stressed masonry walls or beams at their serviceability limit state (SLS) for load‐bearing capacities. Information already presented in E DIN 1053‐3:2008‐03 [N3] is being incorporated as well. Characteristic values for the compressive strength of the masonry parallel to the bed joints f_k,∥ are essential for the design of reinforced masonry, although they are currently not included in national application documents for Germany. For the time being, they can be mathematically calculated using conversion factors for the characteristic compressive strength values vertical to the bed joints f_k or by using the declared axial compressive strengths of the masonry units. The ultimate strains for masonry in general should be set consistently at ?_mu = ∣–0.002∣ as several masonry types do not exhibit higher compressive strain values. The use of steel strains higher than ?_su = 0.005 does not change any measurement results. Varying stress‐strain curves of the constitutive equations on masonry under compressive strain (parabolic, parabolic‐rectangular, tension block) lead to differing values of recordable bending moments despite having the same mechanical reinforcement percentage at higher normal forces. Therefore, clear guidelines should be made for the type of applicable constitutive equation for masonry walls under compressive strain. With the introduction of a tension block, the number values of the reduction factors λ for the compression zone height x, which is dependent on limit strains, and where applicable, reduced compressive strength, need to be determined, as with reinforced concrete construction. A modification of the bending moment based on the second order theory according to [N4] is presented for the calculation of reinforced masonry walls in danger of buckling. The use of reduction factors for the load capacity of the masonry cross section, such as for unreinforced masonry, does not appear to be appropriate as buckling safety evidence because here, the design task is the determination of a required reinforcement cross section.     

Lessons learned from the testing of RC frames with masonry infills and proposals for new solutions / Untersuchungen an mit Mauerwerk ausgefachten Stahlbetonrahmen und neue Lösungsvorschläge

Past experience has shown that inadequate design of unreinforced masonry walls (URM) or inadequate selection of materials can lead to significant economic losses and fatalities in the case of a strong earthquake. In this context, this paper presents the experimental research that has been carried out with the aim of gaining a better insight into the traditional masonry infill walls commonly built in Portugal. The experimental research includes: (1) shaking table tests on reduced‐scale reinforced concrete (RC) buildings with masonry infills with distinct typologies, from traditional solutions to those with enhanced properties and solutions to improve the seismic behaviour; (2) in‐plane static cyclic tests on a representative one‐storey, one‐bay RC frame with masonry infills with distinct typologies but similar to the ones tested in the RC building models. It was concluded that the typology of masonry walls influences the global behaviour of RC buildings, particularly when there is no connection between masonry infill and RC frame. An appropriate design is necessary to prevent an unforeseen failure mechanism due to shear stresses in the RC columns induced by the infill. The in‐plane cyclic tests showed that render plays a central role in the lateral strength and stiffness. Additionally, it was observed that bed joint reinforcement and reinforced render are important measures for controlling damage but do not significantly influence the in‐plane lateral strength and stiffness.     

Masonry buildings at the borderline to high‐rise – Part 2 / Mauerwerksbauten an der Hochhausgrenze – Teil 2

For the verification of framing shear walls of masonry, the decisive combination of actions derives from the interaction of vertical and horizontal actions. In this article, a method based on simple truss models is extended for the transfer of horizontal actions. It is demonstrated how the required verifications of load‐bearing safety can be performed with the results of the structural calculation. As an example, the application of the method for a seven‐storey building with calcium silicate blockwork or Poroton brick masonry is described.     

Burglary resistance of thermal insulating clay unit masonry / Einbruchwiderstand von wärmedämmendem Ziegelmauerwerk

The number of burglaries in Germany has increased during the last 10 years. The weak points in external walls are windows and doors. One important aspect is the fixing of these elements in the external masonry walls. The German Clay Masonry Industry has carried out a number of tests verifying the resistance class RC2 of windows fixed in external thermal insulating clay masonry walls.     

Tragfähigkeitserhöhung bei Mauerwerk durch textilglasgitterverstärkte Mörtelfugen

Increase of the vertical load carrying capacity of masonry due to mortar bed joints with textile glass mesh reinforcement From a structural point of view, one of the most important material parameters in the construction sector is the vertical compressive strength of masonry, which consists of the compressive strength of the bricks as well as of the mortar bed. The interaction between the bricks and the mortar beds is the main reason for compression failures of masonry walls. A close analysis of the deformation behavior of the two components shows that different transverse strains in the contact surface between the bricks and the mortar are the main cause for compression failures. However, the load‐bearing capacity of masonry walls can be increased by using some reinforcement in the mortar beds which counteracts lateral expansion. The impact of textile glass mesh reinforcement on the load‐bearing capacity of masonry was analyzed in a test program on masonry columns with different numbers of textile glass mesh reinforced mortar beds. The results of the analyses show that the load‐bearing capacity of the columns rises with an increased ratio of reinforcement, regardless of the type of bricks used. From the ratio of the height of the reinforcement layers to the thickness of the wall it can be deduced that a higher degree of reinforcement has a positive effect on the load‐bearing capacity of the masonry. On this basis, an increase of the strength and load‐bearing capacity of masonry walls is formulated to be on the safe side.