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.     

Limitation of cracking in AAC masonry under the window zone

The article describes the results of tests on the impact of reinforcement on the appearance of cracks and on the manner of damage to masonry under the window zone. Masonry made of Autoclaved Aerated Concrete units with thin layer mortar was tested. Eight unreinforced test specimens (two series) and four series of test specimens (12 specimens) with reinforcement in the bed joints were subject to testing. Two types of reinforcement were used in the tests. It is demonstrated that the reinforcement has a significant impact on the level of cracking stress and propagation of cracks. It was found that when a pillar is correctly designed, cracks should not occur in the masonry under the window zone.     

Analysis of steel‐reinforced masonry walls regarding maximum shear loads / Traglastberechnung von vertikal bewehrten Mauerwerksscheiben

Loadings on masonry for the earthquake case pose particular challenges for the material. In order to improve the load‐bearing and deformation behaviour, masonry building elements can be strengthened with reinforcement. This article presents an analytical model for the calculation of the load‐bearing capacity of vertically reinforced masonry panels. The masonry is modelled as a homogeneous and anisotropic material and failure conditions are based on the plastic theory. Using uniaxially loaded stress fields and considering the structural constraints, a lower load‐bearing threshold can be given. In order to verify the model, three shear tests on reinforced sand‐lime block masonry were recalculated regarding their load‐bearing capacity. The test panels each contained vertical steel reinforcement in the blocks. The blocks were laid in thin bed mortar.     

Textile reinforcement in the bed joint of basement masonry and infill walls subjected to high wind loads

The successful structural verification of basement walls under earth pressure loading with light vertical loading is often difficult. This situation is often encountered for external basement walls under terrace doors, stairs, masonry light wells, etc., where the vertical loading that is theoretically necessary is absent. This makes it impossible to resist the acting flexural forces from earth using a vertical arch model alone. In such cases the basement wall must also resist the earth pressure in a horizontal direction. However, due to the fact the bending moment capacity of unreinforced masonry parallel to the bed joint is low you have the option here of using a textile‐reinforced bed joint with longitudinal fibres of alkali‐resistant glass or carbon fibre. With an appropriately adapted textile reinforcement in the bed joints, the masonry can fulfil the requirements for load‐bearing capacity against earth pressure with a horizontal load transfer, even under a small vertical load. The same applies to infill walls subjected to high wind loads the bending moment capacities of which are also slightly parallel to and vertically to the bed joint and cannot be provably demonstrated on large infill surfaces and strong wind loads. The load‐bearing can also be increased by improving the flexural strength parallel to the bed joint. The Chair of Structural Design in the Faculty of Architecture of the Technical University (TU) Dresden was carrying out extensive numerical and experimental studies for this purpose. In the journal Mauerwerk 01/2018 [1] first findings from small trial series have already been presented. In the meantime, a series of large‐scale tests have additionally been performed to check the promising results of the small‐scale tests with respect to their real applicability. This report should provide a combined insight into the work of the concluded research project.     

Central Bus Station,Kiel: a perforated brick facade for the parking block

On the occasion of the Olympic sailing competitions in Kiel, the ZOB and the multi‐storey car park above it were built in 1972. The two‐storey multi‐storey car park, equipped for about 560 parking spaces, was originally connected to the railway station quay, the main railway station and the city centre by three pedestrian bridges. These bridges were demolished over the years. The new construction of the Atlantic Hotel in 2009 made it necessary to partially demolish the multi‐storey car park and the ZOB. At the same time, preparations began for the redesign of the remaining ZOB site. However, the original idea of renovating the building, which had been reduced in size by the construction of the new hotel, and additionally increasing it by two parking levels, was rejected. The poor structural condition and the planning of a new attractive bus station ultimately required demolition. In the new planning of the ZOB, two construction sites were defined. The design for the new multi‐storey car park on construction site 2 took into account the specifications for the number of storeys, the spacing areas, the maximum eaves height and the materials used in the neighbouring buildings as an independent building. The rounding of the facade at Stresemannplatz gives passers‐by coming from the west a clearer view of the harbour. The spindle, which is raised above the 6th floor, serves as a recognizable point visible from afar.     

Minimum reinforcement of beam‐type reinforced masonry constructions – proposals for future regulations

The minimum reinforcement of reinforced masonry under bending should according to DIN EN 1996‐1‐1:2013‐02 [N 1], Section 8.2.3(1), be not less than ρ_min = 0.05 % of the effective masonry cross‐section for building elements, in which the reinforcement makes a contribution to the loadbearing capacity of the section, with the effective masonry cross‐section being the product of the effective width (b_ef) and the usable height d of the building element. In order to limit cracking and increase the ductility of the element, the reinforcement area should according to [N 1], Section 8.2.3(3), be not less than 0.03 % of the gross cross‐sectional area (of a wall). Other regulations ([1], [N 2], [N 3], [N 4], [N 5], [N 6], [N 7]) also prescribe minimum reinforcements in order to avoid brittle behaviour of the building element when the first crack forms or to limit cracking. In this specialist article, the figures given in [N 1] for the minimum reinforcement of reinforced masonry beams, like flat lintels or prefabricated lintels, are checked. The work concentrates on avoiding brittle failure when the first crack forms. In addition to geometrical requirements, the amount of minimum reinforcement depends on the tensile strength of the masonry f_t,m. Values of ρ_min vary considerably depending on the magnitude of the tensile strength of the masonry that can be assumed. For lintels over openings in facing brickwork facades, the height of any capping or soldier courses under the reinforcement layer also has an enlarging influence on the value of ρ_min. With regard to future regulations in standards or Allgemeine bauaufsichtliche Zulassungen (national technical approvals), it is recommended not to give lump sum values for ρ_min but to undertake a calculation like for reinforced concrete, using the algorithms given in this article.     

Shear tests on full scale storey‐height specimens constructed with thermally insulating clay unit masonry with thin‐layer mortar

The paper presents results of a series of 6 in‐plane shear tests on storey‐height clay unit masonry panels [1] with thin‐layer mortar, carried out in addition to previous test campaigns [2], [3], and [4]. The walls were constructed with unfilled thermally insulating clay units with a thermal conductivity of λ = 0.09 W/(m · K). The current design rules for clay unit masonry according to DIN EN 1996‐1‐1/NA [5] are conservative compared to the presented test results for thermally insulating clay unit masonry.     

Textile reinforcement in the bed joint of basement masonry – First findings from a current research project

The successful structural verification of basement walls under earth pressure loading with light imposed loading is often difficult. This situation is often encountered for external basement walls under terrace doors, stairs, masonry light wells etc., where the theoretically necessary imposed loading is missing. This makes it impossible to resist the acting bending forces from earth pressure using a vertical arch model. In such cases, the earth pressure has to be resisted in a horizontal direction. Since however the bending moment capacity of unreinforced masonry parallel to the bed joint is low, another possibility is to use a textile‐reinforced bed joint with longitudinal fibres of alkali‐resistant glass or carbon fibre. With an appropriately adapted textile reinforcement in the bed joints, the masonry can fulfil the requirements for load‐bearing capacity against earth pressure with horizontal load transfer, even under a small imposed load. Textile reinforcement has the advantage above all of corrosion resistance compared to conventional steel reinforcement, and textiles can also be inserted into thin bed joints. The Chair of Structural Design in the Faculty of Architecture of the TU Dresden is currently carrying out extensive numerical and experimental studies for this purpose. The objective is to develop an optimal configuration of material and textile form for use as bed joint reinforcement. The investigations are concentrating on the tension strength, bonding and durability of the composite material ”textile mortar“. This report should give a brief overview of the state of the work in the currently running research project.     

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.     

Bracing systems in masonry buildings. Part 1: Simple application of FE programs / Aussteifungssysteme im Mauerwerksbau. Teil 1: Einfache Anwendung von FE‐Programmen

Due to the low tensile strength of masonry perpendicular to the bed joint, masonry wall panels have non‐linear material properties. Assuming simple elastic constitutive laws, this article presents two modelling variants, which consider the lack of tensile strength in a simple manner. Both variants are investigated for their advantages and disadvantages. In a second part of the article, the application of the methods will be illustrated through the example of a four‐storey building.     

Load‐bearing behaviour and characteristic load‐bearing capacity of injection anchors in masonry

Fixings with injection anchors are post‐installed chemical fastenings, which are generally described as bonded anchors. For bonded anchors in masonry, only injection systems are approved, since safe application of capsule systems cannot be guaranteed due to the presence of cavities in the masonry, for example due to joints, grip holes or the use of perforated blocks. The present article collects the current state of knowledge and describes the usual “engineeering” approaches.     

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.     

Pull‐out strength of anchor pins for brickwork masonry and earth block masonry / Auszugsfestigkeit von Verpressankern für Ziegel‐ und Lehmsteinmauerwerk

In this paper results of the experimental testing performed on brick masonry and earth block masonry are presented. The paper outlines the development of the testing procedures for two different types of anchors. For this purpose, two experimental campaigns of pull‐out tests on masonry corner connections strengthened by metallic rod grouted were carried out. Experimental results proved that the implemented testing procedures are suitable to determine the most recurring failure modes of the anchor pins. Moreover, a procedure is proposed to estimate the capacity of grouted anchor pins based on experimental studies.     

Monolithic lightweight concrete masonry for multi‐storey apartment buildings

Affordable living space has become one of the main talking points in Germany next to the threat of climate change. The SMEs of the German lightweight concrete industry offer regional masonry solutions for detached, semi‐detached, and terraced houses as well as multi‐storey apartment buildings. Particularly in densely populated urban centres, the need for multi‐storey apartment buildings arises constantly. In the following the performance of monolithic lightweight concrete masonry will be described and compared with the relevant requirements for multi‐storey apartment buildings. It will be demonstrated that masonry with supposedly low compressive strength can still fulfil all requirements. Of particular significance here are the external wall‐slab junctions.     

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.     

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.     

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.     

Confined Masonry subjected to Lateral Loads / Eingefasstes Mauerwerk unter Plattenbeanspruchung

Just as with shear stress on the edges of masonry walls, prestressing through the confinement and restraint of all four sides of the wall improves the load‐carrying capacity under lateral loads. The extra load arising from prestressing leads to increased flexural strength of the masonry. The confinement of the edges results in relatively smaller span moments. In this case, the torsional stiffness of the reinforced concrete frame is important. This is determined by the frame itself as well as by its integration within the building. As a supplement to [4], an examination of panel loading was also performed within the guidelines of a research project at the TU Dresden, Chair for Structural Design, on behalf of the Federal Office for Building and Regional Planning on the subject of “Confined Masonry as an Option for Increasing the Load‐Carrying Capacity of Stiffening Walls”[9]. The various influences are to be initially researched on the basis of various analytical observations and a small numerical study. A thorough, experimentally‐based clarification of the load‐carrying capacity of the panels was not possible within the framework of the research project.     

The reconstruction of the historic facades of the Berlin Palace

The masonry and wall building for the reconstruction of the historic facades for the rebuilding of the Berlin Palace as the Humboldt Forum represent a unique challenge for the art of masonry, structural design and detailed design. In front of the modern reinforced concrete structure of the new palace building, the massive solid brick masonry wall, separated from it by mineral insulation, leads to an overall thickness for the historically reconstructed external wall that comes near to the average thickness of the baroque palace walls. The exceptional thickness of the brick wall serves as a substrate for the facade decoration elements of sandstone and together with the internal insulation, enables the requirements of the energy‐saving regulations (EnEV) to be clearly exceeded.