Schubtragfähigkeit von Wänden aus Kalksand‐Planelementen mit geringem Überbindemaß — Experiment und rechnerische Simulation

Der Querkraftwiderstand V_R von Mauerwerkswänden, die in ihrer Ebene durch Wind‐ oder Erdbebeneinwirkungen beansprucht werden, hängt auch vom Überbindemaß ü bzw. vom Verhältnis des Überbindemaßes zur Steinhöhe ü/h_st ab. Das nach Norm derzeit zulässige Überbindemaß von ü ≥ 0,4 h_st kann bei der Verwendung von Planelementen in der Praxis nicht immer eingehalten werden. Für diese Fälle ist in den allgemeinen bauaufsichtlichen Zulassungen (abZ) des Deutschen Instituts für Bautechnik (DIBt) für Kalksand‐Planelemente im Bereich 0,4 > ü ≥ 0,2 h_st bzw. 12,5 cm bisher ein verminderter zulässiger Rechenwert der charakteristischen Schubfestigkeit f_vk von 60 % des Wertes nach DIN 1053‐100:2007‐09 (ü ≥ 0,4 h_st ) anzuwenden. Diese, auf Ergebnissen alter Versuche mit überholten Prüfanordnungen beruhenden, hohen Tragfähigkeitseinbußen waren im Zuge der Aufnahme von Planelementen in die Bemessungsnormen für Mauerwerk mit neuem Schubbemessungskonzept zu überprüfen. Daher wurden umfangreiche experimentelle und theoretische Untersuchungen an 17,5 cm dicken, 2,50 m hohen Schubwänden aus Kalksand‐Planelementmauerwerk mit Dünnbettmörtel und unvermörtelten Stoßfugen durchgeführt. Ziel war es, den Einfluss geringer Überbindemaße ü/h_st < 0,4 auf die Schubtragfähigkeit dieser Wände, insbesondere bei statisch‐zyklischen Horizontalverformungen in Wandebene, quantitativ zu bestimmen. Als Versuchsparameter wurden die Wandauflast (σ = 0,5/1,0/1,43 N/mm²), das Überbindemaß (ü/h_st = 0,2/0,4) und die Einspannung am Wandkopf und ‐fuß variiert. Die Untersuchungen ergaben im Bereich der normativ bemessungs relevanten geringen Überbindemaße 0,2 ″ ü/h_st ″ 0,4 keine signifikanten Traglasteinbußen. Bei erweiterten theoretischen FE‐Analysen für das baupraktisch übliche Spektrum vorhandener Überbindemaße 0,2 ″ ü/h_st ″ 1,0 von Wänden mit Auflastspannungen von 0,5 N/mm² bzw. 1,0 N/mm² wurde eine Traglastminderung von maximal 12 bis 16 % berechnet. Der Abtrag der Horizontallast vom Wandkopf zum Wandfuß erfolgt über ein schräges Druckspannungsfeld. Im Überbindebereich der Elemente auftretende Spannungskonzentrationen können zu örtlich begrenzten Rissbildungen führen, ohne dass die Tragfähigkeit der Wand hierdurch beeinträchtigt wird. Diese ist erst dann erschöpft, wenn insbesondere am Wandfuß die vom gerissenen Mauerwerk übertragbaren, schrägen Druckspannungen nicht mehr aufgenommen werden können. Shear load bearing capacity of masonry walls made of calcium silicate element units with a low overlap length — Experimental and numerical simulation analysis. The shear force resistance capacity V_R of masonry walls subjected, in their plane, to loads from winds or earthquakes, amongst other things, depends on the overlap length of the units ü or on the ratio of the overlap length and the height of the unit ü/h_st . The currently permissible overlap length, according to German design standards and norms, of ü ≥ 0.4 h_st can not always be adhered to in building practice, when using element units. In such cases and according to general technical approval code (abZ) of the German Institute for Building Technology (DIBt) for calcium silicate element units within the range 0.4 > ü ≥ 0.2 h_st or 12.5 cm, a reduced permissible calculation value of the characteristic shear strength f_vk of 60 % of the value according to DIN 1053‐100:2007‐09 (ü ≥ 0.4 h_st ) has been used to date. This high loss of load bearing capacity, based on results of older experiments with ob solete test setups, was to be tested in the course of the inclusion of element units in the calculation standards for masonry walls, with a new shear calculation concept. As a result, extensive experimental and theoretical tests were carried out on 17.5 cm thick and 2.50 m high shear walls made of masonry calcium silicate element units and ungrouted butt joints. The objective was to quantatively determine the influence of low overlap length ü/h_st < 0.4 on the shear resistance of these masonry walls and in particular with static‐cyclical horizontal displacement at the wall top. The vertical load pressure (σ = 0.5/1.0/1.43 N/mm²), the overlap length (ü/h_st = 0.2/0.4) and the fixing at the top and bottom of the wall were varied and used as experimental parameters. Within the range of normative calculation with low overlap lengths 0.2 ″ ü/h_st ″ 0.4, the investigations showed no significant load bearing capacity loss. With more extensive theoretical Finite Element analyses for the normal building practice spectrum of overlap lengths 0.2 ″ ü/h_st ″ 1.0 for walls with a vertical load of 0.5 N/mm² or 1.0 N/mm², a reduction of load bearing capacity of maximum 12 % to 16 % was calculated. The transmission of the horizontal shear load from the top of the wall to the bottom of the wall takes place through a diagonal compression stress field. Cracks may occur in the overlap area of the element units as a result of stress concentration, which are limited to the overlap area and do not cause any impairment to the load bearing capacity of the wall. This capacity is only then exhausted when the trans missible, diagonal compression stress can no longer be absorbed, especially at the bottom of the wall with cracked masonry.     

Analyse von Spannungen und Verformungen im Brüstungsbereich von Wandmodellen aus Porenbeton und Kalksandstein

Stress‐strain analysis in the window zone area of full‐scale wall models made of AAC and calcium silicate units This article presents results of tests on full‐scale wall models with two window openings. Tested walls were made of autoclaved aerated concrete (AAC) units and calcium silicate (C‐S) units. They were erected on thin unfilled perpend joints. This article strictly corresponds to previous tests performed in the spandrel area. The aim of the research was to verify results obtained for smaller models. Stress‐strain analysis of the spandrel area in full‐scale models was performed and results were compared with results obtained for smaller models. According to the analysis of the stress‐strain graphs, it was found that the horizontal stress in the spandrel area was ca. 0.2 N/mm². The software based on the finite element method was used to perform calculations for tested walls. Results from laboratory tests and numerical simulations were analysed to determine the level of stress and strain in tested walls.     

Design of masonry buildings of three‐layered units according to Eurocode 6 / Bemessung von Mauerwerksbauten aus Dreischichtsteinen nach Eurocode 6

In the recent past, the masonry industry has developed many different solutions for optimising the heat protection of buildings. This took place for the building materials, geometric design, but also by development of multiple layered stones in which the components masonry unit, insulation and outer shell have been integrated into a block.     

Experimentelle und analytische Untersuchung des out‐of‐plane‐Verhaltens von unbewehrten Mauerwerkswänden unter Erdbebenbelastung

Experimental and analytical investigation of the seismic out‐of‐plane behavior of unreinforced masonry walls In addition to the vertical and horizontal load‐bearing in‐plane, masonry must also withstand out‐of‐plane loads that occur in earthquake scenarios. The out‐of‐plane behavior of unreinforced masonry walls depends on a variety of parameters and is very complex due to the strong non‐linearity. Current design methods in German codes and various international codes have not been explicitly developed for out‐of‐plane behavior and contain considerable conservatism. In the present work, shaking‐table experiments with heat‐insulating masonry walls have been conducted to investigate the out‐of‐plane behavior of vertical spanning unreinforced masonry walls. As shown in previous numerical investigations, important parameters are neglected in existing design and analysis models and the out‐of‐plane capacity is underestimated significantly. In the conducted experiments the results of these numerical investigations are verified. Furthermore, the development of an analytical design model to determine the force‐displacement relationship and the out‐of‐plane load‐bearing capacity considering all significant parameters is presented.     

The two‐shearfield test – A suitable method for the empirical shear capacity design of masonry / Der Zweifeld‐Schubversuch – Eine praxistaugliche Methode zur versuchsgestützten Bemessung der Schubtragfähigkeit von Bestandsmauerwerk

The investigations [1] demonstrate that the two‐shearfield test is a suitable method for the determination of the shear capacity of masonry. The testing equipment is mounted directly on the wall in order to retain realistic boundary conditions like stiffness, load and prior damage. The behaviour factor q and the capacity curves of certain masonry walls can be directly obtained from the experimental results and realistic material behaviour in earthquake design can be represented. In particular, existing masonry can be assessed realistically with methods like the response spectrum, the push‐over and the capacity spectrum by using the two‐shearfield test.     

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.     

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.     

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.