Christophe Mordant

Seismic Behavior of Thin-Bed Layered Unreinforced Clay Masonry Shear Walls Including Soundproofing Elements

According to the current standards, unreinforced masonry may only be used in regions of low seismicity as the material for the lateral-load resisting system. This requirement may be too safe-sided and leading to not cost-effective solutions for moderately seismic regions. This chapter presents overview of experimental results from shake table tests on unreinforced masonry shear walls carried out in the EQUALS Laboratory of Bristol University, in order to assess, and possibly enhance, the current seismic design rules. The study also includes as additional parameter the presence of soundproofing devices required in buildings with numerous dwellings, in order to achieve the acoustic isolation recommended by recent standards. In practice the required level of acoustic isolation is obtained by locating horizontal rubber layers in the wall. These layers are likely to influence significantly the dynamic response of the wall and hence of the whole structure under seismic actions. Tests are performed on walls realized with masonry units and construction methods typical of North-Western Europe.

Seismic Behaviour of Thin-Bed Layered Unreinforced Clay Masonry Frames with T- or L-Shaped Piers

According to current standards, the use of unreinforced masonry is only recommended in regions of low to moderate seismicity as a resisting system to carry earthquake-induced horizontal forces. This requirement is however felt as rather conservative and leading to uneconomical constructive solutions, in particular for low seismic regions. Moreover, the seismic analysis of masonry structures has to be performed along two main perpendicular directions, usually neglecting the contribution of wall elements perpendicular to the seismic action. Horizontal elements (spandrel, etc.) are also commonly disregarded. In such a context, the present contribution provides an overview of experimental results obtained from shake table tests on unreinforced masonry frames carried out in the EQUALS Laboratory of Bristol University in order to assess, and possibly enhance, current design rules. The study is focused on the contribution of walls perpendicular to the seismic action and on the influence of the frame effect induced by the coupling of the walls through horizontal reinforced concrete elements, such as lintels and floor slabs. Another point of interest of the study is the influence of the gravity loading situation, comparing a floor slab supported by the shear walls as well as by the perpendicular elements, with a floor slab supported by the perpendicular walls only. Tests are performed on walls constructed with units and construction methods typical of the North-Western European region.

Rocking behaviour of simple unreinforced load-bearing masonry walls including soundproofing rubber layers

This paper compares experimental measurements with predictions of different rocking models. These comparisons are carried out on the base of recent experimental results obtained by shake-table tests of four simple unreinforced load-bearing clay masonry walls that have exhibited a significant rocking behaviour for the highest acceleration inputs. In a first stage, the simple model proposed by Housner is used after slight modifications needed to properly consider the actual mass distribution. Two parameters are identified as governing the model response, namely the criterion defining the initiation of motion and the restitution coefficient. Then, a two stacked blocks model is developed and solved by an event-driven strategy. This two-block model is intended to allow a better description of the behaviour of tested specimens through a more precise modelling of the additional mass. Finally, the presence of rubber layers positioned at the top and bottom of two of the tested walls with the purpose of improving their acoustic behaviour required the development of an updated rocking model with viscous and flexible interfaces at the base of the wall and between the two stacked blocks. The properties of these interfaces are deduced from experimental data and their significant influence on the response is evidenced.

Identification of equivalent mechanical properties for unreinforced masonry walls

Transverse vibrations of beams are an interesting topic for numerous engineering fields. The equations of motion develop under various assumptions and associate a frequency equation. This paper expresses the frequency equation for two specific models, using the Timoshenko beam theory. The first model is a typical cantilever beam with an additional mass attached to the free end. The second model considers a beam partially clamped at the base and with an elastic connection of the additional mass to the free end. The relevance of the used theory is discussed and the importance of each term of the equation is studied. These models find applications in unreinforced masonry. They are indeed fitted to identify, from white noise tests, equivalent mechanical properties of unreinforced load-bearing clay masonry walls including soundproofing devices in the perspective of modelling these elements with a macro-scale approach. Discrepancies with respect to current standards are underscored.

Full-scale Testing of Modern Unreinforced Thermal Insulation Clay Block Masonry Houses

In the scope of the transnational access activities of the European research project SERIES, the Laboratorio Nacional de Engenharia Civil (LNEC) has provided access to its 3D shaking table to the international construction company Wienerberger AG and to a group of European experts, in order to perform full-scale seismic tests on an industrial solution for buildings using a modern unreinforced thermal insulation clay block masonry structure. Such solution represents a very common construction method in Central Europe and, although there are cyclic shear test results available, its effective dynamic response under seismic events still requires experimental validation. For this purpose, two full-scale mock-ups with different geometries were tested on the 3D shaking table using a series of seismic records with increasing intensity. This paper focuses on the most relevant experimental results regarding the structural response of the specimens, e.g., the dynamic response evolution, the collapse mechanism identified and the maximum drift values measured. The paper closes with the main conclusions drawn and with proposals for future developments.

SHAKING TABLE TESTS ON UNREINFORCED LOAD-BEARING MASONRY WALLS – COMPARISON WITH SIMPLE ROCKING MODELS.

Assessment of the overall seismic performances of m ulti-storey unreinforced ma- sonry structures requires an appropriate characteri zation of the behaviour of their structural components, in particular when these are subjected to a dynamic ground motion input. In or- der to develop a better understanding on this issue and in a further perspective of investigat- ing the consequences of the presence of 1 cm thick rubber elements used for improving the sound-proofing performances of the building, shakin g table tests have been carried out in the framework of the European project SERIES. Four sing le walls were tested. These were built with high resistance thin-bed layered clay masonry with empty vertical joints. Two of them had an aspect ratio close to 1, while the other two were close to 0.4. One wall of each aspect ratio included rubber devices at its bottom and top to enable comparisons and conclusions about the influence of rubber on the wall behaviour . The test results were then partially com- pared to results obtained with a theoretical rockin g model considering the wall as a rigid body. The results summarized in the present contrib ution evidence a significant rocking be- haviour for the highest input acceleration levels. Characterization of this behaviour is how- ever strongly dependent on the aspect ratio of the wall and on the presence or not of rubber devices in terms of natural frequencies, damping, d ynamic amplifications and progressive damage with increasing acceleration levels. It is a lso showed that the theoretical rocking predictions are in good agreement with the experime ntal results for high acceleration levels, while the behaviour is closer to the one of a canti lever for the lower levels. It is finally evi- denced that, in presence of acoustic rubber devices , amplitudes of the rocking motion are in- creased but with a more limited damaging of the wal l because of the capacity of the rubber to absorb the impact energy. Results of this study on single walls are expected to be further ex- tended to global masonry structures, account taken for the influence of actual boundary con- ditions of the wall.