Overcome of bed-joint imperfections and improvement of actual contact in dry-stacked masonry

in Construction and Building Materials (2020)

Several researchers studied dry-stacked masonry walls (DSM) and inferred that the actual contact surface between the different block rows and the compressive strength in such walls are reduced by bed ... [more ▼]

Several researchers studied dry-stacked masonry walls (DSM) and inferred that the actual contact surface between the different block rows and the compressive strength in such walls are reduced by bed-joint imperfections as well as by height differences between different masonry blocks leading both to high stress concentration. This paper concentrates on the first type on imperfections. Through experimental tests, it analyses the influence of bed-joint roughness on the load bearing capacity and investigates a strategy to improve the load-bearing capacity of DSM by placing an additional horizontal layer on the top face of raw masonry blocks. First, different contact layers using conventional and auxetic materials were applied. Then 20 dry-stacked masonry prisms built with raw and improved masonry blocks were tested under axial compressive load until failure. Prescale Fujifilm strips were used to measure the actual contact in the bed-joints. Experimental tests show that the use of a contact layer with well-defined material properties enables firstly to increase the actual contact area in the bed-joints from 23% to 98% of the nominal contact area and secondly to increase the load-bearing capacity by 14 to 97%. In addition, the contact layer with an auxetic material shows a significant capacity in altering the lateral expansion in the block units. The outcomes show that although the bed joint roughness influences the stress distribution in a dry-stacked masonry block, a contact layer with well-defined material properties enables to overcome the roughness induced by the bed-joint imperfections. [less ▲]

IMPROVEMENT OF THE LOAD-BEARING CAPACITY OF DRY-STACKED MASONRY

Doctoral thesis (2019)

Mortar bonded masonry is one of the oldest construction technics traditionally used around the world. However, dry-stacked masonry (DSM) is a competitive system that confers significant assets to masonry ... [more ▼]

Mortar bonded masonry is one of the oldest construction technics traditionally used around the world. However, dry-stacked masonry (DSM) is a competitive system that confers significant assets to masonry in the sense that, concisely, it saves construction time, requires less skill labourers and ease the construction as well as the de-construction. Despite all this major benefits, the current use of DSM is hindered by the geometric imperfections of the block units and the lack of adapted design codes. Indeed, the block geometric imperfections, i.e. the bed-joint roughness and the height difference, cause a significant uneven load-distribution in DSM, which generally leads to a premature cracking and a drop of the wall compressive strength. On the other hand, the lack of adapted design codes entail significant safety hazards in the construction of such masonry walls. In view of the foregoing, through systematic numerical, experimental and analytical investigations, the present thesis aims to analyse the impacts of the block bed-joint imperfections on the mechanical response of DSM axially loaded. Furthermore, the current thesis aims to develop a strategy to overcome the block geometric imperfections and alleviate its impacts on the load-bearing capacity of DSM. Finally, the present thesis intends to develop a design model for predicting the load-bearing capacity of DSM, while taking into account the effects of the block geometric imperfections for a safe design. First of all, at the beginning of the research project, a new dry-stacked masonry block is designed and labelled ‘M-Block’. The impact of the bed-joint roughness and the block height variation on the stress distribution in a DSM is analysed through numerical modelling. It is shown that the block height difference yields five potential load cases that block units may suffer upon the axial compression of a DSM wall. Accordingly, it is also shown that a nominal DSM wall can exhibit different load percolation paths and different damages. Further, a strategy is presented to overcome the bed-joint imperfections, increase the actual contact area in the bed-joints and ultimately improve the load-bearing capacity of DSM, by adding a material layer (the ‘contact layer’) on the raw DSMb. The capacity of the contact layer to increase the actual contact and level the stress distribution was first investigated through numerical models then evidenced through experimental tests on masonry triplets. The contact layer was also investigated for improving the load-bearing capacity of dry-stacked masonry, with satisfactory results obtained on wallets tested in the lab. As the finite element modelling is cumbersome and the experimental investigations onerous and laborious, an analytical model has then been developed for predicting the load-bearing capacity of DSM. A statistical modelling has been developed for determining a factor δh, which stands for the reduction of the nominal section of a DSM generated by the block height variation. Experimental tests were also performed on masonry triplets for measuring the ultimate actual contact in the bed-joints and defining a factor δr, which stands for the reduction of the nominal contact area generated by the block bed-joint roughness. The two defined parameters were then exploited to establish the design model that takes into account the block imperfections in the prediction of the load-bearing capacity of DSM. The design model was shown quite well capable of predicting the load-bearing capacity of DSM with a mean accuracy of 93% - 106% and a standard deviation of 12% - 10%. [less ▲]

Impact of the height imperfections of masonry blocks on the load bearing capacity of dry-stack masonry walls

in Journal of Construction and Building Materials (2018), 165

Dry-stacked masonry walls gives rise to geometric imperfections: the height variation of different masonry blocks ΔH and the roughness of the support area Δh. This paper studies the effect of ΔH on the ... [more ▼]

Dry-stacked masonry walls gives rise to geometric imperfections: the height variation of different masonry blocks ΔH and the roughness of the support area Δh. This paper studies the effect of ΔH on the structural response and the load bearing capacity of masonry walls by highlighting the load percolation. Furthermore, an algorithm was developed to define a stress multiplier coefficient respecting the imperfections ΔH. The algorithm allowed predicting 77% of the amplified stress compared to the FE analysis and showed that the geometric imperfections govern the load percolation in a wall as well as the cracking mode and the bearing capacity. [less ▲]

Prédiction de la résistance mécanique d’un bloc de maçonnerie sans joint par calcul numérique

Presentation (2016, July 06)

La nouvelle génération de blocs de maçonnerie montés à sec (sans joint) et muni d’éléments d’engrenages ou d’emboîtement présente des avantages substantiels tant en précision et vitesse de pose, qu’en ... [more ▼]

La nouvelle génération de blocs de maçonnerie montés à sec (sans joint) et muni d’éléments d’engrenages ou d’emboîtement présente des avantages substantiels tant en précision et vitesse de pose, qu’en résistance aux déplacements transversaux, en économie de matériaux et en facilité de démontage. La performance d’un mur en maçonnerie est étroitement liée à sa stabilité générale et à la résistance mécanique des blocs de maçonnerie qui le composent. L’un des objectifs de cette étude était de rechercher un optimum entre cinq paramètres importants dans la conception d’une maçonnerie à savoir le poids, le coût, la facilité de production, mais surtout la résistance mécanique et la résistance thermique. La conception du nouveau bloc a ainsi été entreprise par calculs numériques. [less ▲]