Triplet Tests Research Articles

Shear Failure of Historic Masonry Walls

Shear behaviour of masonry has been studied for modern masonry and few experimental results are available for historic un-reinforced masonry walls (HURM) under seismic loads. A series of triplet tests, racking and cyclic shear wall tests have been experimentally conducted by the authors to investigate shear failure mechanisms and strength of HURM walls.

Experimental Investigation and Numerical Modeling of Peak Shear Stress of Brick Masonry Mortar Joint under Compression

AbstractThis paper presents a study on the shear load-displacement behavior of horizontal joints in unreinforced brick masonry subjected to constant compression. In general, under static shear loading masonry joints show a peak shear stress followed by a residual shear strength. To investigate these aspects in greater detail, triplet tests were conducted on masonry specimens using different types of mortar. The results found in this study and previous tests show that normal compressive stresses acting on the interface and the interface mortar strength affect the peak shear stress and the residual strength in a rather similar way. The cohesion and the internal friction angle, i.e., the two parameters required by the Mohr-Coulomb criterion, are then derived from a linear regression of the test results. The pre-peak and post-peak response of a masonry bed joint can best be represented by simple equations, and their shear stiffness depends on material properties and the magnitude of the normal compression. Co...

Experimental assessment of shear strength parameters on rubble stone masonry specimens

Rubble stone masonry walls were widely used in traditional buildings in Mediterranean countries. However, the mechanical behaviour of those walls is not completely characterized due to a lack of experimental data. This paper presents an experimental campaign carried out to characterize the shear strength parameters of traditional Mediterranean rubble stone masonry walls. Fifteen masonry specimens were built using old techniques and traditional materials. Two types of mortar were used in the specimens’ execution, air and hydraulic lime mortars, with intend to simulate different masonry construction periods. The goal of the experimental campaign was to evaluate the most important mechanical parameters needed for numerical modelling of traditional rubble stone masonry walls, namely, the compressive strength and Young’s modulus through compression tests; the cohesion and friction coefficient by triplet tests; and the diagonal tensile strength via diagonal compression tests. The tests’ setup and load–displacement diagrams are presented for all tests and the obtained shear strength parameters are compared with values from the literature.

Evaluating shear test methods for stabilised rammed earth

Rammed earth is an accessible, sustainable and increasingly popular building material. Owing to a lack of research, current design standards for rammed earth have taken a conservative stance on material attributes like shear strength. Evaluating the shear strength of rammed earth is particularly important in seismic areas because of the material's high mass, low ductility and propensity to fail in shear. Shear test methods designed for other materials have typically been used in practice to determine the shear strength of rammed earth. In this research the design shear strength guidance available in current earth building standards was compared with experimental shear strength results for stabilised rammed earth. The triaxial (geotechnical) and triplet (masonry) tests were used to evaluate specimens reinforced with natural fibres: sisal and New Zealand flax. Both shear test methods showed that the shear strength capacity of cement-stabilised rammed earth was greater than the current guidance provided in the earth building standards. Recommendations were made to use the triaxial test to evaluate the shear strength of stabilised rammed earth and to allow the use of design shear strength equal to 7% of the compressive strength.

Damage Thresholds in Unreinforced Masonry

In various regions of Australia, mines and quarries employ blasting, which some home owners believe causes cracking of non-structural components such as brick veneer. The first part of this paper reports on properties affecting damage thresholds of masonry subjected to shear load at a localised unit/mortar scale using off-axis prism tests and triplet tests. The second part reports on the performance of a full-scale unreinforced masonry wall with a window penetration subjected to an increasing racking displacement. Drift and the associated strains required to initiate cracking are reported, and a correlation between drift and rate of crack propagation is proposed.

Role of Nest‐paper Hydrocarbons in Nestmate Recognition of Dolichovespula maculata (L.) Workers (Hymenoptera: Vespidae)

AbstractThe role of nest‐paper hydrocarbons in nestmate recognition was examined in the social wasp Dolichovespula maculata. Pupae were excised from nine colonies of D. maculata and placed in separate gel capsules in the laboratory. When workers emerged, they were isolated in the absence of other wasps in one of four conditions: 1. With an untreated fragment of their natal nest; 2. With a fragment of their nest that had been extracted with hexane to remove surface hydrocarbons; 3. With a fragment of their nest that had been extracted with hexane, and had then had the extract containing the surface hydrocarbons reapplied; or 4. In the absence of any nest fragment. After 4 d, the newly emerged workers were tested for nestmate recognition with an experienced nestmate and an experienced non‐nestmate in blind triplet tests. Prior exposure to nest‐paper hydrocarbons had no significant effect upon the ability of newly emerged or experienced wasps to recognize their nestmates. Moreover, nestmate recognition did not occur in any treatment group.

Social wasps use nest paper hydrocarbons for nestmate recognition

The role of nest paper hydrocarbons in nestmate recognition was examined in the social wasp Polistes metricus. Newly emerged workers were allowed to spend 4 days on their nest in the absence of other wasps. The nests were either (1) untreated, (2) extracted with hexane to remove surface hydrocarbons, or (3) extracted with hexane and then reapplied with surface hydrocarbons. The newly emerged workers were tested for nestmate recognition with a nestmate and a non-nestmate in blind triplet tests. These tests indicated that it was necessary for the surface hydrocarbons to be on the nest paper for newly emerged wasps to recognize their nestmate.