Behavior Of Masonry Material Research Articles

Experimental calibration of flat jacks for in-situ testing of masonry

ABSTRACTFlat-jack testing method is one of the most commonly used techniques for the structural assessment of existing masonry structures. Single and double flat jacks are usually adopted to evaluate the acting normal stress, or the compressive behaviour of masonry material. Test procedures are codified by international standards (e.g., A.S.T.M D4729-87; C1196-04; C1197-04, R.I.L.E.M TC 177–MDT D.4; R.I.L.E.M. TC 177–MDT D.5), which provide the preliminary calibration of an experimental coefficient (km) and of the effective area (Aeff), which determination influences significantly the reliability of the test. This article presents the result of an experimental study on the calibration of flat jacks for masonry testing. The problem is investigated by several tests carried out on two types of common flat jacks, which differ for geometry and producer. Two calibration methods are adopted in order to relate the pressure values of the flat jack with those of the hydraulic press and load cycles are performed in two different pressure ranges. Finally, a theoretical interpretation of results is made, which gives good predictions of calibration parameters. Results of this investigation highlight the influence of constructive features and service pressure of the jack adopted, for obtaining reliable results from the tests on masonry structures.

A Nonlinear Transformation Field Procedure for Periodic Masonry Based on an Equivalent Cosserat Medium

The paper deals with the problem of the determination of the in-plane behavior of periodic masonry material. The masonry is considered as a composite material obtained as a regular distribution of blocks connected by horizontal and vertical mortar joints. The macromechanical equivalent Cosserat medium is derived by a rational homogenization procedure based on the Transformation Field Analysis. The micromechanical analysis is developed considering a Cauchy model for the masonry components. In particular, linear elastic constitutive relationship is considered for the blocks, while nonlinear constitutive law is adopted for the mortar joints, accounting for the damage and friction phenomena occurring during the loading history. Numerical applications are performed in order to assess the performances of the proposed procedure in reproducing the mechanical behavior of the masonry material.