Author
G MOHAMAD(1), P B LOURENCO(2) and H R ROMAN(3)
(1) PhD Student of Civil Engineering department of Minho University, CAPES-MEC-UNIVALI-UNESC, Azurém- Postal Code: 4800-058, Guimarães-Portugal
(2) Associate Professor- Civil Engineering department of Minho University – Azurém- Postal Code: 4800-058, Guimarães-Portugal
(3) Professor- Civil Engineering department of Federal University of Santa Catarina, Postal Code: 88049-900, Florianópolis-Brazil

Abstract
The main goal of this work is to understand the tri-axial compression capacity of joint mortar through the Poisson behaviour. The conclusions drawn from the present study are the following: the behaviour of stress-strain diagram is strongly non-linear and depends on the increase of lateral stress. In all studies present here, the ultimate strength envelope can be represented by a linear function in the p-q plane and the angular coefficient is quite similar. The initial elasticity modulus of confined mortar decreases with the increase in the confining stress for mortar type 1:1:6 in studies of KHOO [1] and MOHAMAD [3], in opposition with the results from ATKINSON and NOLAND [2]. All authors observed a significant reduction in Poisson ratio of mortar when the confined stress increases. Apparently this decrease shows to be exponential for mortars types 1:1:6 and 1:2:9 and linear for mortars type 1:1/4:3 and 1:1/2:4.5. A simple model is proposed to represent the modification of Poisson ratio throughout the normalized stress range.