Closed-Form Equations for Hardening of Sand-Lime Mortar Joints

Experimental and analytical investigations have shown that sand-lime mortar joints harden in a nonlinear manner after initial yield; then upon reloading, respond in a linear elastic manner under certain conditions of thrust and moment. This paper presents a method to predict this behavior using an exponential hardening model for the sand-lime mortar. Equations are developed to predict: (1) the joint rotation and shortening for three unique stress states; and (2) the moment/thrust yield conditions under which linear elastic responses are possible upon reloading the joint after the mortar hardens. Results show that joint rotation and shortening are influenced greatly by the thrust intensity and eccentricity. Once the material yields, the nonlinear hardening characteristics of the mortar significantly affect the joint's behavior under loading. Plots of moment/thrust hardening surfaces are presented for various loading conditions of the joint. The results are consistent with earlier findings obtained by using a nonlinear finite element model of a sand-lime mortar joint.