Elasto-plastic hardening and shakedown of masonry arch joints

The behavior of joints made of sand-lime mortar, such as used in a wide var iety of structures from ancient times through the early twentieth century, can be clearly distinguished from the behavior of joints made with hydrauli c cement mortar. Experiments on confined mortar specimens have confirmed th at the weaker and more ductile sand-lime mortar can be accurately modeled a s a Drucker-Prager material with a compression cap and exponential hardenin g on the cap portion of the yield surface. Joints of sand-lime mortar subje ct to axial thrust and moment are found experimentally to yield under very small loads, and to follow a linear hardening rule beyond the yield point. This behavior can be replicated analytically using a Drucker-Prager constit utive law with exponential hardening. The yield surface and hardening funct ion for an entire mortar joint are representable by Maier's theory of piece wise linear yield function and interacting yield planes. As a consequence, an arch jointed with sand-lime mortar is found to shake down under moving l oads above the yield limit and below the collapse load. The shakedown behav ior of a sand-lime mortar jointed masonry arch is confirmed experimentally.