ABSTRACT
A strain is defined as a displacement per unit length. To find the three strain components in various directions, a rotating d-r coordinate system is introduced. The three strain components in this rotating coordinate system are εd, εr and γdr. The relationship between the rotating strain components εd, εr and γdr and the stationary strain components εl, εt and γlt is the strain transformation. The transformation geometry showing the relationship between the rotating d-r axes and the stationary l-t axes is illustrated. Similar to the stress transformation, the basic sign convention has the same two weaknesses when applied to the strain transformation: γlt is always negative in the truss model for reinforced concrete, and the clockwise direction of rotation in the Mohr strain circle is opposite to the counterclockwise direction of rotation in the actual stress field. The strain compatibility equations can also be used for the analysis of cracking condition at the yielding of steel.
