Structural member bend radius sensor apparatus 90 comprises three fibre Bragg grating (FBG) strain sensors 102 provided within three optical fibres 14, 16, 18. The optical fibres 14, 16, 18 and the FBGs 102 are embedded within a part-cylindrical shaped carrier member 92. The fibres 14, 16, 18 are provided at three spaced locations across the shaped carrier member 92 so that, in use, the three respective FBG strain sensors will be located at three different angular positions around the circumference of the structural member (pipe) 68. Structural member shape measurement apparatus 100 comprises four bend radius sensor apparatus 90 provided at four bend radius measurement positions along the pipe 68. The four bend radius sensor apparatus 90 shown share their optical fibres 14, 16, 18, and a single shaped carrier member 92. The shape measurement apparatus 100 further comprises FBG interrogation apparatus 104.