A loading device, a monitoring system, and a method thereof can measure stiffness of a structural member (SM) and monitor progress or property thereof over time. The loading device includes two types of displacement sensors, one type being an antenna. As the SM, which is in a magnetic or electromagnetic field and electromagnetically coupled to the antenna without contact, undergoes displacement under known loads, characteristics of the electromagnetic field coupling between the antenna and the SM change over time due to the displacement of the SM. The shift in the characteristics of the electromagnetic field coupling between the antenna and the SM can be used to determine the displacement of the SM. Based on the changes in the displacement over time, diagnosis of the SM being monitored over an evaluation period can be made. The loading device includes at least one movable frame to apply a preload to the SM.