Vibration-based damage detection has become a major research topic of structural dynamics in the past few decades. Since modal characteristics of a structure, i.e., natural frequencies, mode shapes, and modal damping ratios, are directly related to physical properties of the structure, such as mass, stiffness, and damping, measured modal characteristics can be processed to detect, locate, and characterize damage in the structure [1]. Methods that use changes of natural frequencies due to existence of damage have been investigated by many researchers. Some methods require minimum amounts of vibration measurements and can yield accurate estimation of positions and extent of damage, since natural frequencies are global characteristics of a structure and relatively easy to measure [2–5]. However, natural frequencies do not directly provide spatial information of structural changes due to damage, and accurate and physics-based models are needed to apply the methods, which can be difficult to construct in practice. Unlike natural frequencies, mode shapes directly provide spatial information of structural changes due to damage. Curvature mode shapes can be more sensitive to small damage than mode shapes and are often used to identify damage [6]. Comparing a curvature mode shape of a damaged beam with that of an undamaged beam, one can see that there is a global trend in the curvature mode shape of the damaged beam, which is similar to that of the undamaged one, and local abrupt abnormalities due to damage need to be isolated from the trend in order to identify the damage. Pandey et al. [6] showed that differences between curvature mode shapes of damaged and undamaged beams mainly exist in damage regions and increase as damage sizes increase. Ratcliffe [7] proposed a gapped smoothing method to identify damage in beams by inspecting smoothnesses of CODSs without using CODSs of undamaged beams. In the gapped smoothing method, the global trend of a curvature mode shape or CODS at a measurement point is eliminated using a gapped cubic polynomial that fits the curvature mode shape or CODS of its neighboring measurement points. However, the technique can be computationally inefficient for a large-sized dense measurement grid. Yoon et al. [8] combined the gapped smoothing method and a global fitting method to identify damage in beams, where generic mode shapes were used to fit measured mode shapes of damaged beams. However, accurate models are required to yield generic mode shapes, which can be unavailable in practice. Xu et al. [9] proposed a curvature mode-shape-based method to identify embedded horizontal cracks in beams, where global trends of curvature mode shapes were eliminated using curvature mode shapes from polynomials with properly determined orders that fit mode shapes of damaged beams. Xu et al. [10] proposed a noise-robust damage identification method for bars that used multiscale slope vibration shapes, which were calculated by applying a wavelet transform to slopes of longitudinal vibration shapes.