The three-dimensional structures based on the quadrant classification of the tangential Reynolds stress (Qs), are studied in direct numerical simulations of cylinder-wake/boundary-layer interaction with a moderate gap ratio (G/D=1.0) and low or middle Reynolds numbers. In this paper, direct numerical simulations are performed using the immersed boundary lattice Boltzmann method (LBM). We utilize a three-dimensional clustering method to identify Reynolds shear stress structures (Qs-structures) associated with intense events. The kinematic characteristics of coherent structures are discussed through the statistical properties of Qs-structures. The spatial relationship of between vortex clusters and Qs-structures (mainly Q2-structures as well as Q4-structures) is explained by their evolution characteristics. The spatial distribution of Qs-structures, determined by the volume distribution of the minimum and maximum wall distances (ymin and ymax), are found to be similar to that of vortex clusters in the cylinder/wall interaction. In the near-wall statistical region, the secondary vortex clusters are surrounded by the parallel Q2 and Q4 pairs, and mostly lodged within the Q2. During the evolution process of coherent structures, the Q2-structures and the secondary vortex clusters developed into hairpin-like structures, respectively. The conditional average results demonstrated that the generated hairpin vortex structures are attributed to the momentum transfers.