Topological Floquet engineering of a one-dimensional optical lattice via resonant shaking with two harmonic frequencies

We investigate the topological properties of a resonantly shaken one-dimensional optical lattice system, where the lattice position is periodically driven with two harmonic frequencies to generate one- and two-photon couplings between the two lowest orbitals. In a two-band approximation, we numerically show that degenerate edge states appear under a certain driving condition and that the corresponding topological phase is protected by the chiral symmetry of the periodically driven system. The system's micromotion is characterized with oscillating Zak phases and we find that the Zak phases are quantized only at the time when the chiral symmetry condition is explicitly satisfied. Finally, we describe the topological charge pumping effect which arises when the driving parameters are slowly modulated around a critical point, and investigate its adiabaticity with increasing modulation frequency.11Nsciescopu

Static performance of square CFDST chord to steel SHS brace T-joints

In this paper, static performance of square concrete-filled double-skin steel tube (CFDST) chord to steel square hollow section (SHS) brace T-joints are investigated through experimental and numerical studies. Twelve specimens, including 8 T-joints with square CFDST chord, 2 T-joints with square concrete-filled steel tube (CFST) chord and 2 T-joints with steel SHS chord as counterparts, were tested under continuously increasing compressive force on the brace with concentric compression load applied simultaneously to the chord. The influence of chord type, brace-to-chord width ratio (β) and concentric compression level of the chord (n) on the static performance of the T-joints was examined. It is found that the composite T-joints have enhanced static performance than their steel counterparts. For the composite T-joints, the failure pattern varies from compression-flexure-shear failure of composite chord to local buckling of steel SHS brace when β reduces. Moreover, while only the composite chord failure occurs, the bearing capacity of the specimens augments with growing of hollow ratio of CFDST chord (χ), β and n; however, when only steel SHS brace of the composite joints fails, the chord type has a moderate influence on the bearing capacity of the specimens. The static performance of the T-joints was simulated using a finite element (FE) model, which is validated against the observations in the experiment. On the basis of the experimental and numerical research, the design formulae for bearing capacity of the composite T-joints were developed, and a good accuracy of the computations was achieved