  A geometrically nonlinear finite element model is developed for the bending
analysis of micropolar Timoshenko beams using the principle of virtual
displacements and linear Lagrange interpolation functions. The nonlinearity
enters the model via a nonlinear von K\'arm\'an strain term that allows the
micropolar beam to undergo moderate rotations. The nonlinear micropolar
Timoshenko beam is used as an equivalent single layer model to study four
different lattice core sandwich beams. A two-scale energy method is used to
derive the micropolar constitutive equations for web, hexagonal, Y-frame and
corrugated core topologies. Various bending cases are studied numerically using
the developed 1-D finite element model. Reduced integration techniques are used
to overcome the shear and membrane locking. The present 1-D results are in good
agreement with the corresponding 2-D finite element beam frame results for
global bending.
