Internal force and deformation of concrete-filled steel plate composite coupling beams

• The steel plate strain response and stress distributions are studied.
• The internal forces in concrete and steel, and force flow are analyzed.
• The displacement components due to different deformations are analyzed.

Two or more steel plate composite shear walls connected with steel plate composite coupling beams are an efficient system for resisting seismic forces. Based on test results from six concrete-filled steel plate composite coupling beam specimens, the internal force and deformation responses of the composite coupling beams are studied in this paper. At the onset of yielding in steel web plates, the shear forces were between 61% and 76% of the corresponding maximum shear capacities. The increase in shear capacity after the steel plates yielded was primarily attributed to the increase of concrete stresses along a diagonal compression strut. It was shown that the neutral axis in the steel shifted toward the compression face as the concrete compression strut gained strength. The steel and concrete both resisted shear and moment with the steel plates sustaining approximately 50% and 70% of the maximum shear force and associated bending moment, respectively. Besides the flexural and shear deformations of the coupling beam, the beam end rotations caused by the local deformations at the connection regions and steel plate fractures at the beam ends were significant. By decomposing the contributions of each to the lateral displacement of the coupling beam, it was found that end rotations and shear deformations were the largest contributors to displacement for long and short coupling beams, respectively.