EWECS (Engineering Wood Encased Concrete-Steel) composite structural system consists of concrete, steel and glued laminated timber. In experimental studies on EWECS columns and EWECS beam-column joints, it was confirmed that the EWECS structural system showed good and stable hysteresis characteristics. However, the structural performance of the EWECS column-beam joints with slab have not been examined in these studies. In this study, static loading tests and three-dimensional (3D) FEM analyses for EWECS column-steel beam interior joints with slab were conducted to investigate the structural performance. Outlines and results of the tests and analyses are described in this paper.
Four EWECS column-steel beam interior joints with slab which were one-half scale were tested. The variable investigated were the thicknesses of steel web in joint panel, and the cross-sectional shape of the column steel. Specimens BF and BFO which were designed to be a flexural yielding of steel web had a thick web. On the other hand, Specimens JS and JSO, which were designed to be a shear failure of the joint panel, had a thin web in the joint panel. In addition, Specimens BF and JS had an H-shaped steel of column, and Specimens BFO and JSO had a cross-shaped steel of column and transverse steel beam.
The shear failure of joint panel occurred in Specimen JS. The flexural failure of the beam occurred in Specimens BF, BFO and JSO. The maximum capacities of the Specimens BF, BFO and JSO which had flexural failure of the beam were almost the same. That of Specimen JS which had a panel shear failure was lower than that of specimens which had a flexural failure of the beams. It was confirmed that shear forces of all specimens after maximum capacities decreased slowly regardless of failure modes. The flexural strength of the steel beams with slab calculated by the superposed strength theory and the shear strength of the joint panel calculated by the proposal in Ref. 6) agree with test result for all specimens. However, the failure mode by the ultimate strength evaluation for Specimen JSO which had a cross-shaped steel of column did not agree with that of the experimental result. Furthermore, the evaluation methods of panel shear strength did not take into account the effect of the slab.
Analytical results of shear versus drift angle relationships and stress transitions of the steel web in the joint panel showed good agreements with experimental results in all specimens. It was indicated from the analytical results that the high compressive stresses were occurred of concrete in the joint panel regardless of the confinement effect from steel due to the compressive force transmitted from the slab concrete. Moreover, the shear forces of the beams on both sides and the lower column decreased drastically at the steel flange in the joint panel. On the other hand, that of the upper column decreased drastically from the upper end of the slab to the upper flange of the beam. Therefore, the effective depth and height of the joint panel were assumed to be the distance between the centroids of the steel flanges in the column, and that between the centroids from the slab to the lower flange in the beam, respectively. The effective width was assumed by the method in Ref. 8) considering the effect of the slab width subjected to compression. The panel shear strength modified AIJ standard for SRC structures based on the analysis results can evaluate the maximum capacity of EWECS column-beam joint with slab which had an H-shaped steel of column.
