Abstract
Four composite joint specimens consisted of concrete-encased steel beams and concrete-encased concrete-filled steel tube (CFST) columns were tested under lateral cyclic loading, in which three specimens were prestressed and the other was not. In the tests, crack distributions and failure modes of the joint specimens were acquired, and the energy dissipation, rigidity degeneration, ductility, and residential deformation were investigated. Meanwhile, the strain variation of longitudinal rebars and I-steel flanges at beam ends as well as steel tubes in panel zones were analysed. The experimental results showed that a type of mixed mode consisting of shear failure in the panel zone and flexural failure at beam ends was found for three prestressed joint specimens, whilst only flexural failure at beam ends was observed for the non-prestressed one, and all joint specimens showed good hysteretic behaviour. In addition, as can be seen from the skeleton curves, the lateral peak loads of prestressed joint specimens could be enhanced to some extent by increasing the prestressing level, and the axial compression ratio had little effect on lateral loads; meanwhile, the ductility and energy dissipation for prestressed joint specimens also could be reduced by increasing the prestressing level and axial compression ratio.
Highlights
Prestressed concrete-encased steel frames combined the advantages of concrete-encased steel frames and prestressed reinforced concrete frames, such as higher sectional bearing capacities, preferable ductility, better energy dissipation, and smaller deflection and crack widths; they have been extensively studied and utilized in China in recent years [1,2,3,4,5].In general, H-steels or I-steels are used in beams, and two crossed H-steels are welded together in columns for prestressed concrete-encased steel frames
Engineering practices indicate that the prestressing tendons in beams are likely to run through the flanges of H-steels in the panel zones, which results in complex connection details; in addition, the shear capacities in panel zones could be decreased by the prestressing ducts. erefore, an innovative prestressed composite frame was proposed, as shown in Figure 1, in which the conventional composite columns were replaced by concrete-encased concrete filled steel tube (CFST) columns [6]
Tests on three prestressed and one non-prestressed interior joint specimens with concrete-encased CFST columns were performed under lateral cyclic loading, and the following conclusions were achieved: (1) e lateral load-displacement hysteretic curves of all specimens were plump, and it means that joint specimens which were prestressed showed good ductility and energy dissipation capacity
Summary
Prestressed concrete-encased steel frames combined the advantages of concrete-encased steel frames and prestressed reinforced concrete frames, such as higher sectional bearing capacities, preferable ductility, better energy dissipation, and smaller deflection and crack widths; they have been extensively studied and utilized in China in recent years [1,2,3,4,5]. Li et al [28] tested the seismic performance of two kinds of CFST column-RC beam joints that are connected by vertical or U-shaped steel plates and studs and bending capacity of joints increased compared to the RC joints; Qian and Jiang [29] tested the joints consisting of reinforced concrete beams and concrete-encased CFST columns under cyclic loading, and it is observed that the energy dissipation capacity could be enhanced and the shear deformation could be decreased when the stirrup spacing reduced in the panel zones for weak joints; Liao et al [30] and Nie et al [31] pointed out that the composite joints consisting of reinforced concrete beams and concreteencased CFST columns with the outer stiffening ring showed good hysteretic behaviour; Qian et al [32] investigated the mechanical mechanism of composite joints consisting of steel beams and concrete-encased CFST columns by validated numerical model, and it is found that the positive and negative capacities of the spatial joints under bidirectional loading were about 14% and 18% lower than those of the planar joints; Deng et al [33] experimentally studied the crack development and rigidity of joints consisting of prestressed reinforced concrete beams and concrete-encased CFST columns. The crack development and failure modes were observed, and rigidity degeneration, deformation restoring capacity, ductility, energy dissipation, shear deformation, and strain variations were analysed. e testing results could provide a basis for promoting the application of such frame structures in seismic zones
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