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The lateral confinement of stirrups can improve the load‐bearing capacity and ductility of reactive powder concrete (RPC) columns. To explore the compression behavior of RPC confined with high‐strength stirrups, 45 specimens were prepared and tested under axial compression. The concrete strength was in the range of 99.86–138.24 MPa, the tensile strength of stirrups was Grade 800, Grade 970, and Grade 1270, and the volumetric ratios of stirrups were in the range of 0.9%–2.0%. The results showed that the failure modes of RPC confined with stirrups were shear expansion failure. The compressive strength and ductility of confined RPC were improved with the increase of stirrups volumetric ratios, while stirrups strength slightly affected the compressive strength and ductility. In addition, the peak stress, peak strain, and residual stress prediction models were proposed. Furthermore, the ductility index prediction models were proposed, which can be applied to determine the volumetric ratio of stirrups in stirrups confined concrete columns. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the seismic behavior of RC columns jacketed with a large welded octagonal stirrup at the center and four small spiral stirrups at the corners. Six full-scale RC columns jacketed with the modified multi-spiral stirrups were tested under lateral cyclic load. The effects of axial compression ratio of existing column, shear span ratio and stirrups volumetric ratio in jacket on the seismic behavior of jacketed columns were analyzed. The specimens exhibited excellent deformability and the ultimate drift ratios ranged from 0.046 to 0.063, 2.30–3.15 times as much as specified limit (0.02) of rare earthquake. Additionally, the finite element extended parameter analysis was supplemented after the finite element model verified by the experiment. Finally, an empirical formula for predicting the ductility factor was proposed and exhibited good correlations with the available data of concrete jacketed columns. [ABSTRACT FROM AUTHOR]

The lateral confinement of stirrups can effectively restrain the unstable lateral expansion of confined concrete and improve the load capacity and the ductility of concrete. The lateral response of stirrups affects the effective confinements on confined concrete and the dilation of core concrete. However, the lateral response of confined concrete has not received enough attention. In this paper, the lateral responses of 24 ultra‐high performance concrete (UHPC) and ultra‐high fiber‐reinforced performance concrete (UHPFRC) columns confined with high strength stirrups were obtained by experiments. The investigated parameters included concrete strength, stirrups volumetric ratio, and steel fibers contents. The axial stress‐lateral strain curves and lateral strain‐axial strain responses of specimens were presented to understand the dilation of concrete. The results showed that high strength concrete and high steel fibers contents decreased the dilation of concrete, when stirrups volumetric ratio increased from 1.0 to 2.0%, the dilation of concrete increased by 1.45~2.09 times. Furthermore, the lateral strain‐axial strain response prediction models were developed by introducing the effects of steel fibers, which were suitable for predicting the lateral strain‐axial strain of confined concrete. [ABSTRACT FROM AUTHOR]

• Failure modes of UHPC and CUHPC were compared. • Stress-strain behavior of UHPC and CUHPC was analyzed. • Effects of concrete strength, volumetric ratio of stirrups, and CFRP on compressive strength and ductility of UHPC and CUHPC were analyzed. • Existing models for peak stress and peak strain of confined UHPC should be modified. To understand the compressive behavior of UHPC confined by both lateral steel and CFRP, an experiment was presented with the compressive strength of UHPC up to 120.92 MPa in this paper. The specimens were confined by Grade 970 with volumetric ratio in a range of 0.0–2.0% and two layers CFRP laminates. The experimental results showed that the failure modes of confined UHPC were failure in brittle, shear failure, and expansion failure corresponding to specimens with no, low, and high volumetric ratios, respectively, while the failure modes of CFRP confined UHPC were expansion failure. The stress-strain behavior of confined UHPC were divided into three stages included linear stage, nonlinear stage, and descending stage. The stress-strain behavior of CFRP confined UHPC had five stages: linear stage, near linear stage, the stress declined gradually until stress decline sharply, the stress dropped abruptly to a stress platform, and a gradual stress decrease until specimens failed. Concrete Strength, transverse reinforcements volumetric ratio, and CFRP had influence on the load capacity and the ductility of specimens. Furthermore, by comparing experimental results with existing models, none of existing models was suitable for predicting the peak stress and peak strain of confined UHPC without fibers, and the existing model should be modified. [ABSTRACT FROM AUTHOR]

• The shear-compression failure modes confined UHPC were explained, and the effects of parameters on the axial stress–strain curves of confined UHPC were analyzed. • The prediction models for the axial stress–strain curves of confined UHPC were established. • The prediction models for the peak stress and peak strain curves of confined UHPC were developed. The axial stress–strain models of confined ultra-high performance concrete (UHPC) were important key inputs for analytical programs to predict the full-range loading deformation of confined UHPC. The concrete columns confined with stirrups under axial compression tended to be a failure in shear-compression failure. However, the existing models for evaluating the axial stress–strain models of confined UHPC did not consider the shear-compression failure. In this paper, an experiment on the axial stress–strain behaviour of confined UHPC was presented. The specimens consisted of 75 UHPC with compressive strength up to 155.45 MPa were confined by spiral stirrups. According to test results, a theoretical model for axial stress–strain curves of confined UHPC by considering the shear-compression mechanism of UHPC was developed. In the proposed models, the real lateral stress of stirrups was adopted to calculate the lateral confinement of stirrups, rather than assumed that the stirrups reached the yield strength. In addition, the effects of dowel action of stirrups and longitudinal reinforcement were considered. Furthermore, the prediction models for the compression behaviour indicators of confined UHPC included peak stress, peak strain, initial tangent modulus, residual stress, and residual strain were proposed. By comparing with existing models, the proposed analytical models of axial stress–strain curves of confined UHPC had high accuracy and high stability. [ABSTRACT FROM AUTHOR]