• Steel and Composite Structures
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• v.33 no.6
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• pp.849-864
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• 2019

One way to achieve sustainable construction is to reduce concrete consumption by use of more sustainable and higher strength concrete. Modern building codes do not cover the use of ultra-high strength concrete (UHSC) in the design of composite structures. Against such background, this paper investigates experimentally the mechanical properties of steel fibre-reinforced UHSC and then the structural behaviors of UHSC encased steel (CES) members under both concentric and eccentric compressions as well as pure bending. The effects of steel-fibre dosage and spacing of stirrups were studied, and the applicability of Eurocode 4 design approach was checked. The test results revealed that the strength of steel stirrups could not be fully utilized to provide confinement to the UHSC. The bond strength between UHSC and steel section was improved by adding the steel fibres into the UHSC. Reducing the spacing of stirrups or increasing the dosage of steel fibres was beneficial to prevent premature spalling of the concrete cover thus mobilize the steel section strength to achieve higher compressive capacity. Closer spacing of stirrups and adding 0.5% steel fibres in UHSC enhanced the post-peak ductility of CES columns. It is concluded that the code-specified reduction factors applied to the concrete strength and moment resistance can account for the loss of load capacity due to the premature spalling of concrete cover and partial yielding of the encased steel section.

• International Journal of Concrete Structures and Materials
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• v.18 no.1E
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• pp.11-16
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• 2006

The use of the current ACI 318 stress block parameters has been reported to provide unconservative estimations of the moment capacities for high-strength concrete columns. Accordingly, several concrete stress block parameters have been recently proposed. This paper discusses various concrete stress block parameters for high-strength concrete and their influences on the code provisions. In order to adopt the proposed stress block parameters to the design code, it is necessary to understand the impact of the change of the stress block parameters on various aspects of the code provisions. For this purpose, the influence of using of different stress block parameters on the location of the neutral axis and the tensile strain in extreme tension steel as well as the axial and moment capacities are investigated. In addition, the influence on the prestressed concrete members is also elucididated.

• Steel and Composite Structures
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• v.37 no.5
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• pp.503-516
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• 2020

A novel spiral confined angle-steel reinforced concrete (SCARC) column was developed in this study. A total of 16 specimens were prepared and tested (eight of them were tested under axial loading, the other eight were tested under eccentric loading). The failure processes and load-displacement relationships of specimens under axial and eccentric loads were examined, respectively. The load-carrying capacity and ductility were evaluated by parametric analysis. A calculation approach was developed to predict the axial and eccentric load-carrying capacity of these novel columns. Results showed that the spiral reinforcement provided enough confinement in SCARC columns under axial and low eccentric loads, but was not effective in that under high eccentric loads. The axial load-carrying capacity and ductility of SCARC columns were improved significantly due to the satisfactory confinement from spirals. The outer reinforcement and other construction measures were necessary for SCARC columns to prevent premature spalling of the concrete cover. The proposed calculation approach provided a reliable prediction of the load-carrying capacity of SCARC columns.