Foreword

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This document was prepared by Technical Committee ISO/TC 71, Concrete, reinforced concrete and pre-stressed concrete, Subcommittee SC 9, Steel-concrete composite and hybrid structures.

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Introduction

This document provides informative design examples of concrete-filled steel tubular (CFST) hybrid structures in accordance with ISO 16521, Design of concrete-filled steel tubular (CFST) hybrid structures. ISO 16521 stipulates the conceptional design, refined analysis method, simplified design formulae based on refined analysis and experimental verifications, and detailing design of CFST hybrid structures. Detailed calculations are provided in the design examples and the corresponding reference subclauses in ISO 16521 are indicated.

For trussed CFST hybrid structures, four design examples are provided, which include a three-chord structure and two four-chord structures without concrete slab, and a four-chord structure with a concrete slab. General requirements are verified and indices for cross-sections are calculated. The resistances of the hybrid structures as well as the CFST chords in compression, bending, combined compression and bending, and shear, are calculated in accordance with ISO 16521:2024, Clause 11. The protective design of corrosion resistance and impact resistance is presented in accordance with ISO 16521:2024, Clause 14. The detailing requirements and the resistances of the joints are verified in accordance with ISO 16521:2024, Clause 15. Finally, the verification of the limiting value of the core concrete void in the steel tube is carried out in accordance with ISO 16521:2024, Clause 16.

For concrete-encased CFST hybrid structures, four design examples are presented, i.e., a single-chord structure, a six-chord structure, and a four-chord structure with circular CFST members and a four-chord structure with rectangular CFST members. General requirements are verified and indices for cross-sections are calculated. Resistances in compression, combined compression and bending, resistance considering long-term load effects, shear resistance, are verified in accordance with ISO 16521:2024, Clause 12. Fire resistance is calculated in accordance with ISO 16521:2024, Clause 14.

Clause 6 of this document presents a global structural analysis example. A concrete-encased CFST hybrid arch structure is analysed in accordance with ISO 16521:2024, Clause 10, which employs a fibre-based model. It includes the determination of load, model establishment, load-displacement relationship analysis, deformation analysis, and stress and strain analysis.

Annex A is provided in this document to present some experimental data on CFST hybrid structures. These published experimental data serve as an important basis for the development of ISO 16521. Furthermore, they provide verifications of the design methods of CFST hybrid structures and examples for design of the structures based on experimental data, as stipulated in the standard.

It is worth pointing out that the design examples are only provided to help readers in using ISO 16521 and they are not based on any specific engineering projects.

1 Scope

This document provides design examples of concrete-filled steel tubular (CFST) hybrid structures in accordance with ISO 16521.

This document includes the design calculation of major structural types in ISO 16521, i.e., trussed CFST hybrid structures, concrete-encased CFST hybrid structures. The design examples cover the major loading cases for the structures and follow the design procedure presented in ISO 16521:2024, Clause 6.

2 Normative references

3 Terms and definitions

4 Design examples of trussed CFST hybrid structures

4.1 General requirements

4.2 Calculation of indices for cross-sections

4.3 Calculation of structural resistances

4.4 Protective design

4.5 Design of connections

4.6 Calculation of core concrete void ratio (ISO 16521:2024, 16.3.10)

5 Design examples of concrete-encased CFST hybrid structures

5.1 General requirements

5.2 Calculation of indices for cross-sections

5.3 Calculation of structural resistances

5.4 Protective design for fire resistance (ISO 16521:2024, 14.3)

6 Structural analysis example of concrete-encased CFST hybrid arch

6.1 Description of the arch structure

6.2 Load conditions

6.3 Establishment of the fibre model

6.4 Analysis of load-displacement relationship

6.5 Analysis of deformation

6.6 Analysis of stress in steel and concrete

Bibliography