Zhuojin Pipe Fitting Co., LtdDesign Method and Reliability Analysis of Concrete-Filled Steel Tubular Structure Technical Specification DBJ 13-51-2003
Literature Overview
This paper by Yao Guohuang from Fuzhou University and Han Linhai from Tsinghua University was published in Industrial Construction in 2006 (Vol. 36, No. 1, pp. 66–70). Funded by the National Science Fund for Distinguished Young Scholars (Grant No. 50425823), the study evaluates the design formulas in the Fujian Province local standard DBJ 13-51-2003 for concrete-filled steel tubular structures and conducts reliability analysis using the First-Order Second-Moment (FOSM) method.
Core Technical Content
Standard Overview
DBJ 13-51-2003 is a provincial engineering construction standard for Fujian Province that provides design formulas for concrete-filled steel tubular (CFT) structural members. The standard covers:
- Circular CFT columns and beams
- Square and rectangular CFT columns and beams
- Axially compressed members
- Purely bent members
- Combined compression-bending members
Design Formula Verification
The authors collected experimental test data from published literature and compared the calculated results from DBJ 13-51-2003 with actual test capacities. The comparison revealed:
| Member Type | Loading Condition | Average Ratio (Test/Calculated) | Coefficient of Variation |
|---|---|---|---|
| Circular CFT | Axial compression | 1.05–1.10 | 0.08–0.12 |
| Square CFT | Axial compression | 1.02–1.08 | 0.10–0.15 |
| Circular CFT | Pure bending | 1.03–1.09 | 0.09–0.13 |
| Square CFT | Pure bending | 1.01–1.07 | 0.11–0.16 |
| Combined members | Compression-bending | 1.04–1.12 | 0.10–0.18 |
The overall agreement between calculated and test results is satisfactory, with calculated values generally being slightly conservative (test capacity exceeds calculated capacity).
Reliability Analysis Methodology
The reliability analysis follows the procedure of GB 50068-2001 (Unified Standard for Reliability Design of Building Structures):
| Analysis Parameter | Specification |
|---|---|
| Method | First-Order Second-Moment (FOSM) |
| Reference standard | GB 50068-2001 |
| Target reliability index | β ≥ 3.2 (for plastic materials) |
| Random variables | Material strengths, loads, geometric dimensions |
| Analysis type | Structural reliability calibration |
Reliability Results
| Member Type | Loading Condition | Reliability Index (β) | Meets Standard |
|---|---|---|---|
| Circular CFT | Axial compression | 3.2–3.8 | Yes |
| Square CFT | Axial compression | 3.1–3.6 | Mostly yes |
| Circular CFT | Pure bending | 3.3–3.9 | Yes |
| Square CFT | Pure bending | 3.0–3.5 | Borderline |
| Combined members | Compression-bending | 3.1–3.7 | Mostly yes |
Standards Comparison and Interpretation
Comparison with National Standards
The Fujian local standard DBJ 13-51-2003 was developed before the national standard GB 50992-2013 for concrete-filled steel tubular structures. Key differences include:
| Aspect | DBJ 13-51-2003 | GB 50992-2013 |
|---|---|---|
| Design philosophy | Allowable stress + limit state | Limit state design |
| Partial safety factors | Region-specific | Nationally calibrated |
| Confined concrete model | Simplified | More refined |
| Interaction curves | Simplified | Comprehensive |
| Applicability | Fujian Province | National |
Material Model Considerations
The confined concrete strength enhancement model used in DBJ 13-51-2003 is based on the principle that the steel tube provides lateral confinement to the concrete core, increasing its compressive strength. For circular sections, the confinement is uniform; for square sections, it varies with position. The standard adopts:
- Uniform confinement assumption for circular CFT members
- Reduced effective confinement factor for square/rectangular sections
- Steel tube yield strength as the primary parameter for confinement pressure calculation
Key Reflections and Study Insights
This study represents an important contribution to the reliability calibration of Chinese CFT design standards. The FOSM method, while approximate, provides a practical framework for evaluating whether design formulas achieve the target reliability level specified in the unified standard.
The finding that most design formulas in DBJ 13-51-2003 meet the target reliability index is reassuring for engineers who used this standard in practice. However, the borderline cases for square CFT members under pure bending suggest that additional caution is warranted for those specific applications.
Han Linhai, as one of the leading researchers in CFT structures in China, brought significant expertise to this analysis. The National Science Fund for Distinguished Young Scholars grant indicates the recognized importance of this research direction. The study contributes to the broader effort of harmonizing local standards with national reliability requirements.
From a practical standpoint, this research validates the use of DBJ 13-51-2003 for routine CFT structural design in Fujian Province while identifying areas where more conservative design approaches may be appropriate. The reliability analysis methodology demonstrated here can be applied to other local standards and design codes to ensure consistent safety levels across different regions and structural systems.
The study also underscores the importance of collecting and compiling experimental data for reliability calibration. Without a comprehensive database of test results, reliability analysis cannot be performed with confidence. The accumulated test data used in this study represents years of collaborative research effort and remains a valuable resource for future standard development.