Zhuojin Pipe Fitting Co., LtdStatic Performance of Steel Tube High-Performance Concrete Flexural Members
Literature Overview
The paper by Wang Qingli, Liu Xiaochen, Li Qinggang, and Wang Yue (published in Industrial Construction, 2013, Vol. 43, Issue 3, pp. 13–17) investigates the static performance of steel tube high-performance concrete (STHPC) flexural members. The research was supported by the Liaoning Province Engineering Construction Local Standard Compilation Plan Project (200708). The work was conducted at Shenyang Jianzhu University and Liaoning Provincial Architectural Design Research Institute.
Core Technical Content
Through static tests on 18 specimens (with self-consolidating concrete having a compressive strength standard value of 96 MPa), the study found that the mid-span moment-curvature curves of STHPC flexural members can be divided into elastic stage, elastoplastic stage, and descending stage. The deflection curves of specimens approach sinusoidal half-wave curves, and the longitudinal strain of the steel tube basically conforms to the plane section assumption.
Test Configuration
| Parameter | Description |
|---|---|
| Number of specimens | 18 |
| Concrete type | Self-consolidating high-performance concrete |
| Concrete compressive strength | 96 MPa (standard cube strength) |
| Test type | Static four-point or three-point bending |
| Measured outputs | Moment-curvature curves, deflection curves, strain distribution |
Key Findings
- Moment-curvature behavior: Three distinct stages identified - elastic, elastoplastic, and descending.
- Deflection curve shape: Approaches sinusoidal half-wave curve, consistent with theoretical expectations.
- Strain distribution: Steel tube longitudinal strain basically conforms to plane section assumption.
- Confinement effect: Steel tube under transverse compression provides no confinement force to the concrete in flexural members.
- Overall behavior: No essential difference between STHPC flexural members and conventional SRC flexural members.
Technical Analysis
Stress-Strain Behavior Stages
| Stage | Characteristic | Behavior Description |
|---|---|---|
| Elastic stage | Linear relationship | Both steel and concrete behave elastically |
| Elastoplastic stage | Nonlinear relationship | Concrete begins to crack, steel yields gradually |
| Descending stage | Load capacity decreases | Significant cracking, steel yields extensively |
Confinement Effect in Flexural Members
A significant finding is that the steel tube under transverse compression provides no confinement force to the concrete in flexural members. This contrasts with axial compression members where the steel tube provides effective confinement. The reason is that in flexural members, the concrete is primarily in tension or compression parallel to the steel tube axis, rather than being confined laterally by the steel tube.
Integration with Steel Pipe Engineering Practice
For steel pipe manufacturers, this research confirms that standard structural steel tubes can be used in flexural applications with high-performance concrete without requiring special modifications. The steel tube serves primarily as a formwork during construction and as a tension reinforcement in flexural members.
Steel Tube Specification for Flexural Applications
| Parameter | Typical Specification | Notes |
|---|---|---|
| Steel grade | Q235 or Q345 | Higher grade provides better ductility |
| Tube shape | Circular or rectangular | Rectangular may be more efficient for flexure |
| Wall thickness | 6–12 mm | Depends on span and load |
| Connection type | Welded or bolted | Welded connections preferred for continuity |
Welding Considerations for Flexural Members
When steel tube flexural members are connected to other structural elements, the welding quality is critical for ensuring proper load transfer. Common welding methods include:
- SMAW (Shielded Metal Arc Welding): Suitable for field welding and repair work.
- GTAW (Gas Tungsten Arc Welding): Preferred for high-quality welds on thin-walled tubes.
- GMAW (Gas Metal Arc Welding): Efficient for thicker sections and production welding.
The heat-affected zone (HAZ) properties near weld connections must be carefully controlled to avoid premature failure under cyclic loading. Preheating and post-weld heat treatment may be required for higher-grade steels (Q345 and above) to prevent hydrogen-induced cracking.
Study Insights and Reflections
This research provides valuable data for the development of local design standards for steel tube high-performance concrete flexural members. The finding that STHPC flexural members behave similarly to conventional SRC flexural members simplifies design calculations and standard development.
From a steel pipe manufacturing perspective, the research validates the use of standard structural steel tubes in flexural applications with high-performance concrete. The key implication is that steel pipe manufacturers do not need to develop special grades for this application, provided standard quality control measures are maintained.
The research also highlights the importance of concrete-steel bond quality in flexural members, even though the confinement effect is minimal. Proper surface preparation and concrete placement techniques should be employed to ensure adequate bond strength for composite action.
The study's findings support the continued development of high-performance concrete applications in steel tube composite structures, with appropriate design considerations for flexural behavior.