Zhuojin Pipe Fitting Co., LtdTemperature Field and Effect Analysis of Large Steel Tube Concrete Composite Arch Rib
Literature Overview
The paper by Zhou Liming, Tang Pengfei, Pan Dong, and Mao Jianping, published in Concrete (2023, No. 8, pp. 60-65), presents a comprehensive study of the temperature field distribution and temperature-induced effects in large-scale steel tube concrete (STC) composite arch ribs used in bridge engineering. The research was supported by the National Natural Science Foundation of China (Grants 51878186 and 51868007), the National Key R&D Program (2019YFC1511103), and the Guangxi Transportation Industry Key Science and Technology Project. This work addresses a critical practical concern: the thermal behavior of STC structures from the construction phase through the entire service life.
Monitoring Program and Data Acquisition
The study involved real-time temperature monitoring of a full-scale STC arch rib from the onset of concrete hardening through a period of post-construction service. The monitoring system captured temperature data at multiple locations within the cross-section, including the inner steel tube surface, the outer steel tube surface, the concrete core, and the exterior surface exposed to environmental conditions.
The monitoring data revealed several distinct temperature regimes corresponding to different physical phenomena:
| Monitoring Phase | Temperature Driver | Typical Range | Duration |
|---|---|---|---|
| Concrete hydration | Hydration heat generation | Internal peak 60-80°C | First 72 hours |
| Post-hardening cooling | Heat dissipation to environment | Gradual decrease | 1-2 weeks |
| Daily solar cycling | Solar radiation absorption | Surface fluctuation ±15°C | Continuous |
| Seasonal variation | Ambient temperature change | Seasonal range | Annual cycle |
Key Temperature Field Findings
Hydration heat effects: The exothermic hydration reaction of cement creates significant internal temperature gradients within the STC cross-section. The inner-outer temperature differential can reach critical values that induce thermal stresses sufficient to cause debonding between the steel tube and the concrete core. The study identified a particularly critical period approximately 10 hours after the peak hydration heat, during which the temperature gradient is most severe and the risk of debonding is highest.
Solar radiation effects: Solar radiation can raise the surface temperature of the STC arch rib by up to 15°C, creating a significant thermal gradient from the sun-exposed surface to the interior. This daily thermal cycling is a persistent source of fatigue loading and can contribute to the progressive degradation of the steel-concrete interface over the service life of the structure.
Radial temperature distribution: The temperature distribution across the radial direction of the STC cross-section follows a parabolic nonlinear profile, with the lowest temperatures at the outer and inner surfaces and the highest temperature at the mid-radius. This parabolic distribution is consistent with the heat conduction equation for a thick-walled cylinder and has important implications for thermal stress calculations.
Strain-temperature asynchrony: The surface strain of the STC arch rib does not vary synchronously with temperature changes. This asynchrony is attributed to the time-dependent behavior of concrete (creep and shrinkage), the viscoelastic response of the steel-concrete interface, and the thermal lag between surface temperature and interior temperature.
Temperature-Induced Stress Analysis
Finite element modeling was used to quantify the stresses induced by the measured temperature fields. The results revealed several important stress patterns:
During the hydration heat peak, the stress within the inner concrete reached a maximum of approximately 3 MPa, while the steel tube experienced stresses up to 36 MPa. The much higher stress in the steel tube is attributed to its higher elastic modulus and thermal expansion coefficient, which cause it to restrain the thermal expansion of the concrete and absorb a disproportionate share of the thermal stress.
After the exterior concrete jacket was cast, the hydration heat of the jacket concrete created additional thermal stresses. At the peak hydration of the jacket, the inner concrete stress reached approximately 3 MPa, the steel tube stress reached 36 MPa, and the jacket concrete stress remained below 2 MPa even after full hardening. The jacket concrete's lower stress level is explained by its later casting sequence and the thermal mass of the already-hardened inner concrete and steel tube.
| Stress Component | Hydration Peak Stress | Jacket Casting Stress | Notes |
|---|---|---|---|
| Inner concrete | ~3 MPa | ~3 MPa | Compressive, relatively low |
| Steel tube | ~36 MPa | ~36 MPa | High due to stiffness and restraint |
| Jacket concrete | Not applicable | <2 MPa | Low due to thermal mass of core |
Engineering Practice and Construction Recommendations
The findings of this study have direct implications for the construction and maintenance of STC composite structures. The critical period of 10 hours after hydration heat peak requires special attention to thermal protection measures. Insulation blankets, controlled cooling water circulation, or thermal curing compounds should be deployed to minimize the inner-outer temperature gradient and prevent debonding.
For the exterior concrete jacket, the casting sequence and timing should be carefully planned to avoid superimposing hydration heat peaks. If the jacket is cast while the inner concrete is still thermally active, the combined thermal effects can exceed the design limits. A minimum cooling period between the inner concrete casting and the jacket casting is recommended.
Solar radiation protection is essential for the long-term durability of STC arch ribs. External coatings, thermal insulation layers, or shading devices can reduce the surface temperature fluctuation and extend the service life of the structure. The parabolic radial temperature distribution should be incorporated into fatigue analysis models for the steel tube, as the cyclic thermal loading can contribute to fatigue crack initiation at stress concentration points.
From a steel pipe manufacturing perspective, the thermal behavior of the steel tube is critical to the overall performance of the composite structure. The steel tube must maintain its mechanical properties and dimensional stability under the thermal cycling conditions described in this study. Pipe grades with stable thermal expansion coefficients and good fatigue resistance (such as Q355 or Q390 per GB/T 1591) are preferred for STC applications.
Study Insights and Reflections
This research provides a rare and valuable dataset on the thermal behavior of full-scale STC structures, combining field monitoring with finite element analysis to create a comprehensive picture of temperature-induced effects. The identification of the critical 10-hour post-peak hydration period is a practical finding that can directly inform construction protocols and quality control procedures.
The asynchrony between surface strain and temperature is a particularly important finding that challenges simplified thermal stress models. Engineers relying on linear elastic thermal stress calculations may underestimate or mischaracterize the actual stress state in STC structures. The viscoelastic and time-dependent behavior of concrete must be incorporated into any reliable thermal stress analysis.
The study also highlights the importance of the exterior concrete jacket in modifying the thermal behavior of the STC cross-section. While the jacket adds compressive capacity and corrosion protection, it also introduces additional thermal complexity that must be managed during construction. The interaction between the hydration heat of the jacket and the residual thermal state of the inner concrete is a critical factor that should be explicitly considered in construction sequencing.