Failure Mechanism Research of Steel Tube Concrete Support Component Circular Arc Arch

Literature Overview

This paper by Shan Renliang, Xiao Yuhang, Liu Keming, Dai Xu, Zhao Wei, Yan Wei, and Chen Yuxiang from China University of Mining and Technology (Beijing) and other institutions, published in the Journal of Coal (2018, Vol. 43, No. 7, pp. 1918-1929), investigates the failure mechanism of quarter-circular arc arches used in steel tube concrete support systems for deep soft rock roadways. Supported by the National Natural Science Foundation of China (51474218) and the Hainan Provincial Major Science and Technology Program (ZDKJ2016014), the research combines experimental testing, numerical simulation, and theoretical analysis to establish design criteria for these critical mining support components.

Experimental Program and Loading Configuration

The quarter-circular arc arch specimens were subjected to six-point equal-value loading, simulating the uniform pressure distribution that these arches experience in roadway support applications. This loading configuration is representative of the actual stress conditions in deep soft rock roadways, where the surrounding rock exerts approximately uniform radial pressure on the support structure.

The six-point loading setup ensures that the arch is loaded in a manner consistent with its intended structural behavior, where the arch action distributes loads efficiently through compression and bending.

Key Experimental Findings

The finding that both the arch bottom and arch crown are the weakest cross-sections is critical for design. The arch bottom is subjected to combined compression, bending, and shear, making it the most complex stress state and the first location to fail. The arch crown, while subjected primarily to compression, is also a critical section due to the concentration of compressive stress.

The effect of rise-to-span ratio is straightforward: larger ratios provide higher bearing capacity and stiffness. This is consistent with classical arch theory, where the rise-to-span ratio determines the efficiency of arch action and the magnitude of thrust forces.

Steel Fiber Reinforcement Effects

The finding that steel fiber volume fractions of 1% to 1.5% are optimal is practically significant. Below this range, the fibers do not provide sufficient reinforcement to significantly improve performance. Above this range, the excessive fiber content disrupts the concrete matrix, leading to increased stiffness but reduced ultimate load capacity. This non-monotonic relationship between fiber content and performance is important for design optimization.

Theoretical Analysis and Design Formulas

The authors conducted theoretical analysis from three perspectives: cross-sectional strength, local instability, and overall instability. The local instability analysis identifies the conditions under which the steel tube wall buckles under combined stress, while the overall instability analysis considers the global buckling of the arch structure.

The proposed bearing capacity calculation formula for steel tube concrete circular arc arches accounts for:

1. Cross-sectional strength: The combined capacity of the steel tube and concrete under compression and bending.
2. Local instability: The critical stress at which the steel tube wall buckles locally.
3. Overall instability: The critical load at which the entire arch structure buckles globally.

The governing failure mode is the lowest of these three capacities, following the standard structural design philosophy that the weakest link determines the overall capacity.

Engineering Practice Implications

For mining engineers designing steel tube concrete support systems for deep soft rock roadways, this research provides:

The practical design recommendations emphasize the importance of geometric optimization (rise-to-span ratio) and material optimization (steel fiber content) in achieving efficient and safe support systems. The identification of local instability as the governing failure mode directs design attention to the steel tube wall thickness and local stiffening requirements.

Study Insights and Reflections

This research contributes valuable knowledge to the design of steel tube concrete support systems in mining applications, where the harsh conditions of deep soft rock roadways demand robust and reliable support solutions. The combination of experimental testing, numerical simulation, and theoretical analysis provides a comprehensive understanding of the failure mechanisms that govern these structures.

The identification of the arch bottom as the first failure location, subjected to combined compression, bending, and shear, has direct implications for construction quality control. The welding quality of the steel tube at the arch bottom region is particularly critical, as any weld defects or geometric imperfections in this zone could initiate premature failure. From a welding engineering perspective, the arch bottom welds should be inspected with particular rigor, using ultrasonic testing for volumetric defects and magnetic particle testing for surface cracks.

The finding that steel fiber content above 1.5% is detrimental to ultimate load capacity is counterintuitive and highlights the importance of material optimization rather than simple maximization. This finding should guide material selection and mix design for steel tube concrete support applications, ensuring that the steel fiber content is within the optimal range rather than being maximized without regard to the non-monotonic performance relationship.