Experimental study on compression and bending performance of steel pipe sleeve grouting connection

Abstract A set of axial pressure specimens and three groups of compression and bending specimens were designed and produced to explore the compression and bending mechanical properties of steel pipe sleeve grouting connections. The damage morphology, hysteresis properties, skeleton curves, bearing capacity, energy consumption, and sleeve strains of grouting connection segments were investigated via monotonic and reciprocating loading tests. The effects of axial pressure ratios and loading methods on the horizontal bearing capacity were discussed. The results show that under the action of compression-bending load, specimens exhibit damage patterns characterized by crushing and wrinkling of grout near shear keys within the grouted joint section. This failure mechanism prevents continued vertical load-bearing capacity, leading to extrusion and damage of the steel pipe. Compared to specimen group GC-BM-0.2, the GC-BM-0.4 and GC-BM-0.6 groups exhibited reduced load-bearing capacities by 13.57% and 32.79%, respectively, along with decreased ductility by 18.64% and 5.37%, The maximum interlayer displacement angle decreased from 2.5% to 1%. As the axial pressure ratio increases, the second-order effect becomes significant. Meanwhile, the horizontal displacement required for specimens to reach the damage point decreased, and energy dissipation significantly diminished. Under 20 high-stress loading cycles, the lateral stiffness degradation rate for each specimen ranged from 0.21% to 4.7%. During secondary-stage cyclic loading, the lateral stiffness degradation effect became more pronounced. The sleeve circumferential strain was analyzed to establish a computational model for the flexural bearing capacity of grouted pipe sleeve connections. Based on the sleeve circumferential strain and the strength value of the grout in the triaxial (compression-compression-tension) state, a calculation formula for the compression-bending bearing capacity of the grouting connection section was proposed. The calculated value was verified using the test data, demonstrating a conservative approach that favors safety.