To study the mechanical behaviors and failure modes of the push-on joints of ductile iron water pipelines under both tension and bending

this paper conducts a series of quasi-static tests on push-on joints to assess their ultimate bending capacity. Four-point bending tests were performed on the push-on joints of DN150 and DN200 pipelines with internal water pressure of 0.2 MPa and without soil coverage. Different loading protocols including coupled tensile and bending tests and monotonous and cyclic loading tests were adopted in the experimental program to investigate the mechanical behaviors and failure modes of the push-on joints. Results show that for push-on joints with different initial openings

the “bending moment-angle” curves of pipeline joints could be roughly divided into three stages: linear growth stage

plastic deformation stage

and the stage corresponding to ultimate load-carrying capacity. When the ratio of the assembling depth to the socket depth was about 0.67

the maximum angles of DN150 and DN200 pipeline joints were 15.9° and 12.8°

and the corresponding bending capacities were 7.8 kN·m and 9.2 kN·m respectively. The pipeline joints with larger assembling depths exhibited higher effective bending stiffness under cyclic loading

but the stiffness degraded significantly under reloading cycles. Buckling deformation occurred at the pipeline joints when the joint reached its ultimate load-carrying capacity

with the maximum residual strain of the pipe bottom being 5.7×10-4 and the ellipticity of joints being 4.2%. The relevant results can provide reference for the research of seismic damage

seismic checking calculation

design

and measures of buried ductile iron pipelines.