Analytical stress model for embedded bar-wrapped cylinder concrete pressure pipe under internal load

摘要

Failure accidents occur in the long-term use of traditional prestressed concrete cylinder pipes (PCCPs) because of internal structural flaws and the effects of the external environment. Accidents occur mainly because of two reasons. First, high-strength steel wire easily becomes embrittled and broken. Second, the mortar protective cover is easily cracked by empty drums. Bar-wrapped cylinder concrete pressure pipe (BCCP), which is a modified pipe with low-stress cold-rolled ribbed prestressed steel bars and a fine aggregate concrete cover, is introduced in this study to improve the safety of water conveyance engineering based on the PCCP structure. The failure process under internal load is analyzed, and calculation models from the prestressed to ultimate failure states are proposed. Formulas for radial and circumferential stresses of each layer in the elastic stage are derived on the basis of uniform pressure distribution on a ring or a cylinder. After cracks occur in the core, the concrete is treated as an orthotropic anisotropic body, and explicit stress calculation formulas are given for each layer. The analytical stress model is applied to an embedded BCCP with an inner diameter of 1800 mm, and a field experiment is designed to validate the model. The obtained internal loads that correspond to the cracking of the protective cover and the concrete core agree well with each other, and the maximum error between the test and model results of the stress of the prestressed bars is less than 10%. This analytical stress model can be utilized as a reference for the structural analysis of pipelines and tunnels under internal loads. In addition, the size of each layer can be optimized on the basis of the results, thereby making the structure economic and reasonable under the premise of meeting the bearing capacity requirements.