Rehabilitation of corroded steel CHS under combined bending and bearing using CFRP

• CFRP strengthened corroded pipes were subjected to 3-point bending.
• Three phases of deformation were observed, namely, denting, bending and denting, and structural collapse.
• CFRP significantly increase the strength of corroded CHS.
• The gain in strength depends on the section slenderness.
• Two lower bounds were developed to predict the combined strength of CHS.

This paper presents experimental results for a series of rehabilitated corroded steel Circular hollow Sections (CHS) under quasi-static large deformation 3-point bending and direct indentation using Carbon Fibre Reinforced Polymers (CFRP). The main parameters examined were the amount of corrosion penetration in the wall thickness, its extent along the pipe, the type and number of the CFRP sheets. The corrosion in the wall thickness was artificially induced 360° around the circumference by machining. Four different severity of corrosion were examined of 20%, 40%, 60%, and 80%. The testing program included the rehabilitation of 12 artificially degraded CHS with limited corrosion repaired using externally wrapped CFRP sheets. The extent of corrosion along the pipeline was in the range of Lc / Dn = 1.0 to 3.0, where Lc = length of corrosion and Dn is the nominal diameter of the CHS. The external diameter-to-thickness ratio examined in this paper was in the range of D0 / ts = 20.3 to 93.6. The CFRP sheets were wrapped around the section in the longitudinal and transverse direction with a sufficient overlap. The percent increase in strength was mostly affected by the corrosion level where the maximum gain was 282% obtained for the most severe 80% corrosion. The average increase in the load carrying capacity was 97%. Two new lower bound design equations based on the bare and composite section properties were developed to predict the strength of the bare and repaired CHS using CFRP under combined bending and bearing.