Experimental and numerical study on structural performance of reinforced concrete box sewer with localized extreme defect

An experimental and numerical investigation into the structural performance of reinforced concrete box sewers with typical corrosion-related extreme defects localized at the ceiling was conducted.Firstly,during the large-scale laboratory test,some key struc-tural responses were captured and evaluated,including the crack width development process(via digital image correlation measurement),ceiling deflection,and material strains of both complete and typical defective boxes.The failure modes and load-carrying mechanism throughout the specimen loading phases were analyzed.Furthermore,the specimen failure process was simulated using a damage-basedfinite element method,and a related parameter sensitivity analysis was performed.The results indicate that the defective ceiling cracked at mid-span under a low load value,but the bending capacity loss can be substituted by two shoulders and carry three tofive times more load before completely collapsing.The simulation matched the lab test qualitatively,and with the suggested set strategy of material parameters,the load-deflection feature curve could provide a practical prediction of the ultimate bearing capacity of the defec-tive sewers,with a 10–15%error on the safe side.

Advanced Unified Failure Model on Uniformly Reinforced Concrete Box Section Members

Based on the traditional Nielsen model,a unified failure model on the uniformly reinforced concrete box section members under combined forces was introduced by Luo and Liu.One of their contributions is adjustment of the shear carrying capacity of concrete at the member failure surface.In the unified failure model,the comparison with the experimental results verified this adjustment.Nevertheless,it should be pointed out that the adjustment factor of shear carrying capacity at member failure surface for the reinforced concrete members in the unified failure model is a fixed adjustment constant for all experiment data,which is basically determined by curve fitting.However,the adjustment factor should vary with the normal stress at the member failure surface.In this paper,an advanced theoretical model is introduced,in which the adjustment factor of shear carrying capacity at failure surface is a variable related to the normal stress at failure surface.Furthermore,the advanced unified failure model on the uniformly reinforced concrete box section member can still be expressed in a simple form.Finally,the comparison with several groups of test data has verified that this advanced model is more accurate and feasible to be used in design.