Structural Engineering Research Projects:

Behavior of Conventionally Reinforced Concrete Beams with Corrosion Damaged Stirrups

There are approximately 235,000 conventionally reinforced concrete (CRC) bridges in-service on the federal highway system. Of these, over 21,000 were rated as structurally deficient 1, many attributed to chloride-induced corrosion damage 2, although a comprehensive study has not been undertaken to quantify the actual number of corrosion damaged CRC bridges. An example of the type of corrosion damage is shown in Fig. 1.

Fig. 1: Chloride-induced corrosion damage to RCDG beam removed from the Brush Creek Bridge in 1998. Delaminated concrete was removed to expose corroded steel. Shear stirrup A was discontinuous in-service and a section was removed for analysis. Shear stirrup B” was also discontinuous in-service.

The majority of deficient CRC bridges were constructed prior to the 1960's. Due to the large numbers of deficient bridges and lack of resources available to repair or replace them, there is a need to keep aging and deteriorated bridges in service, even as they are subject to increased volume and weight of truck traffic. At the same time, methods that can accurately correlate visual damage with rating categories that are indicative of structural performance are lacking.

An experimental investigation of corrosion on the shear capacity of conventionally reinforced concrete beams was conducted. Large-size specimens were constructed and tested as shown in the photo below. The embedded stirrups were subjected to accelerated corrosion and three different corrosion damage levels were produced.

Fig. 2: a) Schematic and b) photograph of corrosion cell (A-anode (+), B-cathode (-)).

Damage levels ranged from moderate to severe damage as measured by the degree of stirrup area lost. Specimens were inspected and rated per national guidelines prior to testing. The condition ratings did not indicate significant distinction between specimens or indicate differentiation in capacity. Tests indicated that corrosion damaged specimens exhibited reduced shear capacity and reduced overall deformation at failure. Localized and sequential corrosion damage had significant impact on structural performance of the test specimens.

Fig. 3: Fractured shear stirrup near flexural tension steel at locally reduced cross-section from corrosion.

Research Significance

The impact of corrosion on the shear capacity of conventionally reinforced concrete beams has not been widely studied. Existing rating and evaluation guidelines, based on overall visual distress, have not been correlated with actual structural performance for corrosion damaged members. This research contributes to the understanding of shear behavior and will aid in determining the influence of corrosion damage on shear capacity of CRC beams and girders. It further employs condition rating factors and indicates that these may not adequately indicate structural performance.

 

Keywords: shear strength; experiment; corrosion; rating; evaluation; damage

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