RELIABILITY ASSESSMENT OF THE BS 8110-1-1997 SHEAR DESIGN METHOD FOR REINFORCED CONCRETE BEAMS

Abstract

Shear failure is a brittle and undesirable mode of failure in a reinforced concrete structure. By virtue of the complexity involved in accurately modeling shear transfer mechanism, differenttheoretical frameworks that explain this phenomenon exist in the research community. Although the British Code for reinforced concrete design, BS 8110-1-1997, has been withdrawn and replaced with Eurocode 2 (EC2), it nevertheless remains the most favored and widely used reinforced concrete design code in Nigeria. However, it has been reported that the BS 8110 -1-1997 shear model shows the greatest susceptibility to failure (a comparable insufficient bias) at low level of shear reinforcement, hence this research seeks to assess the safety performance of BS 8110-1-1997 shear model based on the principles of probabilistic modelling and structural reliability. In this research, statistical analysis and the total demerit point analysis (TDP) were applied in the comparison of BS 8110-1-1997, Eurocode 2, and the Improved Eurocode 2 shear models for theirsuitability as a general probabilistic model for the reliability analysis. Furthermore, parametric analysis was also conducted on predefined test beams to gain more insight into the performance of BS 8110-1-1997 shear model. Subsequently, the reliability and safety performance of reinforced concrete beams failing in shear were carried out using the simplified probabilistic model limit state equation for the first-order reliability analysis with the COMREL computer program. From the study, the Improved Eurocode 2 shear model has the least mean-value prediction of 1.10 which indicates its proximity to idealizing the experimental observations. With a standard deviation of 0.30, the Improved EC2 shear model has the least level of dispersion about the mean value followed by 0.32 for BS 8110, and then 0.47 for EC2. Based on the total demerit point analysis, the BS 8110 shear model gives the least score of 47 indicating that it is more reliable in predicting shear strength; while the EC2 at 100 gave the worst performance. The trendline pattern for the reliability analysis of the BS 8110 shows a significant level of consistency and uniformity across the parametric shear reinforcement under consideration but fails to meet EN 1990 criteria for resistance target reliability index (β RT = 3.04) for reliability class 2 (RC2) for a reference period of 50 years. This implies an economical design in terms of cost but whose safety is questionable.