Partial Factors for Shear Capacity Assessment of In-Service RC T-Girder Bridges

Abstract

As the infrastructure age, their assessment to carry the loads they are subjected to becomes increasingly important. Also, assessment is needed as part of a regular monitoring programme. Before carrying out a rigorous probabilistic analysis for assessment, it is often required to make a preliminary assessment using simplified procedures, such as that developed using semi-probabilistic approach, in which partial factors are used. In this article an attempt has been made to evolve a framework to determine the partial factors for safety assessment of the in-service T-girder bridges in India against the limit state of shear. Limit state of shear is considered because it is one of the important ultimate limit states for bridge girder that results in brittle failure. The partial factors are derived using first order reliability method. In order to suggest a simple method for safety assessment, statistical properties of modelling error associated with the simplified equation of shear capacity estimation are estimated using test data of 185 beams reported in the literature. To demonstrate the usefulness of the framework developed, an attempt has been made to determine partial factors for assessment for a typical T-girder bridge designed according to the relevant Indian codes. The loading considered corresponds to actual traffic loads on a typical Chennai flyover. The study reported here gains importance as: (i) general guidelines to assess the reliability of in-service bridges are non-existent in the Indian context and (ii) the partial factors suggested for two consequence classes can be used for quick assessment of the safety of existing similar flyover girders against limit state of shear in a more rational way.Keywords: Assessment, RC T girder bridges, partial factors, reliability index. THE safety assessment of bridges plays a key role in a country's economic development. Its increasing importance is felt in most countries. As the processes involved in assessments are complex and time-consuming, various levels of assessment are done; each of the higher level is less conservative and involves more work in terms of computation 1 . When a particular assessment level is found satisfactory, then proceeding through further levels of assessments is not required. The complexity in assessment is thus minimized. Generally, the initial (or preliminary) assessment level is done in a deterministic way using partial factors, evaluated using a probabilistic analysis. Generally, in literature, such methods are referred to as semi-probabilistic methods 2 . Partial factors are commonly used in designing structures. In the assessment, these values are used to determine target resistance values, against which the resistance of an in-service bridge needs to be checked. It is important to note that partial factors to be used in assessment are not the same as the design, because of differences in target reliability indices that are considered 3 . The target reliability levels required for in-service bridges are lower than those of new bri...

Safety assessment of in‐service reinforced concrete T‐girders of bridge decks

“…The reliability index at the end of 50 years becomes 1.28. The target reliability index for the in‐service bridges is based on two philosophies The target reliability index of the in‐service bridges is reduced from that of the new bridges for economic reasons.…”

“…The target reliability indices at design and at 50 years, for bridges which fall under Consequence Class 3 are 5.3 and 3.8 (high consequence of failure) and Consequence Class 2 are 4.8 and 3.4 (medium consequence of failure). The reliability index of considered example was found to be 3.7 at design and 1.28 at the end of 50 years.…”

“…The target reliability index for the in-service bridges is based on two philosophies. 39 • The target reliability index of the in-service bridges is reduced from that of the new bridges for economic reasons. This reduction in the target reliability index is based on consequence of failure and based on four factors-component behavior, system behavior, risk factor, and inspection level.…”