Load distribution in bridge parapet supports in Southern England: re-evaluation, testing and analysis

Abstract

This paper presents the background information, test results, analysis, and conclusions relating to the testing of two model bridge stringcourses subject to simulated parapet impact loading. Mott MacDonald Area 3 were appointed in 2002 by the Highways Agency to undertake the upgrade and replacement of all substandard BACO parapets fixed to existing structures. Area 3 in Southern England has a particularly large number of parapets that do not meet current design standards for normal containment. In many cases a combination of stringcourse geometry and a low assessment of in situ strength based upon a conservative model of load dispersal precluded the simple substitution and replacement of the parapet. Design of the test programme was based upon the composite characteristics of the five weakest bridge stringcourses identified in Area 3. The aim of the testing was fourfold. First, examine the load dispersal through the concrete and the reinforcement. Second, measure the ultimate failure load and calculate the structural reserve. Third, record the mode of failure. Fourth, ratify and produce a set of assessment recommendations. For all the criteria, a correlation
between theoretical prediction using current design standards and in situ performance was sought. The conclusions of this paper identify three important findings: (1) a localised horizontal slicing plane of shear failure across the plinth upstand is very unlikely, (2) only the shear links immediately surrounding the anchorage post are effective, (3) a simple load dispersal angle of 45? is too conservative and should be increased to 65? for assessment calculations. These recommendations have been applied to the current upgrade programme and have produced immediate cost savings for the Highways Agency of several million pounds. This paper highlights the benefits achievable when both client and consultant adopt a forward
thinking and progressive strategy to maximise both best value and structural safety.

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ORCID for S.K. Clubley: orcid.org/0000-0003-3779-242X

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