Reinforced concrete half-joint structures: Implications of reinforcement detailing and deterioration

Dr Pieter Desnerck, Dr Janet Lees, Dr Chris Morley, Dr Geoff Parks

Introduction

A half joint is a particular type of RC structure. Within the existing UK Highways Agency network alone there are 400+ concrete bridges with half joints. The advantages of this structural form include a level running surface along the bridge deck and the support spans, and precast beams can be easily lifted into place and supported during construction. However, a disadvantage inherent in this type of construction is that there are problems associated with leakage through the joint. This enables moisture to accumulate at the beam seats thereby increasing the propensity for the deterioration of the concrete and reinforcement steel. The situation is adversely compounded by limited access to the bearing seat joint which leads to both inspection and maintenance issues. A further complication is that the detail in the beam seat region represents a potentially sensitive structural detail. Some half-joint structural vulnerabilities may have been present from the outset e.g. in the initial design or construction, some may develop with time e.g. deterioration. Half joint details have come under intense scrutiny since the collapse of a section of the de la Concorde Overpass in Quebec, Canada in 2006. Five people were killed and six others injured. Thus, a key challenge is to understand the lessons to be learned from the Concorde Overpass Collapse, and the inherent vulnerabilities in half joint structures.

This project focusses on improving analytical tools and experimental evidence for the more accurate assessment of half-joint structures, and provides guidance on the management strategy for half-joint structures throughout the UK. Overly conservative strength assessments can result in unnecessary closures or vehicle weight limits, both of which are costly. Non-conservative strength assessments potentially put public safety at risk. The outcomes of this project are therefore of national, and international importance.

Aims and Objectives

The behaviour of reinforced concrete structures in shear is notoriously complex and there is no generally accepted unifying theory. This presents a major difficulty in the analysis of half-joint structures. The current work explores, compares, extends, and adapts existing theories in the context of half-joint structures. A further goal is to incorporate detailing deficiencies and/or deterioration within the analytical and experimental approaches to thereby enhance the predictive capability for structures in service. The load-sharing implications in non-compliant details and the sensitivity of the structural performance to a deterioration outcome, such as a loss of strength will be investigated. This approach reflects the type of information that would be collated as part of a destructive or non-destructive testing strategy, and provides a general, robust and repeatable framework from which others can benchmark their results.

Research Directions

Experiments on small and large scale specimens are undertaken to provide the essential validation of the expected behaviour. Small-scale tests are used to characterise the bond anchorage behaviour in a representation of a deteriorated system.

The large-scale tests deliver an experimental database of half-joint structures with non-compliant details and determine the influence of strength reductions in the constituent materials. This will provide an important experimental evidence of the behaviour of such structures, and highlight the most critical detailing and deterioration combinations. While the project has been inspired by, and will address, the difficult challenges faced by those who build, own and maintain reinforced concrete bridges, the development of the underlying fundamental scientific and engineering understanding will have far greater implications. A fuller understanding of the failure modes and sensitivities associated with complex reinforced concrete details will provide insight into the life-time performance of a wide range of existing infrastructure assets.

Collaborators

The research is funded by the EPSRC through grant EP/K016148/1, Reinforced concrete half-joint structures: Structural integrity implications of reinforcement detailing and deterioration. The project partners are Highways England, Parsons Brinckerhoff and Atkins.

Selected references/Further reading

Desnerck, P., Lees, J.M. and Morley, C.T. (2015) "Bond Behaviour of Reinforcing Bars in Cracked Concrete" Construction and Building Materialsv. 94, Sept., pp. 126-136 (open access) (doi)

Desnerck, P., Lees, J.M. and Morley, C. (2015) "Impact of Material Deterioration on the Strength of Reinforced Concrete Half Joint Structures," Proceedings of the 2015 IABSE Workshop on Safety, Robustness and Condition Assessments of Structures, Helsinki, Finland,p. 8 (postprint)

Desnerck, P., Lees, J.M. and Morley, C.T. (2014) "Assessment of Reinforced Concrete Half-joint Structures: Dealing with Deterioration"Proceedings of the 2014 PCI Convention and National Bridge Conference, Washington DC, United States [CD-ROM]