Half-Joint Design: Investigating Causes of Failure After Quebec Overpass Collapse - Essay Sample

Abstract

Due to the collapse of the section of the de le Concorde Overpass in Quebec, Canada in 2006 the Half-Joint design have come under acute scrutiny. Six people were injured and five were killed due to this failure. The lesson to be learned here from this failure is the key challenge and the inherent variability in the half joints structure. This project will help understand the causes of these half joint failures and how to prevent them using the methods provided. Reinforced concrete structures are notable complex structures, which introduces significant difficulty in the analysis of the half joint structure.

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Background

Within the UK Highway Agency Network alone there are more than 400 Half-Joint Bridges Half Joints are a Half Joints were put into use in order to simplify the design and help ease the construction of bridges, but these half joints are exposed to concrete corrosion due to deck expansion and other reasons. The structure and the analysis of the reinforcement is a very critical factor in the functionality of a half joint. The existing specification given is BS 5400: Part 4: 1990. (1) The loss of reinforcement through corrosion can induce higher stress and reduce the safety of the bridge. The major concern is that it is difficult to assess for inspection or maintain because they are located under or over live traffic roads. Besides, the half-joint deteriorate and result to corrosion that take place on the surface of the metals used. Steel is affected by moisture which gets into the inner surface through the leakages that arise in the joints (Lees, Parks and Morley 2013). Corrosion induces the amount of stress hence reducing the safety of the bridge. The greatest challenge is the assessment and maintenance due to their location underneath or over live traffic roads makes the situation more complicated. Compounded with limited access to the bearing seats joint, maintenance and inspection issues arise. During the initial construction, some of the structural vulnerabilities arise and can continuously deteriorate leading to serious problems. Desnerck, Lees and Morley (2018), posited that Concorde Overpass Collapse led to the deaths of five people albeit, it led to an urgent demand for emphasis on the significance of the proper inspections adequate assessment and maintenance techniques. There is lack of suitable standard to measure the effect of the stress and strain on half-joint.

Aims and Objectives

The aim of this project is to assess the half joints and what causes the cracks that occur within the structure by using calculation and doing research. This will help define if the half joint is at risk at high risk or moderate risk or low risk.

The objectives of this projects are:

• Review of Literature on Concrete Half Joints using DMRB standards.
• Development of Excel Programme
• Parametric Study

Research Methodology

In order find the solution to the problem in hand there are couple of steps that need to be taken. The first step in the methodology is "Review of Literature on Concrete Half Joints" which requires the collection and review of data from different sources such as BA39/93 and IAN 53/04 from the ''DMRB'' standards thus helping to understand the topic more in depth. The second step is to ''Develop an Excel Program'' which will be used for the calculations and finding the results on different sets of data that will be provided. Finally, and thirdly the Excel program will be used to ''Carry out Parametric Study'' to find the influence of different reinforcement on cracking potential of concrete Half-Joints.

Literature Review

Concrete Half Joints Using DMRB Standards

Reinforced concrete half-joints are made to provide support capabilities, and as a result are made up of a L-shaped ledge that augments the inverted ledge of a drop-n span. The use of half-joint is highly significant such that it creates a reduced construction depth and allows construction of a level running surface along the bridge deck and the support spans. According to the Interim Advice Note (IAN) half-joint were used as a means for simplifying the design and operations construction. Half-joints have a wide range of uses in various places where structures are needed for support and reinforcement purposes. Due to their need and effectiveness, the joints have gained a wide range of uses in the construction of various structures especially in roads. For instance, the Highways Agency of UK has more than 400 concrete bridges fixed using the half-joints (Lees, Parks and Morley 2013). In the UK, the highways Agency subjects the structures to visual inspection, which is given priority over anything else to ensure that the structure is strong enough to sustain the stress and strain. The wide range of the use of the joins is due to its structural forms that leaves a level running surface over and along the bridge deck and support spans. Besides, the precast beams can be lifted easily from a place to another place. Also, the de la Concorde Overpass is advantageous in that it is highly suitable for precast construction.

One of the challenges experienced and associated with the use of the half-joint is that they can leak causing water and any other fluid to pass through damaging the structure (Lees, Parks and Morley 2013). Another challenge that engineers encounter when using the reinforced concrete half-joint is that they tend to become confronted by the internal steel reinforcement layouts that are not in compliance with the standards set forth. This becomes a problem but calls for the need for the standards that can regulate the use of the half-joints. However, even with standards, the lack of a generally accepted unifying theory is a great problem facing the behaviour of the reinforced concrete half-joints (Desnerck et al., 2018).

The determination of the relevance of the strain and crack widths is a huge challenge to the assessment how long a half-joint can endure. The assessment of the half-joint need to be detailed for the information on geometry obtained to be accurate (Desnerck, Lees and Morley, 2018). The half-joint made of reinforced concrete are the most challenging types of structures and as a result, their assessment is, inspection and repair are susceptible to the type of construction and deterioration with time. Deterioration of the reinforced half-joints occur as a result of corrosion process that take place on the surface of the metals used. Steel is an alloy containing iron which in turn react with oxygen and moisture to produce rust. Moisture gets into the inner surface through the leakages that arise in the joints (Lees, Parks and Morley 2013). Rust makes the surface of the metal to deteriorate with time and this weakens the joint. Besides, corrosion induces the amount of stress hence reducing the safety of the bridge. More worse about the related bridges is that its assessment and maintenance due to their location underneath or over live traffic roads makes the situation more complicated. According to Lees, Parks and Morley (2013), all these challenges compounded with limited access to the bearing seats joint creates maintenance and inspection issues. Both inspection and maintenance become challenging since the structural details at the beam seat region are potentially sensitive (Desnerck et al., 2018). During the initial construction, the some of the structural vulnerabilities arise and can continuously deteriorate leading to serious problems. Such and other challenges have led to the collapse of the structures such as the Concorde Overpass Collapse, which collapsed due to the vulnerabilities in the structural half-joint (Lees, Parks and Morley 2013). According to Desnerck, Lees and Morley (2018), the collapse led to the deaths of five people albeit, it led to an urgent demand for emphasis on the significance of the proper inspections adequate assessment and maintenance techniques.

Due to this complexities, Desnerck, Lees and Morley (2018) posited that reinforced concrete half-joints should be handled with special care in accordance with the asset management programmes. Elsewhere, Desnerck, Lees and Morley (2018) posited that the rising volumes in traffic and load demands in the midst of limited resources, calls for use of assessments that are both accurate and strong. An asset management databases is such a suitable programme that aids in the assessment of the half-joints. Such measures would be suitable in helping the asset managers to allocate the limited resources in a better way especially to critical structures such and half-joint structures (Desnerck, Lees and Morley, 2018).

Besides, the most suitable methods of assessment of the half-joint is the non-destructive methods, and others include the testing and invasive inspection (Desnerck et al., 2018). It, therefore, becomes plausible to arrange and detail the reinforcement of the beams when the half-joint are performing. There are various standards that have been developed such as the Initial Special Inspection (SMIS) that regulates the inspection of the half-joints in the bridges. The standard stipulates that inspection need to be done within a period of six months. However, in case of special inspections, the inspector determines if further assessment or inspection is needed. Agents are obliged to verify that the information in regard to the half-joints is adequately reported. During monitoring process, the visual approach is generally the most prevalent technique used to measure the strain and the movement gauge. Both destructive and non-destructive techniques are suitably used in the monitoring of the half-joint (Beng, Mice, and Thorogood, 1987).

References

Beng, C., Mice, C. F., Thorogood, P. (1987). Serviceability Behaviour of Renforced Concrete Half-Joints. Structural Analysis Unit. Berkshire

BS 5400: Steel, Concrete and Composite Bridges: Part 4. Code of Practice for Design of Concrete Bridges. BSI, 1990. [Implemented by BD 24]

Desnerck, P., Lees, J. and Morley, C. (2018). Strut-and-tie models for deteriorated reinforced concrete half-joints. Engineering Structures, 161, pp.41-54.

Desnerck, P., Valerio, P., Lees, J. and Loudon, N. (2018). Suggestions for improved reinforced concrete half-joint bridge inspection in England. MATEC Web of Conferences, 199, p.06004.