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CROSS Safety Report

Concrete half joints

Report ID: 88 Published: 1 January 2008 Region: CROSS-UK

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Overview

Poor reinforcement detailing and installation in a half joint led to the collapse of a series of beams and precast concrete slabs.

Key Learning Outcomes

For the construction team:

  • Quality control and competent supervision along with a well documented inspection regime on site can help to ensure that the structure is built in accordance with the design

For civil and structural design engineers:

  • If possible, attend site to inspect the installation of critical structural elements such as concrete half joints prior to concrete being poured

  • If you are unable to attend site, ask the contractor for site photos of the installation of critical structural elements

Full Report

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Half joints in concrete structures have been used successfully over many years notably in bridges and buildings, says a reporter. They can offer great advantage in terms of construction and design although their performance depends on good design and detailing and maintenance. Failures in half joints can happen if reinforcement is not detailed properly.

Recently the reporter’s firm has come across a half joint in some precast beams with a very poor reinforcement detail. The beams were erected as planned. However due to one of the defective joints failing, a collapse was initiated which caused the subsequent collapse of a series of beams and precast slabs as shown in Figure 1. The investigation revealed that the position of the steel dowels (for shear) and reinforcement in the beams was incorrect and not sufficient to withstand even dead loads.

Image
Figure 1: precast concrete slab collapse

Expert Panel Comments

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Half joints can be satisfactory in buildings but are not now recommended in external situations where they may be subject to weathering. The Highways Agency says that half joints in bridges pose a risk as due to difficulties of access they cannot be maintained properly. This is in addition to risks that may exist from design or construction defects. In many cases in buildings the thickness of the nib will be small so that the position of the reinforcement is not ideal. Joints should, so far as is possible, be positioned so that they can be inspected and then maintained if necessary.

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