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CROSS Safety Report

Failure of cast-in lifting anchor on precast twin-wall

Report ID: 637 Published: 1 January 2018 Region: CROSS-UK

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Overview

A precast reinforced concrete twin-wall panel was being lifted when one of the cast-in lifting anchors suffered a brittle failure.

Key Learning Outcomes

For precast manufacturers and suppliers:

  • Quality assurance and competent supervision in the precast yard can help to ensure that precast elements are constructed in accordance with the design

  • Consider introducing a quality control procedure for the inspection of safety critical connections such as cast-in lifting anchors

  • A pre-pour and post-pour inspection of lifting anchors can help to identify if they have moved or become dislodged during the pouring process

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A precast reinforced concrete twin-wall panel was lifted approximately 500mm from the tilting frame when one of the designed cast-in lifting anchors suffered a brittle failure (Figure 1). This resulted in the panel swinging from the remaining lifting anchor causing minor damage to the panel, according to the reporter.

The remaining lifting anchor held allowing the panel to be placed safely back on the tilting frame. Due to the planning, control and safe lifting practices adopted for this operation, there were no injuries as a result of this component failure.

Due to the planning, control and safe lifting practices adopted for this operation, there were no injuries as a result of this component failure

Identifying the root cause

In order to identify the root cause, a portion of the failed lifting anchor along with an unused proprietary lifting anchor supplied by the manufacturer were sent to a laboratory for examination. It was concluded that the failed lifting anchor was manufactured from rebar of the same diameter as the specified product.

However, it had been bent to a diameter significantly less than the minimum allowable diameter, as shown in Figure 2. Additionally, the pattern of ribs on the rebar used for the failed lifting anchor indicated that it was of a different type to that used in the proprietary lifting anchors.

Quality control failure

The reporter states that the cause of the significant near miss was a quality control failure during the manufacturing process. The laboratory identified in their report how a visual inspection could identify proprietary and non-proprietary lifting anchors. The reporter now incorporates this visual inspection into all subsequent lifting operations.

According to the reporter, it is essential that all parties involved in the procurement of precast items carry out the necessary checks. This can help ensure that all off-site manufacturing is carried out in accordance with an agreed inspection and test regime such that bespoke items of precast concrete are manufactured strictly in accordance with the design and specification.

The reporter states that cast-in items including lifting anchors should be itemised on the pre-pour and post-pour checklist and inspections and tests should be carried out and recorded by an independent person at planned stages during production and before release for delivery.

Image
Figure 1: brittle failure of cast-in lifting anchor
Image
Figure 2: bent diameter of cast-in lifting anchor

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