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CROSS Safety Report

Failure of load test setup

Report ID: 469 Published: 1 October 2014 Region: CROSS-UK

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Overview

A load test setup used to test a composite steel girder failed due to over estimation of the capacity of the supporting member.

Key Learning Outcomes

For construction professionals:

  • It is good practice to have a load test arrangement designed and assessed by a suitably qualified engineer to ensure the members can accommodate the test load

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A composite steel girder was designed to support the platform for a Metro Rail station, and it was decided to do a working load test on it at the fabrication yard before erection (Figure 1 & 2). Unfortunately, the load test setup failed due to over-estimation of the capacity of the Indian standard steel beam (ISMB) provided for supporting the girder.

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Figure 1: test load setup
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Figure 2: remains of the supporting beam

An investigation into the failure found three contributory causes: 

  1. A detailed 3D analysis simulated the design bearing load over the ISMB-300 member and it was found that the stresses in the member were more than three times greater than yield strength
  2. The design size of the elastomeric bearing pad was greater than the flange width of the ISMB300 so the bearing area was insufficient
  3. The main cause of the failure of the load test was the lack of proper stiffening plates

Expert Panel Comments

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Assuming that it was an overestimation of the strength of the supporting member then the lesson is that test rigs should be designed to the same level of detail as the piece being tested. Safe working loads need to be defined for the test rig, as often the tested piece may be significantly stronger/stiffer than expected and loading to deflection/failure criteria of the test piece can fail the rig.

As is so often the case attention to detailing is required. All elements on the load path need to be looked at - there is always a weakest point.

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