Background

Although this is rather an old story, dating back some twenty years it does demonstrate that, when it is needed, the ability to reconstruct in a controlled environment the situation that led to a dispute can be invaluable.

An extension to the children's hospital at Great Ormond Street encountered difficulties even before it was completed, concrete cracked and the catalyst to a comprehensive investigation was the collapse of a reinforced concrete walkway beam.

Methodology & Results

The subsequent investigation focussed around the consulting engineer that designed the extension, the case being so large that it was sub-divided into a number of issues.  The first of these was the performance of the pile caps supporting the extension, which had cracked.  The company responsible for the designers insurance faced a potentially huge bill based upon the Health Authorities estimate of the repair bill which was based in turn on the advice of their  retained consulting engineer.  The heart of the problem technically was that the reinforcement that was placed in the pile caps under the supervision of the designer was a fraction of that necessary.  The issue then became the size of the repair bill.  The designers' insurance company retained the services of a number of senior consulting engineers from leading practices to consider alternative repair strategies.  However in the circumstances a comparatively simple paper exercise would not suffice and a practical demonstration that alternative strategies were viable was essential.  CERAM was engaged to supply this practical support.

The consortium of consulting engineers developed their ideas as to economical repair strategies and these needed to be tested out in practice.  A full scale reconstruction of an under-reinforced pile cap was cast at CERAM, this was then mounted onto five large diameter hydraulic cylinders, each intended to represent the piles on which the hospital was founded.  Small movements were introduced using the jacks so that the pile cap cracked in much the same way as in the real situation on site.  The proposed repair strategy was applied, which involved post tensioning the pile cap to restore its resistance to bending and shear and the repaired pile cap was tested to demonstrate that it could adequately resist the design loadings.

Conclusion

The result of the exercise could not reduce the designers' responsibility for the errors but did significantly reduce the amount the insurers had to pay.  The reduced payments more than compensated for the work undertaken by the consortium of engineers and CERAM in proving the alternative repair strategy.