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Republic Plaza, with a structural height of 281m, is the tallest building in Singapore. This paper describes measurements of dynamic properties made during the construction period and the detailed modal description obtained for the completed, but unoccupied, structure. The dynamic characteristics show that, despite the apparent simple symmetry, which leads to two very close fundamental translational natural frequencies, many of the higher modes have strong torsional components whose nature has
been determined in the measurements. Finite element modelling of the core wall/steel framing system gives reasonable agreement with the measured translational fundamental frequencies but, without a high level of refinement, cannot reflect the torsional behaviour. There is no evidence that the curtain wall system affects stiffness or damping properties of the structure at low excitation levels.
J.M.W. Brownjohn, T-C. Pan and H-K. Cheong
Dr J. G. M. Wood (F) (Structural Studies & Design Ltd)
I have wrestled with this problem, and my experience confirms a number of points. I think Professor Clark has made a lot of very important new points, and the thing that I think we need to tackle is, you are on a site; the contractor has just built a beautiful column. He is already 1 week late with the contract; the cover is not quite good enough. Do you ask him to tear it down, or is there another simple remedy for his problem, for the owner of the structure and the contractor? In Canada, for failure to achieve strength, they put a standard penalty clause into the contract. If you do not quite get the strength, you live with it, but it hits your pocket, and with some structures you can say to the contractor, ‘right, cope with it’, but you cannot do that in columns at the entrance to a public library where the architect delivers the structures. I think we have got to face up to what you do when you find the cover is wrong,. because a lot of the problem on site is that, when the cover is inadequate, there is not a procedure for remedying this which is sensible within the overall constraints of getting the job done. I think that we need to address that because, if the cover is not quite good enough, but the concrete quality is better than specified, you can allow it through. I think we need to have a strategy in which the client, the Resident Engineer and the contractor can resolve difficulties - I am trying to use non-confrontational language - on site; how does Professor Clark think we can move forward on the site?
Mr R.A. Webb (Prescott Consulting Engineers)
I would like to ask for futher information on the following points from Mr Maranian’s paper.
(1) Fig 1 types 3 (b) & (c) show cracks starting away from the backing strip, and thus it is assumed that they started at some form of inclusion. Is it known how good the original NDE work was -were any inclusions within the Code limit? If so, do these need modifying?