A NEW 33 storey five star London hotel was this week still waiting for full local authority building regulations approval despite being open to the public for more than a year.
Building inspectors have withheld full approval for the Marriott Hotel structure on West India Quay in east London because of concerns about the safety of its ultra-thin prestressed slab floor system.
NCE understands that there is no immediate cause for concern about the building's safety. But checking engineers want reassurance from the floor system's Australian designers that the system will comply with UK design codes.
Instead the hotel has been operating since it opened in November 2004 under an interim occupation before completion certificate. This allows the building to operate even though it is technically incomplete.
The building is owned by West India Quay Developments.
It was built by contractor Multiplex who in turn subcontracted the floor design to Australian consultant Structural Systems.
Tower Hamlets Council granted the occupation before completion certificate. However, a spokeswoman said it was issued even though 'elements of the design in the post-tensioned concrete floor slabs based on an Australian design are under discussion'.
The prestressed thin floor slab design used by Multiplex is relatively new to the UK.
Structural Systems claims the design reduces loads on the building structure and that the reduced thickness means developers can fit 25% more storeys into a building's height.
However, building inspectors are concerned that the floor system used at West India Quay is out of specification and has demanded calculations from Multiplex to prove that it is safe.
NCE understands the 200mm thick floors are cast with steel stressing tendons spaced at 2,150mm intervals running in two directions at right angles across the slabs. The floor slabs span up to 9.5m between columns.
These spacings go beyond those recommended in a Concrete Society report which is being used by Tower Hamlets checking consultant Cameron Taylor Bedford to assess the structure for building regulations compliance.
Concrete Society Technical Report 43 says 'the maximum spacing between tendons should be restricted to 10 times the slab depth'. But the Structural Systems' floor design contains tendons which are spaced at almost 11 times the thickness of the floor slab.
NCE understands that Tower Hamlets' consultants have asked Structural Systems to provide calculations to demonstrate the slab system's ability to cope with loads. They are especially interested in load bearing calculations for slab areas containing ducts.
Confusion over the whereabouts of Structural Systems' calculations - first requested by the Council in February 2004 after planning permission was granted - has delayed full building regulations approval.
It is understood that the Council checking consultant was unable to find the calculations in a box of documents received from Multiplex.
Multiplex insists that the correct calculations were sent to Cameron Taylor Bedford along with other documents.
It claims the calculations were lost and had to be resent.
Structural Systems manager David Pash defended the thin slab system, saying: 'there is nothing wrong with that design'.
The West India Quay building contains 301 hotel rooms plus more than 200 private apartments.