The ODA said it has already showcased the bridges, highways and other infrastructure projects to interested contractors.
RIBA London chairman, Andrew Hanson, who has been campaigning for smaller practices to be considered, said: '[This is] very disappointing to hear, and it flies in the face of what the ODA has been telling us before. We were told they would be using competitions wherever possible.
'I understand that some of the work, such as drainage systems, should be contractor-led, but certainly some of the bridges would have been a fantastic opportunity for smaller firms to get involved.'
The ODA said it will be dividing the number of contract packages depending on size.
An ODA spokesman said: 'It wouldn't be viable to have 12 different people doing 12 different bridges, and we want to keep these structures relatively uniform in design.'