This week we were presented a problem by Arup, the largest consulting engineering firm in the world. The problem revolved around the renovation of Queen St station here in Glasgow, and the challenge of maintaining normal operations of the station as a passenger hub and management office suite throughout the necessary demolition works and subsequent construction phases of the new station façade.
The task of producing a comprehensive program of works is an extremely complex one, which must take into account each and every step of a project from beginning to end and to complicate matters is that there is not necessarily an obviously more efficient method when approaching the task initially. The skeleton of thedesign of a program must follow the 'critical path', which identifies the key points which must be completed before another item on the program can proceed. This acts as the primary source of constraints to a proposed project time-line, and takes into account: lead-in times for specific jobs, key deadlines, necessary prerequisite jobs, windows of time within which specific works can occur and critically; limitations on existing functionality that cannot be lost throughout throughout the project.
In the case of Queen Street station, we were informed that the restraints comprised a list of services which must always be available during operating hours of the station and a list of key dates before which some sections of the work must be completed, or only after which certain works could proceed. The most critical of these were the need to have, at all times, at least two entrances in operation within the station, enough floor space for normal foot traffic, and accommodation for the drivers and managers within the station.
The project we were to construct our program for involved two phases, demolition followed by construction, and the first challenge was to decide which components of the demolition would be approached first, and identify the impacts these would have on the site operation. The principle portions of the existing building that were to be demolished were the existing managers offices and drivers accommodation, Consort House and the Millennium Hotel extension. Each had their own difficulties.
Consort House is a tower building of reinforced concrete on the corner of Dundas St and West George St. built in the 1970's, as such it will have to be checked prior to demolition for the presence of asbestos which adds a significant time delay before demolition can occur. Furthermore, due to its structural design, the method of demolition will have to be to remove components piece by piece working from the top down in order to ensure it does not collapse in an uncontrolled fashion. The Millennium Hotel extension is a more recent construction of a steel frame clad in concrete for fire protection. This design makes it much more easily removable in slightly larger chunks. The challenge with doing so is that the three storey structure spans across the existing south entrance, and so contingencies may need to be made to accommodate the lack of an exit in this direction. Both of these structures also face the problem of where their spoil will eventually be removed as there has been opposition to utilising the busy West George street any more than necessary. The principle problems revolving around the current offices, is the need for new offices to be made available prior to their demolition, and also their possible tie-ins to the roof support structure which is to be left in place throughout the renovation.
From the construction side, the requirements we were to address were for a new basement to be dug beneath the existing hotel extension and tower building, new massive truss structures which would have to be lifted in in four sections each into the southern and western edges of the new building, a new ticket office which would be replacing the to-be-demolished existing arrangement, new offices, and extensions to all four platforms including electrification. The interesting challenge from these as the visiting engineers pointed out was the method of placement of the large trusses which would bear the load of the new roof to cover the atrium and also provide more support to the existing end arches on the existing roof. The lifting of the large components into place would require a large crane which would likely require its own foundations to be set, something which would be dependant on where the crane would have to sit and if any existing buildings on that site had to be demolished first. It was obvious a lot of thought had been put into deciding how best this would be done.
The value in this workshop was in seeing the massive variety of solutions to the problem presented by the Arup engineers. There were several proposals all with different time scales and methodologies regarding how and when to demolish the existing offices, some favouring early demolition following temporary structure completion in the car park, allowing for greater manoeuvrability within the station for installation of the western edge truss. Others chose to concentrate on the southern façade and speedy completion of the basement and new southern entrance due to pressure from the local council, facilitated by early demolition of the hotel extension and Consort House, both if which would require great care to ensure no damage was done to the arched station roof, or indeed passing pedestrians entering or exiting the station. This option was one favoured by my own group which wanted to focus on completion of the south entrance so as the eastern and western could be closed in turn as demolition and construction around them dictated exclusion of the public for safety reasons. What was intriguing though was that this by no means the only option for allowing these works to continue.
Another interesting lesson from this workshop was to work on identifying what the site itself can bring in terms of solutions to any of the problems that arise from such a complex project. In the case of the train station undergoing demolition, it was interesting to see the suggestion that trains rather than roads be used to remove the spoil from site. This would remove the need for negotiation with the council over use of the approaches and exits from the busy city centre with demolition spoil on large trucks. However the cons against using such a method were that it would require almost constant access from any of the demolition sites to at least one of the four tracks which run into Queen St. this is something which could not be guaranteed as it is a solution which would require large proportions of the public space for storage and haulage of the spoil. One other technical difficulty which would need to be overcome would be the presence of electrified lines running above the tracks which have a minimum exclusion zone around them. The innovation of the idea however was extremely interesting though.
Ultimately, the largest lesson of the night was that identification of the most economical path from design to reality is not always clear and fraught with negotiations through a long list of constraints and ever changing requirements and requests from stake holders ranging from local authorities, the clients and industry standards.