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Subject:	Great Ormond Street Hospital
Date:	July 2004
Source:	Construction Manager

 

A problem solved at Great Ormond Street Hospital

 

 

One of the UK’s leading curtain wall and glazing companies has come up with a novel way of solving a construction problem.

 

English Architectural Glazing, based in Mildenhall, Suffolk is part of a group working on the new wing of Great Ormond Street Hospital. With other construction partners the firm has built a life size model of a section to ensure all the elements fitted together before embarking on the real thing. At £40,000 it’s estimated the GOSH rig has saved £300,000 in potential build costs. Ken Bright MCIOB, EAG’s Construction Manager for the project looks at four different ways the mock up helped in pre-construction.

 

These bespoke glass louvres are included in the 2 courtyard screens and allow permanent ventilation for smoke and heat should this occur on any one of the Hospital floors.  The curtain walling and glass louvres create a ‘cascading’ effect to each of the upper floors.  The design of the glass louvres was unique and the design was developed from initial sketches produced by Anshen Dyer.  The louvres are constructed from polished stainless steel arms, hung from a suspension rod carrying glass blades. The glass blades have counter sunk holes for the fixing screws, allowing a flush face to the louvre blade.  The arms were also manufactured to allow bird wires to be incorporated and these wires provide an almost invisible barrier against bird entry.

 

The complete design was unique and as such made structural modeling difficult to apply.  Once the glass louvres were installed on the mock-up, we took the opportunity to check the rigidity of the glass louvre system.  This found that the suspension system – rods and arms – had a greater deflection to that was reached from initial structural calculations.  Upon close inspection of the rod and arms, and under a typical wind load, it showed that although an almost interference fit was being used, small individual movements on each connection allowed excessive deflections; in the same way a bicycle chain would produce a cumulative  and disproportionate movement.

 

With the observed test results, a new method of calculating the deflection confirmed the excessive deflection.  A number of alternatives were considered to lessen the deflection, and working with Anshen Dyer, an agreed structural and aesthetic solution evolved.

 

The final solution involved using a laminated glass fin using toughened glass in the make up of the laminate. The fin was positioned behind, and attached to, the glass louvre suspension rod. 

  

Bringing together the whole project was a major co-ordination job. EAG were the first envelope subcontractor to be appointed and took the lead role in design and dimensional co-ordination. This involved a number of key disciplines.

 

Bricks were purpose made for the project in Germany following ‘set out’ of elevations. There were specials generated for mitres on both internal and external corners.  It was crucial to ensure they fitted and worked according to the design. The structure of the new wing was replicated on the mock up with a steel frame.

 

A real benefit of this approach was the highlighting of blind spots in the design once the structure was applied to the frame. As a result the only effective way to remove these blind spots was to use a BOCAD 3D modeling technique thereby removing the unknown, undefined details. This was a huge potential cost saving. If the mock up had not been created the blind spots would have been found too late while on site.

 

The designer working on the mock up was in regular contact with all other trade contractors and quickly grasped a detailed understanding of their product and its abilities and limitations in respect of application. This allowed all the contractors to see how they’re part of the project fitted in with each other allowed close dialogue long before they were on site.

  

Waterproofing was a major part of ensuring the building was fit for purpose. The bringing together of a coordinated waterproof line for the elevations and detailing effective junctions between the various trades was made possible despite the lack of off site water testing.

 

Bringing the trades together resulted in a cost saving for off site testing and speeded up the process by reducing the lead time to site installation. It also allowed for agreed areas of responsibility to be established for waterproofing.

 

It was essential to have these early discussions between contractors because it enabled the technical detailing of the connections and interfaces to be ironed out and agreed way in advance thus saving time while on site.

 

The mock up allowed EAG to carry out testing of sealants and membranes for compatibility, performance and stain migration. In total 9 material types were involved in this process. The chance to test all these materials allowed EAG and its partners to see if they would be any issues arising once the on site team were underway. All the elements worked well but the mock up testing prevented any hold ups while working in the busy streets of London.   

  

The huge bonus the GOSH rig delivered was the chance for the architect to review his theoretical design in actual life size dimensions. It also enabled him to look at colour texture and component types in their relative positions.

 

We had the chance to determine first and second fix items and as a result we were able to detail a short term programme thus enabling us to maximise our use of resources. What the mock up confirmed for us was that EAG was the lead envelope contractor with our first fix items setting out the brickwork.

 

This allowed all the trades to stand back and assess their own components and allowed a real timeline for the actual construction to be set in advance. This prevented any hold ups on site and gave all the partners the chance to work out the time they would need to spend on site.

 

This in turn meant that the site construction programme was adapted as a direct result of all partners working on the mock up. Had this not been achieved we would all have been feeling our way on site which could have delayed the project. Working out each of the construction sequencing in advance prevented any time loss which meant we could all be on and off site in the shortest possible time. 

 

There is no doubt that bringing all the envelope features together including Brick (stack bonded) Aluminium feature channels, glass louvers, Schuco curtain walling and window profiles, composite windows, glass, handrails, roof paving and support structure and Hydrotech roofing membranes in advance and fitting them together on the mock up made this a cost effective project that saved us time and the client money.

 

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