Engitect Issue 3

The House of Lords - The Stent Shuffle - Secant Pile Walls - CDM and All That - New Department Stores for JLP - Partnership News - And Finally...

ENGITECT

Issue Three - Summer 1998

 

 Introduction

Welcome to the third edition of Engitect, Hurst, Peirce and Malcolm�s newsletter. Our aim is to keep in touch with our clients and friends in the construction sphere and to build on relationships which in some cases extend back to the 1920�s.

We were pleased to find that our photograph in the CDM section of the previous edition showing the Greek painter working precariously at height prompted many of you to write to suggest appropriate captions. More about this later.

We hope you will find this edition interesting and informative.


The House of Lords

In 1995 we were commissioned to provide structural engineering advice for the refurbishment of the main roof over the House of Lords and Royal Gallery at the Palace of Westminster. The brief was subsequently extended to include an adjoining roof and also the introduction of supplementary timber framing and support work to the ornate ceiling over the Royal Gallery.

The House of Lords was built as part of the Palace of Westminster redevelopment designed by Charles Barry, between 1845 and 1850 and was a major engineering structure of its time. Trusses with cast iron compression members and wrought iron tension members span 46 ft. over the chambers. The trusses support a lower ornate timber ceiling and an upper fireproof ceiling of tile creasing arches.

The roof covering comprises cast iron pan tiles measuring 800 x 800mm bolted to wrought iron rafters which are supported on cast iron purlins spanning between the trusses. One of the original truss drawings is reproduced below. This was the first use of cast iron tiles for roof tiling in this country. The idea was imported from France. To afford better corrosion protection the tiles were galvanized. However, after a few years the galvanizing started to break down and rust patches appeared. As a consequence the tiles were painted and the painting has been repeated from time to time ever since. After 150 years it was time to give the tiles a major overhaul. Otherwise, apart from a few fractures to lugs on the cast iron purlins, and leaking, a matter about which Members were less than happy, the roof has performed well.

  House of Lords Roof Truss

The roof also suffered a direct hit from a bomb during the second world war but fortunately with only slight damage.

A pilot study had been carried out by others to assess the feasibility of the roof refurbishment, including the removal of the cast iron tiles for re-galvanising, and with repairs to fractured elements and fittings. One concern was that the extreme thermal range of 70 degrees Celsius to which the tiles are subject was straining the roof and causing fractures to lugs at the end connections of the cast iron purlins. We arranged for the thermal range and relative movement between the roof elements to be monitored during a very hot period and were able to show that with minor modifications to the tile fixings there was sufficient slackness in the roof to accommodate the movement.

Removal of the roof tiles meant that the trusses lost their lateral stability. Rather than introduce an unwieldy system of temporary bracing we were able to devise methods of stiffening the existing cast iron purlins to allow them to act as props.

To keep out the weather, the whole roof was encapsulated in a scaffold enclosure rising some 30m above ground level. The scaffold was portalised and with a minimum of ties to the main structure was a major engineering structure in itself. It required detailed interactive analysis of the scaffold frame by the scaffold designer to satisfy us that neither the scaffold nor the ties to the structure would be overloaded under high wind conditions. The roof works are complete with the repairs to the Royal Gallery ceiling due for completion late this year. 

It is slow because the working hours are restricted to the times when the Lords are not sitting and the Lords sit for more days per year than the Commons.

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The Stent Shuffle

Question: "How many items of plant can one safely operate on a site measuring 12m x 24m?"

Answer: "Quite a few actually."

The question arose when one of our clients decided to proceed with works associated with a hotel development in Knightsbridge. The development is to comprise a luxury hotel with around 200 bedrooms.

The full site is �L� shaped in plan measuring a maximum of 40m x 30m. Five basement levels will be required to accommodate support and �back of house� facilities making it one of the deepest basements in central London.

The perimeter wall is to be formed with secant piles, the construction of which is described in the panel. Even though only part of the site had been cleared and an existing occupied building covers the majority of the area, an opportunity was identified which would hasten the development phase of the project.

Research led us to believe that it was feasible to bore five secant piles across the entrance to the area that had already been partially cleared. Installation of these piles would release this area as the site entrance. Thus, a works package comprising the demolition of a 12 metre free standing wall restrained by flying shoring and the installation of 5 secant and 2 �dummy� piles was prepared and tenders were sought.

The �dummy� pile bores are filled with sand so that the wall can be continued under the next phase of work.

The work had to be carried out to a strict 2 month timetable during November and December of last year.

Griffiths McGee were appointed to carry out the demolition work and Stent Foundations the piling work with Bovis Construction as construction manager and Arup Project Management overseeing contractual matters.

Stent Foundation Work

As you can see from the photograph the site was extremely cramped when the Casagrande C50hydraulic rotary piling rig complete with oscillator was delivered to join the service crane, and mechanical excavator, together with associated plant equipment and not forgetting, of course, the ready mixed concrete truck. However, with careful site management, progress from delivery of the piling rig during the night of 26th November 1997 to its removal on 18th December 1997 was rapid.

The depth of secant cut is in excess of 28 metres which we believe is as deep as has been successfully achieved. Systematic checks on the vertical alignment of the piles using an optical plummet/inverted plumb-bob and total station showed that the accuracy exceeded expectations

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Secant Pile Walls

Secant walls are formed by concrete piles which have a positive interlock with adjacent piles. The sequence of construction is for primary (female) piles to be installed at a spacing to allow intermediate (male) piles to be cut into the female piles. Normally a thick wall casing is oscillated through the female concrete which is of a suitably low early strength, in order that it can be cut. The female piles may be reinforced as well as the males and thus can be used for high lateral loads. The use of casing oscillators ensures a high degree of positional and vertical control and the system is ideal for irregular plan shapes.


CDM and All That

You may recall the article from our last Newsletter which included a photograph of a decorator perched extremely precariously at eaves level on a two storey Greek Villa on the Isle of Chios. A number of readers suggested a caption for the painters colleague standing at ground level in the foreground of the picture.

They included the following:

"'Hey, Zorba, you �ave meezzed a bit.'�

�Stop complaining � Michaelangelo didn�t have all that scaffolding when he was painting the ceiling.'

'Zorba, whatever you do, don�t stand back and admire your handiwork.'"

However, by a unanimous decision of the judging panel Michael Ney�s submission of:

"Man in foreground - 'Oi, Spiros, why don�t you put that board horizontal.'

Reply- �You forget, Yanis, it�s easier like this now my right leg's 50mm shorter since the last accident!�"

was adjudged to be most appropriate. Michael is awarded a bottle of champagne and many thanks to all those who took the time and trouble to reply.

Perhaps you would like to put your mind to the next caption competition. This lion was photographed recently in New York. Suggestions please for what Barry Pitcher is saying to his wife who is taking the photograph.

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Answers on a postcard please addressed to the editor. The winning entry will receive a bottle of champagne

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New Department Stores for JLP

HPM are assisting the John Lewis Partnership with the fitting out of two brand new department stores. One forms a major anchor tenancy on the �700m Bluewater development near Dartford / Ebbsfleet in Kent and the new store in Glasgow is the largest unit in the brand new Buchanan centre at the eastern end of Glasgow�s main shopping thoroughfare, Sauchiehall Street.

The 30,000m� (300,000 sq. ft.) Bluewater store is laid out to trade from 3 levels with stock holding and support facilities in a basement that extends the full width of the retail areas above. The Glasgow store is slightly smaller in terms of overall floor area and will trade from 4 floors reflecting the limitations of the more constricted city centre site. As might be expected, both stores have extensive mechanical and electrical plant, many of which are high quality factory assembled modular units. The largest of these is the generator mounted on the roof at Glasgow, which weighs about 14 tonnes. Part of our involvement has been to ensure that these units can be lifted and supported at the desired location on each building.

The development teams include John Lewis architects, H & V and electrical engineers with Brooker Flynn Architects providing assistance on Bluewater and Legge Ericsson Architects at Glasgow. Davis Langdon and Everest are quantity surveyors to both projects. Both stores are due to open in early 1999.

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Partnership News

We would like to welcome two new members to our technical staff, Peter Bucher and David Hall. Peter brings the skills he learnt when working in a District Surveyor�s office to bear on our review work for the Grosvenor Estates and other projects where we assess tenants work on behalf of major property owners. David has joined our CAD staff to keep pace with our expanding workload

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And Finally...

Continuing our series of articles from the 19th Century on building practices and hazards to health here is one to make the Planning Supervisor go very pale! The article is taken from a book by T. Pridgin Teale, M.A., surgeon to the General Infirmary at Leeds, published in 1879, entitled Dangers to Health.

Arsenical Wall Papers.

T. Pridgin Teale records that incidences of ill health after sleeping in newly wall-papered rooms were common in the mid-19th Century. Research concluded that almost all colours used in paper staining during this period contained arsenic. So beware all those who are involved in the refurbishment of properties from this period where multi-layers of wallpaper are discovered!

Stripping poisonous wall papers

Readers will note that 19th Century decorators were unusually small men, or perhaps the rooms were particularly lofty!