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High rises with a cutting edge

SITE REPORT

Construction management may have had a bad press in recent times, but the team behind the City of London's next big office project, 51 Lime Street, is determined that this form of procurement method is the best way forward. Alasdair Reisner reports

WITH SUPERMAN it was Kryptonite. For Captain Scarlet, high-voltage electricity. Werewolves usually fare badly with a silver bullet. But what about the construction industry?

What is its Achilles' heel?

The recent evidence would suggest that it is construction management - a form of procurement that should surely have wise contractors running scared.

Recently, the ill-fated (and construction-managed) Scottish Parliament project set new records for lousing things up as costs ballooned from £40 million to more than £400 million.

The explosive Holyrood Enquiry report into the project concluded: 'There were some catastrophically expensive decisions taken and principal among those was the decision taken to follow the procurement route of construction management' Then came a damning judgement on the Great Eastern Hotel in the City of London. Laing was forced to pay £10 million damages after completion of the infamous construction management deal was delayed by 44 weeks and almost doubled in price. Construction management certainly doesn't seem the flavour of the month.

Yet, just a short walk from the site of this debacle is 51 Lime Street, the location of the London's next major office scheme.

With a total area of 60,000 sq m across two towers of 29- and 10-storeys, the job is both complex and challenging.Now take a guess on what form of procurement Mace is working under to deliver the shell and core of the scheme.

'I've been working in construction management since 1984. I think it is the way to go.You are working as a complete team from client through to contractors.You are working with a common goal, ' says Nick Moore, Mace's operations director.

Under construction management, the contractor manages the project for a fee while the works are carried out by subcontractors working directly for the client.The benefit of this system is that it allows each firm involved in the project to declare its profits and overheads upfront, giving comfort to its board.

It also avoids conflict with a main contractor looking to make claims and trying to screw subcontractors down.

The truth is that construction management can be successful if the client knows what it wants and those involved work together, as Mr Moore hopes.

To allow this to happen, the 51 Lime Street project has been broken down into four zones or clusters, each managed by a Mace project manager.

'These clusters incorporate the trade contractors, designers, the construction manager and the cost consultant. Everyone has the common goal of creating the best project possible.There isn't necessarily competition between the clusters because they start at different times, ' he says.

Some key workers are involved in more than one cluster, both allowing their skills to be used across the site and offering a simple method of communication between the clusters.'People talk to each other.There is no them and us. It allows much freer flow of information, ' explains Mr Moore.

The team also benefited from a process that is becoming increasingly vital to successful construction projects - early contractor involvement.

'We've been given the opportunity to select the contractors that we have a relationship with.

They are people we have a history with and know we can rely on.As a result, we have brought these guys in on a service agreement. It isn't the overall cost of the packages but compensation for their early involvement.That allows a lot of information flow between them and the designers, ' adds Mr Moore.

For example, five floors of plant had to be installed in the building at high level. By bringing in the plant manufacturer at an early stage, this equipment can be prefabricated, allowing it to be simply craned up and slotted in once the building has reached the correct floor height, rather than stopping the works to allow construction of the plant on site.

Early contractor involvement also allows the 51 Lime Street team to guarantee another key construction resource - project staff.

'When we are negotiating the packages, we are not just selecting the contractor but also the staff.At the end of the day, if you get the wrong man for the job it doesn't matter who he works for.You've got to get the right people.'

In an industry where workers often don't know where they are going to be working in a week or a month's time, bringing the team on board early has ensured that Mace gets the right men for the job.

'We ask for the people and because we have come so early we have the opportunity to get the right people, even if they are currently employed on another job.Their bit of our project might not be starting for another six months but we have got them booked.'

While the 51 Lime Street scheme has barely popped its head above ground level, it is impossible to predict how it will turn out. It is entirely possible that it could end up being another blot in the copybook of construction management. But, given the professional approach of the whole project team and the innovation that is involved in its construction, it is fair to hope that the scheme will actually mark a turnaround in the reputation of construction management.Mr Moore certainly thinks so: 'In the past, clients may have wanted the security of a guaranteed maximum price.That is okay, but you have to realise that you are paying a massive premium with GMP.

'In reality, why would you need to do that if you have the right team? If you have the right consultants, you can almost guarantee the price anyway. I think construction management is the right way to go. I always have.'

Concrete or steel

LIKE THE decision to go down the construction management route, the structural frame of 51 Lime Street also breaks with the recent trend for concrete frames.While post-tensioned concrete is all the rage for towers such as West India Quay in the Docklands, the new Beetham Towers in Birmingham and Manchester and Bridgewater Place in Leeds, 51 Lime Street will return to the old convention of a steel frame around concrete cores.Why the change?

'I loved the idea of using post-tensioned concrete as I have a lot of experience of it from work I've done in the Far East, ' explains Mr Moore.

Yet when the team looked at the weight issues associated with the use of post-tensioned concrete, it would have meant that the piles required for the building would have to be larger.

'In the City, the piles you would have to use would have to go down into the Thanet sands.You are then talking about bentonite, which is slower and more expensive.That precluded the use of post-tensioned steel, ' says Mr Moore.

With post-tensioning ruled out, the team had to look at alternatives.'We then challenged the major steelwork contractors, saying that steel was traditionally problematic, can get winded off and as soon as it rains you don't want to work.They came in and gave us presentations.We selected William Hare because it offered the most innovative solutions.'

This included the use of prefabricated decking to avoid the need for deck cutting on site.Given the problems of being able to stud weld in bad weather, Hare has pre-studded many of the beams as a time-saving measure.

'We are also looking at boltless connections as they help our workers in the light of the new Working at Height regulations, ' adds Mr Moore.

Ribbed piles

THOUGH the piles on the site cannot go too deep (see box on page 23) the site has still seen some interesting work going on beneath the surface.

'We've got Expanded Piling looking at pioneering ribbed piles.They have put in one test pile at the moment, ' says Mr Moore.

Ribbed piles are sunk like a normal pile, but then an auger is put down the hole that over-extends sections of the pile to create 'ribs'.The concrete then forms in the ribs, so as well as skin friction, the piles have an element of bearing friction as well.

Formation of the piles is currently slow as the team has to inspect each pile at every stage of its development to ensure that it is being formed correctly.This involves sending a video camera down the bore of the pile to inspect how well the action of the auger has created the ribs. If the soil is not as cohesive as expected, there is a danger that the ribs won't form, preventing the pile from performing as planned.

While the main piles for the tower are traditional, straight-edged piles, Mr Moore says that they are looking at the results of the test pile with interest and may look to use the method on future Mace projects.

Jump- or slip-form?

WITH the concrete cores, a decision had to be made whether they would be slip- or jump-formed.The team plumped for jumpforming the tower [where a section of the core is formed, allowed to set and then the formwork is 'jumped' up to form the next section] as Mr Moore says that it offers improved accuracy over slip-forming [where the cores are formed in one continuous slow pour].The choice means that the team will be able to install and use lifts in the building even before the cores themselves have topped out.

'When you build a tower, you want to start the service risers and lift installations before you finish the concrete.

To do this you have to have a certain reliance on the plumbness? of the shaft. Jump-forming is best for this as you can reset at each floor if necessary.With slipform, once you set off in a direction, it is hard to bring it back, ' explains Mr Moore.

The core formation is due to start in July and will advance at around a floor a week. But before the core reaches level 29, the team will start installing the goods lift.'One of the critical items on a high rise is the goods lift because it stops on every floor. If you have to wait until you get to level 29 before you put it in then, with another week per floor to install the lift, you have another 29 weeks.We don't have that time' Instead the team will start installing the lift machinery in the lower third of the building as soon as possible.The lift will be installed and operational in the lower third of the building while the team is still pouring concrete on the top floors.

Project details

Building owner: British Land

Client: Stanhope

End user: Willis

Construction manager: Mace

Designer: Foster & Partners

Structural engineers: Whitbybird

Cost consultants: Davis Langdon

Concrete: Laing O'Rourke

Steel: William Hare

Cladding: Schmidlin

Mechanical engineering: Axima

Electrical: Phoenix

Demolition: McGee

Value: £117 million