Case Study:

Vierendeel Truss Installation

London Bridge Station Redevelopment

The Vierendeel Truss at London Bridge supports the station canopy in the “wedge void” area,

dividing the terminating platforms from the through platforms, and creating a full-height, open area

above the main concourse. This case study reviews the key challenges, programme of works,

methodology and logistics associated with its installation.

Through platforms Terminating platforms

Platform Level Concourse Level

1. Key Challenges

• Programme

• Complex Structure and Methodology

• Logistics

• Limited Space

• Proximity to the operational railway.

2. Programme

• The works commenced at the start of December 2015 with the requirement to have the truss itself

installed before the end of the year to release the installation of the platform 10 staircase and escalator.

• With the majority of fit out trades requiring a dry environment, and with southern concourse opening in

August 2016, the entire roof was required to be installed before end of March 2016.

39m 27m 31m

17.5m

5m

V-column arms RC plinth

Gun column

3. Complex Structure

• The truss itself came in six sections due

to logistics and crane restrictions. This

meant that each section had to be held

in position with temporary support

towers and subsequently welded to its

adjacent pieces.

• The Vierendeel truss is supported by the

two arms of the ‘V’ column mounted on

a massive reinforced concrete plinth via

a bespoke fabricated steel saddle.

• The adjacent roof provides the lateral

support to the slender truss and so

extensive temporary works were required until the roof structure was complete.

• The Vierendeel truss had a precamber designed into it to counter the deflection of its own self weight.

4. Methodology

• It was decided to fabricate and install the Vierendeel

truss in six sections. This was a balance between:

o The maximum benefit of off-site

prefabrication and quality control

o Minimising the number of pieces to reduce

site works and save on programme

o Site logistics and crane restrictions.

• The sections of the truss were supported by six

custom built trestles. Trestle 5 and 6 straddled the

central RC plinth to allow installation of the v-column

arms.

• The trestles were designed to:

o Support the sections of the truss as they are

brought together

o Provide lateral restraint

o Provide a covered working platform to

complete the site welding

o Incorporate a jack to allow sequential dejacking post welding to allow for the precamber of the

truss to fall out.

• Each trestle was based on a large steel grillage which spread the loads into the ground slab. This had to

span over the service trench and other access chambers in some places.

• Each trestle weighed approximately 25 tonnes.

• A complex sequence of roof installation, dejacking of the truss and trestle removal was developed to

ensure the truss remained fully restrained in each phase of the install.

• Glazing of the truss also needed to be carefully coordinated due to access.

• The roof structure came in modularised cassettes to significantly improve programme.

5. Logistics

• All material had to be delivered through existing arches and through areas of piling and foundation

works.

• Swept path analysis was completed to ensure that deliveries could be achieved.

• Special transport frames were created to deliver the steel to deal with both restricted head height and

Highways regulations.

6. Limited Space

▪ At its narrowest, the void is only two metres wide between adjacent structures.

▪ A service trench, over one metre deep, ran through the ground slab adding additional restrictions for

both temporary works and plant loadings.

7. Proximity to the operational railway

▪ Operational platforms and tracks immediately adjacent to work site.

▪ Canopy over platform 10 was restrained by temporary works protruding into work site.

▪ All lifting had to be carefully planned to ensure safety of operational railway whilst minimising restricted

hours working.

Live track and platform

Protruding temporary ties

About the author

Case Study produced by Obi Ozonzeadi, Network Rail Infrastructure Projects Development Manager, October

2018

Further information

For more information on this Learning Legacy case study please email

contact@thameslinkprogramme.co.uk