Museum of Liverpool

Introduction
Due to open to the public in 2011, the new Museum of Liverpool will be one of the world’s leading city history museums and the largest newly created national museum in the UK for over a hundred years. Situated alongside the Three Graces in Liverpool’s historic waterfront setting, it will showcase Liverpool’s social history and popular culture while setting a global benchmark for other museums of its kind.
Visible from both the river and city on this UNESCO World Heritage Site, the building is a striking example of contemporary, stylish Scandinavian design as well as being an outstanding example of integrated structural and environmental engineering systems.
The project was won by 3XN Architects and Buro Happold in an architectural design competition in the autumn of 2004, and construction commenced in 2006 on site. The winning design was for a three storey building which is divided into a number of public access galleries and circulation spaces, and private back of house spaces. Public access to the building is available at both ground floor and first floor levels. The back of house spaces contain the staff accommodation, loading bay, storage and plant rooms.
With large 10m high gallery spaces, 9m cantilevers and over 8,000 m² of exhibition space, the project has presented complex engineering challenges. The design provides an integrated engineering approach, allowing the structure and the services design solutions to combine and produce an energy efficient, low carbon solution to meet the high aesthetic demands of the architecture.
The Mersey Railway Tunnel passes directly below the site and the Queensway road tunnel passes under the River Mersey approximately 100m north of the site, providing additional site challenges. The site is reasonably level, the ground level being around +6.5m OD (Ordnance Datum).
The building shell and core is complete and was successfully handed over – on time and budget – in January 2010.

Structural Engineering
Existing Site Constraints
The site for the project was partly occupied by the Liverpool Maritime Museum, including the Great Western Railway Building and the Canning Graving Docks. The northern half of the site was occupied by a car parking area and pedestrian access is possible along the waterfront linking to lawns in front of the Port of Liverpool Authority.
The site is located within a dock area, although the docks are no longer used for commercial purposes. The building foot print sits directly over the Mersey Railway Tunnel on top of a reclaimed dock and therefore presented many challenges for the structural engineering designers. The existing dock walls had also to be maintained for archaeological reasons.

Substructure
The foundation design has been influenced by the following factors:
• The location of the building on made ground, within 12m of the river wall.
• The Network Rail Mersey Rail-Link tunnels, which pass directly beneath the site.
• The proposed British Waterways canal culvert beneath the North East corner of the site.
• The discovery of the archaeologically sensitive Manchester Dock walls beneath the site.
• Certain portions of these walls are required to be retained beneath the building.
The chosen foundation solution is a combination of piles and a compensating cellular raft.
The raft foundation comprises a giant 100m-long and 49m-wide beam that bridges the tunnel and functions like an I-beam, with an upper and lower fl ange separated by a web. The foundation slab has a 400mm-thick lower fl ange with a 300m-deep upper fl ange, and the two are separated by a series of 3.5m-high cross walls. The depth of the raft has been calculated so that the weight of soil removed is equal to the weight of the building, in order to avoid overloading the tunnels beneath. The building will be stable against fl otation in the permanent condition.
Analysis of the raft has been carried out using a range of soil stiff nesses, derived from those obtained during the ground investigation. The weaker soils have been considered beneath the most heavily loaded areas of the raft in order to determine the most onerous likely support conditions. Ground improvement will be carried in some areas where determined necessary during excavation on site.

Superstructure
The superstructure of the building consists of a steel frame on a grid of approximately 9m centres. The steelwork consists of both traditional hot rolled sections and specially fabricated plate girders to achieve the necessary clear spans in the gallery spaces, allowing services to be fully integrated within the cell form beam construction.
Due to the length of the building, it has been necessary to split the structure into three distinct sections to control thermal expansion and associated effects on finishes. Each section relies on two in-situ concrete core elements to provide lateral stability to the structure in the permanent case. By introducing movement joints, it was possible to reduce internal stresses and deflections to a controllable level that would not have a detrimental effect on normal finishes. The detailing of all finishes, connections and structural elements must accommodate the anticipated movements to avoid damage.
The huge cantilevered galleries on the top floor span up to 27m. The box cantilevers 9m over the lower part of the building on the north end and 5m on the south end. As the top floor has no internal columns, it required a complex steel frame that weighed 2,100 tonnes – its size meant it had to be split into three sections to accommodate thermal movement. The frame needed temporary propping while under construction, which proved challenging. Floor to floor heights in the building (approx 5.5m) are larger than typical buildings in order to achieve the necessary access zones for the gallery services.
There are a series of in-situ core elements that provide support to beams. These connections are achieved by a series of cast-in plates or concrete corbels. The cast-in plates are detailed with shear keys and additional anti-crack steel to help resist high point loads. The in-situ core elements rely on the use of in-situ concrete landings to provide tying action to the vertical walls and reduce their slenderness. The in-situ concrete cores have been designed as key elements in accordance with BS 8110-2 for tying and to resist a 34kN/m2 load on any single storey.
The structure has been designed for a 60 minute fire rating either by the use of intumescent paint to protect steelwork elements or by providing a suitable level of cover to the reinforcement for concrete elements.
The theatre structure is a self-contained structure bearing on the ground floor slab. This is constructed using cold formed sections and is designed to be removable in the future without impacting on the primary structure.
The cores in the north and south portion of the building are positioned eccentrically to the centre of gravity of the system. As a result, torsion is induced within these systems. These loads have been assessed by software modelling of the overall system under wind load in two orthogonal axes.

Spiral Staircase
Internally, the centre of the building features a large spiral staircase that is only supported at its base and the intermediate floors. It functions as an H-section beam and is constructed from in-situ concrete.
The concrete stair relies on the support of several members in the permanent case. The edge parapets of the stair act as beams/ struts in combination with these supporting members to make the stair stable. The waist of the stair then spans between these edge beams. Stability is provided through connection to the ground floor raft slab, the stability core, and the first and second floor diaphragm slabs.
When the staircase was completed, the concrete had to be allowed to cure for a 28 days before the supports could be removed.

Facades
The building envelope design adopted a combination of glazing and the use of Jura limestone as an external rainscreen. The limestone is delivered to site fitted into a galvanised steel frame, which is simply bolted on to fixing points.
The geometry of the facade means that the transitions between different types of facade do not align with the typical floor diaphragms or primary floor structures. Hence a second layer of steelwork is required to support the units. The setting out of this steelwork is governed by the joints between units. This second layer of steelwork is used to transfer lateral loads back to the floor diaphragms and the vertical load back to the primary columns.
The facade is stepped on three distinct planes on both east and west facades. This second layer of steelwork and associated cladding units are offset by up to a metre from the centreline of the columns and therefore moment connections are required for the beams that cantilever out to provide vertical support.

Environment and Energy
The brief for the project set out the specifi c indoor climate requirements for the gallery spaces and the design team developed a strategy to ensure that integrated design, selection of materials and use of energy sources provided a sustainable response to the design requirements. The internal gallery spaces are designed to provide close control of the environment. The upper two galleries are fully close controlled spaces and utilise displacement ventilation techniques to provide close control of the occupied zone whilst reducing energy cost. Both these galleries are provided with perimeter buff er zones to reduce the penetration of solar gain from the large glazed elevations, working in conjunction with the high performance glazed facade. The supply and extracts of the buff er zones are positioned and controlled to separate the environmental conditions in the buff er zone eff ectively from the conditions in the close controlled exhibition areas. The lower gallery spaces are provided with comfort cooling to maximise the energy effi ciency in the space.
The high performance glazing systems have been specifi ed with a G value of under 0.4, low e-coatings and excellent U value to meet the thermal performance of the envelope, together with air tightness specifi cation that achieved 3.2m3/hr/m2. The glass is UV controlled to reduce the impact of harmful ultra violet light into the gallery spaces. The museum was designed to Part L2 2006 and its performance was such that it bettered its carbon emissions target by 35%. Energy effi cient light sources coupled to an intelligent lighting control system allow a combination of creative lighting solutions to be provided, together with the functional needs of the building. This is achieved through the use of high effi ciency metal halide lamps and the latest fl uorescent lighting technology, together with a fully fl exible grid of recessed lighting track.
Extensive load profi ling of the building has allowed detailed studies to be undertaken to maximise load matching by alternative energy sources. The use of biomass boilers and dock water cooling were initially considered, together with the option for a Combined Heat and Power (CHP) system. Cost option analysis, together with funding appraisals, led to the adoption of an integrated duel fuel CHP system with absorption chiller to provide a tri-generation energy solution. A new remote energy centre has been created in one of the existing historic buildings on site, the GWR building, and from this energy centre, power and low temperature hot water (LTHW) is distributed across the site to serve the new museum and existing pilotage building.
The CHP system uses a combination of bio-fuel and natural gas fuels to provide low carbon energy generation to meet the demands of the site. Two biodiesel CHP machines, rated at 385kW (e) 319kW(h) and two natural gas machines 768kW(e) 834kW(h), together with two 800kW condensing boiler units provide the installed capacity to the CHP generation plant. The energy centre is provided with parallel mains electricity connections to allow export to the grid during periods of low demand on site, and thus maximise the effi ciency of plant operation. The grid connection also acts as an alternative power supply to serve the essential services within the building.
Power is distributed across the site within an integrated services trench using below ground 2000A rated busbar systems. Low temperature hot water is distributed using 350mm buried pre-insulated pipework.

Sustainability and BREEAM
Sustainability has been one of the key drivers for the design since the inception of the project. The BREEAM process and Bespoke assessment criteria allowed sustainable benchmarks to be carefully weighed up and evaluated against one another to establish the most suitable and beneficial solution for the development. The building achieved a ‘Very Good’ rating under the BREEAM Bespoke 2005 assessment criteria.
The Bespoke criteria is tailored to the development; following on from the submission of floor plans and an area schedule to the BRE, complete with a building questionnaire, which details the uses and requirements for each room.
The careful selection of materials, consideration of renewable and low and zero carbon technologies, building services specifications and operation and maintenance issues are among the key issues that have allowed the building to achieve this outcome.
Rainwater harvesting is provided to meet the high domestic water services demands within the building, coupled with highly efficient sanitary-ware and a leak detection system to minimise potable water use and guard against any potential water leaks.
The building is located on land that has been previously developed and in a highly accessible location, with good transport links and within easy reach of local amenities.
The development scored exceptionally well in the management and health and wellbeing sections of the report. This demonstrates commitment to the running and operation of the building and the building environment for the users, throughout the lifetime of the development.
A low and zero carbon feasibility study was undertaken to establish the optimum energy solution for the development. This took into account everything from the location to payback and carbon emissions. The use of the CHP system, improvements in U values over building regulations and an improvement in air tightness of 50% resulted in the requirements for Part L 2006 being exceeded by 35%.