COPENHAGEN’S ‘KISSING’ BRIDGE WEALTH CREATION

The bridge’s sliding spans are cantilevering, steel box girders. Their undersides follow a smooth wave-like profile in elevation to provide the greatest structural depth at the support where the bending moment is largest. The structural depth then tapers to only 600 millimetres at the cantilever tip at midspan, where the two girders meet and interlock The middle spans on the Inner Harbour Bridge in Copenhagen slide apart to allow large boats to pass through the harbour. The spans then slide back together again and have earned the bridge the nickname Kyssebroen (the Kissing Bridge) © Jasper Carlberg Aside from COWI, the team the opening sections in a sliding focus more on functionality comprised architects Studio manner and create a functional than design. The team wanted Copenhagen is not a city that Bednarski, mechanical and and innovative bridge. to bring that sliding method is short on bridges, but one electrical designers Hardesty & The concept for the bridge of opening to an architectural was needed to link the heart Hanover, and lighting designers was decided early in the pedestrian bridge that would of the city with Christianshavn Speirs & Major Associates. process and the initial sketches create a surprise for onlookers in the east, an area that Working in a close collaborative reasonably reflect how the final who would expect the moving is undergoing substantial team, the designers came up bridge looks. Principal engineer spans to raise or swing rather COPENHAGEN’S development and is home with the innovative sliding Amar Bahra led the day-to-day than slide. Each time it opens, to Henning Larsen’s famous bridge idea in response to the design activity throughout the two curved, steel box girders new Opera House. In 2009, a geometry and character of the project. He worked regularly slide apart and then back again design team led by engineering site. The idea of a bascule bridge with Studio Bednarski to to gently meet at the centre – consultancy Flint & Neill (now (drawbridge) was dismissed as discuss the concept and hence its nickname, Kyssebroen COWI) won an international the designers felt that it would develop ideas, and was in or the Kissing Bridge. ‘KISSING’ BRIDGE design competition for a new, be an excessive visual intrusion close contact with Hardesty & opening pedestrian and cycle on Copenhagen’s cityscape Hanover in New York. From the An innovative sliding bridge opened to the public in Copenhagen in the summer of bridge over Copenhagen’s Inner when raised. Similarly, a swing very early stages, the designers SLIDING 2016. Although the project faced various challenges and delays, the Inner Harbour Harbour. Ten teams competed bridge was avoided as it would coordinated efforts to create a MECHANISMS to design a new crossing in this have compromised free passage structure that was conceived as The team investigated a variety of Bridge (Inderhavnsbroen) has reduced commuting time for thousands of pedestrians historic setting and to create of vessels in adjacent canals. a closely worked combination ways to drive the sliding motion and cyclists in the Danish capital each day, and has also become a popular attraction. what would become the first The required navigation channel of architecture, structure and of the bridge. At one point, the FREng, Director, and Amar Bahra, Principal Engineer, both of COWI, discuss bridge encountered by anyone opening was narrow compared mechanism. engineers considered a motorised entering Copenhagen harbour to the overall harbour width, There are other sliding front wheel that would positively the design and the bridge’s distinctive opening mechanism. from the sea. making it possible to withdraw bridges across the world that engage with a track underneath

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A HIDDEN OPERATION Concrete chambers that house the bridge in the manner of a rack The drive mechanisms are all In cross section, the steel spans supported between fixed twin the motorised winch drums are and pinion to move the spans. housed in underground chambers appear like a W shape, with concrete box girders with a built within the east and west However, a simple winch drive within the quaysides at each end the roller track in the centre of wide eccentric (offset) cantilever quaysides. There are four drums system was eventually chosen, of the bridge, where they can be the underside and the varying carrying the fixed approaches in total, one for each of the four which comprises a series of easily accessed for operation and depth V-shaped box cells on (see image on page 22). concrete approach spans (a pair pulleys and steel winch ropes. maintenance. either side. The steel spans are Each of the moving steel in each chamber). sections is about 53 metres Because the structural long and weighs roughly 230 capacity and integrity of the tonnes. The front support to existing historic quay walls was the cantilever is provided by a unknown, mini-pile foundations pair of large 1.8 metre diameter and ground anchors were used wheels that stand on a fixed to support the buried concrete concrete pier close to the edge chambers, and on the east side, of the navigation channel on a new sheet-piled quay wall was the bridge centreline. The rear established. The steps and ramp support is provided by support at each end are supported by wheels that roll within stainless these chambers. In fact, they are steel tracks set in to the sides of Each drum within the buried chambers has a winch rope wrapped around it, one end of which runs along the track on structurally separate from the the side of the concrete spans and attaches to the rear of the steel span. The other end of the rope routes through the the fixed concrete spans. approach bridge and segregated inside of the concrete box girder, turns 180 degrees around a large deflector sheave (a pulley with a grooved wheel) As the spans slide apart and returns to attach to the steel span a few metres forward of the rear attachment point. Depending on the direction by a linear movement joint in which the drums are turned by the electric motors, the steel spans are made to either open or close to open the bridge, the rear to avoid imposing significant © Hardesty & Hanover support points move away bridge loads onto the existing from the front roller support, challenges in the design and curvature became obvious, and provide good shear resistance. quaysides. and the moving spans change construction. Aside from driving the rumoured ‘misalignment’ Therefore, the solution was to As there is no hydraulically from cantilevers in their service the bridges around these disappeared. While adding divide each inner web panel operated equipment in the position to simply supported curves, which required each complexity, the curvature helped into two triangles by creasing design, the potential risk of girders in the fully retracted of the four winch drums to be the engineers achieve a slightly on the diagonal and welding a oil spillage and consequent position. At each forward and slightly different diameters, the higher navigation clearance tee stiffener along the inside of contamination of the harbour is rear vertical support system, curvature complicated the shape in the middle of the bridge by the crease. As these inner web avoided. The operating system is there are also guide wheels that of the fixed and moving spans. providing more length. elements were the closing panels very efficient and uses very little control the transverse positions As an aside, the curved The steel spans are highly of the steel box girders and power because of the sliding of the moving spans. alignment led to an unfortunate complex in their geometry – no internal access for welding was nature of the movement. This A great advantage of the rumour that there was an error two cross sections are the same not possible in some places, the is a key aspect of the bridge’s design is that the approaches in the horizontal misalignment – and they constantly change tee stiffeners had to stop short low impact, sustainable design. remain open to pedestrians and that this was the reason because of the varying structural of the panel corners. The team The mechanisms and operating throughout the opening cycle. for the delayed delivery of the depths in elevation and the had to revert to first principles systems use simple, well-proven The design therefore had to steel spans. Standing on one curves on plan. The moving steel and non-linear finite element components and arrangements, consider that the opening concrete span and looking girders have four inclined webs modelling to prove that placing with all parts designed to sequence generates a complex straight across the water to the in the cross section: two inner gusset plates to the ends of these permit access for inspection and set of possible load effects in other concrete span, before webs and two outer webs. These stiffeners, at the relatively stiff maintenance. the concrete spans owing to the steel spans came to site, are the elements that primarily corners of the panel, afforded combinations of imposed patch it did indeed appear that the resist shear and torsion (twisting) them sufficient torsional restraint loads from pedestrians together DESIGN CHALLENGES spans were transversely offset. in the girder. The outer webs are to ensure their stability and that with the loads from the moving The sinusoidal plan curvature, However, when the steel spans formed from conical surfaces, of the overall web panel. Top: The front roller and tracks are fixed, so stay where they are while the spans are pulled back. The tipping point is span, which change position, with east and west sides on were eventually delivered which is easily done in steel plate, Another specific aspect that when the centre of gravity of the moving span passes the front roller and the rear support reaction goes to zero and reverses. This continues until the span is fully retracted. Bottom: The winch cables repeat the operation in reverse to magnitude and direction as the opposite curvatures of differing (delayed because of difficulties but the inner webs lie on warped the design team had to deal move the spans together again spans slide. magnitudes, presented certain with the steel fabricators) the surfaces that do not naturally with was a stringent requirement

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relating to pedestrian-induced vibrations. After the well- publicised problems experienced by ’s Millennium Bridge in 2000, when the structure swayed from side to side as hundreds of pedestrians walked across it, the dynamic behaviour of all footbridges has been in the spotlight. COWI (while still Flint & Neill) was closely involved in the investigations and solution development for The underside of the bridge shows where the inner webs were divided into triangles. The gives an interesting crystalline appearance when viewed from the underside as the light reflects off the water. The fixed forward rollers and the London Millennium Bridge the transverse guide wheel are just visible. The guide wheel runs along a slot to control the extending position of the and is an expert in this field. For moving spans © Cezary Bednarski the Inner Harbour Bridge, the importance of achieving the virtually within arm’s reach of the complexity of the structural client wanted to allow for large desired levels of quality. passing vessels. Many people engineering challenge of synchronous crowds dancing to congregate on the bridge to creating the bridge. The result music in phase with the bridge enjoy the views of the harbour, is a bridge that is not only an motion and this resulted in the USER EXPERIENCE as well as using it as a crossing. important commuter route, need for a series of tuned mass Since its opening in July 2016, The design and apparently but has also become a popular dampers installed within the steel more than 10,000 cyclists and simple, quiet and effortless landmark in one of the most spans. These control movement over 20,000 pedestrians use the operating mechanism disguises prominent parts of the city. amplitudes by responding to, bridge daily. It has dramatically and counteracting, the bridge’s reduced commuting times and BIOGRAPHIES motion. improved key transit routes in Ian Firth FREng is Director of COWI. During his career, Ian has The project suffered several the Danish capital. been involved with world-famous bridge projects including the setbacks during construction The main disadvantage for strengthening of the Severn, Erskine and West Gate bridges, including the rejection of sub- bridge users on most opening standard fabrication and the bridges is the fact that they are and the concept design of in Hong Kong. original contractor’s bankruptcy, kept well away from the action He has also been the designer of many smaller, award-winning which in turn led to considerable on the river, such as when a bridges such as the Swansea Sail and Lockmeadow footbridges delays in delivery and the tall ship passes by. The design in the UK. Ian is an advocate of bridge-building charity, Bridges sourcing of a new contractor. of the Inner Harbour Bridge to Prosperity. Up until the end, concerns provides an opportunity for Amar Bahra is Principal Engineer at COWI, which he joined remained about achieving the the bridge user to experience in 2008. Besides the Inner Harbour Bridge, he has worked desired quality of the finishes, the action close hand; people on many high-profile projects including and the smoothness of the can stand on any one of four in , a retractable pitch at a North London football geometry in the face of huge horizontal viewing platforms stadium, Wimbledon No. 1 Court, Royal National Theatre, commercial and programme on the fixed concrete approach London Olympic Stadium, and Messina Bridge between Sicily constraints. The designers spent spans that reach towards the and mainland Italy. a lot of time and energy trying navigation channel, even when to get the client and the new the bridge is operating, which To watch the bridge in operation, please go to contractor to appreciate the enables them to be almost www.youtube.com/watch?v=vJafdcHP73k

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