be closed across the playing field. In 2004 a new roof with an opening along the longitudinal axis was completed for the Olympic stadium in Berlin, Germany, as well as a new roof for the newly renovated Rhein-Energie-Stadium in Cologne, Germany. The soccer World Cup 2010 in South Africa (Cape Town, Durban, Port Elizabeth, Johannesburg) as well as the soccer World Cup 2014 in Brazil have also contributed to the firm's growing resume of sport stadiums. Implemented Projects Vidyasagar Setu or Second Hooghly Bridge, Calcutta, India, construction period 1979–1992 Exhibition Tower in Leipzig, Germany, 1995 Hoern Bridge in Kiel, Germany, 1997 Ting-Kau Bridge in Hong Kong, 1998 Buckel Bridge in Duisburg, Germany, 1999 Schlaich Tower in Weil am Rhein, Germany, 1999 Killesberg Tower in Stuttgart, Germany, 2001 Humboldthafen Bridge in Berlin, Germany, 2002 Cantilevered roof with membrane and glass cladding Olympic Stadium in Berlin, Germany, 2004 Liberty Bridge in Greenville, South Carolina, USA, 2004 Roof RheinEnergieStadium in Cologne, 2004 Membrane roof with convertible membrane inner roof Commerzbank-Arena in Frankfurt am Main, Germany, 2005 Central Bus Station in Hamburg, Germany, 2006, awarded the Outstanding Structure Award of the IABSE Structural design of the roof of the Nelson-Mandela-Bay-Stadium in Port Elizabeth, South Africa, May 2009 Roof structure of the renovation of the FNB-Stadium in Johannesburg, South Africa, 2009 New Roof over BC Place in Vancouver, Canada 2008–2010 Tensile Roof Structure at The Milk Market, Limerick, Ireland, 2009-2010 Roof structure of the National Stadium in Warsaw, Poland, 2009–2012 Spire for One World Trade Center in New York City, 2013 Harp Bridge, Böblingen, Germany, 2016 Utilized structural elements and materials The firm has participated in a multitude of technical innovations for various projects. Gridshells The light, transparent roof over the Hamburg Museum's courtyard bears on the building's structure as little as possible. For this gridshell structure the common kitchen sieve was the inspiration: its quadratic mesh grid can be transformed into any desired geometry by altering the mesh grid into a rhombus shape. In combination with a diagonal cable net, the grid transforms into an ideal shell. Clad with glass panes, the result is a lightweight, transparent roof. The glass panes lie directly on the grid beams, thereby merging the load-bearing structure and glass planes. This serves to eliminate the typically necessary secondary structure. The first application of this concept was the Hamburg Museum, which has now been applied, adapted and further developed to