The challenge in the Gate project executed by Man Enterprise was to connect 2 towers at levels 14, 15, 16 and the roof. The towers are in reinforced concrete structures while the bridge is in steel structure with a span exceeding 30 m. The Consultant proposed a design consisting of beams at each level hanging on a truss erected at the highest level. The idea was brilliant but the execution almost impossible since it implied to erect the truss from top to bottom unless using huge mobile cranes that cannot be accommodated within the surrounding area of the project. Man enterprise Qatar proposed an alternative where the erection would be executed from below to top using existing tower cranes .This method imposed additional insert plates on the concrete columns to install temporary bracing that shall support the structure during erection until reaching the final stage.

The above simply described construction methodology necessitated a lot of care. Prior to proceed with the implementation of the steel structure, we had to design the hangers and the insert plates and verify that the concrete structure would withstand the lateral forces introduced by the new elements. The steel structure members were lifted in a predefined sequence depending on their locations by different tower cranes.In order to reduce the number of fixing or connection when working at height we proceeded partially with the assembly of trusses one by one on the ground taking in consideration the capacity of tower cranes. 14th floor beams were installed one by one including temporary hangers as cantilever to concrete columns at both sides of the bridge, and then we proceeded with the fixing of intermediate beams to connect with the previously installed elements. Once main beams were installed, we proceeded with the erection of lateral beams in order to install the metal decking to slabs. 15th-floor beams were installed following same sequence of 14th-floor beams. Beams of the 16th and 17th floors were erected without temporary hangers; because once the beams of the 14th and 15th floors were completed they were considered as a truss that could hold the weight of 16th and 17th floor beams awaiting the completion of the 17th floor trusses which would hold all columns and subsequently all steel beams. Once all steel members at roof were fixed and joined together and tightened to reach specified torque, the temporary hangers at 14th and 15th floor were progressively removed, after proving by a calculation note that the dynamic load upon releasing the hangers will not affect the structure of the building. It remains to mention that all activities and erection of steel members were executed in accordance with the safety requirement. A safety net was fixed under the beams and covered all the area to prevent falling of workers and tools, and safety wires were tied between columns to fix safety belts.

The Gate Team