Cooltower Rotterdam

Abstract

In Rotterdam underneath the first load bearing sand layer is a layer of compressible soil, called the "Kedichem" layer. Under this layer of compresible soil is another load bearing sand layer located, at approximately -50m NAP, but most of the buildings in Rotterdam are foundated on the first loadbearing sand layer at approximately -23m NAP. Due to this most buildings undergo differential settlements caused by deformations in the Kedichem layer. This differential settlements causes an increase of internal forces in the structure. Highrise buildings are causing higher deformations in the Kedichem layer because a highrise building has a large weight on a relative small area. This thesis is a research of the behaviour of a highrise building on compressible soil. The main research question is: Can a structure be modified to reduce the differential settlements. As a case study the Cooltower will be used. The height of the building is 102m, and the floorplan is 29x29m. The structure of the building is modeled in the structural software Scia Egineer. The differential settlements caused by the deformations in the Kedichem layer are introduced in the structural model by forces on a stiff spring element. The deformations in the Kedichem layer are calculated by using a soil settlement program, called D-settlement. Due to the deformations in the Kedichem layer the force flow in the structure will change. The force flow describes how the forces in the structure are distributed to the foundation. To calculate the final force flow it is needed to perform some iterations between the soil settlement software and the structural computer program To answer the research question there are 2D calculations made to investigate the influence of the connections between the precast elements on the differential settlements. Also the influence of the openings in the structure on the differential settlements is investigated in this part. After this step there are 3D calculations made of the Cooltower. In this part the interaction between core and facade is studied. In this part it is tried to reduce the differential settlements in the facade by adjusting the stiffness of the facade, and it is investigated in which way the differential settlements between the core and the facade can be reduced. The main conclusion of this thesis is that it is difficult to create a general conclusion for the differential settlements due to the many factors that influence the differential settlements in the structure. Most of the researched topics in this thesis don't influence the differential settlements that much. The stiffness of the facade influences the behavior of the Cooltower on compressible soil the most. By making the facade twice as stiff, the differential settlements will be reduced by 37% on average. The conclusion is only valid for the Cooltower. For the Cooltower the extra normal forces in the columns of the facade due to the differential settlement can be estimated to be 15% of the forces in the structure due to the permanent and the variable load. In preliminary design phase the structure can be designed with a unity check of 0,85.