The Cartierheide Tower is a steel observation tower situated in Cartierheide, which is a natural landscape area located in the south of the Netherlands, in the North Brabant province. The design is inspired by a local, endangered snake species: the smooth snake (coronella austriaca). Summum Engineering provided structural engineering services for the tower, from consultancy during the preliminary design phase to member design calculations for the final design.
The tower is 30 meters high in elevation and 4.5 x 4.5 meters wide in plan. It consists of a spiral staircase supported by a compression mast in the center, and a loadbearing façade system made from steel circular hollow sections.
The architectural design has a wavy form as a tribute to the locally endangered smooth snake. The initial winning design featured weathering steel, also known as corten steel, to represent the skin of a snake. The structure was designed as a modular stack of box-like elements with cross-bracing for stability.
To reduce the amount of wind loads, and to create a stable form without the need for additional bracing, Summum Engineering instead proposed the use of cable-net meshes instead of sheet metal, and a structure made of stacked octahedrons. A shape of a single octahedron can be thought of as two pyramids stuck together. This triangulated octahedral geometry gives the tower its desired structural efficiency, allowing for simple joints.
The base module deviates and is a triangular prism instead of an octahedron, to provide for a square base. The base is a bit wider as well to account for high bending moments that may occur due to wind loads. Similarly, the topmost module is also square and wider, to comfortably accommodate and allow for visitors to enjoy the beautiful landscape of the Cartierheide park from this viewing platform.
The tower geometry was modelled parametrically to allow for quick design changes, such that it met the desired structural limits, keeping into mind the fabrication feasibility and maintaining the architectural design constraints. Within the parametric workflow the tower underwent preliminary structural analysis under various load combinations. The orientation of octahedrons and its dimensions were tweaked to optimize structural performance of the tower, mainly under horizontal wind loads. The parametric workflow allowed to quickly implement several interesting design possibilities in the finite element model to check for their structural performance.
The tower has two main loadbearing components. The spiral staircase with central mast to withstand the live loads and the façade structure to withstand the wind loads. The two components are connected to each other using struts which prevent the central mast from buckling under compressive forces. Fulfilling the design intent to have a slender snake-like façade structure which can also efficiently resist the wind loads posed an engineering challenge. The structural design of the tower was optimized by tweaking the parametric geometry in order to find the most optimum design in terms of the total amount of steel. The mass in the tower was distributed to place heavier beam members at the base, and increasingly lighter sections towards the top.
Apart from static analysis, a preliminary dynamic analysis was performed on the design, to check for comfort and resonance-related effects on the tower under wind loads.