Flagshipstore Peek & Cloppenburg

Cologne

structural engineering, special structures Services

Renzo Piano Building Workshop Paris Architect

Department store with a doubly-curved shell structure made of timber strip girders and cable diagonals

Project

The Peek & Cloppenburg department store is located on the historically evolved, highly frequented Schildergasse in Cologne. Part of the building site was created by capping the four lane urban highway. The design responds to this complex, heterogeneous urban context by dividing the building into two parts: a closed, cubic western structure and a free-form, transparent eastern wing. The defining element of the eastern wing is a cantilevered grid shell composed of spaced vertical timber glulam members, horizontal steel tubes, and diagonal bracing cables. This construction challenged the structural design especially regarding the complex geometry, the support on the structural framework, and novel construction details.

Self-supporting, resource-efficient shell structure with a novel, reversible timber lamella connectors

Shell Structure

Due to the difficult support conditions, the transparent building envelope is designed as a self supporting, seamless grid shell. To avoid structural constraints resulting from floor slab edge deflections, the structure is supported on brackets exclusively close to the columns. At the fourth floor level, it spans freely up to the ridge girder, while the lower section is suspended. Prestressed diagonal cables convert the orthogonal grid composed of spatially curved circular steel hollow sections and multi layer glulam members made of Siberian larch into a rigid triangular mesh. The glulam laminations are graduated according to stress distribution and are shear stiffly coupled via tapered cast steel connectors and screwed in threaded sleeves. While telescopic connections compensate for manufacturing tolerances, sliding bearings and radial wind columns allow for low constraint thermal expansion of the shell.

The shell construction was examined using various static models

Static Analysis

The shell structure was analyzed using various models that primarily differed in their level of detail. The geometrically nonlinear calculations were performed using a model in which the discrete timber trusses were represented by equivalent idealized cross-sections. Along with loads from self-weight and snow, requirements derived from temperature and wind studies, as well as the interaction between the façade and the primary structure, had to be considered. Furthermore, erection-stage analyses were performed to determine the required prestressing forces in the diagonal cables as well as the necessary camber and temporary supports. This was achieved by “deconstructing” the structural system according to the erection sequence. The partially prestressed structure was, in some areas, loaded with glass elements to visualize the assembly.