Location: Stuttgart, Germany
Market: Rail
Product: Hollo-Bolt® by Lindapter® 
Quantity: 12,475 
Client: Deutsche Bahn (German Rail)
Engineer / Specifier: Werner & Balci Engineering, Esslingen
Contractor / Steel Fabricator: Max Bögl

Stuttgart 21 is one of Germany’s largest and most complex rail infrastructure projects, involving the construction of a new underground railway station strategically located between Stuttgart Airport and the Stuttgart Fair halls. Designed to significantly improve passenger connectivity and transport capacity, the project required extensive new structural steel frameworks to support vertical circulation elements, including elevator shafts, within a constrained underground environment. Given the scale of the works and the critical nature of the infrastructure, proven and reliable connection solutions were essential.

The client required a bolted connection system for splicing hollow structural sections (HSS) to form new elevator shaft frames within the underground station. Welding was undesirable due to program constraints, underground field conditions and quality control considerations. The solution needed to deliver reliable structural performance, enable efficient installation, and align with the engineer’s preference for a mechanically bolted system that could be installed accurately and repeatedly across many connections.

Hollo-Bolt hexagonal head fasteners in hot dip galvanized finish were specified to meet the project’s structural and durability requirements. A range of sizes, including 1⁄2" and 5⁄8" variants were selected to suit the different load demands and connection geometries across the elevator frame structures. Initially, an alternative Hollo-Bolt configuration was specified; however, Lindapter worked closely with the project team to optimize the solution, refining the specification to ensure the most efficient and appropriate product selection for the application. The resulting design provided a robust bolted splice connection for HSS members, eliminating the need for welding while maintaining high structural integrity.

Hollo-Bolts were used to create splice connections between HSS members, forming the primary steel frames for elevator shaft structures throughout the underground station. These connections were critical in transferring loads safely and accurately within the elevator shafts while allowing construction to proceed efficiently within the confined underground environment.

Installation took place within the new underground station, positioned approximately two minutes’ walk from both the airport terminal and the exhibition halls. The use of Hollo-Bolts allowed the steel to be assembled quickly and precisely in the field, without the need for welding equipment or extended hot-work procedures. This contributed to a smoother installation process and supported progress within the tight logistical and spatial constraints of a major underground transport hub.

The optimized Hollo-Bolt solution delivered a reliable, fully bolted connection system that met the client’s requirements and supported the efficient construction of elevator shaft frames within the Stuttgart 21 station. By avoiding welding and simplifying installation, the solution enhanced build efficiency while ensuring long-term structural performance in a demanding rail infrastructure environment.

• Efficient splicing of HSS members without welding
• Optimized specification through Lindapter’s technical support
• Hot dip galvanized finish for durability and long-term performance
• Suitable for large-scale, complex underground rail infrastructure projects