In the manufacturing of precast concrete columns at a precast factory, the columns frequently have to be made with brackets. The production of brackets is a very elaborate process because the column formwork has to be propped up and forms placed for the brackets. Additional costs will incur for material and labor, and the production time will be extended. H-Bau Technik took up this challenge with „Monocrete“ and tried to optimize the production process of precast concrete columns with brackets, while reducing the said effort without any impact on the product quality or the load-bearing capacity.
The Monocrete bracket connection is the outcome of a development process conducted together with the partners Ideenfabrik, Saigmaringen, Konstanz University of Applied Sciences (HTWG) as well as staff members of a precast concrete plant. This bracket connection is used to connect two separately manufactured concrete components – the column and the bracket – after production without any grout in an absolutely form-locking and force-locking manner.
Moment action transferred
The Monocrete bracket connection itself also consists of two elements: The element on the column side is a metal plate with strongly studded surface. Shear connectors are mounted in the upper part. The element on the bracket side consists of a slab made of ultra-high performance concrete (UHPC). This UHPC slab has a negative profile towards the metal plate on the column side; the upper part is provided with empty conduits.
The element on the column side is attached to the column formwork. The element on the bracket side serves as formwork element of the bracket. When stripping the formwork, the plate on the column side is removed. Now, bracket and column can be connected to each other in a form-locking and force-locking manner by joining both elements together. On the bracket side, threaded rods are screwed in the sleeves on the column side and then fixed by lock nuts on the bracket side.
The moment action is transferred by a couple of forces – the tensile stress in the upper part and the compressive stress in the lower part. The shear stress is transferred through the interlocking joints.
The innovation is composed of the production of an interlocking joint that is made by joining two precast concrete elements together. The UHPC slab used as element on the bracket side allows increasing the loads considerably and creating a ductile behavior of the structural component. The interlocked joint enables achieving the loads of a monolithic connection of up to 100 %. Monolithically designed brackets can be replaced one to one.
Besides the production of Monocrete is cost-efficient. Metal plate, shear connectors, empty conduits, and threaded rods are well-proven materials and available in any design and type. The UHPC slab may also be manufactured with the aid of the respective system formwork without any problems.
The prototype developed was tested by HTWG Konstanz with success in the summer of 2017. The test report was submitted to the jury of the „Innovation Prize of the Supplier Industry for Structural Concrete Products 2018“ as annex to the proposal.