Shortage of skilled labor and deadline pressure lead to a permanently growing demand for making construction faster and increasing the productivity, respectively. Even minor adjustments to the construction process can provide for large savings in time and thus significant cost advantages.
An example in construction with precast concrete elements in the field of building construction and civil engineering is the use of the BT-Spannschloss turnbuckle with national technical approval. The turnbuckle allows the connection of up to three precast concrete elements by means of simple screw connections. Moreover, in case of incorrect installation of the fasteners, tolerances of up to ±2 cm allow for smooth construction progress. Elaborate welding and grouting works in order to achieve the load-bearing capacity of the connection are eliminated, with the result that the assembly is almost independent of the weather conditions. Construction sections and construction projects can be executed faster. Crane times and workloads are reduced, meaning that more projects can be realized in the same time period. In addition, precast elements are manufactured in a high quality for the respective construction sections, enabling a smooth and time-efficient workflow at the construction site.
The BT-Spannschloss turnbuckle is already taken into account in the planning stage. In combination with approved permanent fasteners, the turnbuckle reliably and durably transfers shear and tensile forces. The BT-Spannschloss is available in three sizes (M20, M16 and M12).
At the precast concrete plant, the anchors are embedded at the appropriate positions and recesses are made, if necessary, for the BT-Spannschloss turnbuckles. The most diverse products available can be used as anchors, which are able to absorb predominantly static long-term loading in tensile and transverse direction. The walls to be installed are positioned on the construction site. The BT-Spannschloss turnbuckles are inserted into the provided recesses and the walls are firmly connected by means of screws.
With a clever sequence of assembly, transverse bracing for keeping the walls in their positions can be eliminated to some extent. If façades are assembled with the aid of the BT-Spannschloss turnbuckle, the joint pattern can also be adjusted, thus allowing compensating any unevenness of the precast elements. To achieve a wall that is ready to paint, to increase the corrosion protection or to have the BT-Spannschloss appear less exposed, the clamping position can finally be provided with mortar.
The BT-Spannschloss turnbuckle is approved by DIBt (German Institute for Construction Technology), and in the near future, it will get the CE marking on the basis of the recently successfully passed European Technical Assessment (in short: ETA).
The verification for a connection of two precast concrete elements is simple. It has to be verified that the combination of shear and tensile forces does not exceed 100 % of the load level permitted. The anchoring must be verified separately.
The recently issued ETA-19/0013 also regulates the connection of three precast elements. If three elements are connected, this load transmission must be taken into account additionally.