The new turnbuckle for the construction industry
What is the BT-Spannschloss®?
At concrete plants
At the constuction site
What is the BT-Spannschloss®?
The BT-Spannschloss® is a turnbuckle which is part of an innovative clamping system including screw connections and anchors embedded in prefabricated concrete parts.
With the BT-Spannschloss® it is possible to create efficient, precise assemblies and make durable construction connections of prefabricated concrete parts in the easiest possible way where there is predominantly static load in the direction of the tensile and shear forces.
The BT-Spannschloss® is suitable for bearing major loads due to its specific form and the heavy-duty cast material used for manufacture. In April 2010, the BT-Spannschloss® was awarded the general building regulations authorisation (no. Z-14.4-599) by the German Institute for Building Technology [DiBt], which means the basis for static verification of the selected construction connection was also established. The BT-Spannschloss® is available in three sizes (M20; M16; M12) and can be purchased in uncoated or galvanised form.
Why the BT-Spannschloss®?
The BT-Spannschloss® means that prefabricated concrete parts can be connected without any additional materials or resources.
Without any need to comply with cure times, the connection can immediately bear a full load and thus generates significant time and cost savings in comparison to other established systems.
Area of application
The BT clamping system can be used efficiently and universally in the widest possible range of applications. For instance, in the assembly and connection of angle brackets and shaft elements for road building and underground construction, in building operations in the field of coastal protection, in floor and wall connections for the residential and commercial construction field and many more construction connections for prefabricated concrete parts.
Note: The load bearing capacity of the clamping system depends to a significant extent on the type of anchor used. Several types of authorised anchorage systems can be used according to the application requirements (you can find the data in the manufacturer’s instructions).
In general, the load bearing capacity of the clamping system is many times higher than that of the anchorage system.
- Quick, effective connection of construction elements
- Building elements can be clamped without additional materials or special resources
- Can be combined with all authorised anchorage systems
- Low net weight
- Resistant to tensile and shear forces
- Cost and time savings through reduction of assembly times and elimination of cure times
- No need for time-consuming individual solutions
- Can be assembled whatever the weather
- Precise positioning of the anchor in the manufacturing process via BT magnet technology
- Approval from the DiBt (German Institute for Building Technology) Berlin)
- Static verification of the chosen construction connection
Installation instructions für precast plants
Forming the recess in prefabricated concrete parts plants
Join screws, recess unit and anchor together.
Place the recess unit in the appropriate position.
By marking the formwork and the recess units, the anchors can be fitted precisely and efficiently without the need for any effort in terms of measurement.
The built-in magnets simplify the placement of the recess unit on the steel formwork. Fit the associated reinforcement and pour in the cement.
After the concrete element has cured, the recess units are removed. The recess which has formed is now used to fix the turnbuckle to the fitted anchor.
Note: The recess created will be used to install the turn buckle attaching it to the anchors in place. The standard cavities are fixed to the steel formwork by using the integrated magnets. Of course the cavities are also available in other types like for example for fixation at awood formwork.
Installation instructions for the use on building sites
Assembly of prefabricated concrete parts on building sites
Place the prefabricated concrete parts next to one another with the hoist, so that the turnbuckles can be inserted, the screw connections properly aligned and loosely fixed by hand.
The clamping connections are to be drawn on in parallel and crosswise using a ring ratchet wrench, until the planned joint width is reached or the compression mountings (base plates, elastomer mountings) are firmly clamped.
When the prefabricated concrete parts are under tension, the recesses for the tie points can be sealed using grout.
The joint area can be sealed with appropriate sealing materials and the external filling of the prefabricated concrete parts can be carried out.
Note: It is absolutely essential to ensure the turnbuckle connections are tightened in parallel and crosswise to avoid any canting. To reduce the effort in terms of the amount of load during clamping, the load of the prefabricated concrete part that is to be assembled can be relieved by using a crane during the clamping process.
If spacing or sealing materials are provided between the prefabricated concrete parts, these are to be fitted before the tensioning and to be activated when required. During the tightening of the screw connections, it makes sense to insert a wooden or plastic wedge between the recess and the turnbuckle in order to fix the turnbuckle
a b h a1 b1
|BT-Spannschloss® M12||70 70 50 25 14|
|BT-Spannschloss® M16||90 90 65 30 18|
|BT-Spannschloss® M20||120 100 90 40 22|
|Tensile force Shear force
N [kN] V [kN]
|BT-Spannschloss® M12||37,7 9,4|
|BT-Spannschloss® M16||43,5 26,2|
|BT-Spannschloss® M20||52,2 24,8|
The turnbuckles are made according to a special casting process and later refined. This process means high levels are achieved in terms of stability and toughness properties. This material means that shaping components which are difficult to make can be manufactured for the highest possible mechanical loads, including chassis parts and drives. Its favourable performance in terms of toughness at low temperatures is another aspect which makes it stand out from the rest and fulfils the requirements of a basic material for turnbuckles which are to ensure the durable construction connection of prefabricated concrete parts.
Bolts, threaded bolts, nuts and washers
Only the following are to be used: hexagon bolts of strength grade 8.8 as per DIN EN ISO 4014:2001-03, threaded bolts of strength grade 8.8 as per DIN 976-1:2002-12, nuts of strength grade 8 as per DIN EN ISO 4032:2001-03 and round washers (wide range) as per DIN EN ISO 7093-1:2000-11.
The corrosion protection of turnbuckles is maintained where there is full mortaring with the use of cement mortar as per DIN 1045-2:2008-08, Section 5.3.8 or as per the DafStb [German Reinforced Concrete Commission] directive, grouting mortar with evidence of exposure classes and in compliance with the minimum concrete cover as per DIN 1045-1:2008-08.
DIN 18800-7:2008-11 applies for the corrosion protection of turnbuckles that have not been fully mortared and the connection elements.