Dissipating tensile and compressive forces
Since concrete is able to absorb high compressive forces, but only low tensile forces, attempts to strengthen or reinforce concrete with iron began in the mid-19th Century. In Germany, the iron rods are still named ‘Monier Iron’ after the owner of the first patent in this field, gardener Joseph Monier. Due to the metal braid, tensile forces and – in highly stressed areas – compressive forces are absorbed effectively. The requirements for reinforcement are based on DIN 1045-1. The member companies of the ECS provide various products for reinforcing systems.
The different positioning and product alignment within the association is desired provided that it complies with the association’s quality policy and the common criteria.
ECS members are active in the following reinforcing system-related areas:
Rebar connections provide the join between reinforced concrete elements. Different types of connection are available depending on the element and task:
- threaded couplers connect reinforced concrete elements with each other and are available in different versions.
- clamping connections are used during the restoration of reinforcements and create the connection between old and new sections or to large precast elements, such as central stairways.
- rebending connectors quickly and firmly join precast steel reinforced concrete elements, which are manufactured in different phases of construction.
- shear load connectors or dowels transfer the transversal forces at joints between different building elements, such as concrete slabs or supports.
- column shoes form the connection between the foundation and precast steel reinforced concrete columns. They enable rapid assembly without additional mounting struts.
The products of the member companies of the ECS from this area are either regulated by approvals or type tests and comply with the safety standards of DIN 1045-1 and Eurocode 2.
As a cost-saving construction technique, flat slabs are widely used in concrete construction because in addition to only a small amount of formwork, they also provide optimum space utilisation. The use of punching shear reinforcement in columns enables thin slabs throughout because it absorbs very high shear forces. Rapid construction progress is guaranteed as well as the necessary high level of installation safety. For the installation of punching shear reinforcement, different versions are available for in-situ concrete and prefabricated slabs:
- installation of the punching shear reinforcement from below: shear reinforcement and spacers are placed directly on the formwork; lower and upper steel reinforcement is mounted via the bolt heads;
- installation of the punching shear reinforcement and spacer between the welded wire mash by installing the shear reinforcement after the lower reinforcement layers are positioned;
- installation of the shear reinforcement from above, i.e. after the installation of the lower and upper reinforcement layers.
The fitting of balconies places high demands on the connection systems used. They must:
• satisfy increased requirements for corrosion resistance;
• prevent the formation of condensation inside the building;
• prevent thermal bridges as per the German Energy Savings Act (EnEV);
• meet the requirements for sound decoupling;
• be adapted to the building’s fire rating, and
• cope with the balcony’s environmental conditions.
Accordingly, depending on the situation when installing, different systems are available that absorb bending and/or transversal forces, such as in the case of cantilevered balcony slabs, simple supported balconies, or in loggia areas. Special solutions for precast concrete elements are also available. In addition to balcony fixing, ECS members offer anchor channels and fixing systems suitable for handrails and parapets.
For the durability of reinforced concrete elements and compliance with fire safety requirements, an adequate concrete cover of the inserted reinforcement is of vital importance. Spacers, which fix the reinforcement in place during installation and subsequent concreting, are used to ensure an adequate concrete cover. Since the spacers stay in the reinforced concrete, their material must – also in the long-term – not have an adverse effect on the concrete or reinforcement. Spacers can be divided according to shape (linear, flat or point-like) and material (plastic or cement-based).
The spacers in construction elements that are frequently exposed to freeze-thaw cycles or temperature stresses are subject to special requirements. This applies even if they are used in impermeable reinforced concrete elements. Spacers in exposed concrete elements must be chosen carefully to achieve the best possible appearance. In that respect, it may be necessary to make test slabs with different spacers. At any event, selection of the spacers should be made by the planner and not the construction company since only the planner has all the relevant data.