In the 1960s, experiments to identify alternative raw materials led to the discovery and production of carbon fibres from petroleum derivatives. These fibres, composed of approximately 85% carbon, quickly stood out for their exceptional flexural strength.
Carbon Fiber Reinforced Polymer (CFRP) is a synthetic material consisting of mostly carbon filaments between 6 and 10 μm in diameter. For decades, CFRP has been widely used in the aerospace and automotive industries as a lighter and less maintenance-intensive alternative to traditional steel plates.
But carbon fibres, integrated into CFRP systems, have also proven to be extremely versatile and useful for reinforcing structures and correcting various construction pathologies. The latter include those caused by deterioration due to aggressive environmental conditions, changes in use and/or increased loads, etc. In the case of reinforcements, they have often been used in upgrades to improve the response of buildings to seismic activity.
The main structural applications of CFRP include the following:
–Bending reinforcement: carbon fibre laminates are externally bonded to structural elements such as beams and slabs, in the positive and negative moment zones, to increase their bending strength.
–Shear reinforcement: the effectiveness of this type of reinforcement depends on the ability of the carbon fibre to externally bond and transfer the load, so the available anchorage length is crucial to ensure its efficiency.
-Structural confinement: this procedure is commonly applied in the reinforcement of pillars, silos and tanks. By confining with carbon fibre fabric, the overall strength and axial load capacity of these elements is improved.
Let us now look at the limitations of CFRP and other considerations:
Although carbon fibre has high tensile strength, it has zero ability to absorb compressive stresses due to its slenderness. For this reason, it is not used on the compressed faces of bending beams or in columns. Alternatively, carbon fibre fabrics, placed perpendicular to the compressive stress, can be used in the transverse strapping. This improves the stability of the element and its deformation capacity.
In short, carbon fibres combine lightness, strength and versatility when it comes to structural reinforcement in construction. It is a key technical solution for the rehabilitation and adaptation of structures to the demands of today’s environment.
Images: Sika.
By Jean Carlos Soto, Senior Structural Engineer in Amusement Logic’s Architectural Dept.
