Column’s confinement

RELATED MATERIALS

MEGAWRAP-200 Carbon fabric for structural strengthening

EPOMAX-LD Two-component, epoxy impregnation adhesive for composite fabrics

EPOMAX-EK Two-component epoxy putty

MEGACRET-40 High-strength, fiber-reinforced repairing mortar

 

I. NATURE OF THE PROBLEM – REQUIREMENTS

The columns of a construction are likely to present, under certain circumstances, deficiency in strength or/and ductility (ability to deform in case they have to bear seismic or other unexpected loads). It is therefore essential to reinforce these elements.

The confinement of a column takes place in the following cases:

  • Adjustment of old buildings to regulation amendments.

  • Ageing of construction materials and corrosion of reinforcement elements.

  • Existing construction defects (e.g. inadequate number, distribution and placing of hoops).

  • Load increase or change of use.

  • Repairs in reinforced concrete elements after earthquakes.

II. SOLUTION

Confinement of concrete with a MEGAWRAP-200 jacket offers:

  • Increase of the ability to deform (e.g. in areas with plastic joints).

  • Increase of the compressive strength.

  • Decrease of the possibility of local bending of the reinforcement elements.

  • Improvement of the elements’ coherence at the critical areas with reinforcement splices.

In relation to the conventional reinforcement systems, such as steel or concrete jackets, MEGAWRAP-200 jacket provides the following advantages:

  • Easy and fast work.

  • Increase of the strength and ductility of construction elements without changing their geometry or increasing their rigidity.

  • Resistance against time and protection of reinforcement against corrosion.

III. APPLICATION

The substrate (concrete) must be free of loose parts, plaster, paint, oil or grease. After thorough cleaning, the surface is well rubbed with a hard brush.

Existing cracks should be repaired by resin injections.

The outside edges are carved round in a radius of 10-30 mm.

The substrate should be as flat as possible. Surface imperfections are repaired using MEGACRET-40 fibre-reinforced cement-mortar or EPOMAX-EK epoxy paste.

The efficiently prepared surface is coated with EPOMAX-LD resin. The fabric is cut with a scissor in the desired dimensions, placed carefully well stretched on the wet surface and pressed well with a special plastic roller to achieve better contact with the substrate, thorough impregnation and removal of air bubbles. If, in spite of the careful pressing, there are still some dry spots on the fabric, these are additionally coated externally with EPOMAX-LD. During the wrapping of columns, an overlapping of 15-20 cm is required between edges of adjacent fabric ribbons.

If more than one fabric layers are specified, the application process is repeated. In that case the previous layer should not be completely dry, or else good rubbing will be required once again before the new application.

The last fabric layer is also soaked on the outside with EPOMAX-LD and then quartz sand is broadcast on the still fresh resin coating in order to apply later a subsequent protective cementitious coating.

IV. REMARKS

  • The confinement’s efficiency depends on the sides ratio of the column’s cross-section (as the ratio increases the efficiency decreases), as well as on the curvature radius of the column edges (the bigger the curvature the better the confinement).

  • If the substrate’s strength has to be tested, this is done by the Pulloff method.

  • Special attention should be given during the fabric cutting process in order to prevent folding or crumpling of the fabric. Furthermore, the fabric’s surface must be clean before application, free of dust, grease etc.

  • During wrapping, there is no need for overlapping between successive ribbons in height. Their distance, however, must not exceed 10 mm.

  • Open time of epoxy systems decreases when ambient temperature rises.

  • The temperature of the concrete’s surface during F.R.P. applications must be at least +5οC.

  • Since the development of high temperatures in the construction (e.g. in case of fire) decreases substantially the confinement’s efficiency, external protection of the F.R.P. jacket (by special coatings, gypsum boards etc.) is required. The repaired final surface must also be protected in cases of exposure to solar radiation.

  • The use of protective equipment (gloves, goggles etc.) during application is essential.