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Reinforcement Systems for Reinforced Concrete Structural Members
In reinforced concrete structures, all columns, beams, and wall elements constructed to carry and transfer loads are referred to as structural members. Structural members are expected to safely carry all types of vertical and horizontal loads—primarily their own dead loads—and transfer them to the building foundation, as well as exhibit ductile behavior.
There are three common methods preferred for reinforcing reinforced concrete structural members. These are FRP reinforcement, FRCM reinforcement, and cladding methods. The FRP reinforcement system is a traditional reinforcement method; the abbreviation FRP stands for Fibre-Reinforced Polymer, and it is also known as CFRP (Carbon Fibre-Reinforced Polymer). The system consists of bonding a technical fabric or plate made of carbon fiber to the exterior of a reinforced concrete structural element using epoxy. In addition to the traditional FRP method, another system widely used worldwide is the FRCM reinforcement system. The FRCM reinforcement system, which stands for Fabric-Reinforced Cementitious Matrix, is a modern and up-to-date method used in repair and reinforcement. The reinforcement matrix, in its simplest form, consists of textile reinforcement (also known as reinforcement fabric or technical textile) and a cement- or lime-based mortar. The third method
PRINCIPLES AND APPLICATIONS OF THE FRP METHOD
FRP reinforcement systems are based on the principle that the stresses acting on a load-bearing structural element are also absorbed by carbon polymer material, thereby increasing the load-bearing capacity and making the structure safer. On the other hand, FRCM reinforcement systems are based on the combined action of mortar and textile reinforcement, similar to the way concrete and steel work together in reinforced concrete. In this context, the system operates on the principle that the reinforcement mortar bears the compressive stresses, while the textile reinforcement bears the tensile stresses, in addition to the load-bearing capacity of the structural member being reinforced. Envelope reinforcement systems are the oldest method of reinforcement, relying on enlarging the cross-section of the load-bearing structural element to create a stiffer element capable of carrying greater loads.
In reinforced concrete structural members, damage may occur under various loads due to insufficient material strength, poor system design, construction errors during building, or incorrect calculations.
Damage to reinforced concrete structural members is considered a primary failure from a system perspective and poses a threat to the safety of the structure. Therefore, the necessary care must be exercised in repair and strengthening applications.
STANDARDS RELATED TO THE FRP METHOD
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Turkish Building Seismic Code 2019
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Technical Specifications for Construction Works of the Ministry of Environment and Urbanization of the Republic of Turkey “Reinforced Concrete Works” 2019
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FIB Bulletin 14 “Externally Bonded FRP Reinforcement for RC Structures”
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FIB Bulletin 35 “Retrofitting of Concrete Structures by Externally Bonded FRPs, with Emphasis on Seismic Applications”
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ACI 440.3R-12 “Guide to Test Methods for Fiber-Reinforced Polymers (FRPs) for Reinforcing or Strengthening Concrete Structures”
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JSCE Concrete Engineering Series, No. 41 “Recommendations for Upgrading Concrete Structures Using Continuous Fiber Sheets”
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CNR-DT 200/2004 “Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Existing Structures – Materials, RC and PC Structures, Masonry Structures”
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ISIS Design Manual No. 4 “Strengthening Reinforced Concrete Structures with Externally Bonded Fiber-Reinforced Polymers (FRPs)”
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CNR-DT 2000 R1 / 2013 “Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Existing Structures”
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ACI 549.4R-13 “Guide to the Design and Construction of Externally Bonded Fabric-Reinforced Cementitious
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Matrix (FRCM) Systems for Repair and Strengthening Concrete and Masonry Structures”
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ICC-ES AC434 10-2018 “Acceptance Criteria for Concrete and Masonry Strengthening Using
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Fabric-Reinforced Cementitious Matrix (FRCM) and Steel Reinforced Grout (SRG) Composites”
FRP METODU KULLANILAN ÜRÜNLER
FRP APPLICATION STEPS
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The surface to be treated is cleaned of all foreign matter and dust.
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Areas requiring repair on the reinforced concrete structural element are moistened and repaired using RPM40.
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For repair, RPM40 is mixed with water in the ratio and for the duration specified on the package, then applied to the damaged areas to create a smooth surface for reinforcement.
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EPX Primer components A and B are mixed and prepared in accordance with the instructions in the technical data sheet.
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The prepared EPX Primer is applied to the reinforced concrete structural element.
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If reinforcement is to be performed using Carbon Fabric, the A and B components of EPX FRP are mixed and prepared in accordance with the instructions in the technical data sheet; if reinforcement is to be performed using Carbon Plate, the A and B components of EPX CP are mixed and prepared in accordance with the instructions in the technical data sheet.
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The prepared EPX FRP or EPX CP epoxy is applied to the reinforced concrete structural element.
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Carbon Fiber or Carbon Plate is placed on the epoxy-coated surfaces.
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If reinforcement is being performed using Carbon Fabric, it is anchored to the existing reinforced concrete structural element using the selected mechanical anchoring element.
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After anchoring, a final coat of EPX FRP is applied over the Carbon Fabric.
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RPM40 or RPM60 is applied as the final coat, and the reinforcement is completed.
FRP METHOD: IMPORTANT DETAILS TO CONSIDER
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Reinforcement must be applied directly to the reinforced concrete structural member. Any loose surface layers, such as plaster, ceramic tiles, paint, etc., must be removed. If rust scaling and reinforcement corrosion are observed on the reinforced concrete member, the loose rust layer must be removed, and the rust layer on the reinforcement surface must be cleaned using mechanical methods and repaired with RPM40.
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Carbon fabric or carbon plate must be installed under tension, leaving no gaps.
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Anchors must be installed at a minimum of 4 per square meter.
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No additional additives such as cement should be added to the mortar; the water-to-cement ratio must strictly follow the guidelines in the technical data sheet. Mixing equipment must be capable of achieving the mixing speed specified in the technical data sheet.
Products Made Using the FRP Method
FRCM METHOD APPLICATION STEPS
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The surface to be treated is cleaned of all foreign matter and dust, then moistened.
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The selected reinforcement mesh is cut to the desired size using appropriate cutting tools.
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RPM40 or RPM60 is mixed with water in the ratio and for the duration specified on the package, then applied to the column, beam, or wall surface using a trowel or spray at a thickness of approximately 5 mm.
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The reinforcement mesh is manually placed onto the spread mortar surface, and a load-distribution plate is positioned before anchoring it to the existing reinforced concrete element using the selected mechanical anchoring element.
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RPM40 or RPM60 is reapplied to ensure a final layer thickness of at least 10 mm, and the surface is finished so that the anchors or mesh are not visible.
FRCM METODU DİKKAT EDİLMESİ GEREKEN DETAYLAR
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Güçlendirme, betonarme taşıyıcı eleman üzerine direkt olarak yapılmalıdır. Yüzeydeki gevşek tabaka, sıva, seramik, boya vb. kaldırılmalıdır. Betonarme elemanda pas payı atması ve donatı korozyonu gözleniyorsa, serbest haldeki pas payı tabakası uzaklaştırılmalı ve donatı yüzeyindeki pas tabakası mekanik yöntemlerle temizlenmelidir.
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Güçlendirme filesi, hiç boşluk bırakılmadan ve yaklaşık 20 cm bindirme yapılarak uygulanmalıdır.
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Ankrajlar, metrekarede minimum 4 adet olacak şekilde yerleştirilmelidir.
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Yüzeylerdeki harcın çatlamasını önlemek amacı ile ilk kürlenme tamamlanıp, harç sertleştikten 20 dakika sonra yüzey ıslatılmalıdır.
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Mümkün olduğu durumlarda güçlendirme filesi, uygulama yapılan düzlemde bitirilmemeli, komşu düzleme 20 cm uzatılarak bu düzlemlerde bitirilmelidir.
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Harçlara ek olarak çimento vb. diğer katkılar eklenmemeli, su oranı mutlaka teknik bilgi föyündeki yönergeler doğrultusunda kullanılmalıdır. Karıştırma ekipmanı, teknik bilgi föyünde önerilen karıştırma hızına sahip olmalıdır.
PRODUCTS USING THE EXTERIOR INSULATION AND FINISHED SYSTEM (EIFS)
STEPS FOR APPLYING THE EXTERIOR INSULATION METHOD
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The surfaces of the reinforced concrete structural elements to be insulated are chiseled down to the rust layer, then roughened and cleaned.
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If column and wall reinforcement is to continue on the upper floor, the ceiling concrete of the relevant section is completely broken up and cleaned without damaging the reinforcing bars. If it is not to continue on the upper floor, the ceiling concrete is drilled in a circular pattern to allow for concrete pouring—every 1 meter for walls and at the corners of columns for columns.
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For rebar installation and anchoring applications, holes are drilled to the diameter specified in the V-500 or PE-1000 technical data sheets, as indicated in the project.
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The holes are cleaned in accordance with the chemical anchor technical data sheets, and the rebar installation or anchoring process is performed.
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Formwork suitable for the section specified in the reinforcement project is constructed.
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Ribbed steel reinforcements are placed as specified in the project.
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At the joints between walls and beams, a 5 cm gap is left to be filled with GROUT after concrete placement.
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Concrete is poured at the relevant locations.
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After the formwork is removed, any damaged concrete surfaces are repaired with RPM40.
KEY CONSIDERATIONS FOR THE EXTERNAL INSULATION METHOD
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Reinforcement must be applied directly to the reinforced concrete structural member. Any loose layers, plaster, ceramic tiles, paint, etc., on the surface must be removed. If rust scaling and reinforcement corrosion are observed on the reinforced concrete member, the loose rust scale layer must be removed, and the rust layer on the reinforcement surface must be cleaned using mechanical methods.
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In rebar installation and anchoring applications, the instructions in the technical data sheets for chemical anchors must be followed, and rebar tying should be performed only after the curing periods specified in the product’s ETA certificates have elapsed.
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PE-1000 must be used when installing rebar in core-drilled holes.
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When tying rebar, tie wire must be used, and tie points must be placed at a minimum of 4 per square meter.
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Formwork must be cleaned and lubricated with formwork oil before being nailed down.
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After reinforcing bars are placed, ensure there are no foreign objects inside the formwork before closing it.
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If self-compacting concrete is not used, ensure adequate vibration is applied, and the concrete must be poured in at least three stages.
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After the formwork is removed, ensure the concrete has cured properly.
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No additional additives such as cement should be added to the mortar; the water-to-cement ratio must strictly follow the guidelines in the technical data sheet. The mixing equipment must be capable of achieving the mixing speed recommended in the technical data sheet.
Sample Projects
