A probability study of finite element analysis of near surface mounted carbon fiber reinforced polymer bonded to reinforced concrete

• A structure is typically designed for a long life and it is probable that the demands on it change over time, e.g. carry larger loads or fulfill new standards. The structure might also have been exposed to a harsh environment leading to a degradation of its structural capacity. These reasons, and more, may lead to a need for strengthening the structure. Strengthening of reinforced concrete structures with carbon fiber reinforced polymers (CFRP) has been shown to be a very effective and advantageous retrofitting technique. The weight-to-strength ratio and resistance to corrosion are some of the advantages. Several different strengthening systems are available with CFRP and a relatively new technique is the near surface mounted reinforcement (NSMR) method. As opposed to externally mounted strengthening systems, NSMR is composed of sawing a groove in a concrete member, applying an adhesive in the groove and inserting a CFRP bar. Although the idea of embedding reinforcing tendons in existing structures has been present for several decades [1], acceptance of the method has only been possible with the emergence of the FRP material. As NSMR comprise of the properties and advantages of an ordinary FRP strengthening system, e.g. plates, it also has the benefit of being embedded in the concrete. This means better protection against impact, fire, abrasion and a natural resistance to peeling stresses. Strengthening of concrete members with NSMR have been reported by e.g. [2], [3], [4], and [5]. For NSMR, or indeed for most FRP strengthening techniques, the bond between the concrete and the strengthening material is the most important issue. This is where the transfer of stresses takes place to realize full composite action. The behavior of strengthened reinforced concrete is quite complex and an approach to investigate this is to utilize the finite element (FE) method. Many numerical analyses of reinforced concrete strengthened with CFRP using the FE method have been carried out in recent years. These concern primarily studies of plate bonding though there are a few studies of bonding of NSMR. In [6], concrete beams are strengthened with plates and the analytical shear and peeling stresses are compared with a linear finite element (FE) analysis. Several authors, e.g. [7], have emphasized that sufficiently small elements must be used in a FE analysis to accurately describe stress distributions, particularly at the end of a bonded plate. Teng et al, [8], make further refinement of the FE mesh and examine the interfacial stresses in reinforced concrete beams bonded with a soffit plate. A concern for the element size where stress singularities occur was also raised. Nonlinear FE analyses of reinforced concrete strengthened with NSMR are performed in [3], [4], [5], and [9]. The common failure mode of a strengthening system with plates is in the outermost concrete layer close to the adhesive. This has been reported in many papers, e.g. [9]. The failure mode for NSMR is more complex. It spans from being a failure in the adhesive close to the FRP bar, i.e. pure pullout, to the concrete layer close to the adhesive, as for FRP plates but with the difference that more concrete is dislodged. In between, a mixed mode of failure is present with cracks in both the adhesive and the concrete. Where the failure occurs is determined by geometrical and material parameters. The thickness of the adhesive, the position of the bar in the adhesive, and the bonding length are possible geometrical parameters. Material parameters are the modulus of elasticity and Poisson's ratio of the concrete, adhesive and the FRP, and of course the tensile strength of the concrete and adhesive. Also, the configuration and the properties of the internal reinforcement may determine the failure mode. To study the bond behavior of reinforced concrete strengthened with NSMR, a test for CFRP bar pullout was devised. This is illustrated in Figure 1 and is reported in [10]. The concrete beam has a minimum amount of reinforcing steel not shown in the drawing. In this paper, the pullout of a rectangular NSMR CFRP bar bonded to reinforced concrete is studied by a finite element analysis in the linear elastic domain. Also, a Monte Carlo simulation, with the FE model incorporated, is carried out with the purpose of determining which geometrical and material parameters that are the most important for where the tensile strength is attained; in the adhesive or the concrete. The following simplifications have been made in this study; all materials are considered as isotropic and linear elastic, and the FE model utilizes symmetry.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Samhällsbyggnadsteknik -- Infrastrukturteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Civil Engineering -- Infrastructure Engineering (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Samhällsbyggnadsteknik -- Byggproduktion (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Civil Engineering -- Construction Management (hsv//eng)

Nyckelord

Structural Engineering

Konstruktionsteknik

Byggproduktion

Construction Engineering and Management

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