| 1. |
|
|
| 2. |
|
|
| 3. |
- Enochsson, Ola, et al.
(author)
-
CFRP strengthened openings in two-way concrete slabs : an experimental and numerical study
- 2007
-
In: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 21:4, s. 810-826
-
Journal article (peer-reviewed)abstract
- Rehabilitation and strengthening of concrete structures with externally bonded fibre reinforced polymers (FRPs) has been a viable technique for at least a decade. An interesting and useful application is strengthening of slabs or walls where openings are introduced. In these situations, FRP sheets are very suitable; not only because of their strength, but also due to that they are easy to apply in comparison to traditional steel girders or other lintel systems. Even though many benefits have been shown by strengthening openings with FRPs not much research have been presented in the literature. In this paper, laboratory tests on 11 slabs with openings, loaded with a distributed load are presented together with analytical and numerical evaluations. Six slabs with openings have been strengthened with carbon fibre reinforced polymers (CFRPs) sheets. These slabs are compared with traditionally steel reinforced slabs, both with (four slabs) and without openings (one slab). The slabs are quadratic with a side length of 2.6 m and a thickness of 100 mm. Two different sizes of openings are used, 0.85 × 0.85 m and 1.2 × 1.2 m. The results from the tests show that slabs with openings can be strengthened with externally bonded CFRP sheets. The performance is even better than for traditionally steel reinforced slabs. The numerical and analytical evaluations show good agreement with the experimental results.
|
|
| 4. |
- Lundqvist, Joakim, et al.
(author)
-
A probability study of finite element analysis of near surface mounted carbon fiber reinforced polymer bonded to reinforced concrete
- 2007
-
In: Fiber-Reinforced Polymer Reinforcement for Concrete Structures. - Patras : FRPRCS-8 Symposium Secretariat. - 9789608969100
-
Conference paper (peer-reviewed)abstract
- 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.
|
|
| 5. |
- Lundqvist, Joakim, et al.
(author)
-
Numerical analysis of concrete beams strengthened with CFRP : a study of anchorage lengths
- 2005
-
In: Proceedings of the International Symposium on Bond Behaviour of FRP in Structures. - : International Institute for FRP in Construction. ; , s. 239-246
-
Conference paper (peer-reviewed)abstract
- The advantages of Fibre Reinforced Polymer (FRP) strengthening have been shown time and again during the last decade. All over the world several thousand structures have been retrofitted using FRP. Buildings and civil structures usually have a very long life and it is not uncommon that the demands on the structure change with time. The structures may have to carry larger loads at a later date or fulfil new standards. In extreme cases, a structure may need repair due to an accident, or due to errors made during the design or construction phase. To guarantee the function of the strengthening properties, anchorage of the FRP is essential. Without sufficient anchorage lengths, full utilization of the strengthening material cannot be achieved, leading to possible premature failure. In this paper, experimental work and numerical analyses of three different Carbon Fibre Reinforced Polymer (CFRP) strengthening techniques have been carried out. The techniques are externally bonded plates, sheets and the use of Near Surface Mounted Reinforcement (NSMR). The aim is to find a critical anchorage length, where a longer anchorage length does not contribute to the load bearing capacity. Three different anchorage lengths have been investigated; 100, 200 and 500 mm. The finite element program ABAQUS has been used for the numerical study. The results show that a critical anchorage length exists for plates and sheets as well as for NSMR. However, the present study also shows that an exact critical anchorage length may be difficult to estimate, at least with the present test set-up. Further tests and investigations of the constitutive model for the concrete are needed.
|
|
| 6. |
- Malmdin, Joakim, et al.
(author)
-
Ledare Qvartilen 22-1
- 2007
-
Other publication (pop. science, debate, etc.)
|
|
| 7. |
- Malmdin, Joakim, et al.
(author)
-
Ledare Qvartilen 22-2
- 2007
-
Other publication (pop. science, debate, etc.)
|
|
| 8. |
- Malmdin, Joakim, et al.
(author)
-
Ledare Qvartilen 22-3
- 2007
-
Other publication (pop. science, debate, etc.)
|
|
| 9. |
- Malmdin, Joakim, et al.
(author)
-
Ledare Qvartilen 22-4
- 2007
-
Other publication (pop. science, debate, etc.)
|
|
| 10. |
- Olofsson, Charlotta S, 1971, et al.
(author)
-
Impaired insulin exocytosis in neural cell adhesion molecule-/- mice due to defective reorganization of the submembrane F-actin network.
- 2009
-
In: Endocrinology. - : The Endocrine Society. - 1945-7170 .- 0013-7227. ; 150:7, s. 3067-75
-
Journal article (peer-reviewed)abstract
- The neural cell adhesion molecule (NCAM) is required for cell type segregation during pancreatic islet organogenesis. We have investigated the functional consequences of ablating NCAM on pancreatic beta-cell function. In vivo, NCAM(-/-) mice exhibit impaired glucose tolerance and basal hyperinsulinemia. Insulin secretion from isolated NCAM(-/-) islets is enhanced at glucose concentrations below 15 mM but inhibited at higher concentrations. Glucagon secretion from pancreatic alpha-cells evoked by low glucose was also severely impaired in NCAM(-/-) islets. The diminution of insulin secretion is not attributable to defective glucose metabolism or glucose sensing (documented as glucose-induced changes in intracellular Ca(2+) and K(ATP)-channel activity). Resting K(ATP) conductance was lower in NCAM(-/-) beta-cells than wild-type cells, and this difference was abolished when F-actin was disrupted by cytochalasin D (1 muM). In wild-type beta-cells, the submembrane actin network disassembles within 10 min during glucose stimulation (30 mM), an effect not seen in NCAM(-/-) beta-cells. Cytochalasin D eliminated this difference and normalized insulin and glucagon secretion in NCAM(-/-) islets. Capacitance measurements of exocytosis indicate that replenishment of the readily releasable granule pool is suppressed in NCAM(-/-) alpha- and beta-cells. Our data suggest that remodeling of the submembrane actin network is critical to normal glucose regulation of both insulin and glucagon secretion.
|
|
| 11. |
- Rusinowski, P., et al.
(author)
-
Numerical analysis of two-way concrete slabs with openings strengthened with CFRP
- 2006
-
In: Bridge maintenance, safety, management, life-cycle performance and cost. - London : Taylor & Francis Group. - 0415403154 - 9780415403153 ; , s. 1045-1046, s. 387-390
-
Conference paper (other academic/artistic)abstract
- Carbon Fibre Reinforced Polymers, CFRP, offer excellent corrosion resistance to environmental agents as well as the advantages of high stiffness-to-weight and strength-to-weight ratios when compared to conventional construction materials. Perhaps the biggest advantage of CFRP is its tailorability. One common application for CFRP sheets is to strengthen slabs and walls when openings are to be made. In spite of this, there have not been many studies reported on slabs with openings strengthened with CFRP and especially, not with distributed loading. This paper presents numerical analyses of simply supported two-way concrete slabs with openings strengthened with CFRP sheets. The finite element program ABAQUS is utilized for the analyses. The analyses are compared with full-scale laboratory tests and show a good agreement
|
|
