Fourth International Conference on FRP Composites in Civil Engineering (CICE2008) 22-24July 2008, Zurich, Switzerland

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1 INTRODUCTION

First step is making the numerical models for the main materials such as concrete or masonry blocks in FEM software and verify them by the existing experimental/laboratory specimens. The second step is to build the existing structure or a part of the structure using the proper boundary conditions and load pattern and if possible verify them by existing evaluations. The final step is to create the retrofitted models and compare them to gain the better results.

Since this research is an approach to numerical modeling, it was assumed that the experimen-tal specimens are already evaluated. The below flowchart (Figure 1) shows the procedure of modeling the concrete or masonry structure and retrofitting with FRP material using rebar sur-faces.

A new approach to numerical modeling of the FRP material attached to the concrete or masonry structures using explicit dynamic finite elements method Nima Taghi bekloo Nimavar ArtaVage consulting engineers, Vice president/Structural engineer, Iran

ABSTRACT: During the past decade polymer materials and specially FRP material is one the famous strengthening and retrofitting materials, and due to its weightlessness it is becoming a favorite to earthquake engineers. Hence knowing the behaviors, advantages and also disadvan-tages of the FRP is a must; the common method for designing the FRP materials is more like reinforced concrete design in elastic behavior (L. Podolka and J. Kolísko, 2005 and H. Saadat-manesh and A.M. Malek, 1998). Since the rebar in reinforced concrete is continuous and has frictional behavior and most of all has got the yield point about 10 times more than concrete, the design methods are quite suitable for concrete structures. However using the FRP materials mostly is local and not continuously; also FRP materials have the yield point more than the steel materials with a too narrow plastic range which may cause a brittle cracking especially in mod-erate and high earthquakes. Also locally strengthening the structure may cause stress concentra-tions and crack propagation on the regions that has no strengthening around the strengthened re-gion. Hence realizing the structure behaviors before and after FRP assembling is essential and need some special considerations. This research represents a method for numerically modeling the FRP stripes on concrete or masonry structures and evaluates the behavior of these structures before and after retrofitting. The main advantages of this method are the time saving, low cost and ability to make several models and investigate them for reaching the better resolutions. This research contains a Finite Element method to model the structure either with the FRP stripes or without them.

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Figure 6- Crack patterns of the experimental test specimen. (Hernán Santa Maria, Pablo Alcaino and Carl Luders, 2006)

The summarized conclusion is being described below:

Table 1- Comparison between two specimens

Specimens Max. Stress (Tresca) Avg. Stress (Tres-ca)

Max. Damage Avg. Damage

Specimen With FRP 84 kg/cm2 28 kg/cm2 8.5% 3.5% Specimen Without FRP 62 kg/cm2 16 kg/cm2 9.8% 1%

Figure 7- Base shear vs. Displacement

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Figure 9 shows that the capacities of two specimens are the same, however there is some ma-jor difference in the behavior after the crack acquires and the strengthened specimen resist more than the other one.

3 CONCLUSION

Numerical investigations of structures strengthened by FRP materials is possible if only the behavior of the structure could be identified before and after FRP retrofitting accurate way and fast as well.

The FRP stripes can be simulated using surface elements with rebar definition in any direc-tion (between 0 to 180 degree).

Since the analysis is time consuming, it’s important to build the model with care and choos-ing the right elements and material properties such as shell or solid elements either quad or tri elements. It has to be noticed that tri elements are much more time consuming than quad ele-ments especially in conjunction with FRP surface elements and sometimes it’s about 5 times more.

The contact between FRP stripes and concrete or masonry material has much more strength than the material itself, hence the FRP stripes shall be embedded on the structure surface. How-ever the contact can be simulated as slips or shear rate or even frictional contact regarding the type of resin to be used (ABAQUS/CAE documentation, Sec. 30.1.5).

4 REFERENCES

L. Podolka and J. Kolísko 2005, Experience with strengthening structures using the pre stress FRP materials, 2005 International Institute for FRP in Construction.

H. Saadatmanesh and A.M. Malek 1998, Design guidelines for flexural strengthening of RC beams with FRP plates, Journal of composites for construction.

Hernán Santa Maria, Pablo Alcaino and Carl Luders 2006, Experimental response of maso-nry walls externally reinforced with carbon fiber fabrics

ABAQUS/CAE documentation, Sec. 18.5.3-Concrete damaged plasticity. ABAQUS/CAE documentation, Sec. 30.1.5-Contact property, Frictional behavior ABAQUS/CAE documentation, Sec. 18.3.1-Extended Drucker-Prager models.