plik

�� Ching Chiaw Choo Issam E Harik Modernizacja most�w betonowych przy zastosowaniu CFRP RETROFIT OF CONCRETE BRIDGES USING CFRP Streszczenie W Stanie Kentucky w USA wiele most�w modernizowano ostatnio z wykorzystaniem laminat�w i materiaB�w z polimeru zbrojonego wB�knem wglowym (CFRP). Most z spr- |onych element�w betonowych w Carter County byB modernizowany w aspekcie poprawy wytrzymaBo[ci na [cinanie na wszystkich trzech przsBach z wykorzystaniem materiaBu CFRP. Modernizacja przyniosBa stanowi Kentucky oszczdno[ci w wysoko[ci USD 500.000 w por�wnaniu do pierwotnego rozwizania wymiany caBych nawierzchni. Most w Louisa- Fort Gay, w hrabstwie Lawrence County w Kentucky to czteroprzsBowy monolityczny most z dzwigarami z pByt ze zbrojonego betonu. Most byB modernizowany gB�wnie ze wzgldu na ugicie w odpowiedzi na pknicia obecne w wikszo[ci dzwigar�w. Do mo- dernizacji zastosowano laminaty z CFRP. G�rny odcinek drogi midzystanowej Interstate 65 (I-65) w Louisville w Stanie Kentucky jest modernizowany w trzech lokalizacjach ze wzgldu na powa|ne pknicia spr|onych dzwigar�w betonowych i filar�w z betonu zbrojonego z wykorzystaniem prt�w z CFRP umieszczanych w pobli|u nawierzchni oraz materiaBu CFRP. GB�wnym i najwa|niejszym problemem przy tych naprawach z wykorzystaniem materiaBu CFRP jest prowadzenie modernizacji w spos�b nie zakB�cajcy ruchu pojazd�w. Do tego wszystkiego nale|y doda fakt, i| naprawy przy u|yciu materiaBu CFRP okazaBy si taDsze ni| w przypadku alternatywnych metod. Referat przedstawia analiz, projekt oraz realizacj modernizacji w przypadku tych trzech projekt�w. Abstract A number of bridges have recently been retrofitted in the state of Kentucky, USA using carbon fiber reinforced polymer (CFRP) laminates and fabrics. A prestressed concrete Ph.D. Ching Chiaw Choo Dept. of Civil Engineering, University of Kentucky Ph.D. Issam E Harik Dept. of Civil Engineering, University of Kentucky spread box beam bridge in Carter County was retrofitted for shear in all three spans using CFRP fabric. The retrofit saved Kentucky US $500,000 as compared to the original solution of replacing the entire superstructures. The Louisa-Fort Gay Bridge, in Lawrence County, Kentucky, is a four-span monolithic reinforced concrete slab-girder bridge. The bridge was retrofitted primarily for flexure in response to the flexural cracking present in the majority of the girders. CFRP laminates were used for the retrofit. The elevated portion of Interstate 65 (I-65) in Louisville, Kentucky is being retrofitted at three locations for severe cracking in the prestressed concrete girders and reinforced concrete pedestals using CFRP near surface mounted strips and CFRP fabric. The primary and most important among all these repairs using CFRP material is the conduct of the retrofit without disruption to traffic. This is in addition to the fact that the repairs with CFRP material were less expen- sive than other alternate repair methods. The paper will discuss the analysis, design, and application of the retrofit for the three projects. Retrofit of Concrete Bridges Using CFRP 1. Introduction The use of fiber-reinforced polymer (FRP) in rehabilitation and strengthening of existing infrastructures has become an increasingly common practice due to FRP s unique proper- ties; high strength-to-weight ratio, non-conductivity, magnetic transparency, corrosion- resistance, etc. The composites, among the popular ones are the carbon and glass fiber types, have found their usage in a variety of applications in repairing and strengthening concrete structures or structural elements such as reinforced or prestressed concrete beams, concrete pedestals and reinforced concrete columns, piers and bents, concrete walls and slabs (Avramidou et al. 1999, Chajes et al. 1994, Ehsani et al. 1999, Hamilton & Dolan 2001, Holloway & Leeming 1999, Hutchinson & Rizkalla 1999, Khalifa & Nanni 2000, Karbhari et al. 1999, Lam & Teng 2001, Norris et al. 1997, Tan 1997, Yamakawa et al. 1999, and Zhao et al. 2002). In Kentucky, USA several bridges deficient in one way or another in need to imme- diate repair and strengthening were done so by the use of carbon fiber reinforced polymer (CFRP) in the form of fabrics or laminates: (1) bridge girders of a prestressed concrete bridge in Carter County were retrofitted in shear, (2) reinforced concrete girders and concrete pedestals of a bridge in Lawrence County were strengthened in flexure and in axial, and (3) continuous concrete spans and concrete pedestals of an elevated highway bridge in Jefferson County were also repaired, using this composites. The sections to follow briefly describe the work and the process involved in these retrofits. 2. Retrofit of Concrete Bridge Components Using CFRP Composites 2.1. The bridge in Carter County, KY The retrofit of the prestressed concrete girder spans of a bridge in Carter County was funded by the Innovative Bridge Research & Construction (IBRC) Program one of the Federal Highway Administration s (FHWA) Discretionary Programs intended to deve- lop and promote the use of new materials and construction techniques for the repair, rehabilitation, replacement, or new construction of bridges and other structures and the project was the first full-scale repair performed using FRP composites undertaken in Kentucky. The bridge is located on Route KY-3297 crossing the Little Sandy River in Carter County, KY. The three-span (21-30-13 m) bridge consists of precast prestressed concrete box-beams supporting a 200-mm thick reinforced concrete deck. This bridge was desi- gned for a truck live load 25% over the existing standard HS20-44 truck or lane loads of the AASHTO Standard (2002). The bridge was officially included in the State s Bridge Inventory in 1993 after its completion and inspection. Figure 1 shows the typical precast prestressed box beams at an end abutment. A routine inspection conducted in April 1996, approximately three years since its completion, discovered significant shear cracks had developed in all the box beams at both ends of the 30-m middle span. Initial measurement indicated that the cracks were approximately 3.2 mm wide, and 1.8 to 2.4 m long developing diagonally in the webs (Photo 2). A close-up of a typical crack is shown in Photo 3 where internal reinforcing is 3 Ching Chiaw Choo, Issam E Harik visibly exposed. Due to the severity of the crack, an immediate evaluation was launched and a subsequent inspection to the bridge was scheduled. The analytical evaluation con- firmed that all the prestressed box beams were indeed deficient in shear. Figure 4 shows shear strength of different prestressed box beams of different spans. The subsequent visit to the bridge revealed that the shear cracks in the 30-m middle span were propagating at an alarming rate, and new shear cracks were also beginning to develop in the 21-m end span and the 13-m end span. Phot. 1. Typical precast prestressed box beams at an end abutment Phot. 2. Shear crack at one end of the 30-m middle span Phot. 3. Wide crack exposing the in- ternal reinforcing 4 Retrofit of Concrete Bridges Using CFRP a) 21-m span at the interior Pier 2 b) 30-m span at the interior Pier 2 c) 30-m span at the interior Pier 3 d) 13-m span at the interior Pier 3 Fig. 4. Shear strength of precast prestressed box beams After planning and design of the retrofit, the strengthening of the precast prestres- sed box beams in shear using CFRP fabric was completed in October 2001. In general, the retrofit was done in the following phases: (1) general crack injection and repair; and (2) application of CFRP fabric. One of the goals in crack repair was to restore partially the beam capacity prior to CFRP application. Crack injection and filling also provided additional protection to the exposed reinforcing, in addition to preventing air pockets or bubbles being trapped behind the fabric. Photo 5 depicts the crack repair technique used in this particular project. Once the affected concrete surface have been thoroughly cleaned and dried, a two-part epoxy resin was applied as primary coating. The CFRP fabric was subsequently placed and pressed lightly into the resin via the use of regular paint roller. The fabric was placed 45 degree with respect to the beam axis (i.e. close to being perpendicular to the crack) in hope to maximize the use of the tensile properties of the CFRP fabric. Figure 6 shows how the CFRP fabric is applied onto the concrete surface, and Photo 7 shows the completed work. 5 Ching Chiaw Choo, Issam E Harik a) Mounting of crack injection ports b) Sealing of crack prior to epoxy injection c) High pressure injection of epoxy into d) Grinding of excess epoxy and injection crack ports Phot. 5. Repair of shear crack prior to CFRP application Phot. 6. Application of a CFRP fabric sheet onto the concrete 6 Retrofit of Concrete Bridges Using CFRP Phot. 7. Precast prestressed box beams retrofitted with CFRP fabrics 2.2. The bridge in Lawrence County, KY The 27 year old bridge represents a vital route to the people in two cities of different states with the closest interstate highway to the cities located some forty miles away. The multi-span bridge, carrying two lanes of opposite traffic, consists of spans with steel beam and concrete slab (at the bridge s approaches) and cast-in-place reinforced concrete spans (intermediate span). A schematic of the intermediate cast-in-place reinforced con- crete spans (Labeled as Spans 4-5-6-7) is depicted in Figure 8. Although not shown, the individual longitudinal reinforced concrete girders in the various spans have different reinforcement detailing; owing to the geometric differences and loading. Fig. 8. Reinforced concrete intermediate spans of the bridge is Lawrence County, KY 7 Ching Chiaw Choo, Issam E Harik Load limits are posted for 3-axle, 4-axle, and 5-axle trucks traversing the bridge; with the maximum allowed for a 5 or 6-axle trucks posted at approximately 56 metric ton (126,000 pounds). Based on weigh-in-motion data vehicles weighing in excess of 100 metric ton (225,000 pounds) had crossed the bridge. Inspection at the ground elevation which is approximately 12 m (40 ft) to the spans, showed sign of visible cracking along the bottom surface of many of the reinforced concrete girders; particularly those in Spans 4, 6, and 7. A close-up photo of the cracks at the bottom surface of a reinforced concrete girder obtained using a boom truck is presented in Photo 9. Inspection also concluded that the most developed cracks were located near mid-span of the girders. Phot. 9. Cracking at the bottom surface of a reinforced concrete girder Moment-curvature analysis was carried out on the reinforced concrete girders. Based on the analytical result, it was determined that the bending moments in the girders (i.e. Girders 1 to 5 in Spans 4, 6, and 7) with significant cracking were either exceeding or close to exceeding the allowable service moment defined in AASHTO (2002), the AASHTO allowable service moment is based on 60% of yielding stress (f = 0.6f ). Due to the need s y of an immediate strengthening and crack control, CFRP laminates were selected. Similar moment-curvatures analyses were carried out to determine the amount of CFRP laminates required. Figures 10 and 11 show typical moment-curvature responses of the reinforced concrete girders prior to and after strengthening. Figures. 10.a or 11.a are plotted for service moment-curvature responses (load and resistance factors equal 1.0) whereas Figures. 10.b and 10.c or Figures. 11.b and 11.c are plotted for factored moment-curvature responses. For example, Figure 5.a shows the service moment due to dead load plus overweight truck versus the service moment of AASHTO (2002). It should be mentioned that the live load moment was generated for a single overweight truck and that the weight of the truck is obtain from weigh-in-motion data. When more than one truck exists, which is a real possibility, the live load moment could therefore be significantly higher. The results show that the girders were overloaded and the cracks were due to overweight trucks. 8 Retrofit of Concrete Bridges Using CFRP a) Service load condition for original beam section b) Ultimate load condition for original beam section c) Ultimate load condi- tion for retrofitted beam section Fig. 10. Moment-curvature responses of reinforced concrete Girder 4 in Span 4 (see G4 S4 in Fig. 8) before and after retrofitting with CFRP laminates 9 Ching Chiaw Choo, Issam E Harik a) Service load condition for original beam section b) Ultimate load condition for original beam section c) Ultimate load condition for retrofitted beam section Fig. 11. Moment-curvature re- sponses of reinforced concrete Girder 2 in Span 7 (see G2 S7 in Fig. 8) before and after retro- fitting with CFRP laminates 10 Retrofit of Concrete Bridges Using CFRP The repair carried out using CFRP laminates was similar to the procedure used in the previous bridge. Here, Photo 12 shows a worker preparing the concrete surface co- nveniently using a hand grinder. Photo 13 shows how a CFRP laminate is being attached to the soffit of the reinforced concrete beam; in the figure, one can see that clamps are used along the beam to keep the laminate in place while the epoxy harden to the desired strength. Photo 14 shows the retrofitted girders in Span 4. Phot. 12. The concrete surface is being prepared using a hand grinder Phot. 13. CFRP laminate is being attached to the soffit of a concrete beam 11 Ching Chiaw Choo, Issam E Harik Phot. 14. Retrofitted girders in Span 4 2.3. The elevated I-65 Expressway bridge in Jefferson County, KY The interstate 65 elevated highway bridges in Louisville span across a number of streets in the heart of Louisville, Jefferson County, KY. The bridge was completed in 1979, and a number of cracks had developed in many of the prestressed concrete girders over the years. As depicted in Photo 15, the cracks are mostly vertical and are located near or at the supporting piers. Phot. 15. Typical crack in a prestressed concrete girder Preliminary investigations indicated that these cracks may have developed due to shrinkage. The cracks are especially apparent at piers with fixed restraints where the axial shortening of girders is prevented. Cracking due shrinkage is inevitable in concrete structures and must be controlled to prevent severe serviceability problems. To control cracking CFRP fabric is used at seventy one locations of the bridge. A schematic diagram showing how the fabric is applied is presented in Figure 16. In this particular case, CFRP fabric has been selected as the primary retrofitting material because of its tremendous flexibility and conformity, in addition to having excellent tensile strength. 12 Retrofit of Concrete Bridges Using CFRP Fig. 16. Crack control in prestressed concrete girders using CFRP fabric In addition to cracking of prestressed concrete girders, several concrete pedestals supporting of the superstructure of I-65 Expressway were also repaired due to severe cracking, and in some cases, spalling of concrete cover, as depicted in Photo 17. The repair of these concrete pedestals was done by wrapping CFRP around them. In the case where severe spalling of concrete has occurred, the repair was first done by removing the loose a) Cracking on short concrete pedestal b) Cracking on concrete pedestal built-in integrally with web wall Phot. 17. Damaged concrete pe- destals 13 Ching Chiaw Choo, Issam E Harik concrete and debric of the pedestal. It was then followed by patching of new concrete prior to CFRP wrapping. For pedestals with relatively small cracking, the cracks were injected with epoxy similar to the one described in Section 2.1 of this paper. The retrofitted concrete pedestals are shown in Photo 18. Phot. 18. Retrofitted concrete pedestals 3. Summary and conclusions This paper presents three bridge retrofitting projects done in the state of Kentucky, USA. The repairs were done (1) to strengthen prestressed concrete spread box beams in shear, (2) to repair and strength reinforced concrete girders in flexure, and (3) to control cracking in prestressed concrete I-beams and to confine concrete pedestals, using either CFRP fabrics or laminates. Based on these experiences, the followings can be concluded for repair using these composite materials: The repair generally involves the use of light-weight hand tools and kits; The repair minimizes the need for traffic control. In all cases reported herein, no di- sruption of traffic has occurred, since all lanes were open to traffic while work was being performed underneath the bridge. In the repair of precast prestressed spread box beams, the project saved the state ap- proximately US $500,000 as compared to the original solution of replacing the entire superstructures. The cost analysis for two others was not performed. While not presented in this paper, the effectiveness of the repair for beam elements in shear or in flexure was monitored using crack monitoring gauges which were installed immediately after each retrofit. Thus far no crack movement has been observed. 14 Retrofit of Concrete Bridges Using CFRP References [1] AASHTO. 2002. Standard Specifications for Highway Bridge. 17th Ed. American Association of State Highway and Transportation Officials. Washington, D.C. [2] Avramidou, N., Drdacky, M.F., & Prochazka, P.P. 1999. Strengthening Against Damage of Brick Walls by Yarn Composites. Proceeding of the 6th International Conference on Inspection, Appraisal, Repairs & Maintenance of Buildings & Structures, Melbourne, Australia. [3] Chajes, M. J., Thomson, T. A., Januszka, T. F. and Finch, W. W. Jr. 1994. Flexural Strengthening of Concrete Beams Using Externally Bonded Composite Materials. Construction and Building Materials, Vol. 8, No. 3. [4] Ehsani, M. R., Saadatmanesh, H. and Velazquez-Dimas, J. I. 1999. Behavior of Retrofitted URM Walls under Simulated Earthquake Loading. ASCE Journal of Composites for Construction. Vol. 3, Issue 3. pp. 134-142. [5] Hamilton III, H. R. and Dolan, C. W. 2001. Flexural Capacity of Glass FRP Strengthened Concrete Masonry Walls. ASCE Journal of Composites for Construction. Vol. 5, Issue 3. pp. 170-178. [6] Holloway, L.C., & Leeming, M.B. 1999. Strengthening of Reinforced Concrete Structures using Exter- nally-Bonded FRP Composites in Structural and Civil Engineering. 1st Ed., Cambridge: Woodhead Publishing Limited. [7] Hutchinson R.L. & Rizkalla, S.H. 1999. Shear Strengthening of AASHTO Bridge Girders Using Carbon Fiber Reinforced Plastic Sheets. Fourth International Symposium Fiber Reinforced Polymer Reinfor- cement for Reinforced Concrete Structures, Amercian Concrete Institute, ACI International SP-188, Farmington Hill, Michigan. [8] Khalifa, A. and Nanni, A. 2000. Improving Shear Capacity of Existing RC T-section Beams Using CFRP Composites. Cement and Concrete Composites. Vol. 22. [9] Karbhari, V.M., Seible, F., Seim, W., & Vasquez, A. 1999. Post-Strengthening of Concrete Slabs. Fourth International Symposium Fiber Reinforced Polymer Reinforcement for Reinforced Concrete Structures, American Concrete Institute, ACI International SP-188, Farmington Hill, Michigan. [10] Lam, L. and Teng, J. G. 2001. Strengthening of RC Cantilever Slabs Bonded with GFRP Strips. ASCE Journal of Composites for Construction. Vol. 5, Issue 4. pp. 221-227. [11] Norris, T., Saadatmanesh, H., & Ehsani, M. 1997. Shear and Flexural Strengthening of R/C Beams with Carbon Fiber Sheets. Journal of Structural Engineering, American Society of Civil Engineering (ASCE), Vol.123, N. 7. [12] Tan, K.H. 1997. State-of-the-Art Report on Retrofitting and Strengthening By Continuous Fibers So- utheast Asian Perspective Status, Prospects and Research Needs. Non-Metallic (FRP) Reinforcement for Concrete Structures Proceedings of the Third International Symposium, Vol. 1. [13] Yamakawa, T., Satoh, H., & Zhong, P. 1999. Seismic Performance of Hybrid Reinforced Concrete Cir- cular Columns Confined in Aramid Fiber Reinforced Polymer Tube. Fourth International Symposium Fiber Reinforced Polymer Reinforcement for Reinforced Concrete Structures, American Concrete Institute, ACI International SP-188, Farmington Hill, Michigan. [14] Zhao, T., Zhang, C.J., & Xie, J. 2002. Study and Application on Strengthening the Cracked Brick Walls with Continuous Carbon Fibre Sheet. Advanced Polymer Composites for Structural Applications in Construction, Proceedings of the 1st International Conference, University of Southamption, UK. 15

Wyszukiwarka

Podobne podstrony:
Przykłady zastosowań betonów niekonwencjonalnych w polskim mostownictwie
Projekt wdrożenia metody montażu nawisowego betonowych mostów sprężonych
Przykłady zastosowania technologii betonowania pod wodą w remontach budowli hydrotechnicznych
Badania in situ betonowych obiektów mostowych w aspekcie zapewnienia im wymaganej trwałości A Mocz
Technologia budowy betonowych konstrukcji łukowych z zastosowaniem częsciowej prefabrykacji
Specjalne wymagania stawiane betonom we współczesnym mostownictwie
zastosowanie metod fotometrii absorpcyjnej
Modern Talking Like A Hero
Porady reg przerzutki prz
Odpromienniki i ich praktyczne zastosowanie
rosliny zastosowania pojemnikienclematis main
GDDKiA Instrukcja wyodrebniania elementow drogi na drogowym obiekcie mostowym
The Modern Dispatch 115 Airborne Legionnaire
Konwencja o zastosowaniu do wojny morskiej założeń konwencji genewskiej
29 Konstr betonowe V S1
Mikrokontrolery PIC w praktycznych zastosowaniach mipicp

więcej podobnych podstron