STRUCTURAL STRENGTHENING WITH FRPS IN GREECE

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1 STRUCTURAL STRENGTHENING WITH FRPS IN GREECE Michael J. KARANTZIKIS 1 Dimitris P. KOUTSOUKOS 2 Constantinos P. ANTONOPOULOS Civil Engineer (MSc), Fyfe Europe SA, Athens, Greece Ph.D., P.E., Structural Engineer, Head of the Infrastructure Works Design Department, ERGA OSE. S.A., Athens, Greece Dr. Civil Engineer, ReTech SA, Athens, Greece Keywords: bridges, hospitals, infrastructure, masonry, military, silos, seismic retrofit, tanks 1 INTRODUCTION The first projects with structures strengthened with FRPs in Greece took place in the late 1990 s. The boost of the FRPs used in the construction field in Greece came about and after the disastrous Athens earthquake in Since then several hundreds of projects involving structures strengthened with FRPs have been completed. Several types of structures have been strengthened: residential buildings, hospitals, schools, hotels, malls, bridges, parking structures, stadiums, pipelines, churches, museums, registered buildings, warehouses, factories, silos, towers, tanks, military and sensitive structures. This study presents an overview of the most interesting projects completed in Greece and Cyprus with the use of the Tyfo Fibrwrap Composite System (hereafter TFC System ) [1]. 2 CASES PER PROJECT TYPE 2.1 Building structures The first strengthening project in Greece with the use of the TFC System took place in Thessaloniki in It involved seismic strengthening of the ground floor columns of a multi story building owned by the Agricultural Bank of Greece. Since then more than 200 buildings and similar structures have been strengthened. The most common types of such strengthened structures are residence buildings, banks, hospitals, hotels, offices, schools, cinemas, malls, restaurants, and car exhibition buildings. The State Hospital in Sparta, a city in southern Greece, was built 30 years ago. The refurbishment and seismic upgrade of the hospital to the newest seismic codes required the seismic retrofit of columns with the carbon TFC System. In Figure 1, the strengthened circular columns at the hospital balconies are shown. The project was completed in Fig. 1 State Hospital, City of Sparta. Fig. 2 Hotel Kaningos 21, Athens. As a relative recent example, one can mention the strengthening and renovation of the old Hotel Eretria in downtown Athens (Figure 2), built in The new owner decided to rename it Hotel 1

2 Kaningos 21 and to fully renovate and upgrade it from 3 to 4 stars for the 2004 Athens Olympic Games. For the hotel class upgrade, seismic retrofit and static strengthening due to increased loads was required. The designer specified columns shear and ductility enhancement with glass TFC System and last floor slabs and beams flexural and shear enhancement with carbon strip and glass fabric TFC System due to increased dead and live loads on the terrace (roof garden and bar). According to the Bulletin 14 [1] Guidelines, a 2 hours rating fire protection of the TFC System at the last floor slabs was necessary. This was achieved with the first installation in Europe of the Tyfo AFP (Advanced Fire Protection) System (hereafter AFP System ) over the applied composites (Figure 3). The AFP system is approved by the Underwriters Laboratory [2] as the only currently available material for FRP fire protection. The thirty year old residential building in Plaka, Athens, shown in Figure 4, is six stories tall and sits directly beneath the Acropolis with a view of the Parthenon. Flats in this exclusive neighborhood typically exceed per square meter. The building owner was very concerned about the reduction of useful space if traditional methods of strengthening (such as shotcrete) were used. An Athens based engineering firm performed the required structural analysis for upgrading the building, which was originally constructed to comply with the 1959 Greek Seismic code, while today s renovations and upgrade required compliance to the more demanding seismic codes adopted since then. The strengthening design utilized extensively the TFC System. This design approach was adopted to not only save valuable floor space for the owner but also to reduce the time and cost required for renovation work due to the installation simplicity of the TFC System. Various types of TFC System materials for columns, beams, slabs, bearing walls and slab opening were installed in In addition, the AFP System was utilized on slabs and beams strengthened with bonded carbon fabrics to provide the required fire rating. Fig. 3 AFP System application over carbon strips. Fig. 4 Residential building in Plaka area. Fig. 5 Columns strengthening with TFC System. Fig. 6 Office building damaged by earthquake. 2

3 The Three Seas Hotel in Larnaka, Cyprus, shown in Figure 5, was fully renovated and seismically upgraded by the new owner, an international hotel and resorts company based in the USA. All columns were strengthened with glass TFC System. The 6-story headquarters building of a big electronic appliances trading company shown in Figure 6 was damaged by the 1999 Athens earthquake. The owner repaired and strengthened only the damaged concrete members with the TFC System in short time without interruption of the company s operation. Still the owner and the stuff were feeling quite insecure working in locally strengthened the building and because of growing business, the company decided to build a second headquarters building near the old one and fully renovate, repair and retrofit the first. The designer specified the use of the TFC System for strengthening all internal columns and beams and added new concrete shear walls in the perimeter of the building. The project was completed in The 10-story office tower on the seaside avenue in Limassol, Cyprus, shown in Figure 7, was bought by a shipping company to house its headquarters. The tower construction had been interrupted 15 years ago. Because the initial design was based in older seismic code provisions, the company decided to complete the project and upgrade the concrete bearing structure to the newest codes. All circular columns and elevator shafts were strengthened with glass TFC System. The project was completed in Fig. 7 Office tower in Limasol, Cyprus. Fig. 8 Zea marina, column-beam joints. In the marvelous, full of yachts, Zea Marina, in Piraeus Port, a two-story, 30-year old reinforced concrete café-restaurant was strengthened. Because of the astonishing view to the marina, the architect eliminated both the possibility of adding new bearing members and the use of traditional jacketing methods. The architect approved the use of the TFC System because of it practically results in no increase in the members dimensions. The upgrade of the building to the current seismic codes was achieved through strengthening of columns, beams and concrete walls. Prestressed concrete beam-slabs where strengthened, due to increased live load, with carbon strips at the bottom fiber and glass fabric in U shape at the ends for proper anchorage of the strips (Figure 9). Proper detailing was addressed in column-beam joints (Figure 8). The project was completed in In one of the most seismic-prone areas in southern Greece, the City of Kalamata, the full renovation of a 4-story shopping mall took place in Due a strict requirement for minimum down time of the mall facilities, the designer employed unique strengthening techniques and chose the TFC 3

4 System for the building strengthening. Specifically, the TFC System was applied for flexural enhancement of slabs and beams and shear enhancement of beams and columns (Figure 10). The strengthening of the 5,000 m 2 mall was completed in only 40 days in summer Fig. 9 Zea marina, beam-slabs strengthening. Fig. 10 Mall in Kalamata, columns & beams. 2.2 Infrastructure Important infrastructure structures, such as bridges, parking structures, pipelines and athletic facilities, have been strengthened during the last few years with the TFC System. Some of these projects are presented next. At the Rion-Antirion cable-stayed bridge in Patras, the TFC System was used in 2004 for strengthening the concrete shear keys supporting the seismic absorbers of the bridge approaches (Fig. 11). A 30-year old bridge in Athens (Maroussi Station), owned by the Electric Railway Authority, was strengthened against the today s higher intensity earthquake levels in All 160 piers and superstructure beams were strengthened through the entire bridge length (300 m). Carbon strips of the TFC System, properly anchored at the ends with glass fabrics of the TFC System, were applied for pier flexural enhancement (Fig. 12). As another example, one can mention the strengthening of an old 1944 concrete bridge over the Evinos River near the village of Poros in western Greece. The bridge was strengthened in 2006 for increased vehicle loading. Four layers of unidirectional carbon fabric of the TFC System was applied at the bottom fiber of the main bridge beams (Fig. 13) properly anchored at the ends with carbon fiber anchors because of the high FRP design deformations assumed. A PCCP segment of Aravissos potable water pipeline was strengthened with external application of the same carbon TFC System in Thessaloniki, northern Greece, in This was a pilot project for PCCP strengthening, the first completed in Greece and maybe in Europe. Finally, the building housing the canoe-slalom facilities for the 2004 Athens Olympic Games was also strengthened in 2004 with glass TFC System (Fig. 14). Fig. 11 Rion-Antirion bridge. Fig. 12 Electric railway bridge in Athens. 4

5 Fig. 13 Bridge over Euinos river. Fig. 14 Canoe-slalom building for 2004 Games. 2.3 Heritage and Cultural Structures Many applications involve heritage monument structures and historical registered buildings such as churches, museums, government buildings, palaces and universities. Most of these structures demonstrate the use of a variety of materials and building techniques such as stone, clay tile or adobe masonry walls, wooden slabs and roofs, stone domes, vaults and arches. As a typical project one can mention the three-story registered stone masonry building of the University of Athens Law School, that was strengthened in 2005 with the application of unidirectional carbon TFC System all around the perimeter of the building at its top (Fig. 15), thus strengthening the stone masonry walls against vertical cracks due to increased roof loading and seismic forces. Another example is a (more than 100 years old) registered stone masonry school building in Athens that suffered damages from the 1999 Athens earthquake and was strengthened with the application of carbon strip TFC System on the external wall side in X arrangement (Fig. 16). Fig. 15 Athens Law School strengthening. Fig. 16 Registered school building strengthening. 2.4 Industrial structures A type of structure, where the advantages of the FRP technology have being widely exploited, is industrial facilities. Some unique and interesting projects have been completed in Greece and Cyprus with the application of the TFC System. Such structures are warehouses, factories, silos, bunkers, tanks, towers, and jetties. The types of applied strengthening are static strengthening due to increased service loads, seismic retrofit, corrosion repair and protection, damage repair in general, postearthquake and post-fire strengthening and even protection against possible explosions in the industrial facilities. Typical examples are the following two projects: (a) strengthening of the foundation rings of 4 concrete cylindrical silos, 30.0 m in height, in Milos Island, Greece. The concrete shell of the silos had been previously repaired against extensive corrosion damages and a new concrete shell had 5

6 been added externally. The increased dead weight caused flexural cracks at the foundation rings. Analysis of the silos was performed with the F.E. method and the rings were strengthened with jacketing of carbon TFC System (Figure 17). The project was completed in (b) The perlite Factory in Milos Island, Greece, was built in 1972 and exhibited extensive damage due to reinforcement corrosion and concrete carbonization. This m 2, 5-story building (Figure 18) is the main facility in the industrial perlite production line. Possible damage of the Factory due to an earthquake would be devastating for the Owner, Silver & Baryte S.A., the biggest perlite producer in the world. The Owner decided to repair and seismically upgrade the Factory to the newest Seismic Codes. The design engineer decided to employ extensive use of the TFC System due to not only the very limited space available for retrofit because of the numerous machines and mechanical systems of the factory, but also because of the minimum available Factory down time imposed by the Owner. The project was completed successfully on time and on budget in 2001 by exelkat SA [4] a certified applicator of TFC System. Fig. 17 Silos foundation ring strengthening. Fig. 18 Perlite Factory rehabilitation. 2.5 Military and sensitive structures The use of the TFC System has been proven useful also in military projects. Usual applications have to do with post earthquake repair, seismic retrofit, static strengthening and corrosion protection. However most interesting structural strengthening in this category involves classified structures and has to do with blast mitigation and explosion protection. Extensive full scale blast tests have been conducted with the TFC System (Figures 19 & 20) and special project analysis and design software have been developed. Fig. 19 Un-retrofitted (left) and retrofitted with TFC System (right) columns after blast test. 6

7 Fig. 20 Shock tube tests on as-built (left) and retrofitted with TFC System (right) walls. 3 CONCLUSIONS The FRP technology has been extensively used in the Greek construction industry for strengthening existing structures during the last 10 years. However, it is the authors opinion that the FRP technology has not gained yet the deserved share of the strengthening market due to not only the lack of national guidelines, codes and available commercial design software but also mainly because most of the engineers are not familiar yet with this technology. One thing is certain: Worldwide, the FRP technology has proved to be an efficient and cost effective solution for strengthening structures, especially in seismic regions. With this fact acknowledged, structural engineers involved in repair and strengthening projects should seek the relative knowledge to master this promising technology. ACKNOWLEDGEMENTS The authors would like to express their great thanks and appreciation to all these people who, by practicing pioneering design and construction methods, have been involved in the completion of the above and other projects in Greece and Cyprus. REFERENCES [1] & [2] International Federation for Structural Concrete (FIB), Externally bonded FRP reinforcement for RC structures. Bulletin 14, 2001, Lausanne, Switzerland. [3] [4] 7