FRP STRUCTURE DESIGN METHOD BASED ON THE STIFFNESS EQUIVALENCE: CASE STUDY AND PRACTICE
Article history: Received 08.05.2012. Received in revised form 20.07.2012. Accepted 03.09.2012. Nowadays, fiber reinforced polymer materials are getting widely used in civil engineering. They have some advanced engineering characteristics like high stiffness-to-weight ratio, high strength-toweight ratio, anti-electromagnetic interference, electrical isolation and their long term durability. Metal and concrete, two main kinds of construction materials, are prone to failure during their structure service lives because of environmental adverse effects and atmospheric weathering. Those harsh attacks/impacts are oxidization, acidification, high temperature and alkali corrosion. After various maintenance methods like isolating the attacks or protecting plastic skins, an interface crack between protections can easily propagate and cause some durability concern. Fiber reinforced polymer emerges in a new era of civil engineering and can surely be added to traditional materials and/or traditional materials can surely be substituted by this material. This paper sets out to unfold a case study on how fiber reinforced polymer works in civil structures.
PERFORMANCES OF CONCRETE-FILLED GFRP OR GFRP-STEEL CIRCULAR TUBES SUBJECTED TO FREEZE-THAW CYCLES
This paper presents an experimental investigation of the performances of concrete-filled glass fiber-reinforced polymer (GFRP) and GFRP externally wound steel circular tubes, subjected to freeze-thaw cycles ranging from -18°C to 18°C. The variation in hoop strains of the tubes during the freeze-thaw cycles was monitored by embedded fiber Bragg Grating (FBG) strain sensors in GFRP layers or between GFRP and steel tube. The residual hoop strain after each freeze-thaw cycle indicates the possible degradation of GFRP materials, such as cracks, debonding of GFRP-concrete or GFRP-steel due to mismatch of the coefficient of thermal expansion, as well as water immersion. A synergistic effect of FRP and steel tubes on the confinement of inside concrete was revealed, resulting in well-improved ductility. After 56 freeze-thaw cycles, remarkable degradation were found in the axial strength, modulus, and strain for concrete-filled GFRP tubes. However, the GFRP-steel tube system showed a negligible reduction in the ultimate axial strain by the freeze-thaw cycles with less degradation in the axial strength and modulus.
Precast piles for Route 40 bridge in Virginia using concrete filled FRP tubes
This paper summarizes the construction details and findings of laboratory and field tests of a new generation of precast composite piles used for the first time in the construction of the substructure of the Route 40 highway bridge over the Nottoway River in Virginia. The piles consisted of 24.6 in. (625 mm) diameter concrete-filled glass fiber reinforced polymer (GFRP) circular tubes, with a 0.21 in. (5.3 mm) wall thickness. The composite piles extended above the ground level and were directly embedded into the reinforced concrete cap beam supporting the superstructure. Laboratory tests included two full-scale composite piles loaded to failure using four-point bending configuration. Field testing included a full-scale precast composite pile and a conventional 20 in. (508 mm) square concrete pile prestressed with fourteen 1/2 in. (12.7 mm) diameter strands. This paper presents details of the construction and driving of the piles, comparisons between the behavior of the composite and prestressed concrete piles under axial and lateral loading, the observed failure modes, and the details of the connection between the piles and the reinforced concrete cap beam.