Design of FRP Systems for Strengthening Concrete Girders in Shear (2011) / Chapter Skim
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Attachment A - Recommended Changes to AASHTO LRFD Bridge Design Specifications
Attachment A - Recommended Changes to AASHTO LRFD Bridge Design Specifications
Pages 51-58
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From page 51... ...
A T T A C H M E N T A Recommended Changes to AASHTO LRFD Bridge Design Specifications
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From page 52... ...
fE = modulus of elasticity of FRP reinforcement in Article 5.8.3.3 (ksi) fe = effective strain of FRP reinforcement in Article 5.8.3.3 fu = failure tensile strain of FRP reinforcement in Article 5.8.3.3 Rf = strain reduction factor to account for the effectiveness of FRP strengthening in Article 5.8.3.3 f = FRP shear reinforcement ratio in Article 5.8.3.3 fn = number of plies of FRP reinforcement in Article 5.8.3.3 ft = thickness of one ply of FRP reinforcement in Article 5.8.3.3 (in.)
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From page 53... ...
Transverse steel reinforcement shall consist of: Closed stirrups perpendicular to the longitudinal axis of the member, A closed cage of welded wire fabric with transverse wires perpendicular to the axis of the member, or Spirals. Transverse torsion reinforcement shall be made fully continuous and shall be anchored by 135° standard hooks around longitudinal reinforcement.
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From page 54... ...
Components of inclined flexural compression and/or flexural tension in variable depth members shall be considered when calculating shear resistance. Externally bonded FRP shear reinforcement shall be installed to a beam using: Side bonding, in which the FRP is only bonded C5.8.2.7 Maximum Spacing of Transverse Reinforcement Sections that are highly stressed in shear require more closely spaced reinforcement to provide crack control.
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From page 55... ...
Mechanical anchorage systems consisting of FRP composite plates and concrete anchor bolts shall be proportioned such that the factored bearing resistance of the concrete anchor bolts used to anchor one end of a FRP strip is not less than the tensile force exerted from the FRP strip calculated on the basis of the failure tensile strain of the FRP. The use of additional horizontal strips of FRP as anchorage for FRP shear reinforcement shall not be permitted.
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From page 56... ...
It was concluded that the reason that the application of FRP shear reinforcements did not lead to strength gains in I-girders with slender webs was due to degradation of the diagonal compressive resistance of slender webs when stiff and well bonded FRP reinforcements are glued to the surface of these webs. While the members experiencing this web resistance degradation were all prestressed, it has been concluded that this degradation was due to the slenderness of the webs and not the effect of prestressing [NCHRP Project 12-75]
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From page 57... ...
wf = width of FRP shear reinforcement strips (in.) 5.8.3.5 Longitudinal Reinforcement At each section, the tensile capacity of the longitudinal reinforcement on the flexural tension side of the member shall be proportioned to satisfy: 0.5 0.5 0.5 cotu u ups ps s y p s f v f c v M N VA f A f V V V d (5.8.3.5-1)
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From page 58... ...
; if the procedures of Article 5.8.3.4.3 are used, cot is defined therein f v c = resistance factors taken from Article 5.5.4.2 as appropriate for moment, shear and axial resistance The area of longitudinal reinforcement on the flexural tension side of the member need not exceed the area required to resist the maximum moment acting alone. This provision applies where the reaction force or the load introduces direct compression into the flexural compression face of the member.
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