Issue 38

S. Bennati et alii, Frattura ed Integrità Strutturale, 38 (2016) 377-391; DOI: 10.3221/IGF-ESIS.38.47

Eurocodes [20], Eq. (23) can still be used, provided that M p reduction of the plastic moment due to the axial force:

is replaced by M pN

, which takes into account a possible

      

b n M n a a , for        p b b

1

min 1,

b

1 0.5

(24)

M

pN

2

 

 

 

n a

 

b

b



M n a , for 

1



b           a 1

p

b

b

where, in our notation,

G b G P b P N l N l , , ( ) ( )   





b h

N l

( )

 

  

b f

Q b Q ,





min 1 2 , 0.5 

n

a

(25)

and

b

b

f A

A

yd b

b

By substituting Eqs. (2), (3), and (12) into (23)–(25), and solving for q , the load bearing capacity of the strengthened beam, q s , is determined. Tab. 5 summarises the results obtained for the analysed cases, showing the increase in the load bearing capacity of the system,  q = q s – q u . The percent increase ranges between 30% and 50%.

C ONCLUSIONS

W

e have presented the mechanical model of a simply supported steel beam subjected to uniformly distributed load, strengthened with a pre-stressed FRP laminate. An analytical solution has been determined for the differential problem that describes the structural response of the strengthened beam. The model has been applied to study IPE steel beams strengthened by using the Sika ® CarboDur ® FRP strengthening system. Analysis of the elastic limit states in the steel beam, adhesive, and laminate has shown that the steel beam is always the weakest element of the system. The softening response of the adhesive is not reached in practice being preceded by the plasticisation of steel. For the sake of simplicity, however, we have not analysed the non-linear structural response resulting from the progressive plasticisation of the beam at the mid-span and neighbouring cross sections. This behaviour could indeed be the subject of future studies, which should also take into account the expected large deformations and displacements, as well as the possible lateral torsional buckling. Here, the complete plasticisation of the mid-span cross section of the steel beam has been assumed as the ultimate limit state of the system. Correspondingly, the increased load bearing capacity of the strengthened beam has been evaluated. [1] Bank, L.C., Composites for Construction, John Wiley & Sons, New Jersey (2006). [2] Zhao, X.-L., Zhang, L., State-of-the-art review on FRP strengthened steel structures, Eng. Struct., 29 (2007) 1808– 1823. [3] Gholami, M., Sam, A.R.M., Yatim, J.M., Tahir, M.M., A review on steel/CFRP strengthening systems focusing environmental performance, Constr. Build. Mater., 47 (2013) 301–310. [4] Aslam, M., Shafigh, P., Jumaat, M.Z., Shah, S.N.R., Strengthening of RC beams using prestressed fiber reinforced polymers – A review, Constr. Build. Materi., 82 (2015) 235–256. [5] Haghani, R., Al-Emrani, M., Kliger, R., A new method for strengtheng concrete structures using prestressed FRP laminates, in: Saha, S., Zhang, Y., Yazdani, S., Singh, A. (eds.), Proc. 8 th International Structural Engineering and Construction Conference – ISEC 2015: Implementing Innovative Ideas in Structural Engineering and Project Management, Sydney, Australia (2015). [6] Ghafoori, E., Motavalli, M., Zhao, X.-L., Nussbaumer, A., Fontana, M., Fatigue design criteria for strengthening metallic beams with bonded CFRP plates, Eng. Struct., 101 (2015) 542–557. [7] Smith, S.T., Teng, J.G., Interfacial stresses in plated beams. Engineering Structures, 23(2001) 857–871. R EFERENCES

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