PSI - Issue 11

Luigi Ascione et al. / Procedia Structural Integrity 11 (2018) 202–209 L. Ascione et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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The coefficient  is assumed equal to 1.5. Higher values are allowed but have to be justified by experimental tests performed of structural elements. In all cases, the following inequality shall be verified:   lim,conv ≤  u . In the applications where failure is governed by the tensile strength of the mesh, the values  u,f and and  u,f should be employed.

6. Design values

The design value of a generic property of the FRCM system is obtained as:

k m X X     d

(1)

where η is a conversion factor, X k is the characteristic value of the property considered and  m is the corresponding partial safety factor:  m = 1.5 for the Ultimate Limit State (ULS) and  m = 1.0 for the Serviceability Limit State (SLS). For the ULS, the effects of the environmental actions have to be taken into account. If more specific data are not available, the values of the corresponding conversion factor, η a, provided in Table 3 should be adopted.

Table 3 – Values of η a

Table 4 – Kind of interventions

η a

Kind of exposition

Kind of reinforcement Glass/Basalt Aramid/PBO Carbon/UHTSS Glass/Basalt Aramid/PBO

Kind of structure

Intervention

Indoors

0.80 0.90 0.95 0.70 0.80 0.85 0.90 0.60 0.75 0.85 0.90

Masonry

Panels under in-plane loads Panels under out-of-plane loads Realization of bond beams Simple or double curvature vaults Confinement of axially-loaded columns Beams subjected to gravitational loads Confinement of axially-loaded columns

Outdoors

UHTSS Carbon

Reinforced concrete

Aggressive environment

Glass/Basal Aramid/PBO

UHTSS Carbon

7. Types of strengthening intervention considered in the guideline

The Italian design guideline provides indications for the following strengthening interventions (Table 4):

The predictive formulae provided by the guideline are based on the following assumptions:  Plane sections remain plane;  Perfect adhesion between mesh and matrix as well as between FRCM composite and support. The design of strengthening interventions of masonry elements shall be carried out only with respect to the ultimate limit states, whereas the strengthening of concrete beams subjected to gravitational loads shall be carried out both with respect to the ultimate and serviceability limit states. Furthermore, within the SLS verifications, the maximum tensile stress in the FRCM cannot exceed a limit value in order to take into account the possible phenomenon of creep rupture. If the results of specific analysis are not available, the limit values provided in Table 5 should be respected.

Table 5 – Tensile limit stress in the FRCM strengthening for long-term loading

Type of fibre UHTSS

AR Glass 0,20   u,f

Aramid 0,30  u,f

Basalt

Carbon 0,55   u,f

PBO

0,55  u,f

0,20   u,f

0,30   u,f