Issue 48

M. L. Puppio et alii, Frattura ed Integrità Strutturale, 48 (2019) 706-739; DOI: 10.3221/IGF-ESIS.48.66

E nbs rate of action absorbed by the new bracing system (n.b.s.). It is well known that seismic action varies according to the stiffness of the structure and its natural period. Here it is assumed that E is the maximum action calculated from the plateau of the response spectrum.

Figure 17: Distribution of the seismic action.

The target of the design is to ensure that E nbs is higher than E eb . To achieve this, the new bracing system (nbs) must have adequate stiffness with respect to the existing building (eb). In the hypothesis of a perfect connection between the two structures:

eb E E K K  eb

(2)

nbs

nbs

where: K nbs

stiffness of the new bracing system; stiffness of the existing building. As the capacity of the existing buildings C eb K eb

is lower than of the global seismic action E , it is possible to calculate the action

to transmit to (nbs) E nbs .

(3)

nbs E E C  

eb

Subsequently it is possible to calculate the stiffness of the (nbs) to protect the (es) from the Eq. (2):

E



nbs

(4)

K

K

nbs

eb

E E 

nbs

It is possible to express this as follows:

nbs K K  

(5)

1 eb

Where α 1 is an over-stiffness factor. This factor must be higher than one, to ensure that the structure can be classifiable as braced [24]. This guarantees the respect of the Ultimate Limit State (ULS).

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