Structural engineering:
assessment and intervention

Structural assessments and designs

Re­ha­bil­i­tat­ing a his­toric build­ing and as­sess­ing a pub­lic build­ing for seis­mic vul­ner­a­bil­i­ty both re­quired a study of the whole struc­ture.

One building, multiple owners

The part to be re­ha­bil­i­tat­ed was struc­tural­ly con­tin­u­ous with pri­vate prop­er­ty, re­quir­ing as­sess­ment of the whole build­ing.

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Assessing vulnerability before intervention

In­ves­ti­ga­tions and seis­mic as­sess­ment of sev­er­al struc­tur­al units by a pro­fes­sion­al team. The study was com­plet­ed; sub­se­quent works are sep­a­rate.

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What is a seismic assessment and when is it mandatory?

A seis­mic safe­ty as­sess­ment eval­u­ates a build­ing's ca­pac­i­ty under the ac­tions spec­i­fied by NTC 2018. Sec­tion 8.3 iden­ti­fies sit­u­a­tions re­quir­ing as­sess­ment; §8.4.3 spec­i­fies when up­grad­ing is manda­to­ry, in­clud­ing ad­di­tion­al storeys, cer­tain ex­ten­sions and changes of use that in­crease the total ver­ti­cal foun­da­tion loads by more than 10%. A change of use class trig­gers up­grad­ing when it leads to class III for a school or to class IV, not for every move to a high­er class. As­sess­ment may also be ad­vis­able for older build­ings out­side manda­to­ry cases. Safe­ty in­di­ca­tors can be cal­cu­lat­ed; the A+ to G seis­mic risk clas­si­fi­ca­tion is a sep­a­rate pro­ce­dure and does not au­to­mat­i­cal­ly fol­low every vul­ner­a­bil­i­ty as­sess­ment.

How long does a seismic vulnerability assessment take?

Timescales de­pend on the avail­abil­i­ty of ex­ist­ing doc­u­men­ta­tion and on the com­plex­i­ty of the build­ing. For a pub­lic build­ing or a hos­pi­tal­i­ty struc­ture with the struc­tur­al de­sign avail­able, the as­sess­ment gen­er­al­ly takes 3–6 weeks: site visit and data col­lec­tion (1 week), struc­tur­al model prepa­ra­tion and analy­sis (2–3 weeks), draft­ing of the tech­ni­cal re­port (1–2 weeks). In his­toric build­ings, or those lack­ing orig­i­nal doc­u­men­ta­tion, timescales length­en be­cause of the need for ma­te­r­i­al test­ing (sonic tests, core sam­pling) and de­tailed geo­met­ric sur­vey.

Can I refurbish a historic building while preserving its original character?

Yes. The NTC 2018 code (§8.4) and the MIT 2019 Cir­cu­lar set out spe­cif­ic pro­vi­sions for his­toric build­ings, per­mit­ting con­sol­i­da­tion ap­proach­es that pre­serve the orig­i­nal ty­po­log­i­cal, for­mal and con­struc­tive fea­tures. This often in­volves tech­niques com­pat­i­ble with the ex­ist­ing masonry: steel ring ties, GFRP fibre plat­ing, hy­draulic lime in­jec­tion into the joints, se­lec­tive stitch­ing (cuci-scuci). The ob­jec­tive is to im­prove the build­ing's seis­mic per­for­mance with­out al­ter­ing it, reach­ing the high­est level of seis­mic safe­ty com­pat­i­ble with the pro­tec­tion and con­ser­va­tion re­quire­ments of the asset. This is the guid­ing cri­te­ri­on set out in the Min­istry of Cul­ture's Guide­lines (D.P.C.M. 9/2/2011) for as­sess­ing and re­duc­ing the seis­mic risk of cul­tur­al her­itage, which does not im­pose a fixed per­cent­age thresh­old of up­grad­ing for list­ed build­ings.

Which seismic legislation applies to buildings constructed before 1974?

A build­ing con­struct­ed be­fore 1974 was not nec­es­sar­i­ly de­signed with­out seis­mic provisions: the rules ap­plic­a­ble at the time and the site's seis­mic clas­si­fi­ca­tion must be checked. Today, ex­ist­ing build­ings are as­sessed under NTC 2018 (D.M. 17/01/2018) and its ex­plana­to­ry Cir­cu­lar of 21/01/2019. The knowl­edge level achieved (LC1, LC2 or LC3) and the cor­re­spond­ing con­fi­dence fac­tor af­fect the struc­tur­al model and the re­li­a­bil­i­ty of its re­sults.

What is the difference between statutory inspection (collaudo statico) and structural assessment?

Sta­t­ic test­ing (col­lau­do sta­ti­co) is re­quired by Art. 67 of Pres­i­den­tial De­cree 380/2001 for the works to which that pro­ce­dure applies: an in­de­pen­dent pro­fes­sion­al checks the com­plet­ed work and is­sues a cer­tifi­cate. For re­pairs and local in­ter­ven­tions on ex­ist­ing build­ings, in the cases spec­i­fied by the same ar­ti­cle, the cer­tifi­cate is re­placed by the works su­per­vi­sor's de­c­la­ra­tion of prop­er ex­e­cu­tion. As­sess­ment of an ex­ist­ing build­ing's safe­ty is in­stead pre­ven­tive and eval­u­ates its struc­tur­al ca­pac­i­ty under the rel­e­vant con­di­tions. The two pro­ce­dures have dif­fer­ent pur­pos­es and occur at dif­fer­ent stages.

Does a change of use trigger a mandatory seismic assessment?

It de­pends on the struc­tur­al ef­fects of the change. Under NTC 2018 §8.4.3, up­grad­ing is manda­to­ry if the new use in­creas­es total ver­ti­cal foun­da­tion loads by more than 10%, cal­cu­lat­ed using the char­ac­ter­is­tic com­bi­na­tion of grav­i­ta­tion­al loads, or if the change of use class leads to class III for a school or to class IV. Other changes still re­quire tech­ni­cal as­sess­ment of the ex­ist­ing con­di­tions and pro­posed works: the label of the new use alone can­not es­tab­lish the re­quired pro­ce­dure. Loads, use class and the ap­plic­a­ble struc­tur­al process should be checked be­fore de­sign be­gins.