THE STRUCTURE SECTION OF THE SYSTEM

The user is required to enter into the Structure section of the AESP software the information needed to perform the simplified seismic vulnerability analysis.
The data are provided via the graphical user interface, where drop-down menus, sliders and selection boxes allow to select the proper configuration of the structure among multiple options. No numerical values or textual description are required. By repeatedly modifying the various parameters, rapid and effective examination of a broad range of typical cases is possible.
The information required by the system in the Structure section refers to 6 different aspects: building destination, structural typology, building age, number of floors, average interstorey height and regularity parameters.  At the moment the system considers only buildings complying with the regularity criteria, both in plan and in elevation.
Wherever relevant reference is made to the Eurocode 8 and to the new Italian seismic codes (Ministero delle Infrastrutture, 2005; Ordinanze del Presidente del Consiglio dei Ministri n. 3274, March 20 2003, and n. 3431, May 3 2005).

Building classes 
According to the new Italian Code (i.e., Norme Tecniche per le Costruzioni, DM 14 Sept. 2005, Suppl. Ord. n. 159 della G.U. n. 222 dated 23.09.2005), buildings are classified in 2 importance classes, depending on the consequences of collapse for human life, on their importance for public safety and civil protection in the immediate post-earthquake period, and on the social and economic consequences of collapse. The importance classes are characteriZed by seismic events having different return periods: 

• Class 1: Ordinary buildings with a 50 years estimated service life and a 500 years mean return period to be considered for safety assessment (a 475 years return period is applied for seismic design).
• Class  2: Buildings with a 100 years estimated service life and a 1000 years mean return period to be considered for safety assessment (a 975 years return period is applied for seismic design). It includes buildings whose seismic resistance is of importance in view of the consequences associated with a collapse, and whose integrity during earthquakes is of vital importance for civil protection.

For each class the code identifies two different sub-classes depending on the cost required to improve the safety of the building (i.e., high cost and low cost).
If the user selects the advanced method (see section on geotechnical information) and the building is assigned to Class 1, AESP computes the seismic hazard for a 475 years return period, whereas if the building belongs to Class 2 the seismic hazard is obtained for a return period of 975 years. On the other hand, if the user selects the base method (see section on geotechnical information) and the building is assigned to Class 2, AESP computes the seismic hazard for a return period of 475 years and applies an Importance Factor equal to 1,4.

Structural Typology
The structural characterization represents one of the fundamental steps in defining the proper models and procedures necessary to predict the structural response under the action of earthquakes. Such characterization include the definition of the structural material characteristics as well as the technological and architectonical aspects.  The most commonly used materials are reinforced concrete, steel, masonry and wood, and for each of them it is possible to define under-categories characterized by different resistance systems and construction techniques.  

The current version of the AESP software aims at providing a preliminary evaluation of structural safety for buildings located anywhere in the Italian territory.  Therefore some of the available structural types were defined with reference to typical Italian construction practice.   

The main reference adopted for the typological classification is the EMS-98 (European Macroseismic Scale, Grunthal, 1998), that provides a detailed description of the most common structural typologies in the european context.  In particular, it must be noticed that the EMS-98 scale analyses in depth the masonry buildings as they are often most vulnerable, especially in the Mediterranean area. 

This basic classification of masonry buildings was integrated based on the work by Giovinazzi e Lagomarsino (2001), whereas the information provided by FEMA 178 (BSSC, 1992) e 310 (ASCE, 1998) was applied for steel and reinforced concrete structures. The latter data refer to the American design and construction practice and therefore they are not completely satisfactory when applied to other countries. Possible improvements in this area are currently under investigation. 

The structural typologies considered by AESP are the following:

• Steel Moment Frame (S1)

• Steel Braced Frame (S2)

• Reinforced Concrete Moment Resisting Frames (C1)

• Concrete Shear Walls (C2)

• Precast Concrete Frames  (PC)

• Masonry - rubble stones/fieldstones (M1)

• Masonry - adobe/earth bricks (M2):

• Masonry - simple stones (M3)

• Masonry - massive stones (M4)

• Masonry - unreinforced bricks with wooden floors (M5.1)

• Masonry - unreinforced bricks with masonry vaults (M5.2)

• Masonry - unreinforced bricks with composite steel and masonry floors (M5.3)

• Masonry - unreinforced bricks with reinforced concrete floors (M6)

• Masonry - reinforced or confined (M7)

• Building Age

The AESP system is suited for both new and existing buildings. For the latter case, common practice usually consists of gathering all the available information, such as calculation reports, drawings, testing certificates etc., to be verified at the site. Further investigations may also be needed, depending on the peculiarities of the structure and on the required level of detail. The criterion adopted by the AESP to characterised the building structural capacity according to design and construction practice at the time when the building was constructed is the Building Age. The Building Age parameter is related to the seismic codes which were in use at a particular time; such assumption can be considered adequate for both reinforced concrete and steel, two structural materials broadly used starting from the second world war.  The modifications to the seismic regulations over the years have interested a conspicuous part of the existing building asset.  As far as the masonry structures are concerned, although they may also be considered affected by the new technical codes, the number of new masonry buildings cannot be considered relevant relative to the existing building asset. Therefore masonry buildings are not sorted by the Building Age in our system. 

The above listed classification contains a significant number of typologies which can be considered sufficient to represent the most commonly used masonry constructions at national scale.  In particular the first 7 types represent "historical" masonry buildings, whereas the last two are typical of more recent constructions.

In conclusion, the parameter "Building Age" affects  reinforced concrete and steel buildings only. In the AESP software the building age can be selected by means of a multiple choice selection box that contains the age intervals listed in the following table.

Table 2
Design levels associated to building age for r.c. and steel constructions.

Construction Time	(Design Level)
< 1974	Pre-code
> 1974 in non classified areas	Pre-code
1974-1996 in classified areas	Low-Code
1996 in classified areas	Moderate-Code
New Building	High-Code

The time intervals were defined according to the American methodology described in HAZUS (NIBS, 1999), which includes four different code levels: Pre-Code, Low-Code, Moderate-Code, High-Code. The ages listed in the table are defined by the most significant changes occurred in the Italian seismic regulations during the past 30 years (e.g., De Marco et al, 2000). 

Number of Floors
The number of floors is a very significant parameter as far as the seismic response of the building is concerned. This information, in conjunction with the average interstorey height, provides the total height of the building and helps determining their fundamental period (see next subsection).   

Average Interstorey Height
Knowing the average interstorey height and the number of floors, it is possible to define the total building height and, consequently, to infer the fundamental period of the structure.  There is a number of simplified formulas in the technical literature which provide estimates of the fundamental period of the structure. 

The following relationship, providing the building fundamental period T [s] in function of the structural typology (C) and of the building total height  H [m], is used by the online system : 

The parameter C can be selected from Table 3:

Coefficients for the calculation of the fundamental period depending on the considered structural typology

The C values for Typologies S2 and C2 listed in Table 3 were obtained from the Eurocode 8, whereas for the masonry buildings reference was made to the study by Cattari et al (2005).  Finally, for the typologies S1, C2 and PC, the C values were estimated on the basis of expert opinions (NIBS 1999).

Regularity
Observation of seismic damage suffered by irregular buildings, showed that they are more vulnerable than regular buildings.  Buildings can be irregular both in plan and/or in elevation.
The concept of  structural regularity is stressed in most codes in order to limit torsional effects, hammering, local damage, etc. associated with seismic loads. Regularity is usually defined based on geometrical and mechanical relationships. In particular, plant and elevation regularity criteria are defined also in the Eurocode 8 and in the Italian code.
Within the AESP, at the moment, the user choice is limited to the only case of building regularity both in plan and in elevation.

Bibliography
ASCE, 1998. FEMA 310: Handbook for the Seismic Evaluation of Buildings — A Pre-standard. Prepared by the American Society of Civil Engineers for the Federal Emergency Management Agency, Washington D.C. 

BSSC, 1992. FEMA 178: NEHRP Handbook for the Seismic Evaluation of Existing Buildings. Prepared by the Building Seismic Safety Council for the Federal Emergency Management Agency, Washington D.C. 

Cattari, S., Curti, E., Giovinazzi, S., Lagomarsino, S., Parodi, S., Penna, A. 2005. Un modello meccanico per l’analisi di vulnerabilità del costruito in muratura a scala urbana. Atti del 11° Convegno Nazionale ANIDIS: L’ingegneria Sismica in Italia, Genova, Italia, in Italian. 

De Marco, R., Martini, M.G., Di Pasquale, G., Fralleone, A., Pizza, A.G. 2000. La classificazione e la normativa sismica dal 1909 al 1984. Servizio Sismico Nazionale, Italia, in Italian. 

Eurocode 8 – ENV 1998-1. Design of structures for earthquake resistance. 

Giovinazzi, S., Lagomarsino, S. 2001. Una metodologia per l’analisi di vulnerabilità sismica del costruito. Atti del 10° Convegno Nazionale ANIDIS: L’ingegneria Sismica in Italia, Potenza, Italia, in Italian. 

Grunthal, G. 1998. European Macroseismic Scale 1998. Chaiers du Centre Europèèn de Géodynamique et de Séismologie, Volume 15, Luxembourg. 

Ministero delle Infrastrutture, giugno 2005, Norme Tecniche per le Costruzioni ( Decreto 14 settembre 2005 pubblicato nel Suppl. Ord. n. 159 della G.U. n. 222 del 23.09.2005), in Italian. 

NIBS, 1999. Earthquake Loss Estimation Methodology HAZUS - Technical Manual. Prepared by the National Institute of Building Sciences for the Federal Emergency Management Agency, Washington D.C. 

Ordinanza del Presidente del Consiglio dei Ministri n. 3274 del 20 marzo 2003 (Suppl. Ord. n. 72 alla G.U. n. 105 del 8 maggio 2003). Primi elementi in materia di criteri generali per la classificazione sismica del territorio nazionale e normative tecniche per le costruzioni in zona sismica, in Italian. 

Ordinanza del Presidente del Consiglio dei Ministri n. 3431 del 3 maggio 2005 (Suppl. Ord. n. 85 alla G.U. n. 107 del 10 maggio 2005). Ulteriori modifiche ed integrazioni all'ordinanza del Presidente del Consiglio dei Ministri n. 3274 del 20 marzo 2003, recante «Primi elementi in materia di criteri generali per la classificazione sismica del territorio nazionale e di normative tecniche per le costruzioni in zona sismica» in Italian.