Urban Habitat Constructions under Catastrophic EventsFINAL CONFERENCE. Naples, 16th- 18th September 2010Chair of the Action: Federico Mazzolani, IT, fmm@unina.itCOST Science Officer: Thierry Goger, tgoger@cost.esf.org

COST Action C26

PROBLEMS OF SEISMIC BEHAVIOUR OF BUILDINGS SITUATED IN URBAN HABITATSVictor GIONCU & Federico M. MAZZOLANI“Politehnica University Timisoara, Romania, University of Naples “Federico II“ , Italy

INTRODUCTION

Most of the current seismic codes are inadequate for designing buildings in urban habitats and their use could lead to potentially unsafe constructions. This is mainly due to the fact that the characteristics of ground motions in these areas are very different from the codified ones.

Normally, the building is designed as a singular unit for ground motions of far-of-source type. In reality, the ground motions have the characteristics of near source, influenced by the presence of a group of buildings and the construction belongs to a complex of buildings (Fig.1).

Fig.1

CITY-SITE INTERACTION

Each building becomes a

source of vibrations (Fig.2)

Fig.2

Fig.3

So, the small buildings situated near the tall ones can be destroyed by the waves produced by tall building.

The ground motions under a city are composed by the ones produced by source and by the secondary vibrations produced by buildings (Fig.4)

Fig.4

The result of this double source is an amplification of ground motion (Fig.5). This phenomenon requires to amplify the design accelerations of a minimum of 50%

NEAR-SOURCE EFFECT

Due to the intense World

urbanisation, the number of cities, where the epicentre is

situated under the densely

Fig. 5

constructed areas, increases

( Fig. 6).

Fig.6

In this cases, the ground motions depends on P and S waves and the structure behaviour is governed by the

“last ball” effect (Fig. 7)

Fig.7

This means an increasing of

vertical components and an

high velocity impulses, with important effects of strain-rate

in structure, producing brittle fracture.

COMPLEX BUILT

CONFIGURATIONS

This effect especially refers to the historical centers, where the shape of actual building groups was developed without

any rules during the last Centuries (Fig. 8).

Fig. 8

When all buildings are in contact each other, an arch behaviour can be considered. The out- of-plane collapse mechanism occurs due to the end building pounding (Fig. 9)

Fig.9