research needs in earthquake engineering … · research needs in earthquake engineering...

G. Manfredi, M. Dolce (eds), The state of Earthquake Engineering Research in Italy: the ReLUIS-DPC 2005-2008 Project, 469-480, © 2009 Doppiavoce, Napoli, Italy

RESEARCH NEEDS IN EARTHQUAKE ENGINEERING HIGHLIGHTED BY THE 2009 L’AQUILA EARTHQUAKE

Mauro Dolce a, Gaetano Manfredi b

a Department of Civil Protection, Head of Seismic Risk Section on leave from University of Naples Federico II

b University of Naples Federico II, Head of Department of Structural Engineering, ReLUIS Chairman

1 THE 6TH APRIL 2009 L’AQUILA (ITALY) EARTHQUAKE

On April the 6th 2009, at 1.32 a.m. UTC, the city of L’Aquila and the surrounding Appennines areas comprising 80 municipalities located in one of the regions with the highest seismic hazard in central Italy, were shaken by a large shallow focal depth earthquake ground motion. Such motion initiated in the Earth outer crust, at a depth of about 10-12 kms. The focal mechanism was normal fault: the ground rupture moved upwards, or up-dip (towards the city centre of L’Aquila), and travelled from North-West to South-East, towards the Aterno valley. The magnitude of the main shock was estimated as ML=5.8 by the Italian National Institute of Geophysics and Volcanology (INGV) and Mw = 6.3 by the United States Geological Survey (USGS). The 6th April earthquake was the strongest of a sequence of seismic events that initiated a few months earlier as shown pictorially in Figure 1, where the 23 earthquakes of Mw>4 occurred between 30/03/09 and 23/04/09, including an Mw 5.6 on 07/04 and an Mw 5.4 on 09/04, are reported.

Figure 1 . Sequence of seismic events occurred in L’Aquila and surrounding municipalities (Abruzzo region) during April 2009 (source http://www.ingv.it).

The earthquake-affected zones were densely instrumented at the time of the event because of the high seismicity of Central Appennines Mountains; 57 of the approximately 300 modern digital strong-motion instruments of the National Accelerometer Network (RAN, Rete Accelerometrica Nazionale), managed by the Department Civil Protection (DCP), recorded

M. Dolce, G. Manfredi

470

the main shock (e.g. Cosenza et al., 2009) and allowed the estimation of the peak ground acceleration (PGA) distribution as provided in Figure 2.

Figure 2 . Peak ground horizontal acceleration distribution in the suburbs of L’Aquila (values are

expressed in g).

The computed values of horizontal PGAs exceeded 0.35 g in many stations, especially in the sites located in North of L’Aquila; the corresponding values of peak ground velocities varied between 24.50cm/sec and 26.68cm/sec and the observed maximum horizontal ground deformations were greater than 20cm, as confirmed by the interferometry provided by the satellite image in Figure 3. Local amplifications due to site effects were also observed in many locations, especially between the boroughs of Coppito and Pettino, in the North of the fault trace. Vertical component of ground motions may also have had significant ground and structural effects; such effects are still under investigations. The human and financial losses caused by the 6th April 2009 earthquake are extremely significant. The main shock occurred at L’Aquila caused the death of more than 300 people, injured 1,500, destroyed or damaged an estimated 10,000-15,000 residential buildings, prompted the temporary evacuation of 70,000-80,000 residents, and left nearly 25,000 homeless. The majority of the visual vulnerability assessment of the built environment was carried out by the experts of ReLUIS consortium in collaboration with a DCP delegation. The surveyed damage was widespread to old and modern constructions. Several masonry buildings either collapsed or showed irreparable damage caused by the lacking of seismic conceptual design and detailing (see reconnaissance reports available on http://www.reluis.it). Historical, monumental, government buildings, basilicas and churches, especially in L’Aquila city centre, were destroyed by the seismic events occurred during April 2009. Reinforced concrete multi-storey buildings showed extensive damage chiefly to the non-structural components, such masonry infills and interior partitions (Figure 4).

Research Needs in Earthquake Engineering Highlighted by the 2009 L’Aquila Earthquake

471

Figure 3 . Interferometry of the region affected by the 6th April 2009 earthquake (source

http://www.ingv.it).

Figure 4. Example of damage to masonry infills in RC multi-storey buildings.

Critical facilities were shut down primarily because of the lost of functionality caused the failure of non-structural components and building contents. Lifelines failed in all the areas affected by the earthquake ground motion. Damage at bearing and at connections were detected in many bridges and viaducts. Geotechnical and ground effects were also widespread; landslides caused the interruption of several main roads. A quick emergency response was managed by the DCP in collaboration with several other government and non-government organizations, institutions and professionals. ReLUIS consortium has played a role of paramount importance in the post-earthquake emergency activities. The 6th April 2009 L’Aquila earthquake has taught a number of lessons that are essential for seismic risk mitigation and preparedness. Although some of them are related to topics which were already addressed in the ReLUIS 2005-2008 project (see other papers in this same book),


472

further aspects and crucial research needs emerged as far as earthquake engineering is concerned and they are briefly discussed in the following.

2 RESEARCH NEEDS IN EARTHQUAKE ENGINEERING

The recent 6th April 2009 L’Aquila (Italy) earthquake highlighted the need for deepening of research topics are still pending and they should be addressed in the forthcoming ReLUIS research program. There are numerous engineering seismology issues, non-structural component response and effects, loss assessment, critical buildings assessment and design for operability that require further thorough understanding and investigation (both experimentally and numerically) to mitigate the seismic risk at a societal level. The lessons learnt from the L’Aquila earthquake showed the need of focusing in the near future on the following research thrust areas illustrated hereafter. Reconnaissance reports relative to the L’Aquila earthquake (available on http://www.reluis.it) have also shown that geotechnical effects may be devastating and further research is need (Simonelli et al., 2009). Additionally, seismic vulnerability of large earth and reinforced concrete dams should considered because they failure and/or collapse may undermine the safety of large societal communities.

2.1 Near-source Effects The 6th April L’Aquila (ML=5.8) earthquake caused extensive damage in the triggered areas because of the nature of the fault rupture and measured ground displacements (Figure 5). Significant directivity effects were observed and high acceleration were estimated for both horizontal and vertical components of ground motions (Chioccarelli et al., 2009). Directivity of fault rupture, site effects, dispersion and incoherence may be of paramount importance for the seismic effects at near fault locations (Chioccarelli and Iervolino, 2009).

Figure 5. Directivity of the fault rupture: satellite interferometry (left) and geographical distribution of the main earthquake shocks.

Existing attenuation relationships should be re-assessed and compared with the results derived from the earthquake records. The effects of the vertical component of the earthquake motions on near-fault stiff structures, e.g. low-rise masonry dwellings, should be further investigated.


473

2.2 Effects of non-structural components Numerous surveys carried out in the aftermath of the L’Aquila earthquake showed that the vast majority of the existing RC multi-storey buildings did not collapse. However, non-structural damage was extensive (Figure 6). Masonry infill panels failed primarily with out-of-plane mechanisms because of the weak connections between the interior and exterior walls (eg. Verderame et al., 2009). In several cases, the connections were absent and the brick walls possessed high slenderness. The effects of the masonry infills on the local and global stiffness, strength and ductility of the framed systems should be investigated by performing static and/or dynamic cyclic experimental tests. Analytical models should be calibrated on the basis of the test results and parameter analyses carried out to provide sound design for next generation seismic codes of practice. It is necessary that the masonry infills should be adequately designed and accounted for in the seismic analysis of building structures.

Figure 6. Damage to masonry infills in RC multi-storey framed buildings.

It is of vital importance to protect the occupants from the collapse of ceilings and other suspended components in ordinary buildings, schools, fitness and computer centre. The functionality of several buildings was impaired by the failure of architectural features that are typically used for building structures (Figure 7). The response of such components should be further assessed experimentally and design rules provided for the reliable sizing of their connections to the supporting structure.


474

Figure 7. Failure of ceiling panels.

Handbooks with comprehensive illustrative examples should be issued for the practical use by architects and interior design. Detailed design rules for non-structural components should be formulated and incorporated in the next generation seismic design codes; similarly for the equipments and building contents.

2.3 Critical facilities: hospitals Hospital buildings are critical facilities that should remain operational in the aftermath of moderate-to-high magnitude earthquakes. They are essentials for all the injured people that need medical care and assistance. The performance of all major hospitals located nationwide is undermined by the failure of building contents and non-structural components (Magliulo et al., 2009) under minor-to-moderate earthquakes (Figure 8). Moreover, traditionally based hospital buildings, i.e. even those fulfilling the capacity-design rules, exhibit structural damage when subjected to high-magnitude earthquakes. The use of behaviour (or response modification) factors greater than unity leads to the occurrence of structural damage under moderate-to-large earthquakes.

Figure 8. Damage observed in the Saint Salvador Hospital, L’Aquila.

It is thought that enlightened policy makers, health managers and all stakeholders should rethink the design of hospital buildings and other health care facilities. The functionality of such buildings is of paramount importance for societal communities in the aftermath of an earthquake. Adequate design rules should, therefore, be formulated on the basis of the observed damage and interruption of functionality. Innovative technologies and design should


475

be promoted to enhance the seismic performance of non-structural components, building contents and medical and high-tech equipments which are seriously damaged during earthquakes. Handbooks with practical guidelines for the design of non-structural components, fixing and seismic detailing should be issued to help architects and engineers to design safe hospital buildings.

2.4 Industrial plants The assessment of the seismic risk of industrial plants is a key issue to protect communities from earthquake-induced catastrophes. Chemical power plants located in or near urban centres should be protected adequately and cost-effective retrofitting strategies proposed for those thanks that do not possess sufficient resilience (Figure 9). In so doing innovative technologies may be employed. However, the assessment of the seismic vulnerability of the existing industrial plants should be investigated and prioritization scheduled according to the available funds. Vulnerability functions should be formulated for different types of industrial plan facilities. The limit states for adequate seismic performance should be established.

Figure 9. Damage of metal tanks between the municipality of Onna and L’Aquila.

Simplified methods of analyses should also be implemented in codes of practice to allow a quick estimate the safety of the existing industrial facilities.

2.5 Lifelines The existing national lifeline systems are highly vulnerable to earthquake ground motions. The assessment of the as-built systems is an essential step to estimate the effects of the rupture of gas pipelines, sewage, electrical and telecommunication networks on social communities. Table 1 provides the statistics of a recent survey estimating the Italian major lifelines. It is noted that the dimensions of the networks are a few thousands kilometres (from 4.342 for the oil pipelines to 21.872 of the Terna electrical power network). The transportation systems (highways with their 6.544kms and railways with their 16.295kms) exhibit high seismic risk. Methods and types of retrofitting may be analysed on a national scale. Comparative interventions schemes may be performed to provide cost-effective solutions to the transportation managers. Early warning systems and methodologies may be employed to ensure the safety of the hazardous lifelines, such as oil and gas pipelines, for electrical power networks and high-speed railways.


476

Table 1. Statistics of the Italian major lifelines (Source ISAT – Terna).

Lifeline (type) Dimension (in kms) Owner Electrical power

network 21.872 Terna (since 2006)

Oil pipelines 4.342 Gas pipelines 8.479 (main pipelines)

22.410 (secondary pipelines, only ENI network)

Highways 6.544 Railways 16.295

Ministry of Infrastructure and Transportation (since

2008)

2.6 Small historical centres The 6th April L’Aquila earthquake demonstrated the weakness of the existing historical buildings, which represent the living legacy of a glorious past. A number of damage reports showed that the historical city centres of L’Aquila, Pettino and Onna were severely affected by structural collapses. There are, however, numerous small historical centres (see for example Figure 10), generally located on hilly places or in the suburbs of large urban areas. The analysis of seismic risk of such centres and its mitigation is an essential task that is required to ensure safety to the local populations and to preserve the existent cultural heritage. The evaluation of the seismic risk may be carried out initially at a macro-scale level and then considering the building aggregates and single units of the centres.

Figure 10. Aerial view of the small historical centre of Tempera.

In addition post-earthquake evacuation plans should be assessed on the basis of the easy of access to the sites and the surrounding transportation networks.

2.7 Cultural heritage and monumental buildings The death of nearly 300 people was a great human loss caused by the 2009 L’Aquila earthquake. However, earthquake damage resulting in the collapse of monuments, historical


477

palaces and places of worship and stately buildings (see for example Figure 12) represents an irreplaceable loss in terms of cultural heritage, while their restoration costs is a serious threat of the gross national product. Vulnerability assessment of the cultural heritage and monumental buildings is a fundamental task than the earthquake engineering community should consider as an urgent need. Sound guidelines should be formulated using the experimental data and numerical results achieved in the 2005-2008 ReLUIS-DCP research projects. Additional experimental and numerical work is deemed necessary to enhance the reliability of the structural models, the definition of appropriate limit sates, deformation and strength thresholds for structural components and systems. Health monitoring of landmark structures may be adopted as a viable solution to monitor and prevent the occurrence of structural damage during minor to moderate earthquakes. Retrofitting strategies should be formulated in compliance with the requirements prescribed by the conservation thrusts.

Figure 11. Typical collapse of the dome of the L’Aquila Duomo.

Post-earthquake first aid interventions should be assessed and practical rules formulated for practical applications. In so doing, the reversability of the interventions should be adequately accounted for.

2.8 Emergency management Post-earthquake emergency management is a crucial task that government and non-government institutions and organizations which are in charge of the civil protection need to assess responsibly. The technical support provided by the ReLUIS researchers in the emergency management in the aftermath of the 6th April L’Aquila earthquake showed the effectiveness of a team working. The ReLUIS researchers worked closely with the DCP delegates to coordinate the damage surveys in the areas affected by the earthquakes. Expert groups were formed and visited thousands of buildings, bridges, industrial sites and lifelines. The damage surveys were crucial to establish the safety of structures subjected to the earthquake. The structures were tagged according to the level of observed structural and non-structural damage (Figure 12). The technical checks were based on visual inspections of experts. Databases were compiled using the data collected on site for the inspected structures. It is thought that more efficient intervention plans may be assessed. In so doing, the format of


478

the existing damage collection data should be improved. A further critical issue that should be developed in the future is the temporary housing. Urban and architectural planning, structural types, material of constructions, constructability, maintenance and re-use of temporary houses should be assessed.

Figure 12. Visualization of the damage scenario of large urban centres.

2.9 Quick damage evaluation The evaluation of the damage caused by earthquakes is of paramount importance for the scheduling of the retrofitting or the reconstruction of the structures. This approach was experimented during the 2009 L’Aquila earthquake with regards to the cultural and historical buildings. For such buildings cost estimates were carried out using an approximate approach that allows the evaluation of the total sum needed for the repair of a single structure. The repair costs was estimated chiefly for churches, palaces and monuments. The cost was derived by the interventions needed to repair the failure caused by the earthquake. It is essential to extend the quick estimation of the cost of the damage repair to other constructions. Back-analyses are also deemed necessary to establish the soundness of the approach adopted in the estimations. Parameter analyses may be carried out to assess the cost-effectiveness of alternative retrofitting schemes.

Note: -- OObbsseerrvveedd ddaammaaggee - Absent / uncertain damage


479

2.10 Safety and sustainability Structural safety is essential for building occupants but is should be achieved using sustainable materials and technologies. The reconstruction initiated after the 2009 L’Aquila earthquake was based on green approaches. The project C.A.S.E. (Complessi Antisismici Sostenibili Eco-Compatibili, Seismic Resistant Blocks Sustainable Eco-Friendly) which is financially supported by the Italian Government is aimed at providing 150 residential buildings to homeless people. The buildings employ base isolation systems and are built with green technologies in compliance with the most recent environmental regulations. The conceptual approach of green buildings (Figure 13) may be further developed and application is seismic zones promoted.

Figure 13. Safe “green” building structure.

The environmental efficiency should be used along with the cost-effectiveness of prefabricated modular type building systems which may minimize the construction time and hence are optimal solution particularly in the post-earthquake reconstruction.

3 REFERENCES

Chioccarelli, E., Iervolino, I. (2009). Direttività e azione sismica: discussione per l'evento de L'Aquila. Proc. of XIII Convegno Nazionale "L'Ingegneria Sismica in Italia", Bologna, Italy.

Cosenza, E., Chioccarelli, E. and Iervolino, I. (2009). Preliminary study of L’Aquila earthquake in near fault region, v.1.00, available at http://www.reluis.it

Chioccarelli, E., De Luca, F. and Iervolino, I. (2009). Preliminary study of the L’Aquila earthquake ground motion records, v.5.20, available at http://www.reluis.it


480

Magliulo, G., Pentangelo and Manfredi, G. (2009). Rapporto su Il danneggiamento delle controsoffittature a seguito del terremoto dell’Aquila dell’Aprile 2009. v.1.00, available at http://www.reluis.it (in Italian).

Simonelli, A., Sica, S., Moccia, F., Penna, A., Lucadamo, C., Mitrione, A., Mosca, P., Moscato, T., Rotella, M., Spatola, M.G., Zarra, S., Santo, A. (2009). Rapporto preliminare sugli effetti indotti sull’ambiente fisico dalla sequenza sismica dell’Aquilano. Gruppo di Lavoro UNISANNIO-CIMA-DIGA, available at http://www.reluis.it (in Italian).

Verderame, G.M., Iervolino, I. and Ricci, P. (2009). Report on the damages on buildings following the seismic event of the 6th of April 2009, v.1.20, available at http://www.reluis.it

research needs in earthquake engineering … · research needs in earthquake engineering...

Documents