The Behavior of Retrofitted Buildings During Earthquakes: New Technologies

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1 Chapter 20 The Behavior of Retrofitted Buildings During Earthquakes: New Technologies Mikayel Melkumyan Five years have passed since buildings were retrofitted under the World Bank financed Armenia Earthquake Zone Reconstruction Project. During this period several earthquakes of varying intensities occurred in northern Armenia. Intense usage of these buildings has been taking place as all are occupied. Considering these factors, there are lessons that can be drawn from the retrofitting, which uses new technologies, to learn whether these technologies can be applied to critical facilities. Different types of laminated rubber bearings were used to improve earthquake resistance in numerous buildings. Following the earthquakes, these bearings were examined and their performance was evaluated. Lessons learned from the experience should now be passed along to decisionmakers responsible for construction policies. Also, if the new technologies are deemed appropriate, they should be applied to critical facilities. The study of these retrofitting measures also included analysis of the sustainability and effectiveness of the new technologies for critical facilities such as schools and hospitals. On the basis of the study, a report was prepared on the findings outlined below. The conclusions reached and recommendations made can be supported by the data received and working papers submitted that are kept in a permanent file. Project Scope The objectives of the assignment were to assess the behavior of retrofitted buildings, to learn lessons based on the consequences of earthquakes of different intensities, and to justify the possibility of the practical application of new technologies to critical facilities. More specifically, the study required the following: 1. Visual inspections of three isolated buildings in Vanadzor (one building with base isolation and two buildings with isolated upper floors). Possible damage in isolation systems and to structures below and above was to be revealed and assessed. 2. Instrumental investigation of dynamic characteristics of the buildings. The values of vibration periods and damping factors were to be obtained and compared with the design values at small deformations. 3. Based on visual inspection and instrumental investigations, assess the technical conditions of the buildings. 4. Survey the tenants regarding the behavior of buildings during the various earthquakes that occurred in the last five years. 5. Based on the findings, assess the behavior of buildings during earthquakes and draw lessons from retrofitting using new technologies. 6. Justify the possibility of the practical application and effectiveness of new technologies to critical facilities. 7. Prepare recommendations to influence decisionmakers in construction policy for further implementation of new technologies in Armenia and other countries where similar projects are financed by the World Bank and other international financial institutions. In addition to the above scope, a similar study was carried out for one building in Spitak. This paper was written with the participation of A. Azaryan, T. Nersesyan, S. Saroyan, A. Avagyan, G. Goulanyan, A. Ghevondyan, A. Karapetyan, G. Voskanyan, K. Avanesova, and M. Begumyan. 293

2 294 Building Safer Cities: The Future of Disaster Risk Visual and Instrumental Inspection of Three Buildings in Vanadzor and One in Spitak: Assessment of the Technical Conditions The three buildings in Vanadzor were strengthened within the framework of the strengthening subcomponent of the World Bank-financed Earthquake Zone Reconstruction Project. This subcomponent funded the strengthening of structures damaged and weakened by the 1988 earthquake that could be made habitable through retrofitted structural reinforcing or seismic isolation systems. Also this subcomponent has established new technologies for the strengthening of existing structures, notably new techniques for installing seismic isolation systems in new and existing occupied buildings. The project is the worldwide pioneer for several techniques, and two project pilot structures have attracted international professional attention by establishing appropriate low technology methods for the strengthening of existing structures. 1 In the proceedings of the 7th International Seminar on Seismic Isolation, Passive Energy Dissipation and Active Control of Vibration of Structures (Assisi, Italy, 2 5 October, 2001) it is mentioned: As far as the ordinary apartment buildings are concerned, the number of new applications of the Innovative Antiseismic (IAS) techniques is particularly large in Japan and the P.R. China and Armenia (page xxiii); with regard to the interest in the IAS techniques it is now extending to new countries like, for instance, Turkey, Iran and India. Some other countries are beginning to follow the excellent example of Armenia, where seismic isolators are locally manufactured also for foreign markets, like Syria (page xxv); Very interesting on-site tests of an existing bank building at Irkutsk-City in Russia, retrofitted by applying the technology invented by Prof. M. Melkumyan in Armenia (page xxv). The building inspected in Spitak was constructed under the terms of the World Bank project. It is a fourstory apartment building on Shahumyan Street with reinforced-concrete bearing walls. This is the first newly constructed building in Armenia using the seismic (base) isolation system. Following the 1988 Spitak earthquake, no buildings over two stories were constructed. With base isolation, however, a four-story building was constructed for the first time after the earthquake. Presently, where the isolation system is located, renovation work is going on with the purpose of establishing a museum dedicated to the 1988 Spitak earthquake. This project was initiated by the Armenian Association for Earthquake Engineering. A visual inspection was carried out for three buildings in Vanadzor (one building with base isolation and two buildings with Additional Isolated Upper Floor (AIUF)) in addition to the building with base isolation in Spitak. Hairline cracks were found in some reinforcedconcrete elements below and above the isolation system and some violations of the rules of exploitation were revealed in the building Yerevanyan #149. While the cracks are not dangerous for the building, the violation of rules of exploitation in the form of filled seismic gap by stones, mortar, soil, and wood is absolutely inadmissible. All filled materials that restrict the displacement of the isolation system must be removed immediately. The roof layers and some parts of exterior nonbearing structures in the building Isahakyan #4 were significantly damaged due to violation of the rules of exploitation of the building by tenants. As a result, the seismic isolators of AIUF were immediately influenced by atmospheric precipitations, seriously deteriorating the surface of six isolators. Also in buildings Isahakyan #4 and Cherkassi #1, the seismic isolators are not appropriately protected from low temperatures. The roof and nonbearing exterior structures of the Isahakyan #4 building must be repaired and six seismic isolators must be replaced. All isolators in both Isahakyan #4 and Cherkassi #1 buildings must be taken into special jackets due to light insulation materials. The estimated cost for jacketing, replacement of isolators, and repair work for both buildings is about US$15,000. No damage was revealed in reinforced-concrete structures below and above the isolation system of Shahumyan building. Seismic isolators were also in a normal technical state. Instrumental investigations of all four buildings were carried out. The rubber hardness and dynamic characteristics of buildings were measured. The increase in rubber hardness due to low outside temperatures was observed in the Isahakyan #4 and Cherkassi #1 buildings. The dynamic characteristics of the Yerevanyan #149 and Shahumyan buildings fully correspond to the design values of total initial stiffness of isolation systems. The dynamic characteristics of the Isahakyan #4 and Cherkassi #1

3 The Behavior of Retrofitted Buildings During Earthquakes: New Technologies 295 buildings are 1.4 times less on average than the design values as a result of increased rubber hardness. The proposed jacketing of seismic isolators of AIUF in both buildings will help to avoid disturbing their tuning in order to keep effective seismic protection of the buildings. Based on visual and instrumental investigations, the technical conditions of the buildings were assessed. It is stated that in three buildings, Yerevanyan #149, Cherkassi #1, and Shahumyan, all systems that provide increased earthquake resistance are in satisfactory condition from a technical point of view. Nonbearing structures of AIUF and some seismic isolators in Isahakyan #4 building are in bad technical condition. Data on the Earthquakes Recorded in Northern Armenia from 1996 to 2002 Practically all of the territory of Armenia is situated in a seismically active zone. The size of earthquakes ranges up to M = 7.1 (according to historical and paleoseismic estimations). Focal depth is, on average, 10 kilometers. All sources are located on active faults with an average slip rate of about one centimeter per year. During the last seven years, more than 20 earthquakes were recorded in northern Armenia. By geographical location of the epicenters of the earthquakes, the distances between the epicenters and the cities of Vanadzor and Spitak were calculated and the maximum possible intensity values in Vanadzor and Spitak were in the range of III to V. Such seismic impacts are not a hazard for the buildings inspected, but they cause distress in the population. From this point of view, the opinions of the buildings tenants are important for assessing the behavior of buildings during earthquakes. The behavior of people for each level of intensity from III to V is described in table Survey of the Tenants of the Four Buildings Examined A survey among tenants of apartment buildings with base isolation or AIUF was carried out on February 6, 2002 in the cities of Vanadzor and Spitak. The objective of the survey was to find out how safe the tenants feel in the buildings that were newly constructed or retrofitted by new technologies, and to ascertain the advisability of applying AIUF and base isolation not only to apartment Table 20.1 Short form of the European Microseismic Scale EMS-98 EMS Definition of Description of typical observed effects intensity earthquake (abstracted) III Weak Felt indoors by a few people. People at rest feel a swaying or light trembling. IV Largely Felt indoors by many people, outdoors observed by very few. A few people are awakened. Windows, doors, and dishes rattle. V Strong Felt indoors by most, outdoors by few. Many sleeping people awake. A few are frightened. Buildings tremble througout. Hanging objects swing considerably. Small objects are shifted. Doors and windows swing open and shut. buildings but also to schools, hospitals, kindergartens, and other critical facilities. Appropriate questionnaires were elaborated to carry out the survey (a sample questionnaire is given below). An analysis of the results showed that 94 percent of all respondents were aware of the advantages of their building over others, 77 percent felt safe during earthquakes, and 93 percent would like to apply seismic protection systems if constructing their own houses. One hundred percent of tenants considered the application of seismic protection systems to critical facilities to be a priority and 100 percent wished to see an increase in the number of buildings with seismic protection systems to reliably protect people from earthquakes in Armenia. Other comments from respondents included: Usually we learn from tenants of neighboring buildings that an earthquake has occurred. We have felt few earthquakes in this building during the past several years. We are glad to live in this type of building. We feel safe and protected. If I don t experience any vibration during earthquakes, it means I am safe. We bought this apartment because we knew the building was improved with a seismic protection system. We believe that the existence of the seismic protection system makes the building safer. We invite our neighbors from close apartment buildings to take refuge at our place when an earthquake occurs. I have learned about earthquake occurrences only from the radio.

4 296 Building Safer Cities: The Future of Disaster Risk When there is noise and lights are switched on in the front building, I assume that an earthquake occurred. We believe that schools, hospitals, and kindergartens should be seismically isolated first of all. We would like all of the buildings in our city to be safe, and all people to feel safe. I am safer here in this house than in the temporary dwelling-wagon. Sample Questionnaire for Tenants of the Nine-Story Apartment Building #4 with AIUF in Isahakyan Street, Vanadzor Several buildings in Vanadzor were provided with base isolation or other seismic protection systems from We would like to know your opinion on the advisability of applying such seismic protection systems. This research is being carried out under a World Bank contract. Your sincere answers will help to make our research effective. Thank you in advance. 1. Where were you when the earthquake of 1988 occurred? Out of Armenia In Armenia In the Earthquake Zone 2. For how long have you been living in this building? a) more than 14 b) 6-14 years c) up to 6 years 3. Do you know the advantage of your building over the others? 4. How many times have you experienced earthquakes or have you heard that an earthquake has occurred? a) have experienced b) have not c) have heard d) have not e) find difficulty...times experienced...times heard in responding 5. If 4a). Did you feel safe at home during the earthquakes? 6. What kind of apartment (building) did you live in before the earthquake of 1988, and what is the difference between it and the one you live in now? 7. If you would construct your own house, would you like to apply seismic protection systems? 8. Do you consider seismic protection systems advisable to be applied not only to apartment buildings but also to schools, hospitals and other critical facilities? 9. What can you say about your neighboring apartment buildings tenants behavior during the earthquakes? 10. Based on your experience would you like to see increase of the number of buildings with seismic protection systems in Armenia? Floor apartment # Age Sex Male Female Education Secondary Technical college Incomplete higher Higher

5 The Behavior of Retrofitted Buildings During Earthquakes: New Technologies 297 Thus, in the course of the last seven years, the buildings studied were struck by some 10 earthquakes of different intensities in the range of III V by EMS-98. No serious damage was evident in bearing structures and isolators. Therefore, the behavior of buildings was assessed based on the tenant survey. The results obtained demonstrate that the seismic isolation and seismic protection systems implemented behaved during the earthquakes in the manner envisaged at the design stage. The results of the study represent a strong argument for the further use of seismic isolation, not only for apartment buildings but also for critical facilities. In an article published in the newspaper AZG Armenian Daily #219, November, , Professor Nazaretyan, who conducted an independent study of the building, wrote that, During the 1999 Spitak earthquake with an intensity of 5 6, the tenants of the Shahumyan Street building in Spitak and the Yerevanyan #149 building in Vanadzor did not feel the earthquake, while people from neighboring buildings ran outside. 5. Seismic (base) isolation provides high reliability for all structures and the buildings with seismic isolation are virtually safe from earthquakes. AIUF in comparison with base isolation provides less reliability, but earthquake resistance is still increased times. 6. People feel very safe in the buildings protected by seismic (base) isolation or by AIUF. In their opinion, the new technologies must be used extensively and not only for apartment buildings but also for schools, hospitals, and other critical facilities. 7. During earthquakes of different intensities, buildings protected by seismic isolation or AIUF exhibit the behavior envisaged at the design stage. This is an objective reality showing that seismic isolation technologies will provide high efficacy in retrofitting existing or constructing new critical facilities. 8. Maintaining buildings with the application of seismic isolation technologies, as for any other type of building, is an important factor. Unsatisfactory maintenance decreases the effectiveness of seismic protection. Lessons Drawn from Retrofitting Existing Buildings and from Constructing New Buildings Using Seismic Isolation and Protection Systems 1. Retrofitting existing buildings with seismic (base) isolation or constructing new seismic (base) isolated buildings can be realized in a relatively short time. Building Yerevanyan #149 in Vanadzor was retrofitted in one year and the Shahumyan building in Spitak was constructed in just over one year. For comparison, it should be noted that strengthening a building similar to Yerevanyan #149 by conventional methods takes more than two years. 2. Retrofitting existing buildings using new technologies (seismic isolation or AIUF) does not require interruption of the use of the buildings. While performing the retrofitting, tenants can stay in their apartments. On the contrary, strengthening by conventional methods requires evacuation. 3. The cost of retrofitting with new technologies is significantly cheaper (two-thirds less) than the cost of conventional strengthening. It is even cheaper when funds for temporary housing are factored in. 4. The cost of construction of new buildings using seismic isolation technologies is around 30 percent less than the cost of construction of conventional buildings. Justification for the Possibility of Practical Application and Effectiveness of New Technologies to Critical Facilities After completion of the World Bank financed Earthquake Zone Reconstruction Project and successful implementation of new technologies in , the application of seismic isolation continued in Armenia. Moreover, technologies developed in Armenia were also implemented in Russia and Syria. Armenian factories, namely Nairit and Yerevan Factory of Rubber Technical Articles (YFRTA), are now able to manufacture seismic isolators and bridge rubber bearings at a high quality and to international standards. The life expectancy of the bearings is guaranteed by the factories for 45 years. After the guarantee period, the bearings should be inspected. If the elastic properties (hardness) of the rubber are unchanged, they can continue to be used. Bearings should also be inspected following strong earthquakes. From , 14 seismic-isolated buildings were designed in Armenia. Included were 12 apartment buildings for the new Huntsman Village in Gyumri city, one house for a single family in Proshyan, and one school in Vanadzor, which will be retrofitted using seismic isolation. The school project in Vanadzor is actually the

6 298 Building Safer Cities: The Future of Disaster Risk first application of new, advanced seismic isolation technology to a critical facility. Building construction in Huntsman Village was financed by American John Huntsman. The construction of the single-family house was financed by the owner, an Armenian citizen. This is the first application of base isolation in private construction in Armenia. The retrofitting of the school in Vanadzor was financed by Swiss CARITAS. An important factor for the application of such technologies in Armenia is the presence of Armenia s chemical industry, which is able to locally manufacture high-quality isolators. Another factor is the presence of scientific and engineering sources capable of designing, investigating, testing, and improving the systems using new technologies. It is appropriate to note that retrofitting technologies were developed, designed, and implemented for the first time in Armenia. This fact is recognized by the international scientific and engineering community. Although the buildings studied were struck by medium-strength earthquakes, the experience showed that seismic isolation technology is extremely reliable. For example during the destructive 1995 earthquake in Kobe, Japan, the two seismic-isolated buildings were not affected at all, while a very large number of conventionally designed buildings collapsed. AIUF as a seismic protection method is very efficient for tall, flexible structures where base isolation is inappropriate. Although AIUF increases the seismic resistance of flexible buildings less than base isolation increases the seismic resistance of rigid buildings, the application of AIUF provides resiliency to buildings during future earthquakes. AIUF is the only method currently developed in Armenia that allows increasing seismic resistance of existing occupied flexible buildings. With such capabilities, the retrofitting or construction of ordinary (apartment) buildings and critical facilities using seismic isolation costs much less than conventionally designed buildings. For example, a comparative analysis was carried out for the Huntsman Village Project. Some average results of that analysis are given in table 20.2 for a four-story building. Two situations are considered: one building is designed with an ordinary type of foundation (conventional design), and the other is seismic-isolated. The cost of the bearing structure of this building (defined through a tender) is around $270,000. Based Table 20.2 Results of comparative analysis of seismic-(base)-isolated and fixed-base (conventionally designed) buildings Fixed-base Seismic-isolated Name of parameter building building Total shear force (kn) Required reinforcement (ton) Required reinforcement per 1 m of the area of the building (kg) Distance between the reinforcing bars in the walls (cm) Grade of the concrete B20 (M250) B10 (M150) Required cement (ton) Required cement per 1 m 2 of the area of the building (kg) Cost of reinforcement $144,000 $41,600 Cost of cement $32,210 $17,550 Cost of seismic isolators $24,700 Total cost of bearing structure $270,000 $177,640 Cost of bearing structure per 1 m 2 $83 $55 of the area of the building Seismic isolation will cost in U.S. dollars: ($144,000 + $32,210) ($41,600 + $17,550 + $24,700) = $92,360 on this amount, it can be concluded that, with seismic isolation, costs can be reduced by 30 percent. Almost the same results were obtained for the school project in Vanadzor. In this case, seismic isolation reduced building materials by 15 tons of steel and 250 cubic meters of concrete. Generally, the Armenian experience has shown that savings due to seismic isolation for retrofitting of existing buildings could be much higher, some 2 to 2.5 times, in comparison with conventional strengthening. Also, seismic isolation allows acceleration of the whole construction process. These factors encouraged Swiss CARITAS, donors for the school project, to undertake seismic isolation for this critical facility. Presently the Huntsman Village, as well as a school in Vanadzor, are under construction. Thus, the successful implementation of new technologies during the last eight years; the presence of capable industry that can locally manufacture seismic isolators; the presence of capable scientific and engineering sources locally developing and designing seismic isolation systems; the possibility of retrofitting by seismic isolation without interruption of facilities use; the low cost of retrofitting and new construction using seismic isolation; the possibility of accelerating the whole construction process; and high reliability of seismic isolation fully justify further practical application and effectiveness of

7 The Behavior of Retrofitted Buildings During Earthquakes: New Technologies 299 the advanced seismic isolation technologies to critical facilities. Recommendations Influencing Decisionmakers for Construction Policies for Further Implementation of New Technologies 1. It is recommended that International Financial Institutions (IFIs) implement the new advanced technologies in relevant projects in Armenia and other countries. Such technologies were born within the framework of the World Bank Earthquake Zone Reconstruction Project in Armenia, and it would be desirable to encourage the use of these technologies, especially for critical facilities. 2. It is recommended that IFIs encourage the Government of Armenia and others involved in construction financing to continue the application of new advanced technologies, not only for apartment buildings but for critical facilities as well. A booklet briefly describing all of the advantages of these technologies could be prepared and distributed among the interested parties. 3. IFIs should be consistent in insisting that construction funded includes reliable earthquake-resistant technologies. Special attention should be paid to construction companies, since many are reluctant to use new technologies and are not interested in obtaining smaller contracts. 4. A series of lectures should be organized to train those in construction companies, the Ministry of Urban Development, design institutes, and donor organizations about the new technologies. 5. A Center of Anti-Seismic Technologies should be established, possibly at the American University of Armenia. Such a center could train people working in the construction industry to deal with the development of new designs and further improve new technologies and their application to critical facilities. 6. Guidelines for seismic isolation and the protection of buildings and structures should be developed and published to promote further implementation of new technologies in the country (and in the region). 7. The experience of Armenia with retrofitting and seismic isolation should be shared with authorities in other countries with similar earthquake risk. 8. Local authorities and tenants of buildings where new technologies were implemented should be well trained in building maintenance to ensure that the technologies perform well during earthquakes. The Government of Armenia and donors should provide funds for jacketing isolators and repairing nonstructural elements in some buildings. 9. The 8th World Seminar on Seismic Isolation, Passive Energy Dissipation and Active Vibration Control of Structures will take place in October 2003 in Yerevan. This decision was made in recognition of the work undertaken in Armenia in the field of seismic isolation. The participation of decisionmakers in construction policy from Armenia and other countries should be encouraged in that high-level forum. Note 1. See World Bank ICR No , Armenia Earthquake Zone Reconstruction Project, December 1997.