Özgür BOZDAĞ Mutlu SEÇER Dokuz Eylül University Katip Çelebi University Izmir, Turkey SEISMIC RETROFITTING OF AN EXISTING INDUSTRIAL STRUCTURE FOR CONVERTING INTO AN EDUCATION BUILDING

Introduction  After the destructive earthquakes occurred in last decades, ensuring the safety of existing buildings has become one of the most important tasks of architects and engineers.  It is well known that vast amount of existing buildings in Turkey and in earthquake prone zones of Europe have poor seismic performance, since most of them were built before modern seismic codes.  Earthquakes may cause heavy damage or collapse a building before its predicted life time.  In this case, building waste and other kinds of wastes are suddenly emerged and removal of these wastes becomes a great problem.

Introduction  Under these circumstances, there is a significant need to perform adequate assessment of existing buildings and to investigate possible retrofitting schemes prior to future seismic events.  Another benefit of seismic retrofit is to prevent the occurrence of sudden structural failure or damage before predicted lifetime in the design phase of the building.

Introduction  Improvement of safety of existing buildings can be ensured in two ways:  demolition of existing building and the construction of new building according to modern codes.  retrofitting the existing building.  The first solution is simple and easieri however high impact on the environment due to demolition wastes.  The second solution is challenging for architects and engineers, because of the complexity of ensuring structural safety and all sustainability requirements at the same time. However, it seems like a necessity when considering huge amount of existing building stocks in cities.  At the present paper seismic retrofitting of an existing industrial structure for converting into an education building is presented.

Building Sustainability and Seismic Rehabilitation  Sustainable building can be referred as a building which has the least impact on the natural environment, both in terms of the building itself and its surroundings and global settings.  For constructing a new building or retrofitting existing structure to ensure seismic safety in a sustainable way, minimization of non-renewable resource consumption and enhancement of the natural environment are basic requirements to be followed.

Building Sustainability and Seismic Rehabilitation  Parallel to rapid development in building sector, safe and sustainable building concept and life cycle analysis methods become more popular issue in recent years.  The lifecycle of a building project starts before any physical construction activates and ends after its useable life.  In life cycle analysis, a building should be able to fulfill the estimated service life which includes all these phases.  However, buildings may reach to the end of its usable life before the predicted lifetime in the design phase due to natural disasters like earthquakes.

Building Sustainability and Seismic Rehabilitation  The concept of service life is a key parameter for the life cycle consideration and it relates to performance based design.  Structural components such as materials, construction technique, isolation details etc. are selected according to building facilities and estimated service life.  Since service life influences initial cost, the building should be able to sustain the predicted life time.  All life cycle considerations estimated in the design phase of a building may become waste with a destructive earthquake.

Building Sustainability and Seismic Rehabilitation  After catastrophic earthquakes occurred especially in last 20 years, improving the seismic safety of existing buildings against earthquakes have gained attention.  In order to assess the structural performance of a building several methodologies are established and many guidelines are prepared such as Vision2000, ATC-40, FEMA-356 and FEMA-440.  Furthermore, some countries like Turkey, these methodologies have become a part of the seismic design codes for evaluating the seismic performance of RC buildings.  In general, retrofitting strategy of building intends to improve the seismic performance of a building to life safety performance level.

Building Sustainability and Seismic Rehabilitation  For evaluating seismic performance of existing buildings, these modern design codes play a leading role.  Based on the results, it is possible to decide one of the two options:  demolition and reconstruction of existing building  retrofitting for ensuring adequate seismic safety  From the economic point of view, retrofitting of existing building is not the best solution for some cases.  For this reason, conversion of structural function after retrofitting may be an alternative solution for reducing depreciation time.

Rehabilitation of the industrial building  Investigated building was built as a part of the large industrial complex around 1970 in Izmir city of Turkey.  Parallel to economic developments, vicinity of the building become one of the most rapid growing areas of the city and it is needed to evaluate existing structures in the region.  At the present time, investigated building is placed among the educational buildings and there is no any active industrial facility.  There are two options:  demolition of building  inversion of building into educational facility after retrofitting.

Building features  Existing industrial structure is six story building with a basement.  Based on the in situ investigations, building plan dimensions are measured as m and m.  Total building height is m from the ground.  Existing structural system is an ordinary RC frame system with some irregularities.  Since the weak soil conditions under the foundation, considerable amount of settlement was observed.  Tests on the concrete specimens shown that existing compressional strength of concrete is about 7.9 MPa which does not satisfy neither current nor previous code requirements.  Based on weak structural system and low material quality, safety of the structure is evaluated as insufficient against earthquakes.

Retrofitting strategy  Since seismic resistance of the building is not enough to satisfy code requirements, retrofitting is required.  However, it is not possible to use the building as industrial facility because of inversion of area where building is placed. For this reason, it is decided to convert the structure into an education building.  For improving structural resistance of the structure, shear walls are added into the exterior frames. These additional shear walls are planned from base to top of the building.  Furthermore, columns are mantled according to specifications in the Turkish Seismic Code for increasing the lateral stiffness of the building and for improving shear resistance of the columns.

Evaluation of proposed repairing and retrofitting system  Structural performance of the building is evaluated according to Turkish Earthquake Code.  In this code, performance objectives for educational structures are;  life safety for earthquakes probability of exceedance 2% in 50 years and  immediate occupancy for earthquakes probability of exceedance 10% in 50 years.

Evaluation of proposed repairing and retrofitting system  Building is analysed by pushover analysis and lateral loads are increased until top level of the building reach the target displacement at analysis direction.  Analyses show that seismic performance of the building fulfil the code requirements with proposed retrofitting technique. Capacity curves and target displacements for %10 probability of exceedance a) X direction b) Y direction Capacity curves and target displacements for %2 probability of exceedance a) X direction b) Y direction

Evaluation of proposed interventions from sustainability perspective  Life cycle analyses of the buildings are performed based on several stages. During analyses, it is assumed that building reaches end of life without any sudden interruption.  For the earthquake prone areas, this assumption is not satisfied in some circumstances.  In the preresent study, strengthening elongates the service life of the existing industrial building and minimizes the risk of the building to collapse due to earthquakes before reaching its economic life.  Durability, maintenance, energy efficiency and structural safety will be improved accounting the benefits of structural strengthening.  Moreover, the strengthening of the building gives opportunity for maintenance and non-structural renovations of constructions.

Conclusions  Earthquakes occurred especially in last decades indicate that seismic performance of the existing buildings do not meet the modern design codes requirements.  According to seismic performance analyses, demolition of the buildings is generally more suitable solution compared to retrofitting due to economical perspective. However, demolition of building may cause great amount of waste and this is not admissible from environmental point of view.  In the present paper, performance analysis of an existing industrial building with insufficient seismic safety is explained. Retrofitting expenses become acceptable by converting existing industrial building into educational building. This study showed that conversion of the building into another facility can be an alternative solution instead of demolition.

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