1999+Kocaeli-Golcuk+&+Duzce-Bolu+Turkey+Summary+&+Lessons+Learned

**1999 Kocaeli-Golcuk & Duzce-Bolu Turkey Earthquake Summary & Lessons Learned** //Kyle Tennant - BAE/MAE - Penn State - 2011// toc

Introduction
On August 17, 1999 a magnitude 7.4 earthquake rocked western Turkey at 3:02 a.m. for 45 seconds near the city of Izmit in the Kocaeli province (Bellamy 2010). The earthquake occurred along the North Anatolian fault, a strike-slip fault similar to that of the San Andreas fault in the San Francisco, California region. The result was a large number of casualties and damage to buildings and infrastructure in the region. There were approximately 20,000 people killed and 50,000 injured along with over $30 billion in damage (Anderson 2001). At least 20,000 buildings that sustained heavy damage or collapsed (EQE 1999). Many buildings collapsed due to liquefaction of soil near the Izmit Bay, but a large percentage also were either not properly designed or constructed. This earthquake was considered by many to be the most destructive in Turkey's strong seismic history due to the timing and location near a highly populated region with poorly constructed buildings. Many lessons about earthquake prediction from stress buildup and building construction from damage observed can be learned from the 1999 Kocaeli-Golcuk & Duzce-Bolu Turkey Earthquake.

//Keywords: Turkey, Kocaeli, North Anatolian Fault, San Andreas Fault, Liquefaction, Turkish Earthquake Code, Reinforced Concrete,//

__Earthquake__
The earthquake occurred on August 17, 1999 in the early morning hours in the North Anatolian fault system. The 7.4 richter earthquake shook for 45 seconds and produced a 40% acceleration from gravity at the epicenter (Bellamy 2010). The long duration of the event was one contributing factor to the high level of destruction. Shaking at the epicenter originated at a shallow depth of 10.5 miles below the surface (EQE 1999). The epicenter was found to be about 9 miles to the east of Golcuk and about 4.5 miles to the southeast of Izmit. The worst of the damage went from Yalova and Korfez all the way to 62 miles east of the epicenter at Duzce, with the total length of fault rupture being about 68 miles (U.S. Geological Survey 1999). There were lateral offsets of up to 8 feet or greater found at the surface along with some significant vertical displacement that caused permanent flooding in some regions (EQE 1999). The heavy faulting in populated areas led to widespread destruction directly due to structures straddling the fault.

__Regional History__
There are many active faults in Turkey that lead to an average of a destructive earthquake every 7 months, along with an annual average of 1,000 deaths and 7,000 building collapses (Tatlidede 2008). The North Anatolian fault system is the world's longest strike-slip fault and one of the most active and well studied seismic regions (EQE 1999). This is a region prone to seismic activity, the history of seismic events along the North Anatolian fault and build up of stress from previous earthquakes made it plausible to believe a seismic event was possible in this area, shown in Figure 1. The 1999 Kocaeli-Golcuk and Duzce-Bolu Turkey Earthquake is the northernmost major earthquake on the North Anatolian Fault and last in a series of major earthquakes that started in 1939, and to many was considered to be just a matter of time before it occurred. Two years before the 1999 Turkey Earthquake it was proposed that the westward progression of stress transfer, originated in the 1939 earthquake, puts the city of Izmit next in line (Alarcon 2009). This prediction would soon come true and was worsened by the local soil conditions. The Turkey region is an important area for research into earthquake prediction.

__Geotechnical Conditions__
The geotechnical conditions of the Turkey region and specifically areas around the 1999 Kocaeli-Golcuk and Duzce-Bolu Turkey Earthquake added to the magnitude and destruction of the ground shaking. The majority of soils are soft, which act to amplify seismic loads that buildings feel (Anderson 2001). But the more destructive problem with soft soils is that they tend to be susceptible to liquefaction. This is a process when soils become fluid-like during shaking events. Longer shaking leads to more liquefaction and to settling and spreading out of the soil. This process is even greater in areas of soil saturation along rivers and seas. That is why cities such as Golcuk and Sapanca near large bodies of water and Adapazari along the young floodplain of the Sakarya River are particular areas that suffered greatly from poor soil conditions that were combined with a shallow ground water table (U.S. Geological Survey 1999). Subsidence and loss of coastal lands due to liquefaction and cyclic failure was also a common theme in the Izmit Bay areas for the same reasons (Altun 2008). Around the city of Golcuk a specific soil sample showed the soil profile to be "soft silty clay, loose to medium density gravel and sand, medium/stiff clay, dense gravel and stiff clay layers" (Altun 2008). It is then possible to look at the soils present and determine the Plasticity Index (PI) of the soil and therefore how easily the soil can be liquified. Soils with a lower PI and confining stress tend to require less seismic energy in order to cause cyclic failure (Altun 2008). These were naturally occurring conditions in many locations that were hit by the 1999 Turkey Earthquake, but also many construction sites were hastily filled with cheap soft soils that only aggravated the issue. A second geotechnical condition of the earthquake that led to many issues is the the type of fault that makes up the North Anatolian Fault. It is a strike-slip fault where primarily two plates are moving horizontally different from each other until the stress builds up to a point that a rupture along the fault occurs thus breaking the two tectonic plates from each other and briefly allowing movement. The North Anatolian Fault is the intersection of Eurasian Plate and the Anatolian Block. The Anatolian Block is a wedge that is between the fairly stable Eurasian Plate and the African and Arabian Plates that are trying to move northward. The shape of the Anatolian Block pushes it and most of Turkey westward at a rate of 10-20 mm/yr (U.S. Geological Survey 1999), Figure 2 shows the regions plate tectonics. This is how stress has built up at a somewhat predictable rate along the fault and lead to Turkey's seismic history. This significant movement of up to 8 feet at the fault rupture during the 1999 Turkey Earthquake led directly to property, infrastructure, and building damage (EQE 1999). Along with the horizontal movement, the Eurasian Plate to the north of the fault was also generally pushed down 2 feet with respect to the fault (EQE 1999). The drop of the northern side of the fault added to subsidence issues in areas such as Golcuk and Sapanca leading to permanent flooding along the Izmit Bay and bodies of water.

Turkish Earthquake Code (TEC) Prior to 1999 Earthquake
Turkey first started to develop seismic codes for building design in the early 1940s following the Great Erzincan Earthquake of 1939 (Alarcon 2009). This would be a good approach considering it would be the first of a string of 7 major earthquakes up the North Anatolian Fault in the upcoming 60 years. With plenty of good hands on experiences to learn from Turkey has continued to make advances with the two most recent notable code updates being in 1975 and 1998, both of which directly affecting the buildings that had to withstand the 1999 Kocaeli-Golcuk and Duzce-Bolu Turkey Earthquake. The buildings designed to meet 1998 TEC requirements were mainly, if not all still under construction, and there were few large changes from the previous code.

In the 1975 code there was an emphasis on reinforced concrete frame buildings with masonry infill walls due to the fact that they were widely used throughout Turkey's high risk areas. In the code most structures ended up with a design base shear of 8 - 12% of the building weight, depending on whether the frame was considered ductile or non-ductile. The code had the detailing required to make sure that the structural frame would act ductile. There are specifications to make sure that columns are confined by rebar at the ends where there could be plastic hinging. There were also requirements for transverse reinforcement and longitudinal bars over column locations (Anderson 2001). It is clear that government officials knew that masonry infill walls are brittle and would crack, so the concrete frame would need to be ductile in order for the buildings to remain safely standing.
 * //1975 Turkish Earthquake Code//**

Building Performance
In Turkey many thousands of buildings collapsed due to the 1999 Kocaeli-Golcukand Duzce-Bolu Turkey Earthquake, with many more thousand sustaining severe damage. Statistics show that 6% of buildings totally collapsed, with most casualties occurring in these and only 5% of those trapped being rescued from the rubble. Also 7% suffered severe damage, 12% medium, 14% light, and 61% no damage at all (Tatlidede 2008). The even more alarming thing is that a great percentage of these failures occurred in recently constructed reinforced concrete structures that were suppose to be designed according to earthquake-resistant code requirements adapted from Uniform Building Code in California. Engineers were surprised to find that building failures covered a wide variety of possible earthquake failures such as the following; pancaking, total subsidence, sunken buildings, sea water inundation, and many more (EQE 1999). The building failures affected all sectors of the building industry, from small residential to large industrial plants. The focus of this case study will be spent covering medium size reinforced concrete structures, since this was the majority of the type designed, damaged, and investigated post earthquake. There are few steel buildings or unreinforced masonry buildings in Turkey. Concrete is locally available and generally preferred for economic and experience reasons (Anderson 2001).

__Failure Types__
When looking at the reasons for building damage and collapse many of them go back to negligence either by the owner or engineer in order to cut corners and save money and/or time on the project. Building flaws came in all phases of the project, from planning, to site investigation, code compliant design, proper construction, and more. All of these will be investigated further by looking at how they fall into two broader sections of failures to the structure itself and failure to the ground that supports it.

These failures include anything that led to the direct demise of the structural system, in most cases reinforced concrete frame.
 * //Structural Failures//**
 * No design engineer was consulted for all or part of the building (Hasgul 2007), in some cases buildings were built based directly off of a previously built building and not directly for the specific site and loading conditions (EQE 1999).
 * Improper or misinterpreted computer models that led to under designed buildings and strong column/weak beam failures (Hasgul 2007).
 * Construction errors such as poor workmanship, not following engineering design, no engineer on site to assure proper construction.
 * Poor concrete that was not able to develop the compressive strength that was assumed during the design phase. A study of the not effected city of Istanbul after the 1999 Turkey Earthquake showed that 101 of 244 tested structures contain concrete with compressive values below design standards, with large variation between type of concrete, project, and production day (Akcay 2004).
 * Damage or modification to structure once occupied, such as adding or removing components after construction without revisiting calculations (Hasgul 2007).
 * Damage from previous earthquakes that was not repaired (Hasgul 2007).
 * Failure to use updated earthquake zone maps (Hasgul 2007).
 * Failure to meet earthquake code requirements for confinement reinforcing steel, placement of horizontal and vertical reinforcement (EQE 1999)
 * Widespread use of smooth reinforcing steel instead of deformed (EQE 1999).
 * Failure to meet earthquake code requirements for detailing of beams, columns, and joints between the two (EQE 1999).
 * Short-column effects where interference by nonstructural elements cause the column to have increased shear at an unintended level. This could occur because by things such as staircase landings framing into columns or above or below windows framed into masonry walls (Anderson 2001).

There are also various structures that sustained zero damage to their superstructure but still failed due to the ground under their foundations. The before mentioned geotechnical conditions of the region led to the various types of building failures. These problems occurred because of a lack of soil investigation at the site or a disregard for the fact that the building was planned to be constructed on soils known to be susceptible to liquefaction. Matters were often made worse by adding cheap fill to a site or building too close the the sea where soils are more saturated and less stable. Many owners just saw the cheap land as an easier way to make a profit and did not look into either a more suitable site or ways to improve the soil to be built on. The types of building failures due to geotechnical issues that ensued are listed below.
 * //Geotechnical Failures//**[[image:Figure_3_-_Foundation_Weakening_Due_to_Soil_Liquefaction_in_Adapazari_Turkey.jpg align="right" caption="Figure 3: Foundation Weakening Due to Soil Liquefaction in Adapazari, Turkey -  Source: USGS"]]
 * Sea water inundations because buildings were built too close to the sea and soils either laterally spread into the sea or the level of the land dropped if you were in a location to the north of the fault line (Bellamy 2010).
 * Sunken building, where the whole building sinks into the ground because of underlying liquefied soils (Bellamy 2010). One common sign of liquefied soils is sand boils. This is when sandy subsurface material vents to the surface. Sidewalks around sunken buildings were pushed up due to the displacement of material that was previously under the building. One interesting thing to note is that there were cases where objects remained on the shelves in sunken buildings while neighboring buildings on non-liquefied soils were quite shook up (U.S. Geological Survey 1999).
 * Overturned building, this occurred when one side of the building rested on soils that liquefied while the other side remained solid, as shown in Figure 3 (U.S. Geological Survey 1999).

__Reinforced Concrete Structures__
Reinforced concrete structures deserve a closer look because they suffered from the most design/construction issues and caused the majority of the casualties in the 1999 Turkey Earthquake. The largest culprit of the group was medium sized, 4 to 8 story, reinforced concrete frames with masonry infill walls. From inspection a large number of the failed buildings appeared to have little or no seismic design or construction. Without shear walls the concrete frame is relied on to provide the lateral resistance, and in many cases the frame lacked the strength to prevent large deflections and also the ductility to prevent collapse. The lack of seismic detailing in certain areas to add resilience to the structure was previously mentioned in the //Structural Failures// section. This combined with owners frequently desiring to have open store space on the ground floor lead to one of the most frequent failure mechanisms, soft story failure. This is when a story has significantly less structural strength than one above or below it, leading to a collapse at that level as shown in Figure 4. Once again a case where the owner has put lives in jeopardy for the pursuit of the highest profit from his property (Anderson 2001).

A masonry infill system is any structural frame that has masonry units in the space between the beams and columns, particularly on exterior walls. In Turkey's case the structural frame was reinforced concrete and unreinforced masonry was a cheap and easy way to fill the architectural space between the frame and also provide stiffness by not leaving room to allow the frame to sway sideways. But the issue is that masonry is a brittle material that can only take so much tension without cracking and loosing its strength. The masonry infill is stiffer than the concrete frame and thus tends to take a large amount of load until the cyclic tension and compression leads to diagonal cracks that render the masonry useless. Also, to compound the issue there is the fact that masonry is heavy and the extra weight only adds to the load that the structural system must carry. Then in most cases the improperly detailed reinforced concrete frame is neither strong or ductile enough and failure occurs (Anderson 2001).
 * //Masonry Infill Systems//**

Most well seismically designed reinforced concrete frames include some reinforced concrete shear walls to take a great percentage of the lateral load, but in Turkey reinforced concrete shear walls are few and far in between. In the few buildings with reinforced concrete shear walls the buildings tended to survive even if the walls suffered from smaller aspect ratios, poor concrete quality, or a minimum amount of steel reinforcement (Anderson 2001).
 * //Reinforced Concrete Shear Wall Systems//**

Asmolen systems are another type of structural construction that lead to column failure and soft story collapses. This is because the system employs the use of concrete joists with masonry units placed in between with typically columns of smaller size. This concept violates the seismic design concept of strong-column weak-beam. In this system the columns often become overloaded on one or more floor leading to either pancaking or a soft story collapse of the first floor in a similar fashion to that in Figure 4 (Anderson 2001).
 * //Asmolen Systems//**

Another concrete system used in Turkey is precast concrete systems. These systems were commonly used as industrial facilities and numerous were near the epicenter of the earthquake. Overall these systems also tended to not fair well for some of the same reasons as reinforced concrete structures, like lack of column confinement and short-column effect. The typical layout of a precast industrial structure starts with precast concrete columns that are grouted into a socket in the perimeter foundation wall to create a fixed base. These columns have a short cantilever that supports cranked beams and from there precast stringers. The other two main reasons for failure in this type of system are failed connections and flexible diaphragms. For this reason precast concrete structures that were under construction preformed especially bad. But at the same time there were also some finished structures that survived well (Anderson 2001).
 * //Precast Concrete Systems//**

__Industrial Facilities__
As mentioned in the previous section, many industrial buildings were made of precast concrete systems. Other than that there were two other main systems that caused large and destructive industry failures. Many pipelines were ruptured by large displacements and large tanks suffered a number of failures. These two things led to large scale fires and loss of large portions of Turkey's industry for an extended period of time. Tanks can fail in multiple different ways. In a few elevated tanks supports buckled. In others the tank walls buckled in or out, and more specifically buckling of tanks buckled near the bottom, which is called "elephant foot" (Anderson 2001).

Conclusion: Overall Patterns and Lessons Learned
The 1999 Turkey Earthquake provided a variety of useful lessons to learn from dealing with design and construction of so called earthquake resistant buildings. It is important to learn from mistakes and evaluate reconstruction efforts with 96% of Turkey's surface area located in one of the first 4 seismic zones and the threat of a large quake in the near future in the Istanbul area (Tatlidede 2008). Buildings in Turkey are thought to be at least one magnitude more vulnerable than buildings in California. It is crucial that buildings not only be designed according to seismic code, but that followup is also done to make sure that construction meets the needs of the expected design. The process also must be started in the planning phase, it is not just the structural engineers problem. Data gained from the Turkey earthquakes can be used to help focus the reconstruction and design needs on the most likely next target. Large earthquakes happen every year, but the 1999 Turkey Earthquake is a more valuable learning tool since it hit a highly populated region.

__Building Construction Lessons__
Many of the issues that lead to structural disaster were due to negligence by one of the parties, most of these things were done as ways to cut costs. Some things such as this that went wrong were that there was no structural engineer to verify that earthquake-resistant buildings were being built as designed, buildings were built with poor or inappropriate building materials along with poor workmanship, buildings were knowingly built in regions with soils highly prone to liquefaction, and in some causes buildings were built based on previous designs rather than being engineered specifically. Some buildings were not even designed or detailed properly by engineers to handle the predicted seismic loads.
 * //Design Lessons//**

The correct design of a building needs to start in the planning phase with the architect AND structural engineer working together to find a solution. Proper site studies must be done to verify soil conditions and then the building must be designed for the proper lateral load at that site. Design should include a lateral resistance system who's path can clearly be followed down to the base of the structure. Also engineers should think about applying forms of new technology such as seismic isolation and dissipating devices (Tatlidede 2008). One promising sign is that more buildings are being designed with reinforced concrete shear walls included (Alarcon 2009). But many are still experiencing the same issues with quality control and reinforcement detail deficiencies. One other important fact is that the architect must be involved early on to prevent their decisions from leading to structural load path deficiencies (Tatlidede 2008).

The largest thing that can be learned from a code perspective is that Turkey needs to take more quality control measures to assure that buildings are designed and built according to code. The buildings built to code specifications tended to preform well. In 2000 there was a new legislative scheme passed outlining the role of government appointed supervision firms to make sure that buildings are being built as designed. Also the new TEC developed in 2007 for the first time addressed seismic assessment and retrofitting of the existing building infrastructure. Turkey put precedence to looking at areas at the highest risk of an earthquake event and buildings with the highest importance of being useable post earthquake (Alarcon 2009). One such investigation was the look into Istanbul buildings that found out about 42% of buildings have concrete that is below the design strength (Akay 2004).
 * //Code Lessons//**

There are many geotechnical lessons that can be taken from the 1999 Kocaeli-Golcukand Duzce-Bolu Turkey Earthquake, and most of which involve planing the location of buildings. Site investigation needs to be done to make sure that soils have the carrying capacity to withstand a long duration shacking such as the one experience in the 1999 Turkey Earthquake and also to make sure that structures are not built spanning over an active fault (EQE 1999). It was also determined that earth damns founded on weak silts have a much higher likelihood of failure than those on rock foundations (U.S. Geological Survey 1999). Some methods of soil improvement were put to the test in the 1999 Turkey Earthquake yielding important results. It was determined that high modulus jet grout columns at a close spacing are a useful way to eliminate soil liquefaction by reducing cyclic shear strains and pore pressure, and also reducing post-earthquake reconsolidation settlements. This was learned at the site of a shopping complex that was only partially constructed and at the time of the earthquake having some soils improved with jet grout columns and some not (Durgunoglu 2004). Also on this site it was learned that wick drain installation and surcharge fills were not good ways of reducing soil liquefaction.
 * //Geotechnical Lessons//**

__Earthquake Prediction__
Over the past 100 years the North Anatolian Fault System in Turkey has been a great real life lesson in how strike-slip faults work. As previously explained in the //Geotechnical Conditions// section, the Anatolian Block is being wedged westward against the Eurasian Plate to the north at a fairly constant rate (U.S. Geological Survey 1999). As the Anatolian Block tries to move westward stress builds up along the North Anatolian Fault until the crust can no longer stay bonded together and stress is released violently. Models can be developed to help show how the stress is thought to be building up.

Whats remarkable about Turkey's recent earthquake history is that major earthquakes have been sequentially moving westward up the fault since the Great Erzincan Earthquake of 1939 started the series in the east with the culminating rupture being the 1999 Kocaeli-Golcukand Duzce-Bolu Turkey Earthquake, which was predicted two years before it occurred (Alarcon 2009). Over the years researchers have studied the fault system more and more, and continuing with the western movement Istanbul looks to be next in line. Many think the question is when and how large will the earthquake be, not will it happen. It has been predicted that Istanbul has a 62% chance of experiencing a magnitude >7 earthquake over the next 30 years (Alarcon 2009). This is alarming with the population and current state of building and infrastructure in that region. Predictions like this are crucial to help extremely vulnerable structures prepare. But just recently, October 23, 2011, there was a magnitude 7.1 earthquake in Eastern Turkey 9 miles NNE of Van. The question now will be how this rupture in Eastern Turkey has affected the stress build up along the Western portions of the North Anatolian Fault, if at all.

===__United States Implications__=== All earthquakes can serve as learning tools, even for countries with advanced seismic codes such as the United States. The United States has one particular geological feature that makes earthquakes along Turkey's North Anatolian Fault of particular interest, and that is the San Andreas Fault in California. Figure 5 shows a side by side comparison of the two fault systems. They are similar in size, shape, age, and slip rates but the North Anatolian Fault has been much more active over the past century. Scientists can use the shape and geology to help better predict the next likely location for rupture along the San Andreas Fault. Such information has helped geologists come to the conclusion that there is a 70% probability of a magnitude >6.7 in the San Francisco region within the next 30 years, and this was predicted over 10 years ago (U.S. Geological Survey 1999). That leads to another reason why the 1999 Kocaeli-Golcukand Duzce-Bolu Turkey Earthquake is of interest to the United States, because of its proximity to a large population center. Even though the United States has modern engineering, a lot of its buildings were still built before people realized the importance of these types of design. Large earthquakes are a threat to cities such as San Francisco, Salt Lake City, Seattle, Los Angeles, and San Diego.