Turkish Earthquake Code Research Articles

INVESTIGATION OF STRONG COLUMN – WEAK BEAM RATIO IN MULTI-STOREY STRUCTURES

It is expected that the engineering constructions should carry the vertical and horizontal loads during the service within the determined safety margin. Basic principal of having strong column weak beam preference is essential for earthquake resistant structures for all construction types including concrete, steel, wood and prefabricated. The major criteria for having earthquake resistant structure is to ensure that the columns are stronger and carry the most load than the beam in the nodes. This criterion has been widely adopted in earthquake codes in Europe, USA, Japan and India. It is possible to absorb and consume the earthquake energy via beam plastic joint hinges if the columns are constructed to be more durable than the beams. For this, it is foreseen that the ratio of the ultimate strength of the upper and lower columns to the right and left beams (β) should be greater than one (β = 1.2) in the beam-column joints as stated in the Turkish Earthquake Code. This coefficient is usually greater than 1.2 in the earthquake codes adopted in the world. It was observed that many structures were damaged or collapsed due to not meeting the coefficient criteria stated above. This criterion is the most effective one among many to prevent the damage in the structure under seismic action. In this study, the effect of the change in the coefficient on the column and beam moments is investigated under the Turkish Earthquake Code. Different numerical examples are presents for the coefficient of 10. The results of the investigation highlighted that irregularity in the strong column weak beam composition may negatively affect the other irregularities in the structure.

Case study on seismic behavior of aseismically designed reinforced concrete frame structures

In this study, the seismic performances of two aseismically designed plan-irregular reinforced concrete frame (RCF) households damaged during the October 23, 2011 Van earthquake are assessed. Since no strong ground motion recordings from the main shock were available, first, strong ground motion parameters of the event are evaluated and then compatible with these parameters suits of real records are selected and scaled to match with the event’s simulated acceleration spectrum to be used in the analytical investigations. The results of previous reconnaissance studies, in which one of the present authors was involved, are then discussed. Capacities of the considered RCF’s are determined applying a 3D single-run adaptive pushover procedure that is capable of considering the effect of plan irregularities. The performance assessment procedure based on the current 2007 Turkish Earthquake Code is then applied to these investigated buildings. Additionally, nonlinear dynamic time history analyses are carried out using the previously selected time histories. The hysteretic behavior of the considered buildings is examined as the consequence of the conducted analyses and considering the different suits of selected ground motions, the seismic response of the buildings is evaluated in terms of interstorey drifts. None of the buildings are found to satisfy the expected performance level. Moreover, the numerical results are found to have good correlation with the field observation results.

Earthquake response of heavily damaged historical masonry mosques after restoration

Abstract. Restoration works have been accelerated substantially in Turkey in the last decade. Many historical buildings, mosques, minaret, bridges, towers and structures have been restored. With these restorations an important issue arises, namely how restoration work affects the structure. For this reason, we aimed to investigate the restoration effect on the earthquake response of a historical masonry mosque considering the openings on the masonry dome. For this purpose, we used the Hüsrev Pasha Mosque, which is located in the Ortakapı district in the old city of Van, Turkey. The region of Van is in an active seismic zone; therefore, earthquake analyses were performed in this study. Firstly a finite element model of the mosque was constructed considering the restoration drawings and 16 window openings on the dome. Then model was constructed with eight window openings. Structural analyses were performed under dead load and earthquake load, and the mode superposition method was used in analyses. Maximum displacements, maximum–minimum principal stresses and shear stresses are given with contours diagrams. The results are analyzed according to Turkish Earthquake Code (TEC, 2007) and compared between 8 and 16 window openings cases. The results show that reduction of the window openings affected the structural behavior of the mosque positively.

Experimental and analytical studies on different configurations of cold-formed steel structures

Popularity of Cold-Formed Steel (CFS) structures has recently increased considerably in the last years as a consequence of discovered advantages such as lightness of the material, significant energy absorption capacity providing seismic performance against lateral loading, time efficiency and cost effectiveness. CFS structures are composed of shear panels which involve cold-formed steel bare frames coated with different kind of sheathings such as gypsum wallboard (GWB), oriented strand board (OSB), plywood or some infill materials which are connected to the frame. Combination of CFS bare frames and sheathing boards provides the shear panels with lateral load resistance against seismic actions. There are several factors which have a direct influence on the behavior of CFS shear panels such as type of sheathing board, thickness of cold-formed steel, spacing of the screws binding the sheathing board to the bare frame and magnitude of the axial loads. On behalf of observing the impact of these outlined factors upon the behavior of CFS shear panels as well as to attain some experimental data to be utilized in the new Turkish Earthquake Code 2016, a considerable amount of laboratory tests was conducted in Structures Laboratory of Bogazici University on different configurations of CFS shear panels. Posterior to the acquisition of these experimental data, studies upon developing analytical models representing the actual experimental behavior of one of the shear panels have been conducted, thus providing possibilities for 3-D seismic performance assessment of a representative one-story cold-formed steel structure for the final part of this paper.

Behaviour of Strengthened RC Frames with Eccentric Steel Braced Frames

After devastating earthquakes in recent years, strengthening of reinforced concrete buildings became an important research topic. Reinforced concrete buildings can be strengthened by steel braced frames. These steel braced frames may be made of concentrically or eccentrically indicated in Turkish Earthquake Code 2007. In this study pushover analysis of the 1/3 scaled 1 reinforced concrete frame and 1/3 scaled 4 strengthened reinforced concrete frames with internal eccentric steel braced frames were conducted by SAP2000 program. According to the results of the analyses conducted, load-displacement curves of the specimens were compared and evaluated. Adding eccentric steel braces to the bare frame decreased the story drift, and significantly increased strength, stiffness and energy dissipation capacity. In this strengthening method lateral load carrying capacity, stiffness and dissipated energy of the structure can be increased.

Investigation of shear effects on the capacity and demand estimation of RC buildings

Considerable part of reinforced concrete building has suffered from destructive earthquakes in Turkey. This situation makes necessary to determine nonlinear behavior and seismic performance of existing RC buildings. Inelastic response of buildings to static and dynamic actions should be determined by considering both flexural plastic hinges and brittle shear hinges. However, shear capacities of members are generally neglected due to time saving issues and convergence problems and only flexural response of buildings are considered in performance assessment studies. On the other hand, recent earthquakes showed that the performance of older buildings is mostly controlled by shear capacities of members rather than flexure. Demand estimation is as important as capacity estimation for the reliable performance prediction in existing RC buildings. Demand estimation methods based on strength reduction factor (R), ductility (<TEX>${\mu}$</TEX>), and period (T) parameters (<TEX>$R-{\mu}-T$</TEX>) and damping dependent demand formulations are widely discussed and studied by various researchers. Adopted form of <TEX>$R-{\mu}-T$</TEX> based demand estimation method presented in Eurocode 8 and Turkish Earthquake Code-2007 and damping based Capacity Spectrum Method presented in ATC-40 document are the typical examples of these two different approaches. In this study, eight different existing RC buildings, constructed before and after Turkish Earthquake Code-1998, are selected. Capacity curves of selected buildings are obtained with and without considering the brittle shear capacities of members. Seismic drift demands occurred in buildings are determined by using both <TEX>$R-{\mu}-T$</TEX> and damping based estimation methods. Results have shown that not only capacity estimation methods but also demand estimation approaches affect the performance of buildings notably. It is concluded that including or excluding the shear capacity of members in nonlinear modeling of existing buildings significantly affects the strength and deformation capacities and hence the performance of buildings.

Statistical evaluation of drift demands of rc frames using code-compatible real ground motion record sets

Modern performance-based design methods require ways to determine the factual behavior of structures subjected to earthquakes. Drift ratio demands are important measures of structural and/or nonstructural damage of the structures in performance-based design. In this study, global drift ratio and interstory drift ratio demands, obtained by nonlinear time history analysis of three generic RC frames using code-compatible ground motion record sets, are statistically evaluated. Several ground motion record sets compatible with elastic design spectra defined for the local soil classes in Turkish Earthquake Code are used for the analyses. Variation of the drift ratio demands obtained from ground motion records in the sets and difference between the mean of drift ratio demands calculated for ground motion sets are evaluated. The results of the study indicate that i) variation of maximum drift ratio demands in the sets were high; ii) different drift ratio demands are calculated using different ground motion record sets although they are compatible with the same design spectra; iii) the effect of variability due to random causes on the total variability of drift ratio demands is much larger than the effect of variability due to differences between the mean of ground motion record sets; iv) global and interstory drift ratio demands obtained for different ground motion record sets can be accepted as simply random samples of the same population at %95 confidence level. The results are valid for all the generic frames and local soil classes considered in this study.

An Investigation of the Seismic Behaviour of an Ancient Masonry Bastion Using Non-Destructive and Numerical Methods

Determining the structural behavior of masonry structures is a challenge due to their lack of homogeneity. The seismic behavior of masonry structures is especially complex. The aim of this study was to examine the structural behavior of Zaganos Bastion using both experimental and numerical methods. The Operational Modal Analysis technique, including the Enhanced Frequency Domain Decomposition Method, and the Stochastic Subspace Identification Method were used to illustrate experimentally the dynamic characteristic of the bastion. A finite element model was developed using ANSYS software in order that the dynamic characteristics of the bastion, including natural frequencies and mode shapes, could be calculated numerically. Seismic analysis was carried out using the 1999 Kocaeli earthquake ground motion record to determine the linear and nonlinear seismic behavior of the bastion. The Turkish Earthquake Code and its general technical specifications were used to evaluate the seismic results. The results show that the maximum and minimum principal stresses exerted on the masonry components exceeded the code requirements at some points, but in general the requirements for the stresses were satisfied.

English

Cyprus lies in a seismic zone and the whole island (northern and southern part of the island) can be considered as an earthquake vulnerable area. In the last years, earthquake design of reinforced concrete structures becomes an important phenomenon due to unfortunate earthquakes. This amplifies the need to make such buildings earthquake resistant at a reasonably low cost. Most of the buildings are mid-rise reinforced concrete structures in two parts of the island. In this study, Turkish earthquake code 2007 (TEC2007) and Eurocode 8 (EC 8) design rules are examined and both regulations are compared for Northern Cyprus. Each design code use different seismic zoning maps with different peak ground acceleration values. These two regulations are compared with each other in terms of cost according to results of reinforced concrete structure in the range of three to seven storey ordinary apartment buildings, constructed in Nicosia. Key words: TEC2007, EC8, Cyprus.

Seismic performance of RC buildings subjected to past earthquakes in Turkey

This study aims to evaluate seismic performance of existing low and mid-rise reinforced concrete buildings by comparing their displacement capacities and displacement demands under selected ground motions experienced in Turkey as well as demand spectrum provided in 2007 Turkish Earthquake Code for design earthquake with 10% probability of exceedance in 50 years for soil class Z3. It should be noted that typical residential buildings are designed according to demand spectrum of 10% probability of exceedance in 50 years. Three RC building sets as 2-, 4- and 7-story, are selected to represent reference low-and mid-rise buildings located in the high seismicity region of Turkey. The selected buildings are typical beam-column RC frame buildings with no shear walls. The outcomes of detailed field and archive investigation including approximately 500 real residential RC buildings established building models to reflect existing building stock. Total of 72 3-D building models are constructed from the reference buildings to include the effects of some properties such as structural irregularities, concrete strength, seismic codes, structural deficiencies, transverse reinforcement detailing, and number of story on seismic performance of low and mid-rise RC buildings. Capacity curves of building sets are obtained by nonlinear static analyses conducted in two principal directions, resulting in 144 models. The inelastic dynamic characteristics are represented by equivalent Single-Degree-of- Freedom (ESDOF) systems using obtained capacity curves of buildings. Nonlinear time history analysis is used to estimate displacement demands of representative building models idealized with (ESDOF) systems subjected to the selected ground motion records from past earthquakes in Turkey. The results show that the significant number of pre-modern code 4- and 7-story buildings exceeds LS performance level while the modern code 4- and 7-story buildings have better performances. The findings obviously indicate the existence of destructive earthquakes especially for 4- and 7-story buildings. Significant improvements in the performance of the buildings per modern code are also obvious in the study. Almost one third of pre-modern code buildings is exceeding LS level during records in the past earthquakes. This observation also supports the building damages experienced in the past earthquake events in Turkey.

Simulation of the earthquake-induced collapse of a school building in Turkey in 2011 Van Earthquake

Collapses of school or dormitory buildings experienced in recent earthquakes raise the issue of safety as a major challenge for decision makers. A school building is ‘just another structure’ technically speaking, however, the consequences of a collapse in an earthquake could lead to social reactions in the complex aftermath of a seismic tremor more than any other type of structure may possibly cause. In this paper a school building that collapsed during 2011 Tabanli, Van Earthquake in eastern Turkey, is analysed in order to identify the possible reasons that led to collapse. Apart from the inherent deficiencies of RC buildings built in Turkey in the 80's and 90's, its structural design exhibits a strikingly high asymmetry. In the analyses conducted, much attention has been given to the direction of the earthquake load and its coincidence with the bi-axial structural response parameters. The failure of the structure to comply with the 1975 Code, in vigor at the time of construction, has also been evaluated with respect to the structure’s collapse. Among the parameters that controlled the collapse, the high plan asymmetry and the coincidence of the vulnerable directions with the dominant shaking direction were critical, as well as the underestimation of the seismic hazard and the lateral design force level, specified by the then Turkish Earthquake Code.

Experimental and numerical study on moment-rotation relations of welded end-plate tubular connections

Ductile behaviour of steel structures depends on mechanical properties of steel materials and steel structures are designed so that plastic deformations occur on beams particularly in beam-to-column connections under cyclic loads. Details on moment-resisting beam-to-column connections are given only for I-profiles in the Turkish Earthquake Code (TEC, 2007) and no details about beam-to-column connections consisting of box or circular hollow sections is available in the relevant code. That is why there is an uncertainty in the definition of the ductility level of the structural system consisting of box and circular hollow sections. The purpose of this study is to prevent local buckling effects to occur under bending in welded connections of circular hollow sections. In this context, the contribution of cover stiffness plates of different sizes to the behaviour and the effect of plate sizes on the capacity were investigated numerically and experimentally. Results obtained from experimental analysis are given comparatively supported by ANSYS program.

A study on seismic behaviour of masonry mosques after restoration

Historical masonry structures have an important value for cultures and it is essential for every society to strengthen them and confidently transfer to the future. For this reason, determination of the seismic earthquake response, which is the most affecting factor to cause the damage at these structures, gain more importance. In this paper, the seismic earthquake behaviour of Kaya &#x00C7;elebi Mosque, which is located in Turkey and the restoration process has still continued after 2011 Van earthquake, is determined. Firstly the dynamic modal analysis and subsequently the seismic spectral analysis are performed using the finite element model of the mosque constructed with restoration drawings in SAP2000 program. Maximum displacements, tensile, compressive and shear stresses are obtained and presented with contours diagrams. Turkish Earthquake Code and its general technical specifications are considered to evaluate the structural responses. After the analyses, it is seen that the displacements and compressive/shear stresses within the code limits. However, tension stresses exceeded the maximum values at some local regions. For this mosque, this is in tolerance limits considering the whole structure. But, it can be said that the tension stresses is very important for this type of the structures, especially between the stone and mortar. So, some additional strengthening solutions considering the originality of historical structures may be applicable on maximum tensile regions.

Flexural strengthening of RC Beams with low-strength concrete using GFRP and CFRP

The Turkish Earthquake Code was revised in 1998 and 2007. Before these Codes, especially 1998, reinforced concrete (RC) beams with low flexural and shear strength were widely used in the building. In this study, the RC specimens have been produced by taking into consideration the RC beams with insufficient shear and tensile reinforcement having been manufactured with the use of concrete with low strength. The performance of the RC specimens strengthened with different wrapping methods by using of Carbon Fibre Reinforced Polymer (CFRP) and Glass Fibre Reinforced Polymer (GFRP) composites have been examined in terms of flexural strength, ductility and energy absorption capacity. In the strengthening of the RC elements, the use of GFRP composites instead of CFRP composites has also been examined. For this purpose, the experimental results of the RC specimens strengthened by wrapping with CFRP and GFRP are presented and discussed. It has been concluded that although the flexural and shear strengths of the RC beams strengthened with GFRP composites are lower than those of beams reinforced with CFRP, their ductility and energy absorption capacities are very high. Moreover, the RC beams strengthened with CFRP fracture are more brittle when compared to GFRP.

A STUDY ON ECONOMIC LOSSES CAUSED BY EARTHQUAKE

Buildings have been repaired or strengthened for many different reasons throughout of their service life. It can be decided to demolition of buildings when strengthening or repairing is unsuitable. There can be many reasons for repairing, strengthening or demolition buildings. Earthquake is one of these reasons. In this study, firstly performance calculations were made for a RC building according to Turkish Earthquake Code 2007 (TEC’2007) which has been damaged after an earthquake. The results of performance based assessment show that performance level of building is not desired level. The building is not safe and not economical to strengthen so it needs to be demolished. The institution has decided to demolish the building after detailed analysis of building. In this study demolition cost and re-construction cost have been separately calculated. The results have been compared and suggestions have been made. The construction cost of the building has been calculated according to the unit production method using the unit prices of 2014.

Failure analysis of newly constructed RC buildings designed according to 2007 Turkish Seismic Code during the October 23, 2011 Van earthquake

Abstract In the Van Earthquake of magnitude Mw = 7.2 on October 23, 2011, 48,666 buildings were severely damaged or collapsed, 604 people lost their lives and 1301 people were injured. During this earthquake, not only the buildings designed in accordance with the old earthquake codes but also the ones designed in accordance with the current Turkish Earthquake Code (TEC) were severely damaged. The purpose of this study is to reveal the reasons why the RC buildings designed in accordance with the current TEC as a result of static and dynamic calculations were severely damaged in the recent earthquakes. In this study, first, the buildings that were designed in accordance with the last two earthquake codes and damaged during the Van Earthquake on 23 October 2011 have been examined. Then, another severely damaged building that was designed in accordance with the TEC 2007 has been chosen as a possible model for similar situations. In order to explore the reasons behind the damage, detailed examination has been made both in the damaged structure and in its design calculations. Both situations in the project and implementation of the design have been analyzed by using IdeCAD and Sta4CAD modeling, as well as Sap2000 through which weak structural members have been determined. The findings have been evaluated in terms of design and implementation flaws, in compliance with the TEC 2007, modeling and acceptance error. When analyzed by modeling of its project, the building has not revealed any insufficient columns; however, in its implementation analysis, the damaged members have appeared to be insufficient. It has been determined that the damage was due to improper implementation of the project, incompatible production according to the TEC 2007 and lack of inspection. To mitigate possible fatalities and damages in the future earthquakes, implementations should be fully represented in the model of the projects, structural members in the projects should be built identically to their design, attention should be paid to the anticipated limitations in TEC 2007 during implementation, and stages of project and implementation should be inspected sufficiently.

An evaluation of the seismic response of symmetric steel space buildings

This paper evaluates the seismic response of three dimensional steel space buildings using the spread plastic hinge approach. A numerical study was carried out in which a sample steel space building was selected for pushover analysis and incremental nonlinear dynamic time history analysis. For the nonlinear analysis, three earthquake acceleration records were selected to ensure compatibility with the design spectrum defined in the Turkish Earthquake Code. The interstorey drift, capacity curve, maximum responses and dynamic pushover curves of the building were obtained. The analysis results were compared and good correlation was obtained between the idealized dynamic analyses envelopes with and static pushover curves for the selected building. As a result to more accurately account response of steel buildings, dynamic pushover envelopes can be obtained and compared with static pushover curve of the building.

Investigation of Limit States Specified for Reinforced Concrete Column Members in TEC–2007

In this study, the deformation based limit states stipulated for reinforced concrete members in the Turkish Earthquake Code (TEC) were experimentally investigated. Thus four RC cantilever columns which have low concrete compressive strengths and have not adequate confinement, were subjected to constant axial load and cyclic lateral load history. In the study, firstly, the strain values representing the damage limits were converted to top of the column lateral displacements by using fundamentals of structural mechanics. Subsequently the column damages corresponding to the displacement demands were observed, hence limit states were evaluated. After conducting all column tests, it was noted that no column damage was observed for the immediate occupancy (IO) performance level defined in the code. For the life safety (LS) and collapse prevention (CP) performance levels, though somewhat residual deformations occurred on the critical regions, the column members can pretty much sustain their lateral load capacities. It was also observed for all columns that significant damages and strength losses occurred beyond the collapse prevention level. The results of experimental study indicate that the evaluation procedure in the TEC is still in good relationship with the limit states even if the columns have not adequate compressive strength and confinement.

Nonlinear Earthquake Performance Evaluation of a Structure Collapsed during the Van, Turkey, Earthquake on October 23, 2011

AbstractThe paper investigates the structural performance of a seven-story reinforced concrete (RC) building that collapsed during the Van (Turkey) earthquake on October 23, 2011, using nonlinear static and dynamic methods. The selected RC building has two blocks and was designed according to the Turkish Earthquake Code (TEC) in 1975. The site investigation included sections and steel detailing and soil and concrete properties taken after the earthquake. The pushover and nonlinear time history analyses of the building were completed using the existing plan and test and observation data. It is concluded that the building collapses both analysis types.

Cyclic behavior of extended end-plate connections with European steel shapes

The aim of this experimental research is to investigate the conformity of the four-bolt unstiffened moment end-plate connections consisting of European steel sections which do not meet the limitations specified for beam flange width and overall beam depth in ANSI/AISC 358-10 to the requirements of seismic application. However, the connections are satisfactory with the limitations required by Turkish Earthquake Code. For this purpose, four test specimens were designed and cyclic load was applied to three specimens while one was tested under monotonic loading to provide data for the calibration of the analytical models. The moment-rotation hysteresis loops and the failure modes for all test specimens are presented. A full three-dimensional finite element model is also developed for each test specimen for use to predict their behavior and to provide a tool for generating subsequent extensive parametric studies. The test results show that all specimens performed well in terms of rotation capacity and strength. Finite element models are found to be capable of approximating the cyclic behavior of the extended end-plate connection specimens.