Seismic Performance of a High-Rise Building by Using Linear and Non-Linear Methods

7 In this paper, the seismic behavior of existing reinforced concrete tall building is investigated by the 8 linear and nonlinear dynamic analysis. The selected reinforced concrete structure was designed 9 according to “ Turkey Seismic Code-2007 ” (TEC-2007). A typical 41 story reinforced concrete building 10 is designed. Turkey Building Earthquake Code-2018 (TBEC-2018) is utilized for evaluating the 11 seismic performance of the selected building. Natural earthquake acceleration record selected and 12 adjusted for compatibility with the adopted design spectrum, is used. 13 A performance analysis according to the TBEC-2018 in a 41-story reinforced concrete shear wall- 15 framed structure in Istanbul where active fault lines are located. The selected reinforced concrete shear 16 wall unsymmetrical plan tall building is located in Istanbul, Turkey. The performance goals of the 17 reinforced concrete shear wall structure are evaluated by applying procedures of the TBEC-2018 and 18 nonlinear dynamic analysis. According to the Code, the reinforced concrete shear wall building is not 19 expected to satisfy life safety performance levels under design earthquake. 20

Seismic behavior and principles of earthquake. resistant structural design included structural 27 engineering codes of various countries take important part in the code of Turkey. After destructive 28 earthquakes, determination of seismic of existing structures gained great importance. In addition, 29 a large number of existing reinforced concrete shear wall unsymmetrical plan tall buildings in 30 first-degree seismic zone need seismic evaluation because of their unfavorable seismic behavior, 31 types of irregularities in plan and in elevation. 32 Especially serious damages and many losses happened after 1989 Loma Prieta and 1994 33 Northridge earthquakes in the United States of America, 1995 Kobe earthquake in Japan; 1992 34 Erzincan, 1999 Marmara and Duzce and 2011 Van earthquakes in Turkey. Therefore, 35 performance-based design procedures have been investigated for the irregular recently. 36 Performance-based design and evaluation methods have been developed in order to determine 37 building safety more realistically than previous codes or just reastically  process, which is explained further and is based on PEER Performance Based Design approach.

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The tall buildings are defined Class 1 of Buildings that have heights presented in TBEC-2018.

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As shown in Fig In this study, moment-curvature analyses are carried out considering section properties and a 126 constant axial load on the structural element.

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After the appropriate material properties are determined, structural element sections are 129 modeled via XTRACT program. In the section, two concrete models, confined and unconfined 130 concretes, are used. The modeling is concluded by inputting reinforcement steels into the defined 131 section geometry. Thus, moment-curvature relations are determined after analyses.  In Eq. (1), L p is the plastic hinge length, H is the height of section, respectively. 141 Plastic rotation limit values are calculated with Equation 2 for migrant prevention performance 142 target. 143

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(2) 144 In Eq. (2), corresponds to the total pre-collapse curvature obtained from the analysis made 145 by using the concrete-reinforcing steel models given by considering the axial force acting on the 146 section. is yield curvature (m -1 ), Ls is shear opening (m). The last term in the given d b 147 corresponds to the return of reinforcement stripping due to yield penetration for the post-yield 148 condition. thought to be an office and its live load contribution factor is taken as n = 0.3. 173 The asymmetrical irregular tall building was analyzed in detail by performing nonlinear dynamic 174 analyses The vertical loads consist of live and dead loads of slabs, wall loads on beams and dead loads of 186 columns and beams. When determining seismic performance of the selected structure, Seismic 187 Load Reduction Factor is taken as R a =1. In addition, building importance factor is applied as I = 1. 188 The Regarding the definition of irregular buildings whose design and construction should be 222 avoided because of their unfavorable seismic behavior, types of irregularities in plan and in 223 elevation. Irregularity calculations were done by applying the procedures defined in the TBEC-224 2018 for this building. The case where Torsional Irregularity Factor (ƞ bi ), which is defined for any 225 of the two orthogonal earthquake directions as the ratio of the maximum relative story drift at any 226 story to the average relative story drift at the same story in the same direction, is greater than 1.4.

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Since the building examined is 41 storeys, the torsional irregularity coefficient has been calculated 229 for all floors, but the results are given only for the first ten floors in the Tables 1-2. 230 The torsional irregularity coefficient (ƞ bi ) that is calculated in accordance with the elastic linear 231 behavior without considering additional eccentricity should meet the condition ƞ bi < 1.4 for each 232 floor.

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It is seen from Table 1 and Table 2 that the torsional irregularity of the building is not provided. 235 The interstorey stiffness irregularity ratios for first ten story given in Tables 3-4. 236 There are no local slab abrupt reductions in the plane. stiffness and strength of floors and seismic 237 loads are safely. transferred to vertical structural elements. Therefore, floor discontinuities 238 irregularity (A2) does not exist. Since the re-entrant corners in both of the two principal directions 239 in plan do not exist, there is A3 type irregularity in the structure.

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In Eq. (5), G is total dead load, n is the live load participation factor, Q is total live load stories of 256 building, respectively. 257 258  It is assumed that nonlinear dynamic analysis defines structure behavior ideally because of the 276 seismic loads directly applied to structure (Li, 1996). The aim of nonlinear dynamic analysis is 277 integration of equations of the motion of the system step by step by taking into consideration of 278 nonlinear behavior of bearing system. It is calculated for each time increment that displacement, 279 plastic deformation, internal forces occurred in the system and maximum values of them during 280 earthquake. 281 The Newmark's method is used for solving the dynamic equilibrium equations. Although not as 282 simple as the central difference method, it is perhaps the most popular method because of its 283 superior accuracy. 284 The selection and scaling of the acceleration records to be used within the scope of this study 285 were made within the framework of the principles given in TBEC-2018. At least 11 earthquake 286 records should be used for nonlinear time history analyses. Response spectrums for scaled 287 acceleration recordings are given in Fig. 5 and scale coefficients in Table 5. 288 289 290  It is seen from Fig.10 that plastic hinges occurred through X and Y directions as a result of 311 nonlinear dynamic analysis for the RSN-1619. It can be seen from Fig. 10 that these hinges are 312 concentrated on at the ends of the oblique columns. It can be seen from the result of the nonlinear 313 dynamic analysis through the X and Y directions (Fig. 10) that damage is occurred in the columns 314 and beams. It can be also seen from the result of the nonlinear dynamic analysis 23 columns (23%) 315 of total columns are collapsed. It is seen from Fig.10 that collapse damages are occurred especially 316 oblique columns of floors. 317 318 When the analysis results are investigated, it is concluded from nonlinear dynamic analysis that 319 according to damage conditions of elements, the building does not provide life safety (LS) rating 320 in TBEC-2018. The existing building is far from satisfying the expected performance levels. The 321 performance level of the building is determined as advanced damage region (GV).

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In addition, the results of the Duzce earthquake that took place in the area where the building is 324 located are given in Fig. 11. When the articulating elements were examined, it was seen that the 325 hinges took place at the oblique column ends in the lower floors. In this case, the building may be 326 migrated in the form of a floor mechanism in a possible earthquake. The purpose of performance-based earthquake engineering is to design and construct safe 335 structures with seismic demands. The performance-based design method in earthquake engineering 336 is used to determine the expected performance level under the effect of earthquake. For this 337 purpose, different calculation methods have been developed and it is accepted by the scientific 338 circles that the most reliable calculation methods are nonlinear calculation methods.

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In this study, an existing building in Istanbul province is considered. One of the most important 341 reasons for the selection of the existing structure in Istanbul is that the dangerous fault lines are 342 present within the boundaries of this province and this city is under danger of approaching and 343 inevitable Great Istanbul Earthquake likely greater than Mw 7. Thus, investigation of earthquake 344 performances of this or similar tall buildings is very important. In line with this information, linear 345 and nonlinear analysis of an existing structure according to TBEC-2018 was carried out. Mode 346 Superposition Method was used in linear analysis and Non-linear Time History method was used 347 nonlinear analysis method. 348

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 Both linear and nonlinear assessment approaches defined in the most recent Turkey Building 349 Earthquake Code of 2018 (TBEC-2018) can predict the real damages quite certainly.

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 It is accepted that any building that is designed properly will be able to resist seismic 351 excitation without incurring significant damage. Tall building structural designers should take 352 careful note of these areas when designing torsional irregularity and soft story buildings.

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 The determination of the irregular tall building performance levels in the earthquake analysis 354 is an important factor for the safe usability of the structures at the time of the earthquake.

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 As a result of the analyses, irregularity calculations were made according to the 356 displacements in the X and Y direction. In the analysis made according to X and Y directions of 357 the structure, torsional irregularity is seen on the normal floors. As a result of calculations in the X 358 and Y directions, interstorey stiffness irregularity in the structure and as a result of the 359 displacements as a result of the stiffness irregularity was found on second floors.

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 As a result of the non-linear time history analysis, it is seen that in the evaluation of X and Y 361 Direction line in ZC local floor class design earthquake, the level of performance of migration 362 prevention which is the target performance for the buildings is provided. According to the 363 regulations of the existing building, the life safety performance level could not be achieved. In this 364 respect, the building was evaluated according to the level of performance of migration prevention. 365 366