Making Calculations with Mode Combining Method
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Modal Response Spectrum Analysis
Modal Response Spectrum Analysis is chosen for the building as a result of the necessity to be analyzed with the modal analysis method in accordance with Table 4.4 of TBDY 2018. The building can not be analysed with Equivalent Lateral Force Procedure.
Since the building is a has basement structurestorys, it is difficult to provide sufficient mode numbers, the mass participation rate of 95%, to be taken into account consideration in the Mod Combination Method Modal Response Spectrum Analysis for the entire upper section above the rigid basement walls and the lower section containing the basement floors. For this reason, in TBDY 2018 4.8.5.1, two loading status calculations are made in the calculation of basement buildings using modal calculation methodsstage analysis is done with modal analysis.
In this method, the upper part of the building and the lower part with basement are modeled together as a common carrier structural system and two loading cases are calculatedstage analysis is done. In both loading load cases, a mass participation rate ratio of 95% should be achieved.
There are two stages in the analysis of the upper section and the basement floors, as the building consists of a carrier system with no beamsstructural system is flat slabs with special shearwalls. The first stage is the hinged modeling of the frame columns from the lower and upper ends, and the second stage is the monolithic modeling of the structural elements.
In addition, due to the dynamic method of solving the Extra- Eccentricity Effect in the program, 4 modal analyzes are made performed for each stage, since the accidental torsion is resolved with the dynamic method in the program.
In accordance with TBDY 2018 4.5.10.4 clausearticle, it is applied in a full rigid solution to determine the extra-eccentricity effect in floors accidental torsion in slabs with semi-rigid diaphragm adopted as a shell.
Due to all the earthquake seismic code requirements listed above, a total of 20 modal analyzes were are made for this building and the internal forces to be used for the design were are determined.
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Upper Section Analysis (First
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Stage)
In the first loading load model, a common carrier structural system model is established, that is, the entire structure is modeled. The masses of the basements are taken as '0' and their stiffness is used in the mathematical model, while both the mass and stiffness of the basement floors are included in the mathematical model. As a result of this analysis, internal forces are obtained in both the upper section and the basement floor elements.
First of all, the item summaries of the analyzes made with the symbols used by the program are explained in the table below.
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The following table summarizes the dynamic analysis results for the upper section obtained from the monolithic model of frame columns.
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Scaling of the
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Internal Forces and Displacements Made with
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Modal Response Spectrum Analysis According to Equivalent
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Lateral Force Procedure
According to TBDY 4.8.4, the total earthquake seismic load obtained by modal combination method in any direction cannot be less than the total equivalent earthquake load lateral force calculated by the equivalent earthquake load methodlateral force procedure. If it is less, the equivalent base shear force is increased by the magnification factor.
For this calculation, first of all, the maximum value of the dominant vibration period Tp obtained from the mathematical model can not be more than 1.4 times the TpA determined by TBDY 2018 Equation 4.27.
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In buildings where all earthquake effects seismic loads are covered by reinforced concrete walls, Ct is calculated with the following equation. Curtain Shearwall net areas are used in this accountcalculation.
The calculation below has been made manually for the X direction and compared with the program outputs for the sake of example.
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The base shear force of the structure is determined after the period to be used in determining the equivalent earthquake load lateral force is calculateddetermined. How the equivalent earthquake load lateral force is determined is described in TBDY 2018 4.7.2. The base shear force obtained using the equations here is compared with the modal total earthquake seismic load obtained by the program and the coefficient of increase is calculated according to the following equation.
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The E coefficient was used as 0.80 due to the absence of irregularities in the building.
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Second
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Stage (Sub Section - Analysis of Basement Floors)
In the second loading load case of the calculation, only the masses of the sub-section are taken into account consideration in the common single carrier structural system model. The stiffness of both the upper and lower section is included in the mathematical model. As a result of this analysis, the minimum mass participation rate ratio of 95% must be achieved.
At this stage, analysis consisting of two stages is carried out in which the columns are hinged and monolithic models due to the carrier system with no beamsflat slab systems.
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Comparison with equivalent earthquake load method lateral force procedure in basement floors is not made in accordance with the regulation.code.
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