Adjustment and Application of Ground Motion Input in Temporal Analysis of Structure Aseismic

Headnote

Abstract: The input of ground motion in earthquake transient dynamic analysis has been a hot- point subject in the earthquake engineering research. Its primary problem is the input of seismic motion. In this paper, through using the good time-fre-quency localization nature of the wavelet function to analyze the real ground motion, a feasible method based on wavelet analysis is proposed. The actual seismic of ELCentro and TH2TG055 are input and the modulated and transformed seismic of ELCentro and TH2TG055 are adjusted by the method to the structural model. In the process of seismic response analysis, this paper analyzed the results of storey shear force,inter layer displacement, and storey drift angle and so on, which was indicated that the transformed seismic waves could obtain the relative better result, and meet the needs of earthquake resistant engineering. It has certain value in engineering application.

Keywords: Seismic acceleration; high-rise RC corewall structure; ground motion input; security analysis

(ProQuest: ... denotes formulae omitted.)

1. Introduction

The earthquake means crustal vibration caused by the rapid release of energy in the process; earthquake related engineering structure seismic research has been the focus of civil engineering research. Among them, choosing appropriate ground motion input is the first consideration in the study of dynamic response and seismic design of structures, and is also one of the main content of response spectrum method and seismic time history analysis method(Jie, 2013; Changhao, 2012). At present, based on the response spectrum theory and the random theory and other methods, it is more concerned with the non-stationary phase, the phase change, the excellent frequency and the maximum amplitude of the ground motion intensity(Ming, 2007; Lewei, 2009; Abreu, 2015). Due to the randomness and uncertainty of natural ground motion, there is little research on the time frequency characteristics of ground motion, which is the reason why the artificial seismic wave is not consistent with the natural seismic wave. In this paper, wavelet analysis is used to consider the non-stationary, phase, amplitude and time-frequency characteristics of ground motion to adjust the actual ground motion records for seismic time history analysis(Mukherjee, 2002; Qianli, 2008). Results show that wavelet analysis method will be adjusted after the earthquake wave used in high-rise structure dynamic history analysis, comparison of high-rise structure adjustment before and after shock wave seismic response results, to meet the requirements of the "code for seismic design of buildings", the structure of seismic dynamic response and seismic design provides new methods and ideas.

Wavelet analysis method can combine the time domain and frequency domain analysis, to describe seismic wave signal time frequency localization properties. MATLAB has a powerful algorithm development, data visualization and analysis and other functions. In the selection of a double orthogonality, compact support, continuous (discrete wavelet transform characteristics of wavelet function-Daubechies (DBN) application to seismic waves of orthogonal decomposition, divides the frequency domain for different adjacent band, in different frequency bands to adjust and standard design response spectra were fitted (Suarez, 2005; Zuozhou, 2015).

This paper is based on the wavelet analysis technique to adjust the actual ground motion:

1. Select the true vibration record: Reasonable ground motion input is a necessary condition to ensure the reasonable results of structural seismic time history analysis. Selected ground motion records the basic principle is really is the ground motion response spectrum to and site of the proposed project standard response spectrum is consistent; the second is the actual ground motion of the three elements close to the norms of the vibration parameters.

2. According to the provisions of the peak acceleration of the "anti-regulation", the ratio method is adopted to adjust the amplitude of the acceleration of the actual ground motion:

... (1)

In this formula, |A|^sub max^ and a(t) a(t) are the absolute values and the acceleration time history of the maximum time history of natural seismic waves; A'^sub max^ and a'(t) are the specification of the different seismic intensity of the maximum design earthquake acceleration and amplitude modulation after the acceleration of ground motion.

3. Using Nigam method to calculate ground motion response spectrum, Nigam method is that in all of the computation process without introducing any approximate calculation method, will not produce any truncation and roundoff error and has a high precision, so in the current commonly used this exact solution of Nigam method for general processing seismic engineering earthquake record.

4. Comparison of ground motion response spectrum and design response spectrum, In the [0.1, T^sub g^]platform and the structure of the basic cycle T^sub 1^ near [T^sub 1^ - ΔT^sub 1^, T^sub 1^ + AT^sub 2^] platform segment, The mean value of the acceleration response spectrum of ground motion control and the design response spectrum of the proposed engineering site are within 10%, and the mean value of the response spectrum as ΔT^sub 1^ ≥ AT^sub 2^ = 0.5s is suitable.

5. To solve the k^sub 1^, k^sub 2^

... (2)

T'^sub g^ Mean (area) of ground motion response spectrum in [0.1, Tg]

T^sub g^ Design response spectra in the vicinity of the basic structure T^sub 1^ of the structure[T^sub 1^ - ΔT^sub 1^, T^sub 1^ + AT^sub 2^];

T^sub g^ Ground motion response spectrum in the vicinity of the basic structure of the structure [T^sub 1^ - ΔT^sub 1^, T^sub 1^ + ΔT^sub 2^]segment of the mean (area);

6. Wavelet function is used to decompose the amplitude modulated seismic wave in frequency domain, Then each frequency domain is divided into adjacent frequency bands, the corresponding frequency bands and k, k2 phase is multiplied by the mean of the two platforms to achieve the purpose of fitting the standard response spectrum. And then re combine the component to form a adjusted seismic wave, analysis of the peak acceleration to meet the specification requirements; if not meet the requirements, the need to re adjust to meet the requirements of seismic waves.

2. Ground motion wavelet analysis

2.1. Actual vibration selection

Follow the steps mentioned above, this paper selects El Centro wave and TH2TG055 wave. According to the proposed project site seismic fortification intensity is 6 degrees, site classification is II, earthquake are grouped in the third group, the earthquake acceleration time history the biggest value according to table 1 selected. The ratio method is used to adjust the acceleration amplitude of the actual ground motion, and the adjustment of the wavelet transform under the rare earthquake is carried out.

2.2. Wavelet transform and comparison of ground motion

Figure 1 (a) (b) is the amplitude modulated Elcentro wave under earthquake and compared with the design response spectrum. According to figure 1 (b), we can know that the two are in the[0.1,Tg]([0.1,0.45]) platform segment and [T^sub 1^ - ΔT^sub 1^, T^sub 1^ + ΔT^sub 2^] ([0.5,1.5]) segment gap is larger, so the use of wavelet transform to adjust the Elcentro wave fitting design response spectrum. By using Daubechies (db3) to decompose the Elcentro wave, the wave is decomposed into 6 frequency bands. Reconstruction of each layer by using the reconstruction command wrcoef, as shown in Figure 1 (C), Figure 1 (d) is the use of the various layers of the Fu Liye transform, the spectral density curve of each layer. Then use (1.2) to obtain the response spectrum [0.1, T^sub g^] and [T^sub 1^ - ΔT^sub 1^, T^sub 1^ + AT^sub 2^] platform section of the area of the adjustment coefficient, the adjustment coefficient is multiplied by the frequency band of small amplitude value. Figure 2 (a) is re combination of each component is formed after adjustment for seismic wave and the adjustment of seismic wave can be seen using wavelet analysis method to adjust seismic waves can meet the requirements of specification. According to the method of Table 1 and above, the amplitude modulation and wavelet transform of ELCentro wave under rare earthquake are shown in Figure 2 (b), and the fitting error is less than 10%.

In order to verify the rationality of the method and to compare the input high level structure, Figure 3 is the TH2TG055 wave after am and wavelet transform, the results obtained to meet the requirements, can be used as a structural time history analysis of the input ground motion records.

3. Ground motion input high level structure analysis

3.1. Structure system introduction

Ji'nan city commercial complex project of a plot by the senior The Residence Hotel, business building and multi-storey commercial podium, the total construction area is about 28 million square meters. The overall height of the business integrated tower is 150.45m, the ground floor 34, with 3 floors of the basement; comprehensive building standards for 4.1m, the bottom four layers of high are 4.5m;The plane is rectangular, and the length and width of the typical floor are 54.8m and 36.8m respectively. Tower frame - core tube as the anti-lateral force system, the core wall thickness of the outer wall of 700mm~400mm, the internal wall thickness of 300mm~250mm.The structure of the third layer and the bottom ofthe frame column section size is I250mmxi250mm, the fourth layer to the fifteen layer of the frame column section size becomes 1200mmx1200mm, ii50mmxii50mm. The height of each frame beam is 850mm~700mm. Beam and slab concrete grade is C30, column, wall concrete grade is ~C60 C40.

3.2. Establishment and calculation of the model

Projects seismic fortification intensity is 6 degrees, the acceleration 0.05g, earthquake are grouped into the three groups, site class II, cycle characteristics =0.45s and structural damping ratio of 0.05, the basic wind load standard value (according to the wind pressure once in 50 years). Overall structure were calculated using SATWE, rare earthquake is calculated by using the ABAQUS software and take the above adjustment before and after shock wave, considering the effect of elasto-plastic dynamic time history analysis. The structure calculation model is shown in Figure 4.

This paper, taking 15 modes is analyzed, considering the effect of torsion coupling and accidental eccentricity and clear structural mode of vibration, good self-vibration characteristics. The i translational cycle Ti=4.7is (Y direction translation), the cycle than Tt/Ti=0.76; structure in X and y to the maximum displacement and the ratio of average displacement maximum value of i.i3; maximum story drift angle is i/ii05 in the 23rd floor, specification of frame core tube is less than the interlayer displacement angle maximum 1 / 800; structure the stiffness ratio of 1.13, on the twelfth floor of the structure, minimum floor shear bearing capacity of 0.86, vertical structure rules, there is no weak layer. The overall stability of the structure is more than 1.4 but less than 2.7, which indicates that the structural system is stable, but it needs to consider the adverse effects of the two order of gravity. The other indexes all meet the requirements of the standard, and the plane layout of the structure is reasonable and effective.

3.3. The ground motion input to the high-level structure analysis

The dynamic time history analysis to select the second section wavelet transform adjustment before and after the actual vibration - El Centro wave (E wave) and TH2TG055 wave (referred to as H wave), the effective duration of not less than 5 times of fundamental period of the structure; seismic wave by two-way input and primary and secondary direction and speed of the maximum value of the ratio is 1: the conforms to the proposed site often encounter and seldom occurred earthquake requirements.

Figure 5 is in the case of earthquake, before and after the transformation, the E wave, H wave input high level structure elastic time history analysis of the main direction of calculation results. From Figure 5 (a) that each of the seismic base shear values were greater than the mode decomposition response spectrum method to calculate the results of 65%, and the calculation results are not more than 135%; structure base shear average value is greater than that of vibration mode decomposition reaction spectrum 80% of the bottom shear method, selected after adjustment of seismic wave input structure elastic history analysis meet the specification requirements. The interlayer displacement map seen through the transformation of the elastic seismic history analysis results and mean response spectrum calculation results are slightly different, two value 3.90% difference, and transform of seismic wave results mean and response spectrum calculation results the difference between the value of 5.51%; before the adjustment, after seismic wave top layer displacement dispersion of a wave and response spectrum analysis get the top floor displacement respectively, a difference of 15.4% and 12.6%. By comparing Figure 5 (c) and elastic time history analysis and response spectrum method calculated interlayer displacement angle did not exceed the allowable value of drift angle of 1 / 800, can meet the requirements of specification and transform of seismic wave interlayer displacement angle value, the overall to response spectrum curve near.

From Figure 5 shows that using wavelet transform of seismic wave analysis as elastic structure history analysis input, numerical calculation results and the response spectrum method is closer, to calculate the index can meet the requirements of specification, the method for seismic design of engineering provides a new way.

With the continuous improvement of the structural dynamic model and the increase of the efficiency of numerical calculation, the nonlinear dynamic analysis of structures is becoming more and more mature, and it is more and more widely used in the seismic design and performance evaluation of complex structures. Dynamic elastic-plastic time history analysis is an effective method to predict the seismic response of structures and to evaluate the seismic performance of structures. This paper uses ABAQUS for high-rise structure rare met under the action of seismic elastoplastic time history analysis, the figure 2 and figure 3 am and transform the before and after four wave as input wave, before and after the study of wavelet transform to analyze the actual ground motion on the dynamic response of the difference. The model wall concrete constitutive using ABAQUS comes with the damage model of concrete, the concrete beam constitutive using fiber beam model, steel using bilinear kinematic hardening model; panel unit using S4R multi-layer shell element [-], the beam element with B31 unit. The time history analysis is carried out using the display algorithm, and the calculation results are shown in Figure 6.

Rare earthquake is about frequent earthquake and earthquake design level is 7 times and 2.33 times, but from Figure 6 (a) results can be seen rare earthquake and frequent earthquake at the bottom of the structure seismic shear than average is 4 to 5 times, indicating that the component by nonlinear stiffness degradation to reduce earthquake in. Under rare earthquake, the structure can still be kept upright, and the maximum displacement angle of the main direction is 1/294, which is less than the limit value of the norm 1/100. Table 2 shows, as the structural elastoplastic time history analysis input adjustment before, after El Centro wave and TH2TG055 wave of base shear and top displacement, the maximum displacement angle value difference of not more than 20%, in the statistical significance conform to the rules and regulations, identified the selection of earthquake wave effectively. Figure 3.4 (d) is extracted from the structure of the tenth layer of the structure of the internal force time history curve, respectively, when the 2.7s and 5S, the maximum value of internal forces; also, from Figure 6 (E) shows that the maximum value of the displacement angle in 2.3S and 5.8s. From Figure 6 (a) - (E) can be seen, the use of wavelet transforms before and after the 2 kinds of discrete wave of smaller, the curve is smooth and consistent.

4. Conclusions

This article in detail introduced based on the analysis of wavelet transform method to adjust the actual ground motion process, select different periods of different frequency bands reconstruction, re combination of components that match the target response spectrum form adjustment after the earthquake wave, achieve adjusted the vibration frequency nonstationarity. In engineering practice, selection based on the wavelet analysis method in the adjustment of seismic wave as a structural time history analysis input, through comparison of interlinear shear, the interlayer displacement, interstory displacement angle and so on several aspects of the calculation results can get more accurate numerical value, meet the seismic design needs, in the engineering application has a certain reference value to the application and further structural seismic design improvement and perfection to provide a new way.

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