AMBIENT VIBRATION TEST ON DETECTION OF DYNAMIC PROPERTIES OF A REINFORCED CONCRETE BULDING

Size: px

Start display at page:

Download "AMBIENT VIBRATION TEST ON DETECTION OF DYNAMIC PROPERTIES OF A REINFORCED CONCRETE BULDING"

Marcia Harrington
5 years ago
Views:

1 AMBIENT VIBRATION TEST ON DETECTION OF DYNAMIC PROPERTIES OF A REINFORCED CONCRETE BULDING Azer A. Kasimzade, Ondokuz Mayis University Turkey Sertac Tuhta, Ondokuz Mayis University Turkey azer@omu.edu.tr Abstract This paper presents the results of monitoring 11 story reinforced concrete building. Dynamic characteristics were determined by analyzing ambient vibrations of the structure. The natural frequencies and their associated mode shapes were determined using frequency-domain and time - domain techniques. Finite element model of the building was evaluated. The experimental details and data-processing techniques are described. All of devises with appropriate software and necessary instruments for structural monitoring are placed in mobile vehicle designed by our department and use as mobile structural monitoring system ( 1 Introduction As known forced (shaker, impact, pull back or quick release tests) and ambient vibration techniques are available for vibration testing of large structures. Force vibration methods more complex and are generally more expensive than ambient vibration tests. Ambient vibration testing (also called Operational Model Analysis) is the most economical non-destructive testing method to acquire vibration data from large civil engineering structures for Output-Only Model Identification. General Characteristics of structural response (appropriate frequency, displacement, velocity, acceleration rungs), suggested measuring quantity (such as velocity or acceleration) depends on the type of vibrations (Traffic, Acoustic, Machinery inside, Earthquakes, Wind ) are given in [ 1 ]. This structures Response characteristics gives a general idea of the preferred quantity and its rungs to be measured. A few studies the analysis of ambient vibration measurements of buildings from 1982 until 1996 are discussed in [2]. Last ten years Output Only Model Identification studies of buildings are given in appropriate references structural vibration solutions. For the modal updating of the structure it is necessary to estimate sensitivity of reaction of examined system to change of parameters of a building [3]. The objective of this investigation to monitor and to quantify the dynamic characteristics (vibration mode shapes, corresponding periods, damping) of a 11 storey reinforced concrete framed structure system in city Samsun (Turkey). A measurement was conducted in December Description of Building The building is 27.5 m. in height from the ground level. The parking levels are located beneath ground level with a depth of 2.75 m. The first and second storey heights are 3 m and 2.5 m appropriately. Storey slap between this two stories are not. The upper 8 stories are 2.75 m. in height. The residential floors on levels 3 through 10 are x 29.4 = m 2 in area.

2 Construction of the building began in the fall of 1999 and was completed during the winter of Storey slab type mainly (~87%) are ribbed floor (~3% plate floor). A typical floor plan of the building is shown in Fig.1. Figure 1. Typical floor plan of Building. The floor slabs are 0.3 m thick (6.25kN/m 2 ) and the plate floor are 0.1m thick (2.5kN/m 2 ). Walls are 0.15m thick (2kN/m 2 ).In testing study of the building structure elements have not plaster (parget). Eccentricity for each floor in x and y direction are shown in Fig. 2a,b appropriately. a) b) Figure 2. Eccentricity for each floor in x and y direction. Coordinates of centre of rigidity and centre of mass for each floor are shown in Table 1.

3 Floor No Table 1. Coordinates of centre of rigidity and centre of mass for each floor. Weight of floor (kn) Mass of floor (knsn 2 /m) centre of rigidity x (m) y (m) centre of mass Specified concrete strengths in unit MPa for all of the building are summarized as: Column level (1-2) ;(3-5)-8.036;(6-8)-4.936;(9-10)-2.457; Slab and beams 2.7 and 9.155; Footings Building has A1 (Torsional Irregularity) and B2 (Interstorey Stiffness Irregularity -Soft Storey) types of irregularities. A1- The case where Torsional Irregularity Factor η, which is defined for any of the two orthogonal earthquake directions as the ratio of the maximum storey drift at any storey to the average storey drift at the same storey in the same direction, is greater than 1.2 [ η bi = ( i ) max / ( i ) ort > 1.2]. B2- The case where in each of the two orthogonal earthquake directions, Stiffness Irregularity Factor η ki x (m) bi y (m), which is defined as the ratio of the average storey drift at any storey to the average storey drift at the storey immediately above, is greater than 1.5. [ η ki = ( i ) ort / ( i+ 1 ) ort > 1.5]. Concrete C20 (f ck =20Mpa=20000kPa ) and steel S40(f yk =420Mpa=420000kPa ) are respectively used. Foundation type of the building is both direction continuous footing and 0.4 m thickness slabs (plates). The building was designed accordance with Turkish Reinforced Concrete Design Standard TS-500. Typical design live and dead loads for the residential areas were zero(because in study of testing building was out of the exploitation) and 6.25 kpa respectively for testing study. 3 Finite Element Model of the Building A finite element model was generated in SAP-2000 ver 8 and dynamic analysis program (DAP, ver.2, [4]). Beams and columns were modelled as 3D beam-column elements, and shear walls (in Fig.1 shown by the black colour) were modelled as 4-mode membrane elements. Building modelled as a absolutely rigidity floor (rigid diaphragm) insert first floor slap (here floor slap is absent). At the base of the structure in the model, the ends of every element were fixed against translation and rotation for the 6-DOF. In modelling of the beams, columns the young s module E =28000MPa=2.8x10 7 KPa, the material mass density ρ =25KN/m 3, the Poisson ratio µ =0.2.

4 Dynamic analysis result at the finite element building model are shown in Table 2. Table 2. Dynamic analysis result at the FE building model. Mode No Period (sn) Mode Type T + B B T - T T B - B - T + B = Mean Torsion + Bending 4 Test Description Ambient excitation was provided mainly by traffic and partly wind and human activity. Eleven accelero meters were used for the ambient vibration measurements, two of which were allocated as reference sensors always located on the 10 th floor. Nine accelerometers were used as roving sensors. The responses were measured in four data sets (A, B, C, D). For A, B, C, D data sets were used respectively 9,11,11,5(8) degree of freedoms records. Every data sets (A, B, C, D) were measured approximately 45 minutes (for preliminary acceptance ξ=0.05, T=0.675 sec f=1/t=1.48 Hz, t=200/ ξ f=2700 sec 45 min; for T=0.8sec t=3200sec=53.33min). The selected measurement points and directions are shown in Figure 3. Figure 3. Measurement points and direction for each data set (by the bold line are shown the reference sensors).pointer indication is mean the direction of the measured motion (accelerometer) The sensors placed in the same location for each of the four tests. The sensors mounted using anchor bolts. The bolts could remain in place until all of the tests were completed. Acceleration measurements were obtained using force balanced accelerometers (Full scale range:+- 2g; DC to 100Hz bandwidth; digital sensor control; output voltage range 0+-5V). Lengths of cable 100 m were available to connect sensors to the signal conditioner. The maximum possible cable length for the sensors with an allowed power voltage drop of 1 volt in the wire are 450 m. Cable configuration are three twisted pairs. The data acquisition computer was dedicated to acquiring the ambient vibration records. In between measurements, the data files from the previous setup were transferred to the data analysis

5 computer using a software package. This arrangement allowed data to be collected on the computer while the second, and faster, computer could be used to process the data in situ. This approach maintained a good quality control that allowed preliminary analyses of the collected data. If the data showed unexpected signal drifts or unwanted noise or for some unknown reasons, was corrupted, the data set was discarded and the measurements were repeated (the roving sensors could be relocated to the next floor). Before the measurements could begin, the cable used to connect the sensors to the data acquisition, equipment had to be laid out. Following each measurement, the roving sensors were systematically located from floor to floor until the test was completed. Typical test parameters were as follows. Geometry: number of nodes 40(48), number of lines 87(92); number of surfaces 20(22). Data: number of data sets 4; number of reference transducers 2; sampling interval 5 ms; sampling frequency 200 Hz; Nyquist frequency 100 Hz. Number of samples in each record ; duration of each record 2.4 ks. Data source: file size for data sets A, B, C, D, respectively are kb, kb, kb kb; file type ASCII. Signal Processing Settings. Spectral Density Matrices Estimation: number of Frequency Lines 1024, Frequency Line Spacing mhz; Overlap 66.67%; Window Function-Hanning. Correlation Functions Estimation: number of Samples 1024; resulting Correlation Length 5.115s; Estimator Type-Biased. Common SSI Input Matrix Estimation: Maximum number of Structural Modes 10; maximum number of Noise Modes 30; Maximum number of modes 40; maximum State Space Dimension 80. Signal Processing Log. Filtering (irreversible action):class Butterworth; order -8; type-low pass; lower cut off frequency -; upper cut off frequency -45Hz. An other parameters are same as in signal processing settings. Number of estimated modes by: frequency Domain Decomposition (FDD) 10(11); Enhanced Frequency Domain Decomposition (Enhanced FDD) 10(11); Unweighted Principal Component (UPC) 9 ; Principal Component (PC) 8; Canonical Variate Analysis (CVA) 0; 5 System Identification System identification is the process of developing or improving a mathematical representation of a physical system using experimental data [5,6]. In engineering structures there are three types of identification: modal parameter identification; structural-modal parameter identification; controlmodel identification methods are used. In the frequency domain the identification is based on the singular value decomposition of the spectral density matrix and it is denoted Frequency Domain Decomposition (FDD) and its further development Enhanced Frequency Domain Decomposition (EFDD). In the time domain there are three different implementations of the Stochastic Subspace Identification (SSI) technique: Unweighted Principal Component (UPC); Principal component (PC); Canonical Variate Analysis (CVA) are used. Below are shown system identification result by the FDD and SSI techniques.

6 5.1 Identification Result in the Frequency Domain. System identification result in the frequency domain are given in Table 3. Table 3. System Identification result by the FDD. Mode No Frequency (Hz) Period (sec) Std. Frequency Damping Ratio m Std. Damping Ratio m m m m m m m m m m m m m m m m m 431 m m m m 5.2 Identification results in the time domain. System identification results in the time domain by the three different implementations of the Stochastic Subspace Identification (SSI) technique such as UPC, PC, CVA respectively are given in Tables 4,5,6,7,8,9,10,11. Table 4. UPC(PC){CVA}; measurement 1, Model Results-Cursor Model Stable (19.42) (262.2m) Stable Stable Table 5. UPC(PC){CVA}; measurement 1, Model Results- Model Selected for Select and Lin k m NaN Noise m 100 Noise m 100 Noise Unstable

7 Table 6. UPC(PC){CVA}; measurement 2, Model Results-Cursor Model (10.86) (2.256) Stable Stable Stable (24.48) (1.682) Stable Table 7. UPC(PC){CVA}; measurement 2, Model Results- Model Selected for Select and Lin k (10.78){42.28} (1.722){2.861} Stable (14.5) (3.495) Stable Stable (24.61) m (3.114) Stable (29.05) (1.553) Stable Table 8. UPC(PC){CVA}; measurement 3, Model Results-Cursor Model Stable ( ){49.27} ( ){1.444} Stable (20.04) (1.158) Stable Table 9. UPC(PC){CVA}; measurement 3, Model Results- Model Selected for Select and Link (20.07) 1.23(1.699) Stable Stable Table 10. UPC(PC){CVA }; measurement 4, Model Results-Cursor Model Stable (25.42) (464.4m) Stable (26.7) m (1.042) Stable

8 Table 11. UPC(PC){CVA}; measurement 4, Model Results- Model Selected for Select and Link Stable Stable m Stable 6 Conclusion The results of a study on the variability of the dynamic properties of an irregular 11-storey concrete building have been presented. Dynamic characteristics were determined by analyzing ambient vibration of the structure and by finite element modelling. The objectives of this study included determining natural frequencies and corresponding mode shapes and damping. Comparisons were made based on a correlative modal assurance criterion (MAC). MAC values were generated between analytical and experimental mode shapes. The MAC values for the first five modes respectively are 99.75% (well correlated), 69.62%, 43.48%, 64.19%, 63.24%. MAC is one of simplest methods for correlating experimental and analytical mode shapes. However, it does not account for the orthogonality conditions between modes. Other more sophisticated and reliable methods require foreknowledge of the stiffness or mass matrix, or require more extensive computational effort than that required to compute MAC values. Nevertheless, considering the limitation in the MAC analysis, it still permitted to access in a simple manner the correlation between experimental and analytical mode shapes. The result also showed that dynamic characteristics and that modal damping values could not be estimated in a reliable manner. 7 References [1] Vibration of Buildings Quidelines for The Measurements of Vibratins and Their Effects on Buildings, ANSI s (A5A ) [2] Ventura, C.E., Shouster, N.D.: Structural Dynamic Properties of a Reinforced Concrete High-Rise Building During Construction, Con.S.Civ.Eng. 23 : , 1996 [3] Kasimzade A.A., Tuhta S.: Estimation of Sensitivity and Reliability Base Isolated Buildings Under Earthquake Action, International Symposium on Network and Senter Based Research for Smart Structures Technologies and Earthquake Engineering (SE 04), July 6-9, Osaka, Japan, 2004 [4] Kasimzade, A.A.: Structural Dynamic: Theory and Application to Earthquare Engineering (is included education and dynamic analysis programs CD), Istanbul, Birsen Publication, Second Edition, 2004, p.527 (ISBN ) [5] Suang, S.N.: Applied System Identifaciton Prentice Hall PTR, Englwood Cliffs, NS, [6] ARTeMIS.: Theoretical Manual, S.V.S, 2003.

DYNAMIC PROPERTIES OF A 32-STOREY BUILDING DETERMINED FROM DIFFERENT ANALYSIS METHODS OF AMBIENT VIBRATION TEST DATA

DYNAMIC PROPERTIES OF A 32-STOREY BUILDING DETERMINED FROM DIFFERENT ANALYSIS METHODS OF AMBIENT VIBRATION TEST DATA Carlos E. Ventura The University of British Columbia Canada Katherine M. Thibert The