Available online at ScienceDirect. Procedia Engineering 125 (2015 )

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1 Available online at ScienceDirect Procedia Engineering 15 (015 ) Te 5t International Conference of Euro Asia Civil Engineering Forum (EACEF-5) Identification of aerodynamic derivatives of two box girder of cable stayed bridge Sukamta a,, Ireng Guntorojati b a Civil Engineering, Te niversity of Diponegoro, Semarang,5075 Indonesia b Infrastructure Division, PT. Wiratman, Jakarta,1540, Indonesia Abstract Motion or self-induced forces can cause te aeroelastic instability penomenon called flutter. Flutter stability is an important design criterion for long span bridges, because flutter leads to large vibration amplitudes or even te total collapse of te bridge. Te flutter derivatives are te essential parameters in te estimation of te critical flutter wind speed. Te aerodynamic derivatives, also known as flutter derivatives, are coefficients of te matematical model for te aeroelastic forces. Tese coefficients are expressed in a non dimensional form and used to determine te flutter analysis of flexible bridges. One of te coefficients is A, tis coefficient provides very useful information to judge and compare te aerodynamic stability. In order to determine te flutter derivatives, te wind tunnel tests using sectional model are very common. In te present work, te free vibration test metod is used to extract te flutter derivatives of te Musi III cable stayed bridge. Estimated te A coefficient canges from negative to positive values around u/fb =.5, tis value indicates, tat te bridge was in a stable condition at te value for u/fb below.5. To improve te stability of te bridge, te sape of tis bridge deck sould be modified. 015 Publised Te Autors. by Elsevier Publised Ltd. Tis by Elsevier is an open Ltd. access article under te CC BY-NC-ND license (ttp://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of Te 5t International Conference of Euro Asia Civil Engineering Peer-review Forum (EACEF-5). under responsibility of organizing committee of Te 5t International Conference of Euro Asia Civil Engineering Forum (EACEF-5) Keywords: Aerodynamic derivatives; Aeroelastic parameter; cable stayed bridge 1. Introduction Te dynamic response prediction for long-span bridges, subjected to wind, is a complex problem. Te incident of te Old Tacoma Narrows Bridge (SA, 1940) under a relatively low wind speed igligted te importance of Corresponding autor. address: kamt_id@yaoo.com Publised by Elsevier Ltd. Tis is an open access article under te CC BY-NC-ND license (ttp://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of Te 5t International Conference of Euro Asia Civil Engineering Forum (EACEF-5) doi: /j.proeng

2 1066 Sukamta and Ireng Guntorojati / Procedia Engineering 15 ( 015 ) sound aerodynamic design against bridge flutter, a self-induced periodic motion wit divergent amplitudes leading to te destruction of te structure tat occurs wen te critical wind speed is exceeded. Motion or self-induced forces can cause te aeroelastic instability penomenon called flutter. Flutter stability is an important design criterion for long span bridges, because flutter leads to large vibration amplitudes or even te total collapse of te bridge. In aeroelastic stability analysis of a flexible bridge, te flutter derivatives are te essential parameters in te estimation of te critical flutter wind speed. Te unsteady aerodynamic forces due to te bridge deck motion are usually expressed in flutter derivatives [1]. Te flutter derivatives are found to be functions of te cross section geometry of te bridge deck and te reduced wind speed. Te experimental metod used for te determination of te flutter derivatives can be grouped into free or forced vibration metod. Over te years, analytical and numerical metods ave been developed and successfully applied to te quantification of te loading and simulation of te response [1]. Te paper presents its intension on te aerodynamic derivatives for te detail design of Musi III Bridge. Te MSI III bridge is a cable-stayed bridge, wic is part of te Musi - III igways and bridges in te province of Sout Sumatera ( Palembang ). Te bridge as a designed span lengt of 1000 m and a widt of 30 m. Wile te navigational clearance eigt and a widt is 51 m and of 400 m, te actual eigt at mid-span is 53,667 m (Fig.1). Longitudinal section. Design of Te Experimental Apparatus Cross section Fig. 1. Prototype of Musi III Bridge Te experimental tests were conducted in te INDONESIAN LOW SPEED TNNEL (ILST), in a circuit of a closed return type wit atmosperic and closed walled test sections of wind tunnel. Te wind tunnel as a working section of 4 meters in widt, 3 meters in eigt and a total of 10 m in lengt. Te maximum attainable wind speed inside te empty test section is 110 meter per second Section Model Test. A reduced scale of 1/50 was cosen, giving te model a widt of B = 0,59 m. Te properties of te structure and model are sown in Table 1.

3 Sukamta and Ireng Guntorojati / Procedia Engineering 15 ( 015 ) Table 1 Structural properties of prototype and model Properties prototypemodel Widt (m) 9, Dept (m) 3, Bending natural frequency f (Hz) ,0 Torsional natural frequency f (Hz) ,5 f f,1,1 Te measurement of te aerodynamic responses to bending and torsional mode for te sectional model was carried out, were te angle of attack = -3 o, 0 o and +3 o. Te centre of rotation was assumed at te location between te centre of gravity and te sear centre. Te model wit a lengt of 1, m and widt of 0,59 m was suspended by eigt coil springs to enable vertical and torsional motions (Fig.). 3. Identification of Aerodynamic derivatives Fig,. Experimental set up Flutter derivatives of bridge decks are essential parameters necessary to te flutter analysis of flexible bridges suc as long-span suspension bridges. In a teoretical and experimental study by Scanlan and Tomko [], a metod of extracting flutter derivatives of bridge decks from free vibration data was discussed in detail. Tis metod consists of two stages: first, uncoupled terms are obtained separately from pure vertical and torsional free oscillations; and secondly, coupled terms are obtained from coupled oscillation data. Te motion equations of a bridge deck section in smoot wind flow in a wind tunnel can be written according to te flutter analysis teory developed by R.H. Scanlan [] as follows: m Lae ae (1a) I M (1b) were m and I are te models mass and mass inertia moment per unit lengt, respectively, and are te mecanical damping ratios in bending and torsion, respectively, and are te corresponding natural mecanical frequencies, and are te vertical bending displacement and torsion angle, respectively, wile L se and M se are te aerodynamic self-excited force and moment, respectively, given by

4 1068 Sukamta and Ireng Guntorojati / Procedia Engineering 15 ( 015 ) L 1 B L KH KH B K H K H ae M 1 B L KA1 KA B K A K ae 3 4 A B B (a) (b) A H A H A u/fb H 3 u/fb y = 5x A H u/fb Fig. 3. Aerodynamic derivates Based on te results of experiments, aerodynamic derivatives were determined using te equation (1) and () proposed by Scanlan and Tomko []. Figure 3 sows te aerodynamic derivatives, wic were determined from free vibration tests wit an angle of attack α = 3 o. u/fb

5 Sukamta and Ireng Guntorojati / Procedia Engineering 15 ( 015 ) Te A coefficient is an indication of te torsional stability of a bridge section aving te vertical motion restrained. Tis coefficient proves to be a very useful to judge and compare te aerodynamic stability. A steep negative slope is an indication of torsional stability. At ig wind velocity, te flutter derivatives cannot be identified accurately because te aerodynamic damping of te vertical-dominant mode is too ig to obtain vibration data enoug for te identification, tis is in accordance wit te results sown by Iwamoto [3]. Estimated te A coefficient canged from negative to positive value around u/fb=.5. It sows te bridge was stable wit te value of u/fb below.5. Te bridge deck cross-sectional sape modifications are needed to improve te stability of te bridge. 4. Conclusion In accordance wit te results of experiments sowing te bridge in a stable condition at te value of u/fb=.5. At ig wind velocity, te flutter derivatives cannot be identified accurately because te aerodynamic damping of te vertical-dominant mode is too ig to obtain vibration data enoug for te identification. Acknowledgement Te writers would like to acknowledge : 1. Bintek Kementerian P for assigning te design of te Musi III Bridge to PT. Wiratman. Aero Gasdynamics and Vibration Laboratory (LAGG), Puspiptek Agency for Assessment and Application of Tecnology (BPPT) and Dr. Fariduzzaman, MSc. MT. for is cooperation and assistance in te Wind Tunnel Test Procedure of te main cable-stayed bridge. Reference [1] Jones, N.P., Scanlan, R.H., 001. Teory and full-bridge modeling of wind response of cable-supported bridges, Journal of Bridge Engineering, ASCE, 6 (6), [] R.H. Scanlan and J.J. Tomko,1971, Airfoil and bridge deck flutter derivatives, J. Eng. Mec. Div. ASCE 97, No. EM6 (1971) [3] M. Iwamoto., Y. Fujino., 1995.,Identification of flutter derivatives of bridge deck from free vibration data., Journal of Wind Engineering and Industrial Aerodynamics 54/55 (1995) 55-63