Suppression of Bridge Vibrations using Tuned Mass Dampers

Download Full-Text PDF Cite this Publication

Text Only Version

Suppression of Bridge Vibrations using Tuned Mass Dampers

Praveen J V Asst. professor,

Department of Civil Engineering Sri Siddhartha Institute Of Technology,

Tumkur, India.

Sadwini M G M.Tech student,

Department of Civil Engineering, Sri Siddhartha Institute Of Technology,

Tumkur, India.

Abstract The importance of bridge vibrations induced by moving vehicles, which act as an oscillators on a bridged as well as time variant forces, has long been recognized. this vibration can amplify the propagation of existing cracks resulting in further damage to the bridge. it has become one of the causes of reduction in long-term serviceability of the bridge, although major bridges failures are not usually caused directly by moving vehicles. It is also a critical factor to bridge structure fatigue and rapid deterioration since, the vehicle-induced vibration is more critical to bridges with medium to small spans it is worthwhile to investigate the possibility of applying tuned mass damper on these bridges. A TMD is a passive control device with variant of merits in that it has permanent service time and only requires easy management and maintenance efforts and no external power supply source. In order to achieve the above objective a general formulation of the vehicle induced bridge vibration controlled with a TMD system is developed here in the present study, which takes into account the road surface conditions. Then, a comprehensive investigation is made to investigate the efficiency of the TMD for suppressing vibrations of bridge under moving load.

Keywords Tuned mass dampers; truss bridge; suppressing vibration; moving load

  1. INTRODUCTION

    Vehicle-bridge interaction is a complex dynamic phenomenon, which is a non-linear problem dependent on many parameters? These parameters include the type of bridge and its natural frequencies of vibration, vehicle characteristics, vehicle speed and traversing path, the number of vehicles and their relative positions on the bridge, roadway surface irregularities, the damping characteristics of bridge and vehicle etc. The first recorded research into bridge vibration appears to be a report published in the 19th century (Willis, 1849),which discussed the reasons for collapse of the Chester Railway Bridge. In the first half of the 20th century, investigations into bridge vibration were mainly concerned with developing analytical solutions for simple cases of moving force (Timoshenko, 1922; Lowan, 1935; Ayreet al1, 1950; Ayre and Jocobsen, 1950) and moving mass (Jeffcott, 1929).

    The moving force model is the simplest model whereby researchers can capture the essential dynamic characteristics of a bridge under the action of a moving vehicle, although the interaction between the vehicle and bridge is ignored. Where the inertia of the vehicle camion is regarded as small, a moving mass mode is often adopted

    instead. However the moving mass model suffers from its inability to consider the bouncing effect of the moving mass, which is significant in the presence of road surface irregularities or for vehicles running at high speeds.

    The development of cost-effective analysis methods as well as the clear identification of the important parameters that govern dynamic response will certainly be of great help to better understanding of the true behavior of the entire bridge- vehicle system. This thesis therefore focuses on development of effective methods for analyzing the vibration of various types of bridges including girder bridges, railway bridges, slab bridges and cable-stayed bridges under the action of moving vehicles and trains. The vibration analysis of suspension bridges is excluded from this thesis due to the limitation of study period.

    Truss Bridge:

    Truss Girders, lattice girders or open web girders are efficient and economical structural systems, since the members experience essentially axial forces and hence the material is fully utilized. Members of the truss girder bridges can be classified as chord members and web members. Generally, the chord members resist overall bending moment in the form of direct tension and compression and web members carry the shear force in the form of direct tension or compression. Due to their efficiency, truss bridges are built over wide range of spans. Truss bridges compete against plate girders for shorter spans, against box girders for medium spans and cable-stayed bridges for long spans.

    DAMPERS:

    Some vibrations problems are directly related to structural resonances, which are specific frequencies at which dynamic perturbations are, sometimes hugely, amplified. The level of this amplification is inversely proportional to the internal damping of the structure. Hence, in order to reduce vibration problems related to resonances, one will want to increase the structural damping and this can be done by passive (friction joints, viscous material, Tuned Mass Dampers) or by active means.

  2. OBJECTIVE AND METHODOLOGY

    1. Objectives

      The aim of the study is to evaluate the seismic performance of a bridge with & without TMD.

      • To study the feasibility of extraction the fundamental bridge frequency from the dynamic response of a vehicle passing over bridge.

      • To study the impact of a speed of vehicle on the structural response of different components of bridges.

    2. Methodology

      TRUSS bridge which is selected for the study is assumed to be located in zone 5 of India, the factors as listed above could be modeled for the study using the finite element analysis the analysis is carried out in SAP 2000. The dynamic analysis would be carried out to study the impact of speed of the vehicles on the structural response of the bridges. The study will be conducted in the form of parametric study so that the studies could result in design chart. The input values to be used in FEM program shall be selected from the literature review initially and then revised based on the values and refined further if possible by conducting theoretical model studies.

      1. The truss bridge is adopted as a design example for a study.

      2. It is 40m, 60m and 80m long & 12m wide truss bridge with two lanes bridge of traffic.

      3. A span of 40m, 60m and 80m between two piers is chosen for study.

      4. The span is considered to be as simply supported.

      5. The systematic parameters like natural frequency, time period, displacements, acceleration, velocity, model damping energy, kinetic energy are studied.

      6. The vibrations of systematic parameters of bridge with and without TMDs are studied considering Bhuj earthquake data.

      7. The impacts of speed of vehicles on bridge are studied.

      Dynamic Equilibrium Equation of Structure

      The dynamic response of a structure at any instant of time t under an excitation force is defined by its displacement u(t), velocity u (t) and acceleration u(t). The total force acting on a structure is resisted by its inertia F(t)I, damping F(t)D and stiffness F(t)S component of reactive force. The force equilibrium equation of a structure at any instant of time of t, subjected to dynamic load F(t) can be expressed by the following equation.

      F(t)I + F(t)D + F(t)S = F(t)

      Where, F(t)I = m.u(t)

      F(t)D= c.u (t)

      F(t)S = k. u(t)

      Where, m= mass of the system. c = damping of the system

      k= stiffness of the system

      For multi degree of freedom system corresponding equation of motion become

      [M]+ [C]+[K]U(t)={F(t)} (3.11) )(tUtU)

      Where, [M] = The globa mass matrix of structure.

      [C] = The global damping matrix of the structure.

      [K] = The global stiffness matrix of the structure. U(t) = Absolute nodal displacement.

      U (t) = Absolute nodal velocity. U(t) = Absolute nodal acceleration.

      F(t) = Force vector. (For earthquake loading F(t)=- [M].Ug(t) )

      Ug(t)= Ground acceleration due to earthquake.

      The effect of TMD can be considered by adding extra opposite nature force to forcing function.

    3. Parameters considered for the study

    Table.1 parameters considered

    1.

    Type of bridge

    TRUSS BRIDGE

    2.

    Grade of concrete

    M 30

    3.

    Number of lanes

    2

    4.

    Lane width

    4m

    5.

    Length of bridge

    40m, 60m and 80m

    6.

    Yield strength

    250Mpa

    7.

    Youngs modulus, E

    5000fck

    8.

    FRAME SECTION:

    9.

    Deck slab

    300mm

    1. Box section

    2. Bracings (I-section)

    3. Floor beam

    4. Cross beam

    5. Stringer

    6. Portal

  3. MODELS

    In the present study 3-dimensional truss bridge models of different span of 40m, 60m and 80m with fixed base, with and without tuned mass dampers of different mass ratio is made using SAP2000

    Fig. 1. Plans of 40m, 60m and 80m span

    Fig. 2. Elevation of 40m, 60m and 80m span without TMD

    Fig. 3. Elevation with TMD

  4. RESULTS AND DISCUSSION

In the present study 3-dimensional truss bridge models of different span with fixed base, with and without tuned mass dampers of different mass ratio subjected to acceleration v/s time period of Bhuj earthquake is studied. Tuned mass damper is modeled with elastic spring properties. The variation in frequency and the structural responses like Base shear, Displacement and Acceleration for time history data is presented.

  1. VARIATION IN FREQUENCY

    40m SPAN

    60m SPAN

    80m SPAN

  2. VARIATION IN ACCELERATION:

    40m SPAN

    60m SPAN

    80m SPAN

  3. VARIATION IN VERTICAL DISLACEMENT:

    Table.2. 40m SPAN

    Node at midspan

    Maximum Vertical Displacement (m)

    Without TMD

    With TMD

    % Reduction

    106

    0.00189

    0.00121

    35.97884

    106

    0.00189

    0.00104

    44.97354

    106

    0.00189

    0.00085

    55.02646

    Table.3. 60m SPAN

    Node at midspan

    Maximum Vertical Displacement (m)

    Without TMD

    With TMD

    % Reduction

    263

    0.00295

    0.00186

    36.94915

    263

    0.00295

    0.00104

    64.74576

    263

    0.00295

    0.00094

    68.13559

    Table.4. 80m SPAN

    Node at midspan

    Maximum Vertical Displacement (m)

    Without TMD

    With TMD

    % Reduction

    263

    0.00423

    0.0039

    7.801418

    263

    0.00423

    0.00369

    12.76596

    263

    0.00423

    0.00335

    20.80378

    CONCLUSION

    1. Since Frequency decreases, vibration reduces with the increase in mass ratio that is 3% and maximum variation is found in 80m span Steel Truss bridge.

    2. Joint Displacement of a structure increases with increase in span and after the implementation of TMD there is a substantial decrease in Joint Displacement maximum decrease is observed in case of mass ratio 3%.

    3. Joint Acceleration of a structure increases with increase in span and after the implementation of TMD there is a substantial decrease in Joint Acceleration maximum decrease is observed in case of mass ratio 3%.

      REFERENCES

      1. Bridge Dynamic Responses Due To Road Surface Roughness and Braking Of Vehicle By S.S. Law*, X.Q. Zhu, Department Of Civil Engineering, Hong Kong Polytechnic University, Kowloon, Hung Hom, In March 2004.

      2. Dynamic Analysis of a Railway Bridge subjected to High Speed Trains BY Dr.Raid Karoumi (2004).

      3. Dynamic response of highway bridges under a moving truck and development of a rational serviceability requirement by Shabnam Darjani. Department of Civil and Environmental Engineering January 2013.

      4. Dynamic Analysis of Railway Bridges under High Speed Trains Ashish Gupta *, Amandeep Singh Ahuja , Department of Mechanical Engineering, IIT Bombay, Powai, Mumbai, India(2014).

      5. Effect Of Vertical Ground Motion On Earthquake-Induced Derailment Of Railway Vehicles Over Simply-Supported Bridges By Zhibin Jina,C,*, Shilling Peia,B,, Xiaozhen Lia,C, Hongyan Liub, Shizhong Qianga, Department Of Civil And Environmental Engineering, Colorado School Of Mines, Golden,USA, August 2016.

      6. Finite Element Analysis Of Vehicle-Bridge Interaction By, Leslaw Kwasniewskia,*, Hongyi Lib, Jerry Wekezerb, Jerzy Malachowskic, March 2006.

      7. Moving load analysis on skewed railway bridge By, Mehrdad Bisadi Department of Civil and Structural Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Selangor, Malaysia,2013.

      8. Multi-modal vibration control of truss bridges with tuned mass dampers under general loading BY Nirmalendu Debnath, SK Deb, Anjan Dutta February 24, 2015.

      9. Pedestrian excitation of bridges D E Newland Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK.

      10. Random Vibration Analysis of Dynamic Vehicle-Bridge Interaction Due to Road Unevenness By, Geert Lombaert1 and Joel P. Conte, M.ASCE2.

      11. Resonance characteristics of two-span continuous beam under moving high speed trains BY Yingjie Wanga,b, , QingChao Weia , Jin Shia and Xuyou Longa,c.

      12. Suppression of Vehicle-induced Bridge Vibration Using Tuned Mass Damper BY Xiaomin Shi, C.S. Cai July 1, 2008.

      13. Suppression of vehicle-induced bridge vibrations Dr.N.S.Kumar Director (R&D) Civil Engineering, Ghousia College of Engineering, Ramanagara, Bangalore, India.

Leave a Reply

Your email address will not be published. Required fields are marked *