Dynamic Analysis of Suspension Bridge using SAP 2000
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S-JPSET : Vol. 10, Issue Supplementary, ISSN : 2229-7111 (Print) and ISSN : 2454-5767 (Online) copyright © samriddhi, 2010-2019 176 Dynamic Analysis of Suspension Bridge using SAP 2000 Preethi H G 1 , Avinash Deshpande 2 , Madhu B E 2 1 Post-Graduation Student, School of Civil Engineering, REVA University, Rukmini Knowledge Park, Bengaluru, Karnataka, India. 2 Assistant Professor, School of Civil Engineering, REVA University, Rukmini Knowledge Park, Bengaluru, Karnataka, India. Publication Info Article history: Received : 16 September 2019 Accepted : 20 November 2019 DOI: 10.18090/samriddhi. v11iSUP-1.17110 Keywords: Suspension bridge, SAP2000, time history analysis, vertical hangers, inclined hangers, additional stiffeners. *Corresponding author: Preethi H G e-mail: [email protected] 1. INTRODUCTION Bridge is a structure built to hold the roadway, railway or path etc. across a road, valley or other obstacles. There are many type of bridge designs that every serve a specific cause subjecting to the exclusive situations. Consequently for longer span purpose, suspension and cable stayed bridges are very much appropriate. The distinction between suspension bridge and cable stayed bridge is that, in suspension bridge the cables supporting the deck are suspended vertically from main cables where as in cable stayed, deck assisting cables are connected directly from towers. In their simplest form suspension bridges had been constructed using timber and rope. But conventional suspension bridges are made from a box section roadways carried by high tensile strength cables. In 1801, the first iron chain suspension bridge was made across Jacob’s Creek in Westmoreland County which is located in the U.S state of Pennsylvania. This is referred to the earliest bridge to possess all the essential parts of modern suspension bridge and was designed by James Finley who patented this system in 1808. So that this year is considered as a beginning era to the modern suspension bridges. Suspension bridges is most expensive to build, but this type is most appropriate for very long span bridges and represents more than 20 longest span bridges in the world. As these are long and flexible structures most exposed to dynamic loading. The vibration analysis become very significant in predicting the behavior of bridge under various dynamic loads such as wind load, vehicular load and Earthquake load. Suspension bridges can span distances from 600m to 2100m longest than any other type of bridges. The world’s longest suspension bridge is Akashi-kaikyo Bridge in Japan, having main span of 1991m. It has 6 lanes with a complete length of 3911m. 1.1. Components of Suspension Bridge Deck, Main suspension cables, hangers, pylons, pylon foundation and anchorages. Hangers: Hangers are used to associate the stiffening girder and deck of the bridge to the main cables firmly. In this papers suspension bridges with vertical and inclined hangers are compared for different spans. Pylons: The principle function of pylon is to support the main cables. The terminals of the main cable is joined to the pylon at an appropriate height to provide cable sag. In this paper we studied seismic response of suspension bridge having truss and portal shape pylons. 1.2. Time History Analysis It is a step by step analysis of the dynamic response of a structure to a specified loading that may vary with time. Time history analysis is used to determine the seismic response of a structure under dynamic loading of representative earthquake. In this study time history data file is considered from El Centro site Imperial Valley irrigation District. Abstract A Suspension Bridge is a type of bridge which has cables suspended between two towers and from where a series of hangers are connected which holds the deck. Suspension bridge is more suitable for the medium to long spans. As these are long and flexible structures most exposed to dynamic loading, hence the vibration analysis become very significant in predicting the behavior of bridge under various dynamic loads. This research presents the analysis of suspension bridges subjected to dynamic time history loads and determining the suitability for specific span length. Suspension Bridge works by tension and compression, in which most of the bridge weight is carried by the suspension cables which is then transferred to the Pylons. Hence, the Pylon has been further stiffened by stiffening beams (portal and truss patterns) and effect of dynamic time history response has been studied. And also the present study aims to characterize the effect of both vertical and inclined hangers on the dynamic behavior of suspension bridge. For these arrangements, a finite element software SAP 2000(V-14) has been used for modelling and analyzing of Suspension Bridge.
Transcript of Dynamic Analysis of Suspension Bridge using SAP 2000
S-JPSET : Vol. 10, Issue Supplementary, ISSN : 2229-7111 (Print) and ISSN : 2454-5767 (Online) copyright © samriddhi, 2010-2019176
Dynamic Analysis of Suspension Bridge using SAP 2000Preethi H G1, Avinash Deshpande2, Madhu B E2
1Post-Graduation Student, School of Civil Engineering, REVA University, Rukmini Knowledge Park, Bengaluru, Karnataka, India. 2Assistant Professor, School of Civil Engineering, REVA University, Rukmini Knowledge Park, Bengaluru, Karnataka, India.
Publication InfoArticle history: Received : 16 September 2019 Accepted : 20 November 2019 DOI: 10.18090/samriddhi.v11iSUP-1.17110Keywords: Suspension bridge, SAP2000, time history analysis, vertical hangers, inclined hangers, additional stiffeners.*Corresponding author: Preethi H G e-mail: [email protected]
1. INTRODUCTIONBridge is a structure built to hold the roadway, railway or path etc. across a road, valley or other obstacles. There are many type of bridge designs that every serve a specific cause subjecting to the exclusive situations. Consequently for longer span purpose, suspension and cable stayed bridges are very much appropriate. The distinction between suspension bridge and cable stayed bridge is that, in suspension bridge the cables supporting the deck are suspended vertically from main cables where as in cable stayed, deck assisting cables are connected directly from towers. In their simplest form suspension bridges had been constructed using timber and rope. But conventional suspension bridges are made from a box section roadways carried by high tensile strength cables. In 1801, the first iron chain suspension bridge was made across Jacob’s Creek in Westmoreland County which is located in the U.S state of Pennsylvania. This is referred to the earliest bridge to possess all the essential parts of modern suspension bridge and was designed by James Finley who patented this system in 1808. So that this year is considered as a beginning era to the modern suspension bridges.
Suspension bridges is most expensive to build, but this type is most appropriate for very long span bridges and represents more than 20 longest span bridges in the world. As these are long and flexible structures most exposed to dynamic loading. The vibration analysis become very significant in predicting the behavior of bridge under
various dynamic loads such as wind load, vehicular load and Earthquake load. Suspension bridges can span distances from 600m to 2100m longest than any other type of bridges. The world’s longest suspension bridge is Akashi-kaikyo Bridge in Japan, having main span of 1991m. It has 6 lanes with a complete length of 3911m.
1.1. Components of Suspension Bridge Deck, Main suspension cables, hangers, pylons, pylon foundation and anchorages.Hangers: Hangers are used to associate the stiffening girder and deck of the bridge to the main cables firmly. In this papers suspension bridges with vertical and inclined hangers are compared for different spans.Pylons: The principle function of pylon is to support the main cables. The terminals of the main cable is joined to the pylon at an appropriate height to provide cable sag. In this paper we studied seismic response of suspension bridge having truss and portal shape pylons.
1.2. Time History AnalysisIt is a step by step analysis of the dynamic response of a structure to a specified loading that may vary with time. Time history analysis is used to determine the seismic response of a structure under dynamic loading of representative earthquake. In this study time history data file is considered from El Centro site Imperial Valley irrigation District.
AbstractA Suspension Bridge is a type of bridge which has cables suspended between two towers and from where a series of hangers are connected which holds the deck. Suspension bridge is more suitable for the medium to long spans. As these are long and flexible structures most exposed to dynamic loading, hence the vibration analysis become very significant in predicting the behavior of bridge under various dynamic loads. This research presents the analysis of suspension bridges subjected to dynamic time history loads and determining the suitability for specific span length. Suspension Bridge works by tension and compression, in which most of the bridge weight is carried by the suspension cables which is then transferred to the Pylons. Hence, the Pylon has been further stiffened by stiffening beams (portal and truss patterns) and effect of dynamic time history response has been studied. And also the present study aims to characterize the effect of both vertical and inclined hangers on the dynamic behavior of suspension bridge. For these arrangements, a finite element software SAP 2000(V-14) has been used for modelling and analyzing of Suspension Bridge.
Preethi H G, Madhu B E
copyright © samriddhi, 2010-2018 S-JPSET : Vol. 10, Issue Supplementary, ISSN : 2229-7111 (Print) and ISSN : 2454-5767 (Online)177
1.3. Objectives• Modelling and analysis of Suspension Bridge for two
different type of hangers (vertical and inclined) using SAP 2000 software.
• To study the performance of suspension bridge subjected to dynamic time history loads.
• To study effect of additional stiffeners to pylons on over all behavior of suspension bridge.
• To determine the suitability for specific span length, type of suspenders dependent on the results obtained in static and dynamic analysis.
2. METHODOLOGY• Suspension bridge will be modelled using SAP 2000
for two different spans.• Also, the existing pylon has been further stiffened by
stiffening beams and effect on dynamic time history response has been studied.
• Initially modal analysis is carried out to know the mode shapes, time period and frequency of suspension bridge.
• Later all the suspension bridges are analysed for static and dynamic time history loads.
• From static analysis vertical deflection of deck and pylon are found out.
• Results like deformation of pylon, forces in cables and deck deflection due to static loads and peak acceleration, peak displacement due to dynamic time history loads are extracted.
• Based on the results extracted, discussions will be written and conclusions are made.
2.1. Software for AnalysisSAP 2000 software is used for the analysis of suspension bridge based on previous studies. SAP 2000 is particularly valuable for practicing professionals which has incorporated
modelling templates, advanced analysis options, code-based loading assignments, and customizable output reports. In this regard, SAP 2000(V-14) software package have been taken as tool to accomplish the dynamic time history analysis and all the basic structural systems are modelled as space frames.
2.1.1. Loads to be considered• Dead Load• Live Load(Class 70R)• Time History Load(El Centro Data)
2.1.2. Description of Bridge ModelsSuspension Bridge is modelled for three different central spans namely, 250m, 600m and 1000m with side span of 75m, 150m and 250m and total height of pylons 100m, 175m and 275m respectively. The width of Deck is 10m with 2 lanes. Suspension Bridge with vertical and inclined
Figure 1: Time history of ground motion acceleration of 1940 El Centro Earthquake (Imperial Valley)
Figure 2: 3D view of Vertical Hanger Suspension Bridge
Figure 3: 2D view of Vertical Hanger Suspension Bridge
Figure 4: 3D view of Inclined Hanger Suspension Bridge
Dynamic Analysis of Suspension Bridge using SAP 2000
S-JPSET : Vol. 10, Issue Supplementary, ISSN : 2229-7111 (Print) and ISSN : 2454-5767 (Online) copyright © samriddhi, 2010-2019178
hanger arrangements are used for the analysis. And pylons with truss and portal shapes are modelled for 1000 m spans.
3. RESULTS AND DISCUSSIONFinite element analysis of suspension bridge subjected to dynamic time history loads is carried out using SAP 2000 software to determine the behavior bridge. The results obtained are as shown in the below graphs. Based on the results obtained from the analysis the comparison is made between different parameters like time period, frequency, deflection and peak acceleration.
3.1. Modal AnalysisModal Analysis has been carried out to understand the vibrational characteristics of the Suspension Bridge. From the below graphs it is shown that suspension bridge with vertical hanger has more time period than inclined hangers
Figure 5: 2D view of Inclined Hanger Suspension Bridge
Figure 6: Truss shape pylon in XY-plane
Figure 7: Portal shape pylon in XY-plane
Figure 8: The graph of mode vs. time period for vertical and inclined hanger suspension bridge
Figure 10: The graph of mode vs. time period for vertical and inclined hanger suspension bridge
Figure 9: The graph of mode vs. time period for vertical and inclined hanger suspension bridge
for larger spans(600m and 1000m). Among truss and portal shape pylons, time period of portal shape pylon in vertical hanger suspension bridge is greater than the truss shape. As time period is more frequency will be less, hence the models with more time period shows better performance against seismic loads.
Preethi H G, Madhu B E
copyright © samriddhi, 2010-2018 S-JPSET : Vol. 10, Issue Supplementary, ISSN : 2229-7111 (Print) and ISSN : 2454-5767 (Online)179
3.2. Static Analysis ResultsFrom the static analysis, the variation of pylon reactions and cable forces for different suspension bridge models has been plotted as shown below. And it is found that with increase in span, the pylon reaction increases and cable force decreases for both vertical and inclined hanger arrangement. As seen from figure 13, the portal shape pylon shows better performance than truss shape.
3.3. Time History Analysis ResultsFrom time history analysis, we can observe that the maximum deck deflection due to dead load and dynamic load is found to be in vertical hanger suspension bridge. From the graphs it is shown that, pylon displacement is found to be very less under time history loading.
Figure 11: The graph of mode vs. time period for truss and portal shape pylons in suspension bridge
Figure 12: The graph of Pylon Reactions in different spans for vertical and inclined hanger suspension bridge
Figure 14: The graph of Cable Forces in different spans for vertical and inclined hanger suspension bridge
Figure 16: The graph of Deck Deflection in different spans for vertical and inclined hanger suspension bridge
Figure 13: The graph of Pylon Reactions for suspension bridge with truss and portal shape pylons
Figure 15: The graph of Cable Forces for suspension bridge with truss and portal shape pylons
Dynamic Analysis of Suspension Bridge using SAP 2000
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Table 2: Peak acceleration values for different pylonsPeak AccelerationTruss PortalVertical Hangers Inclined Hangers Vertical Hangers Inclined Hangers3.429 3.429 3.077 3.132
Table 1: Peak acceleration values for different hangersPeak AccelerationVertical Hangers Inclined Hangers250m Span 600m Span 1000m Span 250m Span 600m Span 1000m Span3.483 2.995 3.031 3.085 3.025 3.117
Figure 18: The graph of Pylon Displacement in different spans for vertical and inclined hanger suspension bridge
Peak Acceleration response due to Time HistoryFigure 20: Graph indicating minimum and maximum values of
acceleration under time history analysis
Figure 19: The graph of Pylon Displacement for vertical and inclined hanger suspension bridge with truss and portal shape
pylons
Figure 17: The graph of Deck Deflection for vertical and inclined hanger suspension bridge with truss and portal shape pylons
4. CONCLUSION• From the Modal Analysis results it can be shown
that, the time period (Sec) and frequency (Hz) are proportional to the span of the bridge. Hence Suspension bridge with 1000m span has more time period and less frequency compared to smaller spans.
• Therefore it is concluded that, longer span suspension bridge with vertical hangers and portal shape pylon is more efficient compared to other cases. For smaller spans, suspension bridge with inclined hangers shows better performance.
• As seen from the Static Analysis results, pylon
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reaction is dependent on the span of the bridge and shape of pylon.
• Cable force depends on the span of the bridge but pylon shape has no influence on cable forces. Smaller span suspension bridge has less cable force compared to larger spans.
• Deck deflection and pylon displacement, both depends on the shape of the hangers and not on the shape of pylon. Suspension Bridge with vertical hangers has more pylon displacement and deck deflection compared to inclined hanger arrangement.
• From Time History Analysis it can be decided that, peak acceleration response is maximum in vertical hanger suspension bridge.
• From overall study of the work and above conclusions, it can be suggested that, for large span suspension bridge, vertical hangers and portal shape pylon can be adopted for better performance.
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