Performance of Reinforced Concrete Bridges during ... · Performance of Reinforced Concrete Bridges...

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Volume-6, Issue-4, July-August 2016

International Journal of Engineering and Management Research

Page Number: 445-449

Performance of Reinforced Concrete Bridges during Earthquake - A Review

Nishant Sharma1, Parmod Kumar2

1Assistant Professor, Department of Civil Engineering, BRCM-CET, Bahal, Bhiwani, INDIA 2

M.Tech Scholar, Department of Civil Engineering, BRCM-CET, Bahal, Bhiwani, INDIA

Abstract

Earthquake are naturally occurring vibratory ground motions. There are number of causes for earthquake, which include tectonic ground motion, volcanism, landslides, rock bursts, and manmade explosions. Most important of which are caused by fracture and sliding of rock along tectonic faults within the earth crust. Earthquake damage to a bridge have severe consequences. Collapse of bridge places people on or below the bridges at risk and it must be replaced after the earthquake unless alternative transportation paths are identified. The purpose of this paper is to identify and classify of damages to bridges that earthquake commonly induce and where possible, to identify the causes of damages. Damage usually results from a complex and interacting set of contributing variables. Even when cause of a particular collapse is well understood, it is difficult to find the cause of bridge damage. Keywords---- Earthquake, Dynamic analysis, Motions

I. INTRODUCTION

Roads and bridges are important parts of infrastructure. Bridges are primarily design to carry the vertical loads due to its own weight and traffic over a span. During the expected service life of a bridge natural or manmade extreme hazards conditions may arise. Even after natural disaster like earthquake, bridges should continue to function for speed recovery and relief operation.

Now a day’s it’s become necessary to conduct survey for assessing the damages to infrastructure. After these survey studies shows that bridges are highly vulnerable to earthquake induced damages and these type damages are superstructure failure, column failure, expansion joint unseating, beam failure and failure of other parts like diaphragms, joints, abutments, foundation and approaches.

An earthquake can cause damage to buildings, civil structures, railways and bridges. In past few decades earthquakes damage many bridges and highways. Some of recent studies on seismic effected

bridge and failure of bridge due to earthquake are, Ghobarah and Tso(1973), conducted a study about dynamic response of skew bridge, Maragakis investigated the rotational and translational displacement of the skew bridge deck by considering the bridge deck as a rigid one, Wakefield et al., analysed the Foothill Boulevard Overcrossing, Meng and Lui in their detailed study about skew bridge found that the superstructure flexibility is vital and should not be discarded in dynamic analysis, Pottatheere and Renault studied the vulnerability of skew bridge by developing fragility curves for the skew bridges with skew angle of 0̊,12.23˚ and 45̊ and Kalantari and Amjadian found an approximate hand- method for dynamic analysis of a skewed highway bridge with continuous rigid deck using a 3 DOFs analytical model.

II. PERFORMANCE OF BRIDGES DURING PAST EARTHQUAKE

In past earthquakes, many bridges have

experienced either different types of damage or collapsed. The bridge collapses due to earthquake are based on the structure elements like girder, column, bearing and deck etc. that failed. During the 1990s, some major earthquake in Japan and the U.S. caused dozens of bridge structure to collapse. Some of the bridge failure in past describe below. 2.1 Showa bridge in 1964 Niigata earthquake

Niigata earthquake on 14th June 1964 registered 7.5 Richter scale. Showa bridge total length was 307 m with main girder span 28 m. Each span was composed of 12 composite girder, making the bridge about 24 m wide, and it was supported on nine 600 mm diameter steel piles of wall thickness 9 to 16 mm. Bridges girder are with movable and fixed joints which allow thermal expansion of bridge. After investigation some cause of failure are noted. Movement of riverbank soil could not cause any significant loads on central pile rows, due to negligible thickness of spreading soil. The failure of piles was due to combined effect of axial load and second order P-∆ moments cause by earthquake residual



lateral displacement on the piles. At critical depth, the combination of superstructure loading, earthquake imposed lateral imperfections and reduced lateral

support from liquefied soil, resulted in collapse due to structural instability of central piles.

Fig.:1 Showa bridge after Niigata earthquake in 1964

2.2 Hanshin expressway in 1996 Kobe earthquake.

Hanshin expressway, an eighteen span bridge located in Japan, was designed based on 1964 design specification with the allowable stress design approach. Bridge deck simply supported and made with pre-stressed concrete to the length of 22 m. One meter diameter piles constructed with length of 10-15 m to support piers. After the catastrophic failure, different investigations have been conducted to find the causes.

Three major problems find during the investigation in design of bridge. First, allowable shear stress in the code design was overestimated and one in the code was less than 60% of design stress. Second , the termination of longitudinal bars at mid-height. Third cause was insufficient amount of tie bars. In strong ground motion piers collapsed due to insufficient amount of longitudinal bars and improper length of termination.

Fig.:2 Collapsed highway bridge after the great Kobe Earthquake

2.3 Gavin canyon undercrossing failure in Northridge earthquake

Gavin canyon undercrossing had five spans with pre-stressed concrete box girder, which was

designed in 1964 and constructed in Los Angeles, California in 1967. About a 66 degree skew alignment, structure consisted two parallel bridges. Structure is simply supported with a structural hidge near each of

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two pier bents. This bridge had experienced 1971 San Fernando earthquake without any visual damage except some retrofitting in 1974 for hinges. Seat length of bridge is one of the features that showed the difference with improvement of codes. Seat length was 200 mm at hinges, which by current design standards would be

considered inadequate. This was probably reason for failure of three of the four end spans of the bridge. Another important cause of the failure was the skewed alignment in conjunction with the tall and flexible piers of the two centre bents of the bridge.

Fig.:3 Gavin Canyon Undercrossing collapse.

2.4 Wushi bridge damage in Taiwan 921 earthquake.

The total length of Wushi bridge is 624.5 m and the total width is 26 m. Northbound bridge was finished in 1960’s having substructure are wall type concrete pier and southbound one was completed in 1973 having substructures are hammerhead concrete piers. They all supported by 6 m diameter, 13-16 m shaft foundations. Superstructure used prestressed concrete I-beams with constant span length of 34.84m. During investigation it was noticed that due to slip movement, the first and second spans of the northbound bridge fell to the ground and the third span clearly showed lateral movement.

Northern end abutment of the northbound bridge was pushed by the span and the jigsaw type of expansion joint and the back wall board were demolished. Backfill was pushed by superstructure and moved upward under pressure. Substantial shear crack showed on the southbound hammerhead concrete pier due to horizontal vibration. East side exterior PCI beams were flexure and cap of first pier of northbound bridge cracked. End diaphragms and shear blocks designed to prevent concrete beams from moving laterally were crushed as the whole superstructure moved westward.

Fig.:4 Collapse of span in Wushi bridge during earthquake.

2.5 Miaoziping bridge in 2008, china earthquake.

Miaoziping bridge located at Duwen Highway crossing the Zipingpu dam reservoir and min river. It is consists of three span continuous prestressed box girder and prestressed concrete girder approach bridges of two, four and five spans. Total length of bridge is 1440 m and

main structure is 450 m long three span continuous prestressed concrete frame bridge with a main span of 220 m. One prestressed concrete girder was constructed by connecting 50 m long, simply supported PC T-girder bridges with concrete slabs. Girder was supported by elastomeric bearings. All span were supported by 100 m



tall reinforced concrete piers resting on pile foundation in dam reservoir. At the time of earthquake, deck connections of T-girder bridges were almost complete and expansion joints were not yet set. One of two end spans of five span continuous T-girder bridge collapses. Distance between two adjacent piers which support fallen span was extended by about 0.69 m at top. Piers suffered small cracks at their base. Because piers were 100 m tall, only

1% drift can result in 1 m lateral displacement at the deck level. A 300 mm offset take place between two adjacent T-girder bridge in the transverse direction. Almost all the side block suffers the damage. On the other hand, concrete slab on T-girder span next to the fallen span, when adjacent span started to fall at other side, the concrete slab was subjected to tension and was torn off.

Fig.:5 Concrete slab torn off due to fall of the girder bridge from the other side

2.6 Previous studies

A large number of researchers and investigation about the dynamic and static behaviour of skew bridges carried out in past. Few of them are briefly discuss below In 1947, Ghobarah and Tso(1973), conducted a study about dynamic response of skew bridge using a beam model capable of undergoing torsional and flexural modes of deformation. Study was conducted on the model of Foothill Boulevard undercrossing, S.E. Bridge in San Fernando Valley. Model is analysed under the vertical component of earthquake motion. Bridge deck is model as a beam fixed to the abutment walls at its end. They find the conclusion that the coupled torsional and flexural motions of the bridge dominated the failure. This study results also matched well with the observed damage pattern of the Foothill bridge during the 1971 San Fernando earthquake. In 1984, Maragakis investigated the rotational and translational displacement of the skew bridge deck by considering the bridge deck as a rigid one. A simple model of bridge was made with bridge deck represented by a rigid rod, which was restricted by the abutment and columns. In-plane rotation of the bridge deck was illustrated, which triggered after the closure of the gap between the deck and abutment. During dynamic loading in vertical or horizontal direction, the skew bridge can pose a problem. The eccentric masses can lead to the amplification of one or more of the six main modes, namely: (1) rigid-body longitudinal translation; (2) rigid-body lateral translation; (3) rigid-body in-plane rotation

of deck; (4) lateral flexure; (5) vertical flexure; (6) torsional distortion of bridge deck. Wakefield et al., in 1991 analysed the Foothill Boulevard Overcrossing using a simplified beam model and a more complex built up plate model and the time-history analyses showed that the rigid body modes dominated the earthquake response of bridge, which led to the conclusion that under dynamic loads, short stiff skewed bridge behave essentially as rigid bodies, if the deck is not rigidly fixed to the abutments. This study thus gives an explanation of the seismic failure of rigid skew RC bridges that agrees with the field observation of the failure of Foothill Boulevard Undercrossing. The results confirm the validity of assumption made by Maragakis(1984) in derivation of his model for skew bridges, namely, the bridge deck behaved as a rigid body. But, Maragakis modelled the bridge deck as a rigid bar, neglecting its flexural and torsional deformations. The Foothill Boulevard Undercrossing is more complex than the bridge treated as Maragakis. It is not symmetrical as Maragakis modelled. Rather it has three column bents instead of two. In 2002, Meng and Lui in their detailed study about skew bridge found that the superstructure flexibility is vital and should not be discarded in dynamic analysis. In-plane rotation dominates the fundamental modes, which can be pronounced if distribution of bent stiffness becomes uneven. They also used Foothill Boulevard Overcrossing model for the seismic analysis and assessment of skew bridge. Assumption the deck to be rigid would be underestimate



the natural period of the deck slab. Skewness importance was very well reported in this work. Large skewness induces vibratory modes such as torsion and lateral flexure, which may cause increase in axial force, shear moment and torque in supporting columns as well as an increase in deck displacements. The use of proper boundary conditions for supporting columns can outweigh the detrimental effect of skewness. However, in general, it is found that considering the deck as rigid gives almost similar results as that of the one considering the flexibility of the deck. Pottatheere and Renault in 2008 studied the vulnerability of skew bridge by developing fragility curves for the skew bridges with skew angle of 0̊,12.23˚ and 45˚. Fragility curves were developed for four states of damages and the same was done for bridge piers as well as bearings. For capturing the torsional effects due to skewness, a non linear 3-D finite element bridge model was used for study. Sixty synthetic acceleration time histories were applied on the different models. Further, peak responses were studies and a probabilistic demand model was developed. In 2010, Kalantari and Amjadian found an approximate hand- method for dynamic analysis of a skewed highway bridge with continuous rigid deck using a 3 DOFs analytical model. The capability and efficiency of the proposed method are compared with the results of the finite element modelling of Foothill Boulevard Overcrossing using SAP 2000, v14.0.0-Advanced (2009). The preliminary values obtained from the proposed method can be used to design skew bridges approximately in a preliminary phase. Also, it helps to identify the unknown errors occurring during finite element modelling of the structure in commercial programs.

III. CONCLUSION From this study results we reach on conclusion that mostly bridge are fail during earthquake due to inadequate design standard. Hanshin expressway,

Miaoziping and Gavin Canyen undercrossing are fail because their design are not according to current standard. Combined effect of axial and earthquake loads are reason of bridge failure. Torsional and flexural motion of bridge dominated the failure. By using the proper design specification and design the bridge for the load combination like axial and earthquake can prevent bridge structure from damage.

REFERENCES [1] A.A. Kerciker, S. Bhattacharya, Z.A. Lubkowski and H.J. Burd. “Failure of showa bridge during the 1964 Niigata earthquake”. Proceeding, 14th

[2] Jack P.Moehle and Marc O. Eberhead.“ Earthquake damage to bridges”. Bridge engineering handbook.

World conference on Earthquake Engineering.

[3] Yao T. Hsu and Chung C. Fu.“ Study of Damaged Wushi Bridge in Taiwan 921 earthquake”. Journal of structure engineering [4] George C. Lee, Satish B. Mohan, Chao Huang and Bastam N. Fard.“ A study of U.S. bridge failures (1998-2012)”. Technical report MCEER. [5] Kazuhiko KAWASHIMA, Y. TAKAHASHI, Hanbin GE, Zhishen WU, Jiandony ZHANG. “Damage of bridge in 2008 Wenchian, China earthquake” [6] Pie-chang Huang, Yao T. Hsu, Antonio Nanni. “Assessment and proposed structural repair strategies for bridge piles in Taiwan damage”. [7] George Mylonakis, Costis Syngros. “ The collapse of fuke ( hanshin expressway ) bridge, kobe, 1995”. [8] Meng, J.-Y. And Lui, E.M. (2002). “ Seismic Analysis and Assessement of a skew highway bridge”. Engineering Structures. [9] Kalantari, A. and Amjadian, M. (2010). “ An approximate method for dynamic analysis of skew highway bridge with continuousm rigid”. Engineering structure. [10] Maragakis, E. (1984). “ A model for rigid body motions of skew bridges”. PhD thesis, California Institue of Technology, Pasadena.

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