Comparative Study of Bearing and Integral Type Bridges as Per Indian Standards

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1 IJSTE - International Journal of Science Technology & Engineering Volume 1 Issue 11 May 2015 ISSN (online): X Comparative Study of Bearing and Integral Type Bridges as Per Indian Standards Tejas N Rathi Prof. (Dr.) B. J. Shah PG Student Professor Department of Applied Mechanics Department of Applied Mechanics L. D. College of Engineering L. D. College of Engineering Abstract Integral Bridges are the joint less continuous bridges without any expansion joint and bearings. The monolithic construction eliminates the weak links like expansion joints and bearings. However due to continuity, additional stresses and moments due to temperature, braking forces and earth pressure are observed in superstructure. These effects adds up to the complexity in design. In this paper, the design moments for the different components of superstructure are compared for both types of bridges. However design has been carried out for superstructure according to working stress design philosophy, and the reinforcement area is also compared for both type of bridges. Analysis and design has been carried out for one span, two span and three span bridges of both type. Keywords: Integral Bridge, Bearing Bridge, Working Stress Design Philosophy, Comparative Study, Bridge I. INTRODUCTION Highway bridges traditionally have a system of expansion joint, abutment bearing and other structural releases to negotiate cyclic thermal expansion and contraction, creep and shrinkage, and are known as Bearing Bridges. While integral type bridge structures, on the other hand, are single or multiple span bridges that have their superstructure cast integral with their substructure. Integral bridges accommodate superstructure movements without conventional expansion joints. Due to the elimination of the bridge deck expansion joints, construction and maintenance costs are reduced, but additional stresses due to temperature and braking forces are observed to be significant. The earliest examples of integral bridges (IB) are masonry arch bridges. The construction of IB has been pursued in various countries like U.S.A, Canada, U.K, Sweden, Poland, Germany and Japan. Due to the rigid connection between superstructure and piers/abutments, the effect of temperature change causes moments to generate and transfers it from superstructure to abutment/piers and from abutment/piers to foundation. This moments and displacements can be negotiated by combined action of superstructure and substructure. The rigid connection, as shown in figure 1, allows the abutment and the superstructure to act as a single structural unit. Fig. 1: Simplified Geometry of an Integral Abutment Bridge All rights reserved by 98

2 II. GEOMETRY OF THE STRUCTURE AND MODELLING Fig. 2: Geometry of Superstructure Span length 25 m No of lanes 2 Fig. 3: Geometry of substructure Pier/Abutment Foundation A. STAAD Model: Fig. 4: Grillage Model for Bearing Bridge Superstructure Fig. 5: Grillage Model for Integral Bridge Superstructure All rights reserved by 99

3 III. LOADS DESCRIPTION Loads considered and calculated in accordance with the IRC: for analysis purpose are briefed as below: A. Dead Load: Dead load comprises of the self-weight of the components of the bridge superstructure and substructure. However, load are not assigned as self-weight for all members, except pier and abutment, instead it is applied as floor load for weight of deck, wearing coat and crash barrier on the floor occupied by the same, while self-weight of girders and diaphragms are assigned as uniform load throughout the length of member. B. Live Load: Live load are considered as per IRC: , for two lane bridges, i.e. two lanes of class A and one lane of class 70R (W). EARTHQUAKE (EQ) FORCE EQ forces are calculated based on the dead load and live load on pier/abutment. These forces are applied at the pier/abutmentdeck junction of bridge, in longitudinal as well as transverse direction. C. Wind Force: Wind forces are calculated for the basic data of site located in the Ahmedabad city of Gujarat, India. Which are applied at the pier/abutment-deck junction of bridge, in longitudinal as well as transverse direction. D. Temperature Force: Forces due to temperature loading are calculated for, expansion as well as contraction conditions. These forces are applied at the abutment-deck junction of bridge, in longitudinal direction only at both the ends of bridge. E. Braking Force: Live load braking force is applied similarly as temperature forces but at only one end of the bridge in traffic direction. F. Earth Pressure: Earth pressure are calculated based on the coefficient of earth pressure, which in case of integral bridge is dependent on net displacement due to temperature and braking forces, while for bearing bridges the coefficient of earth pressure is considered as active earth pressure coefficient. G. Load Cases Considered: Load cases are considered on the working stress design philosophy. In case of bearing bridges, the load cases considered are DL + LL. While for integral bridges, due to continuity in construction, the load cases considered are as follows: Table 1 Load Cases Considered for Integral Bridges DL SIDL LL TL BL SP WL Eqx Eqz Load Case Load Case Load Case Load Case All rights reserved by 100

4 Load Case Load Case Load Case Load Case IV. RESULTS Results are compared for the design moments in deck slab, girder, and diaphragms of superstructure, for one span, two span and three span integral and bearing type bridges. A. Design Moments in Deck Slab: Design of deck slab for one span, two span and three span bridges of both the types is going to remain same, hence calculation is done for one span of bearing bridge and integral bridge. Table - 2 Comparison of Moments in Deck Slab (Hogging (+ve), Sagging ( ve)) Bearing Integral % Decrease Design Moments Max Span Max Support Max Span Max Support Max Span Max Support B. Reinforcement Comparison: Table 3 Reinforcement Comparison Bearing Bridge Integral Bridge Max Span Max Support Max Span Max Support Main Main Main Main Ast (mm 2 ) Above reinforcement is calculated for per meter length, and the area of steel is in mm2. Bar charts are prepared for the comparison purpose: Fig. 6: Comparison of Moments in Deck Slab All rights reserved by 101

5 Fig. 7: Comparison of Reinforcement in Deck Slab C. Design Moments in Girder: For comparison purpose of moments and reinforcements of both type bridge, the load cases for integral bridges are taken similar as bearing bridges, i.e. DL + LL. Moments and reinforcement are considered for only sagging case. Table 4 Design Moments in Girder Integral Bearing % decrease 1 Span Span Span D. Reinforcement Comparison: Table 5 Reinforcement Comparison Integral Bearing % decrease 1 Span Span Span Fig. 8: Comparison of Bearing and Integral Bridge Sagging Moment All rights reserved by 102

6 Fig. 9: Comparison of Reinforcement in Bearing and Integral Bridge E. Design Moments for Internal Diaphragm: Table 6 Design Moments for Internal Diaphragm Integral Bearing % decrease Sagging Hogging Sagging Hogging Sagging Hogging 1 Span Span Span F. Reinforcement Comparison for Internal Diaphragm: Table 7 Reinforcement Comparison for Internal Diaphragm Integral Bearing % Decrease 1 Span Span Span Fig. 10: Comparison of Sagging Moment All rights reserved by 103

7 Fig. 11: Comparison of Hogging Moment Fig. 12: Comparison of Reinforcement in Diaphragm V. CONCLUSION 1) Comparing moments in deck slab, it can be observed in this case that the span moment (Sagging) is 40.6%, while support moment (Hogging) is 26.16% lesser in integral bridges compared to bearing bridges. 2) Corresponding to these moments the calculated reinforcements are also lesser compared to bearing bridges. 3) Comparison in girders are made only for sagging moments and it can be seen that there is 25.09%, 31.06% and 31.66% decrease in moments value, for one span two span and three span integral bridge compared to one span, two span and three span bearing bridges, respectively. 4) However, it can be concluded that as the number of span increases the rate of reduction in sagging moments also reduces in integral bridges compared to bearing bridges. 5) In case of internal diaphragm, it can be said that, for this case the sagging moment is found to be almost similar in one span, two span and three span integral bridges. However, hogging moment is found to be decreasing compared to bearing bridge diaphragm, with the increase in number of span. REFERENCES [1] IRC:6-2014, Standard specifications and code of practice for road bridges, section-ii loads and stresses (revised edition) [2] IRC: , Standard specifications and code of practice for road bridges, section-iii Cement Concrete (Plain and Reinforced) (third edition) [3] IRC: , Standard specifications and code of practice for road bridges, section-vii- Foundations and Substructures (Revised Edition) [4] BA: 42/96, Amendment No 1 Design of Integral Bridges [5] Semih Erhan, Murat Dicleli (2014), Comparative assessment of the seismic performance of integral and conventional bridges with respect to the differences at the abutments, Bull Earthquake Eng, All rights reserved by 104

8 [6] Shaikh Tausif, L. G. Kalurkar (2014), Behaviour of Integral Abutment Bridge with spring Analysis, Proceedings of 07th IRF International Conference, Bengaluru. [7] Zhihui Zhu, Michael T. Davidson, Issam E. Harik, Liecheng Sun, Kevin Sandefur (2014), Effect of Superstructure Temperature Changes on Intermediate Pier Foundation Stresses in Integral Abutment Bridges, ASCE. [8] WooSeok Kim, Jeffrey A. Laman (2010), Integral abutment bridge response under thermal loading, Engineering Structures. [9] Leo E. Rodriguez, Paul J. Barr, Marv W. Halling (2014), Temperature effects on a box girder integral abutment bridge, ASCE. [10] Surana C. S., Grillage Analogy, Narosa publishing house, New Delhi. [11] Hambly E. C., Bridge Deck Behaviour, Second Edition, E & FN Spon. [12] B. A. Nicholson, Integral Abutment for Pre-stressed Beam Bridges, Uniskull Ltd., Leicester. [13] H. J. Shah, Reinforced Concrete Vol-1, tenth edition, charotar publication house, Anand. All rights reserved by 105