Parametric Study On Underpass RCC Bridge With Soil Structure Interaction

Parametric Study On Underpass RCC Bridge With Soil Structure Interaction

Vinayak Demane 1and Prof. Swapnil Cholekar 2

1-Post Graduate Student, Department of Civil Engineering, KLEMSSCET, Belgaum,

Karnataka, India, 590008

2- Professor, Department of Civil Engineering, KLEMSSCET, Belgaum, Karnataka, India, 590008

Abstract

The bridges are structure, which provides means of communication over a gap. Bridges provided passage for vehicular or other type of traffic. The Underpass RCC Bridge is very rarely adopted in bridge construction but recently the Underpass RCC Bridge is being used for traffic movement. Hence constructing Underpass Bridge is a better option where there is a constraint of space or land.

The model is analyzed for bending moment, shear force and axial thrust for different loading combinations as per IRC: 6-2010 standards. As the box structure directly rests on soil and also soil pressure acts at the side walls. It is important to study the soil structure interaction of such structure. To study the response of structure with rigid supports, with soil structure interaction applied to base only and with soil structure interaction applied to base and side walls of the structure and comparing the results.

1. Introduction

   The Underpass RCC Bridge is adopted in bridge construction and used for traffic movement and control. Since the availability of land in the city is less, such type of bridge utilizes less space for its construction. Hence constructing Underpass Bridge is a better option where there is a constraint of space or land. The RCC Bridge consists of two horizontal and two vertical slabs. These are economical due to their rigidity and monolithic action. Separate foundations are not required, since the bottom slab resting directly on the soil, serves as raft slab. The barrel of the underpass should be of sufficient length to accommodate the carriageway and kerbs.

   For a Underpass bridge, the top slab is required to withstand dead loads, live loads from moving traffic, earth pressure on sidewalls and pressure on the bottom slab besides self weight of the slab.

2. Details of the Structure

   1. Modelling and Analysis

      For the present study Two-dimensional cross sectional model is considered for the analysis. The analysis is carried out in STAAD.Pro V8i software. For the cross section model two-dimensional cross section of unit width is taken center-to-center distance between vertical members is taken as effective span for the horizontal members. For this model three types of foundation conditions are taken for the study:

      Case A: Rigid frame with manually calculated upward pressure

      Case B: Bottom slab resting on uniformly spaced springs with stiffness equal to modulus of subgrade reaction of soil.

      Case C: Bottom slab and Sidewalls resting on uniformly spaced springs with stiffness equal to modulus of subgrade reaction of soil.

   2. Assumptions

      In the proposed study, the single cell box structure of span 5.6m and length 24.3m subjected to vehicle loading, dead load, lateral earth pressure and pedestrian load was taken for the proposed study.

   3. Geometric Properties

      . Overall width of bridge = 24.30m

      . Thickness of the top slab = 0.500m

      . Thickness of the bottom slab = 0.500m

      . Thickness of the vertical wall = 0.500m

      . Thickness of wearing coat = 0.081m

      . Effective horizontal span for Bridge =5.1+ 0.5 = 5.6m

      . Effective vertical span =2.9+0.5 = 3.4m

      Live load is calculated manually and it is found that class AA wheel load is maximum compared to other class loading as per IRC: 21-2000.

   4. Idealization of the Structure

      CASE A: – For this case the structure is idealized as shown in the figure 1. In this case the following types of

      supports are provided below the vertical members. At the nodes 1, 2 supports are pinned.

      CASE B: – In this case the nodes are at equal spacing i.e. 0.56m in the bottom slab and spring supports having modulus of sub-grade reaction as stiffness are given at each node. The parametric study is carried out for different values of sub-grade modulus in the practical range named Ks = (5000, 10000, 20000, 30000, 50000,

      70000) kN/m2/m.

      CASE C: – In this case the nodes are at equal spacing i.e. of 0.56m in the bottom slab and side walls and spring supports having modulus of sub-grade reaction as stiffness are given at each node. The parametric study is carried out for different values of sub-grade

      modulus in the practical range named Ks = (5000, 10000, 20000, 30000, 50000, 70000)kN/m2/m.

3. Parametric Study

The Underpass Bridge has been analyzed for its self- weight superimposed dead load (due to wearing coat), live load (IRC Class AA Wheeled Vehicle) and earth pressure on sidewalls. The following loads to be considered for the analysis:

1. Dead Load

2. Live Load

3. Concentrated loads

4. Uniform distributed load

5. Weight of side walls

6. Earth pressure on vertical side walls

7. Uniform lateral load on side walls

The following load combinations are considered for the analysis:

1. Dead Load + Live Load + Earth Pressure (Dry Condition) + Pedestrian Load + Base Pressure + Surcharge.

2. Dead Load + Live Load + Earth Pressure (Dry Condition) + Base Pressure + Surcharge.

3. Dead Load + Earth Pressure (Dry Condition) + Base Pressure + Surcharge.

4. Dead Load + Live Load + Earth Pressure (Submerged)

   + Base Pressure + Surcharge.

5. Dead Load + Live Load + Earth Pressure (Submerged)

   + Pedestrian Load + Base Pressure + Surcharge.

6. Dead Load + Earth Pressure (Submerged) + Base Pressure + Surcharge.

   The above analysis is carried out for following support cases:

   Case 1: Rigid supports with uniform soil pressure beneath the bottom slab.

   Case 2: Spring supports at base with different sub-grade modulus

   Case 3: Springs supports at Base as well as side walls for different sub-grade modular

   i.e.

   a. Ks = 5000 kN/m2/m. b. Ks = 10000 kN/m2/m. c. Ks = 30000 kN/m2/m. d. Ks = 50000 kN/m2/m. e. Ks = 70000 kN/m2/m.

   1. Results and Discussions

      From the soil structure interaction studies, it is seen that structure analyzed with rigid supports give erroneous results as compared to soil structure interaction at base and at base and side walls. Therefore neglecting soil structure interaction is not feasible. It has been seen that shear force and bending moments values lower With Soil Structure Interaction Base and side wall.

      Table 4.1 Results for Load case 1 at Base Spring only

      Fig. 4.1 Variation of Load case 1 at Base Spring only

      Table 4.2 Results for Load case 1 at Base and Side Wall Springs only

      Fig. 4.2 Variation of Load case 1 at Base and Side Wall Spring only

      Table 4.3 Results for Load case 2 at Base Springs only

      Fig. 4.3 Variation of Load case 2 at Base Spring only

      Table 4.4 Results for Load case 2 at Base and Side Wall Springs only

      only

      Fig. 4.4 Variation of Load case 2 at Base and Side Wall Spring only

      Table 4.5 Results for Load case 3 at Base Springs only

      Fig. 4.5 Variation of Load case 3 at Base Spring only

      Table 4.6 Results for Load case 3 at Base and Side Wall Springs

      only

      Fig. 4.6 Variation of Load case 3 at Base and Side Wall Spring

      Table 4.7 Results for Load case 4 at Base Springs only

      Table 4.8 Results for Load case 4 at Base and Side Wall Springs only

      Fig. 4.7 Variation of Load case 4 at Base Spring only

      Fig. 4.8 Variation of Load case 4 at Base and Side Wall Springs only

      Table 4.9 Results for Load case 5 at Base Springs only

      Fig. 4.9 Variation of Load case 5 at Base Spring only

      Table 4.10 Results for Load case 5 at Base and Side Wall Springs only

      Fig. 4.10 Variation of Load case 5 at Base and Side Wall Springs only

      Table 4.11 Results for Load case 6 at Base Springs only

      Fig. 4.11 Variation of Load case 6 at Base Spring only

      Table 4.12 Results for Load case 6 at Base and Side Wall Springs only

      Fig. 4.12 Variation of Load case 6 at Base and Side Wall Springs only

      1. THOMAS C. SANDFORD Soil-Structure Interaction of Buried StructuresA2K04: Committee on Subsurface Soil-Structure Interaction

      2. D,Johnson Victor, Essential of Bridge Engineering (1991), Oxford & IBH publishing Pvt. Ltd. New Delhi.

      3. N. Krishna Raju, Design of Bridges (2009), Oxford & IBH publishing Pvt. Ltd. New Delhi.

      4. IRC: 21:2000, Standard Specifications And Code Of Practice Road Bridges The Indian Road Congress.

      5. IS 456:2000, Plain and Reinforced concrete code for practice Bureau of Indian Standards.

   2. Conclusions

1. The bottom slab shear force, corner bending moment and mid span bending moment values decreases about 50%, 60%, 40% from rigid support condition to soil structure interaction respectively at base only.

2. The top slab shear force is similar in both cases and corner bending moment is increases and mid span bending moment values decreases about 5% to 10% from Rigid support condition to soil structure interaction at base only.

3. The side wall shear force, corner bending moment and mid span bending moment values decreases about 30%, 40%, 50% from rigid support condition to soil structure interaction respectively at base only.

4. The bottom slab shear force, corner bending moment and mid span bending moment values decreases with increase in stiffness of soil for all the load conditions at base and side walls.

5. The top slab shear force is similar in both cases and corner bending moment is increases and mid span bending moment values decreases about 20% to 30% from rigid support condition to soil structure interaction at base and side walls.

6. The side wall shear force is increase about 10% to 15% and corner bending moment and mid span bending moment values decreases with increase in stiffness of soil at base and side walls.

6. References

1. Mohankar.R.H , Ronghe.G.N, Analysis and Design of Underpass RCC Bridge International Journal Of Civil And Structural Engineering Volume 1, No 3, 2010

2. Mohankar R. H., Pidurkar M. D., Patil P.R. Analysis Of Underpass RCC Bridge International Journal of Engineering Research & Technology (IJERT) Vol. 1 Issue10, December- 2012 ISSN: 2278-0181