Analysis and Design of Underpass RCC Bridge.pdf

INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 1, No 3, 2010

© Copyright 2010 All rights reserved Integrated Publishing services Research article ISSN 0976 – 4399

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Analysis and Design of Underpass RCC Bridge Mohankar.R.H 1 , Ronghe.G.N 2

1 Lecturer, Civil Engineering Dept., G.H Raisoni College of Engineering, Nagpur, India. 2 Professor, Applied Mechanics Dept., Visvesvaraya National Institute of Technology,

Nagpur, India [email protected]

ABSTRACT

The Underpass RCC Bridge is very rarely adopted in bridge construction but recently the Underpass RCC Bridge is being used for traffic movement. In this paper, the analysis of the underpass RCC bridge is carried out. The analysis of this underpass RCC bridge is done by considering fixed end condition. Finite Element Method (FEM) analysis is performed and results are presented. Comparison of different forces between 2D and 3D models for fixed end condition is provided. In this study we show a 2D model can be effectively used for analysis purpose for all the loading condition mentioned in IRC: 6, “Standard Specifications and Code of Practice Road Bridges” The Indian Roads Congress and Directorate of bridges & structures (2004), “Code of practice for the design of substructures and foundations of bridges” Indian Railway Standard.

Keywords: RCC Underpass bridge, FEM analysis.

1. Introduction

The Underpass RCC Bridge is very rarely adopted in bridge construction but recently the Underpass RCC Bridge is being used for traffic movement. This underpass RCC bridge is pushed inside the embankment by means of hydraulic jack system 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. Detailed analysis and design of underpass RCC bridge has not been carried out till date. Ronghe G. N. and Gatfane Y. M (20042005) have worked on the analysis and design of 2D underpass RCC bridge model. In this paper 2D along with 3D analysis of underpass RCC bridge is carried out considering six different loading conditions and eight different loading combinations which are considering from IRC: 62000, “Standard Specifications And Code Of Practice Road Bridges” The Indian Roads Congress and Directorate of bridges & structures (2004), “Code of practice for the design of substructures and foundations of bridges” Indian Railway Standard. The end condition is considered to be fixed for both 2D and 3D underpass RCC bridge model.

1.1 Modeling of system

For the study of Underpass RCC bridge, earth pressure acting on side walls of underpass RCC bridge because structure embedded as well as vertical loading due to imposed load



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and live load from Bridge rules, “Rules specifying the loads for designing the super structure and substructure of bridges and for assessing the strength of existing bridges” (Indian Railway Standard code) on the top of underpass RCC bridge is considered. As there is a top loading, there is reaction at bottom also. This underpass RCC bridge is provided for city traffic also. For that purpose live load from IRC: 62000 inside the underpass RCC bridge is considered.

Figure 1: 2D Model of RCC Underpass Bridge

2D underpass RCC bridge model shown in Figure 1 is analyzed considering without soil structure interaction.

Figure 2: 3D Model of RCC Underpass Bridge 3D underpass RCC bridge model shown in figure 2 is analyzed considering without soil structure interaction.

Vertical

Earth Pressure due to backfill

Earth Pressure due to backfill

Reaction at bottom



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2. Formulation

2.1 Loads on the top of slab

Total load for bending moment and shear force is considered from IRS code rules specifying the loads for designing the superstructure and substructure of bridges and for assessing the strength of existing bridges. For span of 8m total load for bending moment 981kN and total load for shear force is 1154kN is considered. Dead load of earth fill over the box = Area x depth x density 1.1 Total vertical pressure on top slab = Imposed load + Dead load + Live load 1.2

2.2 Loads on sidewalls

The coefficient of active earth pressure of the soil is given by the equation ( )

( ) ( ) ( ) ( ) ( )

2

2

2

cos cos sin sin 1 cos cos

cos

− − − − − +

+ × + ×

− =

i i

Ka

α δ α φ δ φ δ α α

α φ

1.3 where, γ = Density of soil, ф = Angle of internal friction,δ = angle of friction between wall and earth fill Where value of δ is not determined by actual tests, the following values may be assumed. (i) δ = 1/3 ø for concrete structures. (ii) δ = 2/3 ø for masonry structures. i = Angle which the earth surface makes with the horizontal behind the earth retaining structure ( i =0 0 for embedded structure). Since this concrete structure is embedded in soil, the value of δ is considered as 1/3 ø (for concrete structures) considered for calculation of coefficient of active earth pressure of the soil.

2.3 Earth pressure acting on the sidewalls:

2.3. a) Earth pressure due to backfill

Earth pressure center of top slab = H Ka × × γ 1.4 Earth pressure center of bottom slab = H Ka × × γ 1.5

2.3. b) Earth pressure due to dead load surcharge

Earth pressure acting on sidewalls: At Top = Imposed load of track + Earth pressure on the top of slab + Live load 1.6 AT Bottom = Horizontal effect of surcharge + Earth pressure center of bottom slab 1.7



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2.4 Reaction at the bottom of box

Self weight of box = Weight of top slab + Weight of bottom slab + Weight of side walls 1.8

Total reaction at bottom=Self weight of box +Weight of imposed load +Weight of live load 1.9

The boundary condition considered is fixed.

3. Analysis of 2D underpass RCC bridge model

A 2D underpass RCC bridge (Figure 1) is modeled considering 1m length for the following details shown below. Box dimensions: 1mx7.5mx4.1m (LxWxH) (Center to center). In addition to the dimensions mentioned in Figure 3, following parameters are considered for the 2D analysis. Keeping all the parameters same, the analysis is carried out using two methods viz. conventional slope deflection method (manual calculations) and other by using SAP2000 (programming software). The manually calculated values for the bending moment at corner A is 205kNm and corner C is 302kNm for dead load case. For the same corners A & C, the SAP results are found to be 203kNm and 298kN m respectively.

(a) (b)

Figure 3: (a) Center to center Dimensions of RCC Underpass Bridge (b) Dimensions of RCC Underpass Bridge

Dimensions of underpass RCC bridge Clear horizontal opening 7 m Clear vertical opening 3.5 m Slab thickness 0.6 m Wall thickness 0.5 m Outer to outer horizontal width 8 m Outer to outer vertical height 4.7 m Length underpass RCC bridge 1 m Angle of internal friction (ф) 25 o Density of soil (γ) 19 kN/m 3 Grade of concrete M40

7.5m

4.1

A B

C D

8 m

3.5 m

0.6 m

0. 6

7 m 0. 5

0.5 m

4.7



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Grade of steel Fe415 The max BM and SF obtained for 2D underpass RCC bridge model considering without soil stiffness are shown in Table 1. Shear force and bending moment diagram after analysis is shown in Figure 4 (a) & (b)

(a) (b)

Figure 4: (a) SF diagram for 2D Analysis (b) BMD For 2D Analysis

3.1 Validation of results

The bending moment results obtained by slope deflection method and SAP2000 program for 2 dimensional model of underpass RCC bridge are approximately same. The slight variation of results may be due to the variation of moment of inertia values. Based on this validity of results further analysis of same 2D model for various combinations of loading cases was carried out. Also it was observed that was the same corners of the 3D model the bending moment results obtained were same and hence 3D analysis was carried out using SAP2000.

Table 1: Max BM and Max SF of 2D

Member Results Max BM & Max SF of 2D model without soil stiffness (kNm)

Max SF 456.33 BM Mid Span 572.72 Top

Slab BM Corner 339.94 Max SF 259.92 BM Mid Span 372.73 Bottom

Slab BM Corner 147.11 Max SF 79.68 BM Mid Span 204.67 Side

Walls BM Corner 339.94



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3.2 Analysis of 3D underpass RCC bridge model A 3D underpass RCC bridge is modeled considering total length 13m with details shown above and there is no change in details except length. Box dimensions: 13mx7.5mx4.1m (LxWxH) (Center to center).The max BM and SF obtained for 3D underpass RCC bridge model considering without soil stiffness are shown in Table 2.

Table 2: Max BM and Max SF of 3D

Member Results Max BM & Max SF of 3D model without soil stiffness(kNm)

Max SF 458.85 BM Mid Span 530.49 Top Slab BM Corner 413.63 Max SF 282.49 BM Mid Span 377.87 Bottom

Slab BM Corner 154.14 Max SF 78.93 BM Mid Span 220.74 Side

Walls BM Corner 413.63

4. Comparison of Result of 2d & 3d Underpass Rcc Bridge Model The comparison of the maximum bending moment and shear force values obtained for 2D and 3D underpass RCC bridge models which are considered without soil stiffness are compared. The comparison between these two results (Table 3) shows that the values of bending moment and shear force for 2D and 3D model for all loading cases considered for the analysis purpose from IRC: 62000, “Standard Specifications and Code of Practice Road Bridges” The Indian Roads Congress and combinations, are approximately same.

Table 3: Comparison of Max BM and Max SF of 2D model and 3D model of the box

Comparison of Max BM of 2D & 3D model without soil stiffness

Member Results Max BM of 2D

model without soil stiffness (kNm)

Max BM of 3D model without soil stiffness (kNm)

% Difference

Max SF 456.33 458.85 0.55 BM Mid Span 572.72 530.49 7.96 Top Slab BM Corner 339.94 413.63 17.82



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Max SF 259.92 282.49 7.99 BM Mid Span 372.73 377.87 1.36 Bottom

Slab BM Corner 147.11 154.14 4.56 Max SF 79.68 78.93 0.95 BM Mid Span 204.67 220.74 7.28 Side

Walls BM Corner 339.94 413.63 17.82

5. Conclusions From the analysis it can be observed that bending moment and shear force obtained for 2D and 3D model are approximately same. A 2D model can be effectively used for analysis purpose for all the loading condition mentioned in IRC: 6 and Directorate of bridges & structures (2004),“Code of practice for the design of substructures and foundations of bridges” Indian Railway Standard. Further research is needed to verify the use of 2D model for different parameters such as dynamic analysis, soil structure interaction etc.

6. REFERENCES 1. Ronghe G.N. And Gatfane Y.M. "Analysis And Design Of A Bridge By A Push Back System.” A Dissertation of M.tech In structural Engineering. 20042005.

2. Directorate of bridges & structures (2004), “Code of practice for the design of substructures and foundations of bridges” Indian Railway Standard.

3. IRC: 212000, “Standard Specifications And Code Of Practice Road Bridges” The Indian Road Congress.

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

5. IRC: 62000, “Standard Specifications And Code Of Practice Road Bridges” The Indian Road Congress.

6. IRC: 82000, “Design criteria for prestressed concrete road bridges (PostTension concrete)” The Indian Roads Congress.

Analysis and Design of Underpass RCC Bridge.pdf

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