SAFETY AUDIT OF FOUR RAILWAY BRIDGES IN MADURAI …

SAFETY AUDIT OF FOUR RAILWAY BRIDGES IN

MADURAI DIVISION OF SOUTHERN RAILWAY

A Report on

FIELD INSPECTION AND STRUCTURAL DESIGN CHECK OF

1613C FOOT OVER BRIDGE, AT KOVILPATTI STATION

for

MADURAI DIVISION

SOUTHERN RAILWAY

by

DEPARTMENT OF CIVIL ENGINEERING

INDIAN INSTITUTE OF TECHNOLOGY MADRAS

CHENNAI – 600 036

I

CONTENTS

LIST OF FIGURES ............................................................................................................ I

LIST OF TABLES ............................................................................................................. I

EXECUTIVE SUMMARY ............................................................................................... II

1 INTRODUCTION .............................................................................................................. 1

1.1 GENERAL APPROACH ........................................................................................ 3

1.2 SCOPE ..................................................................................................................... 3

1.3 CONDITION ASSESSMENT ................................................................................ 4

1.4 METHODOLOGY .................................................................................................. 4

2 FIELD INSPECTION ........................................................................................................ 4

3 STRUCTURAL DESIGN CHECK.................................................................................... 6

3.1 CONCLUSIONSFROM THE DESIGN CHECK ................................................. 10

4 FINDINGS AND RECOMMENDATIONS .................................................................... 11

5 FURTHER TESTING REQUIREMENTS ...................................................................... 11

REFERENCES: ....................................................................................................................... 12

APPENDIX - A........................................................................................................................... i

LIST OF FIGURES

Figure 1 Photograph of FOB 1613C at Kovilpatti station. ....................................................... 1

Figure 2 Top view plan of FOB 1613C ..................................................................................... 2

Figure 3 Photograph of elevation of stairway for FOB 1613C .................................................. 3

Figure 4 Representational line diagram for FOB 1613C ........................................................... 5

LIST OF TABLES

Table 1 Field inspection observations....................................................................................... 5

II

EXECUTIVE SUMMARY

IIT Madras along with EPMCR is assessing the condition of existing bridges in Madurai

Division as third party consultant for Southern Railway. IITM has agreed to execute the

safety auditing of the bridges in two stages:

Stage I – Preliminary condition assessment by field inspection and structural design

check.

Stage II – Advanced condition assessment by sample collection and testing,

instrumentation, and detailed design checks.

This report consists of the Stage 1 assessment of 1613C Foot Over Bridge (FOB) at

Kovilpatti station. The FOB 1613C has a single span structure with 20.4m gangway length

and stairway landing length of 2.4m. In this report, the findings from the field inspection

(walk through only) and the structural design checks are presented. During the field

inspection, members of stairway, gangway, stanchion, and precast deck were assessed. The

structural safety of foundation could not be assessed due to lack of drawings and the

geotechnical data. The general observations on most of the elements are related to lateral

deflection of bottom chord, peeling of paint, wrong erection methodology, and missing

connections.

Working stress method was used for the structural design checks, with minimum yield

strength of steel assumed as 26kg/mm2, as per IRS: Steel Bridge Code(RDSO 2003). The

effective live load on foot over bridge has been considered as per IRS Bridge Rule: Foot over

bridges and footpaths (RDSO 2014). Detailed drawings are not available and standard

reference drawings used in railway design has been adopted for design checks. For the given

sections as per drawings, with the loading condition specified in bridge rule, without

accounting for any possible defects, the structure satisfies safety and stability conditions

according to IRS: Steel Bridge Code(RDSO 2003). Recommendations for rectifying the

defects on the bridge are given.

1

1 INTRODUCTION

Figure 1 shows the photograph of the foot over bridge 1613C at Kovilpatti station. The FOB

is a IRS type truss structure, constructed in year 2002. The FOB gangway has a span length

of 20.4m and width of 2.5m. The stairway landing length and width are 2.54 m and 2.54m

respectively. Figures 2 shows plan view of the FOB. Figure 3 shows the photograph of

elevation of the FOB stairway. The height of bridge from rail top of railway line at ground

level to bottom of gangway is 6.355m. The structural system consists of stanchions, gangway

top chord and bottom chord, precast deck and stairway. The foundation details of the FOB

are unavailable in the given drawings. The superstructure is IRS type portal rigid frame

structure where the main beams are spliced to the columns.

Figure 1 Photograph of FOB 1613C at Kovilpatti station.

2

Figure 2 Top view plan of FOB 1613C

3

Figure 3 Photograph of elevation of stairway for FOB 1613C

1.1 GENERAL APPROACH

The general approach followed in the project is as follows:

• The current condition of the bridge is assessed with available data. All the

uncertainties considered and assumptions made involved are stated.

• Suggestions for repair are made, if required.

1.2 SCOPE

Stage I covers the following scope:

i. Detailed inspection, checking of physical condition, collection of necessary

data for analyzing;

ii. Checking of adequacy of bridges to carry present day loading condition.

iii. Submission of detailed report on current state with replacement/rehabilitation

strategy and design details.

4

1.3 CONDITION ASSESSMENT

The condition assessment is defined as the process, where a set of indicators are obtained

from the results of a field inspection of an existing structure, which are used to develop a

definition or to arrive at a calculation of the so-called condition state. The condition state

indicates the state of conservation of the structure.

1.4 METHODOLOGY

The assessment started with the review of the available documents, followed by the field

inspection of the bridge. The data acquired from the field inspection was analyzed and a

condition state was provided for different elements of the bridge. The structural design check

was done to assess the load carrying capacity of the bridge and the report is drafted with the

necessary findings and recommendations. The methodology was executed in the following

sequence:

• Review of the bridge information sheet and available drawings;

• Field inspection of the bridge to identify any physical deterioration, structural damage

and the surrounding environment;

• Analysis of the data from the field inspection to assign a ‘condition state’ for different

elements;

• Detailed checking of structural design. Design parameters are verified to be within

limits given in IS codes under the current loading conditions; and

• Drafting a report with all the details, findings and recommendations.

2 FIELD INSPECTION

The bridge was inspected to assess its current conditions, which are expressed as Structural,

Non-Structural and Preventive Maintenance condition states. “Structural” means that the

defect has an implication on structural safety and stability and may need detailed analysis

with the recommendation for repair. “Non-Structural” means that there is no structural

5

implication on stability and safety, but it may lead to deterioration; this shall be addressed

with minimal repairs. “Preventive maintenance” requires routine maintenance procedures to

be adopted to avoid further deterioration. The details of the field inspection are given in

Appendix - A. The details of the defects observed in different elements of the bridge are

given in decreasing order of extent of defect in Table 1, where C, TC, BC, SS, R, and D

represents column, top chord, bottom chord, stairway stringer, rafter anddeck slab

respectively as per figure 4. The detail of defects observed from the visual inspection on 05-

02-2020 are summarized below.

Figure 4 Representational line diagram for FOB 1613C

Table 1 Field inspection observations

Structural Elements

Count Components C2 TC C4 SS1 R BC D

Def

ects

Missing bolts ✓ ✓ ✓

3

Misalignment ✓ ✓ ✓ 3

Paint peeling ✓

1

Lateral deflection ✓

1

Corrosion ✓

1

6

The primary reason for the defects listed in Table 1 is assumed to be wrong erection

methodology of members.

Legend

C - Column

TC - Top chord

SS - Stairway stringer

R - Rafter

BC - Bottom chord

D - Deck slab

3 STRUCTURAL DESIGN CHECK

The detailed structural design check was done using working stress method and the summary

is given below. Live load is taken by referring to IRS Bridge rule. Bending moment and shear

forces are calculated for self-weight, super imposed dead load and live load. Stresses for

members have been calculated and compared with the permissible stresses in structural steel

referring to IRS Steel Bridge code Table II. Analysis have been done for the members by

taking the live load as well as the dead load. Members of foot over bridge are checked for

axial (compressive or tensile), bending and shear stresses.

Basic Assumptions

1. The basic geometry is taken from the general drawings submitted by Southern Railways-

Madurai Division (Drawing No. BE 1125 / 79; BE 1134 / 79; CBE/SK/511/2002; FOOT

OVER BRIDGE-CVP No-1613 C (1 x 20.93m) IRS TYPE)

2. The minimum yield strength of the Structural Steel is taken as *26kg/mm2

3. Percentage deductions of area of bolts are assumed to be 15%.

4. For vertical member, a simplified conservative model is used instead of 3D model to

calculate the forces in this member. It is assumed that the wind load on the roof between

two vertical members is entirely resisted by the reaction provided by these vertical

members. It is assumed that the member bends like a cantilever to resist the horizontal

component of the wind load acting at the top of the member.

7

Inputs

Effective Span = 20.40 m

No. of panels = 12 Nos.

Length of each panel = 1.70 m

Width of walkway = 2.534 m

Panel size = 1.70 m x 2.70 m

Roof panel = 2.00 m x 1.30 m

Sloped length of roof = 1.30 m

Load calculations

Self-weight of RCC Slab (Gangway)

Density of Concrete = 25 kN/m2

Thickness of Gangway/ Stairway slab

(Ref. Dwg. 1134/79 GENL)

= 0.10 m

Adding 5% Extra for Hand rails and other misc.

Floor Load = 2.63 kN/m2

Live Load on gangway = 4.80 kN/m2

Wind load from roof

Wind Load (IRS Bridge Rule) = 0.74 kN/m2

Load combinations

DL+LL combinations have been taken.

Permissible stress limitations

IRS Steel bridge Code, Table II - Basic permissible stresses in structural steel

Axial Compressive or Tensile stress = 151 N/mm2

Bending Compressive or Tensile stress = 167 N/mm2

Truss analysis for gangway

Load per meter on one horizontal member = 9.41 kN/m

Load at supports on walkway = 16 kN

Reaction at supports (DL + WL case) = 90.96 kN

Reaction at supports (DL + LL case) = 109.8 kN

Maximum Forces are extracted from the truss analysis by method of joints

8

Maximum load in different members

Member Unit DL+WL DL+LL

Top chord = kN 177 Comp. 212 Comp.

Diagonal member = kN 108 Comp. 128 Comp.

Diagonal member = kN 81 Tens. 97 Tens.

Bottom chord = kN 172 Tens. 207 Tens.

Vertical member = kN 24 Tens. 24 Tens.

Vertical member = kN 2 Comp.

Check for top chord of gangway

(a) Check for compression

Maximum forces under normal loads = 212 kN

Load carrying capacity = 241 kN

Maximum force under normal loads is within total load carrying capacity

Check for Bottom chord of gangway

(a) Check for tension


Area required = 1367 mm2

Net area of section provided = 1935 mm2

Area of section provided is sufficient to carry the maximum force in the member

Check for Diagonal members of Gangway

(a) Check for Compression




(b) Check for Tension


9




Check for vertical members of Gangway

(a) Check for compression




(b) Check for bending

Permissible bending stress = 167 N/mm2

Actual compressive bending stress = 151 N/mm2

Actual tensile bending stress = 128 N/mm2

Stresses under normal loads are within permissible limits

(c) Check for Tension





Check for purlin

Section modulus Z required = 1010 mm3

Section modulus Z provided = 1900 mm3

Section provided is sufficient to carry the wind load

Stability check on column

Allowable stress = 40 N/mm2

Actual direct compressive stress = 17 N/mm2

Stresses under normal loads are within permissible limits

10

3.1 CONCLUSIONS FROM THE DESIGN CHECK

With the loading conditions according to Bridge rules (Rules specifying the loads for design

of super structure and sub structure of bridges and assessment of the strength of the existing

bridges) without accounting for any defects & erection methodology, the structure satisfies

safety and stability conditions.

11

4 FINDINGS AND RECOMMENDATIONS

The findings and recommendations from the field inspection and structural design check are

given as follows:

i. Major lateral deflection of bottom chord members has been observed. This is due to

erection and loading of FOB without top chord bracings, which were erected at a later

stage. The effect of the lateral deflection on the structural behavior needs to be

investigated by taking measurements under controlled conditions. Strain, vibrations

and deflections need to be measured for an accurate evaluation of the performance of

the structure. Only then it can be ascertained whether the bridge is safe for public use

or there is a need to dismantle the bridge and re-construct it.

ii. There are defects in few members due to poor erection methodology, which should be

disassembled and re-erected during maintenance schedule.

iii. The assumptions made in the design due to non-availability of data need to be

verified.

The following aspects have not been considered in the present study:

• The structural safety of foundation could not be assessed due to lack of drawings and

the geotechnical data.

5 FURTHER TESTING REQUIREMENTS

Though lateral deflection was observed, the extent of deflection cannot be ascertained by

visual inspection alone. Hence detailed instrumentation and measurements are recommended

in stage-II for this bridge. Strain, vibrations and deflections need to be measured under

controlled loading condition.

12

REFERENCES:

RDSO. (2003). Indian railway standard code of practice for the design of steel or wrought

iron bridges carrying rail, road or pedestrian traffic (Steel Bridge Code). Research

design and standards organisation (RDSO), Lucknow, India, 78.

RDSO. (2014). Rules specifying the loads for design of super-structure and sub-structure of

bridges and for assessment of the existing bridges. Research design and standards

organisation (RDSO), 102.

IRS Bridge Rule. Rules specifying the loads for design of super structure and sub structure of

bridges and for assessment of the strength of existing bridges. Research design and

standards organization (RDSO).

IS: 432(part 2) – 1982: Specification for mild steel and medium tensile steel bars and hard-

drawn steel wire for concrete reinforcement.

i

APPENDIX - A

Name of the bridge: 1613C Foot over bridge

Location of the bridge: Kovilpatti railway station, Madurai

Inspection date and time: 05-02-2020; 02:40 PM

Classification of condition state:

Condition state Description

Structural The defect has an implication on structural safety and stability

and may need detailed analysis with the recommendation for

repair

Non – Structural The defect has no structural implication on stability and safety,

but it may lead to deterioration; this shall be addressed with

minimal repairs

Preventive Maintenance The defect requires routine maintenance procedures to be

adopted to avoid further deterioration

ii

IMAGE NO. 1

BRIDGE ID 1613C

SPAN NO 1

COMPONENT Column

COMPONENT ID C2

DEFECT Missing bolts

OBSERVATION

Bolt missing in

column – rafter

connection

CONDITION STATE Non-structural

IMAGE NO. 2

BRIDGE ID 1613C

SPAN NO 1

COMPONENT Top chord

COMPONENT ID TC

DEFECT Missing bolts

OBSERVATION Bolts missing in top

chord gusset plate

CONDITION

STATE Non-structural

IMAGE NO. 3

BRIDGE ID 1613C

SPAN NO 1

COMPONENT Top chord

COMPONENT ID TC

DEFECT Peeling of paint

OBSERVATION

Peeling of paint in top

chord gusset plate

connection

CONDITION

STATE Preventive maintenance

iii

IMAGE NO. 4

BRIDGE ID 1613C

SPAN NO 1

COMPONENT Column

COMPONENT ID C4

DEFECT Missing bolt

OBSERVATION Bolt missing in column

bracing

CONDITION

STATE Preventive maintenance

IMAGE NO. 5

BRIDGE ID 1613C

SPAN NO 1

COMPONENT Stairway Stringer

COMPONENT ID SS1

DEFECT Bolt hole misalignment

OBSERVATION Bolt hole misaligned in

stringer beam

CONDITION


IMAGE NO. 6

BRIDGE ID 1613C

SPAN NO 1

COMPONENT Rafter

COMPONENT ID R

DEFECT Misalignment

OBSERVATION Misalignment of rafter-

purlin connection

CONDITION


C

o

iv

IMAGE NO. 7

BRIDGE ID 1613C

SPAN NO 1

COMPONENT Bottom chord

COMPONENT ID BC

DEFECT Lateral deflection

OBSERVATION Lateral deflection of

bottom chord member

CONDITION

STATE Structural

IMAGE NO. 8

BRIDGE ID 1613C

SPAN NO 1

COMPONENT Floor cross beam

COMPONENT ID D

DEFECT Corrosion

OBSERVATION

Corrosion observed in

floor beam and

connecting members

CONDITION


IMAGE NO. 9

BRIDGE ID 1613C

SPAN NO 1

COMPONENT Column

COMPONENT ID C4

DEFECT Misalignment

OBSERVATION

Misalignment of

vertical centerline

observed in column

bracings

CONDITION

STATE Non-Structural

Documents

SAFETY AUDIT OF FOUR RAILWAY BRIDGES IN MADURAI …