condition assessment and load rating of arched …

9th Austroads Bridge Conference, Sydney, New South Wales 2014

© ARRB Group Ltd and Authors 2014 1

CONDITION ASSESSMENT AND LOAD RATING OF ARCHED BAILEY BRIDGE Peng Yi , GHD Pty Ltd, Australia Gunvant Vaghela, GHD Pty Ltd, Australia Andrew Buckland, Defence Support and Reform Group, Australia

ABSTRACT The Bailey bridge system was originally invented for military usage during World War II. Since then, it has been the used to meet emergency or temporary bridge needs. It has also been widely used as a permanent solution for pedestrian and road bridge needs in remote locations.

Most Bailey bridges are through-type truss bridges. However, the bridge discussed in this paper is a unique two –pinned arch bridge spanning 55m across 15m deep valley. This may be the longest arched Bailey bridge in Australian. The bridge is currently in a military reserve and has not been in service for many years. No structural details or drawings are available of the bridge.

The paper herein presents the methodology adopted to access existing condition, find load carrying capacity and reinstate the bridge to service. The paper describes collection of historical data and used in the development of structure model and analysis of this complicated structure. It also discusses the “Rating Rules” to military standard. The bridge is load tested to ensure condition of the joints and capacity of hidden elements.

INTRODUCTION

An arch bailey bridge called “Engineers Bridge” in Holsworthy Range is 55m long crossing Punchbowl Creek is a double through single story configuration and a double single two-pinned arch. Design drawings for this bridge are not available. Based on the article ENGINEERS BRIDGE, this bridge was designed as Class 30 military load in accordance with the Military Load Classification (MLC).

Due to the corrosion on some steel components and the deterioration in the timber bridge decking, vehicle access has been prohibited on this bridge.

Figure 1: Bridge elevation

If the bridge is brought to service, it would provide access across the gully that would save over an hour traveling time for Range staffs that currently have to travel via a ring road.



Figure 2: Existing Bridge Condition

BAILEY BRIDGE HISTORY The Bailey bridge was invented by an English civil engineer Donald Coleman Bailey in1941, and it was initially designed for the British War Office. The Bailey bridge has several distinctive features. It is built by manpower alone. It is made entirely from prefabricated parts, the most notable of which are its light-steel panels linked by pinned joints. It is a through-type bridge and easy to move from one site to other. Donald Bailey was knighted in 1946 for his contribution to the Allied victory in World War II.

Figure 3: Bailey Bridge Assembly

There are three types Bailey Bridge around the world, which are M1, M2 &M3.

The M1 Bailey Bridge is the one that designed by Donald Bailey, and was used by the British War Office in World War II.



Figure 4: Type M1 cross section

At the outset of World War II, the United States (US) Army revised the design of M1 Bailey Bridge to provide a greater roadway width and designated it the M2 Bailey Bridge.


The British then modified the US version by further widening the bridge, thus producing the extra-wide M3 Bailey bridge.


STRUCTURAL LOAD RATING

Structural Load Determination Structural assessment is carried out to Military Load Classifications (MLC) and current AS4100, AS5100.2 & AS5100.7.

• Dead Load (DL) – Self weight of the steel bridge

• Superimposed Dead Loads (SDL) – Weight of the timber decking

• Live Load – MLC ‘Class 16’ and ‘Class 30’ T44 in accordance with AS5100.7,



Dead Loads

In accordance with AS5100.2 the following ‘dead’ loads (i.e. permanent loads) were applied to the bridge:

• Gself-weight: Calculated by the measured steel member sizes times the steel density

• Gsdl Calculated by the measured decking sizes times the timber density

Live Loads

The design vehicular loads used in the assessment consist of the following design vehicles:

T44 Truck Loading (Total mass on axle is 44 tonnes):

Class 30 – Tracked Vehicle – Military Load Classification

Class 30 – Wheeled Vehicle – Military Load Classification

Class 16 – Tracked Vehicle – Military Load Classification



Class 16 – Wheeled Vehicle – Military Load Classification

MLC Class 12 – Tracked Vehicle - Military Load Classification:

MLC Class 12 – Wheeled Vehicle - Military Load Classification

Figure 7: Live load configurations considered in assessment

Design Loading Combinations Military Load Classification and STANAG 2021 provide below details for safety factor and dynamic impact.

A safety factor appropriate to the bridge type and purpose must be included in the consideration when determining a bridge rating. The safety factor should reflect a high degree of confidence for the bridge under specific loading levels and frequencies and consider both the static and fatigue life characteristics of the bridge. Due to the fact each country has its own procedure and safety factors, no specific method will imposed.

Dynamic effect (sometimes called ’impact’), must be taken into account when establishing the bridge MLC rating. No rules for this impact factor are given, but it should conform to the standard practice of the nation for bridge and vehicle types expected to use the bridge.

Table 1: Load Factors

Load SLS

(Serviceability Limit State)

ULS

(Ultimate Limit State)

Dead Load 1.2 (1.0 in AS5100.2, increased to include the self-weights of the steel links and steel bolts )

1.5 (1.1 in AS5100.2, increased to include the self-weights of the steel links and steel bolts )

Superimposed Dead Load 1.3 2.0

T44 Truck Loading 1.0 2.0

MLC Class 30 1.0 1.5

MLC Class 16 1.0 1.5



Dynamic Load Allowance (DLA) adopted 0.4 for T44 Truck Load, MLC Class 16 & 30 loads.

Load Combinations

The following loading combinations were used in accordance with AS 5100.2 for the analysis of the bridge:

Ultimate Limit States:

• 1.5Gself-weight + 2.0Gsdl + 2.0Qlive x (1.0 + Dynamic Load Factor) T44 Truck Load

• 1.5Gself-weight + 2.0Gsdl + 1.5Qlive x (1.0 + Dynamic Load Factor) MLC Class 16 & 30 loads

Serviceability Limit States:

• 1.2Gself-weight + 1.3Gsdl + 1.0Qlive x (1.0 + Dynamic Load Factor)

Material Properties Bailey Bridge Manual (FM 5-277) suggests panels, end posts, transoms, and ramps are a low alloy, high-tensile steel. All other parts are carbon structural steel.

The material grades used for analysis are in accordance with BS15-1948 Structure Steel and BS548 – 1941 (War emergency standard) High Tensile Structural Steel for Bridge and General Building Purposes, and are assumed as follows:

• Mild Steel Yield Strength: fyield = 16 tons/sq.in = 247 MPa

• Mild Steel Ultimate Tensile Strength: f tensile = 28 tons/sq.in = 432 MPa

• High Tensile Steel Yield Strength: fyield = 21 tons/sq.in = 324 MPa

• High Tensile Steel Ultimate Tensile Strength: ftensile = 33 tons/sq.in = 455 MPa

Structural Modelling As no As-Built drawings were available for the assessment, the bridge was initially modelled in AutoCAD 2010 by using the geometries derived from the site measurements and the known standard Bailey Bridge Panel sizes, and then a 3-D AutoCAD model was imported to Microstran V8 for analysis. Microstran is a structural analysis and design program for 2D and 3D frames, trusses and beams. It is suitable for the analysis of steel beams, trusses and portal frames through to large high rise buildings, towers and bridges.

The analysis involved a comparison between design actions produced from the load cases and combinations set out above and the each member’s section capacity, and is summarised in Table 2: Summary of Engineers Bridge Rating.



Figure 8: Microstran 3D Model – Full Bridge

Figure 9: Bridge 3D Model

Discussion of Results

Difference in Design Factors and Criteria

Engineers Bridge is a Bailey bridge originally designed for military use, and the majority of this type of bridges is temporary structure. As such, the load factors would have been less from the civilian bridges.

The above can be summarised by stating that the original design ‘rules’ adopted are expected to be different to the current Australia Standards, and any conclusions made should not be interpreted as a reflection upon the original design.



Assumptions in the Modelling

Assumptions have been made in the computer modelling as below:

• All the bridge components have the same geometries, section properties and material properties, and the model input data are from the measurements of a typical panel on site.

• Bailey components are high tensile steel, and the steel yield strength 324 MPa was from British Standard BS-968 (1943) and adopted in assessment.

• Stress cycle is very low for this bridge, and no fatigue signs have been found in the site inspection. Fatigue hasn’t been considered in the assessment.

• Design lane is assumed for MLC Class 16 & Class 30 wheeled vehicles to be the vehicle width plus 600mm from centre of the wheel to the edge of the lane at each side.

• “As-existing” capacity has considered 15% section loss at panels, bracing frames, stringer, transoms and end posts. No section loss for the panel pin. (Ref to: 176219 - Condition Assessment)

• No earthquake & wind load has been considered in the rating analysis.

Results of the analysis

Table 2: Summary of Engineers Bridge Rating

Ultimate Limit-State Rating

Remarks

T44 Truck – As New 50 % Not Acceptable for T44 Truck Loading

Class 30 – As New 58 % Not Acceptable for Class 30 Loading

Class 16 – As New

Class 16 – As Existing

100 %

85 %

Acceptable for Class 16 Loading

Not Acceptable for Class 16 Loading

Downgraded to Class 12 or locally strengthened on some members in 5 locations for Class 16 usage.

Class 12 – As Existing 115% Acceptable for Class 12

Figure 10: Bridge Strengthening Locations for Class 16 Loading

LOAD TESTING

The load testing methodology is: applying testing loads on certain positions of the bridge deck, and getting the deflection changes at those positions. Then compare those deflection changes measured from site to the values from the computer modelling.



Load testing of the bridge was carried out by a specialised survey company on 26th June 2012. The testing load is the self-weight of a 4.1 tonnes truck, and three testing points were selected at the 1/4 span, middle span and 3/4 span. Load testing points are as shown in figure 10 below.

Figure 11: Bridge elevation

Table 3: Comparison between Survey Deflection & Analysed Deflection:

Testing Point One

(CH 14.4)

Testing Point Two

(CH 28.4)

Testing Point Three

(CH 40.8)

Survey Deflection 4.4 mm 1.0 mm 4.6 mm

Analysed Deflection 4.2 mm 1.2 mm 4.5 mm

Difference 0.2 mm 0.2 mm 0.1 mm

*survey equipment accuracy is 0.2 mm.

As shown in the Table 3 that the deflection difference between the analysis and survey is within the survey equipment’s accuracy, and the Engineers Bridge has passed the loading test. As such, it confirmed that the computer modelling was simulating the bridge very well.

RECOMMENDATION AND REFURBISHMENT The following is recommended:

• Strengthen bridge members as indicated in Figure 10 (for Class 16 Usage).

• Replace the existing timber decking.

• Remove rust, clean and repaint the bridge before opening.

• Undertake other recommended actions as indicated in section 6 of GHD Report 21/21187/178398.

After the assessment, the Engineers Bridge has been classified as Class 12 bridge by the client, however, the refurbishment work has been done as per the recommendations above, with locally strengthening for Class 16 Load usage.



CONCLUSION

The paper has demonstrated the techniques of using 3-D software to simulate an Aged Arched Bailey Bridge without the design or As-Built drawings. The bridge’s analysis model was a combination of the site survey, an elevation from a related paper and some assumptions based on the reference documents.

The military bridge design and load rating standards are different to the civilian ones, and this paper has given an example of how to assess and rate an old military bridge, using the available military bridge design information from the USA and UK.

Due to the site limitation, load testing (4.1 tonnes) in this paper is not sufficient to rate the bridge as Class 12(12 tonnes) or Class 16(16 tonnes). However, it has been approved to be a cheap and reliable way to confirm the computer simulation model of the assessment and load rating, given so many assumptions & uncertain factors have been used in the analysis.

REFERENCES 1, GHD Report 176219 - Report for Holsworthy Range Engineers Bridge Condition Assessment.

2, GHD Report 178398 - Addendum for Holsworthy Range Engineers Bridge Condition Assessment-Arch Footing Investigation

3, Australian Standard AS 5100 Section 2 Design loads

4, Australian Standard AS 5100 Section 7 Rating of existing bridges

5, Australian Standard AS 4100 Steel structures Standards Australia

6, MLC-STANAG 2021 (Edition 6) NATO Standardisation Agreement DTIC USA

7, FM 5-277 (1986) Bailey Bridge Department of the Army USA

8, Captain Neil Turner RAE (ARes) Engineers Bridge

9, W. Bates CEng FIStructE Historical Structural Steelwork Handbook

AUTHOR BIOGRAPHIES Gunvant Vaghela is a Structural Engineer with B E (Civil) from Gujarat University. He has completed Post Graduate Dip (EQ) from IIT Roorkee with Gold Medal. Since migrated to Australia in 1990, he worked on major infrastructure projects which include upgrade of various sections of Pacific Highway, M7, Gateway upgrade, Airport Link etc. Gunvant is currently working with GHD on Light rail project.

Peng Yi is a Senior Bridge Engineer with B E (Civil Engineering)& M E (Bridge and Tunnelling Engineering ) from Tongji University, Shanghai. Peng has been working in China & African before he migrated to Australia in 1996, and his Australia local experience includes Victoria Road Alliance (Iron Cove Bridge Upgrade) in Sydney, Port Botany Expansion in Sydney and Hale Street Link in Brisbane. Peng is currently working with GHD on Northern Road Upgrade Detail Design.

Andy Buckland is a Facilities Manager with the Defence. He has worked in varying roles on Facilities and Construction and Electrical tasks in Australia and the South Pacific region. Has a Diploma in Construction Management and has worked for Defence for over 30 Years



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condition assessment and load rating of arched …

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