Demonstration bridge C: Masonry Arch Structure: Sustainable Bridges Background document 7.4

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Demonstration bridge C: masonry arch structure Background document SB7.4

PRIORITY 6

SUSTAINABLE DEVELOPMENT GLOBAL CHANGE & ECOSYSTEMS

INTEGRATED PROJECT

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This report is one of the deliverables from the Integrated Research Project “Sustainable Bridges - Assessment for Future Traffic Demands and Longer Lives” funded by the European Commission within 6^th Framework Pro- gramme. The Project aims to help European railways to meet increasing transportation demands, which can only be accommodated on the existing railway network by allowing the passage of heavier freight trains and faster passenger trains. This requires that the existing bridges within the network have to be upgraded without causing unnecessary disruption to the carriage of goods and passengers, and without compromising the safety and econ- omy of the railways.

A consortium, consisting of 32 partners drawn from railway bridge owners, consultants, contractors, research institutes and universities, has carried out the Project, which has a gross budget of more than 10 million Euros.

The European Commission has provided substantial funding, with the balancing funding has been coming from the Project partners. Skanska Sverige AB has provided the overall co-ordination of the Project, whilst Luleå Tech- nical University has undertaken the scientific leadership.

The Project has developed improved procedures and methods for inspection, testing, monitoring and condition assessment, of railway bridges. Furthermore, it has developed advanced methodologies for assessing the safe carrying capacity of bridges and better engineering solutions for repair and strengthening of bridges that are found to be in need of attention.

The authors of this report have used their best endeavours to ensure that the information presented here is of the highest quality. However, no liability can be accepted by the authors for any loss caused by its use.

Project acronym: Sustainable Bridges

Project full title: Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives Contract number: TIP3-CT-2003-001653

Project start and end date: 2003-12-01 -- 2007-11-30 Duration 48 months

Document number: Deliverable D7.4 Abbreviation SB-7.4

Author/s: J. Bień, K. Jakubowski, T. Kamiński, H. Nowak, P. Rawa, WUT, Ch. Trela, R. Hel- merich, E. Niederleithinger, BAM, M. Reis, UMinho, Z. Kubiak, PLK

Date of original release: 2007-11-30 Revision date: 2007-11-30

Project co-funded by the European Commission within the Sixth Framework Programme (2002-2006)

Dissemination Level

PU Public X

PP Restricted to other programme participants (including the Commission Services) RE Restricted to a group specified by the consortium (including the Commission Services) CO Confidential, only for members of the consortium (including the Commission Services)

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General remarks

This report is prepared on the basis of Contract No. TIP3-CT-2003-001653 between the European Community represented by the Commission of the European Commu- nities and Skanska Teknik AB contractor acting as coordinator of the Consortium.

The content of the report is related to workpackage WP7 “Demonstration - Field Test- ing of Bridges” and is concerned with demonstration tests. First, WP 7 helps to select bridges in agreement with needs and requirements from bridge owners and research teams. Then, when bridges are identified, instrumentation and assessment are performed.

The main objective of WP7 is to serve as a demonstration workpackage. This means to test techniques and methods developed in the different workpackages. For this reason, the connection with other workpackage is a crucial issue.

WP 7 is organised in five steps:

1. release of questionnaires for identifying problems and techniques requiring tests, 2. identification of test bridges,

3. definition of instrumentation plans,

4. data collection process, processing and analysis, 5. conclusions.

This report is dedicated to demonstration of testing of a masonry arch bridge structure.

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Summary

Presented bridge was selected as a typical masonry arch bridge for demonstration and testing of the project achievements. The age, construction and span length of the structure are representative for masonry bridges in Europe. The bridge also doesn't have any technical documentation as most of old masonry bridges. From the practical point of view it is interesting that the track in service is placed asymmetrically, just on one side of the bridge.

At the initial stage of the project the following information about the bridge was available:

• details of the bridge location for easy access of potential testing groups,

• basic information on railway track crossing the bridge and on bridge operational conditions,

• technical data of the bridge structure including drawings,

• general description of the bridge condition illustrated by photos and drawings.

Selected demonstration bridge created opportunity to present various testing techniques (WP3), different methods of load capacity evaluation (WP4) and technologies of bridge condition monitoring (WP5). The whole activity comprises a challenge to the participant for fruitful cooperation and exchange of experiences.

Within the works performed on the bridge the following activities can be distinguished:

• NDT testing of the structure geometry and material in situ,

• laboratory test of specimens taken form the structure,

numerical analyses for evaluation of the bridge load capacity and the ultimate load.

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1 Description of the bridge 1.1 Location

Bridge is located in Poland (Figure 1.1), around 30 km from Wrocław city (Figure 1.2). The reference point is 1.727 km on Oleśnica – Chojnice line. Obstacles are local road and small brook which provide easy access to the structure and possibilities for setting up the measurement devices under the bridge.

Figure 1.1: Location of the demonstration bridge C in Poland

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Figure 1.2: Demonstration bridge C – location on local map

Figure 1.3: Location of the demonstration bridge C (city map)

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1.2 Basic technical data 1.2.1 Railway line description

The bridge is under one line, number 281, from Oleśnica to Chojnice. There is space for two tracks on the bridge, however currently only one track is present and perma- nently used (Figure 1.4).

Figure 1.4: Top view

Track structure details:

• electrificated,

• maximum speed: 40 km/h,

• axle load: 22.5 t,

• rail type: UIC 60,

• sleeper: wooden, 14x24 cm,

• backfill thickness: ca. 70 cm.

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1.2.2 Bridge details

Present manager of the bridge is PKP PLK S.A. Construction type of the bridge is masonry arch structure with masonry spandrel walls. Basic geometric dimensions are presented on Figure 1.5 and Figure 1.6.

Structure details:

• construction:

o year of construction - 1875, o number of spans - 1, o arch barrel shape - circular, o plan shape - rectangular,

• span:

o horizontal clearance - 9.93 m, o width - 8.55 m, o vertical clearance - 5.84 m, o arch radius - 4,97 m, o arch material - brick, o backfill material - unknown,

o brick dimensions - 6.5 x 12 x 25 cm, o joint thickness - 1 ÷ 1.5 cm, o brick strength - unknown, o joint strength - unknown,

• obstacles:

o local road - under commune manager, very low local traffic, o small brook - with scrub, foot bridge in the vicinity,

• equipment:

o railing (Figure 1.12),

o both sides, symmetrical wing walls (Figure 1.11), o drain pipes (Figure 1.13),

• other installations on bridge:

o pipeline (Figure 1.4), o power line (Figure 1.12),

• formal documentation:

o original project and drawings – missing,

o inventory card (04.1965) and sketch drawing (12.1953),

• pictures and drawings for use in the project:

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o photographs (10.2004),

o side view and cross section drawings (Figure 1.5 and Figure 1.6).

Figure 1.5: Side view

Figure 1.6: Cross section in crown

1.2.3 Technical condition

The bridge has got defects typical for masonry structures and the most important ones of them are presented on pictures below (according to the taxonomy proposed in SB-CAI 2007):

• salt concentration increase (Figure 1.7),

• deterioration and loss of material (Figure 1.8);

• longitudinal cracks (Figure 1.8).

Loss of bricks and joints on both spandrel walls of the bridge was filled up with concrete and new bricks (Figure 1.9). Figure 1.10 presents location of the defects.

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Figure 1.7: Salt concentration increase

Figure 1.8: Material deterioration, loss of material and cracks

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Figure 1.9: Filled losses of masonry

Figure 1.10: Localization of damages

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1.3 Photos of the bridge

Figure 1.11: General view of the bridge

Figure 1.12: Top view of the bridge

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Figure 1.13: Drainage pipe

Figure 1.14: Other installations on bridge

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2 Field tests of the bridge

2.1 General information 2.1.1 Aim of the study

The aim of the field tests was demonstration of the application possibilities and effec- tiveness of non-destructive and semi-destructive methods in examination of existing old bridge structures. Realization of the tests on the considered bridge was especially important and practical due to lack of any documentation or original drawings of the structure. Therefore the desirable result of the tests was measurement of the geometry and material properties and also examination of structural behaviour under live load.

2.1.2 Scope of the study

Within the confines of the field test a few techniques were applied:

• deformation measurements,

• radar measurements,

• electrical conductivity tests,

• coring,

• endoscopy,

• thermography.

2.1.3 Realization

The field tests were carried out by BAM, WUT and IDS in four separate sessions (participants given in brackets):

• 17-18.11.2005 (BAM+WUT),

• 13.07.2006 (WUT),

• 20-22.09.2006 (BAM+WUT),

• 14-16.05.2007 (BAM+WUT+IDS).

2.2 Deformation measurements 2.2.1 General description

Displacement measurement was carried out to investigate the deformation of the arch barrel under traffic loading. The reaction of the structure under loading charac- terizes the real acting structural system at the moment of the measurement and can be used to calibrate the numerical model for the load and resistance assessment of the existing bridge structure. The displacement measurements were carried out by means of three independently working systems:

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1. laser measurements below the axis of the track in the middle of the span (L1) – operated by BAM,

2. microradar measurements from 2 different radar positions in 5 points of the middle cross sections (R1-R5) and in 2 points in quarter point sections (R6, R7) – operated by IDS,

3. LVDT measurements in 3 points in the middle of the span (D1-D3) – operated by WUT.

Additionally accelerations of selected points (A1-A4) were monitored by WUT.

Configuration of the measurement points for all measuring systems are shown in Figure 2.1.

Figure 2.1: Location of the measurement points and load configurations

For the load tests, the Polish railway PKP PLK SA, provided 2-boggie-engine with three axles in each bogie, with axle load equal to 200 kN, see Figure 2.2.

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6 x 200 kN, boggie distance: 6,80 m, axle distance in a boggie: 1,75 m

Figure 2.2: Locomotive for deformation measurements Aim of the test:

• measurement of deformation under static and dynamic loads (standing and moving locomotive),

2.2.1.1 Laser displacement measurements

These measurements were carried out by BAM. First feasibility measurements in September 2006 showed, that the reaction of the middle of the arch was much higher, than the reaction of the quarter points. In difference to arch bridges, e.g.

made of steel, the backfill and the ballast distribute the load quite well. During this testing session only velocities were measured, thus only the relative load distribution was estimated.

In May 2007, the displacement measurement was refined with a displacement laser of the latest generation.

Equipment:

- displacement laser of the latest generation from Polytech GmbH (Figure 2.3).

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Figure 2.3: Left: Laser located below the track axis, right: measurement points for three independent working displacement systems. The laser system uses the same reflecting point as the microradar system

2.2.1.2 Microradar displacement measurements

Microradar displacement measurements were carried out In May 2007 by IDS. De- pendent on the location of the measurement points two different positions of the radar were applied: A and B (Figure 2.4). For displacement measurements of the points nos. R1-R5 (Figure 2.1) located along the transverse profile the lateral position (A) of the radar against the bridge was chosen. For displacement measurements of the points nos. R6 and R7 located along the longitudinal profile under the track axis the radar was located under the bridge (B).

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Figure 2.4:Positions of the radar transmiters/receivers

Equipment:

- IBIS-S radar system with 5 reflecting corners, see Figure 2.5

Figure 2.5: Microradar measurement system: transmitter/receiver (left)

and reflecting corners in the crown cross-section of the arch (right)

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2.2.1.3 LVDT displacement measurements

These measurements were carried out in May 2007 by WUT. LVDT gauges were located in points nos. D1-D3 (Figure 2.1) located along the transverse profile half a meter from the crown cross-section.

Equipment:

- 3 LVDT gauges on tripods, see Figure 2.6

Figure 2.6: Set for LVDT displacement measurements

2.2.2 Tests performance

The measurements were composed of the static and dynamic tests. In the static tests three load configurations were applied: one of the engine boogie located in 1/4, 1/2 and 3/4 of the span. The load configurations are presented in Figure 2.1. For each configuration parallel measurements with all the three systems were carried out. The radar system was operating from two position with each static loading configuration.

Within the confines of the dynamic tests the engine was passing the bridge in both directions (South North and North South) with 5 km/h, 20 km/h, 40 km/h, 60 km/h and 80 km/h. The different speeds allowed comparing, whether there is a speed dependent difference in the dynamic excitation of the arch barrel in the middle of the arch.

During the main displacement measurement in May 2007, the displacement in the middle of the arch, below the axis of the track was measured with laser equipment using a sampling rate of 200Hz. Figure 2.3 shows the laser set-up and the reflection point. The laser system used the same reflection point which were used by the microradar measurement system.

The maximum speed of the engine passing the bridge was 80 km/h.

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2.2.3 Results

Exemplary results for radar measurements are presented in Figure 2.7. It shows displacements of point R1-R5 from the static loading configuration no. 1 (engine boogie located over 1/4 of the span).

Figure 2.7: Exemplary results for radar measurements – displacements of points:

Rbin 76=R1, Rbin 87=R2, Rbin 100=R3,Rbin 114=R4, Rbin 126=R5 for loading in 1/4 of the span (received from IDS 2007)

Exemplary results for LVDT measurements are presented in Figure 2.8 and Figure 2.9. It shows displacements of point D1-D3 from the static loading configuration no. 1 and 2 (engine boogie located over 1/4 and 1/2 of the span).

Figure 2.8: Exemplary results for LVDT measurements – displacements of points D1- D3 for loading in 1/4 of the span

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Figure 2.9: Exemplary results for LVDT measurements – displacements of points D1- D3 for loading in 1/2 of the span

In Table 2.1 selected engine passes with speeds of 20 km/h, 40 km/h and 80 km/h registered with the laser equipment are shown. The diagrams visualize the increasing dynamic effect with increasing speed.

Table 2.1: Examples for the transfer of the engine at different speeds

Speed

[km/h] 2.2.3.1.1 Transfer recorded as time-displacement diagram

20

20km/h North --> South

-0,2 0,0 0,2 0,4 0,6 0,8

5,0 7,0 9,0 11,0 13,0 15,0

Time [s]

Displacement [mm]

40

40 km/h S-->N

-0,1 0,1 0,3 0,5 0,7

5 6 7 8 9 10 11

Time [s]

Displacement [mm]

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Speed

[km/h] 2.2.3.1.1 Transfer recorded as time-displacement diagram

80

0 0,2 0,4 0,6 0,8

300 400 500 600 700 800

Fre que ncy [200/s]

Displacement [mm]

80 km/h S-->N

The Table 2.1 shows the maximum displacement registered with the laser equipment. Besides the maximum displacement differences during train passage, the dynamic effect was calculated for the maximum measured speed.

Table 2.1: Maximum displacement measured with the laser equipment Speed

[km/h]

North South [mm]

South North [mm]

Dynamic excitation λ

5 0.677 0.670 -

20 0.639 0.642 1,0064

40 0.611 0.651 1.0358

60 0.621 0.621 1.0400

80 0.555 0.657 1.1123

The measured displacement from the static loading indicate only selected components of the total displacement of each point in the direction imposed by the given system. Thus, the values measured with laser and LVDT gauges show displacements in the vertical direction and the values measured with radar indicate measurements in the direction from the reflecting corners to the radar transmitter/receiver.

Measurement by means of the radar transmitter located in position B enables finding an approximate vertical displacement of the point nos. R2, R6 and R7 from the all load configurations. The solution is possible assuming that there is symmetry in the behaviour of the structure between cases of loading in 1/4 and 3/4 of the span. Then e.g. the radial displacement of the point R2 for load configuration no. 3 measured from the position B should be the same as the radial displacement of the point in the direction of the symmetrical virtual position B’ from the load configuration no. 1 (Figure 2.10). The real displacement d₂ reaches the lines normal to the radial directions what is presented in Figure 2.10. It is also possible to act analogically for loading in 1/2 of the span assuming that in this case structure is deformed symetrically

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against the middle of the span. The real dispalcements d₂, d₆, d₇ and their horizontal and vertical components for the points R2, R6 and R7 from the loading in 1/4 of the span are shown in Figure 2.10. Also the real dispalcements d’₂, d’₆, d’₇ and their horizontal and vertical components for the points R2, R6 and R7 from the loading in 1/2 of the span are shown in Figure 2.10.

Figure 2.10: Finding the vertical and horizontal components of displacements of the point R2, R6 and R7 for loading in 1/4 (top) and 1/2 (bottom) of the span Displacement results measured with all applied methods are collected in Table 2.2.

The table shows as well radial (measured along the direction of the gauge) compo- nents of the displacement as the horizontal d_H and vertical d_V components of the total displacement.

Table 2.2: Displacement results measured with all applied methods

A A B A A A B B

point D1 D2 D3 R1 R2 R2 R3 R4 R5 R6 R7 L1

Quantity Load location

1/2 -0.630 -0.550 -0.220 -0.424 -0.382 -0.430 -0.328 -0.156 -0.091 -0.281 0.036 -0.701 1/4 -0.420 -0.390 -0.180 -0.287 -0.255 -0.066 -0.202 -0.123 -0.082 -0.287 0.250 -0.367 3/4 -0.390 -0.340 -0.150 -0.358 -0.349 -0.508 -0.193 -0.109 -0.071 -0.247 -0.375 -0.490

dH - - - - - 0.000 - - - -0.200 0.200 -

dV -0.630 -0.550 -0.220 -0.557 -0.567 -0.540 -0.543 -0.279 -0.177 -0.220 -0.220 -0.701

dH - - - - - 0.366 - - - 0.184 0.381 -

dV -0.405 -0.365 -0.165 -0.423 -0.449 -0.360 -0.327 -0.208 -0.149 -0.390 -0.106 -0.429 Radial

displace ment

1/2

1/4

Radar position

LVDT LASER

Method

IBIS

The displacements monitored with the various systems of the arch barrel points located along the crown cross-section and the longitudinal profile under the track axis are presented in Figure 2.11 and Figure 2.12 respectively. Although, the points monitored with LVDT gauges were located 50 cm away from the crown cross-section they are also presented in Figure 2.11 as expected to be similar to the other ones. Gener- ally just two different locations of the load are distinguished: at L/4 and at L/2. Due to symmetry of the structure and load configurations both cases with the engine located

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at 1/4 and 3/4 of the span are treated as the same case. Thus the displacements given in the figures indicate average value from these both cases for symmetrically corresponding points. In Figure 2.11 vertical components of the displacements only are given and Figure 2.12 shows vertical and horizontal displacements included within the longitudinal vertical plane.

Figure 2.11: Vertical displacements of the arch barrel points at the crown cross- section under the load located at L/4 (a) and L/2 (b) measured from radar position A

Figure 2.12: Displacements of the arch barrel points along the longitudinal profile un- der the track axis for load located at L/4 (a) and L/2 (b) measured from radar position B

2.3 Radar measurements 2.3.1 General description

The radar measurements were carried out according to recommendations included in SB3.5 Radar (2004), SB3.6 Scanning (2006), SB3.17-1 Tests (2007) and SB3.17-2 Tests (2007).

Aim of the test:

• measurement of masonry elements’ thicknesses (arch barrel, abutment and wing walls),

• detection of voids or structural anomalies in masonry elements and backfill,

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• evaluation of moisture or water content.

Equipment:

• Ground Penetrating Radar (GPR) with various antennas: 500 MHz, 900 MHz and 1.5 GHz (Figure 2.13)

• wooden frame for moving radars along the track (Figure 2.15),

• running metal frame for moving radars along the track (Figure 2.15),

• metal frame with automated system for radar mapping of the south-east wing wall (Figure 2.13).

2.3.2 Tests performance

Tests carried out on the bridge:

• horizontal profiles along the southern abutment and backfill behind it (17- 18.11.2005) – Figure 2.14,

• longitudinal and transverse profiles at the bottom of the arch barrel (20- 22.09.2006) – Figure 2.13

• map of the south-east wing wall (20-22.09.2006) – Figure 2.13,

• longitudinal profile at the top of the bridge (20-22.09.2006) – Figure 2.15,

Figure 2.13: View on the radar measurements: left: longitudinal (red) and transverse (blue) profiles at the ceiling with the 900 MHz antenna; right: testing area using an automatic 2D radar scanning system with the 1.5 GHz antenna

Technical details and location of the radar measurements are compiled in Table 2.3 and Figure 2.17.

Table 2.3 Set of different data acquisition modes at different location of the bridge

Location of the profiles

Measurement characterization Set-up parameter and used antenna frequency

at the ceiling transverse profiles of different length

data collection based on the rotation of the survey wheel (scans per meter), automatically inserting markers,

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longitudinal profiles of different length

500 MHz and 900 MHz antenna

at the left and right wall under the bridge

horizontal and vertical profiles data collection based on the rotation of the survey wheel (scans per meter), automatically inserting markers, 500 MHz, 900 MHz, 1.5 GHz antenna at the left wing

wall

33 horizontal and vertical profiles at 2 testing areas of 1.53 m x 1.60 m

2D scanning system inserting manual electronic markers, continuous data collection based on scanner movement triggering (scans per meter), 1.5 GHz antenna

Top of the bridge and on the dam

horizontal and vertical profiles continuous data collection with manual marker every 1 m with the 500 MHz antenna

Figure 2.14: View on the radar measurements using a survey wheel from left to right edges on the south abutment (measurement campaign 2005): left: on the horizontal (H6) profiles with the 900 MHz antenna; right: on the horizontal (H5) profiles with the 1.5 GHz antenna

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Figure 2.15: Radar measurements from the top of the bridge – longitudinal profiles:

left: with the 500 MHz antenna (2005); right: Multi-offset antenna array for ballast investigation (2006)

Additionally a multi-offset array radar measurement for ballast investigation was carried out on the railway track, see Figure 2.15. It was applied in four different configurations (see Table 2.4). The direction of the linear array was altered between along and across track and the elevation was changed between two heights. Each measurement track was about 50 m long.

Table 2.4 Set up of antenna array configurations (^*with regard to track)

configuration array direction^* elevation

1 across 15cm

2 across 30cm

3 along 15cm

4 along 30cm

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Figure 2.16: Marked radar measurements from 2005 to 2007, top: at the ceiling of the arch with length values (L) from the apex to the south (Ls) and to the north (Ln) of the radial measurements, bottom: at the south wing walls and abut- ment

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Figure 2.17: Marked radar measurements from 2005 to 2007 on the top of the bridge and on the slope of the fill

2.3.3 Results

Most results are given in form of radargrams representing profiles of the structural elements perpendicular to their surfaces, e.g. Figure 2.18. More dark areas of the radargrams indicate anomalies in material which can be:

• wet areas,

• boundaries between masonry and backfill or ballast,

• brick layer bond with or without cracks.

2.3.3.1 Detection of constructional elements

Radar antennas of different frequencies (having different penetration depth) have been used to estimate the thickness of the walls. Figure 2.18 shows an example of the radar measurements with different antenna frequencies on the same position at the south abutment. Because of high attenuation in the inner masonry structure the measurements have not produced satisfying results regarding thickness estimation.

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nearly planar reflections

Figure 2.18: Radargrams of the horizontal profiles H5 (SIP profile SIP4, measure- ment campaign 2005 and 2006) carried out with different antenna fre- quency on the south abutment (reflection zones marked with arrows) At the horizontal profile H5 in Figure 2.18 nearly planar reflections from the brick layers are visible between 1 m and 4.5 m. A clear reflection of the back wall is not de- tectable. Moreover, the different frequencies do not show the brick layers at the same time (or depth after migration). This is due to signal broadening and interference ef- fects The first reflection band belongs to the first brick layer, however, it is conceiv- able that later reflections are only multiple reflections from the first brick layer and surface and do not correspond to further brick layers. Additionally at the radargram with the 500 MHz strong interferences of the reflected waves are caused by the low frequency (large wavelength in comparison to the brick geometry) prohibit the sepa- ration of the different layers. Generally, with lower frequencies the depth range in- creases but the resolution of structural information decrease.

Observations in the radargram measured from the top of the bridge are shown in Figure 2.19.

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Figure 2.19: Radargram of the 500 MHz antenna over the bridge with the schematic contour of the bridge (measurement campaign 2005); red marked the as- sumed back surface of the masonry structure

According to the geotechnical investigations of WUT the strong reflector can be identified as concrete cover of the bridge.

Based on the geometry of typical arch bridges of this time given by Henz (1869), a probable profile as marked in Figure 2.19 is assumed, so that a wall thickness at the abutment of 2 m is expected.

Figure 2.20: Drawing of the profile of a bridge No.17 from Henz (1869)

The reflected signals in Figure 2.19 do not show the accurate shape of the abutment, because of the opening angle (>0°) of the transmitted electromagnetic waves. Reflec- tions from inclined interfaces like the abutment are detected at wrong time or after conversion to depth at a wrong depth and lateral position. Measurements with a bistatic antenna are except for the distance between transmitter and receiver antenna zero offset measurements, that means that the recorded signal is reflected perpendicular to the reflector. In case of inclined reflectors the origin of recorded reflection of the subsurface structure is not to find lateral at the antenna position. Data have to be migrated by a known velocity distribution. Attempts of migration with a homogeneous velocity were not successful because no good focusing effect was observable.

strong reflexion zone

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Small drill cores or cone penetration tests from the top of the bridge can be used to calibrate the depth axis of the radargram and indicate the shape of the abutment. But because of no homogeneous velocity distribution inside the masonry and embankment due to different moisture content a velocity between 0.10 m/ns and 0.15 m/ns was applied to transform the time scale to a depth scale. A more correct localization of the structural elements require a migration of the data with a 2D velocity model, which is not available.

Figure 2.21: Two parallel profiles from the edge of the bridge to the middle (top:

northern part; bottom: southern part) on the top of the bridge with marked reflection from the bridge cover

In Figure 2.21 the marked reflections from the upper edge of the bridge cover show a time delay of 3 to 5 ns over 2.5 m length. Assuming a homogenous subsurface material and given the propagation velocity is 0.1 m/ns the observed time delay equals a depth difference of 20 cm. This corresponds a concrete layer inclination of 4.5°. From the excavation in Figure 2.58 is known that the upper edge of the bridge cover is slightly inclined of approximately 1° and made of concrete. The higher inclination determined by radar can be explained with lower velocity toward the middle of the bridge due to higher moisture content and more ballast than soil.

The reflection from the upper, rather planar feature and the inclined lower edge of the cover converge towards the center of the bridge.

At the ceiling of the bridge are carried out some more measurements than from the top of the bridge. Figure 2.17 shows the positions of the different vertical and horizontal profiles measured at the ceiling of the bridge.

Observations of these measurements are shown in the radargrams in Figure 2.22 to . In all radargrams a strong, nearly planar reflection from an interface between embankment material and the masonry span in a depth between 80 and 100 cm (velocity of 0.12 m/ns expected) is visible. Examples of reflected and interfered signals parallel to the surface from the masonry structure (brick layers) are shown e.g. in

Upper edge

Lower edge

Interaction of upper edge and lower edge

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Figure 2.22 at the horizontal profiles H0m and H2m. There are also reflections visible from the edges of the bridge in the horizontal profiles. Since nearly 1.5 m from the edges the reflections of the brick layers tend to be later in time (time delay up to 1.7 ns). This observation can be explained by slower velocity (0.09 m/ns; ε=11.3) caused by increased moisture. These estimated values correspond well with velocities or dielectrical constant ε values in the literature for dry bricks of ε=4-8 (v=0.106- 0.15 m/ns) and for wet bricks of ε=8-12 (v=0.087-0.106 m/ns) (DGZfP 2001).

The observed time delay can already be explained with the changes in velocity caused by assumed increased moisture, mentioned above. Thus, the strong reflection in Figure 2.22 seems to be the lower edge from the bridge cover like observed from the measurements on top of the bridge (Figure 2.21) or is the interface between masonry and filling material beneath the bridge cover layer of a large contrast in material properties. Thus the radar measurements could not finally estimate, whether there exist still a layer with filling material between the concrete cover and the masonry structure or not. Neither at the wing walls nor the southern abutment were clear backwall reflections (interface masonry to filling or embankment material) detected;

the contrasts in the electromagnetic material properties must have been insufficient.

V2m V6m V7m

Figure 2.22: Radar measurement with the 900 MHz antenna on the horizontal pro- files H0m (top) and H2m (bottom) at the ceiling of the arch of the bridge, red marked intersection point of the horizontal profiles with the vertical profiles; green marked time delay of reflection on brick layers

The strong, nearly planar reflector in Figure 2.23 seems to represent the concrete cover of the bridge for drainage purpose. In Figure 2.24 are summarized the results of the different radar measurements concerning the detected and localized concrete cover of the bridge. The concrete cover is built up as a trench structure with approxi-

strong reflection behind the inner masonry span

Reflections from different masonry layers

Reflection from bridge edge Time delay of reflection on brick layers

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mately 4° inclination parallel to track direction verified by coring, see Figure 2.63. The inclination perpendicular to the track is 1° determined by excavation and approximately 4° determined by radar, but with uncertainties concerning velocity calibration.

No features in the radragrams could be addressed to the back surface of the bridge elements.

strong nearly planar reflection zone Reflections parallel to the surface caused by brick layers

Figure 2.23: Radar measurement with the 900 MHz antenna on the vertical profile V6m at the ceiling of the arch of the bridge; radargram with radial posi- tioned traces and topography with the schematic contour of the bridge

β ββ β

α

β

Figure 2.24: Drawings of the localised concrete cover (blue) of the radar measure- ments from top of the bridge and at the ceiling from the arch with marked inclination angles

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2.3.3.2 Evaluation of the condition of the masonry (material properties)

Radar measurements have been successfully applied to investigate the moisture distribution in the masonry. These results have been verified by coring and through geoelectrical measurements.

Figure 2.25: Radargram of the horizontal profile H5 with the 500 MHz antenna and results of the moisture content estimation on certain core samples

In Figure 2.25 the horizontal profile H5 at the southern abutment and the results of the moisture content estimation of some core samples of the boreholes L1, L2 and L3 in the height of 1.2 m are shown. Strong reflections and time delays of the reflection horizons correlate well with the increased moisture content in these areas - especially in the area between 5.5 and 7.5 m and near the edge at 1 m.

The bending of the nearly plane reflection horizons of single brick layers towards later time on other locations (like for example at the ceiling of the bridge in Figure 2.22) is therefore caused by increased moisture.

Further extensive radar measurements were carried out on the southern abutment of the bridge. Figure 2.14 shows how the radar equipment was applied for the horizontal profiling in 2005 without a lift. In the measurement campaign in 2006 some horizontal profiles were added, in the height of 220 cm and 80 cm. In Figure 2.26 all radargrams of the horizontal profiles are presented.

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time delay strong reflections

reflections near surface

Figure 2.26: Radargrams of the horizontal profiles at different heights at the south abutment with 900 MHz antenna from the measurement campaign in 2005 and 2006

These distinctive features are particular in the upper radargrams and hint to a faulty area in the brickwork behind the first brick layer, in right upper part, see Figure 2.26.

Probably cracks in the masonry allowed the infiltration of water in this area, which did not reach down to the upper part. There the brickwork seems to be intact. Based on the results of moisture content investigations mentioned above, the observed time delay and the areas with strong reflections in Figure 2.27 can be assigned to increased moisture.

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Figure 2.27: View on the south abutment with a marked area, where in the radar- grams show strong reflections were recorded caused by increased mois- ture

Cracks were studied at two testing areas (Figure 2.17) at the left wing wall of the bridge using an automatic 2D radar scanning system, see Figure 2.13 and generally with some horizontal and vertical profiles at the left and right wing wall and southern abutment with mounted survey wheel. The latter measurements were mostly carried out in 2005.

As shown in Figure 2.28, testing area 1 exhibits the stronger deteriorated area with visible open cracks especially in the left upper part and in the first lower brick layers and areas of repaired brickwork (new bricks and mortar).

Figure 2.28: View on the testing area 1 (left) and testing area 2 (right) of the radar measurements with the automatic 2D radar scanning system on the left wing wall

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33 vertical and horizontal profiles of 5 cm distance were recorded. After some stan- dard data processing steps like cutting and sorting the profiles, the vertical and horizontal radar data were separately reconstructed with the 3D FT-SAFT algorithm - Mayer et al (1990). In a next step the vertical and horizontal profiles were combined using the maximum amplitude of the reconstructed data with a data fusion tool Kohl et al (2004).

This processing sequence allowed the creation of high-resolution depth sections (C- Scans). An example of the testing area 1 and testing area 2 is shown in Figure 2.29.

After one stretcher course, reflections of individual bricks are visible. The strongest reflections correlate well with areas of open cracks and repaired area in Figure 2.28.

Figure 2.29: Times/depth section (C-Scan) after 3D FT SAFT reconstruction and data fusion of horizontal and vertical lines with maximum amplitude: Left: at 14.5 cm of the testing area 1; Right: at 12.5 cm of the testing area 2 3D visualisation of threshold values in different depth intervals with the AMIRA tool- box in Figure 2.30 shows, that no tracking of cracks to the depth is possible. Strong reflections, green and red marked corresponds only to the brick geometry of the first brick layer (stretcher or header course).

Figure 2.30: XZ-plot (B-Scan) of the 3D-visualisation of threshold values in different depth intervals of the testing area 1 after reconstruction and data fusion with marked shape of bricks

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Figure 2.31: XZ-plot (B-Scan) of the 3D-visualisation of threshold values (smaller than in Figure 2.30) in different depth intervals of the testing area 2 after reconstruction and data fusion

Figure 2.32 shows the position of horizontal and vertical profiles carried out with different antennas at the left wing wall in 2005. Example of radargrams of the 1.5 GHz antenna are shown in Figure 2.33 and Figure 2.34.

H1

H2

H3 V7

V1 partly open cracks

Figure 2.32 Left wing wall with marked vertical and horizontal profiles (not the whole length, right cut) and area of partly open cracks (measurement campaign in 2005)

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Cracks on the surface

Cracks and increased moisture

Reflection bands from brick layers

Figure 2.33: Radargrams of the horizontal profiles H1 to H3 on the left wing wall car- ried out with the 1.5 GHz antenna under the bridge on the left wing wall, with marked position of the vertical profile V1 and identified structural fea- tures (measurement campaign 2005)

In Figure 2.32, at the horizontal profiles cracks on the surface as joints between brick and gap filling material (mortar) are clearly visible at the radargrams, but not to track to the depth non-ambiguously. The brickwork is such a complex structure, that every edge of a brick can be a diffraction point. Only areas with higher amplitudes of the recorded signals can be assumed as an area of higher crack distribution mostly combined with increased moisture. Bands of reflection horizons more or less horizontal at different time or corresponding depth are detected, but at different time for the certain horizontal profiles H1 to H3. These seems to be reflections from different brick layers or interference signals. The uncertainty, whether these are reflected or interfered signals are the main difficulty in the interpretation of the radargrams measured at masonry.

Crossing the brick layers, at the vertical profile in Figure 2.33 time undulation of the reflection bands of approximately 0.5 ns correspond well with the material changes of

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brick and mortar between the brick layers in depth. The general structure of the brickwork based on brick layers of different orientation of the bricks (stretcher and header course) is already visible at the small time variation of the reflected signal on the surface. These changes between bricks and mortar are less visible at the horizontal profiles, probably caused by a smearing effect of wave propagating to the depth by the antenna movement along the brick layers.

Reflection bands from brick layers

Figure 2.34: Radargram of the vertical profile V1 at 2 m of the horizontal profiles car- ried out with the 1.5 GHz antenna under the bridge on the left wing wall (measurement campaign 2005)

In general there exist more open crack at the left and right wing wall than on the wall of the south abutment in Figure 2.26, which is supported by the visual inspection.

Many parts of the south abutment are obviously repaired with new bricks and/or new mortar.

At the left wing wall in Figure 2.33 the reflection bands are less strong than in the un- disturbed area between 2 and 4 m at the southern abutment in Figure 2.25. Strong reflections near the surface especially in the upper part on the left side correlate well with the marked partly open cracks in the photo in Figure 2.32. These reflections are continued to the depth and corresponds probably with open cracks and increased moisture.

2.3.3.3 Ballast quality

Results from the radar measurements of 2006 are visible in Figure 2.35. Visual ballast inspection of the rail way track, which was tested by radar, shows a heavy ballast fouling. Air voids of the ballast were completely filled by sand. Even though the propagation velocity of the electromagnetic waves inside ballast is not so different to the underlying layers, the velocity contrast was sufficient to cause reflections. Quanti- tative evaluation of the propagation velocity was not possible and not planed, because the set-up of the system does not allow a synchronization of the radar chan- nels.

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Figure 2.35: B-Scan of the railway track between 10-18 m; distance starts at the milestone 17 in direction from Oleśnica

2.3.3.4 Summary

- the course of the concrete cover for drainage purpose of the arch is visible from the top of the bridge with 500 MHz and additionally with the 900 MHz under the ceiling of the arch, see Figure 2.24,

- a wall thickness of the abutment of approximately 2 m is expected derived from the end of the concrete cover reflection

- changing in stretcher and header course visible at the reflections from the first layer with the 1.5 GHz, not deeper

- different layers visible at the different antenna frequencies - identification of areas with increased moisture

- cracks are visible near the surface up to 0.5 m with the 1.5 GHz antenna - visible open cracks at the surface correlate with reflections near the surface of

the 900 MHz antenna

- no back wall of masonry detected, probably caused by insufficient contrast in dielectrical material properties (εr) between masonry and backfill material/ embankment

ballast bottom reflection sleeper/ballast interaction reflection surface reflection

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2.4 Electrical conductivity tests 2.4.1 General description

Aim of the test:

• detection of voids or structural anomalies in masonry elements and backfill,

• evaluation of moisture or water content,

• general study into the applicability and sensibility of frequency dependent resistivity measurements of masonry structures as part of the current research pro- gram at BAM

Equipment:

• frequency dependent electrical resistivity set - Radic-Research SIP 256C (2005 and 2006) with medical Ag/AgCl-electrodes (masonry profiles) or steel pike electrodes (soil profiles), see Figure 2.36 and Figure 2.37,

• electrical resistivity set – Lippmann 4-Punkt light (2007) with medical Ag/AgCl electrodes or steel pike electrodes, see Figure 2.38 and Figure 2.39

The frequency dependent resistivity measurements were aquired in the frequency range from 1 kHz to 1 mHz. The advantage of spectral induced polarization measurements is its ability to measure not only resistivity magnitudes (like being done in common d.c. resistivity surveys), but also the time shift (resistivity phase) between the applied voltage and resulting current. The resistivity magnitude and phase are recorded as a function of frequency. The resulsting spectra are observed to vary with material properties (e.g. dominant pore size, specific surface) and fluid chemistry.

The equipment used was a SIP 256c System (Radic Research), which is a multi channel device that can measure simultaneously at up to 56 electrodes. The Base Unit (yellow box, Figure 2.36) is powered from an external battery and controlled by a Laptop (left). The profiles consisted generally of 25 electrodes, which were either at- tached to the bridge walls using medical Ag/AgCl electrodes or stainless steel pikes that were installed in the ground. Each electrode is connected to a Remote Unit (RU, Figure 2.37) that contains both current switching and measurement modules. The measurement signals are transferred to the Base Unit by fibre optical cables to avoid any electromagnetic interference.

In the last field campaign in 2007 a 4 Punkt light system (Lippmann) was used, that measures the electrical resistivity after a current injection at 8 Hz. Working at one distinct frequency rather than sweeping through a frequency range allows much quicker data collection. Moreover, by using a different equipment and repeating one of the profiles measured in the previous campaigns it could be looked at the repro- duciblity of the results.

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Figure 2.36: Field equipment SIP 256c.

Base Unit with external battery and connecting Laptop

Figure 2.37: Electrodes with the Remote Units along the Profile 3 of the measurement area 1

Figure 2.38: Field equipment 4-Punkt light (Lippmann) with keyboard and display

Figure 2.39 Active electrodes

2.4.2 Tests performance

Tests carried out on the bridge:

• 1 longitudinal profile on top of the bridge (17-18.11.2005) – Figure 2.40,

• 2 horizontal profiles along the south abutment and south-west wing wall with backfill behind them (17-18.11.2005) – Figure 2.41 (left),

• 7 horizontal profiles along the south abutment and south-east wing wall with backfill behindthem (20-22.09.2006) – Figure 2.41 (right).

• 1 horizontal and 3 vertical profiles at the southern abutment (14.-16.05.2007) - Figure 2.42.

• 1 profile across the bridge embankment 6 m south of the masonry arch (14.- 16.05.2007)

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Figure 2.40: Electrical conductivity measurements on top of the bridge (2005)

Figure 2.41: Electrical conductivity measurements - horizontal profiles at the southern abutment (left) in 2005 and at the south-east wing wall (right) in 2006

Figure 2.42: Electrical conductivity measurements at the southern abutment:

Demonstration bridge C: Masonry Arch Structure: Sustainable Bridges Background document 7.4

Demonstration bridge C: masonry arch structure Background document SB7.4

General remarks

Summary

Table of Contents

1 Description of the bridge 1.1 Location

1.2 Basic technical data 1.2.1 Railway line description

1.2.2 Bridge details

1.2.3 Technical condition

1.3 Photos of the bridge

2 Field tests of the bridge

2.1 General information 2.1.1 Aim of the study

2.1.2 Scope of the study

2.1.3 Realization

2.2 Deformation measurements 2.2.1 General description

2.2.2 Tests performance

2.2.3 Results

2.3 Radar measurements 2.3.1 General description

2.3.2 Tests performance

2.3.3 Results

α

β

2.4 Electrical conductivity tests 2.4.1 General description

2.4.2 Tests performance