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Nhat Tan Bridge Construction Project Report on casting figure, crack happen and Construction Contract Package 3 countermeasure to prevent reoccurrence Tokyu Construction Co., Ltd 2 Thi

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CIVIL ENGINEERING CONSTRUCTION CORPORATION No.4

PROJECT MANAGEMENT BOARD – NHAT TAN P-3

Location: 1 Crack at contiguous location of void and solid section;

2 Location: Crack at angle of contiguous location of void and solid section;

3 Location: Crack of angle on girder end;

4 Location: Traverse crack of girder end;

5 Location: Breaking angle of bottom of girder;

6 Location: Breaking of partition of girder

Reasons:

During process of construction, cracks may be appear: because of Creation of formwork, sequence of disassemble formwork, cut PC strands… are not suitable which cause local stress in concrete of girder over allowable limitation, simultaneously some steel re-bars of girder end is short of length comparing with technical design drawing

Reference of some projects constructed (Ring Road No 3) also happened situation as the above mentioned After applied some solutions to treat, it reached good result, therefore we would like to propose some solutions as follows:

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II Countermeasure:

1 Location: Crack at contiguous location of void and solid section:

(See picture in Appendix 1)

+ Countermeasure: Add more 6 rebars A1-D12, L=1000 mm, @200mm at the connection between void and solid of the girder

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2 Location: Crack at angle of contiguous location of void and solid section:

+ Countermeasure: Add a re-bar A2-D12, L=3421 mm and a re-bar A3-D12, L=2928 mm

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3 Location: Crack of angle on girder end

+ Countermeasure: Add 2 re-bars A4-D12, L=720 mm and add 2 re-bars A5-D12, L=610 mm, @50 mm

And cut 1.3m formwork of girder flange so that when cut cable we can disassemble formwork

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4 Location: Traverse crack of girder end

+ Countermeasure: Extend bar NY10-D16 and bar NY11-D16 with length 1329 mm into length 1440 mm

A

B

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5 Location: Breaking angle of bottom of girder

+ Countermeasure:

- Cutting bottom formwork of girder end and change by rubber cushion (panel)

- Be careful during compacting concrete

6 Location: Breaking of partition of girder

+ Countermeasure:

- Surface grinding of angle of internal formwork, cleaning carefully before installing

- When disassemble internal formwork, using 6 jacks to lift internal formwork up (replace the use 4 jacks as used on site) after that using gantry crane to crane internal formwork out of

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7 We propose change sequence to cut cable as follows:

- The procedure of cutting strands as follows: from strand No 18→ 6→ 30→ 31→ 17→ 19→ 5→ 7→ 29→ 32→ 16→ 20→ 4→ 8 → 28→ 33→ 15→ 21→ 27→ 34→ 14→ 22→ 38→ 39→ 26→ 35→ 13→ 23→ 37→ 40→ 25→ 36 → 12→ 24→ 41→42 → 3→ 9→ 2→10 → 1→11

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Appendix 1

Crack at contiguous location of void and solid section

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Page 9 of 13 Appendix 2 Crack at angle of contiguous location of void and solid section:

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Page 10 of 13 Appendix 3 Crack of angle on top of girder end

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Page 11 of 13 Appendix 4 Traverse crack of girder end

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Page 12 of 13 Appendix 5 Breaking angle of bottom of girder

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Page 13 of 13 Appendix 6 Breaking of partition of girder

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1 2

Pic No 5 & 6

photographs of super t production

Tensioning of PC strand Pic No 3 & 4

Contents: Installation of inner formwork and casting concrete

Contents: Cleaning formwork, Installation of rebar and PC strand Pic No 1 & 2

Contents:

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photographs of super t production

Contents: Checking temperature and slump of concrete Pic No 7 & 8

Contents: Cutting of PC strand Pic No 9 & 10

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Nhat Tan Bridge Construction Project Report on casting figure, crack happen and Construction

Contract Package 3 countermeasure to prevent reoccurrence

Tokyu Construction Co., Ltd

1

TABLE OF CONTENTS 1 General Description 2

2 Report of Casting Figure 2

2.1 Location Map 2

2.2 Casting time 2

2.3 Casting sequence 2

2.4 Curing concrete 2

2.5 Removal of inner formwork 3

2.6 Compressive strength of concrete … 4

3 Cutting PC strand and monitoring camber and cracks……… 4

3.1 Cutting PC strand……… 4

3.2 Monitoring camber……… 4

3.3 Monitoring cracks……….5

3.4 The reasons of incident……… 6

4 Countermeasure to prevent reoccurence……… 11

4.1 Summary of crack locations……… 11

4.2 Countermeasure……….…11

4.2.1 Crack at contiguous location of void and solid section (at girder web)……… 11

4.2.2 Crack at contiguous location of void and solid section (at girder wing)………13

4.2.3 Crack of angle on girder end (wing part)………14

4.2.4 Tranverse crack at girder end……… 16

4.2.5 Breaking at the bottom of girder end……… …17

4.2.6 Breaking of partition of girder……… …… 18

5 Changing of cutting sequence……… 18

6 Appendix 1 ……….19

7 Appendix 2 ……… 21

8 Appendix 3 ……… 23

Total: 24 pages

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Contract Package 3 countermeasure to prevent reoccurrence Tokyu Construction Co., Ltd

2

This report describes actual casting figure of first super T girder of Thiep River bridge, mention the reasons of the

cracks happened after cutting PC strand and cranning girder out of formwork and propose the coutermeasure to

It toke 5 hours to finish casting concrete, this is unexpected time The reasonable countermeasure shall be

propose to shorten the casting time

( See Appendix 2 –Inspection sheet for placing concrete)

Concrete was mixed at site Batching Plant ( 60m3/h) and delivered to casting yard by mixer truck

Temperature and slump of concrete was checked prior to casting concrete to ensure the temperature is

always less than 32oC and the slump is 15 ± 2.5 cm

Concrete was poured directly to girder formwork by concrete chute from mixer truck

Detail ( Appendix 3)

2.4 Curing concrete

Using wet jute sheet to cover on wing of girder after casting concrete 6 hours and supplying water to keep

the jute in wet condition

Curing layout

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3

H.1

2.5 Removal of inner formwork

Inner formwork were removed on 30th May, 2011 Gantry crane was used to crane formwork out with

support of 04 hydraulic jacks

H.2

2.6 Compressive strength of concrete

15 cylinder specimens were casted for 01st super T girder with the Engineer’s approval 06 specimens

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4

were cured on site at the same curing condition of girder, strength test shall be carried out at 03 and 04

days after casting and compressive strength of these specimens will be used to confirm the time for

cutting PC strand, remaining specimens were cured at site Laboratory, strength Test shall be carried out

at 07 and 28 days after casting

Compressive strength at 03 days: 41.3 MPa ( average)

Compressive strength at 04 days: 43.8 Mpa ( average)

Compressive strength at 07 days: 54.45 Mpa ( average)

3 Cutting PC strand and monitoring camber and cracks

3.1 Cutting PC Strand

Cutting PC strand was carried out when compressive strength of concrete is not less than 42.5 Mpa

( 85% design strength)

Date of cutting : 02rd June, 2011

Concrete strength at 04 days : 43.8 MPa

PC strand were cut individually and simultaneously at two end of girder, cutiing procedure was shown as

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Contract Package 3 countermeasure to prevent reoccurrence

Tokyu Construction Co., Ltd

5

H4

b) After cutting PC strand and cranning girder out of formwork, there were some crack appear at the end of girder.( see the sketch below) H.5

c) After cutting PC strand and move girder to stock yard (after 03 days), there were some crack appear

at the end, the web and the wing of girder ( see the sketch below)

+ At girder web and wing:

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6

H.6 + At girder end:

H.7 Abutment side

3.4 The reasons of incident

We suppose the reason that cracks happen as following:

+In case (a) – H4:

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7

When removing of inner formwork, cracks in partition wall may be due to uplift not

parallel at both ends of the inner formwork

+ In case (b)-H.5 :

After cutting PC strand, the girder was deformed but the formwork is hard and fixed as the end of girder

was subsided and the length of girder was shortened so cracks happened as mentioned above

H.7

+ In case (c)- At the girder end (H.7):

There’s crack that appear at the girder end this may be caused by high tensile force and improper

arrangement of rebar( refer to Shop Drawing or below sketch)

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8

Rebar No NY11-D16 – at the abutment end should be extended to the bottom of rebar frame

Rebar No NL11-D16 – at the Pier end should be extended to the bottom of rebar frame

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9

+ In case (d)- At the girder wing and web (H.6):

After cutting PC strand, the tension force became off-center compression force in concrete from girder

heart, bending moment appear and cracks may happen at the variable cross-section

( see sketch below)

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10

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11

4 Countermeasures to prevent reoccurrence

4.1 Summary of crack locations:

Location: 1 Crack at contiguous location of void and solid section (at girder web)

2 Crack at of contiguous location of void and solid section(at girder wing)

3 Crack of angle on girder end (wing part)

4 Traverse crack at girder end

5 Breaking at the bottom of girder end

6 Breaking of partition of girder

4.2 Countermeasure :

4.2.1 Crack at contiguous location of void and solid section (at girder web)

+ Add more 6 rebars A1-D12, L=1000 mm, @200mm at the connection between void and solid of the

girder (See sketch below)

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12

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13

4.2.2 Crack at contiguous location of void and solid section (at girder wing)

+ Add a re-bar A2-D12, L=3421 mm and a re-bar A3-D12, L=2928 mm

(See sketch below)

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14

4.2.3 Crack of angle on girder end (wing part)

+ Add 2 re-bars A4-D12, L=720 mm and add 2 re-bars A5-D12, L=610 mm, @50 mm and treatment

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15

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16

4.2.4 Tranverse crack at girder end

+ Extend bar NY10-D16 and bar NY11-D16 with length 1329 mm into length 1440 mm

(See sketch below)

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17

4.2.5 Breaking at the bottom of girder end

- Cutting bottom formwork of girder end and change by rubber plate with thickness 3cm, rubber plate

shall be fix with frame of bottom formwork to prevent the rising during casting time

4.2.6 Breaking of partition of girder

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18

Surface grinding of angle of internal formwork, cleaning carefully before installing

- When disassemble inner formwork, using 6 jacks to lift inner formwork up (replace the use 4 jacks as

used on site) after that using gantry crane to crane inner formwork out, special attention shall be paid to

keep the paralleled lift at both side of inner formwork

5 Changing Sequence of cutting PC Strand

+ We consider the effect of cutting PC strand sequence to the crack occurrence and propose to change the

cutting sequence as following

- The procedure of cutting strands as follows: from strand No 18 6 30 31 17 19

5 7 29 32 16 20 4 8  28 33 15 21 27 34 14 22 38 39

26 35 13 23 37 40 25 36  12 24 4142  3 9 210  111

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