CIVIL ENGINEERING CONSTRUCTION CORPORATION No.4
PROJECT MANAGEMENT BOARD – NHAT TAN P-3

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REPORT ON COUNTERMEASURE OF CRACKING OF SUPER T GIRDER
I. General
After first girder casting finished, through process of monitoring, we found that there are some cracks and breaking concrete at locations
as follows:

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:
CIVIL ENGINEERING CONSTRUCTION CORPORATION No.4
PROJECT MANAGEMENT BOARD – NHAT TAN P-3

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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


(See picture in Appendix 4)
+ Countermeasure: Extend bar NY10-D16 and bar NY11-D16 with length 1329 mm into length 1440 mm.
A
B
CIVIL ENGINEERING CONSTRUCTION CORPORATION No.4
PROJECT MANAGEMENT BOARD – NHAT TAN P-3

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5. Location: Breaking angle of bottom of girder
(See picture in Appendix 5)
+ 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
(See picture in Appendix 6)
+ 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.

CIVIL ENGINEERING CONSTRUCTION CORPORATION No.4
PROJECT MANAGEMENT BOARD – NHAT TAN P-3

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Appendix 3
Crack of angle on top of girder end CIVIL ENGINEERING CONSTRUCTION CORPORATION No.4
PROJECT MANAGEMENT BOARD – NHAT TAN P-3

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Appendix 4
Traverse crack of girder end
CIVIL ENGINEERING CONSTRUCTION CORPORATION No.4
PROJECT MANAGEMENT BOARD – NHAT TAN P-3

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Appendix 5
Breaking angle of bottom of girder CIVIL ENGINEERING CONSTRUCTION CORPORATION No.4
PROJECT MANAGEMENT BOARD – NHAT TAN P-3

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Appendix 6

Nhat Tan Bridge Construction Project Report on casting figure, crack happen and Construction
Contract Package 3 countermeasure to prevent reoccur
rence
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

Super T girder production for Thiep River Bridge was carried out at Vinh Ngoc Temporary Facilities
( appendix 1).
Girder No. G-1-12
2.2 Casting time :

Casting date : 28
th
, May 2011
Casting duration : 17h30’ to 22h27’
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)
2.3 Casting sequence.
2.3.1. Supplying concrete.
Concrete grade : C50.
Design Slump : 15 ± 2.5 cm.
2.3.2. Work procedure.
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 32
o
C 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.


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 : 02
rd
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
below sketch.

H.3
3.2 Monitoring camber.
- Camber after cutting PC strand : 34 mm
3.3 Monitoring cracks.
a) When removing inner formwork,
Nhat Tan Bridge Construction Project Report on casting figure, crack happen and Construction
Contract Package 3 countermeasure to prevent reoccur
rence
Tokyu Construction Co., Ltd
We suppose the reason that cracks happen as following:
+In case (a) – H4:
Nhat Tan Bridge Construction Project Report on casting figure, crack happen and Construction
Contract Package 3 countermeasure to prevent reoccur
rence
Tokyu Construction Co., Ltd 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).

Rebar No. NL11-D16 – at the Pier end should be extended to the bottom of rebar frame
Nhat Tan Bridge Construction Project Report on casting figure, crack happen and Construction
Contract Package 3 countermeasure to prevent reoccur
rence
Tokyu Construction Co., Ltd 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). Nhat Tan Bridge Construction Project Report on casting figure, crack happen and Construction
Contract Package 3 countermeasure to prevent reoccur
rence
Tokyu Construction Co., Ltd 10