Tài liệu Nhat tan bridge report on casting of 2nd super t girder

Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge TABLE OF CONTENTS 1. General Description ......................................................................................................................... 2 2. Construction Sequence.................................................................... Error! Bookmark not defined. 2.1 Location Map ..................................................................................................................... 2 2.2 Work duration .................................................................................................................... 2 2.3 Casting sequence................................................................................................................ 2 2.4 Curing concrete.................................................................................................................. 2 2.5 Removal of inner formwork............................................................................................... 3 2.6 Compressive strength of concrete ................................................................................. … 3 3. Cutting PC strand and monitoring camber and cracks…………………………………………… . 3 3.1 Cutting PC strand…………………………………………………………………………..3 3.2 Monitoring camber……………………………………………………………………… ..5 3.3 Monitoring cracks………………………………………………………………………….5 3.4 Checking the defect of girder..……………………………………………………………..6 4. Photograph of construction of second super Tgirder……………………………………………..7 5. Appendix 1 ……………………………………………………………………………………….10 6. Appendix 2 …………………………………………………………………………………….....12 7. Appendix 3 …………………………………………………………………………………….....14 Total: 15 pages 1 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd 1 Report on construction of second Super T Girder- Thiep River Bridge General Description This report describes actual construction procedure of second Super T Girder (G-1-5) of Thiep River bridge. The construction of second super T girder was carried out complying with approved Method Statement, Shop Drawing and countermeasures to prevent reoccurrence of crack after first girder construction. 2 Construction Sequence 2.1 Location Map Super T girder production for Thiep River Bridge was carried out at Vinh Ngoc Temporary Facilities ( appendix 1). Girder No. G-1-5 2.2 Work duration : No Description of work Inspection date 1 Fabrication of rebar cage 21st July, 2011 2 Cleaning formwork 21st July, 2011 3 Installation of Rebar cage 21st July, 2011 4 Installation of PC strand 21st July, 2011 5 Tensioning 22nd July, 2011 6 Installation inner formwork and casting 25th July, 2011 7 Cutting PC strand and craning out of formwork 29th July, 2011 Remark 2.3 Casting sequence. 2.3.1. Supplying concrete. Concrete grade : C50. Design Slump : 16 ± 2.5 cm. (Appendix 2 – Record of casting concrete) 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 32oC and the slump is 16 ± 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 the wing of the girder after casting concrete 6 hours and supplying water to keep the jute in wet condition. 2 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge 2.5 Removal of inner formwork. Inner formwork were removed on 26th July, 2011 after casting 24 hours. Gantry crane was used to crane formwork out with support of 04 hydraulic jacks. H.2 2.6 Compressive strength Test of concrete 15 cylinder specimens were casted for 02nd super T girder with the Engineer’s approval. 06 specimens 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. 3. Cutting PC strand, monitoring, cracks, checking camber and other defect. 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 : 29th July, 2011. Concrete strength at 03 days : 46.0 MPa. Side formwork at the girder end were removed before cutting PC strand (below picture) 3 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge PC strand were cut individually and simultaneously at two end of girder, cutiing procedure was shown as below sketch.. - The procedure of cutting strands as follows: from strand No. 4142  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 3 9 210  111. 4 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd 3.2 Report on construction of second Super T Girder- Thiep River Bridge Checking camber. + The camber after cutting PC strand : 33 mm 3.3 Monitoring of cracks. + After craning out of formwork, the surface of the girder was checked carefully. + There was crack found at the girder end (wing part), please see below photograph. Picture A Picture B( Abutment side) Picture C ( Pier side) + The crack at picture A was found after removing a part of side formwork before cutting PC strand and the crack at picture B and picture C was found after craning girder out of formwork and removal of end formwork . A part of concrete was broken at the girder end (pier side). See picture C. No. Picture A Picture B Picture C Crack width 0.3~0.5mm 0.4~0.65mm 0.15~0.3mm 5 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge  The reason of this crack: + By visual checking on site we found that the reasons caused these cracks were not the prestressing force. The shrinkage of concrete due to the high environmental temperature after casting concrete and inadequate curing may cause these cracks. + At picture C, the shrinkage of concrete combined with prestressing force to make the crack grow and rupture of concrete.  The countermeasure to prevent the reoccurrence: After casting concrete, curing of concrete shall be carried out more carefully, especially the concrete casting was carried out under high environmental temperature. + The monitoring of crack shall be continued and reported immediately if other cracks appear . 3.4 Checking defect of girder. After craning girder out of formwork, some defect were found ( see below picture) Picture D Picture E Picture F 6 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge * The defect at picture D and E caused by leaking of laitance during vibrating concrete. - The reason : the surface of form at the corner was cover by plastic sheet to prevent the leaking of laitance during casting time, unfortunately casting concrete carried out under high environmental temperature so the stickiness of the plastic sheet and the formwork is not good, the plastic sheet came of during vibrating of concrete and the laitance leaking out of formwork. - Measure: + The interstices of the form will be inserted with glue and formwork surface must be clean without oil, grease before the paste with plastic sheet. + The vibration of concrete shall be carried out carefully so as not to loosen the plastic sheet. * The defect at picture F is due to the lack of concrete and vibration of concrete is not enough. - The reason : This area is corner prtion at the bottom of girder, many rebar exist and the rebar arangement was close, so difficult to reach by vibrator. - Measure: + Vibrate the concrete more carefully. 4. Photographs of construction of second super T girder. ( Please find the attachment) 7 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge 8 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge 9 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge APPENDIX 1 (Location Map) 10 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge 11 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge APPENDIX 2 ( Casting record) 12 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge 13 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge APPENDIX 3 ( Casting sequence) 14 Nhat Tan Bridge Construction Project Contract Package 3 Tokyu Construction Co., Ltd Report on construction of second Super T Girder- Thiep River Bridge 15