Ho Chi Minh City Urban Railway Construction Project

Ben Thanh - Suoi Tien Section (Line 1)Contract Package 2 : Civil (Elevated & Depot)Doc.No.: HCMC-240-SBRC-CVS-RPT-000XXRev: A

Date: 10th Oct. 2014Page: 9 of 9

TITLE :

Technical Verification about Vertical Reinforcement for Pilecap of Rach Chiec Bridge (RC1~RC-3)

PROJECT TITLE: Ho Chi Minh City Urban Railway Construction ProjectBen Thanh - Suoi Tien Section (Line 1)Contract Package 2 : Civil (Elevated & Depot)

Technical Verification about Vertical Reinforcementfor Pilecap of Rach Chiec Bridge(RC1~RC3)

REVISION STATUS

REV. No.DATEDESCRIPTIONREMARKS

A10th Oct. 2014FIRST ISSUE

PREPARED BYCHECKED BYAPPROVED BY

NAMEH. W. JeeS. H. JunH. D. Vidjak

SIGNATURE

DATE10th Oct. 201410th Oct. 201410th Oct. 2014

TABLE OF CONTENTS31.Introduction

52.Technical Verification about Vertical Reinforcement between Upper and Lower Concrete of Pile Cap of Rach Chiec Bridge (RC1)

52.1.Basis of Check

52.2.Shear Check for Rach Chiec Bridge (RC1 : Thickness 3.0 m)

72.3.Shear Check for Rach Chiec Bridge (RC2 and RC3 : thickness 4.0 m)

92.4.Result of Shear Check

93.Conclusion

1. IntroductionPile caps of Rach Chiec Bridge (RC1~RC3) of Metro Project are considered as massive structure as specified in the outline construction specification (Because RC4 was not received NONO, RC4 will be submitted separately). Therefore, early-age thermal crack on surface of pile cap, which should be strictly controlled, could be induced because of the temperature rise in massive concrete due to hydration heat during initial curing period.For same reason, SCC carried out prediction of probability of crack occurrence through checking cracking index for Pile cap of Saigon Bridge. Report of this hydration analysis was submitted on 17th Dec. 2013 and received NONO on 8th Jan. 2014. (Transmittal Ref. No. UMRTL1-CP2-SBSG-CVS-RPT-00193-B).

According to table 1 Pile Cap Size of Rach Chiec Bridge (RC1~RC3), pile cap size of Rach Chiec Bridge (RC1~RC3) is same or smaller than pile cap size of Saigon Bridge. Because it is clear that bigger size (bigger area and shape of square) have bad influence to thermal crack, pile caps of Rach Chiec Bridge (RC1~RC3) are considered safer than pile cap of Saigon Bridge.Table 1 Pile Cap Size of Saigon Bridge and

Rach Chiec Bridge (RC1~RC3)B (m)D (m)H (m)

Saigon Bridge (Intermediate Pier)16.016.04.0

Saigon Bridge (Side Pier)7.011.53.0

Rach Chiec Bridge (RC1)7.011.53.0

Rach Chiec Bridge (RC2, 3)8.920.54.0

So, SCC would like to propose to apply same curing method of Saigon Bridge as followings to pile cap of Rach Chiec Bridge (RC1~RC3) without Hydration Analysis. Step 1 : Pouring concrete until half height of the pile cap Curing with styrenefoam or glass wool mat (2 W/m2 oC) on side and with water sprinkling on top for 10 days under 30 oC (The 10-day

includes the time of assembling rebars for the upper part of the pile

cap) Step 2 : Pouring concrete for the rest of the pile cap ; Curing with styrenefoam or glass wool mat (2 W/m2 oC) on side and top for 5 days under 30 oC

And technical verification about vertical reinforcement between upper and lower concrete of pile cap of Rach Chiec Bridge (RC1~RC3) is provided in Chapter 2. (This technical verification is provided by Designer)2. Technical Verification about Vertical Reinforcement between Upper and Lower Concrete of Pile Cap of Rach Chiec Bridge (RC1)2.1. Basis of CheckConcerning the construction method for the pile cap of Rach Chiec Bridge (RC1), Contractor proposed to divide the concreting into two lifts with the construction joint at approximate mid-depth of pile cap. Designer has evaluated the possible impact to the structural function of pile cap basing on the potential interface shear at the mentioned construction joint. (Reference 22-TCN-272-05 Chapter 5.8.4.2 Cohesion and Friction) 2.2. Shear Check for Rach Chiec Bridge (RC1 : Thickness 3.0 m)

2.3. Shear Check for Rach Chiec Bridge (RC2 and RC3 : thickness 4.0 m)

2.4. Result of Shear CheckThe result of shear check is that additional vertical reinforcement shall be provided on the area between pier column and piles with the minimum area like as following. This reinforcement shall be anchored to develop full strength tensile force from both side of construction joint. In addition, the surface of the first lift of concrete at construction joint shall be intentionally roughened to amplitude of 6mm, and this surface shall be cleaned up before casting of second lift. This is proposed to be applied to all above mentioned pile caps.Table 2 Additional Vertical Reinforcement of Rach Chiec Bridge (RC1~RC3)

Quantity of Reinforcement

Rach Chiec Bridge (RC1)12.1 cm2 / m2

Rach Chiec Bridge (RC2 and RC3)10.7 cm2 / m2

3. Conclusion About measure of thermal crack on pile cap of Rach Chiec Bridge (RC1~RC3), SCC would like to propose same method used at pile cap of Saigon Bridge without Hydration Analysis.- Step 1 : Pouring concrete until half height of the pile capCuring with styrenefoam or glass wool mat (2 W/m2 oC) on side and with water sprinkling on top for 10 days under 30 oC (The 10-day includes the time of assembling rebars for the upper part of the pile cap)- Step 2 : Intentionally roughen the surface (construction joint) of the lower concrete with an amplitude of 6mm- Step 3 : Pouring concrete for the rest of the pile capCuring with styrenefoam or glass wool mat (2 W/m2 oC) on side and top for 5 days under 30 oCBy proposed method for curing pile cap concrete of Rach Chiec Bridge (RC1~RC3), SCC can avoid thermal crack and ensure quality of pile cap of Rach Chiec Bridge (RC1~RC3).