presentation on retrofittion of broken pile reinforcement at pile cut off level

WELCOME

CONSTRUCTION SUPERVISION CONSULTANT,PMBPBANGLADESH ARMY

RETROFITTING OF BROKEN RE-BARS DURING CONSTRUCTION OF PILES

FOR BRIDGE FOUNDATION

INTRODUCTION

RETROFITTING: Modifying existing equipment or structures

with additional or new components or members.

SPLICING: Connection of existing broken re-bar with

additional rebar by coupler.

COUPLER: A Mechanical device that connects two thing.

EPOXY-TIE ADHESIVE: Epoxy-Tie (ET) is a two-component,

100% solid system for uses as a high strength, non-shrink

anchor grouting material.

TERMINOLOGIES

A CASE STUDY ON

SIKDERKANDI BRIDGE PILE

INCIDENT

At Sikderkandi Bridge 48 numbers (4x12) of pile under 4

piers and 36 numbers (18x2) of pile under 2 abutments

were designed.

For the pier piles 16 numbers of 32 mm and for abutment

piles 23 numbers of 32 mm re-bars were used.

500 grade Anwar Ispat bars were used in the construction

work. All procedure had been followed for source approval.

The 500 grade Anwar Ispat bars were tested from BUET.

The test result was satisfactory.

After curing period pile heads were broken at the cut off

level for onward construction of pile cap.

Pile heads were broken by using concrete breaker

(Pneumatic Drill) and then upper concrete portion were

removed by crane.

During breaking of pile heads some of the re-bars in

number of piles were broken.

INCIDENT

Sl.No

Structures Pile no of

BrokenBars

Total Bars

per pile

No of Bars

broken per pile

% of broken bars

per pile

No ofPiles per

cap

No of bars per

cap

% of broken bars for

cap

Rmks

1

Abutment-1

Pile-2

23

1 4.35

2.17

Narrow Bridge

2 Pile-5 3 13.04

Wide bridge

3 Pile-10 3 13.04 18 414

4 Pile-12 1 4.35

5 Pile-13 1 4.35

Total Numbers of Broken Bars, AB-1= 9

6

Abutment-2

Pile-1

23

1 4.35

7.49

Narrow Bridge7 Pile-2 2 8.70

8 Pile-10 5 21.74 18 414

Wide bridge

9 Pile-12 5 21.74

10 Pile-13 6 26.09

11 Pile-14 10 43.48

12 Pile-15 2 8.70Narrow Bridge

Total Numbers of Broken Bars, AB-2= 32

STATISTICS OF BROKEN BARSABUTMENT

STATISTICS OF BROKEN BARS

Sl.No

Structures Pile no of

BrokenBars

Total Bars

per pile

No of Bars

broken per pile

% of broken bars

per pile

No ofPiles per

cap

No of bars per

cap

% of broken bars for

cap

Rmks

13 Pier-1 Pile-10 16 1 6.25 12 192 0.52Narrow Bridge

Total Numbers of Broken Bars, Pier-1= 1

14 Pier-2 Pile-4 16 3 18.75 12 192 1.56Narrow Bridge

Total Numbers of Broken Bars, Pier-2= 3

15

Pier-3

Pile-1

16

4 25.00 Narrow Bridge

16 Pile-2 2 12.50

17 Pile-3 3 18.75 12 192 5.21 Wide Bridge18 Pile-4 1 6.25

Total Numbers of Broken Bars, Pier-3= 10

19 Pier-4 Pile-1 16 1 6.25 12 192 0.52Narrow Bridge

Total Numbers of Broken Bars, Pier-4= 1

Total no of Bars for the Bridge - 1596 nos Total no of Bars Broken for the Bridge - 55 nos % of Broken Bars for the Bridge - 3.45 % No of Pile for bars Broken - 19 nos

PIER

Sl.No

Structure Name

Total Piles per

Structure

Total Bars per

Structure

Numbers of Bar Broken

% of Broken

Bars

Rmks

1. Aboutment-1 18 414 9 2.17

2.Aboutment-2

18 414 31 7.49

3. Pire-1 12 192 1 0.52

4. Pire-2 12 192 3 1.56

5. Pire-3 12 192 10 5.21

6. Pire-4 12 192 1 0.52

Total 84 1596 55 3.45

STATISTICS OF BROKEN BARS

EXPLANATION OF CONTRACTOR

Likely Reason for Breaking of Re-bar

About 1.0 m long segment of pile head was broken by

removing skin concrete from the pile re-bar above the cut-off

level and further about 50 mm thick concrete was taken out

inside the core of every individual re-bar at 100 mm above

the cut-off level. Electric drill was used for breaking the

concrete.

Likely Reason for Breaking of Re-bar

Single piece of concrete (approx 4.0 ton) was taken out from

the pile head by Crane. During the process of removal of the

broken concrete from pile head, few main 32 mm diameter

re-bar were broken at cut-off level due to lateral pressure

which may be called Cold Shear Cut of bar.

EXPLANATION OF CONTRACTOR

Contractor’s Proposal to Prevent Breaking ofRe-Bar in Future

Previously minimum 1.0 m length of pile head used to be

broken by removing skin concrete from the pile above

the cut-off level. In future pile head shall be broken 300

mm above the cut-off level by removing skin first and

then 50 mm thick concrete will be broken out from inside

the core of the pile. Thus the core concrete will get

free which will be broken by electric drill.

EXPLANATION OF CONTRACTOR

Contractor’s Proposal to Prevent Breaking ofRe-Bar in Future

Then the single piece of concrete will be taken out from

the pile head. Removal of rest 300 mm will be done by

using chisel upto the cut-off level with care.

EXPLANATION OF CONTRACTOR

1. Extension of broken re-bar will be done by mechanical

splicing system (DEXTRA’s Unitec co-axial) consisting of a

sleeve that is fitted with one longitudinal row of redial bolts

through its wall thickness and 2 longitudinal saddles insides

its inner cavity.

2. Existing broken re-bar will be exposed by removing the

concrete around the broken re-bar upto 150 mm depth over

which the coupler of the splicing system is inserted until

contact with centre pin.

CONTRACTOR’S PROPOSED RETROFICATION SYSTEM

3. The end of the other reinforcing bar is inserted into the

sleeve until contact with a centre pin.

4. The bolts are first hand-tightened with an L-wrench for

pre-locking, and then tightened with a pneumatic ¾’’ power

drive until the heads of the screws shear off.

5. In addition re-bars of same diameter (32 mm) to be

anchored chemically with a 40 mm dia hole, at depth of 350

mm @ 150 mm spacing as technically specified in the

manual of Simpson ET-HP Epoxy.

CONTRACTOR’S PROPOSED RETROFICATION SYSTEM

COMMENTS OF CSC DESIGN CONSULTANT

The comments and recommendations of CSC design

consultant were as follows:

The damages were caused by heavy and hard impact

from pile head concrete mass during removal process.

All other secondary reasons might weaken the re-

bars but not adequate for breaking 32 mm dia re-

bars.

Replenishment of re-bars by DEXTRA’s Unitec co-

axial mechanical splicing is OK.

Retrofitting with 16-32 mm re-bars as inner core is

OK both for abutment and pier piles. The depth of

insertion shall be 400 mm in place of 350 mm as

shown on the drawing for SIMPSON ET22 Epoxy-Tie

Adhesive.

After fixing inner core re-bars, 4 numbers of Stiffener

Rings shall be provided as inner ring along the 1.0 m

extended bars. Spiral of 12 mm bar at 75 mm pitch

shall be provided as outer ring around the existing re-

bars.

COMMENTS OF CSC DESIGN CONSULTANT

PICTORIAL VIEW OF PILE HEAD WITH BROKEN BARS AFTER RECTIFICATION

PLAN OF THE PILE WITH BROKEN BARS

CONCLUSION