NCR : Highway Construction : Box Girder Alignment Deviation

 

This case study is from 2012. All project details have been intentionally anonymised to protect confidentiality. I am grateful to the former Superintending Consultant for sharing this valuable reference.

NCR No.: NCR-HWY-...-.... | Date Raised: 202x-0X-xx

Area: Bridge Superstructure : Box Girder Segment B2,

Chainage CH 12+300 to CH 12+320, Gridline C1–C2

Clause Reference: JKR Bridge Works Clause 7.3.2

Severity: Medium | Disposition: Rework (Realignment)

1.0 PROJECT CONTEXT

Highway bridge works involving cast-in-situ reinforced concrete Box Girders.

During routine inspection of the box girder segment placement prior to post-tensioning, an alignment deviation was detected.

2.0 DESCRIPTION OF THE NON-CONFORMANCE

The horizontal alignment of Box Girder Segment B2 deviated +45 mm from approved design centreline after formwork stripping.

2.1 Tolerance Reference

• JKR Specification: Civil Works Clause 7.3.2 – Alignment tolerance for bridge superstructure: ±30 mm,

• BS 5400 / Eurocode / AASHTO: Similar ±25-40 mm depending on span and structure class.

• JKR QA/QC Plan (Project Specific): Alignment control and surveying tolerances.

This deviation exceeds the allowable tolerance (±30 mm)

2.2 Evidence/Attachments

• Site photographs,

• Survey records,

• Inspection checklist,

• Test results

• Sketch/marked-up drawing

Classification : Medium Risk NCR (not severe to halt works but must be corrected before post-tensioning).

3.0 FINDINGS

4.0 REFERENCE

• JKR Specification for Bridge Works,

• JKR Standard Drawings (SJ / SK / SP series),

• BS 5400 / Eurocode 2 / AASHTO LRFD (for reference),

• Project QA/QC Plan & Inspection Test Plan (ITP)

• Survey Control Method Statement

5.0 CALCULATIONS/SURVEY VALIDATION

Survey Data (Before & After)

• Design Line: X = 1,250.000 m

• Measured After Stripping: X = 1,250.045 m

• Deviation: Δ = 0.045 m ⇒ 45 mm

5.1 Tolerance Check

| 0.045m | =45mm>30mm (JKR tolerance)

= OUT OF TOLERANCE

5.2 Effect on Post-Tensioning

Misalignment may induce eccentricities, resulting in:

• Stress redistribution

• Potential cracking

• Post-tensioning stressing inefficiencies

A quick simplified check:

6.0 METHOD FOR CORRECTIVE ACTION (Corrective Realignment of Box Girder Segment B2)

6.1 Activities

Set up precision total station and re-establish control points.

• Verify existing alignment and mark deviation.

• Loosen temporary supports (if any) under segment B2.

• Apply controlled jacking (using hydraulic jacks) to shift girder laterally to design centreline.

• Monitor moves in real time (surveyor continuously records).

• Lock off and resecure formwork anchors and supports.

• Re-survey final position and record in NCR corrective action.

• Pre-stress only after verification by QA/QC and Resident Engineer.

6.2 Resources

• Hydraulic jacks and load cells

• Total station and Optical targets

• Trained survey crew

• Supervision by Structural Engineer

6.2 Acceptance Criteria

• Final alignment within ±20 mm (stricter than JKR tolerance for safety)

• Record updated survey logs

7.0 ROOT CAUSE ANALYSIS

oot Causes

• Survey control points not adequately protected during casting = drifted,

• Inadequate formwork bracing = lateral movement under concrete pressure.

8.0 CORRECTIVE ACTIONS

Immediate:

• Realign girder segment (as per method statement),

• Reestablish and secure all survey control points,

• Resurvey all adjacent segments.

9.0 ROLES, RESPONSIBILITIES AND AUTHORITIES

10.0 PREVENTIVE ACTIONS

• Update Survey Control Method Statement,,

• Install redundant benchmark targets,,

• Daily verification of bracing and formwork stability,

• Pre-pour check sign-off with 2-person independent verification,

• Toolbox talk for crew on tolerance requirements

11.0 IMPACT ASSESSMENT AND RISK REGISTER UPDATE