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Bridge Pavement Repairs Due To Tnb Cable Fault

 

A) INTRODUCTION

TNB 33kV cables caught fire on the Selat Lumut Bridge, FT181 Pulau Indah, Klang, Selangor. The incident occurred on 28/04/16 at 5:50 am, and immediately afterwards the Fire and Rescue Department arrived at the scene for the fire fighting operations. As a result, the FT181 route heading towards KESAS Highway (E8) was closed to traffic, and traffic were diverted to SKVE as an alternative route. At the height of the jam, massive traffic crawls were observed on KESAS bound that stretched several kilometres at the SKVE Jenjarum Exit.

 

B) DAMAGE IMPACT TO BRIDGE PAVEMENT

Black smoke was seen blowing at the stretch where the cables were located under the bridge, through the damaged expansion joints. The fire resulted in heaving pavement, minor spalling underneath concrete deck slab, and impaired expansion joints especially along the stretch of the cables, which is approximately 350m on the slow lane of the 1000m total length of the bridge.

 

C) IMMEDIATE ACTIONS BY AUTHORITIES

PDRM Police Traffic upon consultations from JKR decided to close the road towards KESAS (on both lanes), immediately after the incident. The other side of the bridge heading towards West Port was allowed to open to traffic as it was not affected by the cable fault. In the meantime, JKR had instructed RCSB personnel and Subcontractor to get a close watch of the situation and reported to JKR on hourly basis. Milling works were allowed to proceed on the affected areas, whilst awaiting for the approval for asphalt laying.

 

D) SECOND OCCURRENCE OF POWER CABLE FIRE

It was observed and reported by RCSB personnel on standby, monitoring the situation that another cable caught fire occurred at around 3:15 am. This has prompted RCSB personnel and Subcontractor carrying out the milling works leaving the site for safety. PDRM and Fire and Rescue Department were alerted on this incident, and precautionary measures were taken.

 

Although the fire had been fully contained, TNB and the Fire and Rescue Department were still monitoring the situation at the location during rectification works.

While a full investigation is ongoing, initial findings so far point to suspected vandalism as the cause of the fire, according to TNB. The incident only caused temporary power disruption as TNB was able to feed supply from an alternative cable unaffected by the fire.

 

E) BRIDGE INSPECTION BY AUTHORITIES

The next morning on 29/04/16, Authorities from JKR, TNB, Bomba, PDRM visited the site and held the press conference, led by TKP JKR, Dato’ Ir Roslan Taha. The authorities were brought to the affected areas underneath the bridge to assess the damage and cause of the incident. Immediately after the visit, several measures and actions were taken to immediately restore the situation, and opened the bridge to traffic.

 

Once the fire was brought under control and the fire debris was being cleaned up, JKR set to work to decide if the bridge could be reopened to traffic. Since the fire was isolated to only the bay that contained the duct banks, the associated damage was limited to that area. The bay that was involved with the fire is located under the carriageway of the slow lane, and there was no damage to areas that are subjected to vehicular traffic.

 

F) STRUCTURAL INSPECTION UNDERNEATH BRIDGE

The brief structural inspection was completed and the damage was revealed to be limited to the concrete deck and the concrete girders. The underside of the concrete deck had spalled and exposed some of the reinforcing steel (???).After the brief inspection it was determined that the bridge could not be reopened (Klang Town bound) until the paving works are completed.

JKR also studied and reviewed bridge construction drawings to determine appropriate assessment techniques and to identify key areas susceptible to fire damage and diminished load carrying capacity.

The underside of the concrete deck below the sidewalk was spalled to only a few extents (???). The exposed reinforcing steel was generally in good condition and did not show any signs of damage. It was determined that all spalled areas of concrete and areas of exposed reinforcing steel could be repaired.

Based on professional judgment by JKR, the structural capacity of the concrete deck had not been compromised. The concrete that spalled off was just cover concrete to protect the primary reinforcing. The heat of and length of this fire precluded damage to portions of the deck that may have reduced the structural capacity. JKR, therefore determined that the deck could still support its original design loads.

The repair included saw cutting around the damaged areas, removing deteriorated concrete, sandblasting the underside of the deck (to remove soot and other thin areas of damaged concrete), placement of epoxy coating over exposed reinforcing steel, and patching the concrete with an anchored concrete mortar patch material.

 

G) TESTING CARRIED OUT TO DETERMINE PAVEMENT STRUCTURAL INTEGRITY

Whilst allowing the milling works to proceed, JKR had instructed RCSB to carry out coring works on the deck slab at the affected areas. The purposes of the coring are to determine the structural integrity of the pavement, and the thickness of the slab as a results of the effect of the power cable fire. Construction drawings dated in year 1990 when the bridge was built were also brought to the site as a reference to the cored samples.

Two (2) samples were cored to justify the thickness of the deck slab, and the structural strength, which were later sent to the laboratory for testing.

 

H) RESULTS OF CORED SAMPLES ON THE DECK SLAB

The first cored sample was taken at Sect XXX, which is located at 4600mm from the inside of the kerb. The thickness was found to be 150mm, which is taken at the upper layer of the slab underneath cover. The second cored sample was obtained with the total slab thickness of 165mm.

The Selat Lumut Bridge, FT181 upon cored sampling and testing are declared safe for travel, after the power cables caught fire on the morning of 28/04/16.

 

I) LESSONS LEARNED

After this adverse fire, JKR especially, and we generally, should realize just how vulnerable our infrastructure system was. This incident perhaps has undergone a change in the way we look at our vulnerabilities, and has undertaken an effort to better understand our safety shortcomings.

From now on, each bridge site shall be examined for undesirable accessibility to critical areas, potential fire hazards such as deficient utility conduits, and other areas that could create a potential for damage by vandalism.

For utility provider, especially on the few major bridges that continue to carry utility conduits similar to the ones that occurred on the Selat Lumut Bridge, implementation effort shall be made in installing steel blast plates and insulation to prevent flame and heat impingement from accessing the conduits.

On the part of RCSB, the following measures shall be taken for effective and expedient approach towards handling of such occurrence:-

  • Immediately mark and set out the actual location affected (corridor of TNB cables caught fire which result in heaving pavement, etc) and counter check with the construction drawings.

 

  • Identify list of independent laboratories to carry out relevant testing (especially during emergency when KISB Lab is not immediately available due to other commitments)

 

  • Response team shall be readily available and immediately attend to the incident upon receiving of emergency information

 

  • TMP devices and equipment shall be delivered immediately and sufficiently to the place of incident for the safety of road users (i.e spotlight, blinkers, barriers, etc)

 

  • Necessary equipment related to the remedial works of this nature shall be provided (such as skylift, etc) for the ease of job operations.

 

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