Root of the problem: It is trees on KR Puram bridge

While additionally raising questions over whether authorities are carrying out regular maintenance, BENGALURU: Vegetation growing from cracks, retaining-wall surfaces pointing to feasible moisture ingress, cracking and reinforcement corrosion (rust and breakdown of steel bars inside concrete) at the KR Puram cable-stayed bridge have triggered concern.

Key points

• Agreeing with him, a senior engineer from Greater Bengaluru Authority's Road Infrastructure wing remarked the bridge was designed for the traffic and loading conditions of early 2000s.
• Chandrashekar Sharma, General Manager (Technical), STRUCT REHAB Pvt Ltd, remarked that vegetation emerging through structural or retaining concrete is not just a housekeeping problem.
• One of Bengaluru's technically significant structures, it was commissioned in 2003.
• There is something called Structural Health Monitoring (SHM) of Bridges and Flyovers.
• The engineer continued that a bridge of this age (23 years) should not be judged on visual appearance alone and a comprehensive assessment should be established.

One of Bengaluru's technically significant structures, it was commissioned in 2003. The bridge carries four lanes of traffic over the Krishnarajapuram railway station on a 106-metre cable-stayed main span.

Chandrashekar Sharma, General Manager (Technical), STRUCT REHAB Pvt Ltd, remarked that vegetation emerging through structural or retaining concrete is not just a housekeeping problem. It can indicate cracks, joints, voids, porous concrete or pathways through which moisture has entered, and root expansion can progressively widen openings and retain moisture, accelerating deterioration.

Agreeing with him, a senior engineer from Greater Bengaluru Authority's Road Infrastructure wing remarked the bridge was designed for the traffic and loading conditions of early 2000s. Bengaluru's eastern corridor has since undergone substantial urban and traffic expansion, and the bridge now operates in a far more intense environment.

"There is something called Structural Health Monitoring (SHM) of Bridges and Flyovers. The expansion of trees and their roots becoming stronger by the day is evidence that these factors have not been given prominence. An assessment of all the bridges should be done on priority, " remarked the engineer.

Meanwhile, the assessment should weigh current traffic volume and composition, heavy commercial-vehicle movement, traffic loading and induced vibration, present lane usage and repeated loading, congestion-related effects, and changes in road geometry, drainage and surrounding development to establish whether current operational loading and structural condition remain compatible with the bridge's original design basis and any subsequent modifications.

In practice, the engineer continued that a bridge of this age (23 years) should not be judged on visual appearance alone and a comprehensive assessment should be established.

Its present load-carrying capacity, actual condition of structural concrete, extent and rate of reinforcement corrosion, loss of reinforcement cross-section where corrosion has occurred, development and severity of structural cracks, concrete strength and uniformity, depth and extent of carbonation, chloride penetration, wherever relevant, concrete cover and reinforcement location, condition of bearings, condition of expansion joints, condition of stay cables, anchorages and associated components, feasible loss of prestress or tension in relevant components, excessive deflection or abnormal deformation, foundation and substructure condition, and feasible settlement, condition of piers, abutments, retaining structures and deck, drainage and waterproofing deficiencies, present traffic loading against original design assumptions.

For context, the objective is to move from visible deterioration to measured engineering evidence, the engineer remarked. The assessment should be led by an independent, technically competent bridge/structural engineering team, backed by appropriately accredited testing facilities, he went on.

While traffic volumes, vehicle weights and environmental exposure have grown substantially, sharma remarked a number of major bridges and elevated structures throughout the city have now been in service for decades. Modern repair and rehabilitation technology offers plenty of options for extending service life, but is only effective when the challenge is correctly diagnosed first, he continued.

Meanwhile, a systematic city-wide programme can identify all major aging bridges, flyovers, Railway Over Bridges and Railway Under Bridges and elevated structures and classify them by age, traffic importance, structural condition, deterioration rate and consequence of failure, prioritising detailed assessment and rehabilitation accordingly. The aim is to shift the prevailing pattern, like complaint-driven temporary repair, to deterioration-based management and another complaint to a structured cycle like inventory inspection, structural analysis, diagnosis, repair and design, rehabilitation, corrosion protection monitoring and periodic reassessment, Sharma remarked.

For now, root of the problem: It is trees on KR Puram bridge remains the part of the story worth watching, and further updates are likely as more details are confirmed.