Post-fire structural assessment and seismic retrofit of Kathmandu District Court Building, Nepal: a case study of torsional irregularity induced by asymmetric fire damage
Dibyashree Poudyal Lohani, Eshwar Raj Joshi, Nabaraj Dhungel, Sarmila Khadka, Milan Malla, Santosh GhimirePurpose
This study aims to assess the post-fire structural integrity of an eight-story reinforced concrete government building in Kathmandu, Nepal, following a 24-h fire event during civil unrest. The research evaluates residual material strength through nondestructive and semi-destructive testing (NDT and SDT), identifies seismic vulnerabilities using Extended Three-Dimensional Analysis of Building Systems (ETABS) analysis and develops a cost-effective retrofit strategy. The purpose is to demonstrate that fire-damaged RCC buildings can be structurally restored without demolition, offering a practical alternative to reconstruction in developing countries where design documentation is often incomplete and resources are constrained.
Design/methodology/approach
A multi-tiered investigation was conducted comprising visual damage mapping, nondestructive testing (rebound hammer and ultrasonic pulse velocity), semi-destructive testing (core extraction, carbonation measurement and rebar elongation tests) and three-dimensional ETABS analysis. Three progressive models were developed: Model I (damaged structure), Model II (steel jacketing of columns) and Model III (steel jacketing + X-bracing). Seismic performance was evaluated per IS 1893:2002 criteria, including story drift, torsional irregularity and P-M-M interaction ratios. The retrofit strategy was validated through comparative analysis of pre- and post-retrofit performance.
Findings
Residual concrete strengths in fire-affected zones ranged from 16.83 MPa to 26.47 MPa, with carbonation depths reaching 25 mm. Structural analysis revealed story drift exceeding the 0.004 limit (maximum 0.005424) and torsional irregularity ratios reaching 1.28 against the 1.2 limit. Column steel jacketing alone restored local member capacity but failed to resolve global seismic deficiencies. The addition of steel X-bracing at perimeter frames successfully redistributed lateral stiffness, achieving full code compliance with drift reduced to 0.002227 and torsional ratios below 1.14. Retrofit cost was estimated at 40–50% of replacement cost.
Research limitations/implications
Original design drawings were unavailable; existing reinforcement was characterized using rebar scanning which cannot reliably determine bar diameter or grade. Fire temperature history was not recorded; peak temperatures were inferred from material degradation patterns. Foundation integrity was assessed visually without excavation or load testing. The lowest core strength (16.83 MPa) was conservatively applied to all fire-affected flexural elements, which may overestimate damage in some areas. Full-scale destructive testing was not conducted. These limitations are consistent with typical post-fire assessments where documentation is unavailable and instrumentation was not present during the fire.
Practical implications
The retrofit strategy offers a cost-effective alternative to demolition and reconstruction, with estimated costs of 40–50% of replacement cost and a construction timeline of 8–10 months compared to 24–30 months for new construction. The systematic assessment methodology – combining visual inspection, NDT/SDT and Extended Three-Dimensional Analysis of Building Systems analysis – provides a practical template for evaluating fire-damaged buildings in developing countries where design documentation is often incomplete. The finding that steel jacketing alone is insufficient to resolve torsional irregularity highlights the need for system-level seismic interventions in fire-damaged structures.
Social implications
Preserving the Kathmandu District Court Building avoids relocation of court functions, loss of evidence and records, and significant public inconvenience. The building serves as a vital judicial infrastructure for Kathmandu District, housing courtrooms, judge chambers, administrative offices and record storage. Its restoration ensures continued access to justice for the community without disruption. The study demonstrates that infrastructure damaged during civil unrest can be systematically restored rather than demolished, promoting resilience and continuity of essential government services. The approach is applicable to other public buildings damaged by fire in developing countries.
Originality/value
This study presents the first documented case in Nepal of post-fire seismic retrofit of an RC building integrating field-based damage mapping, NDT/SDT material testing and system-level seismic evaluation. It uniquely demonstrates that asymmetric fire damage to shear walls creates torsional irregularity (max/avg drift 1.28 > 1.2 limit) – a vulnerability that persists after column jacketing and requires system-level intervention. The poor NDT correlation (R2 = 0.0004) provides field evidence that rebound hammer alone is unreliable for fire-damaged concrete assessment. The validated retrofit strategy offers a practical, cost-effective model for similar structures in developing countries.