Airport Terminal Study Finds Upper-Level Drift Requires Closer Attention Than Foundation Safety

Illustration by Ai

FORMOSA NEWS- Manado

A new study by Franky R. Tombokan, Don R. G. Kabo, Herman Alfis Tumengkol, Noldie E. Kondoj, Dwars Soukotta, and Nixon Mantiri from Politeknik Negeri Manado, published in 2026 in the Jurnal Multidisiplin Madani (MUDIMA), reveals that the reinforced concrete airport terminal structure at Bolaang Mongondow Airport, North Sulawesi, Indonesia, remains structurally safe but has a very limited serviceability margin at its upper floor. The findings highlight that while the building's foundation retains substantial reserve capacity, the upper-story lateral drift is approaching its allowable design limit and deserves greater attention during construction and post-construction inspections.

The research provides a fresh perspective on airport terminal structural performance by shifting the focus from conventional strength verification to serviceability assessment. Instead of asking whether the structure is strong enough, the researchers evaluated which structural components have the smallest remaining safety margin after the design process. This approach is particularly important for public buildings such as airport terminals, where uninterrupted operations depend not only on structural integrity but also on the performance of architectural finishes and mechanical systems.

Why Serviceability Matters for Airport Buildings

Modern airport terminals must remain functional during daily operations and continue performing reliably during environmental loading, particularly in earthquake-prone regions such as Indonesia. Even if structural elements like beams and columns satisfy strength requirements, excessive building movement can damage glass façades, ceilings, partitions, mechanical equipment, and utility systems.

This makes serviceability—a structure's ability to remain functional without excessive deformation—just as important as structural strength. Small increases in lateral movement can disrupt airport operations, increase maintenance costs, and reduce passenger safety and comfort.

The Bolaang Mongondow Airport terminal had previously undergone a complete structural design evaluation. However, the new research revisited the existing engineering data to determine which aspects of the structure have the narrowest performance reserve.

Reanalyzing Existing Engineering Data

Rather than creating a new structural model, the researchers conducted a secondary quantitative analysis using previously generated engineering outputs.

The study reorganized structural information from:

·       ETABS v21 structural analysis software

·       Seismic response spectrum calculations

·       Wind pressure analysis

·       Bored-pile foundation capacity

·       Foundation settlement estimates

Instead of presenting raw engineering calculations, the team converted every result into Demand-Capacity Ratios (DCRs). This simple comparison measures how close each structural response is to its allowable limit.

A DCR below 1.0 indicates acceptable performance, while values approaching 1.0 indicate that the available safety margin is becoming small.

Using the same scale allowed the researchers to directly compare three critical indicators:

·       Inter-story drift

·       Foundation bearing capacity

·       Foundation settlement

Upper-Story Drift Emerged as the Critical Indicator

The analysis identified the 10-meter upper floor as the most critical location in the building.

The maximum lateral drift reached:

·       29.04 mm in the X direction

·       29.04 mm in the Y direction

The allowable drift specified in the design was 30.00 mm.

This produced a Demand-Capacity Ratio of 0.968, meaning the structure still satisfies design requirements but retains only about 3.2% remaining drift margin.

Lower stories showed much larger reserves, indicating that lateral deformation is concentrated near the top of the building rather than being evenly distributed throughout the structure.

Although the building remains compliant with engineering standards, the researchers emphasize that such a narrow margin deserves careful verification during construction.

Foundation Performance Remains Strong

Unlike the upper-story drift results, the airport terminal's bored-pile foundation demonstrated a comfortable reserve capacity.

Key findings include:

·       Maximum axial load: 121.02 tons

·       Allowable pile capacity: 169.22 tons

·       Bearing Demand-Capacity Ratio: 0.715

·       Remaining foundation reserve: approximately 39.8%

Settlement performance was even more conservative.

The predicted settlement measured only:

·       4.956 mm

compared with the allowable limit of:

·       25.4 mm

This corresponds to a settlement utilization ratio of 0.195, meaning approximately 80.5% of the allowable settlement capacity remains unused.

These results indicate that the foundation is not currently the limiting factor in the airport terminal's structural performance.

Wind Loads Were Not the Primary Concern

The researchers also reviewed wind loading conditions.

The calculated velocity pressure reached 1092.12 N/m², producing:

·       Windward pressure: 278.49 N/m²

·       Leeward suction: −185.66 N/m²

Although these values remain important for façade panels, roofing systems, anchors, and exterior cladding, the study concludes that wind effects are less critical than seismic-related drift in determining overall serviceability.

Practical Recommendations for Engineers

Based on the reserve-based assessment, the researchers recommend prioritizing inspections and quality control measures that focus on upper-story structural behavior.

Their recommendations include:

·       Rechecking the ETABS model using cracked-section stiffness assumptions.

·       Verifying diaphragm action and load transfer between slabs, beams, and roof framing.

·       Reviewing façade systems, glazing, ceilings, and mechanical supports for drift compatibility.

·       Maintaining quality control for bored-pile construction despite the strong foundation reserve.

·       Monitoring settlement and visible cracking during the building's early operational period.

These steps can improve long-term reliability without requiring major redesign of the structure.

Implications for Airport Infrastructure

The study demonstrates that evaluating remaining performance margins, rather than simply confirming structural safety, provides engineers with more practical information for risk management.

For critical public infrastructure such as airport terminals, understanding which structural components are closest to their allowable limits helps engineers allocate inspection resources more effectively.

The findings also reinforce the importance of integrating structural engineering with architectural and mechanical system design. Nonstructural components—including curtain walls, ceilings, and mechanical installations—can experience operational problems even when the primary structure remains safe.

As Indonesia continues expanding transportation infrastructure in seismic regions, reserve-based serviceability assessments may become valuable tools for improving construction quality, reducing maintenance costs, and enhancing operational resilience.

As the research team from Politeknik Negeri Manado explains, the study shows that the upper-story drift represents the controlling performance indicator, while the bored-pile foundation maintains adequate reserve capacity. This means post-design verification should focus on lateral serviceability, diaphragm behavior, nonstructural compatibility, and construction tolerance rather than foundation strength alone.

Author Profile

Franky R. Tombokan is a researcher in civil and structural engineering at Politeknik Negeri Manado, Indonesia. His research focuses on reinforced concrete structures, structural analysis, seismic engineering, and infrastructure performance evaluation.

Don R. G. Kabo, the corresponding author, is a civil engineering academic at Politeknik Negeri Manado specializing in structural engineering, reinforced concrete design, earthquake-resistant structures, and engineering analysis for public infrastructure.

Co-authors Herman Alfis Tumengkol, Noldie E. Kondoj, Dwars Soukotta, and Nixon Mantiri are also affiliated with Politeknik Negeri Manado and contribute to research in structural engineering, construction technology, and infrastructure development.

Source

Article Title: Serviceability Margin and Foundation Reserve Assessment of a Reinforced Concrete Airport Terminal Structure in Bolaang Mongondow, Indonesia

Journal: Jurnal Multidisiplin Madani (MUDIMA)

Publication Year: 2026

DOI: https://doi.org/10.55927/mudima.v6i6.64