A Bi-Hazard Fragility Curve
Development for the Assessment
of Kagay-an Bridge in Cagayan
de Oro City
DR. MICHAEL B. BAYLON,D.Litt.PICE, SEAD, IABSE, ISHMII
Civil Engineering Department,
College of Engineering
Polytechnic University of the Philippines

The Team: XU
• Nikki Amores
• Garnelo Cupay
• Alexander Christian Doong Legaspi
• Paul Gilbert Legaspi
• Isaiah Alisteir Sudayan Cabanaz
• Prof. Dexter Lo

Aerial view of the Kagay-an Bridge connecting
the Rodelsa Circle and Barangay Carmen

Background
• The Philippine archipelago frequently experiences numerous natural
disasters such as severe tropical storms, earthquakes, and sometimes
volcanic eruptions.
• As defined by the United Nations International Strategy for Disaster Risk
Reduction (UN-ISDR, 2004), disaster is the disruption of the normal
functioning of a society which leads to serious damages and losses to
human lives, properties, economy, and to the environment.
• It also exceeds the capacity of the affected communities to cope up with
the damages.
• Earthquake and flood events are the predominant natural disasters in the
Philippines and they, given their frequent recurrence, make the country
highly vulnerable.

The Anao-aon Bridge after the magnitude-6.7
Surigao del Norte Earthquake
the country had also
experienced strong earthquake
events in the past such as the
magnitude-6.7 Surigao del Norte
Earthquake last February 10,
2017. The communities in the
surrounding provinces were
severely affected, and according
to National Disaster Risk
Reduction Management Council
(2017), the earthquake was an
Intensity VII (Destructive)
earthquake. Infrastructures such
as the Anaoaon Bridge in Surigao
City collapsed.

The Kagay-an Bridge during Severe
Tropical Storm (STS) Vinta last 2017
On the other hand, flooding is defined as
the overflowing of the water level in bodies
of water such as rivers and creeks which
leads to an inundation of a usually dry area
of land. Severe Tropical Storm (STS) Vinta,
internationally known as STS Tembin, had
wreaked havoc in Misamis Oriental last
December 2017 – inundating several
municipalities and cities. In the midst of the
event, the flood threatened to overflow the
Cugman Bridge, a highway bridge in
Cagayan de Oro City. Rappler (2017)
reported that the bridge is no longer
passable at that time due to a crack from
the severe flooding

Objectives
To determine the level of performance of the Kagay-an Bridge when
subjected to flood and seismic events.
More specifically, the study targets to:
1. To determine the physical and structural design specifications of the
Kagayan Bridge in order to create its digital structural model;
2. To determine the design spectral acceleration, and the force due to
wave velocity;
3. To determine the structural capacity of the Kagay-an Bridge when
subjected to different seismic and wave loads;
4. To produce the fragility curve of the Kagay-an Bridge subjected to flood
and seismic events.

Conceptual Framework

Ground Motion Data (time history)

Seismic fragility analysis
• There are different analysis techniques and methodologies that can be used
in assessing the seismic capacity of structures.
• For instance, Zhang, Acero, Conte, Yang, and Elgamal (2004) utilized the
performance-based earthquake engineering (PBEE) methodology to assess
the Humboldt Bay Middle Channel Bridge.
• Whereas, Tehrani and Mitchell (2012) conducted a seismic performance
assessment on bridges in Montreal using Incremental Dynamic Analysis
(IDA) method.
• These and other seismic fragility analyses are represented as either Damage
Probability Matrix (DPM) or Fragility Function.
• On the other hand, Taghipour and Yazdi (2015) utilized two techniques, the
nonlinear static (Pushover) analysis and the nonlinear dynamic analysis on a

Seismic fragility curves
• Seismic fragility is the probability of damage to a structure
given a certain earthquake intensity.
• Seismic fragility curves graphically represent the estimated
structural performance of the bridge structure during
earthquakes.
Fragility Curve of a Bridge as a Function of
Peak Ground Acceleration.

Flood fragility analysis
• Lee J., Lee Y., Kim H., Sim, and Kim J. (2016) proposed a
methodology for deriving flood fragility curves by
means of structural reliability analysis with the failure
modes defined as excessive demands of the
displacement ductility of a bridge under increased
water pressure from accumulated debris and structural
deterioration.

Research Design

Research Design

The Kagay-an Bridge during rush hour.
(Photo was taken by Kaye Quiblat)

The Bridge Model

CAPACITY SPECTRUM METHOD

Flood Fragility Curves

Flood Fragility Curves

Flood Fragility Curves

Flood Fragility Curves

Flood Fragility Curves

CONCLUSION
• According to HAZUS® – MH 2.1 by FEMA, when the
bridge piers reached a 10% probability of having a
“Moderate Damage”, the city’s engineers and other
concerned officials should temporarily close the bridge
and are required to conduct a thorough inspection on
the bridge piers, specifically on the locations where the
critical hinges are.
• This could happen to Kagay-an Bridge if Cagayan de Oro
City experiences an earthquake with PGA of 0.8g (the
PGA of Great Hanshin Earthquake in Kobe, Japan) along
its longitudinal axis, and 1.2g along the transversal axis.

CONCLUSION
• Through quantitative-probabilistic approach, the flood fragility curves
of Kagay-an Bridge pointed out that when water velocity increases,
there is a higher probability that the bridge will experience damage due
to flooding.
• Also, it does not matter if the flood depth reaches the full height of the
columns because if the water only has a velocity of 0-15 m/s, the
probability of “Moderate Damage” in the bridge piers is less than 10%.
• Therefore, flood cannot significantly damage the Kagay-an Bridge
unless the water reaches a velocity higher than 20 m/s, which is very
unlikely.
• This stands true since the past flood events of Typhoons Sendong and
Vinta in Cagayan de Oro City can attest that, even though their flood
depths reached the bridge deck of Kagay-an Bridge, the bridge did not
fail or experienced any damage because the water velocity of these
flood events is less than 16 m/s.

RECOMMENDATION
• Using the fragility curves, structural threshold values are
determined which can be used in structural health monitoring,
that is, the bridge has preventive measures when time comes.

RECOMMENDATION…
• “A study on the numerical modeling of Kagay-an Bridge
with application of Fibre-reinforced Geopolymer
Composites”
• “Performance based assessment of Fibre-reinforced
Geopolymer Composites applied to Kagay-an Bridge: A
multi-hazard fragility analysis approach”

REFERENCES
• Lee, Jaebeom, Lee, Young-Joo, Kim, Hyunjun, and Sim,
Sung-Han (2016). Flood fragility analysis for multiple
failure modes of bridges by finite element reliability
analysis. The 2016 Structures Congress (Structures16).
• Amores, N., Cabanaz , A. S.,Cupay, G. A., Legaspi, A. C.
D., Legaspi, P. G., Isaiah (2019) Flood and seismic
fragility curve analysis of Kagay-an bridge in Cagayan de
Oro City. Undergraduate Thesis. Xavier University. CDO
• Baylon, M.B. (2017) Developing fragility curves in
seismic assessment of bridge. Lambert Academic
Publishing: Berlin Germany

THANK YOU FOR LISTENING.
Dr. Michael B. Baylon
mbbaylon@pup.edu.ph
embylondesign@gmail.com
ikingbalon@gmail.com
FB: Emby Binoe