Citation:
Panaligan, R., T. Azuhata (2019), Earthquake Performance Evaluation of Typical Bridge
Structures Designed by a Force-Based Design Method in the Philippines, Synopsis of IISEE-GRIPS master
report.

EARTHQUAKE PERFORMANCE EVALUATION OF
TYPICAL BRIDGE STRUCTURES DESIGNED BY A
FORCE-BASED DESIGN METHOD IN THE
PHILIPPINES
Robert Jay N. Panaligan1,2

Supervisor:

Tatsuya AZUHATA3ABSTRACT
The Philippines is an archipelagic country consisting of large and small islands. It is essential to havelink structures like bridges. After a disaster like earthquakes, bridges must be maintained to give way
for an effective rescue operation and transporting of relief goods to the affected area. Most of the bridges
in the Philippines were built on designs using the old code, which is based on the traditional approach,the Force-Based Design Method. In this method, demand and capacity are compared in terms of forces,
and the displacement is verified at the end of the design process. Currently, the Displacement-Based
Design method is the new approach in evaluating the seismic performance of a bridge, which is more
precise in terms of assessing damages, in which the seismic displacement is the primary criterion in thisapproach.
In this study, the author tries to apply the Displacement-Based Design methods to anexisting typical bridge in the Philippines to evaluate the damaged deformation capacity by Nonlinear
Dynamic Analysis (Time History Analysis).
In conclusion, the author extracts some earthquake displacement response characteristics
of typical bridges in the Philippines, which have not been evaluated so far and clarifies the merits of thedisplacement-based design method.
Keywords: Force-Based Design, Displacement-Based Design, Displacement.

1. INTRODUCTION
The Philippines is one of the countries located in the Pacific Ring of Fire, and it is vulnerable to disasters
like earthquakes. Regarding transportation and assistance, bridges play an essential role after disasters
happen. When large earthquakes happened in the Philippines in the past, most of the existing bridges
were damaged due to large deformation or displacement of the columns, resulting in collapse andunseating of the superstructure. For many of the existing bridges in the Philippines, the seismic design
was evaluated with old specifications and done by the traditional approach called the Force-Based
Design Method (FBD) where the force is the main criterion in evaluating the demand and capacity of
the component of structure; therefore, displacement was not checked and also the seismic performanceof bridges could not be evaluated. The linearly elastic procedure is effective as along as the structure1

Department of Public Works and Highways-Bureau of Design, Philippines.
IISEE-GRIPS master course student
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International Institute of Seismology and Earthquake Engineering, Building Research Institute.
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performs within elastic limits. Recently, there is a new approach in evaluating the seismic performance;
this method is called the Displacement-Based Method Design (DBD). Under this method, the primary
criterion is based on displacement, where damage can be checked better (Priestley 2000). The
Displacement-Based Design Method is more reliable to identify the limit states that cause damage,leading to collapse, and in other cases, the results are more efficient in designs against collapse.

2. TARGET STRUCTURE AND APPLIED DESIGN METHOD
The target structure is shown in Figure 1. was designed using DPWH Design Guidelines, Criteria andStandards, 2004 edition and DPWH Department Order No.75, Series of 1992 for seismic design. TheDPWH Design Guidelines, Criteria, and Standards, 2004 edition adopt the concept of AASHTO
Standard Specification for Highway Bridges, 19th Edition, 2002.

Figure 1. General Plan and Elevation of the target bridge.
The target structure considered in this study is a typical bridge structure commonly used inthe Philippines. The bridge structure adopted in this study is located in the southern part of Luzon. Thisbridge crosses a river to connect two significant barangays of the municipalities. The bridge is a threespan prestressed girder bridge with a total length of 60.80 linear meters with seat type abutments. It isa two-way bridge with a total width of 9.34 meters with shoulders. The bridge is supported by two
circular columns, which are confined columns on bored pile foundation. The diameter of the column is
1.0 meter, the unsupported length is 7.35 meters, and 9.95 meters is the height from the bottom of thecolumn to the center of the superstructure. The total weight W, supported by the columns, is 6690 kN.
The column is reinforced longitudinally with deformed bars whose diameter is 18 pcs – 25 mm andwith reinforcement spirals whose diameter is 16 mm. They are used to confine the concrete core, witha space of 70 mm at the plastic region and 100 mm at the center portion of the pier.
In computation of superstructure and substructure weight, we consider 24 kN/m3 for theconcrete weight ratio and 28 Mpa for the compressive strength of concrete for casting in place concrete,
276 Mpa for Reinforcing Steel Yield Stress for Grade 40 and 414 Mpa for Grade 60.
The bridge properties are used as a reference in the creating of analyses model for this study
using the Japan Road Association Specifications for Highway Bridges, Part V, Seismic Design, 2002
(JRA, 2002). The target structure considered in this study is only one of the typical type of bridge
structure in the Philippines. In this study will focus only on the effect for RC piers of the bridge, and it
will conduct analyses with a condition of fix support at the bottom of the pier.
3. SEISMIC RESPONSE ANALYSES ON TARGET BRIDGE FOR THIS STUDY
The objective of this chapter is to evaluate the seismic performance of an existing bridge that is typicalin the Philippines using the Displacement-Based Method to evaluate the effect on the nonlinear
displacement in the bridge structure. The bridge is a three-span bridge supported with two columns pile2

bent pier and abutment. For this evaluation, nonlinear dynamic analysis (time history analysis) will be
used to evaluate the bridge model.
3.1. Outline of the Analysis by Displacement-Based Design Method
In the Displacement-Based Design Method, the main philosophy used in this approach is that thestructure in the seismic region can be designed on specific displacement. This specific displacement
may be characterized by either serviceability or an ultimate criterion. This criterion is likely to be definedby strain limits, which can be related to displacements or drifts of the structure geometry in both cases.
(Kowalsky et al. 1995). For the Displacement-Based Method, we need to evaluate deformation limit,
and deformation response since it predicts the response displacement.
When inelastic behavior is expected, linear static and linear dynamic analyses cannot be
reliable to quantify structural performance precisely; therefore, nonlinear methods must be used. In thisstudy, the nonlinear dynamic analysis, often called the “time-history analysis” is used to evaluate thenonlinear deformation capacity of the system and the numerical model is according to Japan Road
Association Specifications for Highway Bridges, Part V, March 2002 (JRA, 2002).
3.2. Methodology and Analyses Model
The objective of this analysis is to evaluate the nonlinear earthquake response displacement of the target
structures. The following steps were carried out:
1. Evaluation of the Force-deformation relationship
2. Determination of the Limit State for Seismic Performance evaluation.
3. Execution of Nonlinear response time history analysis.
4. Consideration of Seismic Performance based on Capacity Spectrum Method
The bridge structure was modeled as a three-dimensional finite element model with six
degrees of freedom at nodes, as shown in Figure 2.

RollerRoller

Figure 2. Analyses Model.
3.3. Seismic ground motion
Three records of waveform were selected since it is preferable to use as the input earthquake groundmotion as recommended by the Specification of Highways Bridge of Japan Roads Association (JRA,2002) and it is recommended when time history response analysis is used as dynamic analysis method,
it is specified that accelerogram made up of past strong earthquake motion records must be amplitude
to be adjusted so that the characteristics of acceleration response spectra in case of 5% damping ratio ofseismic waves on the base ground surface must match the standard acceleration spectra.
4. ANALYSES OF THE RESULTS
4.1. Time History Analyses results3

In these results, the artificial earthquake ground motions of the Philippines design ground motion arepresented.
The result of the natural period frequency of the bridge is shown in Table 1; this natural
period of a bridge is one of the important parameters to check the elastic response acceleration of thebridge.
Table 1. Natural Time period and frequency of the bridge in this study.

Table 2 shows the result of the response displacement and the limit displacement of thebridge model. It shows that maximum response displacement is less than the allowable or the limit
displacement, which indicates the model bridge is safe.
Table 2. Response Displacement at top.

Table 3 showed that the residual displacement calculated by the JRA method (JRA, 2002)
is in the allowable limit for the Tohoku phase, but it exceeds the allowable limit for the Kobe phase.
Table 3. Residual Displacement at top.

Table 4 shows the result of the shear strength of the reinforced concrete pier. By assessing
the shear strength of the concrete pier, the failure mode of the reinforced concrete can be evaluated. As
the results show, the shear strength is greater than shear forced. Therefore, there is no shear failure in
the pier of the bridge model.
Table 4. Pier Shear Strength.

4.2. Evaluation based on Capacity Spectrum Method
The Capacity Spectrum Method (CSM), will compare the strength capacity of a structure to the demandsof earthquake represented by response spectra (Freeman et al.,1978) (Otani et al., 2000). Response4spectra represent the demands of the earthquake. Linear elastic response spectra, assumed at 5%
damping, are adjusted to represent the effects of nonlinear response by substituting higher damped
response spectra to account for the hysteretic nonlinear response of the structure.

Figure 3. Results of Capacity Spectrum Method.
4.3. Evaluation result of revised model
The result of the evaluation of the revised section for Case 1 (Diameter:1.5m, Number of steel bars
36pcs-32mmϕ) and Case 2 (Diameter:1.5m, Number of steel bars 24pcs-32mmϕ), respectively showsthat the revised section satisfies the demand spectrum curve.

Figure 4. Results of CSM for revised section.

5. CONCLUSIONS
Using a new method like the displacement-based method in evaluating the earthquake performance ofbridge structures, the displacement is the main parameter, which is more precise in terms of assessing
damages. After examining the results of the nonlinear time history analysis, conclusions are as follows:
1. The results of the time history analyses showed that the response displacement did not exceed
the limit displacement. It means that the target bridge will not collapse for severe earthquake
expected by the seismic code of the Philippines.
2. Although the response displacements predicted by the capacity spectrum method corresponded
well to those by the time history analyses, the predicted value exceeded the limit displacement.
3. From the above second results, the author considered that it would be better to make the safetyof the target bridge higher and proposed the revised sections.
4. The results of the capacity spectral method showed the response displacements of the bridge
whose section was revised became smaller than limit displacements.

55. The revised models also satisfy the current seismic code of the Philippines, which was recently
revised in 2013. At this code revision, the R-factor was reduced to 5 to 3 with the same type ofthe bridge
6. We should evaluate the ability of the bridges to return to their original position as well as thedeformation capacity for rapid recovery after earthquakes. The residual displacements
correspond to such ability. The results of this study showed that the residual displacement is in
the allowable limit for the Tohoku phase, but it exceeds the allowable limit for the Kobe phase.
We can express the limit states such as immediate occupancy, life safety, collapse, etc. by
the corresponding limit displacements. By comparing such limit displacements with an earthquake
response displacement, we can precisely predict damage aspects of the structure and assess its seismicperformance.
The limit displacements for the structural design reflects specifications and details of eachstructure which structural engineers adapt flexibly under various construction conditions. Using suchparameters, we can evaluate the seismic performance of the structure according to its uniquecharacteristics. This fact may enable us to extend the design freedom.
Also, by focusing on residual displacements of a structure, we can evaluate thefunctionality or the reparability of the bridge after earthquakes.
And, the author considers that we need the following items to implement the DBD efficiently.
1. Technical guideline to provide how to evaluate force-deformation relationships of a structure
and to determine limit displacements which correspond to some limit states.
2. Practical design computer software, which has functions to evaluate force-deformation
relationships from specifications and details of a structure and so on.

ACKNOWLEDGEMENTS
This research was conducted during the individual study period of the training course “Seismology,
Earthquake Engineering and Tsunami Disaster Mitigation” by the Building Research Institute, JICA,and GRIPS.I want to express my heartiest gratitude to Dr. Jun Yamazaki, a thoughtful person ofsuperlative wisdom, who shared his knowledge with me and gave me useful advice for writing this work.
I also give my most profound gratitude to Dr. Tatsuya Azuhata for guiding me and supporting my work
since I came to Japan. And also I would like to thanks Cosmo Engineering Co., Ltd where I conducted
the part of this research.

REFERENCES
JAPAN ROAD ASSOCIATION (JRA) March 2002, Specification for Highway Bridges, PART V,
SEISMIC DESIGN.
Freeman, S. A., Prediction of response of concrete buildings to severe earthquake motion, Douglas
McHenry International Symposium on Concrete and Concrete Structures, SP-55, ACI, 1978, pp.589605.
Kowalsky MJ, Priestly MJN, Macrae, G., 1995, Displacement-Based Design of RC Bridge Column inSeismic Regions, Published by John Wiley & Sons, Ltd.
Otani, S., Hiraishi, H. Midorikawa., and Teshigawara, M., New Seismic Design Provisions in Japan,
ACI Special Publication Volume, ACI Annual Convention in Toronto, October 16, 2000, pp.87-104.
Priestly MJN, Kowalsky MJ, 2000, “Direct Displacement Based-Seismic Design of Concrete Buildings,”
Bulletin of the New Zealand National Society for Earthquake Engineering Vol. 3, No.4.

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