This document provides guidelines for seismic bridge design in the Philippines. It defines three operational classifications for bridges based on their importance and expected performance after an earthquake. It also establishes two levels of ground motion and provides maps showing peak ground acceleration, short period spectral acceleration, and long period spectral acceleration for level 2 ground motion. Finally, it defines procedures for determining the design response spectrum and elastic seismic response coefficient based on the bridge's period and the site classification.

1. RESPONSE SPECTRUM
Bridges Division
Bureau of Design

2. The DPWH Guide Specifications for Seismic
Bridge Design is prepared under the
Project for Study on Improvement of
Bridges through Disaster Mitigating
Measure for Large Scale Earthquakes in
the Republic of the Philippines

3. Applicability of Specifications
These Specifications shall be taken to apply to the design and
construction of conventional bridges to resist the effects of earthquake
motion.
Conventional bridges:
• Flat Slab
• Reinforced Concrete Deck Girder (RCDG)
• Prestressed Concrete Deck Girder (PSCG)

4. Bridge Operational Classification
Operational Classification (OC) Serviceability Performance
OC-I (Critical Bridges) Brides that must remain open to all traffic after the Level 2
design earthquake.
OC-II (Essential Bridges) Bridges that should be as a minimum, be open to emergency
vehicles and for security/defense purposes within a short period
after the Level 2 design earthquake.
OC-III (Other Bridges) All other bridges not required to satisfy OC-I or OC-II
performance.
Note:
The DPWH or those having jurisdiction shall classify the bridge into one of the above three operational categories.
Detailed descriptions of Operational Classification (OC) can found in Table 3.2-1 Operational Classification of Bridges

5. Earthquake Ground Motion
Level 1
Approximately 100-year Return Period
Level 2
Approximately 1000-year Return Period

6. Peak Ground Acceleration
PGA = 0.45
Figure 3B-02 Horizontal Peak Ground
Acceleration Coefficient (PGA) for Level 2
Earthquake Ground Motion (Region I)

7. Response Spectral at
Short Period
SS = 0.9
Figure 3B-20 Horizontal Response Spectral
Acceleration Coefficient at Period of 0.20-sec
(SS) for Level 2 Earthquake Ground Motion
(Region I)

8. Response Spectral at
Long Period
S1 = 0.35
Figure 3B-38 Horizontal Response Spectral
Acceleration Coefficient at Period of 1.0-sec
(S1) for Level 2 Earthquake Ground Motion
(Region I)

9. Ground Types Definitions (Site Class Definitions)
Shear Wave Velocity Measurements
-Seismic Refraction Survey
-Seismic Reflection Survey
-Surface Wave Methods
-Crosshole Method
-Downhole Method
-Suspension Logging

10. Site Factors (Fpga)
Ground Type PGA = 0.45
I 1.00
II 0.95
III 0.85
Fpga=

11. Site Factors (Fa and Fv)
Ground Type S1 = 0.35
I 1.45
II 1.70
III 2.60
Ground Type SS = 1.3
I 1.040
II 1.080
III 1.020
Fa
Fv

12. Design Response Spectrum, 𝜉 = 0.05
LRFD BSDS Section 3 Figure 3.6.1-1
Zero-Period
Short-Period Range
Long-Period Range

13. Elastic Seismic Response Coefficient, 𝐶𝑠𝑚
Zero-Period
𝐶𝑠𝑚 = 𝐴𝑠 + 𝑆𝐷𝑆 − 𝐴𝑠 ൗ
𝑇𝑚
𝑇0
where,
𝐴𝑠 = 𝐹𝑝𝑔𝑎 ∙ 𝑃𝐺𝐴
𝑆𝐷𝑆 = 𝐹𝑎 ∙ 𝑆𝑆
Definitions can be located in Section 3.6.2

14. Elastic Seismic Response Coefficient, 𝐶𝑠𝑚
Short-Period Range
𝐶𝑠𝑚 = 𝑆𝐷𝑆
Long-Period Range
𝐶𝑠𝑚 = ൗ
𝑆𝐷1
𝑇𝑚
where,
𝑆𝐷1 = 𝐹𝑣 ⋅ 𝑆1
Definitions can be located in Section 3.6.2

15. Design Response Spectrum, 𝜉 = 0.05
LRFD BSDS Section 3 Figure 3.6.1-1
Nine equal spacing
from Ts to 5.0s

16. Summary
Ground Type I II III
PGA 0.450
Fpga 1.000 0.950 0.850
AS = Fpga PGA 0.450 0.428 0.383
SS 0.900
Fa 1.040 1.080 1.020
SDS = Fa SS 0.936 0.972 0.918
S1 0.350
Fv 1.450 1.700 2.600
SD1 = Fv S1 0.508 0.595 0.910
TS = SD1/SDS 0.542 0.612 0.991
TO = 0.2 TS 0.108 0.122 0.198

17. Summary
Type I
Tm Csm
0.00 0.45
0.11 0.94
0.54 0.94
1.03 0.49
1.53 0.33
2.03 0.25
2.52 0.20
3.02 0.17
3.51 0.14
4.01 0.13
4.50 0.11
5.00 0.10
Type II
Tm Csm
0.00 0.45
0.13 0.97
0.64 0.97
1.13 0.54
1.61 0.37
2.10 0.29
2.58 0.23
3.06 0.20
3.55 0.17
4.03 0.15
4.52 0.13
5.00 0.12
Type III
Tm Csm
0.00 0.45
0.23 0.92
1.16 0.92
1.59 0.63
2.01 0.48
2.44 0.39
2.87 0.33
3.29 0.28
3.72 0.25
4.15 0.22
4.57 0.20
5.00 0.18

18. Design Response Spectrum
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 1 2 3 4 5 6
Elastic
Seismic
Coefficient,
Csm
Period, Tm (sec)
Type I
Type II
Type III

19. End
Bridges Division