LTFRB Regulation of TNC and TNVS

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DEPARTMENT ORDER NO. 2018-013: LTFRB Regulation of TNC & TNVS

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Title Source: Supreme Court: DPWH Advisory on Seismic Bridge Design

Law: Dpwh Department Order No. 75

Decision Date: Jul 17, 1992

DPWH Department Order No. 75 mandates that all bridge designs adhere to updated AASHTO seismic specifications to ensure structural integrity and safety during earthquakes, emphasizing continuous bridge structures and essential reinforcement techniques.

Law Summary

Philosophy and Objectives of Seismic Bridge Design

Bridges should withstand small to moderate earthquakes elastically without significant damage.
During large earthquakes, bridges may sustain damage but must not collapse or lose critical parts.
Damage should be easily detectable for inspection and repair.
Seismic design aims to prevent or mitigate earthquake-induced damages to bridges.

Mandatory Compliance with AASHTO Specifications

Minimum design standards require adherence to:
- Current AASHTO Standard Specifications for Highway Bridges, 14th Edition.
- Guide Specifications for Seismic Design, 1989 or latest edition.
- 1991 AASHTO Standard Specifications adopting the Guide Specifications (Interim Specification-Bridge).

Preferred Structural Design Concepts

Continuous bridges with monolithic multi-column bents are preferred for seismic resistance due to high redundancy.
Expansion joints, hinges, suspended spans, brackets, and rockers are to be minimized or avoided.
Where multi-span simple spans are used, decks must be continuous.
Restrainers are required at all joints following AASHTO seismic guidelines.
Generous seat widths at piers and abutments help prevent loss-of-span failures.

Reinforcement and Structural Detailing

Transverse reinforcement is critical in yielding zones of reinforced concrete columns to:
- Confine longitudinal reinforcement and concrete.
- Prevent buckling of main reinforcement.
Plastic hinging should occur in ductile regions of columns rather than foundations.

Protection of Abutment Piles and Soil-Structure Interaction

Abutment piles are protected by designing backwalls to shear off under seismic forces to prevent pile failure.
The overall stiffness of the bridge must be factored into seismic analysis.
Soil-structure interaction is essential, particularly in irregular structures.

Effectivity and Amendments

This advisory amends existing DPWH guidelines on seismic design of bridges.
The advisory takes effect immediately upon issuance on July 17, 1992.
Issued by the Secretary of DPWH, Jose P. De Jesus.

END