JMEC was prime design consultant for preparing PS&E of six bridges, and was consultant for the independent check of PS&E for three other bridges.   JMEC performed seismic analysis and design, determined retrofit strategies, prepared plans, specifications and estimates, provided technical support for environment studies and review process, and provided as-needed construction design support services.

The East Fork Road over North Fork San Gabriel River is a 642-ft 4-span riveted steel deck truss.   Typical span is 160-ft and carry two lanes of traffic.  The bridge was analyzed using a nonlinear time history analysis with site specific ground motion.  Due to the weak lacing members, it was determined that bridge strengthening was neither cost effective nor environmentally feasible.  Considering costs and impacts to the creek and environment, an alternative retrofit strategy using seismic isolation bearings in conjunction with local member strengthening was finally used for the retrofit.  Retrofit work in the river was avoided and the environment was protected.  The environmental process was also kept to minimum.  The retrofit measures included:
  • Replace bearings with seismic isolation bearings
  • Strengthen end diaphragms at piers and abutments
  • Selective replacement of rivets by HS bolts
  • Tie trusses across expansion joints
  • Replace portion of bottom lateral bracings
  • Install vertical cable restrainers at piers
Project Role:  Prime Consultant for Bridge Design

Clients:  Los Angeles County Department of Public Works

Special Issues:  Worked with bearing supplier in the bearing prototype design and testing to ensure that the production bearings met the design requirements.  Construction access was entirely from the bridge deck and no falsework was needed in the river.  Temporary supports used for raising the bridge were supported from existing piers and abutments.

Schedule:  Construction was completed in May 2016

Awards:  ASCE MLAB Outstanding Structural Engineering Project of the Year 2016 and
ASCE LA Section Structural Engineering Project of the Year 2016
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