Patent 5,920,938
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Bridge Hinge Answer
 
Smith Point Bridge
 Concrete Hinge Bearing Pad Replacement Demonstration
  Patent 5,920,938  Award

By :  Stanley E. Elcock, P.E. and Stanley D. Elcock

 
HISTORICALLY
  • Bridge hinge repairs are very expensive
  • 24 hour traffic control required
  • Environmental permit issues
  • Repairs are temporary
 OUR PATENTED TECHNOLOGY
  • 20-1000 times less expensive
  • Only requires daily lane closures
  • No permit requirements
  • Repairs are permanent
  • Repairs are easily monitored
  • Work site access costs are minimal
     

A BRIEF HISTORY

Bridge hinges are designed to mitigate temperature and construction forces

Before the Seismic Retrofit Program in California, bridge hinges were not connected

During the Seismic Retrofit Program bridges hinges were connected by steel cables, tie rods,
and finally by large steel pipe restrainer pins shown below.

Bearing pads are designed to cushion the impact from traffic loading.

Bearing pads were installed prior to the concrete pour for the bridge itself, which left no practical means for bearing pad replacement after compression failure.

                                                            

Bearing pads are installed the same way today

 

Earlier Repair Attempts:

                                           

                                                         Hinge failure at X Street in Sacramento
                                  Piers were constructed under the failed hinge in order to prevent collapse

 

Our Patent Demonstration on the Smith Point Bridge in Humboldt County:

Smith Point Bridge is a 9 span, 1424 foot long structure located in Humboldt County 5 miles south of Garberville, California on US Highway 101.  Built in 1980, it is two conventionally reinforced 2 cell concrete box girder bridges with common pier walls. 

After review of the as-built plans the “stabilized” compression was in fact complete bearing pad failure.  The hinges were bearing concrete-on-concrete and that it appeared that the south hinge shear keys were crushed.  The Standard Drawing in the as-builts only required 1" of expanded polystyrene on top of the concrete shear keys.  This accounted for the "stabilized compression" noted in previous Caltrans Bridge Inspection Reports.   Crushed concrete shear keys would account for the compression over 1".

 

Patented Success:

The patent demonstration resulted in replacement of the exterior bearing pads and installation of belting material from inside the cored holes at a fraction of the cost of conventional methods and without the need for expensive temporary supports, right-of-way, or environmental permits.  However, during the demonstration existing hinge damage was identified that had gone unnoticed until this time.   An additional benefit to utilizing this patented technology is the easy assessment of the actual condition of concrete hinges.

Seismic Retrofit Hindsight:

 By 1997 the Seismic Retrofit strategy for concrete hinges had changed by enlarging the 9" cored hole to 10".  This allows for about 5/8" clearance around the pipe restrainer.  Caltrans  Structures Design originally detailed minimal clearance ( 1/8" ) around the pipe restrainer on Seismic Retrofit contracts prior to 1997.  The Smith Point Bridge Project revealed daily hinge deterioration due to the cyclic deflection of the bridge simply from normal traffic loading.   Consequently, when the hinge seismic pipe restrainer clearance in the planned cored holes is less than the deflection of the span due to truck traffic, the retrofitted hinge will eventually destroy all hinge Seismic Retrofit work due to the pipe restrainer pounding against the hinge interior every time a truck crosses the bridge.  Instead of solid concrete shear keys and solid concrete surrounding the hinge pipe restrainers, Caltrans and its partners have introduced a design flaw that results in the destruction of the concrete bridge hinge, which compromises the bridge structural integrity and more importantly public safety.

 

Interior bridge hinge photos during the Patent Demonstration on the Smith Point Bridge.

 

Klamath River Bridge on Highway 101 in Del Norte County January 2006:

One of the Klamath River Bridge hinges on Highway 101 in Del Norte County
This large crack was the result of failed bearing pads and newly installed Seismic Pipe Restrainers

 

 Klamath River Bridge Emergency Repair 2006.  Total cost $ 4,000,000.00
Our Patented Technology cost less than $100,000.00.

 
Bay Bridge Skyway Section
                                  

The seismic pipe restrainer on steroids

(Sheet 787 of the Bay Bridge Plans)

This hinge is supported by the 6 foot diameter pipe restrainers shown above. 
Typical seismic pipe restrainers are less than 9 inches in diameter

For more information e-mail:  stanelcock@yahoo.com

 

 Stanley E. Elcock is a Professional Civil Engineer, owner of SEE Civil Engineering, and co-owner of patent 5,920,938 with over 20 years experience in highways and bridges.  Recent publications include collaboration on the Rock Creek Bridge Project.

 Stanley D. Elcock is a retired materials testing engineer, NICET certified Senior Engineering Technician with NICET Level IV certifications in soils, concrete and asphalt.  His engineering roots can be traced back to Boulder City, where his father Stanley T. Elcock worked as a Civil Engineer for the Bureau of Reclamation on the Hoover Dam and later on Shasta Dam.   He is also co-owner of patent 5,920,938.

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