Summer 1998 Newsletter
The San Mateo-Hayward Bridge (SMHB) featuring
the first major orthotropic steel spans in the United States was opened
to Bay Area traffic in 1967. This unique bridge links the peninsula cities
of Foster City and San Mateo on the west and Hayward on the east shores
on San Francisco Bay. The 7.1-mile long, 4-lane structure carries in excess
of 77,000 vehicles in each direction each day as part of the "normal" bay
area commuter gridlock. The bridge is comprised of a 5 mile long low level
trestle traversing the shallow mud flats on the Hayward (east) side of
the bay and a 1.9 mile high level section crossing the navigation channel
and finally dropping into Foster City on the west side of the bay.
As with all of the Bay area Bridges that
serve as life lines to the San Francisco Peninsula, the San Mateo-Hayward
Bridge needed strengthening to withstand a maximum credible earthquake
with minimal risk of collapse.
The retrofit program on the SMHB is divided
into three phases:
Phase 1 - West Approach & Pier 1 &
Pier 1A (Awarded to Dillingham Construction $2,400,000)
Phase 2 - High rise portion (Awarded to
Morrison Knudsen / Traylor Bros. / Weeks JV $102,000,000)
Phase 3 - Seat extenders, Miscellaneous
Piling and Seismic Instruments, (Trestle section) (Awarded to West Coast
Bridge $7,500,000)
On November 4, 1997, Traylor Pacific, in
joint venture with Morrison Knudsen, of Boise, Idaho, and Weeks Marine,
of Cranford, New Jersey, (MK/T/W) was low bidder on the largest and
most complex contract of this retrofit program.
Work began in mid-March on the project
after a long mobilization of a marine fleet by the JV Partners. Before
the year is out, this team will have developed schemes and techniques to
strengthen this structure in ways uncommon even in the retrofit market.
These techniques include:
á Expansion & Tied Hinges for Main
Structure: New vertical hanger rod assemblies will be installed except
at the expansion and tied joints of the channel span, which will have vertical
hairpin shaped assemblies. New longitudinal rod restrainer systems will
also be installed at all expansion and tied joints. The shear lock assemblies
in the box girders will be removed and replaced with larger assemblies.
á Expansion Joints at Piers 1 & 38:
The expansion joint capacities will be increased to two feet by using 2"
thick steel cover plates.
á Bearings at Piers 2-37: New vertical
restrainer bar assemblies will be installed. Existing bearing pins
will be strengthened with new steel pipe key assemblies except at Piers
19 & 20. The bearing plate assemblies at Piers 19 & 20 will be
strengthened with new reinforcement.
á Steel Towers at Piers 12-27: Steel plates
will be installed on the vertical faces of the towers, and stiffener members
will be installed in the spandrel beams. Over 250,000 stitch bolts will
attach the new plates to the tower faces. Additional vertical anchor rod
assemblies will be installed at the base of the towers, and six-feet of
reinforced concrete will be placed inside the base of the steel towers.
á Concrete Spandrel Beams at Piers 2-18
& 21-37: The spandrel beams and joints at Piers 2-11 & 28-37 will
be jacketed with post-tensioned concrete cover. The lower hollow spandrel
beams at Piers 12-18 & 21-29 will be filled with grout and post tensioned
vertically.
á Rectangular Foundations at Piers 2-13
& 30-37: A cofferdam will be installed to access and place a concrete
overlay on top of the pile cap. Four open-ended large diameter (12’0" dia.
X 2 ¹" thick) steel shell piles, weighing up to 275 tons will be
driven at the corners of each pile cap. The top 15’ of the piles will be
filled with concrete. A new precast concrete "dog-bone" collar will encase
the newly thickened pile cap footing. Each precast frame weighing in excess
of 500 tons will be fabricated in two halves, floated into position around
the pier, connected and stressed, then lowered down onto the large diameter
steel shell piles.
á Bell Foundations at Piers 14-18 &
21-29: Excavation to the bottom of each pile cap will be required for the
placement of the steel jackets to encase the cylindrical portions of the
bell foundation. After the steel jackets are installed, grout will be injected
to fill the void between the existing concrete and steel jacket.
Currently dredging operations have begun
on Pier 31, 30, 21 & 12. Concrete spandrel work has begun on piers
31 & 30. Structural steel has begun with the opening of access holes
at the 38 hinge areas on the superstructure. Current project completion
is scheduled for December 1999.
Greetings from the cowboys over yonder in Grove, Oklahoma! Work is well
under way at the ranch in this lake resort town. Despite the constant 90
plus degree weather, Traylor Bros. is getting some hard work out of the
crews in the casting yard. Having cast 57 of the 356 superstructure segments
for the Sailboat Bridge, everyone is finally starting to see some tangible
results for all those long hours on the clock. The drilled shaft crew over
at the bridge site is also working hard, as they have poured the drilled
shafts for abutment 26 and pier 24. Back at the casting yard, construction
of the precast tubs for the footings has just begun, as the first of 48
footings is being formed. When the drilled shaft construction gets into
full swing, the bridge site will become very busy. The placement of the
footings, columns, and caps for the northbound lane will soon follow, and
the citizens of Grove will see their tax dollars being put to good use.
Erection of the northbound superstructure is slated to begin this winter,
and the transfer of traffic to the new bridge is set for late May of 1999.
New workers are being hired every day to accommodate the footing
construction and to increase production of the precast segments. Even more
help will be needed when we start working a night shift. The plan is to
set and strip during the day and pour at night to beat the heat; we are
not allowed to pour when the ambient temperature exceeds 95 degrees, which
will happen too often this summer.
Only a handful of readers will ever have the opportunity to seismically
retrofit a bridge in Southern California. Even fewer will have the
opportunity to retrofit a suspension bridge in the area. Traylor Pacific
has both.
Over the next few issues of the Traylor newsletter, we will explain
some of the unique elements of the Vincent Thomas Bridge project. The first
article explains the installation of the truss fuse.
The truss fuse system utilizes viscous dampers coupled with hinged
connections to provide a movable section of the bridge. The purpose of
the truss fuse is to dissipate energy transmitted to the bridge by an earthquake.
The truss fuse consists of:
* Pin Plate Assemblies - These assemblies provide a pinned
connection at the top chord of the stiffening truss. This connection acts
as a hinge, or pivot point, for movement generated by a seismic event.
* Viscous Dampers - The viscous dampers connect the severed
bottom chord of the stiffening truss. These dampers are similar to hydraulic
shock absorbers on a car. They transform kinetic energy (movement of the
bridge created by an earthquake) into heat. This helps avoid structural
damage to the bridge members. The silicon impregnated viscous dampers have
a range of motion of 16" and can withstand axial loads of 265 kips.
* Link Plates - The link plates connect the severed bottom
chord of the suspended truss. These plates are designed to break at a pre-determined
point. Once enough force is generated to break the plates, the forces on
this chord are transferred to the viscous dampers.
* Shear Tongue - The shear tongue assembly allows the bridge
to move axially while prohibiting lateral movement. If a seismic event
created enough force to break the link plates and transfer the load to
the dampers, the shear tongue would provide the needed lateral support.
Work is done on the weekends, while the bridge is shut off to
traffic, so that no unnecessary loads are imposed. Crews work around the
clock to complete the following work before the bridge is to open again
Monday morning:
* The shear tongue assembly is installed in the floor truss
system.
* Ironworkers torch-cut the top and bottom chords of the
suspended truss in order to install the hinged connections and the dampers.
Temporary supports are installed to hold the truss together while the cuts
are made.
* Hinge plates are installed on each end of the severed
top chord. An 8" pin is driven through holes in the plates to form a hinged
connection.
* Link plates are installed connecting the severed bottom
chord of the suspended truss.
* The viscous
dampers are installed in the bottom chord of the truss.
Thanks to the hard work of the Traylor Pacific staff and crew,
four truss fuses were installed in the month of June - one each weekend.
Roger Foreman has been promoted to President of Traylor Bros. The decision was announced at the annual meeting of the Board of Directors
in April.
Tom Traylor, former president, retains the titles of Chairman
of the Board and Chief Executive Officer.
Congratulations, Roger!
Let's test your safety knowledge! See how many of the five questions you can answer without looking at any reference material. The correct answers, in accordance with federal OSHA Construction Industry Standard, are provided _______________.
1. How many pounds of force must an anchor point be able to withstand?
(a) 500 (b) 50,000
(c) 5,000 (d) 50
2. OSHA 1926.501 requires employers to provide fall protection when employees are exposed to a fall of ____ feet or more.
(a) 5 (b) 10
(c) 6 (d) 25
3. OSHA uses the 5(a)1 General Duty clause to cite employers for all health and safety violations?
(a) True (b) False
4. As defined by OSHA in Subpart M, a HOLE means "a gap or void ____ inches or more in its least dimension, ..."
(a) 2 (b) 10
(c) 12 (d) 4
5. According to OSHA, the top rail in a guardrail system must be capable of withstanding a force of ____ lbs in any direction.
(a) 200 (b) 5,000
(c) 2,000 (d) 50,000
How did you do? If you answered any of the questions incorrectly,
you may want to check with your foreman for more information concerning
these topics. Remember, information is knowledge, and well-informed employees
are able to work smarter and safer.
Our goal, as always, is to "Build America Safely."
Answers to Safety Quiz:
(1) c
(2) c
(3) False
(4) a
(5) a