Light rail across I-90 floating bridge will be first of its kind; closures of HOV lanes start June 3

Sound Transit’s $3.7 billion project connecting light rail to the Eastside over the I-90 bridge gets started June 1. The project is part of the East Link rail service that will create 14 miles of rail connecting the Eastside to Seattle, part of that stretch will mean trains traveling over the I-90 floating bridge.

Plans to add light rail to the I-90 bridge between Seattle and Mercer Island are underway. But the floating bridge moves with Lake Washington’s water level and must be kept buoyant despite the new weight of tracks, ties and trains, installed in the existing express lanes. (Steve Ringman/The Seattle Times)

The project was approved by voters for the Sound Transit 2 measure, bringing 14 miles of rail to the Eastside, including across I-90, which would make for a 15-minute commute from Bellevue into downtown Seattle.

The floating elements of the I-90 bridge made the engineering and design even more challenging.

“The bridge goes up and down, also when the wind blows the bridge will go slightly north or south, because it’s on anchor cables much like a boat will kind of move around. And, then as traffic loads, the bridge will also move a little left and right,” said Sleavin.

Engineers had to accommodate six degrees of motion.

The transition point between the fixed and floating structure of the bridge was a standout place to maneuver.

At this transition, the rails will rest on bearings and plates allowing movement with the changing lake and bridge conditions. Sound Transit partnered with a company in Tacoma to build two full-size track bridges and test them under simulated operating conditions at a transportation technology center in Pueblo, Colorado.

Sound Transit said it passed all the critical tests.

Trains ran hundreds of times over the test tracks, mimicking the force and movement it’ll experience during normal operations at a speed of 55 mph.

“It’s weight, it’s balance, it’s trim, it’s basically, it’s a 3,500-foot-long boat we’re driving across,” said Sleavin.

Sound Transit says in the rare event of a strong windstorm, with winds between 30 to 40 mph that generate strong waves, it could cause train service to be reduced.

Four car trains are projected to start running in 2023, “And those will be at 8 minute headways in the peak hours, each direction, so about every four minutes there will be a train crossing the I-90 bridge,” said Sleavin.



Researchers from National Institute of Standards and Technology have developed a new technology that will help people detect early signs of deterioration in a building.

When water and oxygen damage iron, they leave by-products, with the two most common being goethite and hematite.

“The brown rust that forms when you leave a hammer out in the rain is mostly goethite, and when a steel reinforcing bar (rebar) corrodes inside a concrete bridge deck, that is mostly hematite,” said NIST physical chemist Dave Plusquellic. “We have shown in our new study with goethite, and our previous work with hematite, that terahertz radiation – electromagnetic waves with frequencies 10 to 100 times higher than the microwaves used to cook food – can detect both corrosion products in the early stages of formation.”

People usually assess corrosion with the physical changes on a structure like cracks in exterior bricks or displaced molding. These warning signs show that more dramatic changes are already taking place in a foundation.

How To Make BBS of Column in Details?


bbs of column
Column Cross Section of Building
Top view of column section

Two type of load acts on column lateral load and axial load. When you will cut cross- section you will find six vertical bars. Out of which 4 is 25Ø and 2 is 16 Ø.

Floor to floor dimension is shown in figure above. Column clear length is 3m.

At top where column ends, there column outer reinforcement will go Ld (development length) distance in roof slab.

Ld= 50d, where d is dia of bar.

Column size= 300mm *600mm

Clear cover in column=40mm

Clear cover in footing=50mm

Clear cover in slab=30mm

Dia of Stirrup= 8mm

Considering column between two slab

Here column we have divided in two zone. Now L/6 from top and bottom of  is Zone A. Remaining at center there is Zone B. We always try column Lap always lie in Zone B not in Zone A. Because when load is applied on column moment is more at bottom in Zone A. So we avoid lap in Zone A. Spacing of Stirrup in Zone A is less than Zone B. See in figure above in L/6 portion spacing is 100c/c and in Zone B it is 150c/c.


Vertical Bar Calculation:

Length of 20 Ø

= 300+ (1500-50-25-25)+600+200+(3000*4)+(175*3)+(50*20)-(2*2*20)+50*20

=16945 mm = 16.945 m>12m


Length of 20 Ø = Ld+Footing depth – cover of footing- Main bar of footing- Bar of footing+depth upto ground floor+200+ Floor to Floor height*4+ (Slab thk *3)+ Development length- Two bend+ one lap

where Development length, Ld= 50d, Lap=50d, Bend=2d

Total no. of 20 Ø bar= 4

Total length of 20 Ø bar = 16.945 * 4= 67.78m

Length of 16 Ø

= 300+(1500-50-25)+600+200+(3000*4)+(!75*3)+(50*16)-(2*2*16)+(50*16)

 =16586 mm = 16.586 m

Total no. of 16 Ø bar= 2

Total length of 16 Ø bar = 16.586 * 2= 33.172 m


Cutting Length of Vertical Bars:

Lapping detail M


Lapping detail S

Lap distance from center of column is 75 mm. Hence end to end distance of lap is 150mm.

For 20 Ø 

Part 1:  300+(1500-50-25-25)+600+200+(3000*2)+(175*2)+(1500-75)-1*2*20

              =10235 mm = 10.235 m

              where bend= 1*2*20, b’ = 1500-75= 1425mm

Part 2:  (1500+75+1000)+175+3000+1000-(1*2*d)

            = 6710 mm = 6.71m

             where a’ = 1500 +75+Ld= 1500+75+1000= 2575 mm

                         Ld = 50 * 20 = 1000mm

For 16 Ø 

Part 1 : 300+(1500-50-25)+600+200+b-bend

            = 300+ (1500-50-25)+600+200+2375-(1*2*16)

             =4868 mm or 4.868 m

           where b= 1500 + 75 + (50*16) = 2375 mm

Part 2 : a+ (175*3)+ (3000*3)+Ld- (1*2*16)

          =11718 mm = 11.718 m

         where a= 1500- 75 = 1425 mm


Cutting Length of Stirrups

a= 600-40*2-8/2-8/2= 512mm

b= 300-40*2-8/2-8/2= 212mm

Cutting length=(2*a)+(2*b)+(2*10*d)-(5*2*d), where hook=2*10d and bend = 5*2d


=1528 mm = 1.528 m


No of Stirrups: = Length/ spacing+1



Part A = 2700/100 +1 =28 nos

Part B = 2000/150 -1=12 Nos*4 = 48 Nos

Part C = 1175/100+1= 13 Nos *3 = 39 Nos

Part D = (650-30)/100+1= 7 Nos

Total Nos = A+B+C+D =122 Nos

1st U-Girder Launched for Mumbai Metro’s Line-7 at Malad

Earlier this morning at 2:30 am, J Kumar Infraprojects launched the first 24.90 meter long U-girder at Pathanwadi (Malad) for constructing te elevated viaduct of Mumbai Metro’s 16.5 km Line-7 project. This milestone at pier#62 & 63 was witnessed by the Chief Minister of Maharashtra, Devendra Fadnavis, who took a tour of both Line-2 and Line-7’s construction sites and casting yards prior to the event. The U-girder weighs about 150 tons and a few northbound lanes of the Western Express Highway were closed down to facilitate its launch.

J Kumar is responsible for constructing package CA-02, from Aarey Station to Magathane Station, of the line and completed casting their first pier in December 2016 and erecting the 1st pier cap in March 2017. They completed casting the first batch of U-girders for both the 18.6 km Line-2 and Line-7 at the Bandra yard in January 2017, and as per the MMRDA’s website, a total of 109 U-girders had been cast by all 3 contractors of the line by April 26 2017.