Flyover Engineering and Construction

Steel Tendons and Corrosion

• High-tension steel tendons in flyovers are protected in conduits
• Corrosion of these tendons can impact structural integrity over time

Flyover Construction Process

Box Girders

• Modern flyovers use box girders
• Box girders allow male-to-female interlock of segments
• Steel tendons are inserted and tightened to affect load-carrying capacity

Weight Transfer Mechanism

• Weight from vehicles and structure is transferred from:
  1. Superstructure to bridge bearing
  2. Bridge bearing to pier
  3. Pier to pile cap
  4. Pile cap to piles
• Finding hard strata layer is critical for stability

Pile Foundation

• Reinforcement bars inserted
• Concrete poured and cured (14 days)
• Foundation bears tremendous force

Pier and Box Girder Fabrication

• Piers constructed with concrete pumps
• Box girders are prefabricated at a fabrication site
• Assembly involves hydraulic power and removal of formwork

Segmental Launching Gantry

• Used for assembling box girders
• Moves between segments using four legs
• Supports and repositions itself over piers

Post-Stressing of Concrete

• Engineers insert and tighten steel tendon wires through box girders
• Post-stressing increases load capacity
• Prevents cracks from developing in the girders

Hydraulic Jack and Wedge Mechanism

• Hydraulic jacks tighten tendons
• Wedges maintain tension post-tightening
• Prevents cables from retracting to original length

Interchange Design

• Three-Way Interchange: Efficient for terminating roads
• Cloverleaf Interchange: Allows free movement without signals
• Diamond Interchange: Efficient for moderate traffic, minimal land use
• Partial Cloverleaf: Reduces space requirements, minimizes weaving

Post-Tensioning Cables

• Can be bonded with grout or kept unbonded in conduits
• Bonded cables have greater corrosion resistance
• Unbonded methods require grease to prevent corrosion

Expansion Joints

• Allow for thermal expansion/contraction
• Support member floats on bearings to accommodate movement

Steel vs. Concrete Flyovers

• Steel flyovers: Used for quick construction, lighter and stronger
• More costly than concrete structures

3D Printing in Engineering

• 3D printing used to model hydraulic jacks and post-stressing mechanisms
• Demonstrates tensioning process and engineering design

This lecture detailed the structural engineering principles, processes, and materials involved in flyover construction, emphasizing the importance of post-stressing and the clever use of engineering techniques to ensure structural integrity and longevity.