Kindly read the following conversation between two structural engineers and suggest a practical solution to the given problem:
Friend (1)
if you have spliced steel box girder (composite type with top concrete deck) with internal tendons (harped shape), when will be the time to pull the internal tendons. not that the bridge has 3 segment of 16-18-16 curved in shape to developed circular arc ?
Friend(2):
-For a steel box girder bridge with internal tendons and a top concrete deck, the timing for pulling the internal tendons is crucial to ensure proper tensioning and structural integrity. Here are some general guidelines:
-Initial Erection: The steel box girder segments are typically erected first, forming the main structural framework.
Concrete Deck Placement: The concrete deck is then cast and cured on top of the steel box girder.
Tendon Installation: Internal tendons are installed within the box girder, usually before the concrete deck is fully cured.
-Tendon Tensioning: The internal tendons are pulled and tensioned after the concrete deck has achieved sufficient strength to support the applied forces.
-This is typically done once the concrete has reached a minimum compressive strength, often around 3,000 psi (20 MPa) or higher, depending on the specific design requirements and environmental conditions.
Key Considerations:
-Strength and Stability: Ensure the concrete deck is strong enough to handle the tensioning forces without cracking or excessive deflection.
Load Distribution: Properly distribute the tensioning forces to avoid overstressing any part of the structure.
Construction Sequence: Follow the construction sequence carefully to maintain structural integrity and safety.
Friend(1):
so, if the work crow did pull the tendons before the topping of concrete deck (i.e. just with open top steel box shape and the segments attached via HT Bolts) is that critical ?
Friend(2)
Yes, pulling the internal tendons before the concrete deck is in place can be critical. The concrete deck is essential for distributing the forces and providing additional stiffness and strength to the overall structure.
Here’s why:
Key Concerns:
-Structural Integrity: Without the concrete deck, the steel box girder alone might not have sufficient stiffness and strength to handle the tensioning forces from the internal tendons.
-Load Distribution: The concrete deck helps distribute the loads and tension forces across the entire structure, reducing stress concentrations that
could lead to damage or failure.
-Flexural Strength: The concrete deck contributes significantly to the flexural strength of the composite girder system. Without it, the structure may not perform as intended under load.
-Stability: The deck provides lateral stability to the steel box girder, which is crucial for maintaining the alignment and geometry of the structure during and after tendon tensioning.
-Tensioning the tendons before the concrete deck is placed could lead to excessive deflection, local buckling, or even failure of the steel box girder. It’s crucial to follow the proper construction sequence to ensure the structural integrity and safety of the bridge.
Friend(1):
are the bolts capable at top flange (of open top box girder) for the spliced girder to withstand the pulling tensile force from bottom tendons ?
Friend(2)
-The bolts at the top flange of an open-top steel box girder are generally designed to handle significant loads, including the tension forces from the internal tendons. However, the specific capacity of these bolts depends on several factors, such as:
-Bolt Size and Grade: Larger and higher-grade bolts can handle greater loads.
-Bolt Spacing and Pattern: Proper spacing and pattern ensure even distribution of forces.
-Material Properties: The strength and ductility of the materials used for both the bolts and the flange.
-Load Conditions: The magnitude and direction of the applied loads, including tension from the tendons and any additional loads from the concrete deck or traffic.
Friend(1):
lets assume they will designed. still are the process of pulling the bottom tendons is extremely wrong and critical ?
Friend(2):
Yes, it's critical to pull the internal tendons only after the concrete deck is in place and has achieved sufficient strength. Even with well-designed bolts capable of withstanding the tensile forces, the absence of the concrete deck compromises the overall structural integrity.
Without the concrete deck:
-Insufficient stiffness and strength: The steel box girder alone may lack the necessary stiffness and strength, leading to excessive deflection or local buckling.
-Uneven load distribution: The concrete deck helps distribute the loads and tension forces more evenly. Without it, the forces may create stress concentrations that could lead to damage or failure.
-Lack of composite action: The concrete deck and steel box girder act together to resist loads. Tensioning tendons without the deck undermines this composite action, affecting the structural performance.
-So, even if the top flange bolts are designed to handle the loads, it's essential to follow the proper construction sequence.
My Answer is to cut-off the internal tendons and redone the post-tensioning process adequately.
Note: The proposed Bridge still not open for public transport. your views are welcomed
Friend (1)
if you have spliced steel box girder (composite type with top concrete deck) with internal tendons (harped shape), when will be the time to pull the internal tendons. not that the bridge has 3 segment of 16-18-16 curved in shape to developed circular arc ?
Friend(2):
-For a steel box girder bridge with internal tendons and a top concrete deck, the timing for pulling the internal tendons is crucial to ensure proper tensioning and structural integrity. Here are some general guidelines:
-Initial Erection: The steel box girder segments are typically erected first, forming the main structural framework.
Concrete Deck Placement: The concrete deck is then cast and cured on top of the steel box girder.
Tendon Installation: Internal tendons are installed within the box girder, usually before the concrete deck is fully cured.
-Tendon Tensioning: The internal tendons are pulled and tensioned after the concrete deck has achieved sufficient strength to support the applied forces.
-This is typically done once the concrete has reached a minimum compressive strength, often around 3,000 psi (20 MPa) or higher, depending on the specific design requirements and environmental conditions.
Key Considerations:
-Strength and Stability: Ensure the concrete deck is strong enough to handle the tensioning forces without cracking or excessive deflection.
Load Distribution: Properly distribute the tensioning forces to avoid overstressing any part of the structure.
Construction Sequence: Follow the construction sequence carefully to maintain structural integrity and safety.
Friend(1):
so, if the work crow did pull the tendons before the topping of concrete deck (i.e. just with open top steel box shape and the segments attached via HT Bolts) is that critical ?
Friend(2)
Yes, pulling the internal tendons before the concrete deck is in place can be critical. The concrete deck is essential for distributing the forces and providing additional stiffness and strength to the overall structure.
Here’s why:
Key Concerns:
-Structural Integrity: Without the concrete deck, the steel box girder alone might not have sufficient stiffness and strength to handle the tensioning forces from the internal tendons.
-Load Distribution: The concrete deck helps distribute the loads and tension forces across the entire structure, reducing stress concentrations that
could lead to damage or failure.
-Flexural Strength: The concrete deck contributes significantly to the flexural strength of the composite girder system. Without it, the structure may not perform as intended under load.
-Stability: The deck provides lateral stability to the steel box girder, which is crucial for maintaining the alignment and geometry of the structure during and after tendon tensioning.
-Tensioning the tendons before the concrete deck is placed could lead to excessive deflection, local buckling, or even failure of the steel box girder. It’s crucial to follow the proper construction sequence to ensure the structural integrity and safety of the bridge.
Friend(1):
are the bolts capable at top flange (of open top box girder) for the spliced girder to withstand the pulling tensile force from bottom tendons ?
Friend(2)
-The bolts at the top flange of an open-top steel box girder are generally designed to handle significant loads, including the tension forces from the internal tendons. However, the specific capacity of these bolts depends on several factors, such as:
-Bolt Size and Grade: Larger and higher-grade bolts can handle greater loads.
-Bolt Spacing and Pattern: Proper spacing and pattern ensure even distribution of forces.
-Material Properties: The strength and ductility of the materials used for both the bolts and the flange.
-Load Conditions: The magnitude and direction of the applied loads, including tension from the tendons and any additional loads from the concrete deck or traffic.
Friend(1):
lets assume they will designed. still are the process of pulling the bottom tendons is extremely wrong and critical ?
Friend(2):
Yes, it's critical to pull the internal tendons only after the concrete deck is in place and has achieved sufficient strength. Even with well-designed bolts capable of withstanding the tensile forces, the absence of the concrete deck compromises the overall structural integrity.
Without the concrete deck:
-Insufficient stiffness and strength: The steel box girder alone may lack the necessary stiffness and strength, leading to excessive deflection or local buckling.
-Uneven load distribution: The concrete deck helps distribute the loads and tension forces more evenly. Without it, the forces may create stress concentrations that could lead to damage or failure.
-Lack of composite action: The concrete deck and steel box girder act together to resist loads. Tensioning tendons without the deck undermines this composite action, affecting the structural performance.
-So, even if the top flange bolts are designed to handle the loads, it's essential to follow the proper construction sequence.
My Answer is to cut-off the internal tendons and redone the post-tensioning process adequately.
Note: The proposed Bridge still not open for public transport. your views are welcomed
