×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Pouring sequence for box girder bridge on flexible truss scaffolding

## Pouring sequence for box girder bridge on flexible truss scaffolding

(OP)
What should be the concrete pouring sequence for a 58 m span post tensioned box girder simply supported bridge supported on a flexible steel truss scaffolding spanning between the piers so that no significant stressed are set up in the first pour of concrete? Can the insignificant stresses be estimated mathematically? Any reference to a bridge which is constructed in this manner before would be appreciated.

### RE: Pouring sequence for box girder bridge on flexible truss scaffolding

I believe that you may be asking for the impossible in aiming for "insignificant" inbuilt stresses.  It depends very much what you consider to be "insignificant".

Common practice would be to cast your section in two pours, with construction joints close to the top of the webs.

If you cannot cast each section in one continuous pour, then it would keep your inbuilt stresses down if you cast the ends prior to casting the midspan portion.

Estimating the inbuilt stresses is not all that difficult, provided that you can assess the stiffness of each previously cast section of the girder at the time of each new pour.

Just calculate the bending moments due to each new pour, and distribute them between the supporting truss and any previously cast concrete in proportion to the relative flexural stiffnesses.

That is, the bending moment in the concrete at any location Mconc = Mtotal * (Econc*Iconc)/(Etruss*Itruss + Econc*Iconc).

Then apply Mconc to the concrete section to determine the stresses you are looking for.

### RE: Pouring sequence for box girder bridge on flexible truss scaffolding

This appears to be an extension of a previous thread.

My suggestion would be to concrete the central 50% or more of the
span in the first pour, and then the ends. This way, the scaffolding
deflection when the central portion of the concrete is green. This part
of the concrete is not stressed. The ends are cast later. The load
at the ends would not result in high central deflection. Since the
concrete is green at the ends, it would take the shape of the
deflected scaffolding without inducing any stress in that region. The
central portion would be subject to only a small additional deflection,
and the stresses would be quite small.

The formula suggested by austim would be valid if the span is
concreted in multiple pours in horizontal layers. For concreting the
way mentioned above, that would not be applicable. Assuming that the
central part would have set by the time the ends are concreted, the
following course of action is to be followed:

(a) Assume that the concrete girder is only supported at the ends of
the first pour. Compute the self-weight deflection at the centre. Compute
the additional deflection of the truss scaffolding due to the weight of the
concrete (relative deflection between support point mentioned above
and centre of the span). If the girder deflection is more than the truss
deflection, the truss supports the girder. Otherwise the girder is
supported only at ends.
(b) Find the compatible deflection pattern of the girder and truss. From
the deflection pattern, the bending moment and stresses can be
computed.

This is a convoluted and iterative procedure. May be one trial would

Good luck,

M. Hariharan

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!