Incremetally Launched Box Girder Bridge-Shear of Cracked Section 2

[Upasena]

Dear Sirs,

I am working on the design of an incrementally launched box girder bridge whose parameters are as follows:
2Nos. End spans 26.5 m each.
4 Nos. Internal Spans 46.5 m each.
All bearings are laminated elastomeric after launching. During the launching Teflon bearings are used to minimize the friction.
Cross section area of the box girder is 9.27 sq.m.
Width of the bridge deck 11 m.
Height of the box girder 3.2 m, yt=1.395 m, yb=1.805 m.
Moment of inertia of the box girder=13.06 m^4.
Post tension straight tendons 32 near supports each having 143 sq.mm csa.
CG of tendons are located 320 mm above the CG of the box girder.
Post tension straight tendons 28 in spans each having 143 sq.mm csa.
CG of tendons is located 258 mm below the CG of the box girder.
The bride is launched with a nose in front and on Teflon bearings, 10 m sections.
The bridge is designed for HB30 and HA loadings as per BS 5400.

I am new to the ILM bridge design. Proper analyses were carried out with Midas and Staad-pro
As our bridge cross section suffers no tension at any stage.

My question is: Have got to check the stresses for the ultimate shear resistance of a section cracked in flexure, Vcr. If so why? Are cracks likely form from thermal and creep effects?. I shall thank you to enlighten me on this crack stresses check. Is it usual to assume a cracked section?

K. W. Upasena

 

[cooperDBM]

Assuming that you're using a limit state design (or LRFD) code, shear strength is an ultimate limit state check that isn't directly dependent on actual loading or prestress. The shear strength that you will determine represents the condition of the beam prior to failure with the section cracked diagonally. The crack either starting from a flexural crack or from web cracking. This is similar in concept to the ultimate flexural strength of the section. Since the section is cracked you're checking forces, not stresses which have been redistributed. Obviously these strengths are checked against the actual loading that has been factored up.

 

[Upasena]

cooperDBM (Structural)

Thank you very much, Sir. My question is well answered

Upasena

 

[Upasena]

cooperDBM (Structural)

Thank you very much, Sir. My question is well answered

Upasena

 

[Upasena]

cooperDBM (Structural)
Thank you very much. My question is well answered.

Upasena

 

[asixth]

Depends on how well the superstructure is articulated as to whether cracks develop from temperature, creep and shrinkage. Because your bridge is 300m in length I would assume there would be a least 2 expansion joints. Without looking at the analysis myself I would think the elastomeric bearing at this joint should allow sufficient movement as to not cause any tensile stresses within your section.

 

[Upasena]

asixth(Structural)
Thank you, Sir
Upasena