ENGINEERING LESSONS - EPISODE 7 COMPARISION BETWEEN BOX & T GRDERS
Generally, for Bridge Super Structure we would construct Box Girder, I/T Girders, Void Beam, etc... So, we require a better understanding of Super Structure Section which best suited for a particular Spans, cost wise & Constructability point of views.
Software used: CSI Bridge
FEM method is economical than the one-dimensional analysis.
Box girder is found to
be Costlier for 16.3 m Span whereas for 31 m span the box girder is economical.
Box girder are more suitable in terms of stability and economy as compared to T
beam girder bridge superstructure.
For longer spans the
depth of T-beam Girder increases drastically which makes it uneconomical.
Therefore, for higher spans more than 25m the Box Girder is always suitable due
to its higher torsional rigidity. For lesser spans I Girders are economical.
Number of cells in the
box girder can be increased to decrease the overall depth of the girder for
higher spans. Further, if the span is more than 100m or 200m than the box
girder with more than two cells can be adopted.
Comparative design of
RCC & PSC sections concludes that the Shear Force and Bending Moments for
PSC T-beam girder are lesser than RCC T-beam Girder Bridge. It is always
suitable to adopt PSC sections rather than RCC, which is economical and
Suitable for spans 24m and above.
Life span of PSC
Structures is very long as compared to RCC and Steel Structures.
Allowable stress design
method supports the adaptation of T beam girder for shorter span and box girder
for longer spans. Contrary to this, strength design method reveals that box
girder is better than T beam girder even for shorter span when it comes to structural
and economic efficiency.
Design shear and moment
values were found more in case of box girder which added to its stiffness as
well as confinement. Box Girder bridge requires lesser quantities of concrete and
Prestressing steel but it needs more quantity of reinforced mild steel.
Service
Dead load bending moments and Shear force for T-beam girder are lesser than two
cell Box Girder Bridge. Which allow designer to have lesser heavier section for
T-Beam Girder than Box Girder for lesser than 25 m span.
Moment of
resistance of Steel for both has been evaluated and conclusions drawn that
T-Beam Girder has more capacity for 25 m span. Shear force resistance of T-Beam
Girder is more compared to two cell Box Girder for 25 m span.
Principal stresses are
more in T-beam girder bridge than box girder bridge. Plain stresses of box
girder bridge are increases due to less span.
Maximum displacement of
T-beam bridge is more for large spans.
Bending moment &
Shear Force Results are more in T-beam girder than box girder bridge.
Constructability point
of view Precast I Girders can be preferred only when Girder can be casted in
the nearby location to the erection site or having good accessibility to the
construction site. Box Girder Segment Launching is most widely used in metro
cities with huge traffics.
These are the conclusions
arrived from below Published Articles.
1.Analysis
and Design of Box Girder and T-Beam Bridge
2.Comparison
of T-Beam Girder Bridge with Box Girder Bridge
3. Comparative
Analysis of I Girder & Box Girder
4. Comparative
Analysis of T Girder & Box Girder
5. Comparative
Study of Effect of Varying Span Metro Bridges
