CSiBridge – 12 Segmental Balanced-Cantilever Bridge: Watch & Learn


this tutorial will demonstrate the use
of the segmental template in CSiBridge this template allows for the rapid
modeling of segmental post-tensioned bridges using either balanced cantilever
or span by span construction techniques the use of the segmental bridge template
allows for modeling of bridges using cast-in-place segments or precast segments our tutorial will create a balanced
cantilever cast-in-place bridge we will now start our model on the new
model form we will use the segmental template this template can significantly
reduce the time needed to model segmental post-tensioned bridges the quick
segmental bridge template form is where the layout line length is specified as
well as basic bridge properties our bridge will have a total layout line of
200 feet or 2400 inches our actual bridge will be 160 feet long and will be
cantilevered off a single pier we have a number of choices for the bridge section
type and we will use the AASHTO PCI ASBI standard section
clicking the modify show button we can review the specific properties of this
deck section if some modification is required we could click the convert to
editable section button which would then allow for property edits the last items
on the form are used to specify the post-tensioning material and load
pattern we will leave as is for the time being on the segmental bridge span assembly
form we have three discretization’s the first is the span at the start abutment
the second is the balanced cantilever span and the last is the span at the end
abutment although we are doing a balanced cantilever with a single pier
we could also do span by span construction and if so desired we could add
additional discretizations using the various add and insert buttons we will
use the three discretizations as shown the start and end abutment segments are
each 20 feet or 240 inches long and we will not alter these however we are
going to modify the length of the balanced cantilever segment currently
the bridge has a total length of 200 feet and we will shorten it by 40 feet
20 feet off each span we do this by clicking on the span discretization plus
button on the segmental span discretization definitions form
highlight the balanced cantilever 1 segment and click the modify show button
on the form verify that the span type is set to balanced cantilever the down
station table is on the left and the segments up station from the pier are
shown on the right starting from the pier centerline each side has a rigid
segment 60 inches long next are the pier tables 120 inches on
the left and 60 inches on the right we are going to make them symmetric so
we’ll modify the table on the left to 60 next are CIP or cast-in-place segments
six at 120 inches on the left and seven at 120 inches on the right followed by
one last 60 inch CIP segment on the left we are doing a cast-in-place model but
could also do a precast segmental model we are going to remove CIP segments from
each side and again will make them symmetric on the left change the 6 to a 5
and click modify on the right change the 7 to a
5 and click modify we will delete the last shorter CIP segment on the left
the length of the balanced cantilevers on each side is now 720 inches
we are now done with this form note that the total bridge length is now
1920 inches or 160 feet clicking the view renamed segments button shows all
of the segments that make up the bridge the nomenclature used throughout the
table is shown on the form for example SA and EA for start and end abutments D
and U down and up stations and the various prefixes the user may alter
these if so desired in this area of the form we can set the support labeling
perhaps rather than starting with 1 we start with 5 and go in the down
station direction see how the labels change
we can also specify the span numbering but we will use the defaults in this model the segment’s can be identified by color
which the user can switch on and off if desired on the table the first segments deal
with the start abutment denoted by SA there are two cast in place segments
and one closure strip the next group of segments define the down station balanced
cantilevered segments from the pier a total of five segments
the next five segments deal with the pier two pier tables one at the down station side and
one at the up station side two rigid segments and the pier itself the next
five segments define the up station balanced cantilever segments the last
segments define the segment’s associated with the end abutment as identified by
the EA prefix and again include a closure strip once we are satisfied with
the segment definitions and verify that the total length is correct 1920 inches
or 160 feet we can click OK the bridge deck is now displayed
based on the discretization we’ve just defined the program has automatically
generated groups which will be used in the erection sequencing we can review
these groups by going to the bridge tab and clicking groups looking at the
groups we can see the correlation with the segment names in the previous table such as PT for the pier table RG for the
rigid segments and SG for the cast-in-place segments highlighting P01
SGO1D and clicking modify this is the first segment down station which has a
length of 10 feet and ends at the pier table at station 840 switching to the home tab we will take a
quick look at how the groups are assembled to create the bridge using the
select by groups option we will select the same P01 – SGO1D group
we see that it is just down station of the pier if we select the next group we see that it
is just up station and so on if we move to the end of the selection list we
can see the groups that are used at the start abutment the next step will be to define the
post-tensioning tendons for use in the model on the bridge tab click the
prestress tendons button on the define segmental bridge tendons form
select segmental cantilever from the categories drop-down list we will start
by defining the cantilever tendons and then click the define segmental tendon
button here we are going to use the auto fill option and will mirror the tendons
about the centerline of the deck this powerful feature will automatically
generate the layout of the tendons for each segment clicking auto fill note
that we now have a total of twelve tendons with two anchorages for each
segment and pier table in both the down station and up station locations a reference plan for the top slab is shown
if we select the show mirrored tendons option we can see the layout to
each side of the centerline and we can also see the work point to adjust the tendon parameters click
the add modify button note that we currently have only a single tendon
parameter Tparam1 here we can review and edit parameters as needed including
tendon area and the loss parameters such as those due to friction and the
long-term losses we will set the load pattern to prestress and we are going
to change the material property we will add a property of A416 grade
270 we are also going to revise the tendon
area based on a quick and somewhat approximate calculation we are going to
use a tendon with eight strands of 0.6 inch diameter we will also revise the duct diameter to
2.99 inches and the tendon load to a stress of 202.5 ksi we leave all other
parameters as shown while still on the cantilever tendons
definition form we can click the select tendon duct template button to review
the layout of the ducts returning to the define segmental bridge
tendons form note that there are now a total of 24 tendons 12 distributed to
each side of the centerline show all tendons again shows the plan layout and
scrolling through the cross-section shows how they are clustered around the
webs however these are just the cantilever
tendons typically continuity tendons are needed as well so next we will add some
additional continuity tendons for placement in the bottom span
we will define a new tendon by making a copy of our first tendon TParam1 our new tendon
will use four 0.6 inch strands again all the tendon selections are somewhat
arbitrary at this point simply to show the process they have not been
determined from strength requirements with the first span selected we are
going to add a tendon that runs from the start abutment segment all the way to
the pier table using our new tendon again we are replicating about the
centerline we will add a second tendon that starts and ends one segment shorter
on each end switching to span 2 we will replicate
the tendons just added on the up station side again the tendons are added
symmetrically closing this form
note that eight tendons have now been defined
for the bottom span clicking the show all tendons shows the location of these
continuity tendons we could also add continuity tendons for
the top if needed the model now has tendons next we will
move on to the scheduling on the bridge tab go to the erection button and click
traveler travelers are needed to support formwork for cast in place concrete note that two travelers have been
defined one for down station and one for up station to see the properties of the
traveler click the modify button the traveler weighs 20 Kips and has a
stiffness of 50 Kips per inch this means it will deflect 1 inch for each 50
Kips of load the eccentricity defines where the center of gravity of the
traveler lies relative to the end of the supporting segment in the longitudinal
direction positive is away from the free end we will not alter these values
next we will click on the schedule wizard here we can set the time required
for each stage in the construction schedule from constructing the
foundation and pier to the time required to cast and stress a segment and then
launch the traveler which in our case is 4 days we will not change any of the
duration settings we can also specify how the segments are to be erected one
by one or in pairs we will erect the segments in pairs on this form we can
also set which traveler is down station and up station and specify any
additional structure loads such as wearing surfaces and barriers click the
generate schedule button to generate a detailed construction schedule the schedule is broken down into four
primary operations first the cantilevered portion of the bridge at
the pier second the non cantilevered structure that is the end abutments
third the closure segments and fourth the time-lapse analyses each operation
shown in the table is also graphed in the adjacent Gantt chart
expanding the operations the schedule starts with the foundation and the pier then the pier
table then adds the travellers then starts the casting of the segments note that the typical cycle is again
four days 80 to 83 on the schedule and that four tendons are tensioned in each cycle the travelers are advanced the segments
are cast and all four tendons are stressed as a side note although we have not
adjusted any of the program’s generated durations these may be
edited and all operations that are descendants
of the edited operation would have their timing adjusted accordingly the construction of the start and end
abutments occurs early in the schedule while the closures are constructed late
in the schedule the last tendons being stressed are the
continuity tendons in the bottom slab once we are satisfied with our detailed
schedule we can click OK to save it we will next move on to showing how the
program takes the scheduling information and generates the load cases needed to
perform the analysis on the analysis tab select the wizard scheduled load case
and click the modify button from the scheduler the program has created a
nonlinear staged construction load case with a total of 51 stages
again the typical cycle is that the travelers are set a two-day time lapse stage while the
segments are placed the next stage adds the segments and loads them another
time lapse stage for the tensioning and the tendons are added and loaded Changes cannot be made to this load case
because it was generated directly from the schedule wizard as a last step prior to running the
analysis we will look at the erection sequencing of the segmental bridge which
can be done using the show tree button here we can see segments being cast and
then post-tensioned as well as seeing how the travelers move with that we are now ready to run the
analysis with the analysis complete we can
display the deformed shape for our staged construction case we can step through each stage note that
the travelers are shown with straight lines we will also display the force diagram
for our staged construction case this time using the F11 component this concludes this tutorial on using
the segmental template in CSiBridge for modeling segmental balanced
cantilever bridges

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