Perform bridge girder analysis

00:03

Following on from our preliminary design using the line beam analysis,

00:07

we're going to generate automatically a complete grill model.

00:14

Using the refined analysis option,

00:16

we can configure how the grill is to be generated.

00:21

Once the generation has been completed,

00:23

we can then preview the results

00:26

and then load the model into structural bridge design.

00:33

In this example, the first three spans were chosen for generation

00:37

and we can see that all the necessary parts are available including the alignment,

00:42

roadway layout,

00:44

the grilled meshes

00:45

supports and the longitudinal and transverse beam definitions.

00:51

All that remains now is to apply the loading.

00:54

Now, structural bridge design includes all the necessary bridge loading types.

00:59

However,

00:59

in order to circumvent the need for any

01:01

manual entry of dead or superimposed dead loading,

01:05

there is a tip that we can use.

01:10

If we quickly open the file we used for

01:12

the preliminary design that used the line beam method.

01:15

We can see that there were some automatically generated dead loads.

01:20

All we need to do is remove the live load entries

01:23

and then export what is left to a load file.

01:27

This can then be used back in the refined bridge model.

01:40

So to use those saved loads, we can just navigate to the correct beam

01:45

and then import the loading.

01:48

We can now see that we have dead and superimposed dead loading for that beam

01:52

and we can now proceed to the live loading.

01:56

So the process of generating the live loads is

01:59

via a live load optimization guided by influence surfaces.

02:04

Once the influence surface generation panel is active,

02:08

the designer chooses the beam

02:10

that will be the focus of the influence surface generation

02:14

and then configures the effects and scope required.

02:18

We will keep this simple for the example.

02:20

But for actual bridge work, this list could be extensive.

02:25

Once the influence surfaces are generated,

02:27

it is easy to see the effect of loads placed on the beam,

02:30

not only for the beam itself but for the whole structure.

02:35

With this knowledge, the designer can press on to the actual load optimization.

02:39

This process is co dependent and the

02:41

designer will choose which limit states to satisfy

02:44

together with other critical criteria.

02:47

Once the loading patterns have been established,

02:49

the model can then be analyzed

02:51

and the results explored.

02:55

Once in the results viewer,

02:57

the view will need to be configured in a number of

02:59

ways in order to be able to examine the relevant data.

03:05

So in our example,

03:06

we will be looking for envelope result types relevant

03:10

to the specific beam we are interested in.

03:13

This is done by manipulating the drop down list at the top of the viewer.

03:16

And then by filtering the model, so as only to reveal those results of interest,

03:22

we can then see the table of results.

03:25

However,

03:25

it may be interesting to the designer to gain a little

03:28

more insight into the makeup of each of the values.

03:32

This can be done by using the drill down feature

03:35

which will reveal the makeup of each value together with any factors used.

03:41

Now that we have the analysis results,

03:43

we can transfer those over to the beam. In question.

03:46

Once completed,

03:48

we can see that they have now joined the dead loads

03:50

from earlier and we can proceed to the beam design.

03:55

So the beam design is carried out in a very visual manner

03:59

using a stress plot as a guide together with

04:02

the various low cases that the designer is considering.

04:06

The stress plot is basically a plot of the compressive stresses in the concrete.

04:11

And these are shown by the red and

04:13

green curves denoting failure or success respectively.

04:17

The blue lines displaying the limits from the design code.

04:21

So in order to reduce the concrete stresses to an acceptable level,

04:25

the designer is able to invoke a tendon optimization.

04:29

The designer chooses the criteria for the optimization

04:33

which will include whether the beam is to be symmetric and whether to consider de

04:37

bonded or harped tendons

04:39

together with a variety of other controls,

04:41

including comparative costs for the various tendon layouts,

04:46

a generative design process then ensues and after all options

04:50

are considered the least cost workable solution is presented,

04:55

this solution can then be tested against the other cases.

04:60

The fully formatted design reports for any point along the length

05:04

of the beam can be generated and explored at any time

05:07

in both text and PDF formats.

05:13

If for any reason,

05:14

the designer feels the need to make changes to the automatic design.

05:18

It is possible to manually interact with the tendon

05:21

layout directly for full control of the design.

05:28

During the design process, it is usual to iterate many times on any given design

05:34

and more critically for steel section designs,

05:37

the designer will need any design changes made in structural bridge design

05:41

to be reflected within the infra works model.

05:45

So we can see in this example that the steel beam is failing

05:50

and the designer will need to examine the design in structural bridge design

05:54

in order to identify the exact cause and find a solution.

05:59

Once the designer has explored the results

06:02

and interacted with the design,

06:04

the way forward in this case is to make some minor changes to the steel section

06:11

to achieve this.

06:12

The designer uses the beam definition forms to make a small change in depth and also a

06:19

change to the thickness of the bottom frane

06:23

with the design. Now working

06:25

the structural bridge design file is saved

06:27

and then back in infra works update from A SBD is used

06:32

to bring the still section changes back into the infra works model.

06:47

So in this last section,

06:49

we will examine how we can use the automatic refined analysis model generation

06:54

to create a full finite element model of a tub girder

06:58

arrangement.

07:00

The generation process is very similar to that used for the grilled model

07:05

except that the designer chooses tub girder under the analytical model type.

07:10

Again,

07:11

the controls need to be uh quickly configured and an option

07:15

as to whether a hybrid grilled fe model is required.

07:21

In this case, a hybrid model was requested.

07:24

And when the generation is complete,

07:25

the resulting model can be previewed and

07:27

then loaded into structural bridge design.

07:31

As with the grilled model earlier,

07:33

all the necessary parts of the model are there

07:36

including the alignment and road layout, et cetera.

07:40

The loading process is also similar to that which we have already seen earlier.

07:44

And in this case,

07:45

we will test the integrity of the fe model with the built in test loads.

07:51

Once the analysis has taken place,

07:54

the designer can then as before use the results viewer

07:58

to see the outcome of the analysis.