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Perform shear checks at SLS and ULS.
Type:
Tutorial
Length:
5 min.
Transcript
00:03
In Structural Bridge Design, once you design a beam and apply loads,
00:08
you are ready to perform shear checks, under both serviceability and ultimate limit states.
00:14
At SLS, you can check for web shearing and cracking
00:17
to ensure that the beam remains functional and serviceable under normal conditions.
00:22
At ULS, you can check for direct vertical shear to ensure that the beam can withstand maximum loads.
00:30
In this scenario, a composite, pretensioned, precast beam
00:35
and a 21-meter-long, 2-meter-wide concrete slab are designed with dead loads, construction loads, live loads,
00:43
a differential temperature profile, and a tendon layout already applied.
00:49
At this point, you can perform shear checks.
00:53
Keep in mind the following:
00:55
Shear link spacing in the beam needs to be determined to resist transverse and longitudinal shear forces.
01:02
The reinforcement grade for the shear links is the same as for the main reinforcement,
01:07
and vertical shear is resistant to the precast beam only.
01:11
For longitudinal shear, the interface surface is type two.
01:17
Here, the design is open, with Pre-tensioned Prestressed active in the Design Beam group
01:22
and the Pre-tensioned Beam Analysis form open.
01:26
In the form, expand the Analyse for drop-down and select the Shear option.
01:32
Click OK in the Warning.
01:35
Now, set the Limit State to 6. 15 SLS Frequent.
01:40
In the graphic, note the reduction in the tensile principal stress effect.
01:45
While the beam appears to fail at the ends, it is within the cast-in-place diaphragm.
01:50
As a result, web shear cracking is not a concern.
01:55
Now, change the Limit State to ULS Persistent / Transient.
01:60
This calculates vertical shear, where you can determine the requirements for shear links.
02:05
Here, even with the default minimum strut angle, the section will adequately carry the design shear effects,
02:12
giving a minimum link spacing of 160 millimeters.
02:16
To examine this in the Results Viewer, in the form, click Results.
02:22
Next, you need to merge the vertical, or direct, shear link requirements with the longitudinal shear link requirements.
02:30
In this instance, it may be optimal to increase the strut angle.
02:35
While this increases the number of shear links required for direct shear,
02:39
it reduces the requirement for additional longitudinal steel,
02:42
even if no additional longitudinal reinforcement is required at any angle.
02:47
In most cases, this is a better approach, as the requirement for direct shear links and interface shear links will be closer,
02:55
resulting in minimal addition.
02:58
To achieve this, you need to adjust the shear calculation parameters.
03:02
First, Close the Viewer.
03:05
Back in the Pre-tensioned Beam Analysis form, change the Set parameters for drop-down to Shear calculations.
03:14
In the Design Data for Shear form, set the Angle between strut and beam axis to 45;
03:20
and change the Surface condition to Rough, to determine the correct cohesion and friction factors.
03:26
Then, change the Surface condition to User Defined to activate these factors.
03:32
Click OK.
03:34
Back in the form, click Results again.
03:38
In the Results Viewer, scroll down to view the values of Mrd divided by Med, noting that they are always greater than one.
03:47
This means that no additional longitudinal reinforcement is necessary for shear requirements.
03:54
Now that the beam design passes for the direct shear case,
03:57
you can design the shear links and merge the requirements of the direct and interface shear cases.
04:03
Close the Viewer.
04:05
In the Pre-tensioned Beam Analysis form, change the Analyse for drop-down to the Interface shear option.
04:12
In the graphic, the interface shear requirement is represented by the red dashed line,
04:17
while the interface shear resistance supplied by the links for direct shear is represented by the solid blue line.
04:24
As you can see, additional links are required only in the areas where the red dotted line extends above the blue solid line.
04:32
Back in the form, change the design location by setting the Result Point of Interest to 1.
04:38
Click Results again, then scroll to find and verify the reinforcement requirement.
04:45
Close the Viewer.
04:48
In the graphics window, select the isometric view to review the graphic from a different angle.
04:54
Now, you are ready to save the file.
04:57
After closing all forms, click File > Save As, type a File name in the Save File dialog, and then click Save.
05:07
You have now performed SLS and ULS shear checks on your beam.
Video transcript
00:03
In Structural Bridge Design, once you design a beam and apply loads,
00:08
you are ready to perform shear checks, under both serviceability and ultimate limit states.
00:14
At SLS, you can check for web shearing and cracking
00:17
to ensure that the beam remains functional and serviceable under normal conditions.
00:22
At ULS, you can check for direct vertical shear to ensure that the beam can withstand maximum loads.
00:30
In this scenario, a composite, pretensioned, precast beam
00:35
and a 21-meter-long, 2-meter-wide concrete slab are designed with dead loads, construction loads, live loads,
00:43
a differential temperature profile, and a tendon layout already applied.
00:49
At this point, you can perform shear checks.
00:53
Keep in mind the following:
00:55
Shear link spacing in the beam needs to be determined to resist transverse and longitudinal shear forces.
01:02
The reinforcement grade for the shear links is the same as for the main reinforcement,
01:07
and vertical shear is resistant to the precast beam only.
01:11
For longitudinal shear, the interface surface is type two.
01:17
Here, the design is open, with Pre-tensioned Prestressed active in the Design Beam group
01:22
and the Pre-tensioned Beam Analysis form open.
01:26
In the form, expand the Analyse for drop-down and select the Shear option.
01:32
Click OK in the Warning.
01:35
Now, set the Limit State to 6. 15 SLS Frequent.
01:40
In the graphic, note the reduction in the tensile principal stress effect.
01:45
While the beam appears to fail at the ends, it is within the cast-in-place diaphragm.
01:50
As a result, web shear cracking is not a concern.
01:55
Now, change the Limit State to ULS Persistent / Transient.
01:60
This calculates vertical shear, where you can determine the requirements for shear links.
02:05
Here, even with the default minimum strut angle, the section will adequately carry the design shear effects,
02:12
giving a minimum link spacing of 160 millimeters.
02:16
To examine this in the Results Viewer, in the form, click Results.
02:22
Next, you need to merge the vertical, or direct, shear link requirements with the longitudinal shear link requirements.
02:30
In this instance, it may be optimal to increase the strut angle.
02:35
While this increases the number of shear links required for direct shear,
02:39
it reduces the requirement for additional longitudinal steel,
02:42
even if no additional longitudinal reinforcement is required at any angle.
02:47
In most cases, this is a better approach, as the requirement for direct shear links and interface shear links will be closer,
02:55
resulting in minimal addition.
02:58
To achieve this, you need to adjust the shear calculation parameters.
03:02
First, Close the Viewer.
03:05
Back in the Pre-tensioned Beam Analysis form, change the Set parameters for drop-down to Shear calculations.
03:14
In the Design Data for Shear form, set the Angle between strut and beam axis to 45;
03:20
and change the Surface condition to Rough, to determine the correct cohesion and friction factors.
03:26
Then, change the Surface condition to User Defined to activate these factors.
03:32
Click OK.
03:34
Back in the form, click Results again.
03:38
In the Results Viewer, scroll down to view the values of Mrd divided by Med, noting that they are always greater than one.
03:47
This means that no additional longitudinal reinforcement is necessary for shear requirements.
03:54
Now that the beam design passes for the direct shear case,
03:57
you can design the shear links and merge the requirements of the direct and interface shear cases.
04:03
Close the Viewer.
04:05
In the Pre-tensioned Beam Analysis form, change the Analyse for drop-down to the Interface shear option.
04:12
In the graphic, the interface shear requirement is represented by the red dashed line,
04:17
while the interface shear resistance supplied by the links for direct shear is represented by the solid blue line.
04:24
As you can see, additional links are required only in the areas where the red dotted line extends above the blue solid line.
04:32
Back in the form, change the design location by setting the Result Point of Interest to 1.
04:38
Click Results again, then scroll to find and verify the reinforcement requirement.
04:45
Close the Viewer.
04:48
In the graphics window, select the isometric view to review the graphic from a different angle.
04:54
Now, you are ready to save the file.
04:57
After closing all forms, click File > Save As, type a File name in the Save File dialog, and then click Save.
05:07
You have now performed SLS and ULS shear checks on your beam.
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