Impresión a dos caras automática

Calculated by data item. Click on to close the titles form.

Defining Load Effects

3. To define the loading effects open the Define Composite Beam Loads form using the Data|Define Loading... menu item. The construction loading is defined first.

4. Set the Loading Description field to Construction Stage 1A. As the beam is simply supported we can use the “Generate” button to create the bending moments and shears for this case. This will open up the Generate Beam Loads data form, after the display of an information message explaining the limitations of the method.

5. The steel and concrete dead loads have been automatically calculated using the material density and areas defined. An additional component representing

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the temporary construction load is added by clicking on the “+ Add Load Component” button. Click on the tab of this additional component and set the Component Ref: field to “Temp Const Load”. Then enter “1.0” into both the Start and End Fields of the UDL Intensity. The load factor for both ULS and SLS can be changed to “1.0”. The ULS load factor for the Steel dead load should be changed to “1.05”. Set the Beam span equally divided by field to “20”. Click on the “OK” button to save this data and close the Generate Beam Loads form.

6. Set the Loading Description field to “String course dead load” and use the “Generate” button to create the bending moments and shears for this case. Again, the program automatically calculates the dead load intensity of the edge section. Set the Beam span equally divided by field to “20” and accept the

defaults by clicking on .

7. Set the Loading Description field to “SDL non-structural concrete etc”. This will be used to represent the removal of the temporary construction loading by applying a negative factor to the load. Use the “Generate” button to open the data form then enter “1.0” into the Start and End fields of the UDL intensity. The ULS and SLS Load factors are changed to “-1”. The component ref field can be changed to “Temp const load rem” to make it clear what this represents. Set the Beam span equally divided by field to “20” before clicking on to accept the data.

8. Set the Loading Description field to “Superimposed dead load” (The ID no. is left at “1” as there is only one SDL load case to consider). An information message may be displayed warning that there are hogging moments, for the previous case, where sagging moments are expected. This is of course

intended so can be accepted. Use the “Generate” button to open the data form then enter “3.2” into the Start and End fields of the UDL intensity. The ULS and SLS load factors are left at the default values. Set the Beam span equally divided by field to “20” before clicking on to accept the data.

9. The effects for two live load cases need to be considered: Sagging Bending Moments with associated Shear Max Shears with associated Bending moments

These are loaded from an ASCII file which has been prepared using a standard text editor. This file has a file extension “.sld” and can be imported by using the “Interface” button on the Define Composite Beam Loads form. Select the Direct ASCII File Import radio button option before clicking on which will then display a standard file browser allowing the selection of the file called “BS_Composite_Beam_Simple.SLD”. The imported effects can be inspected by selecting the appropriate option in the Loading Description field. It should be noted that there are values for both combination 1 and 3 and these can be viewed by changing the Load Combination field accordingly.

10. All main loading effects are now defined so the Define Composite Beam Loads form can be closed by clicking on . An information message is displayed

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indicating that dead load shears are actual values whereas the live load envelopes are all absolute values. Answer “Yes” to the question about

converting the dead load shears to absolute values as this will enable them to be combined correctly.

Design Checks

Setting the Differential Temperature Profile and Shrinkage strains and calculating the primary stresses

11. Open the Composite Beam Analysis form by using the Calculate|Analyse... menu item. Change the Set parameters for: field to “Differential temp. Appx C”. Set the field Surfacing: to “Surfaced” and the Surfacing Thickness: to “0.075”. Also set the Depth of concrete above steel: to “0.275” (the slab plus the

haunch).

From the graphical representation of the profile it can be seen that the program takes the top of the concrete as the top of the edge detail, whereas it should be the top of the slab. It can be assumed that the temperature in the upstand is constant at the top of slab temperature. We therefore need to modify the temperature profile to move it down by the height of the upstand.

12. Close the Appendix C profile form by clicking on and then change the Set parameters for: field to “Differential temp. defined”. The initial profile shown is that previously defined, but this can be edited to the following values. Change the values and then close this form by clicking on to set the correct profile.

5-7 13. Set the Set parameters for: field to

“Shrinkage and Creep” which will display the Data for Shrinkage & Creep data form. The Shrinkage strain: should be set to “-0.00025” and all the other values left as the default settings. Close the parameters forms by clicking on .

14. To determine the primary stresses in the section due to differential temperature and differential shrinkage set the Analyse for: field to “Diff temp primary stress”.

This will produce a graphical result of the stresses. More details can be found by using the “Results” button.

The same process can be carried out for differential shrinkage.

15. Close the Composite Beam Analysis form by clicking on to save this data. Construction stages

16. The first design check will be to ensure the ULS capacity of the steel girder, on its own, is greater than the applied load effects during construction. Open the Composite Beam Analysis form by using the Calculate|Analyse... menu item

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and set the Analyse for: field to “BM’s during construction”. The calculation is done automatically.

17. It can be seen from the graphics that the actual mid span construction moment just exceeds the bending capacity of this compact section.

18. The resulting calculation for this can be seen by first moving the vertical red line on the beam elevation to the mid span point and then clicking on the “Results” button. The vertical red line is moved by using the direction buttons at the end of the field Result Point of Interest.

19. Inspection of the results shows that the slenderness of the girder has reduced the bending capacity of the section by virtue of lateral torsional buckling of the top flange. This could be improved by supplying a torsional restraint to the mid span point of the beam. To do this, change the Set parameter for: to “Bending and Buckling calculations” which displays the appropriate data form.

20. Set the current tab to “Effective Length – Erection” and set the Restraint Type: to “torsional restraints”. The Number of equally spaced restraints is left as “1” to enable a restraint at mid-span.

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21. Reduce the value of Rotation of restraint per kNm of torque, R from “1.0” to “0.8”.

We can see that the section then works (note that the BM diagram turns green). This indicates that a transverse restraint is required at mid-span with sufficient bending stiffness so that the restraint end will not rotate by more than 0.8 degrees if a moment of 1.0kNm is applied at the end.

The beam therefore passes this design check.

22. Close the Design Data for Bending & Buckling form by clicking on the “OK“ button and then click on the “Results” button on the Composite Beam Analysis form which will open the Results Viewer window displaying the full calculations for the current section. These can be printed if required.

Close the Results Viewer using the ‘Exit’ button.

Bending Moments under BS 5400 Combination Loading

23. Only sagging moments need to be considered as the beam is simply

supported. Change Analyse for: data field to “BM’s for sagging load case 1 load comb 1”. Limit State should be set to “Ultimate” and Display: set to

“Moments”. The graphics clearly shows that the design moments are less than the resistance moments along the whole of the beam length.

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By changing the Display field to “Steel” or “Slab Stresses” a message indicates that due to the section being compact, stress checks are not required.

24. Now set the Limit State to “Serviceability” and the Display: to “Steel stresses”. Both top and bottom flange design stresses, shown in the graphics, are below the maximum allowable stresses.

The same can be shown for the concrete slab stresses by clicking on the “Slab stresses” radio button (a warning message about adding local to global effects will appear – click “OK” on this message). The section therefore passes this design check. Full calculations can be viewed/printed by using the “Results” button as required.

25. It should be noted that the stress calculations are based upon the use of the correct section modulus taking into account the effect of shear lag. Shear lag is represented by using an effective breadth of concrete flange which is determined by the

program in accordance with the code of practice. The parameters affecting these calculations are defined in the Criteria for SLS calculations form which can be displayed by selecting “SLS Criteria” in the Set parameters for: field. In most cases the default values are acceptable. The form is closed using the “OK” button.

26. Repeat the above exercise for combination 3, by selecting “...load case 1 comb 3” in the Analyse for: field and verify that the beam passes. Also verify that temperature stresses are being added by viewing the results.

Vertical Shear under BS 5400 Combination Loading

27. In the Analyse for: data field, select “Shear Force load case 1 load comb 1” from the dropdown selection; it can be seen that only Ultimate Limit State is available for checking. The graphics clearly shows that the design shears are less than the permissible shear along the whole of the beam length.

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The section therefore passes this design check and full calculations of these can be viewed/printed by using the “Results” button as before.

Combined Bending and Shear Design Checks

28. The combined effect of bending and shear are checked using the unity equations of 9.9.3.1 in BS 5400. In the Analyse for: data field, select

“Combined Bending and Shear” from the dropdown selection to display the graphical results. Both Max Moments with Associated shears and Max Shears with associated moments are checked giving two lines on the diagram.

Design for Longitudinal Shear

Longitudinal shear resistance is checked along two planes. The first is the plane of the interface between the steel and concrete and is resisted by shear connectors welded to the top flange and cast into the concrete slab. The second is the vertical plane through the slab adjacent to the edge of the top flange and is resisted by the dowel action of the transverse reinforcement. Before the design checks can be carried out it is first necessary to specify a default shear connector arrangement and transverse reinforcement. The arrangements and reinforcement quantities can then be adjusted to fit the requirements.

29. First close the Composite Beam Analysis form by clicking on and then open the Define Composite Beam form using the toolbar button.

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30. To define the shear connectors, use the drop down list in the Define and locate span features: field to select “Longitudinal Shear Connectors” which will display the Location of Shear Connectors form. Accept the default arrangement by closing the form by clicking on . (Note that the slab reinforcement is shown in the graphics view – zoom in to see this in greater detail).

31. The same thing can be done with transverse slab reinforcement before closing the Define Composite Beam form by clicking on .

32. To check the adequacy of the default shear connectors and transverse reinforcement open the Composite Beam Analysis form using the

Calculate|Analyse... menu item and change Analyse for: to “Longitudinal shear 1 load comb. 1” and Display: to “Shear connectors”.

The graphics display shows that the default shear stud type and spacing is not quite satisfactory at the places of max shear flow. Hence, we would install additional shear links near the ends of the beam in this case.

33. Now change the Display radio button to “Transverse reinforcement” and the graphic display now shows that the permissible shear flow is several times the actual resistance at the critical shear plane, so the reinforcement can be reduced.

5-13 34. Close the Composite Beam Analysis form by

clicking and return to the Location of Shear Connectors form (see 29... above). The shear connector type and size will remain the same but the spacing can be increased toward the centre of the beam. Additional rows of data can be added in the form by selecting, in the next available row, the same connector type as the previous lines. This will display a Shear Connector Details form to define the stud size and strength.

Accept the defaults by clicking on then edit the data in the other columns as shown below.

Close the form by clicking on and then open the Transverse

Reinforcement in Slab form using Define and locate span features. Change the bar diameters to 16mm and the spacing to 225 in top, bottom and haunch locations and then close the form by clicking on .

35. Open the Composite Beam Analysis form and check that the effects of the changes made to the shear connectors and transverse reinforcement are acceptable.

When the analysis form is open the results graphs can be displayed in a 3D isometric window by clicking on the icon on the graphics window (see below).

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Also, it is worth noting that when the print preview window is opened by clicking on the icon at the top of the graphic window, a pdf of the graphic window can be generated by clicking on the icon at the top of the print preview window.

36. Click on the File|Save As... menu item and save the file as “My BS Example