ETABS. Integrated Building Design Software. Concrete Frame Design Manual. Computers and Structures, Inc. Berkeley, California, USA

Computers and Structures, Inc.

Berkeley, California, USA January 2002^{Version 8}

ETABS ^®

Integrated Building Design Software

Concrete Frame Design Manual

 Copyright Computers and Structures, Inc., 1978-2002.

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Copyright

The computer program ETABS and all associated documentation are proprietary and copyrighted products. Worldwide rights of ownership rest with Computers and Structures, Inc. Unlicensed use of the program or reproduction of the documentation in any form, without prior written authorization from Computers and Structures, Inc., is explicitly prohibited.

Further information and copies of this documentation may be obtained from:

Computers and Structures, Inc.

1995 University Avenue Berkeley, California 94704 USA

Phone: (510) 845-2177 FAX: (510) 845-4096

e-mail: [email protected] (for general questions) e-mail: [email protected] (for technical support questions)

web: www.csiberkeley.com

DISCLAIMER

CONSIDERABLE TIME, EFFORT AND EXPENSE HAVE GONE INTO THE DEVELOPMENT AND DOCUMENTATION OF ETABS. THE PROGRAM HAS BEEN THOROUGHLY TESTED AND USED. IN USING THE PROGRAM, HOWEVER, THE USER ACCEPTS AND UNDERSTANDS THAT NO WARRANTY IS EXPRESSED OR IMPLIED BY THE DEVELOPERS OR THE DISTRIBUTORS ON THE ACCURACY OR THE RELIABILITY OF THE PROGRAM.

THIS PROGRAM IS A VERY PRACTICAL TOOL FOR THE DESIGN/CHECK OF CONCRETE STRUCTURES. HOWEVER, THE USER MUST THOROUGHLY READ THE MANUAL AND CLEARLY RECOGNIZE THE ASPECTS OF CONCRETE DESIGN THAT THE PROGRAM ALGORITHMS DO NOT ADDRESS.

THE USER MUST EXPLICITLY UNDERSTAND THE ASSUMPTIONS OF THE PROGRAM AND MUST INDEPENDENTLY VERIFY THE RESULTS.

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Contents

General Concrete Frame Design Information

1 General Design Information

Design Codes 1-1

Units 1-1

Overwriting the Frame Design Procedure for a Con- crete Frame

1-1

Design Load Combinations 1-2

Design of Beams 1-2

Design of Columns 1-3

Beam/Column Flexural Capacity Ratios 1-4

Second Order P-Delta Effects 1-4

Element Unsupported Lengths 1-6

Analysis Sections and Design Sections 1-7 2 Concrete Frame Design Process

Concrete Frame Design Procedure 2-1

3 Interactive Concrete Frame Design

General 3-1

Concrete Design Information Form 3-1

4 Output Data Plotted Directly on the Model

Overview 4-1

Using the Print Design Tables Form 4-1

Design Input 4-2

Design Output 4-2

Concrete Frame Design Manual

ii

Concrete Frame Design Specific to UBC97

5 General and Notation

Introduction to the UBC 97 Series of Technical Notes 5-1

Notation 5-2

6 Preferences

General 6-1

Using the Preferences Form 6-1

Preferences 6-2

7 Overwrites

General 7-1

Overwrites 7-1

Making Changes in the Overwrites Form 7-3 Resetting Concrete Frame Overwrites to Default

Values

7-4

8 Design Load Combinations 9 Strength Reduction Factors 10 Column Design

Overview 10-1

Generation of Biaxial Interaction Surfaces 10-2

Calculate Column Capacity Ratio 10-5

Determine Factored Moments and Forces 10-6 Determine Moment Magnification Factors 10-6

Determine Capacity Ratio 10-8

Required Reinforcing Area 10-10

Design Column Shear Reinforcement 10-10 Determine Required Shear Reinforcement 10-14

Reference 10-15

11 Beam Design

Overview 11-1

Design Beam Flexural Reinforcement 11-1

Determine Factored Moments 11-2

Determine Required Flexural Reinforcement 11-2

Contents

iii

Design Beam Shear Reinforcement 11-10

12 Joint Design

Overview 12-1

Determine the Panel Zone Shear Force 12-1 Determine the Effective Area of Joint 12-5

Check Panel Zone Shear Stress 12-5

Beam/Column Flexural Capacity Ratios 12-6 13 Input Data

Input data 13-1

Using the Print Design Tables Form 13-3 14 Output Details

Using the Print Design Tables Form 14-3

Concrete Frame Design Specific to ACI-318-99

15 General and Notation

Introduction to the ACI318-99 Series of Technical Notes

15-1

Notation 15-2

16 Preferences

General 16-1

Using the Preferences Form 16-1

Preferences 16-2

17 Overwrites

General 17-1

Overwrites 17-1

Making Changes in the Overwrites Form 17-3 Resetting Concrete Frame Overwrites to Default

Values

17-4

18 Design Load Combinations 19 Strength Reduction Factors

Concrete Frame Design Manual

iv

20 Column Design

Overview 20-1

Generation of Biaxial Interaction Surfaces 20-2

Calculate Column Capacity Ratio 20-5

Determine Factored Moments and Forces 20-6 Determine Moment Magnification Factors 20-6

Determine Capacity Ratio 20-9

Required Reinforcing Area 20-10

Design Column Shear Reinforcement 20-10

Determine Section Forces 20-11

Determine Concrete Shear Capacity 20-12 Determine Required Shear Reinforcement 20-13

References 20-15

21 Beam Design

Overview 21-1

Design Beam Flexural Reinforcement 21-1

Determine Factored Moments 21-2

Determine Required Flexural Reinforcement 21-2

Design for T-Beam 21-5

Minimum Tensile Reinforcement 21-8

Special Consideration for Seismic Design 21-8

Design Beam Shear Reinforcement 21-9

Determine Shear Force and Moment 21-11 Determine Concrete Shear Capacity 21-12 Determine Required Shear Reinforcement 21-13 22 Joint Design

Overview 22-1

Determine the Panel Zone Shear Force 22-1 Determine the Effective Area of Joint 22-4

Check Panel Zone Shear Stress 22-4

Beam/Column Flexural Capacity Ratios 22-6 23 Input Data

Input Data 23-1

Using the Print Design Tables Form 23-3

Contents

v 24 Output Details

Using the Print Design Tables Form 24-3

Design Codes Technical Note 1 - 1

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Technical Note 1 General Design Information

This Technical Note presents some basic information and concepts helpful when performing concrete frame design using this program.

Design Codes

The design code is set using the Options menu > Preferences > Concrete Frame Design command. You can choose to design for any one design code in any one design run. You cannot design some elements for one code and others for a different code in the same design run. You can, however, perform different design runs using different design codes without rerunning the analysis.

Units

For concrete frame design in this program, any set of consistent units can be used for input. You can change the system of units at any time. Typically, de- sign codes are based on one specific set of units.

Overwriting the Frame Design Procedure for a Concrete Frame

The two design procedures possible for concrete beam design are:

ƒ Concrete frame design

ƒ No design

If a line object is assigned a frame section property that has a concrete ma- terial property, its default design procedure is Concrete Frame Design. A con- crete frame element can be switched between the Concrete Frame Design and the "None" design procedure. Assign a concrete frame element the "None"

design procedure if you do not want it designed by the Concrete Frame De- sign postprocessor.

General Design Information Concrete Frame Design

Technical Note 1 - 2 Design Load Combinations

Change the default design procedure used for concrete frame elements by selecting the element(s) and clicking Design menu > Overwrite Frame Design Procedure. This change is only successful if the design procedure assigned to an element is valid for that element. For example, if you select a concrete element and attempt to change the design procedure to Steel Frame Design, the program will not allow the change because a concrete element cannot be changed to a steel frame element.

Design Load Combinations

The program creates a number of default design load combinations for con- crete frame design. You can add in your own design load combinations. You can also modify or delete the program default load combinations. An unlim- ited number of design load combinations can be specified.

To define a design load combination, simply specify one or more load cases, each with its own scale factor. For more information see Concrete Frame De- sign UBC97 Technical Note 8 Design Load Combination and Concrete Frame Design ACI 318-99 Technical Note 18 Design Load Combination.

Design of Beams

The program designs all concrete frame elements designated as beam sec- tions in their Frame Section Properties as beams (see Define menu >Frame Sections command and click the Reinforcement button). In the design of concrete beams, in general, the program calculates and reports the required areas of steel for flexure and shear based on the beam moments, shears, load combination factors, and other criteria, which are described in detail in Con- crete Frame UBC97 Technical Note Beam Design 11 and Concrete Frame ACI 318-99 Technical Note 21 Beam Design. The reinforcement requirements are calculated at each output station along the beam span.

All the beams are designed for major direction flexure and shear only.

Effects resulting from any axial forces, minor direction bending, and torsion that may exist in the beams must be investigated independ- ently by the user.

In designing the flexural reinforcement for the major moment at a particular section of a particular beam, the steps involve the determination of the maximum factored moments and the determination of the reinforcing steel.

Concrete Frame Design General Design Information

Design of Beams Technical Note 1 - 3

The beam section is designed for the maximum positive and maximum nega- tive factored moment envelopes obtained from all of the load combinations.

Negative beam moments produce top steel. In such cases, the beam is al- ways designed as a rectangular section. Positive beam moments produce bottom steel. In such cases, the beam may be designed as a rectangular- or T-beam. For the design of flexural reinforcement, the beam is first designed as a singly reinforced beam. If the beam section is not adequate, the required compression reinforcement is calculated.

In designing the shear reinforcement for a particular beam for a particular set of loading combinations at a particular station resulting from the beam major shear, the steps involve the determination of the factored shear force, the determination of the shear force that can be resisted by concrete, and the determination of the reinforcement steel required to carry the balance.

Design of Columns

The program designs all concrete frame elements designated as column sec- tions in their Frame Section Properties as columns (see Define menu

>Frame Sections command and click the Reinforcement button). In the design of the columns, the program calculates the required longitudinal steel, or if the longitudinal steel is specified, the column stress condition is reported in terms of a column capacity ratio. The capacity ratio is a factor that gives an indication of the stress condition of the column with respect to the capacity of the column. The design procedure for reinforced concrete columns involves the following steps:

ƒ Generate axial force-biaxial moment interaction surfaces for all of the dif- ferent concrete section types of the model.

ƒ Check the capacity of each column for the factored axial force and bending moments obtained from each load combination at each end of the column.

This step is also used to calculate the required reinforcement (if none was specified) that will produce a capacity ratio of 1.0.

ƒ Design the column shear reinforcement.

The shear reinforcement design procedure for columns is very similar to that for beams, except that the effect of the axial force on the concrete shear ca- pacity needs to be considered. See Concrete Frame UBC97 Technical Note 10

General Design Information Concrete Frame Design

Technical Note 1 - 4 Second Order P-Delta Effects

Column Design and Concrete Frame ACI 318-99 Technical Note 20 Column Design for more information.

Beam/Column Flexural Capacity Ratios

When the ACI 318-99 or UBC97 code is selected, the program calculates the ratio of the sum of the beam moment capacities to the sum of the column moment capacities at a particular joint for a particular column direction, ma- jor or minor. The capacities are calculated with no reinforcing overstrength factor, α, and including ϕ factors. The beam capacities are calculated for re- versed situations and the maximum summation obtained is used.

The moment capacities of beams that frame into the joint in a direction that is not parallel to the major or minor direction of the column are resolved along the direction that is being investigated and the resolved components are added to the summation.

The column capacity summation includes the column above and the column below the joint. For each load combination, the axial force, P_u, in each of the columns is calculated from the program analysis load combinations. For each load combination, the moment capacity of each column under the influence of the corresponding axial load P_u is then determined separately for the major and minor directions of the column, using the uniaxial column interaction dia- gram. The moment capacities of the two columns are added to give the ca- pacity summation for the corresponding load combination. The maximum ca- pacity summations obtained from all of the load combinations is used for the beam/column capacity ratio.

The beam/column flexural capacity ratios are only reported for Special Mo- ment-Resisting Frames involving seismic design load combinations.

See Beam/Column Flexural Capacity Ratios in Concrete Frame UBC97 Techni- cal Note 12 Joint Design or in Concrete Frame ACI 318-99 Technical Note 22 Joint Design for more information.

Second Order P-Delta Effects

Typically, design codes require that second order P-Delta effects be consid- ered when designing concrete frames. The P-Delta effects come from two sources. They are the global lateral translation of the frame and the local de- formation of elements within the frame.

Concrete Frame Design General Design Information

Second Order P-Delta Effects Technical Note 1 - 5

Consider the frame element shown in Figure 1, which is extracted from a story level of a larger structure. The overall global translation of this frame element is indicated by ∆. The local deformation of the element is shown as δ.

The total second order P-Delta effects on this frame element are those caused by both ∆ and δ.

The program has an option to consider P-Delta effects in the analysis. Con- trols for considering this effect are found using the Analyze menu > Set Analysis Options command and then clicking the Set P-Delta Parameters button. When you consider P-Delta effects in the analysis, the program does a good job of capturing the effect due to the ∆ deformation shown in Figure 1, but it does not typically capture the effect of the δ deformation (unless, in the model, the frame element is broken into multiple pieces over its length).

In design codes, consideration of the second order P-Delta effects is generally achieved by computing the flexural design capacity using a formula similar to that shown in Equation. 1.

MCAP = aMnt + bMlt Eqn. 1

where,

MCAP = Flexural design capacity

∆

δ

Original position of frame element shown by vertical line

Position of frame element as a result of global lateral translation, ∆, shown by dashed line

Final deflected position of frame element that includes the global lateral translation, ∆, and the local deformation of the element, δ

Figure 1: The Total Second Order P-Delta Effects on a Frame Element Caused by Both ∆∆∆∆ and δδδδ

General Design Information Concrete Frame Design

Technical Note 1 - 6 Element Unsupported Lengths

Mnt = Required flexural capacity of the member assuming there is no translation of the frame (i.e., associated with the δ defor- mation in Figure 1)

Mlt = Required flexural capacity of the member as a result of lateral translation of the frame only (i.e., associated with the ∆ de- formation in Figure 1)

a = Unitless factor multiplying M_nt

b = Unitless factor multiplying Mlt (assumed equal to 1 by the program; see below)

When the program performs concrete frame design, it assumes that the factor b is equal to 1 and it uses code-specific formulas to calculate the factor a.

That b = 1 assumes that you have considered P-Delta effects in the analysis, as previously described. Thus, in general, if you are performing concrete frame design in this program, you should consider P-Delta effects in the analysis before running the design.

Element Unsupported Lengths

The column unsupported lengths are required to account for column slender- ness effects. The program automatically determines these unsupported lengths. They can also be overwritten by the user on an element-by-element basis, if desired, using the Design menu > Concrete Frame Design >

View/Revise Overwrites command.

There are two unsupported lengths to consider. They are L33 and L22, as shown in Figure 2. These are the lengths between support points of the ele- ment in the corresponding directions. The length L33 corresponds to instability about the 3-3 axis (major axis), and L22 corresponds to instability about the 2-2 axis (minor axis). The length L22 is also used for lateral-torsional buckling caused by major direction bending (i.e., about the 3-3 axis).

In determining the values for L22 and L33 of the elements, the program recog- nizes various aspects of the structure that have an effect on these lengths, such as member connectivity, diaphragm constraints and support points. The program automatically locates the element support points and evaluates the corresponding unsupported length.

Concrete Frame Design General Design Information

Analysis Sections and Design Sections Technical Note 1 - 7 Figure 2: Major and Minor Axes of Bending

It is possible for the unsupported length of a frame element to be evaluated by the program as greater than the corresponding element length. For exam- ple, assume a column has a beam framing into it in one direction, but not the other, at a floor level. In this case, the column is assumed to be supported in one direction only at that story level, and its unsupported length in the other direction will exceed the story height.

Analysis Sections and Design Sections

Analysis sections are those section properties used to analyze the model when you click the Analyze menu > Run Analysis command. The design section is whatever section has most currently been designed and thus desig- nated the current design section.

Tip:

It is important to understand the difference between analysis sections and design sec- tions.

General Design Information Concrete Frame Design

Technical Note 1 - 8 Analysis Sections and Design Sections It is possible for the last used analysis section and the current design section to be different. For example, you may have run your analysis using a W18X35 beam and then found in the design that a W16X31 beam worked. In that case, the last used analysis section is the W18X35 and the current design section is the W16X31. Before you complete the design process, verify that the last used analysis section and the current design section are the same.

The Design menu > Concrete Frame Design > Verify Analysis vs De- sign Section command is useful for this task.

The program keeps track of the analysis section and the design section separately. Note the following about analysis and design sections:

ƒ Assigning a beam a frame section property using the Assign menu >

Frame/Line > Frame Section command assigns the section as both the analysis section and the design section.

ƒ Running an analysis using the Analyze menu > Run Analysis command (or its associated toolbar button) always sets the analysis section to be the same as the current design section.

ƒ Assigning an auto select list to a frame section using the Assign menu >

Frame/Line > Frame Section command initially sets the design section to be the beam with the median weight in the auto select list.

ƒ Unlocking a model deletes the design results, but it does not delete or change the design section.

ƒ Using the Design menu > Concrete Frame Design > Select Design Combo command to change a design load combination deletes the design results, but it does not delete or change the design section.

ƒ Using the Define menu > Load Combinations command to change a de- sign load combination deletes the design results, but it does not delete or change the design section.

ƒ Using the Options menu > Preferences > Concrete Frame Design command to change any of the composite beam design preferences deletes the design results, but it does not delete or change the design section.

ƒ Deleting the static nonlinear analysis results also deletes the design results for any load combination that includes static nonlinear forces. Typically,

Concrete Frame Design General Design Information

Analysis Sections and Design Sections Technical Note 1 - 9 static nonlinear analysis and design results are deleted when one of the following actions is taken:

9 Use the Define menu > Frame Nonlinear Hinge Properties com- mand to redefine existing or define new hinges.

9 Use the Define menu > Static Nonlinear/Pushover Cases com- mand to redefine existing or define new static nonlinear load cases.

9 Use the Assign menu > Frame/Line > Frame Nonlinear Hinges command to add or delete hinges.

Again, note that these actions delete only results for load combinations that include static nonlinear forces.

Concrete Frame Design Procedure Technical Note 2 - 1

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Technical Note 2 Concrete Frame Design Process

This Technical Note describes a basic concrete frame design process using this program. Although the exact steps you follow may vary, the basic design process should be similar to that described herein. Other Technical Notes in the Concrete Frame Design series provide additional information, including the distinction between analysis sections and design sections (see Analysis Sections and Design Sections in Concrete Frame Design Technical Note 1 General Design Information).

The concrete frame design postprocessor can design or check concrete col- umns and can design concrete beams.

Important note: A concrete frame element is designed as a beam or a col- umn, depending on how its frame section property was designated when it was defined using the Define menu > Frame Sections command. Note that when using this command, after you have specified that a section has a con- crete material property, you can click on the Reinforcement button and specify whether it is a beam or a column.

Concrete Frame Design Procedure

The following sequence describes a typical concrete frame design process for a new building. Note that although the sequence of steps you follow may vary, the basic process probably will be essentially the same.

1. Use the Options menu > Preferences > Concrete Frame Design command to choose the concrete frame design code and to review other concrete frame design preferences and revise them if necessary. Note that default values are provided for all concrete frame design prefer- ences, so it is unnecessary to define any preferences unless you want to change some of the default values. See Concrete Frame Design ACI UBC97 Technical Notes 6 Preferences and Concrete Frame Design ACI 318-99 Technical Notes 16 Preferences for more information.

Concrete Frame Design Process Concrete Frame Design

Technical Note 2 - 2 Concrete Frame Design Procedure 2. Create the building model.

3. Run the building analysis using the Analyze menu > Run Analysis command.

4. Assign concrete frame overwrites, if needed, using the Design menu >

Concrete Frame Design > View/Revise Overwrites command. Note that you must select frame elements before using this command. Also note that default values are provided for all concrete frame design over- writes, so it is unnecessary to define any overwrites unless you want to change some of the default values. Note that the overwrites can be as- signed before or after the analysis is run. See Concrete Frame Design UBC97 Technical Note 7 Overwrites and Concrete Frame Design ACI 318-99 Technical Note 17 Overwrites for more information.

5. To use any design load combinations other than the defaults created by the program for your concrete frame design, click the Design menu >

Concrete Frame Design > Select Design Combo command. Note that you must have already created your own design combos by clicking the Define menu > Load Combinations command. See Concrete Frame Design UBC97 Technical Note 8 Design Load Combinations and Concrete Frame Design ACI 318-99 Technical Note 18 Design Load Combinations for more information.

6. Click the Design menu > Concrete Frame Design > Start De- sign/Check of Structure command to run the concrete frame design.

7. Review the concrete frame design results by doing one of the following:

a. Click the Design menu > Concrete Frame Design > Display De- sign Info command to display design input and output information on the model. See Concrete Frame Design Technical Note 4 Output Data Plotted Directly on the Model for more information.

b. Right click on a frame element while the design results are displayed on it to enter the interactive design mode and interactively design the frame element. Note that while you are in this mode, you can revise overwrites and immediately see the results of the new design. See Concrete Frame Design Technical Note 3 Interactive Concrete Frame Design for more information.

Concrete Frame Design Concrete Frame Design Process

Concrete Frame Design Procedure Technical Note 2 - 3 If design results are not currently displayed (and the design has been run), click the Design menu > Concrete Frame Design > Interac- tive Concrete Frame Design command and then right click a frame element to enter the interactive design mode for that element.

8. Use the File menu > Print Tables > Concrete Frame Design com- mand to print concrete frame design data. If you select frame elements before using this command, data is printed only for the selected ele- ments. See Concrete Frame Design UBC97 Technical Note 14 Output Details and Concrete Frame Design ACI 318-99 Technical Note 24 Out- put Details for more information.

9. Use the Design menu > Concrete Frame Design > Change Design Section command to change the design section properties for selected frame elements.

10. Click the Design menu > Concrete Frame Design > Start De- sign/Check of Structure command to rerun the concrete frame design with the new section properties. Review the results using the procedures described in Item 7.

11. Rerun the building analysis using the Analyze menu > Run Analysis command. Note that the section properties used for the analysis are the last specified design section properties.

12. Click the Design menu > Concrete Frame Design > Start De- sign/Check of Structure command to rerun the concrete frame design with the new analysis results and new section properties. Review the re- sults using the procedures described above.

13. Again use the Design menu > Concrete Frame Design > Change Design Section command to change the design section properties for selected frame elements, if necessary.

14. Repeat the processes in steps 10, 11 and 12 as many times as neces- sary.

15. Rerun the building analysis using the Analyze menu > Run Analysis command. Note that the section properties used for the analysis are the last specified design section properties.

Concrete Frame Design Process Concrete Frame Design

Technical Note 2 - 4 Concrete Frame Design Procedure Note:

Concrete frame design is an iterative process. Typically, the analysis and design will be rerun multiple times to complete a design.

16. Click the Design menu > Concrete Frame Design > Start De- sign/Check of Structure command to rerun the concrete frame design with the new section properties. Review the results using the procedures described in Item 7.

17. Click the Design menu > Concrete Frame Design > Verify Analysis vs Design Section command to verify that all of the final design sec- tions are the same as the last used analysis sections.

18. Use the File menu > Print Tables > Concrete Frame Design com- mand to print selected concrete frame design results, if desired.

It is important to note that design is an iterative process. The sections used in the original analysis are not typically the same as those obtained at the end of the design process. Always run the building analysis using the final frame section sizes and then run a design check using the forces obtained from that analysis. Use the Design menu > Concrete Frame Design > Verify Analysis vs Design Section command to verify that the design sections are the same as the analysis sections.

General Technical Note 3 - 1

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Technical Note 3

Interactive Concrete Frame Design

This Technical Note describes interactive concrete frame design and review, which is a powerful mode that allows the user to review the design results for any concrete frame design and interactively revise the design assumptions and immediately review the revised results.

General

Note that a design must have been run for the interactive design mode to be available. To run a design, click the Design menu > Concrete Frame De- sign > Start Design/Check of Structure command.

Right click on a frame element while the design results are displayed on it to enter the interactive design mode and interactively design the element in the Concrete Design Information form. If design results are not currently dis- played (and a design has been run), click the Design menu > Concrete Frame Design > Interactive Concrete Frame Design command and then right click a frame element to enter the interactive design mode for that ele- ment.

Important note: A concrete frame element is designed as a beam or a col- umn, depending on how its frame section property was designated when it was defined using the Define menu > Frame Sections command and the Reinforcement button, which is only available if it is a concrete section.

Concrete Design Information Form

Table 1 describe the features that are included in the Concrete Design Infor- mation form.

Interactive Concrete Frame Design Concrete Frame Design

Technical Note 3 - 2 Table 1 Concrete Design Information Form

Table 1 Concrete Design Information Form

Item DESCRIPTION

Story This is the story level ID associated with the frame element.

Beam This is the label associated with a frame element that has been assigned a concrete frame section property that is designated as a beam. See the important note previously in this Technical Note for more information.

Column This is the label associated with a frame element that has been assigned a concrete frame section property that is designated as a column. See the important note previously in this Techni- cal Note for more information.

Section Name This is the label associated with a frame element that has been assigned a concrete frame section property.

Reinforcement Information

The reinforcement information table on the Concrete Design Information form shows the output information obtained for each design load combination at each output station along the frame element. For columns that are designed by this program, the item with the largest required amount of longitudinal reinforcing is initially highlighted. For columns that are checked by this program, the item with the largest capacity ratio is initially high- lighted. For beams, the item with the largest required amount of bottom steel is initially highlighted. Following are the possible headings in the table:

Combo ID This is the name of the design load combination considered.

Station location This is the location of the station considered, measured from the i-end of the frame element.

Longitudinal reinforcement

This item applies to columns only. It also only applies to col- umns for which the program designs the longitudinal reinforc- ing. It is the total required area of longitudinal reinforcing steel.

Capacity ratio This item applies to columns only. It also only applies to col- umns for which you have specified the location and size of re- inforcing bars and thus the program checks the design. This item is the capacity ratio.

Concrete Frame Design Interactive Concrete Frame Design

Table 1 Concrete Design Information Form Technical Note 3 - 3

Table 1 Concrete Design Information Form

Item DESCRIPTION

The capacity ratio is determined by first extending a line from the origin of the PMM interaction surface to the point repre- senting the P, M2 and M3 values for the designated load com- bination. Assume the length of this first line is designated L1.

Next, a second line is extended from the origin of the PMM in- teraction surface through the point representing the P, M2 and M3 values for the designated load combination until it intersects the interaction surface. Assume the length of this line from the origin to the interaction surface is designated L2. The capacity ratio is equal to L1/L2.

Major shear reinforcement

This item applies to columns only. It is the total required area of shear reinforcing per unit length for shear acting in the column major direction.

Minor shear reinforcement

This item applies to columns only. It is the total required area of shear reinforcing per unit length for shear acting in the column minor direction.

Top steel This item applies to beams only. It is the total required area of longitudinal top steel at the specified station.

Bottom steel This item applies to beams only. It is the total required area of longitudinal bottom steel at the specified station.

Shear steel This item applies to beams only. It is the total required area of shear reinforcing per unit length at the specified station for loads acting in the local 2-axis direction of the beam.

Overwrites Button Click this button to access and make revisions to the concrete frame overwrites and then immediately see the new design re- sults. If you modify some overwrites in this mode and you exit both the Concrete Frame Design Overwrites form and the Con- crete Design Information form by clicking their respective OK buttons, the changes to the overwrites are saved permanently.

When you exit the Concrete Frame Design Overwrites form by clicking the OK button the changes are temporarily saved. If you then exit the Concrete Design Information form by clicking the Cancel button the changes you made to the concrete frame overwrites are considered temporary only and are not perma- nently saved. Permanent saving of the overwrites does not ac- tually occur until you click the OK button in the Concrete Design Information form as well as the Concrete Frame Design Over- writes form.

Interactive Concrete Frame Design Concrete Frame Design

Technical Note 3 - 4 Table 1 Concrete Design Information Form

Table 1 Concrete Design Information Form

Item DESCRIPTION

Details Button Clicking this button displays design details for the frame ele- ment. Print this information by selecting Print from the File menu that appears at the top of the window displaying the de- sign details.

Interaction Button Clicking this button displays the biaxial interaction curve for the concrete section at the location in the element that is high- lighted in the table.

Overview Technical Note 4 - 1

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Technical Note 4 Output Data Plotted Directly on the Model

This Technical Note describes the input and output data that can be plotted directly on the model.

Overview

Use the Design menu > Concrete Frame Design > Display Design Info command to display on-screen output plotted directly on the program model.

If desired, the screen graphics can then be printed using the File menu >

Print Graphics command. The on-screen display data presents input and output data.

Using the Print Design Tables Form

To print the concrete frame input summary directly to a printer, use the File menu > Print Tables > Concrete Frame Design command and click the check box on the Print Design Tables form. Click the OK button to send the print to your printer. Click the Cancel button rather than the OK button to cancel the print. Use the File menu > Print Setup command and the Setup>> button to change printers, if necessary.

To print the concrete frame input summary to a file, click the Print to File check box on the Print Design Tables form. Click the Filename>> button to change the path or filename. Use the appropriate file extension for the de- sired format (e.g., .txt, .xls, .doc). Click the OK buttons on the Open File for Printing Tables form and the Print Design Tables form to complete the re- quest.

Note:

The File menu > Display Input/Output Text Files command is useful for displaying out- put that is printed to a text file.

The Append check box allows you to add data to an existing file. The path and filename of the current file is displayed in the box near the bottom of the Print Design Tables form. Data will be added to this file. Or use the Filename

Output Data Plotted Directly on the Model Concrete Frame Design

Technical Note 4 - 2 Design Input

button to locate another file, and when the Open File for Printing Tables cau- tion box appears, click Yes to replace the existing file.

If you select a specific concrete frame element(s) before using the File menu

> Print Tables > concrete Frame Design command, the Selection Only check box will be checked. The print will be for the selected steel frame ele- ment(s) only.

Design Input

The following types of data can be displayed directly on the model by select- ing the data type (shown in bold type) from the drop-down list on the Display Design Results form. Display this form by selecting he Design menu > Con- crete Frame Design > Display Design Info command.

ƒ Design Sections

ƒ Design Type

ƒ Live Load Red Factors

ƒ Unbraced L_Ratios

ƒ Eff Length K-Factors

ƒ Cm Factors

ƒ DNS Factors

ƒ DS Factors

Each of these items is described in the code-specific Concrete Frame Design UBC97 Technical Note 13 Input Data and Concrete Frame Design ACI 318-99 Technical Note 23 Input Data.

Design Output

The following types of data can be displayed directly on the model by select- ing the data type (shown in bold type) from the drop-down list on the Display Design Results form. Display this form by selecting he Design menu > Con- crete Frame Design > Display Design Info command.

Concrete Frame Design Output Data Plotted Directly on the Model

Design Output Technical Note 4 - 3

ƒ Longitudinal Reinforcing

ƒ Shear Reinforcing

ƒ Column Capacity Ratios

ƒ Joint Shear Capacity Ratios

ƒ Beam/Column Capacity Ratios

Each of these items is described in the code-specific Concrete Frame Design ACI 318-99 Technical Note 24 Output Details and Concrete Frame Design UBC97 Technical Note 14 Output Details.

General and Notation Technical Note 5 - 1

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Technical Note 5

General and Notation Introduction to the UBC97 Series of Technical Notes

The Concrete Frame Design UBC97 series of Technical Notes describes in de- tail the various aspects of the concrete design procedure that is used by this program when the user selects the UBC97 Design Code (ICBO 1997). The various notations used in this series are listed herein.

The design is based on user-specified loading combinations. The program provides a set of default load combinations that should satisfy requirements for the design of most building type structures. See Concrete Frame Design UBC97 Technical Note 8 Design Load Combinations for more information.

When using the UBC 97 option, a frame is assigned to one of the following five Seismic Zones (UBC 2213, 2214):

ƒ Zone 0

ƒ Zone 1

ƒ Zone 2

ƒ Zone 3

ƒ Zone 4

By default the Seismic Zone is taken as Zone 4 in the program. However, the Seismic Zone can be overwritten in the Preference form to change the de- fault. See Concrete Frame Design UBC97 Technical Note 6 Preferences for more information.

When using the UBC 97 option, the following Framing Systems are recognized and designed according to the UBC design provisions (UBC 1627, 1921):

ƒ Ordinary Moment-Resisting Frame (OMF)

General and Notation Concrete Frame Design UBC97

Technical Note 5 - 2 General and Notation

ƒ Intermediate Moment-Resisting Frame (IMRF)

ƒ Special Moment-Resisting Frame (SMRF)

The Ordinary Moment-Resisting Frame (OMF) is appropriate in minimal seis- mic risk areas, especially in Seismic Zones 0 and 1. The Intermediate Mo- ment-Resisting Frame (IMRF) is appropriate in moderate seismic risk areas, specially in Seismic Zone 2. The Special Moment-Resisting Frame (SMRF) is appropriate in high seismic risk areas, specially in Seismic Zones 3 and 4. The UBC seismic design provisions are considered in the program. The details of the design criteria used for the different framing systems are described in Concrete Frame Design UBC97 Technical Note 9 Strength Reduction Factors, Concrete Frame Design UBC97 Technical Note 10 Column Design, Concrete Frame Design UBC97 Technical Note 11 Beam Design, and Concrete Frame Design UBC97 Technical Note 12 Joint Design.

By default the frame type is taken in the program as OMRF in Seismic Zone 0 and 1, as IMRF in Seismic Zone 2, and as SMRF in Seismic Zone 3 and 4.

However, the frame type can be overwritten in the Overwrites form on a member-by-member basis. See Concrete Frame Design UBC97 Technical Note 7 Overwrites for more information. If any member is assigned with a frame type, the change of the Seismic Zone in the Preferences will not modify the frame type of an individual member that has been assigned a frame type.

The program also provides input and output data summaries, which are de- scribed in Concrete Frame Design UBC97 Technical Note 13 Input Data and Concrete Frame Design UBC97 Technical Note 14 Output Details.

English as well as SI and MKS metric units can be used for input. The code is based on Inch-Pound-Second units. For simplicity, all equations and descrip- tions presented in this Technical Note correspond to Inch-Pound-Second units unless otherwise noted.

Notation

A_cv Area of concrete used to determine shear stress, sq-in A_g Gross area of concrete, sq-in

A_s Area of tension reinforcement, sq-in

Concrete Frame Design UBC97 General and Notation

General and Notation Technical Note 5 - 3

s'

A Area of compression reinforcement, sq-in

As(required) Area of steel required for tension reinforcement, sq-in A_st Total area of column longitudinal reinforcement, sq-in A_v Area of shear reinforcement, sq-in

C_m Coefficient, dependent upon column curvature, used to calculate moment magnification factor

D' Diameter of hoop, in

E_c Modulus of elasticity of concrete, psi

E_s Modulus of elasticity of reinforcement, assumed as 29,000,000 psi (UBC 1980.5.2)

I_g Moment of inertia of gross concrete section about centroidal axis, neglecting reinforcement, in⁴

I_se Moment of inertia of reinforcement about centroidal axis of mem- ber cross section, in⁴

L Clear unsupported length, in

M₁ Smaller factored end moment in a column, lb-in M₂ Larger factored end moment in a column, lb-in M_c Factored moment to be used in design, lb-in

M_ns Nonsway component of factored end moment, lb-in M_s Sway component of factored end moment, lb-in M_u Factored moment at section, lb-in

M_ux Factored moment at section about X-axis, lb-in M_uy Factored moment at section about Y-axis, lb-in P_b Axial load capacity at balanced strain conditions, lb

General and Notation Concrete Frame Design UBC97

Technical Note 5 - 4 General and Notation

P_c Critical buckling strength of column, lb P_max Maximum axial load strength allowed, lb P₀ Acial load capacity at zero eccentricity, lb P_u Factored axial load at section, lb

V_c Shear resisted by concrete, lb

V_E Shear force caused by earthquake loads, lb V_D+L Shear force from span loading, lb

V_u Factored shear force at a section, lb

V_p Shear force computed from probable moment capacity, lb a Depth of compression block, in

a_b Depth of compression block at balanced condition, in b Width of member, in

b_f Effective width of flange (T-Beam section), in b_w Width of web (T-Beam section), in

c Depth to neutral axis, in

c_b Depth to neutral axis at balanced conditions, in

d Distance from compression face to tension reinforcement, in d' Concrete cover to center of reinforcing, in

d_s Thickness of slab (T-Beam section), in

c'

f Specified compressive strength of concrete, psi f_y Specified yield strength of flexural reinforcement, psi

fy ≤ 80,000 psi (UBC 1909.4)

Concrete Frame Design UBC97 General and Notation

General and Notation Technical Note 5 - 5

f_ys Specified yield strength of flexural reinforcement, psi h Dimension of column, in

k Effective length factor

r Radius of gyration of column section, in α Reinforcing steel overstrength factor

β1 Factor for obtaining depth of compression block in concrete

βd Absolute value of ratio of maximum factored axial dead load to maximum factored axial total load

δs Moment magnification factor for sway moments δns Moment magnification factor for nonsway moments εc Strain in concrete

εs Strain in reinforcing steel ϕ Strength reduction factor

General Technical Note 6 - 1

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Technical Note 6 Preferences

This Technical Note describes the items in the Preferences form.

General

The concrete frame design preferences in this program are basic assignments that apply to all concrete frame elements. Use the Options menu > Prefer- ences > Concrete Frame Design command to access the Preferences form where you can view and revise the concrete frame design preferences.

Default values are provided for all concrete frame design preference items.

Thus, it is not required that you specify or change any of the preferences. You should, however, at least review the default values for the preference items to make sure they are acceptable to you.

Using the Preferences Form

To view preferences, select the Options menu > Preferences > Concrete Frame Design. The Preferences form will display. The preference options are displayed in a two-column spreadsheet. The left column of the spread- sheet displays the preference item name. The right column of the spreadsheet displays the preference item value.

To change a preference item, left click the desired preference item in either the left or right column of the spreadsheet. This activates a drop-down box or highlights the current preference value. If the drop-down box appears, select a new value. If the cell is highlighted, type in the desired value. The prefer- ence value will update accordingly. You cannot overwrite values in the drop- down boxes.

When you have finished making changes to the concrete frame preferences, click the OK button to close the form. You must click the OK button for the changes to be accepted by the program. If you click the Cancel button to exit

Preferences Concrete Frame Design UBC97

Technical Note 6 - 2 Preferences

the form, any changes made to the preferences are ignored and the form is closed.

Preferences

For purposes of explanation in this Technical Note, the preference items are presented in Table 1. The column headings in the table are described as fol- lows:

ƒ Item: The name of the preference item as it appears in the cells at the left side of the Preferences form.

ƒ Possible Values: The possible values that the associated preference item can have.

ƒ Default Value: The built-in default value that the program assumes for the associated preference item.

ƒ Description: A description of the associated preference item.

Table 1: Concrete Frame Preferences

Item

Possible Values

Default

Value Description

Design Code Any code in the program

UBC97 Design code used for design of concrete frame elements.

Phi Bending Tension

>0 0.9 Unitless strength reduction factor per UBC 1909.

Phi Compres- sion Tied

>0 0.7 Unitless strength reduction factor per UBC 1909.

Phi Compres- sion Spiral

>0 0.75 Unitless strength reduction factor per UBC 1909.

Phi Shear >0 0.85 Unitless strength reduction factor per UBC 1909.

Number Inter- action Curves

≥4.0 24 Number of equally spaced interaction curves used to create a full 360-degree interaction surface (this item should be a multiple of four). We recommend that you use 24 for this item.

Concrete Frame Design UBC97 Preferences

Preferences Technical Note 6 - 3

Table 1: Concrete Frame Preferences

Item

Possible Values

Default

Value Description

Number Inter- action Points

Any odd value

≥1.0

11 Number of points used for defining a single curve in a concrete frame interaction surface (this item should be odd).

Time History Design

Envelopes or Step-by-Step

Envelopes Toggle for design load combinations that include a time history designed for the envelope of the time history, or designed step-by-step for the entire time history. If a single design load combination has more than one time history case in it, that design load combination is designed for the envelopes of the time histories, regardless of what is specified here.

Overwrites Technical Note 7 - 1

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Technical Note 7

Overwrites General

The concrete frame design overwrites are basic assignments that apply only to those elements to which they are assigned. This Technical Note describes concrete frame design overwrites for UBC97. To access the overwrites, select an element and click the Design menu > Concrete Frame Design >

View/Revise Overwrites command.

Default values are provided for all overwrite items. Thus, you do not need to specify or change any of the overwrites. However, at least review the default values for the overwrite items to make sure they are acceptable. When changes are made to overwrite items, the program applies the changes only to the elements to which they are specifically assigned; that is, to the ele- ments that are selected when the overwrites are changed.

Overwrites

For explanation purposes in this Technical Note, the overwrites are presented in Table 1. The column headings in the table are described as follows.

ƒ Item: The name of the overwrite item as it appears in the program. To save space in the formes, these names are generally short.

ƒ Possible Values: The possible values that the associated overwrite item can have.

ƒ Default Value: The default value that the program assumes for the asso- ciated overwrite item.

ƒ Description: A description of the associated overwrite item.

An explanation of how to change an overwrite is provided at the end of this Technical Note.

Overwrites Concrete Frame Design UBC97

Technical Note 7 - 2 Overwrites

Table 1 Concrete Frame Design Overwrites

Item

Possible Values

Default

Value Description

Element Section

Element Type

Sway Special, Sway Interme-

diate, Sway Ordinary NonSway

Sway Special Frame type; see UBC 1910.11 to 1910.13.

Live Load Reduction Factor

>0

≤1.0

1. Used to reduce the live load contribu- tion to the factored loading.

Horizontal Earthquake

Factor

>0

≤1.0

1.

Unbraced Length Ratio

(Major)

>0

≤1.0

1.0

Unbraced Length Ratio

(Minor)

>0

≤1.0

1.0

Effective Length Factor

(K Major)

>0

≤1.0

1 See UBC 1910.12.1.

Effective Length Factor

(K Minor)

>0

≤1.0

1 See UBC 1910.12.1.

Moment Coefficient (Cm Major)

>0

≤1.0

1 See UBC 1910.12.3.1 relates actual moment diagram to an equivalent uni- form moment diagram.

Moment Coefficient (Cm Minor)

>0

≤1.0

1 See UBC 1910.12.3.1 relates actual moment diagram to an equivalent uni- form moment diagram.

NonSway Moment Factor

(Dns Major)

>0

≤1.0

1 See UBC 1910.12.

Concrete Frame Design UBC97 Overwrites

Overwrites Technical Note 7 - 3

Table 1 Concrete Frame Design Overwrites

Item

Possible Values

Default

Value Description

NonSway Moment Factor

(Dns Minor)

1 See UBC 1910.12.

Sway Moment Factor (Ds Major)

1 See UBC 1910.12.

Sway Moment Factor (Ds Minor)

1 See UBC 1910.12.

Making Changes in the Overwrites Form

To access the concrete frame overwrites, select an element and click the De- sign menu > Concrete Frame Design > View/Revise Overwrites com- mand.

The overwrites are displayed in the form with a column of check boxes and a two-column spreadsheet. The left column of the spreadsheet contains the name of the overwrite item. The right column of the spreadsheet contains the overwrites values.

Initially, the check boxes in the Concrete Frame Design Overwrites form are all unchecked and all of the cells in the spreadsheet have a gray background to indicate that they are inactive and the items in the cells cannot be changed. The names of the overwrite items are displayed in the first column of the spreadsheet. The values of the overwrite items are visible in the second column of the spreadsheet if only one element was selected before the over- writes form was accessed. If multiple elements were selected, no values show for the overwrite items in the second column of the spreadsheet.

After selecting one or multiple elements, check the box to the left of an over- write item to change it. Then left click in either column of the spreadsheet to activate a drop-down box or highlight the contents in the cell in the right col- umn of the spreadsheet. If the drop-down box appears, select a value from

Overwrites Concrete Frame Design UBC97

Technical Note 7 - 4 Overwrites

the box. If the cell contents is highlighted, type in the desired value. The overwrite will reflect the change. You cannot change the values of the drop- down boxes.

When changes to the overwrites have been completed, click the OK button to close the form. The program then changes all of the overwrite items whose associated check boxes are checked for the selected members. You must click the OK button for the changes to be accepted by the program. If you click the Cancel button to exit the form, any changes made to the overwrites are ig- nored and the form is closed.

Resetting Concrete Frame Overwrites to Default Values

Use the Design menu > Concrete Frame Design > Reset All Overwrites command to reset all of the steel frame overwrites. All current design results will be deleted when this command is executed.

Important note about resetting overwrites: The program defaults for the overwrite items are built into the program. The concrete frame overwrite val- ues that were in a .edb file that you used to initialize your model may be dif- ferent from the built-in program default values. When you reset overwrites, the program resets the overwrite values to its built-in values, not to the val- ues that were in the .edb file used to initialize the model.

Design Load Combinations Technical Note 8 - 1

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Technical Note 8

Design Load Combinations

The design load combinations are the various combinations of the prescribed load cases for which the structure needs to be checked. For the UBC 97 code, if a structure is subjected to dead load (DL) and live load (LL) only, the stress check may need only one load combination, namely 1.4 DL + 1.7 LL (UBC 1909.2.1). However, in addition to the dead and live loads, if the structure is subjected to wind (WL) and earthquake (EL) loads, and considering that wind and earthquake forces are reversible, the following load combinations may need to be considered (UBC 1909.2).

1.4 DL (UBC 1909.2.1)

1.4 DL + 1.7 LL (UBC 1909.2.1)

0.9 DL ± 1.3 WL (UBC 1909.2.2)

0.75 (1.4 DL + 1.7 LL ± 1.7 WL) (UBC 1909.2.2)

0.9 DL ± 1.0 EL (UBC 1909.2.3, 1612.2.1)

1.2 DL + 0.5 LL ± 1.0 EL) (UBC 1909.2.3, 1612.2.1)

These are also the default design load combinations in the program whenever the UBC97 code is used.

Live load reduction factors can be applied to the member forces of the live load condition on an element-by-element basis to reduce the contribution of the live load to the factored loading. See Concrete Frame Design UBC97 Technical Note 7 Overwrites for more information.

Strength Reduction Factors Technical Note 9 - 1

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Technical Note 9

Strength Reduction Factors

The strength reduction factors, ϕ, are applied on the nominal strength to ob- tain the design strength provided by a member. The ϕ factors for flexure, ax- ial force, shear, and torsion are as follows:

ϕ = 0.90 for flexure (UBC 1909.3.2.1)

ϕ = 0.90 for axial tension (UBC 1909.3.2.2)

ϕ = 0.90 for axial tension and flexure (UBC 1909.3.2.2) ϕ = 0.75 for axial compression, and axial compression

and flexure (spirally reinforced column) (UBC 1909.3.2.2) ϕ = 0.70 for axial compression, and axial compression

and flexure (tied column) (UBC 1909.3.2.2) ϕ = 0.85 for shear and torsion (non-seismic design) (UBC 1909.3.2.3)

ϕ = 0.60 for shear and torsion (UBC 1909.3.2.3)

Overview Technical Note 10 - 1

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Technical Note 10

Column Design

This Technical Note describes how the program checks column capacity or de- signs reinforced concrete columns when the UBC97 code is selected.

Overview

The program can be used to check column capacity or to design columns. If you define the geometry of the reinforcing bar configuration of each concrete column section, the program will check the column capacity. Alternatively, the program can calculate the amount of reinforcing required to design the col- umn. The design procedure for the reinforced concrete columns of the struc- ture involves the following steps:

ƒ Generate axial force/biaxial moment interaction surfaces for all of the dif- ferent concrete section types of the model. A typical biaxial interaction surface is shown in Figure 1. When the steel is undefined, the program generates the interaction surfaces for the range of allowable reinforce- ment1 to 8 percent for Ordinary and Intermediate moment resisting frames (UBC 1910.9.1) and 1 to 6 percent for Special moment resisting frames (UBC 1921.4.3.1).

ƒ Calculate the capacity ratio or the required reinforcing area for the fac- tored axial force and biaxial (or uniaxial) bending moments obtained from each loading combination at each station of the column. The target capac- ity ratio is taken as 1 when calculating the required reinforcing area.

ƒ Design the column shear reinforcement.

The following four subsections describe in detail the algorithms associated with this process.

Column Design Concrete Frame Design UBC97

Technical Note 10 - 2 Generation of Biaxial Interaction Surfaces Figure 1 A Typical Column Interaction Surface

Generation of Biaxial Interaction Surfaces

The column capacity interaction volume is numerically described by a series of discrete points that are generated on the three-dimensional interaction failure surface. In addition to axial compression and biaxial bending, the for- mulation allows for axial tension and biaxial bending considerations. A typical interaction diagram is shown in Figure 1.