In ETABS, shell or area element has two types of stiffnesses i.e. inplane stiffness refers as f11, f22 and f12 and out-of-plane stiffness refers as m11, m22 and m12. Refer to the below Figure which shows the direction of local axes and their corresponding stiffnesses:
Crack width is a complex and tough topic. Most people still use 20 years old method defined in ACI 318-95. The situation becomes more complex if axial tension force and moment is combined to calculate crack width. Order information: ACI documents are available in print, by download, on CD-ROM, through electronic subscription, or reprint and may be obtained by contacting ACI. Most ACI standards and committee reports are gathered together in the annually revised ACI Manual of Concrete Practice (MCP). American Concrete Institute 38800 Country Club Drive. Calculate the required reinforcement to resist the interior support negative moment: Mu t Use #8 bars with 1.5 in. Concrete cover per ACI 318-14 (Table 20.6.1.3.1). The distance from extreme compression fiber to the centroid of longitudinal tension reinforcement, d, is calculated below: 8. FOR WATER TIGHT STRUCTURES Crack width is a complex and tough topic. Most people still use 20 years old method defined in ACI 318-95. The situation becomes more complex if axial tension force and moment is combined to calculate crack width. One of the examples is large water tanks above ground. This tutorial aims at.
Crack width calculation methods in large concrete structures” carried out by Reignard Tan. The seminar is to be hosted by NTNU and Multiconsult ASA in a joint collaboration. The main goal is to increase the understanding and knowledge of crack width calculations for relatively large concrete structures in the Serviceability Limit State. W= crack-opening width, in. (mm) ∆w= change in crack-opening width, in. (mm) ∆ 10%= displacement measured at 10% of ultimate load in tension test, lb (N) ∆ 30%= displacement measured at 30% of ultimate load in tension test, lb (N) β = axial stiffness of anchor in service load range, lb/in. 6) Check transfer of load from column to footing: ACI 16.3 a) Find load transferred by bearing on concrete in column: ACI 22.8 basic: P n 0.85f c A 1 where = 0.65 and A 1 is the area of the column with confinement: 1 2 0.85 1 A A P n f c A where 1 2 A A cannot exceed 2. IF the column concrete strength is lower than the footing, calculate P n.
For shear wall (both piers and spandrels), the flexural and axial behavior is modified by either f11 or f22 depending on the orientation of the local axis and the shear behavior is controlled by f12. In column and code terms f11 or f22 would correspond to modifications of EI or EA and f12 would correspond to modifications to GAshear. The code recommendations in Section 10.10 of ACI 318 code are related to slenderness effects where flexural deformations govern so they have recommended modifying EI (corresponding to f11 or f22 for shear walls). There is no recommendation about reducing the GAshear. You should, however, note that some of our users use modifiers for f12 also, where they expect deterioration of shear stiffness and want to be realistic in their modeling.
The above discussion applies assuming the local axes 1 and 2 of the shear wall area object are either vertical or horizontal. This is under user control. When drawing in ETABS the default is to have the 1 axis horizontal and the 2 axis vertical. This means that the flexural modifier for EI should be applied to f22 for wall piers and to f11 for spandrels. If you apply the modifier to both f11 and f22 it hardly affects the results.
For slabs where bending is always in the out-of-plane direction, modifiers m11, m22 and m12 are required to model cracking behavior.
Summary
Assuming beams and columns are modeled as frame then the stiffness modifier table is as follows:
ACI ETABS
Beams........................................0.35*Ig I22 = I33 = 0.35
Columns....................................0.70*Ig I22 = I33 = 0.70
Walls-Uncracked.................0.70*Ig modeled as shell – f11, f22 = 0.70
Walls-Cracked......................0.35*Ig similar to Walls-Uncracked (with modifiers of 0.35)
NOTE:
Walls are generally not designed for out-of-plane bending to avoid excessive longitudinal reinforcement. In this case, use a small modifier say 0.1 for m11, m22 and m12 so numerical instabilities could be avoided. However, use m11, m22, m12 = 0.70 (or 0.35) when considering the out-of-plane bending in wall.
Flat Plates & Flat Slabs....0.25*Ig modeled as membrane – f11, f22, f12 = 0.25 / modeled as shell – f11, f22, f12, m11, m22, m12 = 0.25 (for both cases fxx is not important if rigid diaphragm is assigned)
Concrete Member - Design
- The 2019, 2014, 2011, 2008, 2005, 2002 and 1999 Editions of ACI 318
- The 1997 Edition of the British code (BS 8110)
- The 1992 EuroCode (EC2) and the British publication of the 2014 and 2004 Eurocode (BSEN)
- The 1994 and 2004 Editions of the Canadian code (CSA A23.3)
- The 2000 Edition of the Indian code (IS 456)
- The 2001 Edition of the Australian code (AS 3600)
- The 1995 Edition of the New Zealand code (NZS 3101)
- The 2004 Edition of the Mexican code (NTC-DF)
- The 2007 Edition of the Saudi Building Code (SBC 304)
Note:
- Unless otherwise specified, all code references below are to ACI 318-14.
- Beams and Columns designed in RISA meet all of the requirements for Ordinary Moment Frames except for the additional requirements indicated in ACI 318-14 Section 18.3. Those provisions should be checked by hand outside of RISA.
The program will design the longitudinal and shear reinforcement for rectangular beams
Concrete Parameters (General):
ACI 318 Design Parameters:
British Eurocode Design Parameters
Known Limitations:
To Apply a Concrete Design Code
- On the Code tab of Model Settings Dialog, select the concrete code from the drop down list.
- Click Apply or OK.
Concrete Spans
Beam member
Column member
Note
- The quickest way to create new joints at beam / column intersections is to run a Model Merge.
- The program's ability to recognize spans is important because it will give you more relevant span to span information without overwhelming you with independent design results for each finite element segment that comprises your physical member.
- For continuous beam members, the program will evaluate the framing to determine which beams elements are supporting other beam elements so that only supporting members are treated as supports and not vice versa.
- Currently, members of type HBrace, VBrace, and None do not affect the span distances. Nor do any arbitrary joints within each span along a member.
Concrete Design Parameters - Columns
The Concrete
The following parameters can be defined for each concrete column.
Label
Shape
The member Shape or Section Set is reported in the second column. This value is listed for reference only and may not be edited as it is dictated by the entry in the Section/Shape column on the Primary tab.
Length
The member Length is reported in the third column. This value may not be edited as it is dependent on the member end coordinates listed on the Primary Data tab. It is listed here as a reference for unbraced lengths which are discussed in the next section.
Unbraced Length
You may specify unbraced lengths or have RISA-3D calculate them for you. The unbraced lengths are Lu-yy and Lu-zz.
The Lu values, Lu-yy and Lu-zz, represent the unbraced length of column members with respect to column type buckling about the member's local y and z axes, respectively. These Lu values are used to check the column for Euler buckling, and for the Moment Magnification Procedure in older editions of the ACI code.
If left blank these unbraced lengths all default to the member's full length.
For physical members, you can enter the code “Segment” in the unbraced length fields and the length of each segment will be used. A “segment” is the distance between the joints that are on the physical member. For example, suppose you have a physical member that is 20 feet in length, and there are two joints along the physical member, one 5 feet from the end and one at 15 feet. An unbraced length of 5 feet will be used for the first segment, then a value of 10 feet will be used in the middle segment, and again a value of 5 feet would be used in the last segment.
Note
- When the 'segment' code is used, ALL joints on a column will be considered to brace the column for that type of buckling, even if a joint is associated with a member that would actually only brace the column against buckling in the other local axis. Therefore, the 'segment' code should only be used for columns that are truly braced in that direction at each interior joint.
- The calculated unbraced lengths are listed on the Member Detail report.
For additional advice on this topic, please see the RISA Tips & Tricks website: www.risa.com/post/support. Type in Search keywords: Unbraced Lengths.
K Factors (Effective Length Factors)
The K Factors are also referred to as effective length factors. Kyy is for column type buckling about the member's local y-y axis and Kzz is for buckling about the local z-z axis.
If a value is entered for a K Factor, that value will be used for
RISA-3D is able to approximate the K-values for a column based on the member's sway condition and end release configuration. The K-factor approximation is based on the idealized tables given in the AISC steel specification. The following table gives the values used for various conditions.
| Table Case | End Conditions | Sidesway? | K-Value |
|---|---|---|---|
(a) | Fixed-Fixed | No | .65 |
(b) | Fixed-Pinned | No | .80 |
(c) | Fixed-Fixed | Yes | 1.2 |
(d) | Pinned-Pinned | No | 1.0 |
(e) | Fixed-Free | Yes | 2.1 |
(f) | Pinned-Fixed | Yes | 2.0 |
Note
- This is an approximation of K-values and is NOT based on the Jackson and Moreland Alignment Charts presented in ACI 318-14 Section R6.2.5.
RISA-3D will recognize a pinned boundary condition for the K approximation for a full pin, i.e. if all the rotations in the boundary condition are released. If any of the rotations in a boundary condition are restrained, the boundary condition is considered “fixed” for the K approximation.
Any configuration not described here will be given the default value of 1.0.
If any value that influences these K values is changed, the K approximation should be redone. For instance, if you have RISA-3D approximate K-values then change some end release designations, you should redo the K approximations.
Remember that the K-values are approximations, and you should check to make sure you agree with all K-values RISA-3D assigns. You can always override a K-value after an approximation by directly entering the value that you want in the appropriate field. Keep in mind that a subsequent approximation will overwrite any manually input values so you will need to override the approximation each time it is performed.
Limitation:
RISA-3D will currently neglect the influence of adjoining framing members when those members are connected at a joint that also has degrees of freedom restrained by boundary conditions. For example, suppose a column and beam member connect at a joint that is restrained for translation in all directions (I.e. the joint is “pinned”). The K factor approximation will neglect the beam member when it calculates the K factor for the column and vice versa. The effect will be that the ends of the members at that joint will be seen as “pinned” and not “fixed” for the K-factor approximation.
Sway Flags
The Sway Flags indicate whether the member is to be considered subject to sidesway for bending about its local y and z axes. The y sway field is for y-y axis bending and the z sway field is for z-z axis bending. Click on the field to check the box and indicate that the member is subject to sway for that particular direction, or leave the entry blank if the member is braced against sway. These sway flags influence the calculation of the K Factors as well as the Cm.
Cm – Equivalent Moment Correction Factor
The Cm Coefficients are used to check the column for Euler buckling, and for the Moment Magnification Procedure in older editions of the ACI code. Cm-yy is for bending about the columns's local y-y axis and Cm-zz is for bending about the local z-z axis. If these entries are left blank they will be automatically calculated.
In the ACI design code, the Cm values are only applicable for non-sway frames. Therefore, this value will be ignored if the corresponding sway flag is checked.
Flexural and Shear Rebar Layout
The user may choose to manually create the reinforcement layout for the column. This must be done if the user wishes to take advantage of bundled bars, multiple layers of reinforcement, or an unequal number of bars per face. See the section on the Concrete Database and Rebar Layouts for more information. If 'Default' is specified, then the program will design for an equal number of bars in each face of the rectangular column and may vary that reinforcing based on ACI minimums, maximums and the moment and shear demand at each section along the span.
Icr Factors (Cracked Moment of Inertia Factors)
The Icr Factor is used to reduce the bending stiffness of concrete columns per ACI 318-14 Table 6.6.3.1.1(a) (ACI 318-11 Section 10.10.4.1). If this entry is left blank, default values of 0.35 for beams and 0.70 for columns will be used.
Note
- The Icr Factor will be ignored if the “Use Cracked Sections” box is not checked on the Concrete tab of the Model Settings dialog.
- The alternative calculations in ACI 318-14 Table 6.6.3.1.1(b) (ACI 318-11 Equations 10-8 and 10-9) are not considered.
- The sustained load reduction of ACI 318-14 Section 6.6.3.1.1 (ACI 318-11 Section 10.10.4.2) is not considered.
Service Level Stiffness
Due to cracking and material non-linearity, modeling the stiffness of concrete members is more complex than it is for steel or wood members.
For typical applications, ACI 318-14 Section 6.6.3.1 (ACI 318-11 Section 10.10.4) requires that member stiffness be reduced to account for the cracking that occurs when a member is subjected to ultimate level loads. As described in the previous section, RISA uses the Icr Factor to account for this stiffness reduction. However, for service level analysis, the level of cracking will be significantly less. Therefore, the stiffness used in your analysis should be representative of the reduced loading and reduced cracking. Per the ACI 318-14 Section R6.6.3.2.2 (ACI 318-11 Section R10.10.4.1), the program will account for this increased stiffness by applying a factor of 1.43 to the cracked section properties for any load combination that has the “Service Load” flag checked on the Design tab of the Load Combinations Spreadsheet.
Note
Concrete Design Parameters - Beams
The Concrete Beam tab on the Members Spreadsheet records the design parameters for the code checks of concrete beams. These parameters may also be assigned graphically. See Modifying Member Design Parameters to learn how to do this.
The following parameters can be defined for each concrete member.
Label
You may assign a unique Label to all of the members. Each label must be unique, so if you try to enter the same label more than once you will get an error message.
Shape
The member Shape or Section Set is reported in the second column. This value is listed for reference only and may not be edited as it is dictated by the entry in the Section/Shape column on the Primary tab.
Length
The
Flexural and Shear Rebar Layout
The user may choose to manually create the reinforcement layout for the beam. This must be done if the user wishes to take advantage of compression steel, or multiple layers of reinforcement. See Concrete Database - Rebar Layouts for more information. If Use Design Rule is specified, then the program will design for one layer of reinforcing and may vary that reinforcing based on ACI minimums, maximums, and the moment and shear demand at each section along the span using the Member Design Rules as the parameters of the reinforcement selection. If you define your own rebar layout, and compression reinforcement is defined, then the program will consider the compression reinforcement in the analysis.
Icr Factors (Cracked Moment of Inertia Factors)
The Icr Factor is used to reduce the bending stiffness of concrete beams.
For ACI and Canadian codes (ACI 318-14 Section 6.6.3.1 and A23.3-04 section 9.2.1.2), if this entry is left blank, the Icr factor will default to a value of 0.35 for beams and 0.70 for columns.
For Australian and New Zealand codes (per section 6.6.2 of AS3600-2001), this will default to a value of 0.4 for beams and 0.8 for columns.
For Indian and Saudi codes, this entry will default to a value of 1.0 for beams and columns.
Note
- The Icr Factor will be ignored if the “Use Cracked Stiffness” box is not checked on the Concrete tab of the Model Settings dialog.
Service Level Stiffness
Due to cracking and material non-linearity, modeling the stiffness of concrete members is more complex than it is for steel or wood members.
For typical applications, ACI 318-14 Section 6.6.3.1 (ACI 318-11 Section 10.10.4) requires that member stiffness be reduced to account for the cracking that occurs when a member is subjected to ultimate level loads. As described in the previous section, RISA uses the Icr Factor to account for this stiffness reduction. However, for service level analysis, the level of cracking will be significantly less. Therefore, the stiffness used in your analysis should be representative of the reduced loading and reduced cracking. Per ACI 318-14 Section R6.6.3.1.1 (ACI 318-11 Section R10.10.4.1), the program will account for this increased stiffness by applying a factor of 1.43 to the cracked section properties for any load combination that has the “Service Load” flag checked on the Design tab of the Load Combinations Spreadsheet.
Note
T-beam & L-beam Sections
T-beams and L-beams may be specified by assigning effective slab widths and slab thicknesses for the left and right side of the beam on the Concrete Beam tab of the Members Spreadsheet. These modifications may also be made graphically via the Modify Properties tab of the Draw Members tool.
RISA-3D will automatically trim the effective slab widths, B-eff Left and B-eff Right, to the maximum values indicated in ACI 318-14 Table 6.3.2.1 (ACI 318-11 Sections 8.12.2(a) and 8.12.3(a) & (b)) if the value entered by the user is greater than that allowed by the code. It should be noted that RISA-3D does not check ACI 318-14 Table 6.3.2.1 portions referring to adjacent framing (ACI 318-11 Sections 8.12.2(b) and 8.12.3(c)) because no adjacent framing checks are performed.
If the values of either B-eff Left or B-eff Right are left blank, a value of zero will be assumed, indicating no additional slab width beyond 1/2 the beam width on that side.
Note:
- B-eff Right corresponds to the positive local z-axis of the beam. Subsequently, B-eff Left corresponds to the negative local z-axis.
Parabolic vs. Rectangular Stress Blocks
You can specify whether you want your concrete design to be performed with a rectangular stress block, or with a more accurate parabolic stress block. While most hand calculations are performed using a rectangular stress block, the parabolic stress block is more accurate. In fact, most of the PCA design aids are based upon the parabolic stress distribution. A good reference on the parabolic stress block is the PCA Notes on ACI 318-99.
Biaxial Bending of Columns
You can specify whether you want your column design to be performed by using Exact Integration, or by using the PCA Load Contour Method. While most hand calculations are performed using the Load Contour Method, this method is merely an approximation based on the uniaxial failure conditions and the Parme Beta factor. In contrast, the Exact Integration method uses the true biaxial strain state to design the member. A good reference on the Load Contour Method is chapter 12 of the PCA Notes on ACI 318-99.
British Eurocode Design Parameters (BS EN 1992-1-1: 2004)
General
- f’ck – Can not be more than 50 MPa (7252 psi) for normal strength concrete
- αcc is assumed to be 1 (recommended value) : See 3.1.6
- Effective length of T and L: Lo=.7*span length and beff,i =Lo/10
- φconcrete = 1.5
- φrebar = 1.15
- Maximum bar spacing for beams = 300 mm
Tension Development Length
αct= 1 (assumed in Eq 3.16)
η1= η2=1 (assumed in Eq 8.2 to calculate bond stress)
λ3, λ5, λ4=1 (assumed in Eq 8.4)
Cd in Table 8.2 assumed to be 1 bar diameter rebar spacing
Development length when hooks are provided uses same assumptions as BS 8110-1: 1997
Shear Capacity of Concrete
To compute the shear capacity of concrete the following recommended values are being used:
CRd,c =0.18/γc for Eq 6.2.a
vmin =0.035 k3/2 fck1/2
ν =.6*[1- fck /250]
Vmax is calculated from Eq. 6.5.
θ is assumed 45 degrees in Eq 6.8.
Slender Column Design
Biaxial column design done using Eq. 5.39
- Design based on nominal curvature
λlim = 20 A B C/n1/2 (A=.7, B= 1.1, C=0.7 for unbraced)
Kϕ =1 in Eq 5.34; the effect of creep is neglected.
Limitations - General
Torsion – Beams
Crack Width Calculation As Per Aci 318 14 Free
Creep / Long Term Deflections – No considerations are taken in the analysis to account for the effects of creep or long term deflections.
Beam Design – Beams are not designed for weak axis y-y bending, weak axis shear, or axial forces. A message is shown in the detail report to remind you of this.
Column Design – Columns with biaxial moment and no axial load will currently be designed using the PCA Load Contour Method even if Exact Integration is selected on the Model Settings dialog. This is shown on the detail report.
Limitations - ACI
Shear Design –When ACI 318-19 is selected, the shear strength of concrete (Vc) uses equations in Table 22.5.5.1. Note that for members meeting the minimum shear reinforcement requirement (Av≥Av,min), Vc is taken as the larger of the results calculated by the equations (a) and (b) in the table. ACI 318-19 code suggests ρw may be taken as the sum of the areas of longitudinal bars located more than two-thirds of the overall member depth away from the extreme compression fiber. Therefore, RISA calculates ρw as the sum of the areas of longitudinal bars on the tension face.
When other ACI 318 editions are selected, the shear strength of the concrete alone is limited to the standard 2*λ*sqrt (f'c) equation from ACI 318-14 Section 22.5.5.1 (ACI 318-11 Section 11.2.1.1) and does not use the more detailed calculations of ACI 318-14 Table 22.5.5.1 (ACI 318-11 Section 11.2.2). Also, note that for members with significant axial tension (greater than 0) the program designs the shear reinforcement to carry the total shear per ACI 318-14 Section R22.5.7.1 (ACI 318-11 Section 11.2.1.3).
Deep Beam Design – The program does not design deep beams as defined in ACI 318-14 Section 9.9.1.1(a) (ACI 318-11 Section 10.7).
Limitations - Canadian Code
Concrete Stress Profile – Concrete stress strain curve (parabolic) is assumed same as PCA method for the Canadian codes.
Bi-Axial Bending - The program uses the simplified uniaxial solution provided in the Canadian specification rather than performing a complete biaxial condition.
Mid-Depth Flexural Strain for Shear Design - The program uses the code equation (per the General Method) to calculate exwith the moment and shear at the section taken from the envelope diagrams. The maximum ex for each span is conservatively assumed for the entire span. Currently the program has no option for pre-stressing, so Vp and Ap are both taken as zero.
Shear Design - The shear strength of concrete is calculated using β and θ, which are both calculated per the General Method (Clause 11.3.6.4 from the 2004 CSA A23.3). Sze is calculated per equation 11-10 and ag is always assumed to equal 20 mm (maximum aggregate size).
Limitations - Australian and New Zealand Codes
Concrete Stress Profile – Concrete stress strain curve (parabolic) is assumed same as ACI for the New Zealand and Australian codes.
Neutral Axis Parameter – Ku in AS code is always assumed to be less than 0.4.
Rebar Spacing – NZS and AS codes: max spacing of rebar (beam) is 300 mm and minimum spacing is one bar diameter or 25mm whichever is bigger.
Shear Strength in Beams – In AS code, when calculating the shear strength of a beam β2, β3 are always assumed to be unity. This is always conservative for beams will little axial load, or beams in compression. But, may be unconservative for members subjected to significant net tension.
Bi-Axial Bending – The New Zealand code does not appear to give a simplified method for solving biaxial column design. Therefore, the PCA load contour method is being used instead.
Shear Tie Spacing – Column/beam shear tie spacing is based on (a) and (c) of NZS 9.3.5.4 :1995.
Development Length – Development length in NZS is based on NZS 7.3.7.2 where αa is conservative assumed to be 1.3 (top bars) for all cases. For the AS code, it is assumed that K1=1 and K2=2.4 in clause 13.1.2.1 of AS 3600:2001.
Slender Column Calculations – EI is assumed to be equal to 0.25EcIg (with βd =0.6) in slender column calculations in AS and NZS codes (like in ACI).
Limitations - British
Concrete Stress Profile – Concrete stress strain curve (parabolic) is taken from the British specification.
Cracked Sections – Icracked defaults to 1.0 for the British code. But, a user entered value may be entered if desired. Service level stiffness is assumed to be 1.43 times the strength stiffness, but is not allowed to exceed Igross.
Bi-Axial Bending – The program uses the simplified uniaxial solution provided in the British specification rather than performing a complete biaxial condition.
Limitations - Euro
Concrete Stress Profile – Concrete stress strain curve (parabolic) is taken from the EuroCode specification.
Cracked Sections – Icracked defaults to 1.0 for EuroCode. But, a user entered value may be entered if desired. Service level stiffness is assumed to be 1.43 times the strength stiffness, but is not allowed to exceed Igross.
Bi-Axial Bending – The program uses the simplified uniaxial solution provided in the EuroCode rather than performing a complete biaxial condition.
Limitations - Indian
Concrete Stress Profile – Concrete stress strain curve (parabolic) is taken from the Indian specification.
Cracked Sections – Icracked defaults to 1.0 for the Indian code. But, a user entered value may be entered if desired. Service level stiffness is assumed to be 1.43 times the strength stiffness, but is not allowed to exceed Igross.
Bi-Axial Bending – The program uses the simplified uniaxial solution provided in the Indian specification rather than performing a complete biaxial condition.
Limitations - Saudi Code
Concrete Stress Profile – Concrete stress strain curve (parabolic) is assumed to be the same as the ACI code.
Shear Strength– The shear strength is based on 11.3.1.1 and does not include the more detailed provisions of section 11.3.1.2.
Yield Strength of Shear Ties - The yield strength of shear ties is not allowed to exceed 420MPa.
Shear Tie Spacing - Minimum spacing of shear ties is set to 50mm
Bi-Axial Bending – Both the Exact Integration and the PCA Load Contour methods for bi-axial bending are supported in the Saudi code.
Special Messages
In some instances code checks are not performed for a particular
No Load Combinations for Concrete Design have been run.
Crack Width Calculation As Per Aci 318 14 Pdf
Warning: No design for spans with less than 5 sections.
Certain very short spans in physical members can end up with less than 5 design sections. No design is attempted without at least 5 sections because maximum values may be missed and an un-conservative design may result.
Warning: No design for spans less than 1 ft.
Certain very short spans in physical members can end up with lengths less than 1 foot. No design is attempted for these sections.
Warning: Member is slender and can sway, but P-Delta Analysis was NOT run.
Under older ACI codes slender sway members need to be run with the P-Delta option turned on to account for secondary forces and moments. In some situations, a preliminary design without P-Delta is useful and so a design is performed and this warning is shown to remind you to run the final analysis including P-Delta effects. Alternately, if you’re using the redesign feature, the next suggested column may resolve this issue if it’s not slender.
Warning: Slender Compression Failure (Pu > .75Pc). No Slender calculations done.
Since RISA-3D allows you to specify a starting column size, it’s possible that for slender columns under substantial axial load you'll exceed the critical buckling load used in the slenderness equations in ACI 318-14 Section 6.6.4.5.2 (ACI 318-11 Section 10.10.6). Design results are still shown so the suggested shapes can be used to pick a new suggested column size that will not have this problem. Note that the design results shown are NOT valued because the slender moment effects have NOT been considered.
Warning: KL/r > 100 for this compression member. See ACI 318-05 Section 10.11.5
Members that violate the KL/r limit still have design results calculated and shown.
Warning: Exact Integration selected but PCA method used
This message is shown when you've requested the Exact Integration option on the Model Settings Dialog, but we weren't able to converge a solution for the column in question. When Exact Integration does not converge, the PCA Method is used instead to give an idea of the demand vs. the capacity.
Warning: PCA Method Failed. Axial Load > Axial Capacity.
One of the limitations of the PCA Method is that it requires the column being checked to have a greater axial capacity than the axial demand. Since RISA-3Dallows you to set a starting size, it’s possible that the demand may be greater than the capacity. In this case a very rough estimate of the capacity is calculated by using the independent moment capacity about each axis considering the axial load. The resulting code check value is then based on the combined demand vector over the combined capacity vector and will always be greater than 1.0. The purpose of the results in this case is to show the column failed, not to give an accurate estimate of the over-demand. The redesign feature will suggest a larger shape to resolve this issue.
Warning: The shear tie spacing does not meet the code Minimum Requirement
This warning is stating that either minimum spacing or strength requirements are not being met for the shear reinforcement in the concrete member.
P-Delta analysis required for all ACI 318-14/11/08 Load Combinations
A second order analysis is required as of the 2014, 2011 and 2008 editions of the ACI 318 code. A code check will only be given if P-Delta is turned on in the Load Combinations spreadsheet, or if this requirement is intentionally waived in the Application Settings.