Design Property and Steel Design tabs are not displayed for members which have not been designed. Are you sure you are clicking a member for which the design has been done? Sometimes, when ratios are annotated on the screen, the picture may become quite cluttered with data and in an effort to double click on a designed member, one may end up clicking on a member for which design has not been performed. So, first check that the member you are double-clicking has indeed been designed. If you are certain that STAAD has done the design and evidence of that exists in the analysis output file and in the postprocessing Unity Check tables, but still you are not able to see these tabs in the dialog box which comes up when you double click on the member, please send us your .std model and our support representatives will look into that.
You have to use the LOAD LIST command to achieve this. Supposing you want to check deflection for combination cases 81 and 82. And assume that L/Deflection has a limit of 240. The command sequence required to achieve this is
LOAD LIST 81 82PARAMETERCODE AISCDFF 240 ALLCHECK CODE ALL
However, after these commands, you have to reset DFF to a very small number so that deflection does not become a criteria for any further design operations. That is because, once a parameter is specified in STAAD, it stays that way till it is changed again. So, after the above, you need to specify
PARAMETERCODE AISCDFF 1 ALL
The code has requirements which say that the KL/r ratios for a member should not exceed certain allowable limits. For members subjected to tensile forces, the code suggests one limit, and for members subjected to compressive forces, there is another limit.
This check does not consider the amount of the axial force. It only looks at the sign of the force to determine if it is a tensile force or compressive force.
In most codes, this is the first check STAAD does on a member. If the member fails the check, no further calculations are done for that member.
So, STAAD performs these checks by default. However, the code does not offer any guidelines on what must be the minimum magnitude of the axial force for the member to become a candidate for this check.
So, in STAAD, two parameters are available - one called MAIN and another called TMAIN if you wish to bypass this check (TMAIN is available for some codes only). MAIN=1 is for bypassing the slenderness check in compression, and TMAIN=1 is for bypassing the slenderness check in tension.
During steel design per the AISC ASD code, there are two types of deflection checks you can perform with STAAD. They are
LOCAL DEFLECTION is defined as the maximum deflection between the 2 ends of the beam relative to a straight line connecting the 2 ends of that member in its deflected position.
If you go to
Help - Contents - Technical Reference - Commands and Input Instructions - Printing Section Displacements for Members
you will find a diagram indicating this is in figure 5.41.
To obtain more information on the difference between the 2 methods of deflection checking, please go to
Help - Contents - Technical Reference - American Steel Design - Design Parameters (which comes after Allowables per AISC code)
It will bring up section "2.4 Design Parameters"
At the end of the parameters table, you will see several notes. Please read Notes items 1 through 4 for the description of the two methods.
As you can see there, the default condition, which is also represented by a value of zero for the CAN parameter, is to perform the LOCAL DEFLECTION check.
Your question indicates that what you are looking for is a check of the nodal deflections. The cantilever style check STAAD offers is probably the solution for your problem. If so, specify the CAN parameter with a value of 1.
The steel design output for several members is accompanied by the following warning message :
WARNING : THE VALUE OF E FOR MEMBER 21 DOES NOT SEEM RIGHT.
WARNING : THE VALUE OF E FOR MEMBER 22 DOES NOT SEEM RIGHT.
WARNING : THE VALUE OF E FOR MEMBER 23 DOES NOT SEEM RIGHT.
During steel design, there is a check for ensuring that the Modulus of Elasticity (E) specified for the member is within the range that is normal for steel. This is because, E is a crucial term that appears in many equations for calculating section capacities and the program wants you to know if the value appears to be abnormal.
In STAAD, you specify E either explicitly under the CONSTANTS command block or through the DEFINE MATERIAL block, as in the examples below.
Example 1 :
UNIT KIP INCHCONSTANTSE 29000 ALLDENSITY 0.283E-3 ALL
Example 2 :
UNIT METER KNSDEFINE MATERIAL STARTISOTROPIC STEELE 2.05e+008POISSON 0.3DENSITY 76.8195ALPHA 1.2e-005DAMP 0.03END DEFINE MATERIALCONSTANTSMATERIAL STEEL MEMBER 101 TO 121
So, if you are specifying an E value which is significantly different from that for steel, such as say, Aluminum, and then later asking the member to be designed according to a steel code, as in the following example, the above-mentioned warning message will appear.
UNIT FEET POUNDDEFINE MATERIAL STARTISOTROPIC ALUMINUME 1.44e+009POISSON 0.33DENSITY 169.344ALPHA 1.28e-005DAMP 0.03END DEFINE MATERIAL
CONSTANTSMATERIAL ALUMINUM MEMBER 21 TO 30
....PARAMETERCODE AISCCHECK CODE MEMBER 21 TO 30
For single angles, the local Y and Z axes are the principal axes as shown below:
The KL/r value is computed using ry and rz which are based on the principal axis system. Chances are that your handculation uses the geometric axes.
There are 2 methods for finding just those members which have failed the steel design checks.
The terms reported in the TRACK 2 output for American LRFD are :
AX = Cross section Area.AY : Area used in computing shear stresses along local Y axis.AZ : Area used in computing shear stresses along local Z axis.PY : Plastic Section modulus about local Y axis.PZ : Plastic Section modulus about local Z axis.RY : Radius of gyration about local Y axis.RZ : Radius of gyration about local Z axis.
PNC : Axial compression capacity.
pnc : Axial compressive force used in critical condition.
PNT : Axial tensile capacity.
pnt : Axial tensile force used in critical condition.
MNZ : Nominal bending capacity about local Z axis.
mnz : Bending moment about local Z axis, used in critical condition.
MNY : Nominal bending capacity about local Y axis.
mny : Bending moment about local Y axis, used in critical condition.
VN : Shear capacity.
vn : Shear force associated with critical load case and section location.
DFF : Permissible limit for checking length to deflection ratio.
dff : Actual length to deflection ratio.
The terms reported in the TRACK 2 output for AISC ASD are :
AX = Cross section AreaAY : Area used in computing shear stresses along local Y axisAZ : Area used in computing shear stresses along local Z axisSY : Elastic Section modulus about local Y axisSZ : Elastic Section modulus about local Z axisRY : Radius of gyration about local Y axisRZ : Radius of gyration about local Z axis
FA : Allowable axial stress. If failure condition involves axial tension, this is the allowable axial tensile stress. If failure condition involves axial compression, this is the allowable axial compressive stress.
fa : Actual axial stress.
FCZ : Allowable bending compressive stress about local Z axis.
FTZ : Allowable bending tensile stress about local Z axis.
FCY : Allowable bending compressive stress about local Y axis
FTY : Allowable bending tensile stress about local Y axis.
fbz : Actual bending stress about local Z axis, used in the design condition
fby : Actual bending stress about local Y axis, used in the design condition.
FV : Allowable shear stress.
Fey : Euler stress for buckling about local Y axis.
Fez : Euler stress for buckling about local Z axis.
In STAAD.Pro 2003, you can use the Auto-Form member option to let the program automatically create physical members for you. From the Member Design page in the Steel Design Mode, go to Member Design | Physical Members | Auto Form Members. The rules it uses to create physical members are as follows:
If you wish to use LRFD 3rd Edition Code, you can write CODE LRFD3 when providing the design parameters.The 3rd edition of the American LRFD steel code has been implemented along with the 2nd edition. In general, the principles outlined in the code for design for axial tension, compression, flexure, shear etc., are quite similar to those in earlier versions of the code. The major differences are in the form of incorporation of the Young’s modulus of steel in the various equations for determining various limits like slenderness and capacities. Consequently, the general procedure used in STAAD for design of steel members per the AISC-LRFD code has not changed significantly. Users may refer to Section 2 of the STAAD.Pro Technical Reference manual for these procedures.Those who wish to use the 1994 edition of the code can still do so by specifying the code name as:CODE LRFD2An example of commands used for performing design based on the new and old codes are as shown.Example for the LRFD-2001 code (3rd Ed)UNIT KIP INCHPARAMETERCODE LRFDorCODE LRFD3FYLD 50 ALLUNT 72 MEMBER 1 TO 10UNB 72 MEMB 1 TO 10MAIN 1.0 MEMB 17 20SELECT MEMB 30 TO 40CHECK CODE MEMB 1 TO 30Example for the LRFD-1994 code (2nd Ed)UNIT KIP INCHPARAMETERCODE LRFD2FYLD 50 ALLUNT 72 MEMBER 1 TO 10UNB 72 MEMB 1 TO 10MAIN 1.0 MEMB 17 20SELECT MEMB 30 TO 40CHECK CODE MEMB 1 TO 30
For example, if I have a truss whose top chord is laterally supported at every other node (i.e. two member lengths being unsupported), then should I highlight every two members (of the top chord) seperately and then tell the program to take their combined length as being unsupported, or should I highlight the entire top chord and then specify the correct unsupported length.
The value you specify for UNL is what STAAD uses for the expression Lb which you will find in Chapter F of the AISC ASD & LRFD codes. Starting from Version 2001, UNL has been replaced with UNT and UNB for these codes. If the Lb value for the top flange is different from that for the bottom flange, you have to specify the corresponding values for UNT & UNB.
So if the bracing points are at every alternate node, first determine the distance between the alternate nodes. Then assign that value for both beams which exist between those nodes.
For example, if you have
Member 5 connected between nodes 10 and 11, and is 6.5 ft longMember 6 connected between nodes 11 and 12, and is 7.3 ft long
and both the top and bottom flanges are braced at nodes 10 & 12, you can assign
UNIT FEETPARAMETERCODE AISCUNT 13.8 MEMB 5 6UNB 13.8 MEMB 5 6
To assign these parameters using the GUI, while in the Modelling mode, select the Design page from the left side of the screen. Make sure the focus is on the Steel sub-page. On the right side, select the proper code name from the list box on the top. Click on the Define Parameters button along the bottom right side. In the dialog box which comes up, select the tab for UNT and UNB, specify the value, and assign it to the appropriate members.
At present, sections whose data is specified using a "User Provided Table" (see section 5.19 of the Technical reference manual for details) cannot be designed or checked per the AISI code. However, the following approach may be used to get around this limitation.
You may add your section to the STAAD AISI section database, so that your section becomes a permanent part of the database. This can be done using the following method.
From the Tools menu, select Modify Section database. The various steel databases available in the program will be listed in a dialog box. You will find ColdFormed (US) at the end of this list. Expand this list, and choose Channel with Lips or Channel without Lips as the case may be. On the right half of the dialog box, the Add option will become activated. Select that, and you will now be provided with an interface through which you can add your channel to the list. Save and Close it.
You can now go to the Commands menu, and choose Member property - Steel Table - AISI Table to obtain visual confirmation that this new section is permanently included among the list of channel sections. You should now be able to assign this new section to the members through the usual property pages and menus.
In the design input parameters, I set NSF to .85 for my steel design. The design output result showed a failure ratio of 1.063 on Member 1. I then proceeded to change the NSF parameter to 1.0. This time, the design output result showed the same failure ratio of 1.063. It seems that nothing has changed. I increased the net section factor by 0.15, but the stress ratio hasn't changed?
The NSF value has an effect only on allowable axial tensile capacity, and the actual tensile stress.
If axial tension, or axial tension plus bending, are not what determine the critical condition, changing the value of NSF will not have any impact on the failure ratio. For example, if the critical failure condition for a member is compression, changing NSF will have no impact.
Check to see what the critical condition is. It will show up in the form of expressions such as:
AISC H1-1 or Slenderness, etc.
In the earlier versions of STAAD (STAAD-III), the code check for prismatic sections was done using allowable stresses which are arbitrarily chosen as 0.6 x Fy. However, this assumption of 0.6Fy was not based on any code specific requirements. The word PRISMATIC is meant to indicate a section of any arbitrary shape. But neither the AISC nor LRFD codes provide guidelines for design of arbitrary shapes. Section capacities are dependent upon aspects such as the width to thickness ratio of flanges and webs, lateral torsional buckling etc. From that standpoint, using an allowable stress of 0.6Fy for PRISMATIC sections was not always conservative.
A way around this limitation (lack of specific guidelines) would have been to use the rules of a known shape, such as a Wide Flange, for designing prismatic shapes. That would require knowledge of equivalent flange and web dimensions. When the properties are defined using the PRISMATIC option, there is no means to convey information such as dimensions of flanges or webs to the STAAD design facility. Hence, the design of PRISMATIC shapes is not supported in STAAD/Pro. You may get around this problem by defining the properties using the GENERAL section in a User Provided Table. For a GENERAL section, STAAD provides the means for providing dimensions of the components that are critical from the standpoint of computing allowable stresses. The allowable stresses for a GENERAL section are computed using the rules of a wide flange shape (I shape). As a result, the allowable stress value will be dependent on attributes such as dimensions of the cross section, length of the member, etc.
For singly symmetric shapes such as Tees and Double Angles, the KL/r value for the Y axis is calculated by STAAD using the rules for flexural torsional buckling as explained in page 3-53 of the AISC ASD manual. It is not calculated as Ky multiplied by Ly divided by ry.
There are 2 sets of data associated with analysing and designing a composite beam.
Step 1 : Define the member properties as a composite beam. To do this, one has to use the "TA CM" option as explained in Section 5.20.1 of the STAAD.Pro Technical reference Manual. For example, if member 1 is a composite beam made up of a 3.0 inch thick slab on top of a W18X35, and the grade of concrete is 4.0ksi, one would have to specify
UNIT INCH KIPMEMBER PROPERTIES1 TA CM W18X35 CT 3.0 FC 4.0
Step 2 : Parameters for steel design. This is what you find in Section 2.9 of the STAAD.Pro Technical reference Manual. These are the attributes which are to be used in the actual design equations, using the expression PARAMETER, as in,
PARAMETERCODE AISCBEAM 1 ALLTRACK 2 ALLFYLD 50 ALLCMP 1 ALLDR1 0.3 ALLWID 60 ALLFPC 4 ALLTHK 4 ALLSHR 0 ALLDIA 0.75 ALLHGT 4 ALLRBH 2 ALLCHECK CODE ALL
The most important thing to note here is the usage of the parameter CMP. Unless it is set to 1.0, STAAD does not design the beam as a composite section. The beam will be designed as a pure steel beam section in the absence of the "CMP 1" parameter.
FYLD is one of the items specified as parameters for steel design. The STAAD Technical Reference manual and International Design Codes manual contain information on specifying parameters for steel design.
There are example problems in the STAAD Example manual demonstrating how parameters are specified for design. The example below shows some typical post-analysis commands.
PERFORM ANALYSIS PRINT STATICS CHECKPRINT MEMBER FORCES LIST 5 7PRINT ELEMENT STRESSES LIST 10 TO 16UNIT KIP INCHPARAMETERSCODE AISCUNT 1.0 ALLUNB 20.0 ALLLY 60 MEMBER 36 40LZ 60 MEMBER 36 40FYLD 46.0 MEMBER 47 50CHECK CODE ALLFINISH
If you prefer to use the graphical method, this is how you can specify it. From the left side of the screen, select the Design page. Make sure the sub-page says Steel. On the right hand side of the screen, go to the top, and choose the appropriate code.
Select the members on the structure for which you wish to assign the FYLD parameter.
Then, on the bottom right hand side of the screen, you will find a button called Define Parameters. Click on that button. Select the FYLD tab. Specify the value, and click on Assign.
In versions of STAAD prior to STAAD/Pro 2000, the mechanism for specifying the unsupported length of the compression flange was through the means of the UNL parameter. However, the drawback of this command is that if the value for the top flange is different from that of the bottom flange, there wasn't any means to communicate that information to STAAD.
Consequently, 2 new commands were introduced, namely, UNT and UNB.
UNT stands for the unsupported length of the TOP flange of the member for calculating the capacity in bending compression and bending tension.
UNB stands for the unsupported length of the BOTTOM flange for calculating the capacity in bending compression and bending tension.
To avoid the confusion that may arise from having 3 separate parameters to specify 2 items of input, we no longer mention the UNL parameter. However, to enable the current versions of STAAD to analyze input files created using the older versions of STAAD, the UNL parameter continues to work the way it did.
These 2 new parameters are to be used in place of UNL. If UNT/UNB is specified in addition to UNL, UNL will be ignored. If neither UNT nor UNB are specified, but UNL is specified, the value of UNL will be used for both top and bottom flange.
In steel design per the AISC ASD code, the elements of the cross section (flange, web etc.) have to be put through some tests per Chapter B of the code. These tests are required to classify the cross section into one of 3 types - Compact, Non-compact, Slender.
If a section is classified as slender, the allowable stresses on the section have to be determined per the rules of Appendix B of the code. For slender "stiffened elements", which is the type a tube falls into, the effective section properties have to be calculated and those effective properties must then be used in computing the actual stresses.
The extent of the cross section deemed effective depends on the bending moment on that section. It is very likely that for the critical load case, the effective properties are less than the gross section properties, which is why you see the reduced Sz and Sy in the output.
If you have STAAD.Pro 2001 Build 1005 or Build 1006, you can specify a command called
PRINT STORY DRIFT
in your input file. Run the analysis. Then check your output file, The drift for each story will be reported. You will have to manually verify that this is within your allowable limits.
If my joint displacement printout says that joint of a column/beam joint has moved 1.42 inch in the global X, then my drift ratio is 18x12/1.42 = 152.11, but the "dff" says 1072 for the same column, then where is the dff being measured?
When the DFF parameter is specified, the deflection checks during steel design are performed on the basis of so called "local axis deflection", not the nodal displacements in the global axis. For this reason, it is not possible to include storey drift checks into the steel design calculations at present.
If you want additional information on local axis deflection, please refer to example # 13, and Section 5.42 of the STAAD Technical Reference Manual.
Yes. However, rather than check the deflection for each axis independently, STAAD finds the resultant deflection "d" and compares the "L/d" (length to deflection ratio) against the allowable limit specified by you through the DFF parameter.
When STAAD performs steel design (code checking as well as member selection), it checks several conditions required by the code. The one which gives rise to the highest unity check is the one determined as critical. If the deflection criteria ends up being the worst condition, you will see it being reported as the critical condition.
You can verify whether a member has passed the deflection check by looking at the terms "DFF" and "dff" in the steel design output. "DFF" is the value you input. "dff" is the value the program calculates as the actual "L/d" ratio. If "dff" is larger than "DFF", the member is deemed safe for deflection.
1) DFF : This is the value which indicates the allowable limit for L/d ratio. For example, if a user wishes to instruct the program that L/d cannot be smaller than 900, the DFF value should be specified as 900. The default value for DFF is 0. In other words, if this parameter is not specified as an input, a deflection check will not be performed.
2) DJ1 and DJ2 : These 2 quantities affect the "L" as well as the "d" in the calculated L/d ratio. They represent node numbers that form the basis for determining L and d.
By default, DJ1 and DJ2 are the start and end nodes of the member for which the design is being performed, and "L" is the length of the member, namely, the distance between DJ1 and DJ2. However, if that member is a component segment of a larger beam, and the user wishes to instruct STAAD that the end nodes of the larger beam are to be used in the evaluation of L/d, then he/she may input DJ1 and DJ2 as the end nodes of the larger beam. Also, the "d" in L/d is calculated as the maximum local displacement of the member between the points DJ1 and DJ2. The definition of local displacement is available in Section 5.42 of the STAADPro Technical Reference Manual, as well as in Example problem # 13 in the STAADPro Examples Manual.
A pictorial representation of DJ1 and DJ2, as well additional information on these topics is available under the "Notes" section following Table 2.1 in Section 2.8 of the STAADPro Technical Reference Manual.
If you use the design parameter TRACK 2.0, you will see a term called "dff" in the STAAD output file. This terms stands for the actual length to deflection ratio computed by STAAD. If "dff" is smaller than "DFF", it means the member has violated the safety requirement for deflection, and will be treated as having failed.
I am using tapered tubular section properties in my model. When I try to design those members using the AISC code.
The AISC code currently does not have the rules for designing tubular sections which are 6 sided, 8 sided, 12 sided, etc. That is why you cannot currently design them per the AISC code.
There is a code from ASCE called the ASCE publication # 72. That document contains the rules for designing these shapes. Those rules are implemented in STAAD's transmission tower code, and if you have purchased that code, you should be able to design them.
You will notice that, for the member which failed, the cause of the failure is reported using the phrase "L/R-EXCEEDS". This means that the member has failed the slenderness check.
When STAAD performs steel design on a member per the AISC code, it adopts the following sequence :
It first sets the allowable KL/r in compression to 200 and the allowable KL/r in tension to 300.
For the member being designed, it goes through all the active load cases to see if the member is subjected to axial compression and/or axial tension.
Next, it compares the actual KL/r against the allowable KL/r. If this check results in a FAILure, the member is declared as FAILed, and design for that member is immediately terminated. The requirement to check this condition is in Section B of the AISC specifications.
If the member passes the KL/r check, only then does the program go on to do the remainder of the checks such as axial compression + bending, shear, etc.
It must be noted that failure to satisfy the KL/r check is a reflection of the slenderness of the member, not the capacity of the section to carry the loads which act on it. Even if the axial load or bending moment acting on the member is a negligible quantity, the fact is, failure to satisfy KL/r will result in the member being declared as unsafe as per the code requirement.
If you do not want the KL/r condition to be checked, you can switch off that check using a parameter called MAIN. Set MAIN to 1.0 for a specific member and it won't be checked for slenderness. See Table 2.1 of the STAAD.Pro Technical Reference Manual for details.
NSF 0.85 ALLBEAM 1.0 ALLKY 1.2 ALLRATIO 0.9 ALLLY 18 ALLLZ 18 ALLCHECK CODE ALL
NSF 0.85: This parameter is called Net Section Factor. One of the criteria used in determining the capacity of a section in Axial Tension is fracture of the net section. The capacity is calculated as NSF X Gross Area X Ultimate Tensile Strength of steel in tension
BEAM 1.0: This means the design or code checking of the member will be done by determining the safety of the member at a total of 13 points along the length of the member. Those 13 points are the start, the end, and 11 intermediate points along the length. If this parameter is not set, design will be performed by checking the safety at only those locations governed by the SECTION command.
KY 1.2: The KY value is used to determine the KL/r for the Y axis -Ky multipled by Ly divided by Ry.
RATIO 0.9: The code requires one to check the safety of a member by verifying several interaction equations for compression, bending, tension, etc. The right hand side of these equations is usually 1.0. The RATIO parameter allows one to set the right hand side to the value of the RATIO parameter, in this case 0.9.
LY 18: The LY value is used in calculating the KL/r for the Y axis -Ky multipled by Ly divided by Ry.
LZ 18: The LZ value is used in calculating the KL/r for the Z axis -Kz multipled by Lz divided by Rz.
CHECK CODE ALL : For ALL members, the safety of the section is determined by evaluating the ratio of applied loading to section capacity as per the code requirements.
The checks done as per the AISC ASD 9th edition code are :
CHECK CODE ALL
DESIGN NOT PERFORMED WITH PRISMATIC PROPERTIESUSER-TABLE MAY BE USED TO DESIGN PRISMATIC SECTIONS
The program is not designing the steel members defined as "Prismatic" in the UP Table, whereas all other members defined otherwise as Tee, Channel etc are being designed. Also I couldn't understand the meaning of the last line "User-Table may be used to design prismatic sections".
Since PRISMATIC sections by definition are those whose section shape is not one of the standard shapes like a W, C, Angle, etc., there are no readily available rules in the code to follow. Due to this reason, prismatic shapes are presently not designed per the BS code nor the ACI code.
You may get around this problem by defining the properties using the GENERAL section in a User Provided Table. For a GENERAL section, STAAD provides the means for providing dimensions of the components that are critical from the standpoint of computing allowable stresses, such as flange, web, etc. The allowable stresses for a GENERAL section are computed using the rules of a wide flange shape (I shape). As a result, the allowable stress value will be dependent on attributes such as dimensions of the cross section, length of the member, etc.
The parameters UNT and UNB are for specifying the unsupported length of the compression flange for the purpose of computing allowable stresses in bending compression.
If you want to specify the unbraced length for the purpose of computing allowable stresses in axial compression, use the parameters LY and LZ. See Table 2.1 of the STAAD.Pro Technical Reference Manual for details.
You would need to use the "LOAD LIST" command. For example, if you only were interested in the 1st, 3rd and 5th load cases for the RATIO parameter you would need to write:
LOAD LIST 1 3 5RATIO 0.5
In your input file.
The results of this code check show some very strange numbers in as far as code ratio using AISC- H1-1 formulation is concerned. Reference result output for members number 62 to 74 for example. Other ratios do not seem right either.
If you look at the AISC equation H1-1, you will find that there are 2 terms in the denominator, called
If the value of fa equals or exceeds Fey or Fez (Euler stresses), the respective terms become zero or negative, which is not a desirable event. In such a situation, STAAD replaces that negative number with the value 0.0001. The consequence of this is that, that part of the interaction equation becomes magnified by 10000, which will cause the overall value of the left hand side of equation H1-1 to increase significantly.
The above scenario is what occurs in the case of several of the members in the list 62 to 74. If you want to obtain proof of this, you may do the following. Change the value of the TRACK parameter from 1 to 2, and you will get a more detailed design output. That output will include the values of fa, Fey, Fez, etc.
To remedy the problem, you need to use a larger cross section so that "fa" becomes smaller, or use one with a smaller KL/r value so that Fey and/or Fez become larger.
The LX is the parameter used in calculating the axial compression capacity for flexural torsional buckling
A single angle is subjected to 2 buckling modes :
You should check whether the flexural torsional buckling mode governs in your case. The KL/r calculated for the flexural torsional mode, if it happens to the largest of the 3 values, is reported only with a TRACK 1.0 detail of output. It does not get reported for TRACK 0 or TRACK 2 level of detail of output. In other words, if you want to see the KL/r in the flexural torsional buckling mode, use the parameter TRACK 1.0.
SSY and SSZ are terms which dictate how sidesway criteria should be used in computing the Cm coefficients. For both of them, a value of 0.0 means sidesway is present for the corresponding axis, and, a value of 1.0 means sidesway is not present for the corresponding axis.
When SSY is set to 0.0, Cmy is set to 0.85 as per page 5-55 of AISC ASD.
When SSZ is set to 0.0, Cmz is set to 0.85 as per page 5-55 of AISC ASD.
When SSY is set to 1.0, Cmy is calculated as per the equations on page 5-55 of AISC ASD.
When SSZ is set to 1.0, Cmz is calculated as per the equations on page 5-55 of AISC ASD.
If the CMY parameter is specified (and the value is a valid one), that value is used, regardless of what the value of SSY is.
If the CMZ parameter specified (and the value is a valid one), that value is used, regardless of what the value of SSZ is.
For singly symmetric shapes such as Tees and Double Angles, the KL/r value for the Y axis is calculated by STAAD using the rules for flexural torsional buckling as explained in page 3-53 of the AISC ASD manual. It is not calculated as Ky multiplied by Ly divided by ry.
Deflection of a beam or a column can be included as one of the criteria during code checking or member selection with most steel design codes inSTAAD. The ratio of length to maximum deflection of a beam (L/d ratio) will be calculated by STAAD. STAAD will then check that quantity against the allowable limit which the user specifies under the PARAMETERS option.
What are the design parameters which control deflection check ?
1. DFF : This is the value which indicates the allowable limit for L/d ratio. For example, if a user wishes to instruct the program that L/dcannot be smaller than 900, the DFF value should be specified as 900. The default value for DFF is 0. In other words, if this parameter is notspecified as an input, a deflection check will not be performed.
2. DJ1 and DJ2 : These 2 quantities affect the "L" as well as the "d" in the calculated L/d ratio. They represent node numbers that form the basis for determining L and d.
By default, DJ1 and DJ2 are the start and end nodes of the member for which the design is being performed, and "L" is the length of the member, namely, the distance between DJ1 and DJ2. However, if that member is a component segment of a larger beam, and the user wishes to instruct STAAD that the end nodes of the larger beam are to be used in the evaluation of L/d, thenhe/she may input DJ1 and DJ2 as the end nodes of the larger beam. Also, the "d" in L/d is calculated as the maximum local displacement of the member between the points DJ1 and DJ2. The definition of local displacement is available in Section 5.42 of the STAADPro Technical Reference Manual, as well as in Example problem # 13 in the STAADPro Examples Manual.
What are the results one gets from STAAD for the deflection check?
If the steel design parameter called TRACK is set to 2.0, the L/d ratio calculated for the member can be obtained in the STAAD output file. The value is reported against the term "dff". Notice that the expression is in lower-case letters as opposed to the upper-case "DFF" which stands for the allowable L/d.
If "dff" is smaller than "DFF", that means that the displacements exceeds the allowable limit, and that leads to the unity check exceeding 1.0. This is usually a cause for failure, unless the RATIO parameter is set to a value higher than 1.0. If "DFF" divided by "dff" exceeds the value of the parameter RATIO, the member is assumed to have failed the deflection check.
What are the limitations of this check?
Since the "d" in L/d is the local deflection, this approach is not applicable in the case of a member which deflects like a cantilever beam.That is because, the maximum deflection in a cantilever beam is the absolute quantity at the free end, rather than the local deflection. Check whether STAAD offers a parameter called CAN for the code that you are designing to. If it is available, set CAN to 1 for a cantilever style deflection check.
Since the deflection which is checked is a span deflection and not a node displacement, the check is also not useful if the user wishes to limit story drift on a structure.
"dff" is the value of actual length divided by local deflection. The actual length value is the distance between the nodes DJ1 and DJ2 which default to the actual end nodes of the member. The deflection used is the maximum local deflection between the points DJ1 and DJ2. You can get the Max. Local Displacement value by looking at the output of the PRINT SECTION DISPLACEMENT command. The definition of DFF, DJ1 and DJ2 may be found in Table 2.1 of the Technical Reference Manual for STAAD/Pro.The word PRISMATIC is meant to indicate a section of any arbitrary shape. But the AISC code does not provide guidelines for design of arbitrary shapes.Section capacities are dependent upon aspects such as the width to thickness ratio of flanges and webs, lateral torsional buckling etc. From that standpoint, using an allowable stress of 0.6Fy for PRISMATIC sections was not always conservative.
In the earlier versions of STAAD, the code check for prismatic sections was done using allowable stresses which are arbitrarily chosen as 0.6 Fy. However, this assumption of 0.6Fy was not based on any code specific requirements.
The word PRISMATIC is meant to indicate a section of any arbitrary shape. But the AISC code does not provide guidelines for design of arbitrary shapes. Section capacities are dependent upon aspects such as the width to thickness ratio of flanges and webs, lateral torsional buckling etc. From that standpoint, using an allowable stress of 0.6Fy for PRISMATIC sections was not always conservative.
A way around this limitation (lack of specific guidelines) would have been to use the rules of a known shape, such as a Wide Flange, for designing prismatic shapes. That would require knowledge of equivalent flange and web dimensions. When the properties are defined using the PRISMATIC option, there is no means to convey information such as dimensions of flanges or webs to the STAAD design facility. Hence, the design of PRISMATIC shapes is not supported in STAAD/Pro.
You may get around this problem by defining the properties using the GENERAL section in a User Provided Table. For a GENERAL section, STAAD provides the means for providing dimensions of the components that are critical from the standpoint of computing allowable stresses. The allowable stresses for a GENERAL section are computed using the rules of a wide flange shape (I shape). As a result, the allowable stress value will be dependent on attributes such as dimensions of the cross section, length of the member, etc.
In steel design, the Pass/Fail status of a member is determined according to various conditions. According to most design codes, the member has to be checked for failure against axial compression and axial tension, slenderness, compressive & tensile stresses caused by axial compressive force + bending moments, failure caused by shear stresses, etc. For each of these conditions, determination of whether the member is safe or unsafe is done by checking whether the actual values due to the loading exceed or are less than the allowable values. The amount by which the member is stressed for each of these conditions is quantified in the form of the Ratio. For example, take the case of equation H1-1 of Section H of the AISC-89 specifications. The number obtained by computing the left hand side of that equation is the Ratio corresponding to that equation.
The postprocessing Beam >Unity Check page can report the design results only for the final set of design. This is a limitation in STAAD.Pro as the program architecture does not allow that results of multiple design sets to be made available at the same time graphically. The analysis output file is the only place where you can view results for all design sets. The only way to view the results of a previous design cycle graphically is
The shear stress calculated by STAAD is the maximum shear stress by default which is based on the standard formula VQ/Ib, where
V = Shear force
Q = Moment of area of the part of the cross section thatis above ( or below ) the plane where shear stress is being calculated, aboutthe neutral axis
I = Moment of Inertia
b= Width of the section at the plane where the stress isbeing calculated
So the term Ib/Q is reported as the shear area that corresponds to this shear stress calculation.
If required one can get STAAD to calculate the average shear stress instead of the maximum. There is a SHE design parameter that can be used to influence how STAAD calculates the shear stress. When the parameter is set to 0 ( default ), stress is calculated as mentioned above. However when this parameter is set to 1, average shear stress will be calculated based on the formula V/Ay (or Az ) where Ay or Az are the shear area for the cross section.
AISI 2007 code is being developed, but as part of the STAAD(X) project rather than STAAD.Pro. It should be released in mid next year (2014).
There are a couple of ways to handle this. One is during the design phase and another is during the analysis phase.
Check during design phase
To ensure that beams are checked appropriately for deflection, using the physical member length as opposed to the length of the analytical segments, please refer to the Note 2 under section 184.108.40.206 ( Design Parameters) from the Technical Reference Manual ( can be accessed through Help > Contents > Technical Reference ) which explains how the design parameters like DJ1, DJ2 and DFF can be used to check deflection for the physical member. In your case, you would specify DFF as 500 for the beam to be checked against an allowable deflection limit of L/500.
Checking during analysis phase
If you are not planning to go for design and would just like to check the deflection based on analysis results, you may define the entire beam as a physical member (PMEMBER). After analysis you will then be able to double click on the physical member ( ensure that your selection cursor is the physical member cursor ) and see the local deflection for the entire physical member.
For the values to be accepted by the software, you need to ensure that these parameters are added to the input file before the CHECK CODE or SELECT command. For example if you need to specify FYLD as 50 ksi for members 1 and 2, you should have the commands in the following order
PARAMETER 1CODE ......FYLD 50 MEMB 1 2 CHECK CODE ALL
If you add the parameters after the CHECK CODE as shown next, the design would not consider those
PARAMETER 1CODE ......CHECK CODE ALLFYLD 50 MEMB 1 2 ...
Yes, the design (CODE CHECK) can be performed for some specific group of members. Let's say we have a group called TEST which was created by going to Tools -> Create New Group. In order to perform a design for the members which are defined in that group only, you need to go to the STAAD Editor (Edit -> Edit Input Command File) and find a CHECK CODE ALL line (if that command is already added). This command line should be changed to line CHECK CODE MEMB _TEST.
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Please clarify according to AISC 9th edition, how to calculate UNT and UNB for beams.
Please clarify that the Staad V8i is have the facility to do the steel design using IS 800:2007 code?...
does Staad has the capability of Torsional check of steel members subjected to Torsion??
You would likely be better served posting technical, STAAD-related inquiries in this community's forum -- select the Forum tab and then click on the "New Post" to create a new thread.
IF STRUCTURE FAILS WHAT IS THE PROCEDURE TO MAKE IT PASS IN STAAD PRO