***WARNING: THE VALUE OF MOMENT AMPLIFICATION FACTORS KY OR KZ IS GREATER THAN 1.4 FOR MEMBER # XXX FOR LOADCASE- XXX. SECOND-ORDER ELASTIC ANALYSIS MUST BE PERFORMED AS PER SECTION 4.4.2 of IS800-2007.

I am sure you have understood the reason for this warning as mentioned in the linked post. Following are few clarifications --

Q1. It is not a bug. At this moment, this warning is reported for all types of member. During design, program does not consider the truss specification and design it as a general member with 0 bending forces. So though you have specified a member as truss member for which bending and interaction checks are not required, still program reports this warning. You can simply ignore this warning for truss member. 

Q2. If this warning is reported for any member which is subjected to axial compression + bending, then as per cl.4.4.2, first order analysis + moment amplification method is not sufficient to consider the second order effects and you need to perform second order analysis. In such case, program does not terminate the design and you can still use the design results. But if you want to follow codal provisions, then you should change all load combinations to repeat load cases and perform second order analysis like pdelta analysis.

Q3. To remove these warnings, either you can perform second order analysis or use SET NOWARNING command which will instruct program not to print any warning in the output file. If you use this command, then you have to use the latest CONNECT Edition as there was a bug in the older version which has been fixed now.   

If you look at the equation of Ky and Kz, you can notice this depends on non-dimensional effective slenderness ratio and ratio of applied compressive force/compression capacity. If you can increase the overall compression capacity of the member by increasing the r value or by reducing the euler buckling stress, then both lamdaY and ny value reduces which eventually decrease the ky/kz value. In other words, chance of buckling and second order effects reduce for a short stiff member rather than a ling slender section, correct? 

I am sure you have understood the reason for this warning as mentioned in the linked post. Following are few clarifications --

Q1. It is not a bug. At this moment, this warning is reported for all types of member. During design, program does not consider the truss specification and design it as a general member with 0 bending forces. So though you have specified a member as truss member for which bending and interaction checks are not required, still program reports this warning. You can simply ignore this warning for truss member. 

Q2. If this warning is reported for any member which is subjected to axial compression + bending, then as per cl.4.4.2, first order analysis + moment amplification method is not sufficient to consider the second order effects and you need to perform second order analysis. In such case, program does not terminate the design and you can still use the design results. But if you want to follow codal provisions, then you should change all load combinations to repeat load cases and perform second order analysis like pdelta analysis.

Q3. To remove these warnings, either you can perform second order analysis or use SET NOWARNING command which will instruct program not to print any warning in the output file. If you use this command, then you have to use the latest CONNECT Edition as there was a bug in the older version which has been fixed now.   

If you look at the equation of Ky and Kz, you can notice this depends on non-dimensional effective slenderness ratio and ratio of applied compressive force/compression capacity. If you can increase the overall compression capacity of the member by increasing the r value or by reducing the euler buckling stress, then both lamdaY and ny value reduces which eventually decrease the ky/kz value. In other words, chance of buckling and second order effects reduce for a short stiff member rather than a ling slender section, correct? 

Hello Surojit,

Thankyou for your pointwise replies, that helped a lot in understanding.

Can you also help me below Message coming in STADD pro- ***NOTE: Static Seismic Analysis for IS1893 (Part-4): 2015 should be carried
out with P-Delta Analysis as per 10.3

As per IS1893 P-delta analysis is required for all structural category in all zones. I tried adding Pdelta analysis in STADD model as per below syntax, could you please help me in verifying if I am using correct syntax/philosophy for Pdelta analysis for seismic case.

Kindly note that I have used SEISMIC definition in this case and called the same in Pure Seismic Load case along with Seismic loadings from different components mounted on Steel structure i.e Vessel/Piping etc. and added Pdelta analysis with Change Command at end. Kindly advise if below will provide accurate results.

STADD SYNTAX

DEFINE IS1893 2015 LOAD PART4
ZONE 0.16 RF 4 I 1.5 SS 2 ST 2 DM 0.02
FLOOR WEIGHT
YRANGE 0 8 FLOAD 0.5 XRANGE 0 15 ZRANGE 0 10 GY
MEMBER WEIGHT
38 39 43 TO 46 49 52 53 56 57 60 TO 62 65 68 TO 72 76 TO 81 86 87 101 TO 106 -
109 112 113 118 124 125 138 TO 140 152 154 TO 157 161 TO 164 167 182 186 -
189 191 193 259 261 277 279 283 284 302 306 310 320 324 325 336 337 342 347 -
364 369 370 373 375 397 399 402 UNI 0.25
*324 UNI 0 0.25 0
*68 UNI 0 0.25 0.95
*68 UNI 0 0.25 0
170 TO 172 175 CON 20.3
191 192 195 196 CON 7.5
203 204 207 208 CON 42.3
275 276 281 282 CON 12.1
FLOOR WEIGHT
YRANGE 12 18 FLOAD 0.5 XRANGE 0 15 ZRANGE 0 10 GY
YRANGE 12 13 FLOAD 0.5 XRANGE 1 3 ZRANGE 1 3.5 GY
JOINT WEIGHT
149 154 WEIGHT 0.9
148 WEIGHT 1.8
150 152 165 173 WEIGHT 2.4
157 WEIGHT 1.35
160 WEIGHT 13.15
163 WEIGHT 11.1
165 WEIGHT 0.2
173 WEIGHT 1.75
177 WEIGHT 1.12
183 WEIGHT 5
184 WEIGHT 37.3
185 WEIGHT 0.1
189 205 WEIGHT 1.05
194 WEIGHT 11.05
199 WEIGHT 0.1
198 WEIGHT 8.3
207 WEIGHT 32.45
209 WEIGHT 26.85
211 WEIGHT 13
217 WEIGHT 0.5
218 WEIGHT 0.1
220 WEIGHT 0.4
221 WEIGHT 0.1
SELFWEIGHT 1.1
************************
LOAD 1 LOADTYPE Seismic TITLE SESIMIC LOAD (+X)
1893 LOAD X 1
MEMBER LOAD
170 TO 172 175 CON GX 8.2
175 CON GY -8.7
172 CON GY 8.7
191 192 195 196 CON GX 3
196 CON GY -18.3
195 CON GY 18.3
275 276 281 282 CON GX 2.8
282 CON GY -17.7
281 CON GY 17.7
203 204 207 208 CON GX 16.9
208 CON GY -155.8
207 CON GY 155.8
JOINT LOAD
149 154 FX 5.8
148 FX 0.2
150 152 165 173 FX 0.8
157 FX 4.35
160 FX 0.3
163 FX 1
165 FX 0.1
173 FX 4.3
177 FX 0.1
183 FX 1.6
184 FX 6.6
185 FX 0.2
189 205 FX 0.1
194 FX 0.8
199 FX 0.1
198 FX 7.3
207 FX 2.15
209 FX 3.2
211 FX 2.25
217 FX 5.35
218 FX 0.4
220 FX 3.3
221 FX 3.7
PDELTA ANALYSIS SMALLDELTA
CHANGE

Hello Surojit, can you reply to above query of mine. That will be helpful.

Thankyou in advance.

Hello,  Surojit,

On this warning, I have other two questions:

1) As per SECTION 4.4.2 & 4.4.3 of IS800-2007 , MOMENT AMPLIFICATION FACTORS is defined as Cy Cz or Cmy Cmz; While in the program warning, MOMENT AMPLIFICATION FACTORS are marked as KY OR KZ? As We know, KX KY or KZ is effective length of members in STAAD. So which are MOMENT AMPLIFICATION FACTORS, Cmy & Cmz or KY & KZ?  

2)As per SECTION 4.4.2 & 4.4.3 &Table 18 of IS800-2007, for members with moment released at both ends (eg. truss member), How does the THE VALUE OF MOMENT AMPLIFICATION FACTORS Cmy  or Cmz  obtained from Table 18 is greater than1.4?

Thanks for your prompt reply!

1. In amendment no. 1 (January 2012), cl.4.4.2 has been modified and moment amplification factor is denoted as Ky, Kz, not Cy,Cz. You can check that for more details. Also, this Ky,Kz is not same as effective length parameter, it is calculated as per cl.9.3.2.2.
2. Currently, STAAD designs all member as general member considering correct design force, which mean, for all member including truss, capacity at relevant sections are calculated and that is compared against the actual design force. So irrespective of any member specification, this warning is reported. 

Check this post for more details -- communities.bentley.com/.../warnings-in-is800-2007