how does increasing the section size effects the reaction load

Question

Sir, 
 Analyzed a steel structure for the seismic loads and derived the support reactions. To reduce the reaction load at supports, tried to increase the steel section by adding plates to its cross section in one direction and could see a reduction in reaction. 
 Clarification: how does an increase in section reduces the reaction load?

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 STAAD SPACE
START JOB INFORMATION
ENGINEER DATE 29-Aug-21
END JOB INFORMATION
INPUT WIDTH 79
UNIT MMS NEWTON
JOINT COORDINATES
1 0 0 0; 2 0 0 -1440; 3 0 0 -1750; 4 0 1830 0;
MEMBER INCIDENCES
1 1 2; 2 2 3; 3 4 2;
START USER TABLE
TABLE 1 C:\USERS\NIRMAL\DESKTOP\250.UPT
END
DEFINE MATERIAL START
ISOTROPIC STEEL
E 199947
POISSON 0.3
DENSITY 7.68191e-005
ALPHA 6e-006
DAMP 0.03
TYPE STEEL
STRENGTH FY 248.21 FU 399.894 RY 1.5 RT 1.2
END DEFINE MATERIAL
MEMBER PROPERTY INDIAN
1 TO 3 TABLE FR ISMC250
CONSTANTS
MATERIAL STEEL ALL
SUPPORTS
1 4 FIXED
LOAD 1 LOADTYPE Dead TITLE DL
SELFWEIGHT Y -1 
JOINT LOAD
3 FY -170
LOAD 3 LOADTYPE None TITLE SL(SSE)
JOINT LOAD
3 FZ 9704
LOAD 5 LOADTYPE None TITLE SL(SSE)-VE
JOINT LOAD
3 FZ -9704
LOAD 9 LOADTYPE Seismic TITLE EQX(SSE)
SELFWEIGHT X 1 
SELFWEIGHT Y 1 
SELFWEIGHT Z 1 
JOINT LOAD
3 FX 9704
3 FZ 9704
3 FZ 9704
3 FX 170
3 FY 170
3 FZ 170
SPECTRUM SRSS X 1 ACC DAMP 0 LIN MIS 0
0.030303 8174.6; 0.0347826 8501.5; 0.0431965 8501.5; 0.0508906 8966.1;
0.0522193 8969.2; 0.058651 8969.2; 0.058997 9123.6; 0.0591716 9327.4;
0.0626959 9644.9; 0.0630915 9729.8; 0.0641026 10133.9; 0.0645161 10213;
0.0649351 10371.2; 0.0657895 10539.8; 0.0701754 10624.9; 0.0719424 10624.9;
0.0724638 10626.2; 0.0738007 10943.3; 0.0740741 11074.5; 0.0760456 11364.1;
0.0766283 11551.6; 0.0775194 11974; 0.078125 12118.7; 0.0787402 12383.8;
0.0793651 12719.2; 0.0796813 13071.5; 0.08 13188.3; 0.0806452 13305.2;
0.0809717 14028.4; 0.0823045 14406.8; 0.0829876 14518.7; 0.083682 14742.4;
0.0843882 15518.5; 0.0851064 15721; 0.0858369 15822.2; 0.0873362 16622.4;
0.0877193 17246.8; 0.0881057 17477.6; 0.0888889 17708.5; 0.0896861 18170.2;
0.0909091 19166; 0.0913242 19422; 0.0921659 19677.9; 0.0925926 19933.9;
0.0930233 20490.5; 0.0938967 20936.8; 0.0943396 21771.6; 0.0970874 22181.7;
0.102564 22181.7; 0.103627 22396.2; 0.104167 23057.5; 0.10582 24736.5;
0.106952 25922.4; 0.108108 26878.7; 0.108696 27241.5; 0.10929 27550.9;
0.148148 27550.9; 0.150376 27456.4; 0.151515 27271.7; 0.152672 27179.3;
0.153846 26916.1; 0.15625 26845; 0.163934 26845; 0.165289 26451.6;
0.168067 26286.3;
0.17094 25463.1; 0.172414 24949.6; 0.173913 23889.9; 0.175439 23343.6;
0.178571 22843.8; 0.18018 22264.1; 0.181818 21301.7; 0.185185 21241.2;
0.186916 21938.2; 0.188679 22902; 0.192308 25096.3; 0.196078 26326.9;
0.20202 27465.4; 0.222222 27465.4; 0.227273 28220.2; 0.229885 28975;
0.243902 34468.2; 0.246914 35054.2; 0.253165 35640.3; 0.27027 37774.7;
0.273973 37988.2; 0.28169 38628.5; 0.294118 38657.8; 0.4 38657.8; 
0.416667 32560.5;
0.425532 27363.2; 0.454545 20917.2; 0.47619 18391.2; 0.487805 15865.3;
0.540541 11633; 0.555556 9960; 0.588235 8286.9; 0.625 8143.3; 0.645161 7695.8;
0.666667 6608; 0.689655 5967.8; 0.8 5168.4; 0.833333 5050.4; 0.869565 4540.4;
0.952381 4257.6; 1 4257.6; 1.05263 4061.5; 1.17647 3856.7; 1.25 3448.6;
1.42857 3238; 1.53846 2813.9; 1.66667 2503.7; 2 2342.5; 2.22222 2061.9;
2.5 1672.5; 2.85714 1485; 4 1240.4; 20 1240.4;
LOAD 10 LOADTYPE Seismic TITLE EQY(SSE)
SPECTRUM SRSS Y 1 ACC DAMP 0 LIN MIS 0
0.030303 5325.7; 0.0452489 6286.1; 0.0457666 6286.1; 0.045977 6291; 
0.0465116 6410;
0.0490196 6410; 0.0492611 6466.4; 0.0493827 6544.2; 0.0496278 6744.1;
0.0502513 6886.6; 0.0506329 7118; 0.0508906 7315.2; 0.0522193 7334.6;
0.0524934 7334.6; 0.0584795 8575.1; 0.058651 8738; 0.0588235 8945.3;
0.0591716 9404.5; 0.0634921 9577.7; 0.0641026 9578.4; 0.0645161 9634;
0.0649351 9745.2; 0.0657895 10592.9; 0.0675676 10784.1; 0.0680272 10887.1;
0.0682594 10990.1; 0.0687285 11610.7; 0.0692042 11718.4; 0.0696864 11772.2;
0.0701754 11879.9; 0.0704225 12331.5; 0.0711744 12812.2; 0.0714286 12875.8;
0.0722022 13208.9; 0.0724638 13390.4; 0.0732601 14086.7; 0.0735294 14214.3;
0.0740741 14597.2; 0.075188 15025; 0.0754717 15173.2; 0.0757576 15342.1;
0.0760456 15615.9; 0.0775194 17226.2; 0.078125 17548.3; 0.0787402 17801;
0.0793651 17888; 0.0796813 17975; 0.0888889 17975; 0.0896861 18035.3;
0.0900901 18288.5; 0.0909091 18838.2; 0.0913242 19002.8; 0.0925926 19331.9;
0.0934579 19371.2; 0.0938967 19487.2; 0.0943396 19689.7; 0.0947867 20049.3;
0.0952381 20544.4; 0.0961538 21670; 0.0970874 22699.1; 0.097561 22699.1;
0.0990099 22708.5; 0.0995025 22745.9; 0.1 22818.5; 0.100503 22930.5;
0.10101 23078.6; 0.101523 23256.3; 0.102041 23456.4; 0.102564 23705.3;
0.103093 23997.7; 0.103627 24321.4; 0.104167 24665.7; 0.104712 25053.3;
0.105263 25494.6; 0.10582 25978.7; 0.106952 26989.5; 0.108108 27776.4;
0.108696 28088.3; 0.10929 28215.1; 0.110497 28414.5; 0.150376 28414.5;
0.151515 27904.4; 0.152672 27649.4; 0.15625 26658.9; 0.15748 25112.2;
0.188679 24914; 0.190476 24677.5; 0.192308 24204.5; 0.19802 23320.8;
0.20202 21597.8; 0.204082 19985.1; 0.206186 19233.9; 0.212766 17215.9;
0.215054 16983.6; 0.21978 16735.1; 0.224719 16702.6; 0.227273 16439;
0.229885 15404.2; 0.232558 14633.2; 0.238095 13780.4; 0.243902 13388;
0.246914 12995.6; 0.253165 12523.4; 0.25974 12582.9; 0.263158 12644.7;
0.27027 12856.5; 0.277778 12962.4; 0.294118 13385.6; 0.4 13385.6; 
0.416667 10524.6;
0.425532 8319.5; 0.454545 5995.9; 0.47619 5462.1; 0.487805 4928.4; 
0.540541 4175.2;
0.555556 3764.7; 0.588235 3354.1; 0.625 3223.5; 0.645161 3104; 0.666667 2849.2;
0.689655 2714.1; 0.8 2523.3; 0.869565 2316.5; 1.05263 2316.5; 1.17647 2221.9;
1.25 2003.3; 1.42857 1920; 1.53846 1699; 1.66667 1609.3; 2 1479.5;
2.22222 1321.4;
2.5 1087.3; 2.85714 958.2; 4 809.5; 20 809.5;
LOAD 11 LOADTYPE Seismic TITLE EQZ(SSE)
SPECTRUM SRSS Z 1 ACC DAMP 0 LIN MIS 0
0.030303 6954.4; 0.0347826 7099.6; 0.0426439 7099.6; 0.0544959 7438.8;
0.0554017 7682.4; 0.0576369 7758.7; 0.058309 7758.7; 0.0588235 7829.8;
0.0591716 8003.5; 0.0630915 8003.5; 0.0657895 8195.4; 0.0696864 8195.4;
0.0711744 8284.8; 0.0732601 8383.1; 0.0740741 8577.5; 0.0775194 9189.3;
0.0784314 9425; 0.0790514 9677.2; 0.0796813 10151.8; 0.08 10290.1; 
0.0806452 10428.4;
0.0809717 11281.1; 0.0823045 11846.4; 0.0829876 11936.8; 0.083682 12117.7;
0.0843882 12623.8; 0.0851064 12823.7; 0.0858369 12923.6; 0.0865801 13322;
0.0873362 13641.4; 0.0877193 14521.2; 0.0881057 14941.7; 0.0888889 15362.3;
0.0896861 16203.3; 0.0909091 16897.7; 0.0913242 16999.9; 0.0917431 17051;
0.0921659 17127.6; 0.0930233 17543.4; 0.0938967 17586.3; 0.119048 17586.3;
0.120482 17650.8; 0.121951 17757; 0.122699 17863.2; 0.124224 18365.1;
0.125786 19487.4; 0.126582 20527.6; 0.12987 22672.1; 0.13245 23952.2;
0.134228 24382.7; 0.136986 24382.7; 0.138889 24500.6; 0.188679 24500.6;
0.190476 23913.5; 0.194175 23734.1; 0.196078 24324.7; 0.20202 25924.7;
0.206186 26743.9; 0.210526 27153.5; 0.222222 29201.6; 0.224719 29767.8;
0.227273 30412.4; 0.229885 31408.3; 0.232558 32579.9; 0.235294 33839.4;
0.238095 35142.7; 0.243902 37793.3; 0.246914 37993.8; 0.253165 38194.3;
0.338983 38194.3; 0.37037 35320.6; 0.377358 34171.1; 0.4 30184.5; 
0.416667 26161.1;
0.425532 22504.4; 0.454545 17569.4; 0.47619 15571.2; 0.487805 13573.1;
0.540541 10721.9; 0.555556 9150.7; 0.588235 7579.5; 0.625 7414.7;
0.645161 7010.6;
0.666667 6111.1; 0.689655 5615.6; 0.740741 5323.9; 0.8 4721.2; 0.833333 4521.3;
0.869565 4110.9; 0.952381 4099.6; 1 4099.6; 1.05263 4071.4; 1.17647 3799;
1.25 3269.2; 1.42857 3157.5; 1.53846 2777.7; 1.66667 2497.3; 2 2298.2;
2.22222 2025.1; 2.5 1671; 2.85714 1482.9; 4 1240.5; 20 1240.5;
LOAD COMB 20 LC1(SSE)
1 1.0 9 1.0 3 1.0 
LOAD COMB 21 LC2(SSE)
1 1.0 10 1.0 3 1.0 
LOAD COMB 22 LC3(SSE)
1 1.0 11 1.0 3 1.0 
LOAD COMB SRSS 23 LC4(SSE)
-1 1.0 9 1.0 10 1.0 11 1.0 -3 1.0 1
LOAD COMB 24 LC1(SSE WITH -VE SL)
1 1.0 5 1.0 9 1.0 
LOAD COMB 25 LC2(SSE WITH -VE SL)
1 1.0 5 1.0 10 1.0 
LOAD COMB 26 LC3(SSE WITH -VE SL)
1 1.0 5 1.0 11 1.0 
LOAD COMB SRSS 27 LC4(SSE WITH -VE SL)
-1 1.0 -5 1.0 9 1.0 10 1.0 11 1.0 1
PERFORM ANALYSIS PRINT STATICS CHECK
FINISH

Fullscreen 
 modified model.txt 
 Download 
 
 STAAD SPACE
START JOB INFORMATION
ENGINEER DATE 29-Aug-21
END JOB INFORMATION
INPUT WIDTH 79
UNIT MMS NEWTON
JOINT COORDINATES
1 0 0 0; 2 0 0 -1440; 3 0 0 -1750; 4 0 1830 0;
MEMBER INCIDENCES
1 1 2; 2 2 3; 3 4 2;
START USER TABLE
TABLE 1 C:\Users\Nirmal\Desktop\250.UPT
END
DEFINE MATERIAL START
ISOTROPIC STEEL
E 199947
POISSON 0.3
DENSITY 7.68191e-005
ALPHA 6e-006
DAMP 0.03
TYPE STEEL
STRENGTH FY 248.21 FU 399.894 RY 1.5 RT 1.2
END DEFINE MATERIAL
MEMBER PROPERTY
1 TO 3 UPTABLE 1 250
CONSTANTS
MATERIAL STEEL ALL
SUPPORTS
1 4 FIXED
LOAD 1 LOADTYPE Dead TITLE DL
SELFWEIGHT Y -1 
JOINT LOAD
3 FY -170
LOAD 3 LOADTYPE None TITLE SL(SSE)
JOINT LOAD
3 FZ 9704
LOAD 5 LOADTYPE None TITLE SL(SSE)-VE
JOINT LOAD
3 FZ -9704
LOAD 9 LOADTYPE Seismic TITLE EQX(SSE)
SELFWEIGHT X 1 
SELFWEIGHT Y 1 
SELFWEIGHT Z 1 
JOINT LOAD
3 FX 9704
3 FZ 9704
3 FZ 9704
3 FX 170
3 FY 170
3 FZ 170
SPECTRUM SRSS X 1 ACC DAMP 0 LIN MIS 0
0.030303 8174.6; 0.0347826 8501.5; 0.0431965 8501.5; 0.0508906 8966.1;
0.0522193 8969.2; 0.058651 8969.2; 0.058997 9123.6; 0.0591716 9327.4;
0.0626959 9644.9; 0.0630915 9729.8; 0.0641026 10133.9; 0.0645161 10213;
0.0649351 10371.2; 0.0657895 10539.8; 0.0701754 10624.9; 0.0719424 10624.9;
0.0724638 10626.2; 0.0738007 10943.3; 0.0740741 11074.5; 0.0760456 11364.1;
0.0766283 11551.6; 0.0775194 11974; 0.078125 12118.7; 0.0787402 12383.8;
0.0793651 12719.2; 0.0796813 13071.5; 0.08 13188.3; 0.0806452 13305.2;
0.0809717 14028.4; 0.0823045 14406.8; 0.0829876 14518.7; 0.083682 14742.4;
0.0843882 15518.5; 0.0851064 15721; 0.0858369 15822.2; 0.0873362 16622.4;
0.0877193 17246.8; 0.0881057 17477.6; 0.0888889 17708.5; 0.0896861 18170.2;
0.0909091 19166; 0.0913242 19422; 0.0921659 19677.9; 0.0925926 19933.9;
0.0930233 20490.5; 0.0938967 20936.8; 0.0943396 21771.6; 0.0970874 22181.7;
0.102564 22181.7; 0.103627 22396.2; 0.104167 23057.5; 0.10582 24736.5;
0.106952 25922.4; 0.108108 26878.7; 0.108696 27241.5; 0.10929 27550.9;
0.148148 27550.9; 0.150376 27456.4; 0.151515 27271.7; 0.152672 27179.3;
0.153846 26916.1; 0.15625 26845; 0.163934 26845; 0.165289 26451.6; 
0.168067 26286.3;
0.17094 25463.1; 0.172414 24949.6; 0.173913 23889.9; 0.175439 23343.6;
0.178571 22843.8; 0.18018 22264.1; 0.181818 21301.7; 0.185185 21241.2;
0.186916 21938.2; 0.188679 22902; 0.192308 25096.3; 0.196078 26326.9;
0.20202 27465.4; 0.222222 27465.4; 0.227273 28220.2; 0.229885 28975;
0.243902 34468.2; 0.246914 35054.2; 0.253165 35640.3; 0.27027 37774.7;
0.273973 37988.2; 0.28169 38628.5; 0.294118 38657.8; 0.4 38657.8; 
0.416667 32560.5;
0.425532 27363.2; 0.454545 20917.2; 0.47619 18391.2; 0.487805 15865.3;
0.540541 11633; 0.555556 9960; 0.588235 8286.9; 0.625 8143.3; 0.645161 7695.8;
0.666667 6608; 0.689655 5967.8; 0.8 5168.4; 0.833333 5050.4; 0.869565 4540.4;
0.952381 4257.6; 1 4257.6; 1.05263 4061.5; 1.17647 3856.7; 1.25 3448.6;
1.42857 3238; 1.53846 2813.9; 1.66667 2503.7; 2 2342.5; 2.22222 2061.9;
2.5 1672.5; 2.85714 1485; 4 1240.4; 20 1240.4;
LOAD 10 LOADTYPE Seismic TITLE EQY(SSE)
SPECTRUM SRSS Y 1 ACC DAMP 0 LIN MIS 0
0.030303 5325.7; 0.0452489 6286.1; 0.0457666 6286.1; 0.045977 6291; 
0.0465116 6410;
0.0490196 6410; 0.0492611 6466.4; 0.0493827 6544.2; 0.0496278 6744.1;
0.0502513 6886.6; 0.0506329 7118; 0.0508906 7315.2; 0.0522193 7334.6;
0.0524934 7334.6; 0.0584795 8575.1; 0.058651 8738; 0.0588235 8945.3;
0.0591716 9404.5; 0.0634921 9577.7; 0.0641026 9578.4; 0.0645161 9634;
0.0649351 9745.2; 0.0657895 10592.9; 0.0675676 10784.1; 0.0680272 10887.1;
0.0682594 10990.1; 0.0687285 11610.7; 0.0692042 11718.4; 0.0696864 11772.2;
0.0701754 11879.9; 0.0704225 12331.5; 0.0711744 12812.2; 0.0714286 12875.8;
0.0722022 13208.9; 0.0724638 13390.4; 0.0732601 14086.7; 0.0735294 14214.3;
0.0740741 14597.2; 0.075188 15025; 0.0754717 15173.2; 0.0757576 15342.1;
0.0760456 15615.9; 0.0775194 17226.2; 0.078125 17548.3; 0.0787402 17801;
0.0793651 17888; 0.0796813 17975; 0.0888889 17975; 0.0896861 18035.3;
0.0900901 18288.5; 0.0909091 18838.2; 0.0913242 19002.8; 0.0925926 19331.9;
0.0934579 19371.2; 0.0938967 19487.2; 0.0943396 19689.7; 0.0947867 20049.3;
0.0952381 20544.4; 0.0961538 21670; 0.0970874 22699.1; 0.097561 22699.1;
0.0990099 22708.5; 0.0995025 22745.9; 0.1 22818.5; 0.100503 22930.5;
0.10101 23078.6; 0.101523 23256.3; 0.102041 23456.4; 0.102564 23705.3;
0.103093 23997.7; 0.103627 24321.4; 0.104167 24665.7; 0.104712 25053.3;
0.105263 25494.6; 0.10582 25978.7; 0.106952 26989.5; 0.108108 27776.4;
0.108696 28088.3; 0.10929 28215.1; 0.110497 28414.5; 0.150376 28414.5;
0.151515 27904.4; 0.152672 27649.4; 0.15625 26658.9; 0.15748 25112.2;
0.188679 24914; 0.190476 24677.5; 0.192308 24204.5; 0.19802 23320.8;
0.20202 21597.8; 0.204082 19985.1; 0.206186 19233.9; 0.212766 17215.9;
0.215054 16983.6; 0.21978 16735.1; 0.224719 16702.6; 0.227273 16439;
0.229885 15404.2; 0.232558 14633.2; 0.238095 13780.4; 0.243902 13388;
0.246914 12995.6; 0.253165 12523.4; 0.25974 12582.9; 0.263158 12644.7;
0.27027 12856.5; 0.277778 12962.4; 0.294118 13385.6; 0.4 13385.6; 
0.416667 10524.6;
0.425532 8319.5; 0.454545 5995.9; 0.47619 5462.1; 0.487805 4928.4;
0.540541 4175.2;
0.555556 3764.7; 0.588235 3354.1; 0.625 3223.5; 0.645161 3104; 0.666667 2849.2;
0.689655 2714.1; 0.8 2523.3; 0.869565 2316.5; 1.05263 2316.5; 1.17647 2221.9;
1.25 2003.3; 1.42857 1920; 1.53846 1699; 1.66667 1609.3; 2 1479.5;
2.22222 1321.4;
2.5 1087.3; 2.85714 958.2; 4 809.5; 20 809.5;
LOAD 11 LOADTYPE Seismic TITLE EQZ(SSE)
SPECTRUM SRSS Z 1 ACC DAMP 0 LIN MIS 0
0.030303 6954.4; 0.0347826 7099.6; 0.0426439 7099.6; 0.0544959 7438.8;
0.0554017 7682.4; 0.0576369 7758.7; 0.058309 7758.7; 0.0588235 7829.8;
0.0591716 8003.5; 0.0630915 8003.5; 0.0657895 8195.4; 0.0696864 8195.4;
0.0711744 8284.8; 0.0732601 8383.1; 0.0740741 8577.5; 0.0775194 9189.3;
0.0784314 9425; 0.0790514 9677.2; 0.0796813 10151.8; 0.08 10290.1; 
0.0806452 10428.4;
0.0809717 11281.1; 0.0823045 11846.4; 0.0829876 11936.8; 0.083682 12117.7;
0.0843882 12623.8; 0.0851064 12823.7; 0.0858369 12923.6; 0.0865801 13322;
0.0873362 13641.4; 0.0877193 14521.2; 0.0881057 14941.7; 0.0888889 15362.3;
0.0896861 16203.3; 0.0909091 16897.7; 0.0913242 16999.9; 0.0917431 17051;
0.0921659 17127.6; 0.0930233 17543.4; 0.0938967 17586.3; 0.119048 17586.3;
0.120482 17650.8; 0.121951 17757; 0.122699 17863.2; 0.124224 18365.1;
0.125786 19487.4; 0.126582 20527.6; 0.12987 22672.1; 0.13245 23952.2;
0.134228 24382.7; 0.136986 24382.7; 0.138889 24500.6; 0.188679 24500.6;
0.190476 23913.5; 0.194175 23734.1; 0.196078 24324.7; 0.20202 25924.7;
0.206186 26743.9; 0.210526 27153.5; 0.222222 29201.6; 0.224719 29767.8;
0.227273 30412.4; 0.229885 31408.3; 0.232558 32579.9; 0.235294 33839.4;
0.238095 35142.7; 0.243902 37793.3; 0.246914 37993.8; 0.253165 38194.3;
0.338983 38194.3; 0.37037 35320.6; 0.377358 34171.1; 0.4 30184.5; 
0.416667 26161.1;
0.425532 22504.4; 0.454545 17569.4; 0.47619 15571.2; 0.487805 13573.1;
0.540541 10721.9; 0.555556 9150.7; 0.588235 7579.5; 0.625 7414.7;
0.645161 7010.6;
0.666667 6111.1; 0.689655 5615.6; 0.740741 5323.9; 0.8 4721.2; 0.833333 4521.3;
0.869565 4110.9; 0.952381 4099.6; 1 4099.6; 1.05263 4071.4; 1.17647 3799;
1.25 3269.2; 1.42857 3157.5; 1.53846 2777.7; 1.66667 2497.3; 2 2298.2;
2.22222 2025.1; 2.5 1671; 2.85714 1482.9; 4 1240.5; 20 1240.5;
LOAD COMB 20 LC1(SSE)
1 1.0 9 1.0 3 1.0 
LOAD COMB 21 LC2(SSE)
1 1.0 10 1.0 3 1.0 
LOAD COMB 22 LC3(SSE)
1 1.0 11 1.0 3 1.0 
LOAD COMB SRSS 23 LC4(SSE)
-1 1.0 9 1.0 10 1.0 11 1.0 -3 1.0 1
LOAD COMB 24 LC1(SSE WITH -VE SL)
1 1.0 5 1.0 9 1.0 
LOAD COMB 25 LC2(SSE WITH -VE SL)
1 1.0 5 1.0 10 1.0 
LOAD COMB 26 LC3(SSE WITH -VE SL)
1 1.0 5 1.0 11 1.0 
LOAD COMB SRSS 27 LC4(SSE WITH -VE SL)
-1 1.0 -5 1.0 9 1.0 10 1.0 11 1.0 1
PERFORM ANALYSIS PRINT STATICS CHECK
FINISH

Both models is attached. Kindly help to understand.

Aswathi A · Accepted Answer

In both models, the first mode has the largest participation along the X direction - more than 99%. 
 
 The period of the 1st mode is 0.103 for the model with the ISMC section, and, 0.078 second for the model with the UPT section. 
 
 The spectral acceleration is 22.4 m/sec^2 (2.2755g) for a period of 0.103 second, and 12.248 m/sec^2 (1.249g) for a period of 0.078 second. 
 
 Thus, even though you have used a section that is heavier, the spectral acceleration is half of what it is for the lighter model. The drop in spectral acceleration more than offsets the increase in weight, so that the base shear drops by some 37% (25277 Newtons for the ISMC versus 14563 newtons for the UPT section). So, the reaction too drops by some 37%.