ADDED DYNAMIC MASS
I have used Staad to perform (response spectra) dynamic analyses before, but
with the types of structures I analyze here, I have only used the added dynamic
mass option once. I have inserted the loads from my model below (minus the dead load case). Just so I could verify the added dynamic
mass, I have commented out the dynamic structure self-weight.
When I run this, and check the mass participation/base
shears from the dynamic output, it looks about right for all three
directions. (the sum of: % mass participation x Sa @ appropriate
frequency x total weight of the dynamic mass)
So, I KNOW the dynamic mass is there.
The mode shapes look like
Here’s the crux: Base
shears look about right, but the members to which I am applying the dynamic
mass below show VERY, VERY little shear and bending…and when I look at the mode
shapes, there doesn’t appear to be any bending in these members. Can anyone comment on this? BTW, the plate loads don’t appear to have the
same problem. The plate is showing
reasonable stresses and deflected shapes
…..thanks
LOAD 10 E/W SEISMIC
*SELFWEIGHT X 1
*SELFWEIGHT Y 1
*SELFWEIGHT Z 1
ELEMENT LOAD
2001 TO 2035 2039 TO 2073 2078 TO 2113 2120 TO 2155 2162 TO
2197 2204 TO 2239 -
2246 TO 2281 2288 TO 2323 2330 TO 2365 2372 TO 2407 2414 TO
2449 -
2456 TO 2491 2498 TO 2533 2540 TO 2575 2581 TO 2615 2619 TO
2653 -
2657 TO 2691 2695 TO 2729 2734 TO 2769 2776 TO 2811 2818 TO
2853 -
2860 TO 2895 2902 TO 2937 2944 TO 2979 2986 TO 3021 3028 TO
3063 -
3070 TO 3105 3112 TO 3147 3154 TO 3189 3196 TO 3231 3237 TO
3271 -
3276 TO 3310 PR GY 104.6
MEMBER LOAD
1703 TO 1705 1717 1718 1723 UNI GX 272.0
1709 TO 1712 1724 1725 1727 1728 UNI GZ 313.7
SPECTRUM SRSS X 1 ACC SCALE 32.2 DAMP 0.05
10 0.001; 5 0.017; 3.333 0.027; 2.5 0.033; 2 0.041; 1.667
0.05; 1.429 0.061;
1.25 0.071; 1.111 0.082; 1 0.093; 0.5 0.194; 0.333 0.279;
0.25 0.406;
0.2 0.566; 0.167 0.863; 0.167 1.175; 0.143 1.175; 0.083
1.175; 0.083 0.923;
0.067 0.923; 0.067 1.107; 0.05 1.107; 0.048 1.107; 0.048
0.974; 0.045 0.802;
0.033 0.582; 0.025 0.456; 0.02 0.378; 0.017 0.344; 0.014
0.315; 0.013 0.295;
0.011 0.281; 0.01 0.27;
LOAD 20 VERTICAL SEISMIC
SPECTRUM SRSS Y 1 ACC SCALE 32.2 DAMP 0.05
10 0.001; 5 0.01; 3.333 0.015; 2.5 0.022; 2 0.031; 1.667
0.041; 1.429 0.051;
1.25 0.061; 1.111 0.071; 1 0.08; 0.5 0.166; 0.333 0.237;
0.25 0.297;
0.2 0.357; 0.167 0.424; 0.143 0.525; 0.143 0.96; 0.04 0.96;
0.04 0.686;
0.033 0.686; 0.029 0.686; 0.029 0.581; 0.025 0.475; 0.02
0.398; 0.017 0.355;
0.014 0.328; 0.013 0.31; 0.011 0.297; 0.01 0.288;
LOAD 30 N/S SEISMIC
SPECTRUM SRSS Z 1 ACC SCALE 32.2 DAMP 0.05
10 0.01; 5 0.042; 3.333 0.065; 2.5 0.082; 2 0.095; 1.667
0.105; 1.429 0.115;
1.25 0.122; 1.111 0.129; 1 0.137; 0.5 0.241; 0.333 0.336;
0.25 0.421;
0.2 0.508; 0.167 0.577; 0.143 0.65; 0.125 0.722; 0.111
0.802; 0.1 1;
0.1 1.347; 0.05 1.347; 0.05 1; 0.033 0.558; 0.025 0.438;
0.02 0.37; 0.017 0.33;
0.014 0.299; 0.013 0.279; 0.011 0.265; 0.01 0.253;