TR.31.8.3 Mass Model Using Reference Load
Mass type reference loads can be used to create mass model which will be used for all types of analysis, including seismic, response spectrum, time history, and any other dynamic analysis.
The program follows the following logic:
- If a reference load type MASS is present, then the mass model is formed by combining all MASS reference loads.
- If reference load type MASS is not present, then the mass model is formed by combining all gravity reference loads. Warnings are displayed in the analysis output to alert you to this fact.
- If neither reference load types MASS nor gravity are present, then the mass model is formed by combining all DEAD reference loads. If any LIVE reference loads are present, then they will also be combined to this mass model. Warnings are displayed in the analysis output to alert you to this fact.
Mass model will be formed from Gravity or Dead/Live reference loads in case Mass reference load types are not present.
General Format
DEFINE REFERENCE LOADS
LOAD Ri title
…
Load header and items
…
LOAD Rj LOADTYPE MASS title
…
Load header and items
…
END DEFINE REFERENCE LOADS
DEFINE UBC/1893/… LOAD
ZONE …
LOAD 1 title
UBC/1893/… LOAD X f1
LOAD 2 title
UBC/1893/… LOAD Z f2
LOAD 3 title
SPECTRUM …
The mass model is defined using the LOADTYPE MASS command. This mass model will be used for all types of analysis, including static equivalent, response spectrum, time history, and simply Eigen solution. If the load type MASS is missing and also no mass is defined in the corresponding seismic or dynamic analysis load cases, the program will report error as mass is missing
If a mass model using reference load type MASS is defined and also a seismic weight table is defined in DEFINE UBC/1893/… DEFINITION (or seismic mass is defined as part of a response spectrum or time history loading), the program will simply the later in place of the former for the seismic weight calculation. The program will issue a warning message in the analysis output. Care should be taken so that the mass model is not defined twice.
Example
UNIT FEET KIP DEFINE REF LOAD LOAD R1 LOADTYPE MASS * MASS MODEL SELFWEIGHT X 1 SELFWEIGHT Y 1 SELFWEIGHT Z 1 JOINT LOAD 17 TO 48 FX 2.5 FY 2.5 FZ 2.5 49 TO 64 FX 1.25 FY 1.25 FZ 1.25 * LOAD R2 SELFWEIGHT Y -1 JOINT LOAD 17 TO 48 FY -2.5 49 TO 64 FY -1.25 END DEF REF LOAD ************************************************************ DEFINE UBC LOAD ZONE 0.38 I 1 RWX 5.6 RWZ 5.6 STYP 2 CT 0.032 NA 1.3 NV 1.6 *********************************************************** DEFINE TIME HISTORY TYPE 1 FORCE 0.0 -0.0001 0.5 0.0449 1.0 0.2244 1.5 0.2244 2.0 0.6731 2.5 -0.6731 TYPE 2 ACCELERATION 0.0 0.001 0.5 -7.721 1.0 -38.61 1.5 -38.61 2.0 -115.82 2.5 115.82 ARRIVAL TIMES 0.0 DAMPING 0.05 *********************************************************** LOAD 1 UBC LOAD X 0.75 *********************************************************** LOAD 2 BC LOAD Z 0.75 *********************************************************** LOAD 3 SPECTRUM CQC X 0.174075 ACC DAMP 0.05 SCALE 32.2 0.03 1.00 ; 0.05 1.35 ; 0.1 1.95 ; 0.2 2.80 ; 0.5 2.80 ; 1.0 1.60 *********************************************************** LOAD 4 SPECTRUM CQC Z 0.174075 ACC DAMP 0.05 SCALE 32.2 0.03 1.00 ; 0.05 1.35 ; 0.1 1.95 ; 0.2 2.80 ; 0.5 2.80 ; 1.0 1.60 ********************************************************** LOAD 5 TIME LOAD 53 57 37 41 21 25 FX 1 1 GROUND MOTION X 2 1 ***********************************************************