Filter
Top Products
STAAD Commands and Input Instructions
Section 5
5-206
Example
DEFINE IBC 2003 LOAD
SDS 0.6 SD1 .36 S1 .3 I 1.0 RX 3 RZ 4 SCL 4 CT 0.032
SELFWEIGHT
JOINT WEIGHT
51 56 93 100 WEIGHT 1440
101 106 143 150 WEIGHT 1000
151 156 193 200 WEIGHT 720
Steps to calculate base shear are as follows:
1. Time Period of the structure is calculated based on section
1617.4.2 of IBC 2000, and section 9.5.5.3 of ASCE 7-02. This
is reported in the output as Ta.
2. The period is also calculated in accordance with the Rayleigh
method. This is reported in the output as T.
3. The user may override the Rayleigh based period by specifying
a value for PX or PZ (Items f7 and f8) depending on the
direction of the IBC load.
4. The governing Time Period of the structure is then chosen
between the above-mentioned two periods, and the additional
guidance provided in clause 1617.4.2 of IBC 2000, and section
9.5.5.3 of ASCE 7-02. The resulting value is reported as "Time
Period used".
5. The Design Base Shear is calculated based on equation 16-34
of IBC 2000 and equation 9.5.5.2-1 of ASCE 7-02. It is then
distributed at each floor using the rules of clause 1617.4.3,
equations 16-41 and 16-42 of IBC 2000, and, clause 9.5.5.4,
equations 9.5.5.4-1 & 9.5.5.4-2 of ASCE 7-02.
6. If the ACCIDENTAL option is specified, the program
calculates the additional torsional moment. The lever arm for
calculating the torsional moment is obtained as 5% of the
building dimension at each floor level perpendicular to the
direction of the IBC load (clause 1617.4.4.4 of IBC 2000 and,
9.5.5.5.2 of ASCE 7-02). At each joint where a weight is
located, the lateral seismic force acting at that joint is