Steel truss bridges - Computational Analysis and Design of Bridge Structures - page 311

y

x

z
Figure 10.14 The case study pedestrian bridge model.

As for horizontal wind, STAAD.Pro provides the wind-load generation
utility for analyzing wind loadings. The utility takes wind pressure at vari-
ous heights as the input and converts it to joint loads in specific load cases.
Meanwhile, an upward vertical linear load of 9.6 × 10 −4 MPa (0.020 ksf)
times the width of the deck should be applied to windward quarter-point of
the deck.
Various methods can be used for performing earthquake analysis.
Response spectrum analysis is used in this example. STAAD.Pro provides a
utility to specify and apply the response spectrum loads for dynamic analy-
sis. The graph of frequency-acceleration pairs are calculated based on the
input requirements of the command and as defined in the code. As mass
is processed in a form of directional load in STAAD.Pro, self-weight that
represents the structure mass has to be applied to all x , y , and z directions
so that accelerations in all these directions will be considered in the 3D
dynamic analysis.
Alternatively, time history analysis can be adopted for earthquake
analysis. This case study uses the explicit definition with the time
versus acceleration data of “IMPERIAL VALLEY 10/16/79 0658,
WESTMORELAND FIRE” from USGS database to generate the time
history analysis table.
STAAD.Pro covered the information of total applied load and struc-
tural reaction for each load case and the response spectrum analysis results
including modal base actions, participation factors, and the eigenvalue
solution for each mode. The first six eigenvalue solutions are 1.759, 1.957,
2.951, 4.146, 4.733, and 6.156 cycles per second. Figure 10.15 shows the
first two mode shapes where the first mode is mainly in lateral ( z ) direction
and the second mode is in vertical ( y ) direction.
Maximum reactions for all degrees of freedom are presented in
Figure 10.16. Reactions output from the analysis are checked first