Bridge Design: Loads, Girder Design, Bearing Design, Bridge Economics

BRIDGE DESIGN
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Question 4
Loads
As the magnitudes of the dead loads can be predicted easily as compared to live loads, the live
load factors are greater.
The impact factor for a bridge is mainly governed by dynamic / moving vehicular loads and
affects the superstructure. But for the expansion joint the effects might not be as pronounced,
thus although it may affect the slab but won't affect the global performance (Shin et al., 2016).
There are numerous load combinations to assess the impact or to find the design load while
designing a bridge. These are dead loads, live loads, earthquake loads, wind loads, etc.
The moving trucks indicate live / dynamic / moving loads which contribute significantly to
bridge failures. Unless we take into account these loads we cannot assess the serviceability of the
structure. These are temporary loads
If we just place a stationary truck then it will only act as dead load to the structure but we won't
be able to assess the impact on the entire bridge span w.r.t. time which is done by influence line
diagram.
For LL, the appropriate load factor actually depends on the combination.
For a combination of LL with DL it is 1.5
For LL with DL and EL it is 1.2
On an average for heavy mining trucks it is 1.33