Dynamic/earthquake analysis - Computational Analysis and Design of Bridge Structures - page 536

• Use of the capacity spectrum for deining the earthquake demand for
each mode.
• The number of modes that should be considered.

Step-by-step extended MPA procedure for bridges was proposed and pre-
sented in detail in the works of Ahmed (2010) and Ahmed and Fu (2012).

17.4 3D illustrateD examPle of
earthquake analysis By sPa, mPa,
anD nl-tha—fhWa BriDge no. 4

This example is used to illustrate the MPA and its comparison with stan-
dard pushover analysis (SPA) and NL-THA. This bridge is one of the
FHWA examples series (Mast et al.) and was modified for nonlinear anal-
yses. It consists of three spans. The total length is 97.5 m (320′) with
span lengths of 30.5-36.6-30.5 m (100′-120′-100′), respectively. All sub-
structure elements are oriented at a 30° skew from a line perpendicular
to a straight bridge centerline alignment. Figure 17.18 shows plan and

L BRG abut A L BRG abut B

320′ 0″

L Bent 1 L Bent 2

100′ 0″ 120′ 0″ 100′ 0″

30° skew
(TYP)

1 3

3

Plan

(a)

EXP FIX

PIN

FIX EXP

PIN

Elevation
(Looking parallel to bents)

(b)

Figure 17.18 (a) Plan and (b) elevation views of illustration example 1. (Data from Mast, R.,
Marsh, L., Spry, C., Johnson, S., Grieenow, R., Guarre, J., and Wilson, W.,
Seismic Design of Bridges—Design Examples 1-7 [FHWA-SA-97-006 thru 012] ,
USDOT/FHWA, September 1996.)