Introduction - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 30

that the stress of the damaged truss member was not effectively redistributed
to other members, except for those adjacent to the damage.
Recently, Cheng et al. [ 1.54 , 1.55 ] performed a numerical study on steel
truss bridges with welded box section members and bowknot integral joints.
The investigation [ 1.54 ] highlighted the linear and nonlinear mechanical
behaviors of the bridges. The truss studied was simply supported at two
end nodes of bottom chords with two concentrated dead and live loads
being applied at each unsupported bottom chord node. The finite element
method was employed to analyze the elastic and elastoplastic behaviors of
trusses with bowknot/conventional integral joints. Based on the study, it
was concluded that the axial forces of members were very insignificantly
enhanced by the section shrinking of the member ends. It was also con-
cluded that the secondary moments at the member ends and the sectional
maximum stresses of the unshrunken segments of the truss are significantly
reduced by the section shrinking of the member ends but the vertical stiffness
and elastic stability of the bowknot truss are deteriorated compared to the
conventional one. Finally, it was shown that when the steel strength of
the shrunken segments has been moderately enhanced, the ultimate bearing
capacities of axially compressed shrunken members and of Warren trusses
with bowknot integral joints are as high as those of uniform members
and of conventional trusses, respectively. The study [ 1.55 ] presented a min-
imum weight optimization based on the provisions of current design codes
for both conventional and bowknot trusses. The optimization investigated
was illustrated through analytic derivation of minimumweight optimization
of a single member. The results of the numerical study indicated that the
member weight reduction increased as the primary stress to secondary stress
ratio, or the end moment reduction, was increased. The authors extended
the minimum weight optimization of the truss on the basis of linear finite
element analysis of the same truss that was discussed in [ 1.54 ] , by the use
of first-order optimization method. It was concluded that the cost rise
due to steel strength enhancement of shrunken segments was taken into
account in the nominal weight of whole truss. Also, a series of requirements
related to truss vertical stiffness, member strength, member stability, and
truss stability were set as constraint functions.
1.3.3 Recent Investigations on Steel-Concrete Composite
Bridges
The short-term and long-term behaviors of composite steel box girder brid-
ges have been investigated theoretically by Kwak et al. [ 1.56 ] . The study