Design of Flexural Steel Members - Design of Modern Steel Railway Bridges - page 300

stiffener connections, particularly when they serve as bracing connection plates, in
order to preclude detrimental out-of-plane web gap weld fatigue effects.

7.2.7 B OX G IRDER D ESIGN
Box girders have a high flexural capacity and torsional rigidity. The design of box
girders is generally analogous to the design of plate girders. However, the large com-
pression flange makes it necessary to utilize stiffened steel plates or concrete slabs.
Steel plate decks are often used when span lengths are large enough that the dead load
from concrete slab decks becomes a disproportionate portion of the total load on the
span. The top flange typically also serves as the ballasted deck.

7.2.7.1 Steel Box Girders

Steel box girders typically employ an orthotropic steel deck plate. The strength (yield
and stability), fatigue, and serviceability design of orthotropic deck plates require
careful consideration of fabrication and details. The design of orthotropic plate deck
bridges is beyond the scope of this topic and the reader is referred to topics by
Wolchuk (1963), Cusens and Pama (1979), Troitsky (1987), and others that provide
definitive information regarding the analysis and design of orthotropic steel deck plate
bridges.

7.2.7.2 Steel-Concrete Composite Box Girders

The design of steel-concrete composite box girder spans is also generally analogous
to that for steel-concrete composite plate girder spans. The latter are discussed in
greater detail in this chapter.

7.3 SERVICEABILITY DESIGN OF NONCOMPOSITE
FLEXURAL MEMBERS
AREMA (2008) recommends that mid-span deflection of simply supported spans
due to live load plus impact,

I, not exceed L /640, where L is the span length.
Some engineers or bridge owners recommend even more severe live load plus impact
deflection criteria to attain stiffer spans, which offer improved performance from a
track-train dynamics perspective.
It is also recommended that camber be provided for dead load deflections in spans
exceeding 90 ft. Camber of truss spans is recommended to account for deflections
from dead load plus a live load of 3000 lb per track foot.
The serviceability criteria for steel railway spans are also discussed in Chapter 5.

Δ LL +

Example 7.1

A 90 ft simple span steel ( F y = 50 ksi) DPG is to be designed for the forces

shown in Table E7.1.