Lecture # 08

The Design of a Deck Slabs

Load Distribution.The truck shown in the figure in the next slide is clearly transferring most of its load to the stringer immediately below the left front and rear tires. However, the two adjacent stringers also carry some of the load of the truck, since the deck serves to transfer loads to other girders. In addition to the deck, other secondary members help transfer loads, such as the channel diaphragms, cross-frames, etc.

The issue is then, how are the loads distributed among the stringers? There are many factors involved in transferring loads, such as:

a) the type of deck,b) the spacing S between stringers (girders),c) the spacing of secondary members,d) the stiffness of the deck and stringers, and of the secondary members,e) the type of lateral bracing used, andf) the size of the loads and their position on the deck.

The distribution is easily amenable to closed-form calculations. However, AASHTO addresses the issue of load distribution using only the first two, via a distribution factor (DF). For example, using Table 3.4 on slide 3, a concrete deck with two lanes and stringers at 14 feet spacing will yield a DF of,

7.0 1.275.5 5.5

& 1.27 20 25.4

S ftDF

DistributedLoad DF one set of front rear wheels kips kips

= = =

= = =

Table 3.4

AASHTOs wheel load distribution in longitudinal beams.

Table 3.5 AASHTO wheel Load Distribution in transverse beams.

Design segment for a reinforced concrete deck slab.

Design Example

This is the final design of the reinforced concrete deck for the design example.

This figure shows the cross-section of an open drain used to drain the runoff from the deck.

Repairs, such as patching, requires the removal of full-depth concrete surrounding the main reinforcing.

Cathodic protection is used to prevent the adverse corrosive effects of chloride on the steel reinforce-ment. An impressed current is introduced to reverse the flow of negative chlorine ions to the positive steel.