Q. Advantages of continuous multiple-span deck over simply supported multiple-span deck?

Movement joints are generally added to bridge structures to accommodate movements because of dimensional changes arising from temperature variation, shrinkage, creep and effect of pre-stress. Though provision of excessive movement joints must be avoided in design since movement joints always encounter problems giving rise to trouble in normal operation and this increases cost of maintenance. 

A number of designers may prefer to add more movement joints to guard against possible occurrence of differential settlements. Though the effect of continuity is disabled by this excessive introduction of movement joints.

From structural point of view, use of continuous deck increases the reduction of bridge deck thickness. Furthermore deck continuity allows the potential increase in headroom in mid-span of bridges by using sucker deck principle. 

Some designers may prefer to employ the use of simply supported multiple-span deck to guard against probable occurrence of differential settlements. But the effect of continuity is undermined by the introduction of movement joints. In essence structural reserve provided by a continuous bridge is destroyed by multiple-span statically determinate structure resulting from the addition of joints.

Furthermore the reduction of joints in bridge structures signifies substantial cost savings arising from construction and maintenance costs of movement joints. Reduction of deck thickness helps to cut the cost for both deck and foundation. Particularly the number of bearings in every piers is substantially decreased when compared with the case of simply supported multiple-span deck.

Advantages of using the bridge form of precast pre-stressed beams supporting in-situ concrete top slab.

The potential benefits of employing the useof bridge form of precast pre-stressed beams supporting in-situ concrete top slab are:

(i)  For bridges which are built on top of rivers and carriageway, this bridge form provides working platform by precast beams so that erection of falsework isn't required.

(ii)  This bridge form normally doesn't require any transverse beams or diaphragms (excepting at the location of bridge supports) leading to reduction of construction cost andtime. 

(iii) It creates the potential for concurrent construction with several spans.