Bridge components, especially bridge decks, are more susceptible to larger deflections and stresses and, consequently, to faster deterioration than other structural element. Maintenance of bridge decks is not only expensive, but it also disrupts traffic, poses safety issues, and affects the safety and economy of the community. Therefore, bridge decks must be strong enough to attain the serviceability requirements. To meet this requirement, one technique could be to use post-tensioning technology on the slab deck. This approach has dual advantages: enhancing strength of the slab and reducing serviceability problems. However, the effect of post-tensioning on other structural elements, such as the girders and abutments, is usually not well studied. This research tries to investigate the strength enhancement of deck and girder due to post-tensioning. In this work more emphasis is given on finite element simulation of post-tensioned composite deck with steel I girder, effect of post-tensioning of the deck on girder and validate the result of finite element output with the theoretical output which is calculated using load balancing principle. This research also attempts to investigate the effect of post-tensioning of the deck on the spacing of girder and geometry of girder. Doing this thesis result with very honest awareness about the stress reduction in deck, section reduction in girder and increment of girder spacing in considerable amount as compare with non-posttensioned deck. When the deck interacts with tendon, which imposed by 23% tendon ultimate capacity, the behavior has changed. As shown in the FEA, at 28.89% tendon ultimate capacity the stress induced in the deck at the central point we reduced by 55.94% from its un-post-tensioned state. The FEA output shows, the girder spacing has increased by 100% and the girder geometry has reduced by 24.13% at 28.89% of tendon ultimate capacity. In this analysis, changing spacing has more sensitive effect for deck or girder response than geometry of girder without PTS applied in tendon that will embedded in the deck.