fter the deck has cured and begun to work with the primary members inresisting loads. From the table 1.1 the designer would separate items such as sidewalks,railings, parapets, signing, utilities, and the wearing of the surface. Pressures due to earth and water are also considered permanent loads. While these loadsprimarily affect substructure elements, they have the potential of impacting superstructureelements as well at points where these two components interface (e.g., at the abutmentbackwall). This gives us a good reminder that while we are discussing the structure'sindividual components, we can not lose sight of the structure as a whole.Temporary loads are those loads, which are placed on a bridge for only a short period oftime. Just as dead loads are the permanent loading condition, live loads represent themajor temporary loading condition. There are, however, several other classes oftemporary loads, which the designer must consider. The temporary loads are: vehicle liveload, earthquake live load, wind loading, channel forces, centrifugal forces, impact forces,and erection loads.The term live load means a load that moves along the length of a span. Therefore, aperson walking along the bridge can be considered live load. Obviously, a highway bridgehas to be designed to withstand more that pedestrian loading. To give designers the abilityto accurately model the live load on a structure, hypothetical design vehicles based ontrucks were developed. In 1935, what was then called the AASHO issued a loading scheme based on a train oftrucks. These are identified as H-20-35 and H-15-35 in figure 2.1.(4) To meet thedemands of heavier trucks, the introduction of five new classes were made in 1944. Theseclasses have the following designations and gross vehicle weights:* H10-44(20,000 lbs. - 9072 kg)* H15-44(30,000 lbs. - 13,608 kg)* H20-44(40,000 lbs. - 18,144 kg)* HS15-44(54,000 lbs. - 24,494 kg)* HS20-44(72,000 lbs. - 32,659 kg)...
