OVERLOAD BEHAVIOR AND STRENGTH IN FLEXURE

OBJECTIVES:

To know the overload conditionTo understand the overload

condition.To able to understand what is

service load.To able to understand what is

factored load.

Overview:The level of service load, this

may be the case up to approximately the actual self-weight of the member plus those superimposed loads that may reasonably be expected to act during the life of the member.

Eventually, with loads increased still further, either the steel or the concrete, or both, will be stressed into their non linear range.

The condition at incipient failure which shows a beam carrying a factored load, equal to some multiple of the expected service load.

For the overload condition, the beam undoubtedly would be in a partially cracked state; a possible pattern of cracking will shown.

Only the concrete in compression is considered to be effective, just as in analysis of ordinary reinforced concrete.

The steel in tension works with the concrete in compression to form an internal force couple, which resist the moment from the applied load.

As can the magnitude of the compressive resultant C, the tensile force T, in the steel, and the distance between the two.

If the internal lever arm is z then the ultimate resisting moment is:Mn = Cz = Tz

The main difference is that the steel used has very high strenght and requires a very large strain to achieve a high stress level.

Review:In this section, it will be clear that

the effects prestressing have been considered from three points of view: providing concrete stress control, creating equivalent transverse loads, and providing overload strength thought creating an internal forces couple, just as in ordinary reinforced concrete.