Lesson 36 Structural Requirements, Code Stipulations and Governing Equations Version 2 CE IIT, Kharagpur
Instructional Objectives: At the end of this lesson, the student should be able to: •state the need to design the tension structures using reinforced concrete though concrete is very weak in tension, •justify the use of working stress method for designing reinforced concrete tension members, •name the two essential requirements for the design of reinforced concrete tension structures, •explain why some amount of cracking may be allowed in such structures, •explain why porous aggregates are not allowed in the reinforced concrete tension structures, •state the basis of design of reinforced concrete tension members, •state the different cases of reinforced concrete tension members, and •establish the governing equations for all the cases of tension members to determine the stresses of concrete and steel following the working stress method of design. 14.36.1 Introduction Reinforced concrete is used in the design of several practical members of tension structures though it is not a potential material due to very inadequate tensile strength of concrete compared to its compression strength. In such cases, reinforced concrete develops tensile stresses either due to direct tension force or combined with bending. Tie members of trusses and arches, walls of rectangular tanks and bunkers, suspended roofs, cylindrical pipes, walls of liquid retaining structures are some of the examples where tension stresses also develop. Traditional elastic approach (working stress method) and the limit state method can be applied for the design of such structures. Based on elastic theory, the working stress method is simpler in concept and applications, while the limit state method, based on cracking behaviour of concrete, is not fully developed yet. Some of the structures or members mentioned above may not be in direct contact with any liquid. On the other hand, some may be in direct contact with liquid. Though control of cracking is important for all types of structures, it is an essential requirement for liquid retaining structures. Impermeability of structure is not only for preventing leakage but also for improving durability, resistance to leaching, chemical action, erosion, frost damage and protecting the reinforcement from corrosion. Version 2 CEIIT, Kharagpur
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