Design Aid for High Strength Reinforced Concrete Members: Beam Design Aids and Column Interaction Charts

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Applicability of high-strength concrete (HSC) in reinforced concrete structures has gained acceptability in the world as it allows efficient utilization of space and enhanced structural performance. The Ethiopian Building Code Standards provides thorough coverage for the design of reinforced concrete structures made of normal strength concrete (NSC) and also provides design aids for NSC. The design considerations and aids provided in the current code cannot be simply extrapolated for use in reinforced HSC. This is because the mechanical properties of HSC under compression, shear and tension are different from that of NSC. Thus a separate design consideration and aids are required for reinforced HSC structural members. The current building code which is under revision will include design consideration for reinforced HSC, however design aids for HSC are missing. This study focuses on constructing design charts and tables for solid rectangular beams and interaction charts for solid rectangular columns sections made of HSC by using an iterative numerical based approaches. Stress-strain relationship for concrete and reinforcing steel is adapted from Euro Code. The effect of strain hardening for reinforcement steel is incorporated in the design aids. Exact method of cross section analysis is used to estimate the ultimate capacity of structural members when developing the design aids. Multiple application of Simpsons 1/3 rule is used to estimate the total compressive force in the concrete when developing design table and charts for beams. The design tables and charts can be used for any class of work as there are no built-in safety factors. Uniaxial and biaxial interaction charts are constructed by applying Green’s Theorem to transform double integrals to line integrals along the compressive perimeter of the concrete section. The line integral itself is evaluated by using Third Order Gauss integration to yield accurate results. Double counting of concrete area that is displaced by the steel bars are taken into account. The algorithms developed for preparation of these design aids are exact and computational efficient.



Concrete Members, Beam Design Aids, Column Interaction