A Simplified Preliminary Design Method for Low-To-Medium Rise Reinforced Concrete Buildings

Abstract eng:
A simplified methodology is proposed in this study for the preliminary design of low-to-medium-rise reinforced concrete buildings without significant structural irregularities. The method is founded on essential principles of earthquake-resistant design; including adequate strength, stiffness, and member/system ductility. Two main classes of building-type structures have been considered for application of the method: (i) buildings consisting solely of moment resisting frames (frame-only systems), and (ii) buildings incorporating frames and structural walls (wall-frame systems). Dimensions of the vertical structural members (columns and walls) are calculated based on simple parameters such as the expected short-period spectral acceleration demand, member tributary areas, estimated gravity loads, total floor area, and the number of floors; whereas beam dimensions are related predominantly to span lengths. The inherent criteria of the method underlying dimensioning of the vertical members include: (i) to limit axial compressive stresses on columns and walls for obtaining adequate member/system ductility, (ii) to provide adequate column and wall areas for avoiding brittle shear failures, and (iii) to achieve adequate lateral stiffness for limiting the interstory drift demands. The method also incorporates a set of minimum cross-sectional dimension and minimum reinforcement (both longitudinal and transverse) requirements for beams, columns, and walls, which can be tailored to satisfy different performance levels. Application of the method does not require any structural analysis, since the method is intended to provide the engineer with a preliminary design of the structural system (in terms of not only member dimensions but also reinforcement) that is safe, yet not overly-conservative. Both real-life and hypothetical building structures, involving 11 frame-only and 14 wall-frame systems with varying numbers of stories (4–8), were designed based on the proposed methodology. These buildings were then modeled and evaluated as per ASCE 41-13 [1] guidelines. Nonlinear static pushover analyses were conducted to assess their expected performance levels under design-level earthquake demands. At the target displacement, the damage levels of the individual beam, column, and wall members were classified in terms of plastic rotations. As well, member shear capacity checks were conducted, and interstory drift ratios were calculated. The analysis results have shown that among the entire building inventory (including both frame-only and wall-frame systems), all of the vertical members (columns and walls) satisfy the life safety performance level stipulated by ASCE 41-13, whereas the performance level of the beams can be adjusted (via adopting different sets of minimum requirements on beam dimensions and reinforcement) to comply with either life safety or collapse prevention performance levels. Shear capacities of all the members were found to be adequate, and interstory drift ratios were acceptable. Overall, the proposed methodology is believed to be a practical approach, which provides engineers with a reliable preliminary design of low-to-medium-rise reinforced concrete moment-resisting-frame or wallframe buildings without pronounced structural irregularities.

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