The Earthquake Engineering Online Archive

Optimum inelastic design of seismic-resistant reinforced concrete frame structures

Zagajeski, Stanley W.; Bertero, Vitelmo V.

UCB/EERC-80/03, Earthquake Engineering Research Center, University of California, Berkeley, 1980-01, 125 pages (620.2/Z22/1980)

The design of seismic-resistant reinforced concrete, moment-resisting frame structures is discussed and an inelastic optimum design procedure described. This procedure is based on the philosophy of comprehensive design and employs a computer-aided iterative technique in a series of five steps. Each step contains two phases, in each of which a weak-girder, strong-column design criterion is imposed. The discussion of the proposed inelastic design procedure concentrates on the preliminary design phase which comprises three steps -- preliminary analysis, preliminary design, and analysis of the preliminary design. Seismic design story shears are found by a spectral modal analysis technique which includes an approximation to the P-delta effect. A nonlinear optimization technique (the cutting-plane method) is employed at each story to find the beam design moment capacities which minimize a function proportional to the volume of flexural reinforcement. Design constraints are imposed to ensure that a safe, serviceable, and practical design results. Actual member design is found employing computer design aids. In the final step, the preliminary design is analyzed to evaluate its acceptability. Acceptability is determined by comparing the results of a series of linear elastic and nonlinear analyses with established design criteria and assumptions made in formulating the design problem. The proposed inelastic design procedure has been used to obtain a series of designs of a ten-story, three-bay frame. The designs differ with respect to the design constraints imposed in the formulation of the optimization problem and with respect to beam steel content. Different sets of practical design constraints were formulated to study the effect on beam moment redistribution of (a) the ratio of the positive and negative moment design capacity at a given design section and (b) the elimination of bar curtailment at interior beam-column joints. Two additional designs were determined following Uniform Building Code seismic design force provisions and considering code-allowed negative moment redistribution.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-80-03.pdf (4 MB)