Abstract
A relative reliability approach for Direct Displacement-Based Design (DDBD) is first proposed in this paper, which is based on the average reliability level implicit in current Chinese design codes. By introducing a relative reliability coefficientα, the determination of reliability from DDBD is transformed to the calculation of its ratio to the average reliability of current Chinese codes. This approach not only follows the reliability principle of current Chinese codes, but also avoids the complex calculation of reliability in general. The calculation of reliability at any performance level can be transformed to the nominal reliability of frequent earthquake for the expected earthquake risk level. Meanwhile, based on the assumption of elasticity, it is shown that, under frequent earthquake risk, the calculated base shear derived from DDBD theoretically equals that from force-based design (FBD). Therefore, a revised calculation of section bearing capacity for DDBD, which follows the expression in current Chinese codes, is advised, according to the numerical study of 24 examples of Partially Prestressed Reinforced Concrete (PPRC) frame structures. Finally, this proposed approach is verified to be effective and superior by a comparative analysis of 10 examples of PPRC frames.
Highlights
Real seismic response of structures shows that a traditional force-based seismic approach is difficult to accord with the expected structural displacement under the designed earthquake risk
In 1995, a Direct Displacement-Based Design (DDBD) method [1] was presented for bridge design; after that, Priestley suggested the improved DDBD method applied to Reinforced Concrete (RC) structures [2, 3]
To establish the reliability approach for DDBD, evaluation of reliability at the given performance target is first transformed to the expected seismic risk level under frequent earthquake risk, while the section bearing capacity of structure is determined by a similar way as force-based design (FBD)
Summary
Real seismic response of structures shows that a traditional force-based seismic approach is difficult to accord with the expected structural displacement under the designed earthquake risk. Gao et al pointed out that, under the confidence 0.05 or 0.1, the ultimate drift ratio of a RC frame obeys a lognormal distribution or an extreme I distribution They studied the seismic reliability of ultimate deformation capacity of RC frames under rare earthquake risk [11, 12]. Complex derivation and excessive assumptions probably lead to large calculation errors in design Towards these problems, in this paper, a relative reliability (relative to the average reliability implicit in current Chinese codes [18, 19]) approach is first proposed for DDBD, without a complex calculation of variation coefficients in the reliability analysis
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