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This paper presents an in-depth study on the short-term stiffness of hybrid prestressed concrete beams with bonded tendons and unbonded tendons. Calculation formulae of short-term stiffness were derived based on the double line theory. Multiple regression analysis is conducted for the reduction coefficient β0.5 used for the termination point of the stiffness calculation, based on the finite element results of 71 beams. Two formulae for the short-term stiffness of the hybrid prestressed concrete beams were proposed based on two different ways of calculating β0.5. The test data of 42 unbonded prestressed concrete beams and 31 bonded prestressed concrete beams collected from existing literatures verified the proposed stiffness formula. It’s suggested that the proposed formulae for short-term stiffness can also be applicable to bonded prestressed concrete beams and unbonded prestressed concrete beams. In addition, this paper presents an assessment of the accuracy of design formulae provided by a number of design standards, including GB 50010—2010, ACI 318-11, EN 1992-1-1:2004, for the short-term stiffness of prestressed concrete flexural members. [ABSTRACT FROM AUTHOR]

The prediction of deformation capacity of reinforced concrete (RC) columns is the foundation to realize performance-based seismic design. This paper presented a critical review of flexural-shear failure of columns based on Chinese design codes. The empirical formulas of ultimate deformation of RC columns were discussed, and the deficiencies of parametric model were revealed. The failure mode of flexural-shear, shear behavior and P-Δ effect are the main reasons for the scattering of the prediction of ultimate displacement. The length of plastic hinge is not a specific statistical sample. The prediction of ultimate displacement on the basis of equivalent plastic hinges method shows large scatter. In order to reveal the real shear demand in RC columns subjected to seismic loadings, the interaction between shear and flexural behaviors in plastic hinge zone should be taken into consideration. However, the corresponding simplified methods need to be improved. An effective method to evaluate the effect of shear on the deformation performance of columns is not available. In the GB 50010—2010 ‘Code for design of concrete structures’, the correction of the shear capacity formula for seismic design can effectively avoid the shear failure of columns under large displacement reversals, but the safety margin is different under varying ductility levels of ultimate displacement. The scatter of the prediction of GB 50010—2010 is larger than that of the original formula. Shear demand of identical columns under different test setups is not same due to the variety of P-Δ effect. The influence of P-Δ effect on the ultimate deformation capacity of RC columns depends failure modes. Finally, according to the relevant research in ultimate deformation, it is suggested that Chinese building code should be supplemented with an empirical formula for lower limit value of ultimate displacement by regression methods to improve performance-based design methods. [ABSTRACT FROM AUTHOR]

In current Chinese timber structure design codes, due to lack of a determination method, design strength value of domestic dimension lumber can only be determined with reference to the design method of sawn and log timber structure, which is dependent only upon wood species and is not related to visual grade and size of dimension lumber. For rational determination of the design strength value of domestic dimension lumber, full scale tests for bending strength were conducted on different visual grades (grade Ic, IIc, IIIc, IVc) of Chinese larch dimension lumber, and then reliability analysis on bending strength of domestic dimension lumber was carried out by the first order second moment method. In order to predict accurately the tail of probability distribution of bending strength, this paper has suggested that the mean value and standard deviation could be determined with the truncated 25% tested data of bending strength. The statistical mean vaule and coefficient of variation of geometry size of Chinese larch dimension lumber should be modified and be equal to 1.00 and 0.05, respectively. Based on reliability analysis results, relationships between reliability index and partial factor for different visual grades dimension lumber under different fitting data, probability distribution models of bending strength, load combinations, and load ratios were investigated. Finally, according to the target reliability requirements specified in the GB 50068—2001 ‘Unified standard for reliability design of building structures’, the partial factors for resistance and the corresponding design values of bending strength for Chinese larch dimension lumber were given. [ABSTRACT FROM AUTHOR]