Bridges

Capacity reduction factors (?) for flexure, shear and axial loadings are derived for reinforced and prestressed concrete structures based on a reliability-based calibration of the Australian Concrete Structures Standard AS3600. The structural reliability analysis considers the bias and variability of material properties, dimensions, loads and model error. The target reliabilities are selected based on consideration of past practice and Australian and international standards. The capacity reduction factor for the new code AS3600-2009 are selected using the most recent statistical parameters for material strengths for 20-100 MPa strength concrete, reinforcing bars, and prestressing strands. The reliabilitybased calibration found that the ?-factor can be increased from 0.80 to 0.85 for members in bending, and increased from 0.60 to 0.65 for axial loading of short (stocky) columns. It is expected that similar increases to capacity reduction factors for AS5100.5 are also possible as observed improvements in concrete and steel quality will be similar for bridge construction. In this case, the proposed increases in capacity reduction factors will result in up to an 8.3% increase in design strength and load ratings. Reliability-based calibration of the bridge code AS5100 has the potential for further changes in capacity reduction factors, load factors, and load ratings.