Pressure-impulse (P-I) diagrams are commonly used in the preliminary design or assessment of protective structures to establish safe response limits for given blast-loading scenarios. Current practice in generating the pressure-impulse diagram for structure components is primarily based on the simplified SDOF model. The damage criterion is usually defined in terms of deformation or displacement response.Under blast loads, structures usually respond at their local modes, the equivalent SDOF system derived using the fundamental structure response mode might not be suitable. Moreover, structure is often damaged owing to brittle shear failure. In this case, the deformation based damage criterion might not be able to give an accurate indication of local damage of a structural component. In this paper, a new damage criterion for RC column is defined based on the residual axial load carrying capacity. A numerical method to generate pressure-impulse diagram for RC column is proposed. Parametric studies are carried out to investigate the effects of column dimension, concrete strength, longitudinal and transverse reinforcement ratio on the pressure-impulse diagram. Based on the numerical results, analytical formulae to predict the pressure-impulse diagram for RC column are derived. A case study shows that the proposed analytical formulae can be easily used to generate pressure-impulse diagram for RC columns accurately. The results are also compared with those obtained from the SDOF approach. It is shown that the proposed method gives better prediction of pressure-impulse diagram than the SDOF approach.

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Many highway bridges were severely damaged or completely collapsed during the 2008 Wenchuan earthquake.A fi eld investigation was carried out in the strongly affected areas and over 320 bridges were examined. Damage to some representative highway bridges is briefl y described and a preliminary analysis of the probable causes of the damage is presented in this paper. The most common damage included shear-fl exural failure of the pier columns, expansion joint failure, shear key failure, and girder sliding in the transversal or longitudinal directions due to weak connections between girder and bearings. Lessons learned from this earthquake are described and recommendations related to the design of curved and skewed bridges, design of bearings and devices to prevent girder collapse, and ductility of bridge piers are presented. Suggestions for future seismic design and retrofi tting techniques for bridges in moderate to severe earthquake areas are also proposed.

Dynamic material properties, in particular the dynamic strength, of concrete material are usually obtained by conducting laboratory tests such as drop-weight test and Split Hopkinson Pressure Bar (SHPB) test. It is commonly agreed that a few parameters associated with stress wave propagation will affect the test results, including the lateral and axial inertial effect, end friction confinement and stress wave reflection and refraction. Many different measures have been proposed to eliminate or limit the influences of these effects in dynamic tests of material properties. However, owing to the nature of dynamic loadings, especially those with high loading rates, it is very unlikely to completely eliminate these influences in physical testing. Moreover, it is also very difficult to quantify these influences from the laboratory testing data. In the present study, a refined mesoscale concrete material model is developed to simulate impact tests and to study the influences of lateral inertial confinement on concrete compressive strength increment at high strain rate. The commercial software AUTODYN is used to perform the numerical simulations. Numerical simulations of concrete specimens of different dimensions and under impact loads of different loading rates are carried out. The results are compared with those obtained from laboratory tests, with those specified in the code and simulated with homogeneous concrete material model. The reliability of the numerical simulation of impact tests is verified. It is found that the influences of lateral inertial confinement effect on Dynamic Increase Factor (DIF) is strain rate and specimen size dependent. Neglecting aggregates in concrete specimen in laboratory tests and numerical simulations lead to underestimation of DIF of concrete material.

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