Effect of variation of modulus of elasticity of concrete on seismic design of bridges.

摘要

The objective of this work is to assess the effects of variation of Modulus of Elasticity of Concrete, Ec, on seismic design of bridge structures. The effects of permeability, compressive strength of concrete, modulus of elasticity of the mortar, aggregate source and compressive strength of aggregate on modulus of elasticity of High Performance Concrete (HPC) were considered. The effect of using weathered aggregate in contrast to unweathered aggregates in concrete mixes on the modulus of elasticity was examined. Inaccuracies in predicting the modulus of elasticity of concrete, Ec, using the seismic design codes were identified. New practical and universal equation to predict the modulus of elasticity of HPC was developed. The proposed equation provides more accurate results than the current design code models for concrete with compressive strength greater than 36 MPa. The effect of inaccurate prediction of E c on the response of concrete structures was examined. The seismic response of concrete structures was divided into elastic response and nonlinear response. The elastic response was studied by carrying out time history analyses and response spectral analyses of equivalent SDF systems and MDF bridge structures. The modulus of elasticity of concrete was systematically varied from the theoretical value of Ec for each group of structures. Structures were divided into three assorted categories based on their seismic response behavior. It was concluded that stiff structures are more sensitive to the variation of Ec. The repercussions for using code equations for calculating Ec on modeling inelastic response of concrete structures were analyzed. Confined and unconfined concrete material properties were determined for a predetermined range of Ec. Moment-curvature curves were established for the concrete sections. Plastic hinge properties were modeled using moment-curvature curves for the concrete elements. The response of the concrete elements was determined under monotonic and quasi-static loading. A new calibration formula was proposed to determine the spectral displacement demand for concrete structures. The proposed formula is used to model the cracked section properties of concrete elements designed to remain elastic during the designed seismic event. For concrete elements designed to experience inelastic response, a procedure was outlined to determine the effective flexural stiffness.