Dr. Lauren K. Stewart

Project Information

PI: Lauren Stewart

Students: Rebecca Nylen

Summary

Mitigating the continuing risk of terrorist threats requires a thorough understanding of the response of structures to extreme loads such as blast and impacts. With concrete being the most commonly used building material, it is important to fully characterize the response of reinforced concrete structures to dynamic loads to ensure safety of the building occupants after an extreme loading event occurs. Once a building is damaged from an impulsive loading event, certain structural elements may be partially damaged and the integrity of the building depends on the residual capacity of these damaged structural elements. Much of the motivation to understand the residual capacity of concrete subjected to impulsive loading is fueled from the progressive collapse of structures such as Ronan Point in 1968 and the Alfred P. Murrah Federal Building in 1995. Disasters such as these have historically pushed large research efforts towards strengthening individual structural components and increasing redundancy of the structure in the event that a structural element is removed. This structural-level focus has remained the primary focus for preventing the progressive collapse of structures and examining the residual capacity of damaged elements and buildings. However, in order to effectively predict the global response of reinforced concrete structures, it is essential to also evaluate the residual capacity and damage of concrete at the local material level.

As numerical modeling becomes an increasingly common method to evaluate the response of structures to extreme events, a structural element-level focus has persisted for progressive collapse prevention. Most experimental test programs continue to focus on the residual capacity of full-scale structural elements, and the results of these large-scale tests are used to calibrate numerical models. However, to calibrate the steel and concrete material models used in the large-scale model, relatively simple material tests are used. For steel, uniaxial tension tests are commonly performed, and for concrete, triaxial compression tests are used to calibrate the material model. However, little has been done to ensure that the damage models are able to accurately predict the residual capacity of the individual material constituents. Sanborn found that commonly used finite element material models were unable to predict the residual capacity of shear damaged bolts without extensive calibration efforts. Currently, no data exists in the literature on the residual capacity of concrete materials subjected to impulsive loads at a material or nonstructural level. Due to the complexity of a large-scale structural model, it is difficult to isolate the accuracy of the concrete material model due to the large number of variables involved with the inclusion of reinforcing steel.

The objective of this research is to step back from the structural level residual capacity studies and critically examine progression of damage that occurs in concrete materials during impulsive loading. Specifically, an experimental test program will be conducted to evaluate what damage mechanisms affect the residual capacity of the material, and how accurately these damage mechanisms are represented in common concrete constitutive models.