Numerical modelling is nowadays commonly employed in the analysis of concrete structures subjected to extreme dynamic loadings such as blast. Sophisticated material models, particularly concrete, are available in commercial codes and they are often applied in their default settings in a diverse range of modelling applications. However, the mechanisms governing different load response scenarios can be characteristically different and as such the actual demands on specific aspects of a material model differ. It is therefore not surprising that a well-calibrated material model may exhibit satisfactory performance in many applications but behave unfavourably in certain other cases. Modelling the response of reinforced concrete structures to blast load presents such an important scenario in which the demands on the concrete material model are considerably different from high-pressure scenarios for example high-velocity impact or penetration. This paper stems from an initial modelling undertaking in association with the Blind Blast Contest organised by the ACI Committee 370, and extends to a detailed scrutiny of the demands on the concrete material model in terms of preserving a realistic representation of the tension/shear behaviour and the implications in a reinforced concrete response environment. Targeted modifications are proposed which demonstrate satisfactory results in terms of rectifying the identified shortcomings and ensuring more robust simulation of reinforced concrete response to blast loading.

It is widely recognized that a competent constitutive model for concrete, and a set of calibrated parameters for it, are important to producing accurate response predictions using the finite element method (FEM). What is not obvious, without having access to a large database of test data and practical experience using and validating the FEM models, is that a host of parameters for the FEM calculation can significantly influence the results. The objective of this paper is to identify these parameters and illustrate their effect by computing the response of some simple concrete structure tests subject to transient loads. Calculations for each of these structures demonstrate that in addition to some of the more nuanced material model parameters, parameters involving boundary conditions, hourglass energy suppression, interface friction, and loading-rate effects, all have a strong effect on the response predictions. The results demonstrate that any of four concrete constitutive models considered in this paper can be used to match any one set of test data, even though they differ in their assumptions and the behaviors modeled through their formulation; however, it is difficult to match the larger set of data without carefully considering each of these parameters. Guidance is provided to produce meaningful computational results using the constitutive model developed by the authors.

A batch of blast resistance reinforced concrete slabs were tested in the shock tube facility at the University of Missouri Kansas City (UMKC). Based on the results from the tests, a blind numerical simulation contest was announced by UMKC in collaboration with the American Concrete Institute (ACI). The authors of this paper participated in the contest and received the test results only after completing their simulations. In this paper two basic numerical approaches are described. The first is a preliminary section rigidity assessment and the second is a full numerical simulation performed with the LS-DYNA code. The numerical results are compared with the UMKC test results and the influence of the numerical parameters is further discussed. The section rigidity assessment approach is then used to explain some unexpected results.

Simulation of structural behavior of Reinforced Concrete (RC) subjected to shock loading is an important aspect of blast-resistant design of military and civilian structures. Depending on the application, different analytical approaches of varying complexities can be used to predict the nonlinear response of various concrete elements to blast loads. This paper reports the findings of a comprehensive study submitted for a Blast Blind Prediction Contest that involved various simulations of blast-loaded concrete slabs. The NSF in collaboration with ACI-447 and ACI-370 committees, Structure-Point and UMKC/ SCE sponsored the contest that included four categories requiring the use of Single Degree Of Freedom (SDOF) and physics-based (HYDROCODE) simulation techniques to predict the responses of one-way reinforced concrete slabs to two levels of blast loading. The study investigated the varying blast response characteristics associated with the use of two classes of concrete, Normal and High Strength and two classes of reinforcement, Normal and High Strength Vanadium. A testing program that encompasses all contest categories was completed at the Blast Loading Simulator (BLS) at the ERDC/ USACE, Vicksburg, MS to collect relevant shock loading and structural response data for various testing configurations. Various SDOF tools (i.e. P-I curves, UFC-3-340-02 charts, RCBlast, and RCProp/ SBEDS) and HYDROCODE constitutive models (LS-DYNA MAT-159, MAT-085, and MAT-072R3) were utilized to simulate various test setup information in order to predict maximum and residual responses and cracking patterns of tested RC slabs. Despite their major differences in modeling capabilities, analytical efforts, and inherent accuracy, all utilized simulation techniques were successful in predicting blast responses of investigated RC slabs with sufficient practical accuracy. Acknowledging their modeling limitations, SDOF simulations exhibited excellent capabilities in predicting overall behavior and maximum responses with a level of accuracy that is well suited for design applications. On the other hand, HYDROCODE simulations proved superior in their response and damage predictions owing to their modeling capabilities that allowed realistic end conditions, material nonlinearities, and strain-rate effects.

Six normal and high-strength reinforced concrete slabs were subjected to simulated blast loading using a Blast Loading Simulator at the U.S. Army Corps of Engineers, Engineering Research and Design Center. A blind prediction contest was sponsored to evaluate the effectiveness of various modelling approaches to predict the blast response of the normal and high-strength concrete slabs. This paper describes a contest submission in the single-degree-of-freedom (SDOF) category generated using software program RCBlast. RCBlast was developed to perform inelastic analysis of structural members subjected to blast-induced shock waves. The program uses a lumped inelasticity approach to generate resistance functions for SDOF analysis. Incorporated into the development of the resistance functions were: material models and dynamic increase factors (DIF) appropriate for normal and high-strength concrete and steel reinforcement; member modelling capable of describing the gradual formation and progression of plastic behavior, and; hysteric modelling to account degradation in stiffness and energy dissipation.