International Concrete Abstracts Portal

The structural response assessment of reinforced concrete slabs subjected to impulsive loads due to a detonation of an explosive is an essential task for the design of blast resistant concrete structures. Nonlinear dynamic finite element methods and analytical modeling provide a valuable tool for predicting the response and assessing the safety of a reinforced concrete component. The proposed Finite Element analysis and analytical modeling approaches were validated using a series of shock tube tests conducted on conventionally constructed and high strength reinforced concrete slabs by the University of Missouri Kansas City at the Engineering Research and Design Center, U.S. Army Corps of Engineers in Vicksburg, Mississippi. The aim of the paper is to present the modeling techniques adopted in both the Finite Element and analytical modeling approaches in order to conduct the structural response assessment of RC slabs subjected to impulsive loads due to detonations. The numerical modeling was conducted utilizing LS-Dyna® finite element software package. The analytical approach utilized a fiber analysis method coupled with a single degree of freedom time stepping method. The constitutive models, loading and boundary conditions utilized are discussed in detail.

Over recent years, numerical simulations have arisen as the most effective method to analyze structures under blast events. However, in order to achieve accurate numerical predictions, reliable constitutive models contrasted against experimental benchmarks are needed. In this work, the experimental tests on normal and high-strength concrete slabs conducted by the University Missouri-Kansas City on the shock tube at the Engineering Research and Design Center, U.S. Army Corps of Engineers at Vicksburg, Mississippi, are modeled by using a novel constitutive model for concrete presented recently by the authors. The model makes extensive use of Fracture Mechanics considerations through the Cohesive Crack Model developed by Hillerborg and co-workers. The numerical predictions obtained show good agreement with the experimental results, especially in the case of the high strength concrete slabs.

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.

Numerical simulations of Reinforced Concrete (RC) panels subjected to blast loads are presented in this paper. In spite of a large number of events such as explosions and bombings in recent years, there is a difficulty in accurately predicting the behavior of structural systems due to blast loading. The effects of blast loads on 64” (L) x 33.75” (W) x 4” (H) RC slabs are studied using both nonlinear finite element analysis and Single Degree of Freedom (SDOF) models, and the analysis results are compared with available test results provided by the University of Missouri-Kansas City. This study investigated the gap between actual and predicted response of reinforced concrete structures subjected to highly dynamic loading such as blast. The effects of concrete strength, reinforcing steel grade, and the magnitude of blast loads on the dynamic response of reinforced concrete panels are considered.

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.