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.

Editors: Ganesh Thiagarajan and Eric Williamson

The mission of ACI-ASCE Committee 447 is to develop and report information on the application of finite element analysis methods to concrete structures. The mission of ACI 370 is to develop and report information on the design of concrete structures subjected to blast, impact, and other short-duration dynamic loads. In this Special Publication (SP) and the accompanying presentations made at the ACI Fall 2013 Convention in Phoenix, Arizona, these committees have joined efforts to report on the state of practice in determining the Behavior of Concrete Structures Subjected to Blast and Impact Loadings. Recently, the (2008-2014) National Science Foundation (NSF) funded a study by University of Missouri Kansas City (UMKC) (CMMI Award No: 0748085, PI: Ganesh Thiagarajan) to perform a series of blast resistance tests on reinforced concrete slabs. Based on these results, a Blast Blind Simulation Contest was sponsored in collaboration with American Concrete Institute (ACI) Committees 447 (Finite Element of Reinforced Concrete Structures) and 370 (Blast and Impact Load Effects) and UMKC School of Computing and Engineering. The goal of the contest was to predict the response of reinforced concrete slabs subjected to a specified blast load using a variety of simulation methods. The blast experiments were performed using a Shock Tube (Blast Loading Simulator) located at the Engineering Research and Design Center, U.S. Army Corps of Engineers at Vicksburg, Mississippi.

Over 40 entries were received from researchers and practitioners worldwide; the competition was open to methods used in both research and practice. There were four categories in the contest: 1) Advanced Modeling of slabs with Normal Strength Concrete and Normal Strength Steel, 2) Analytical or Single-Degree-of-Freedom (SDOF) Modeling of slabs with Normal Strength Concrete and Normal Strength Steel, 3) Advanced Modeling of slabs with High Strength Concrete and High Strength Steel, and 4) Analytical or SDOF Modeling of slabs with High Strength Concrete and High Strength Steel. The first- and second-place winners were invited to present their work at the Fall 2013 convention. Furthermore, all teams were invited to submit papers for this SP, and original experimental data were provided to allow the teams to compare their results with those measured. This SP is a result of all the papers that were submitted and reviewed in accordance with ACI peer review requirements. In this SP, there are three papers from academic researchers and six from industry personnel, providing a healthy cross section of the community that works in this area.

The editors gratefully acknowledge all the hard work by the authors, the reviewers, and ACI staff, especially Ms. Barbara Coleman, who have helped very enthusiastically during every stage of the process. The editors also thank members of ACI Committees 447 and 370 for their continuous support in reviewing the papers.

Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-306

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.

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.

The aim of this research is to study the blast load response of different types of one way reinforced concrete slabs. The slabs include two material combinations based on their strength namely, the High-Strength Concrete with High-Strength Steel reinforcing bars (HSC-V) and Normal-Strength Concrete with Normal-Strength Steel reinforcing bars (NSC-R) and also two different reinforcement ratios. Experimental data obtained from tests conducted on 12 reinforced concrete slabs in a shock tube (Blast Load Simulator) were used to perform advanced finite element analysis to study the behavior of these slabs subjected to blast loading. Finite element models of these 12 slab panels are developed in LS-DYNA and the blast pressures equivalent to those generated in the experiment are applied on them. The response of material combinations to blast loading is studied using two different concrete models available in LS-DYNA namely, Winfrith Concrete Model (WCM) and Concrete Damage Model Release 3 (CDMR3) with steel being modeled using a plastic kinematic model and the results are compared with experimental data. Compared to NSC-R slabs, the experimental deflection of HSC-V slabs was lower by 9% for slabs with the higher - 0.68% - reinforcement ratio. For the slab with the lower - 0.46% - reinforcement ratio, the experimental deflection was lower by 5% for HSC-V slabs compared to NSC-R slabs, indicating that the usage of high strength materials marginally improved the deflection response of the slabs