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.

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

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.

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.