International Concrete Abstracts Portal

This CD-ROM contains 15 papers that were presented at sessions sponsored by ACI Committees 447 and 370 at the ACI Fall 2010 Convention in Pittsburgh, PA. In this publication, engineers report on how they are approaching the challenging task of predicting the response of structures subjected to blast and impact loading. Both experimental and analytical efforts are represented, often in tandem. The analytical approaches taken include single-degree-of-freedom modeling, highly nonlinear transient dynamic finite element simulations, and coupled Lagrangian-Eulerian simulations. Papers in the publication cover the design and evaluation of new and existing structures, as well as techniques for strengthening existing structures. 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-281

The robustness of concrete constitutive material models in explicit finite element codes is typically measured by their ability to match peak dynamic and permanent displacements of a reinforced concrete specimen. In a series of recent shock tube experiments, reinforced concrete slabs were subjected to simulated blast loads. Applied pressure histories were recorded in these tests, as were peak and residual displacements. This paper evaluates the Concrete Damage Model (Material 72, Release 3) and the Continuous Surface Cap Model (Material 159) within LS-DYNA (Version 971), as well as the Applied Engineering Cap model (AEC-3I) in DYNA3D. The results indicate some variation in predicted damage and failure modes between the three material models, but overall, all three models produced satisfactory comparisons to the test with regard to peak positive deflection (i.e., within a factor of 2 of the measured response). A surprising outcome is that the inclusion of rate-dependent material properties actually increased the error in the predicted response. In terms of predicting crack patterns, the AEC-3I model appears to be preferable, whereas MAT72R3 is preferred for predicting peak deflection. Overall, MAT159 was the most consistent predictor and the least sensitive to variations in the rate dependent properties of concrete.

Using a shock tube to subject structures to shock wave loading is a safe, economical and reliable alternative to live explosive testing. The University of Ottawa shock tube testing facility is capable of simulating shock wave induced loading of structures subjected to high explosive blast. The shock tube can accurately generate shock waves with similar properties as those produced by the actual detonation of high explosives. The parameters of the shock waves generated by the shock tube are found to be a function of driver length and driver pressure. Pressure-time histories are found to be in good agreement with similar free-air detonations. Furthermore, shock waves are found to be planar at the testing frame. Blast induced testing of structural elements, such as columns, slabs and masonry walls have been subjected to shock wave induced loading. This paper outlines the parameters of shock tube induced shock waves and explores the benefits of shock tube testing over live high explosive testing.

Concrete structures designed to meet blast criteria often require substantial increases in structural system size, weight, and cost when using conventional materials, but high-strength materials may offer a way to mitigate these increases while achieving desired performance levels. The U.S. Army Engineer Research and Development Center (ERDC), Vicksburg, Mississippi, investigated the effects of using High Strength Low Alloy vanadium microalloyed steel (HSLA-V steel) reinforcing bar coupled with high-strength concrete as a structural system. The combination of high-strength portland cement concrete (HSPCC) and HSLA-V steel can improve a component’s ability to satisfy a given blast resistance criteria while allowing a more efficient structural design than can be achieved with conventional materials. Vanadium is widely used as an alloying element in steel production. Micro-alloying vanadium with steel reinforcing bar contributes to higher yield strengths than can be achieved with traditional Grade 60 rebar, without compromising ductility or formability. The investigators performed dynamic testing of one-third scale reinforced concrete panels using the ERDC Blast Load Simulator (BLS). The panels consisted of double-mat conventional Grade-60 rebar or HSLA-V steel rebar in combination with 4-ksi (27.6 Mpa) or 15-ksi (103 Mpa) concrete. Tests were performed using blast loads to determine the performance of simply-supported concrete panels constructed from different combinations of reinforcing steel and concrete. Measured properties included center-span deflection, average blast pressure, and average impulse. The 4-ksi (27.6 Mpa) concrete in combination with HSLA-V steel rebar provided the best alternative to the use of only high-strength materials, but provided a lower level of blast protection. Permission to publish this paper was granted by the Director of the Geotechnical and Structures Laboratory and the U.S. Army Research Laboratory.

The lack of a complete understanding of shear behavior under high dynamic conditions hindered the efforts for accurate prediction of impact behavior, since severe shear mechanisms may dominate the behavior of RC structures when subjected to impact loads. This current study involves a well-instrumented experimental program that was undertaken to contribute to our understanding of the effects of shear mechanisms on the behavior of reinforced concrete (RC) structures under impact loads. The test results showed that the shear characteristics of the RC beam specimens played an important role in their overall behavior. All specimens, regardless of their shear capacity, developed severe diagonal shear cracks, forming a shear-plug under the impact point. Furthermore, the application of the Disturbed Stress Field Model (DSFM) as an advanced method of modeling shear behavior under impact conditions is also investigated. A two-dimensional nonlinear finite element reinforced concrete analysis program (VecTor2), developed previously for static loads, was modified to include the consideration of dynamic loads such as impacts. VecTor2 analyses of the test specimens were satisfactory in predicting damage levels, and maximum and residual displacements. The methodology employed by VecTor2, based on the DSFM, proved to be successful in predicting the shear-dominant behavior of the specimens under impact.