Waleed Mekky

Validity of SDOF Models for Analyzing Two-Way Reinforced Concrete Panels under Blast Loading

The combined manual TM 5-1300/NAVFAC P-397/AFR 88-22, Structures to Resist the Effects of Accidental Explosions, published by the joint departments of the Army, the Navy, and the Air Force, has been used in all NATO countries for the past 50 years for protective design applications. The manual was recently reformatted to meet the Department of Defense Unified Facility Criteria (UFC). As a first step, the current production of the new document, UFC 3-340-02, focused on making the original TM 5-1300 available in a more functional format so that future technical updates can be facilitated. In this study, a single-degree-of-freedom (SDOF) model, based on the guidelines of the UFC 3-340-02, was used to formulate a FORTRAN code to predict the response of SDOF systems under blast. The code was used to generate pressure-impulse ( P-I ) diagrams for a series of two-way reinforced concrete (RC) panels with different dimensions, aspect and reinforcement ratios, and support conditions. The P-I diagram predictions wer...

Vulnerability Screening and Capacity Assessment of Reinforced Concrete Columns Subjected to Blast

In this study, a nonlinear model is developed to study the response of blast-loaded reinforced concrete (RC) columns. The strain rate dependency and the axial load and P−Δ effects on the flexural rigidity variation along the column heights were implemented in the model. Strain rate and axial load effects on a typical RC column cross section were investigated by developing strain-rate-dependent moment-curvature relationships and force-moment interaction diagrams. Analysis results showed that the column cross section strength and deformation capacity are highly dependent on the level of strain rates. Pressure-impulse diagrams were developed for two different column heights with two different end connection details (ductile and nonductile) and the effects of the axial load on the column midheight deflection and end rotation at failure were evaluated for both connection types. Based on the results of this study, a pressure-impulse band (PIB) technique is proposed. The PIB technique presents a useful tool that...

Response sensitivity of blast-loaded reinforced concrete structures to the number of degrees of freedomThis article is one of a selection of papers published in the Special Issue on Blast Engineering.

Accurate analysis of reinforced concrete (RC) structures under blast loading is very complicated due to the nonlinear behaviour of concrete and reinforcement and the various failure modes to be considered. Although blast loads can excite a large number of modes due to their high frequency content, practical computational tools are usually limited to single-degree-of-freedom (SDOF) models. In addition to oversimplification, SDOF models are known to give inaccurate prediction for shear forces and support reactions. This is because accurate shear force prediction typically requires accounting for modes higher than the fundamental mode. In this study, a multi-degree-of-freedom (MDOF) model is developed that takes into account the nonlinear behaviour of RC structures and the material strength and deformation dependency on the strain rate. Using this model, a series of dynamic analyses were carried out for two typical structural members, with different combination of blast pressure and impulse. The effect of va...

Inference of Blast Wavefront Parameter Uncertainty for Probabilistic Risk Assessment

AbstractProbabilistic risk assessment methodologies are typically employed to optimize resource allocations for blast risk mitigation schemes, which may be necessary for the design of new blast resistant facilities as well as the hardening of existing construction. A key aspect of any blast risk assessment methodology is the quantification of uncertainty inherent in the prediction of shock wave parameters. In this study, a blast pressure database that was generated from arena testing using live explosives is used to infer the probability distributions that best represent the model error affecting the prediction of four key wavefront parameters, namely: the peak pressure, specific impulse, duration, and waveform coefficient of the positive pressure phase. Confidence intervals are given for the descriptors of each distribution and their percentiles. In addition, two sets of partial factors are developed for the blast-resistant design of structures requiring high level of protection (LOP) based on a simplifi...

Response Analysis of Reinforced Concrete Block Infill Panels under Blast

AbstractIncreased exposure to the detrimental effects of blast events has led to the release of several guidelines and the recent publication of two North American standards that provide guidance on the hardening and performance quantification of structures subjected to this type of loading. The safety and security logistics and the high cost associated with performing experimental blast testing has led to a number of codes and guidelines accepting the use of simplified dynamic modeling techniques to analyze the response of structural components. Past research in blast-masonry interaction has primarily focused on the strengthening and retrofit of existing unreinforced masonry wall systems, whereas research related to evaluating the blast response of reinforced masonry (RM) has been limited. The focus of this study is to evaluate the accuracy of using simplified dynamic modeling techniques to predict the blast performance of nonintegral RM infill walls. To evaluate the accuracy of the simplified dynamic mo...

Sympathetic Detonation Wave Attenuation Using Polyurethane Foam

The unintentional initiation of munitions during production, storage, transportation, and handling is among the main sources of explosive hazard. Such unintentional initiation of explosives is termed sympathetic detonation, in which the detonation of a single explosive unit (or warhead) triggers the detonation of another, and subsequently starts a chain reaction. Because of this, the demand for resilient lightweight ammunition-separation systems within shipping or storage containers is increasing. This paper presents the development and testing of a cost-effective lightweight rigid polyurethane foam (RPF) separation system. The scaled gap test approach discussed is used as a practical tool to investigate the initiability of acceptor explosive charges by a blast wave generated from donor charges through the RPF as a blast wave attenuation medium. Different RPF specimens were prepared with different densities and silt particle mix ratios ranging from 0% (no silt) to 30%. The study results demonstrate the capability of the RPF as a lightweight cost-effective technique to attenuate the blast wave effects on acceptor explosives to safe levels.

Development of a high resolution human brain finite element model for restructuring Traumatic Brain Injury

High-resolution finite element models (HRFEM) simulating human heads can be utilized to quantify Traumatic Brain Injury (TBI) threshold due to a direct (e.g. impact) or an indirect (e.g. blast) dynamic shock. With the complex brain structure, for an accurate investigation of the influence of such brain injuries, accurate realistic geometrical brain structures must be developed. The objective of the current simulation study is to present the steps undertaken to generate a high resolution finite element model for human brains that will assist in studying the effects of a wide a spectrum mechanical insult to human heads. In this study, an MRI-T1 DICOM data files for healthy male head have been used for segmenting and extracting the brain structure. The segmented brain model has been meshed using tetrahedral elements with maximum size of 2 mm. This HRFEM for the brain was composed of 116,394 nodes and 607,457 elements. The model was then subjected to a simulated shock wave of 0.3 MPa peak pressure from anterior direction. This was simulated using the ConWep module available in the LSDYNA explicit finite element modeling software. Three dimensional plots of maximum pressure and maximum stress clearly demonstrated significant effects of the dynamic shock load. The generated HRFEM for the brain and the simulation results demonstrate the capability of the modeling approach in describing the brain response under shock-type loads, including those caused by blast wave.

Blast Analysis, Design and Research: A Canadian Perspective

In order to protect structures against accidental or deliberate blast loads, special expertise and knowledge are necessary to ensure adequate performance of the structural systems. Although the structure may require an extensive repair following a blast event, the main goal of the protective design is to avoid structural progressive collapse and minimize fragments. Blast loading is very different from other forms of dynamic loading generally analyzed by structural engineers. Peak pressures are several orders of magnitude higher than those associated with other typical dynamic loads, and blast load durations are usually much shorter than the fundamental period of the structure. This paper will focus on the blast loading phenomena, analysis procedures and design implications as specified by the two recently developed North America’s codes, ASCE SEI59-11 (2011) and CAN CSA S850-12 (2012). In addition, the results of an ongoing multi-year large-scale experimental and analytical program at McMaster University, Canada will be highlighted.Copyright

Use of Reinforced Rigid Polyurethane Foam for Blast Hazard Mitigation

This article presents the development of a cost-effective lightweight protection technique for explosives transporting container and storage facilities employing surface-mounted Rigid Polyurethane Foam (RPF) plates. Different RPF specimens were prepared with different densities and sand particle reinforcement ratios ranging between 0% (unreinforced) and 30%. Mechanical properties characterization was conducted to optimize an RPF formulation to be tested under blast loading using different experimental techniques. Explosive scaling laws were utilized to relate indoor blast test results (performed with small explosive charges) to real-life blast scenarios. Small RDX explosive charges were placed and detonated inside RPF specimens to correlate the size of the resulting cavity to the explosive charge weight and the RPF density. Another set of experiments were conducted to evaluate the maximum deformation depth of lead witness plates resulting from blast waves. In these latter experiments, explosive charges were mounted on the free surface of RPF plates. In general, test results demonstrated the capability of reinforced RPF as a light weight cost-effective technique to mitigate blast load hazard.