The Virginia Tech Infrastructure Protection Research Group
The Infrastructure Protection Research Group is home to the Virginia Tech Shock Tube Testing Facility, a new extreme load testing facility for simulating explosive blast loads on structures. Led by Dr. Eric Jacques, Assistant Professor in CEE Structural Engineering and Materials, the research group is committed to safeguarding the physical security and socio-economic well-being of the public against improvised terrorist bombings and accidental industrial explosions. To achieve this, Dr. Jacques and his group aim to: (1) develop and deploy cutting-edge structural engineering tools, technologies and testing facilities to better protect vulnerable infrastructure, and (2) engage diverse stakeholders in conversation to develop cost-effective, risk-informed mitigation strategies.
Externally-bonded carbon fiber reinforced polymer (CFRP) retrofits were studied for enhancing the blast resistance of reinforced concrete slabs and walls. Companion sets of reinforced concrete wall and slab specimens were subjected to a total of sixty simulated explosions using a shock tube. Externally bonded FRP retrofits were an effective retrofit technique to improve the blast resistance of reinforced concrete structures, provided that debonding of the composite from the concrete substrate is prevented. The test results also indicated that FRP retrofitted reinforced concrete structures may survive initial inbound displacements, only to fail by moment reversals during the negative displacement phase.
Sponsor: CBRNE Research and Technology Initiative (CRTI) project CRTI-06-0150TD, Fyfe Co. LLC, NSERC, and the University of Ottawa
A blast vulnerability assessment of major structural components of the East Block of Parliament Hill was performed. Approximately 60 resistance curves, and pressure-impulse (PI) diagrams were generated for the entire exterior of the structure. The exterior walls were discretized into seven common wall types, considering typical offices, towers, entrance ways, senate chambers, and any other unusual structural configuration. Each wall type was further subdivided by storey level, which affects axial load. The out-of-plane blast resistance of the walls was analyzed using both a one-way and two-way flexural approach.
Sponsor: Public Works and Government Services Canada, Baker Engineering and Risk Consultants
The goal of these tests was to characterize the behavior and performance of various configurations of skin-core construction methodologies used in full-sized blast-resistant steel doors. Quasi-static flexural tests were performed to characterize beam-assembly response under seated and seated loads, as well as establish in-situ capacities of typical hinge and latch hardware.
Sponsor: AMBICO Limited
Computer software BRADS (Blast Resistant Anchor Design Software) was developed for conducting two-degree-of-freedom (TDOF) analysis and window anchor design. The algorithm underlying the software was developed to satisfy the requirements of CSA S852 , the new Canadian standard for Blast Resistant Window Anchor Systems, and was validated against experimental shock tube anchor tests. The tool can compute the required configuration of window retention anchors based on the major parameters known to influence anchorage capacity, including: substrate flexibility, glazing response, window aspect ratio, frame rigidity, the distribution of dynamic reactions, combined stresses, and anchor boundary conditions. The automated analysis procedure evaluates dynamic reactions generated during the pre-break and post-break phases, and considers the possibility of load reversal when determining design anchorage forces during inbound and rebound response.
Sponsor: Canadian Safety and Security Program (CSSP) project CSSP-2014-CP-2011.
An analytical procedure was developed to generate the load-deformation characteristics of laterally restrained reinforced concrete members, a phenomenon commonly referred to as compression membrane arching action. The lateral restraint provided by adjacent structural members generates large internal compressive forces resulting in an overall increase in strength and stiffness characteristics. The procedure assumes that flexure and arching calculations are uncoupled, and that the arching force component will follow a simply supported mode shape with lateral axial restraint. A pure flexure analysis is used to determine the degree of contact between the beam-end and lateral support. The arching contribution to member strength capacity is calculated based on the contact force arising from the projection of the beam-end into the lateral support. The total strength due to arching is the superposition of pure flexure and arching strength components. The methodology can handle supports with both rigid and non-rigid lateral restraint and varying degrees of rotational fixity. The numerical procedure has been verified extensively against static experimental data found in the literature and can be used to model arching action under static conditions, or for inelastic dynamic analysis of structures subjected to blast and impact.
This study applied advances in big data and visual data analytics to the field of protective design. A database of historical terrorist activities was analyzed using the Tableau visual data analytics software package to identify meaningful trends in historical data and demonstrate sensitivity of assets to particular types of terrorist attacks by non-state actors based on key geographic, socioeconomic, and contextual characteristics. The research will support improvements to existing terrorism risk methodologies leading to cost-effective, risk-informed decisions to identify the most vulnerable buildings in a large portfolio of buildings.
The Canadian Safety and Security Program (CSSP) funded the University of Ottawa to develop blast-resistant window retention anchors to improve Canada’s preparedness and prevention capabilities against blast threats. The project included a significant experimental component consisting of shock tube blast testing of full size windows anchored to different substrates (concrete, steel block masonry and stone masonry). The objectives of the tests were to collect much-needed experimental data on anchor performance, develop new design tools and procedures, and develop a new national design standard on blast-resistant window retention anchors, CSA S852. The experimental data obtained from blast testing of windows was used to validate analysis procedures developed for the purpose of blast-resistant window anchorage design and assessment.
Sponsor: Canadian Safety and Security Program (CSSP) project CSSP-2014-CP-2011 and the University of Ottawa
Litebuilt’s 1200 kg/m3 “LiteBlok” lightweight aerated concrete “Jumbo” block product is intended for use in non load-bearing wall construction suitable for interior applications, with a minimum equivalency equal to traditional masonry construction. Experimental tests were conducted to establish the structural behaviour of LiteBlok prisms subjected to concentric and eccentric axial compression, as well as to study the flexural behaviour of LiteBlok walls having a plane of failure parallel and perpendicular to the bed joint. Results showed the importance of using reinforcement in LiteBlok construction to improve capacity and limit the development of cracks in the blocks and in the grout. Furthermore, owing to the use of lightweight aerated concrete and an interlocking bed joint mechanism, LiteBlok was found to benefit from rapid dry-stack construction. Compared to the constructability of conventional masonry, these specific attributes are a major competitive advantage.
Sponsor: LiteBuilt Concrete Canada and National Research Council Canada
As-built and glass-fiber-reinforced polymer (GFRP)-retrofitted reinforced concrete columns were subjected to simulated blast loading using a shock tube. Retrofitting involved various configurations of longitudinal and transverse GFRP layers to enhance flexural and shear capacity. Retrofitting significantly increased the strength and stiffness of reinforced concrete flexural members and greatly improved blast response. Furthermore, the addition of transverse GFRP wraps led to enhancements in the debonding strain and behavior of longitudinal GFRP, as well as an increase in post-peak ductility of concrete.
Sponsor: Fyfe Co. LLC, and the University of Ottawa
High strain-rate loading on the flexural response of typical light-frame wood construction was investigated. Stud grade spruce-pine-fir (S-P-F) lumber specimens were tested within a range of low and high strain-rates between 6×10 -6 1/s to 0.4 1/s using a servohydraulic actuator and a shock tube. A novel single-degree-of-freedom iterative solution procedure was used to compute the high strain-rate modulus of rupture (MOR) and modulus of elasticity (MOE). Material dynamic increase factors (DIF) suitable for blast resistant design of timber structures were presented, and are in agreement with those prescribed by the Canadian Standard for Design and Assessment of Buildings Subjected to Blast Loads, CSA S850.
Sponsor: Canadian Wood Council and the University of Ottawa
Historic sash windows protected by “SecureTM” security blinds were tested under simulated blast loading using a shock tube in order to establish the blast performance of the blinds. The security blinds were placed near the inside face of the windows and consisted of vertical blades and an optional horizontal locking bar. The specimens were tested with different orientations of the blades from fully-closed to fully-open. Reflected pressures on windows ranged between approximately 12 kPa and 70 kPa, with almost constant duration (varying between 13 ms and 16 ms). The shades were effective in reducing the debris generated by blast pressures, however, a failure mode was observed at shade opening greater than 45 degrees whereby wood debris from the frame wedged between the blades and prevented them from closing. No damage or permanent deformation of the shades was observed.
Sponsor: Department of Foreign Affairs and International Trade, and the University of Ottawa
A new line of blast-resistant steel doors for the minimum anti-terrorism market was developed and validated for the manufacturer through combined experimental and analytical research. Full-scale shock tube blast testing was used to determine the response of the doors relative to ASTM F2927 door and glazing classifications. A number of parameters affecting door response were considered, including door aspect ratio, construction methodology, door-frame construction, as well as anchor size and quantity. The experimental portion of the study was complemented by an analytical investigation to develop door design tools. Finite element analysis was employed to generate door resistance curves. This was followed by single-degree-of-freedom dynamic analyses to predict the various levels of protection for the blast scenarios studied.
Sponsor: AMBICO Limit and the University of Ottawa
OverPressure abbreviated is an easy-to-use software tool designed to compute the blast effects caused by the surface detonation of high explosive using UFC 03-0340-02 (2008) blast parameter data. The tool can generate incident and reflected pressure time-histories suitable for use in single-degree-of-freedom (SDOF) analysis. The pressure-time histories generated by can be imported directly into RCBlast (2013) for inelastic dynamic analysis of blast-loaded structures. The software can also be used to back-calculate TNT charge-weight and stand-off distance, given a specific pressure-impulse combination. OverPressure is available as a free download.
RCBlast was developed to conduct dynamic inelastic response history analysis of structural elements subjected to blast-induced shock waves. It can be used to quickly generate SDOF time histories and PI diagrams for user defined blast threats. The software has a built-in structural analysis module that can generate high fidelity resistance curves for common one-way reinforced concrete elements incorporating: advanced material models; externally bonded FRP retrofits; variable axial load; compression membrane arching action; non-linear behavior; and more. Free download from http://www.rcblast.ca/
This study evaluated bond behavior of lap-spliced reinforced concrete beams subjected to high strain rates. Eleven companion pairs of beams, each consisting of two nominally identical specimens, were designed, built and tested. One beam from each companion pair was tested under static loads generating an average strain rate of 10-5 s-1 , while the other was subjected to high strain rates in the range of 1.0 s-1 generated using a shock tube. Average peak dynamic beam resistance increased by 30% relative to the reference static conditions due to high strain rate effects. Part of this increase was attributed to improvements in the load carrying capacity of the lap splices, which on average experienced a dynamic increase factor (DIF) applied to bond strength of 1.28. Regardless of strain rate, it was found that the bond strength of splices with and without transverse reinforcement increased in proportion to the ratios of the minimum cover depth and the splice length to bar diameter, respectively.
Sponsor: PhD Research Topic at the University of Ottawa
A preliminary seismic risk screening tool was developed to exempt buildings from detailed seismic risk assessment if key exemption criteria are met. The exemption criteria are based on: a seismic categorization system linked to anticipated building damage and seismicity; whether or not the building was designed using modern seismic design provisions; and the remaining time that the building will be occupied. The tool also provides a second list of criteria, which if satisfied, will automatically trigger further detailed seismic risk assessment. The decisions rendered by the tool were evaluated against the next level of seismic risk screening tool to ensure consistency. A flowchart was developed to facilitate adoption of the new tool by practicing engineers and other end-users.
Sponsor: Public Works and Government Services Canada and National Research Council Canada
Shock tube testing was used to assess the blast performance of a proprietary metal mesh drapery known as “GuardianCoil”. The system was used to stop projectiles from fragmentation of unreinforced masonry (URM) walls and glazed windows and was installed on the unloaded/interior side of these non-structural elements. Each test sample was subjected to a single, destructive pressure-impulse combination generating high velocity projectiles. The GuardianCoil contained the entirety of the unreinforced masonry block walls and prevented potentially life threatening projectiles from penetrating the test area. It also contained the entirety of the large glass fragments within the first meter of the drapery. The pieces of mortar or glass that penetrated the test area were limited to the weave size, and did not pose a life safety hazard.
Sponsor: Department of Foreign Affairs, Trade, and Development Canada, Cascade Coil, and the University of Ottawa
The demand for Structural Insulated Panels (SIPs) as an alternative to light frame construction in residential and light-commercial buildings is increasing, driving the the need for proper design requirements to satisfy regulatory agencies and building officials. A combined experimental and analytical study was conducted to investigate the structural behavior of OSB-faced Structural Insulated Panels (SIPs) subject to short-term axial loading. Panels with varying types of foam core, thickness, and other construction details were subjected to concentric and eccentric loading. Reliability-based design expressions were developed for the ultimate limit state of SIPs subjected to short duration concentric and eccentric axial loading. The results were also compared to current allowable stress design practices. In addition to presenting important test data for researchers, this study generated a number of practical manufacturing and design recommendations to improve the performance of SIPs.
Sponsor: Consortium of producers, manufacturers, users, and regulatory agencies.
Structural insulated panels (SIPs) are a panelized building system composed of external oriented strandboard wood sheets bonded to a lightweight boardstock or pour-in-place foam core. This project investigated the structural behavior of OSB-faced SIPs subject to short-term out-of-plane transverse loading. A total of 35 panels with varying types of foam core, thickness and other construction details were subjected to partially distributed uniform loading. The results showed that the ultimate shear resistance of SIPs is proportional to the mechanical properties of the core, and inversely proportional to the thickness of the core. The observed relationship between core shear stress at failure and core thickness was used to calibrate a reliability-based design expression to predict the shear strength of full-size panels based on properties obtained from small-scale foam material tests. Sandwich panel theory can accurately predict the initial stiffness of SIPs when behavior remains in the linear range. Finally, recommendations regarding panel design and construction were made to improve the shear behavior of SIPs.
Sponsor: Consortium of producers, manufacturers, users, and regulatory agencies.