Structural Design for Physical Security: State of the Practice

This chapter is intended to introduce the reader to physical security concepts for structures, existing physical security criteria, and the risk management process as it pertains to structures. The typical layers of physical security in the design process are described. A security specialist typically performs risk and vulnerability assessments, works with the project stakeholders to develop risk-based, project specific design requirements, and develops operational and physical security measures to mitigate risks to an acceptable level. The roles of security specialists with demonstrated experience in risk assessment and management, electronic security, physical security design are discussed, An overview is given of existing physical security criteria provided by United States government agencies and professional organizations that may be applicable or adapted to a wide range of building facilities.

This chapter describes the methods for load definition, quantification, and application that are often considered in the structural design of facilities intended for enhanced physical security. These loads are defined in terms of aggressor threats and tactics in the context of intentional events employing explosives, ballistics, forced entry, and vehicle ramming. Factors affecting severity of loading are investigated, including explosive type, weight and standoff distance measured from the center of mass of the explosive to the surface of the intended target, and angle of incidence measuring the degree of off-normal incidence. Ballistic threats are generally specified in terms of a projectile's caliber, impact velocity, impact kinetic energy, and the number of such impacts to be expected or protected against.

Structures that are designed for enhanced physical security incorporate blast resistance, forced entry resistance, ballistic resistance and antiram impact resistance. Because forced entry resistance, ballistic resistance, and vehicle impact resistance are predominantly based on performance testing, this chapter focuses on the quantitative evaluation of blast-resistant design and barrier foundation resistance to vehicle impact. The characteristics of blast loading that affect structural response and damage potential are described. The two main characteristics of blast-resistant design are inertial resistance and ability to deform in a ductile manner. The dynamic nonlinear response characteristics of structural systems are hysteretic, and a variety of ways in which this behavior may be represented analytically are considered.

This chapter provides the practicing structural engineer with technical information and guidance for the design of individual components of a structural system that is designed to resist such impulsive loading effects as blast, forced entry, and ballistic impacts. Construction materials covered include reinforced concrete, prestressed/ posttensioned concrete, structural steel, cold-formed steel, reinforced masonry, and wood. For each structural component, relevant information is provided to assist the designer in understanding the component's primary response characteristics (i.e. geometrical and material influence, flexural, axial and shear response modes, inbound/rebound phases, ductility and end rotations, and penetration resistance) and in implementing best-practice design provisions. The critical role of structural detailing of components in blast design is discussed, particularly for achieving the desired level of component inelastic deformations without experiencing brittle connection failure, or any form of global/local buckling. Recommendations for connection design and ductile detailing are also provided.

This chapter focuses on aspects of structural design for mitigating the effects of physical attack, specifically blast, ballistic, forced entry, and vehicle ramming as they relate solely to nonstructural components. Gaps in data and analytical methods for design of nonstructural components and critical infrastructure are explored. Nonstructural component types are varied in their construction, purpose, and vulnerability to physical attack; the unique attributes of each are identified as they relate to physical security design and interdependencies with, and/or connection to, structural and other building components, particularly for blast mitigation. Also investigated is extension of general best practices often used in security planning and protective design of structural components to nonstructural components and critical infrastructure systems as part of a comprehensive design approach for physical security.

Large flying glazing debris and glass shard hazards cause the vast majority of injuries during deliberate bombing events and accidental explosions, and are therefore a critical aspect of physical security design. This chapter presents the physical security designer with guidance on the methodologies and materials most commonly used in the design and analysis of glazed security facades. Special design considerations for addressing blast, ballistic, and/or forced entry requirements are introduced. Engineers involved in design for physical security must obtain a level of knowledge of the components of glazed systems, their detailing, their anchorage, and interaction with their supporting structure. A description is given of industry standard methods for the analysis of glazing and framing systems for blast loading. Specific focus is on dynamic and static analysis approaches. Industry standard methods for ballistic resistant glazing and framing systems are also described.

This chapter addresses nonwindow openings in the building envelope, including doors and utility opening covers. Each of the non-window-opening systems consists of various components that play important roles in the physical security performance of the system, either by providing protection or by being integrated with those components providing protection. General design criteria and design methodologies that can be used for designing doors and utility opening products are provided. Consensus test standards exist for the empirical evaluation or certification of doors and other opening covers, and can be very useful in evaluating unique or specially designed systems and certification of more commonly manufactured products. Standards related to doors and other opening covers are provided. Physical security design strategies for non-window-opening items that must be incorporated throughout the design process are discussed, with specific emphasis on structural design for physical security.

This chapter addresses the assessment of existing structures in response to blast, ballistic (sans active shooter), and forced entry events in the context of two scenarios: an expected future adversarial event that would require a risk assessment followed by the implementation of mitigation measures, and the aftermath of an event that would initiate a forensic investigation to determine cause and effect. Ultimately, the assessment process for protective design measures considers the results of the risk assessment or established design criteria and design basis threat (DBT) scenarios that define loading and determine the expected performance and subsequent impact of a successful attack. General guidance for the assessment and mitigation of security vulnerabilities is provided and more specific guidance for blast, disproportionate collapse and forced-entry/ballistic is also included.

Protective design measures are typically applied to bridges that are of an iconic nature and/or of asset value to society, or those with a significant cultural or economic value. Therefore, this chapter focuses on features associated with long-span bridges and other important iconic bridge types. It also focuses on applying physical security principles for bridges; threat, vulnerability, and risk assessments; establishment of the Design Basis Threat (DBT); global response of bridges to blast; bridge components, response, and mitigation; and design specifications of new bridges. The particular focus of the last section of this chapter is on the performance of Threat, Vulnerability, and Risk Assessment (TVRA) for a subject bridge that would identify critical, and potentially costly, design requirements.

Testing for physical security performance is undertaken for a number of reasons, ranging from early stage research or prototyping new products to establishing performance for installation at a specific location. This chapter provides an overview of test planning, certification, and common test methods and standards, with the objective of outlining the basic considerations of testing and certification and directing the design practitioner to an appropriate reference to plan the specifics of a test program. The discussion includes testing objectives, product certification, and common test methods for blast, ballistic, forced entry, and vehicle impact. The test methods discussed generally fall into one of the following categories: shock tube testing, open-air explosive testing, and quasi-static pressure loading.