Designing Buildings to Resist Explosive

Threats

by Robert Smilowitz

Weidlinger Associates, Inc.

Last updated: 10-19-2011

Within This Page

Introduction

Description

Relevant Codes and Standards

Additional Resources

Introduction

The four basic physical protection strategies for buildings to resist explosive threats are

1) Establishing a secure perimeter; 2) Mitigating debris hazards resulting from the

damaged façade (see also WBDG Glazing Hazard Mitigation; 3) Preventing progressive

collapse; and 4) Isolating internal threats from occupied spaces. Other considerations,

such as the tethering of non-structural components and the protection of emergency

services, are also key design objectives that require special attention.

Generally, the size of the explosive threat will determine the effectiveness of each of

these protective strategies and the extent of resources needed to protect the occupants.

Therefore, determining the appropriate design threat is fundamental to the design process

and requires careful consideration.

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Description

A. Defining the Design Threat

Comprehensive threat and vulnerability assessments, and risk analysis can help the

design team understand the potential threats, vulnerabilities, and risks associated with a

building as well as determine the design threat for which a building should be designed to

resist. Usually, the definition of the design threat is based on history and expectation.

However, it is limited by the size of the means of delivery. For example, a hand-carried

device, if efficiently packaged, could occupy as little as half a cubic foot of space and

could be easily concealed in a large brief case or small luggage and introduced deep into

the structure where it could do considerable damage. As a result, screening stations at the

entrances, mailrooms, and loading docks provide the best means of preventing hand-

carried satchel threats from entering the occupied spaces. On the other hand, vehicle

threat, which can carry significantly larger explosive charge weights, requires secured

perimeters and comprehensive screening procedures for underground parking structures

or loading docks.

Screening procedures, however, have limitations and the potential for threats to bypass

their scrutiny must be recognized in the physical protection scheme. Therefore, the

selection of the design level explosive threat depends on the features of the building, the

site conditions, and the level of risk the client is prepared to accept.

Blast Loading

Because this Resource Page focuses on explosive threat, one must first understand how a

blast affects its surrounding environment. When an explosive device is detonated at or

near the ground surface, shock waves radiate hemispherically and the peak intensity blast

pressure decays as a function of the distance from the source. The incident peak pressures

are amplified by a reflection factor as the shock wave encounters an object or structure in

its path. Reflection factors depend on the intensity of the shock wave and the angle of

obliquity of the shock front. However, when the explosion is within an occupied space,

the confinement of the explosive by-products produces a quasi-static gas pressure that

needs to be vented into the atmosphere.

The intensity of the blast pressures is therefore a function of the charge weight and the

standoff distance to the protected space. Charges situated extremely close to a target

structure impose a highly impulse, high intensity pressure load over a localized region of

the structure. This high intensity loading tends to shatter or shear through the structural

materials. At greater distances, the intensity of the peak pressure is significantly reduced;

however, the surface area over which it acts is much greater. As a result, the hazard

potential is increased over a larger portion of the structure.

Dynamic Analysis of Building Systems

The performance of building systems in response to explosive loading is highly dynamic,

highly inelastic, and highly interactive. By controlling the flexibility and resulting

deformations, structural or façade components may be designed to dissipate considerable

amounts of blast energy. The phasing of the different responses and the energy that is

dissipated through inelastic deformation must be carefully represented in order to

accurately determine the behavior. The 'sequential single-degree-of freedom (SDOF)

model' approach, commonly used to analyze individual components, is likely to produce

overly conservative designs, while an accurate representation of the structural system

truly requires a complex 'multi-degree-of-freedom (MDOF) model.' These MDOF

models may be developed using appropriate inelastic Finite Element software for which

an explicit formulation of the equations of motion may be solved. The details of the finite

element models, including the interaction between the glass and the support mullions,

will determine the accuracy of the analysis. Only this approach will provide the most

authentic representation of the system's ability to resist the dynamic blast loading AND

provide the most economical design.

Performance Standards

Analytical tools that evaluate the likely performance of curtain-wall façades in response

to blast loads are used to demonstrate compliance with established blast criteria or

performance specifications. Many of these performance specifications contain the

criterion that the building system must be a balanced design. The objective of this

criterion is to realize the capacity of all the materials, maximize the potential energy

dissipated due to deformation, and manage the failure mechanisms. This is accomplished

by assuring a controlled sequence of failure. Depending on the specified performance

conditions, the application of this criterion could have significant impact on the sizing of

the members and the design of the connections between the different components.

The behavior of structural materials, such as steel and aluminum, in response to explosive

loading was the subject of intense investigation by the governments of the United

Kingdom, Israel, and the United States of America. Some of these materials behave very

differently when subjected to high strain rate loading than they do under static conditions.

Furthermore, the inelastic deformation of these members depends on their section

properties, shape functions, and extent of deformation. For compound sections composed

of different pieces and materials, transformed section properties may be used to

characterize an equivalent material and a combined or composite section property may be

used to represent its structural resistance. Care must be taken to calculate composite

section properties when strain compatibility between components can be justified and

combined section properties when deformation compatibility between components is

enforced.

B. Physical Protection Strategies and Features

Perimeter Protection

While it may be possible to predict effects of a certain charge weight at a specified

standoff distance, the actual charge weight of the explosive used by a terrorist, the

efficiency of the chemical reaction, and the source location cannot be reliably predicted.

Given the uncertainties, the most effective means of protecting a structure is to keep the

explosive as far away as possible by maximizing the keep-out or standoff distance.

However, this approach is only necessary if an analysis identifies the building to be at

risk of attack as opposed to suffering collateral damage due to an attack on a nearby

target.

To guarantee the maximum keep-out distance between unscreened vehicles and the

structure, anti-ram bollards or large planters must be placed at the curb around the

perimeter of the building. The site conditions will determine the maximum speeds

attainable, and thus the kinetic energy that must be resisted. Both the bollard and its

foundation must be designed to resist the maximum load. Conversely, if design

restrictions limit the capacity of the bollard or its foundation, then site restrictions will be

required to limit the maximum speed attainable. Furthermore, public parking abutting the

building must be secured or eliminated, and street parking should not be permitted

adjacent to the building. Removing one lane of traffic and turning it into an extended

sidewalk or plaza can gain additional standoff distance. However, the practical benefit of

increasing the standoff depends on the charge weight. If the charge weight is small, this

measure will significantly reduce the forces to a more manageable level. If the threat is a

large charge weight, the blast forces may overwhelm the structure despite the addition of

nine or ten feet to the standoff distance and the measure may not significantly improve

survivability of the occupants or the structure.

Façade Protection

The building's exterior is its first real defense against the effects of a bomb. How the

façade responds to this loading will significantly affect the behavior of the structure.

Hardening of the façade is typically the single most costly and controversial component

of blast protection, and may produce a dramatic change to the exterior appearance of the

structure such as smaller window sizes and more rugged attachments. Moreover, given

the large surface areas of most buildings, modest levels of protection may not be cost-

effective. Therefore, it may be best to concentrate on improving the post-damaged

behavior of the façade.

Except for very thick lights, most glazing materials and components designed to respond

to the blast loads will most likely be damaged by the blast overpressures. To improve the

post-damage behavior of the glazing system, one could specify laminated glass for new

construction or apply anti-shatter film to existing glazing. While these features do little to

improve the strength of the glass, they attempt to hold the shards of glass together and

better protect the occupants from hazardous debris (see also WBDG Glazing Hazard

Mitigation. Laminated glass possesses the best post-damage behavior, may be used with a

wide variety of glazing materials and thickness, and provides the highest degree of safety

to occupants. The effectiveness of Mylar films, on the other hand, depends on the method

of application and the thickness of the film. Common film systems range from a simple

edge-to-edge (daylight) application, to a wet glazed adhesion, to a mechanical attachment

to the existing window frame. The mechanical attachments are most effective when they

are anchored to the underlying structure. Regardless of the method, there are architectural

issues and life-cycle costs associated with the use of anti-shatter films.

Equally important to the design of the glass is the design of the window frames. For the

window to properly fail, the glass must be held in place long enough to fail. Short of that,

the glazing will dislodge from the housing intact and cause serious damage or injury. The

capacity of the frame system to resist blast loading should therefore exceed the

corresponding capacity of the glazing, often referred to as the "glass fail first criteria."

Factors of two to three, over the nominal capacity of the glass to resist breakage, may be

required to design the frames. The bite, including the possible use of structural silicone

sealant, must be adequate to assure the failed glass is retained within the frame.

Depending on the façade, the mullions may be designed to span from floor to floor or tie

into wall panels and must be capable of withstanding the reactions of a window loaded to

failure. Finally, the walls to which the windows are attached must be designed to accept

the reaction forces as well.

Designing glazing systems capable of resisting a specified overpressure requires a

cascade of costly upgrades to the façade, including really thick laminated glass, and

relatively heavy frames and mullions. There are also major construction challenges such

as reinforcement and steel embedments that get in the way of new cast-in-place

reinforced concrete wall construction, and the substantial anchorage required to

accommodate the large reaction forces. Moreover, attaching these window systems to

existing walls may even be a physical impossibility. Because the improved capacity is

likely to fall far short of the pressures associated with a realistic terrorist threat, it is

recommended that for new construction with low threat criteria and limited budgets for

blast protection, the engineer select the weakest laminated glazing that satisfies wind and

serviceability requirements. In this way, the improved post failure behavior provides the

occupants a measure of protection at a reasonable cost.

Curtain Wall Protection

Fig. 1. Sample blast curtain wall engineered to take advantage of a flexible system. Some

protective features may include: insulated glazing unit with laminated inner light; glazing

adhered to mullion with structural silicone sealant; and curtain-wall frame with steel

backup encased in aluminum.

A curtain wall is a nonbearing exterior enclosure that is supported by a building's

structural steel or concrete frame and holds either glass, metal, stone, or precast concrete

panels. Lightweight and composed of relatively slender extruded aluminum members,

curtain-wall façades are considerably more flexible than conventional, hardened punched

window systems. In a blast environment, the mullion support would absorb a portion of

the blast energy and improve the performance of the glazing, allowing the glazing to

sustain greater blast environments (although the mullions themselves should be designed

to resist the forces collected by the glass).

It is important to take into account the inherent flexibility of curtain-wall systems when

sizing members for blast loads and evaluating the glazing for hazard. This enables the

engineer to both ascertain the true blast worthiness of the curtain wall as well as to

properly calculate the reduced load transfer into supporting structural elements.

The design of curtain-wall systems to withstand the effects of explosive loading depends

on the performance of the various elements that comprise the system. Curtain-wall

response software, based on more sophisticated finite element methods than simplified

Single-Degree-of-Freedom glass fragment hazard analytical approaches, was developed

for the Department of Defense, Technical Support Working Group (TSWG) to accurately

represent the capacity of the glazing and the supporting frame members. While the

glazing may be the most brittle component, the performance of the system, and the

reduction of hazard to the occupants depend on the interaction between the capacities of

the various elements. In addition to hardening the individual members that comprise the

curtain-wall system, the attachments to the floor slabs or spandrel beams require special

attention. These connections must be adjustable to compensate for the fabrication

tolerances and accommodate the differential inter-story drifts and thermal deformations

as well as be designed to transfer gravity loads, wind loads, and blast loads.

Energy-Absorbing Catch Systems

Fig. 2. Sample catch system

An alternative approach to blast protection takes the concept of a flexible curtain-wall

system one step further by making full use of the flexibility and capacity of all the

window materials to absorb and dissipate large amounts of blast energy while preventing

debris from entering the occupied space. Energy-absorbing catch systems (a.k.a. Cable

Protected Window Systems (CPWS)) work in such a way that as the glass is damaged it

bears against a cable catch system, which in turn deforms the window frames. Extensive

explosive testing, as well as sophisticated computer simulations, has demonstrated the

effectiveness of these systems.

Floor Slab Reinforcements

A reinforced-concrete, flat-plate structural slab is an economical system that provides for

maximum use of vertical space, particularly for buildings in areas with height restriction.

However, when subjected to a blast load, punching shear and softening of the moment-

resisting capacity of the slabs will reduce the lateral-load-resisting capacity of the system.

Once the moment-resisting capacity of the slabs at the columns is lost, the ability of the

slab to transfer forces to the shear walls is diminished and the structure is severely

weakened. In addition to the failure of the floor slab, the loss of contact between the slab

and the columns may increase the unsupported column lengths, which may lead to the

buckling of those columns. Furthermore, the lateral load resisting system—which

consists of the shear walls, the columns, and the slab diaphragms that transfer the lateral

loads—may be weakened to such an extent that the whole building may become laterally

unstable.

Fig. 3. Floor slabs

Conventional flat-plate design may be upgraded by paying more attention to the design

and detailing of exterior bays and lower floors, which are the most susceptible to an

exterior vehicle explosive threat, and the design of the spandrel beams, which tie the

structure together and enhance the response of the slab edge. Drop panels and column

capitols may be used to shorten the effective slab length and improve the punching shear

resistance. If vertical clearance is a problem, shear-heads embedded in the slab will

improve the shear resistance and improve the ability of the slab to transfer moments to

the columns. Furthermore, the blast pressures that enter the structure through shattered

windows and failed curtain walls will load the underside and subsequently the top

surfaces of the floor slabs along the height of the building. Both the delay in the sequence

of loading and the difference in magnitude of loading will determine the net pressures

acting on the slabs. Consequently, there will be a brief time in which each floor will

receive a net upward loading. This upward load requires that the slab be reinforced to

resist loads opposing the effects of gravity.

Fig. 4. Column heads

The ductility demands and shear capacity required to resist multiple-load reversals often

force the engineer to provide beams to span over critical sections of the slab. The

inclusion of beams will greatly enhance the ability of the framing system to transfer

lateral loads to the shear walls. The slab-column interface should contain closed-hoop

stirrup reinforcement properly anchored around flexural bars within a prescribed distance

from the column face. Bottom reinforcement must be provided continuous through the

column. This reinforcement serves to prevent brittle failure at the connection and

provides an alternate mechanism for developing shear transfer once the concrete has

punched through. The development of membrane action in the slab, once the concrete has

failed at the column interface, provides a safety net for the post-damaged structure.

Continuously tied reinforcement, spanning both directions, must be detailed properly to

ensure that the tensile forces can be developed at the lapped splices. Anchorage of the

reinforcement at the edge of the slab or at a structural discontinuity is required to

guarantee the development of the tensile forces.

In all, the slab should be designed to prevent a punching shear failure that may in turn

develop into a progressive collapse. Although research has shown that punching shear

failures at interior columns are more likely to result in a progressive collapse than a

failure at an exterior column, the external bay around the perimeter of the structure must

be hardened at all intersecting columns for the external car bomb threat.

Column Reinforcements

For blast consideration, the distance from the explosion determines, to a great extent, the

characteristics of the loading on a structure. For example, buildings located at a

substantial distance from a protected perimeter—approximately 100 ft. or more—will be

exposed to relatively low pressures fairly uniformly distributed over the façade; buildings

located at shorter distances from the curb—most typical in urban environments—will be

exposed to more localized, higher intensity blast pressures. Due to direct blast pressures,

the columns of a typical building, which are designed primarily to resist gravity loads

with no special detailing for ductility demands, may experience severe bending

deformations in addition to the axial loads that the columns support. To enhance

protection, the columns must be designed to be sufficiently ductile to sustain the

combined effects of axial load and lateral displacement.

Fig. 5. Direct pressure

In conditions that cause uplift—the net upward load on the slab—the column's tension

will experience a brief tensile force. Conventional reinforced concrete columns not

designed to resist the combined effects of bending may be prone to damage under these

conditions. The lower-floor columns must therefore be designed with adequate ductility

and strength to resist the effects of direct lateral loading from the blast pressure and

impact of explosive debris. Reinforced concrete columns may be designed to resist the

effects of an explosion by providing adequate longitudinal reinforcement, staggering the

bar splices, and providing closely spaced ties at plastic hinge locations. Steel columns

may be sized to withstand the lateral loads and column splices may be detailed to develop

the plastic moments of the section. Existing concrete columns may be encased in a steel

jacket or wrapped with a composite fiber to confine the concrete core and increase the

shear capacity. On the other hand, existing steel columns may be encased in concrete to

add mass and prevent a premature buckling of the thin flanges. For more information on

retrofitting existing buildings, see WBDG Retrofitting Existing Buildings to Resist

Explosive Threats.

Fig. 6. Uplift

Fig. 7. Weakened connection

Preventing Progressive Collapse

In addition to façade debris hazards, building occupants may be vulnerable to heavier

debris resulting from structural damage. Progressive collapse occurs when an initiating

localized failure causes adjoining members to be overloaded and fail, resulting in an

extent of damage that is disproportionate to the originating region of localized failure. A

protective design may avoid structural systems that either facilitate or are vulnerable to a

progression of collapse resulting from the loss of a primary vertical load-bearing

member.

New facilities may be designed to accept the loss of an exterior column for one or

possibly two floors above grade without precipitating further collapse. In these cases, the

design requirements are intended to be threat-independent to protect against an explosion

of indeterminate size that might damage a single column, which results in adequate

redundant load paths in the structure should damage occur due to an unspecified

abnormal loading. The upgrade of existing structures to prevent localized damage from

developing into a progressive collapse may not be easily accomplished through the

alternate path method. This is because the loss of support at a column line would increase

the spans of all beams directly above the zone of damage and require different patterns of

reinforcement and different types of connection details than those typically detailed for

conventional structural design. For more information on retrofitting existing buildings,

see WBDG Retrofitting Existing Buildings to Resist Explosive Threats.

Alternatively, columns may be sized, reinforced, or protected to prevent critical damage

as a result of the design threat charge weight that may be located in close proximity to

them. The vulnerable concrete columns may be jacketed with steel plate or wrapped with

composite materials and the vulnerable steel columns may be encased in concrete to

protect the cross sections and add mass. For the upgrade of existing structures, these

approaches are better for preventing progressive collapse than supplementing the capacity

of the connecting beams and girders, or upgrading them using the alternate path method.

However, the effectiveness of these approaches is predicated on the operational and

technical security procedures that will limit the magnitude of the explosive threat. This

includes the establishment of effective perimeter protection, adequate screening of

vehicles entering an underground parking facility or loading dock, and inspection of

parcels that may be hand carried into the building. For more information on retrofitting

existing buildings, see WBDG Retrofitting Existing Buildings to Resist Explosive

Threats.

Fig. 8. Catenary

Transfer Girder Reinforcements

Transfer girders and the columns supporting transfer girders are particularly vulnerable to

blast loading. Transfer girders typically concentrate the load-bearing system into a fewer

number of structural elements, which contradicts the concept of redundancy desired in a

blast environment. Typically, the transfer girder spans a large opening, such as a loading

dock, or provides the means to shift the location of column lines at a particular floor.

Damage to the girder may leave several lines of columns, which terminate at the girder

from above, totally unsupported. Similarly, the loss of a support column from below will

create a much larger span that bears critical loads. Transfer girders, therefore, create

critical sections the loss of which may result in a progressive collapse. So if a transfer

girder is required and vulnerable to an explosive loading, then the girder should be

designed to be continuous over several supports. There should be substantial structure

framing into the transfer girder to create a two-way redundancy, thereby an alternate load

path in the event of a failure. The column connections, which support the transfer girders,

should be designed as Type 2 connections to provide sustained strength despite inelastic

deformations.

Fig. 9. Transfer girders

Overall Lateral Resistance

The conventional lateral loads—wind and seismic zone 1 forces—to which most

buildings are designed are minimal. These minimal lateral load requirements may be

resisted by a combination of shear walls, braced frames, and moment-resisting frame

action. At each floor level, the slab diaphragms transfer the lateral loads to the lateral-

load resisting system. Each component of the lateral-load resisting system must be

checked to determine its adequacy to resist blast loads. Depending on the results of a

blast analysis, the individual elements of the lateral-load resisting system may require

modification.

Buildings with an irregular floor plan will induce large torsional effects on the lateral-

load resisting system. Typically, symmetrical buildings behave better when subjected to

blast or seismic loading. If the shear core is centrally loaded a large demand is placed on

the diaphragm action of the floor slab to transmit the lateral loads from the perimeter of

the floor into the central shear walls. This effect can be more critical for blast load than

for seismic load. Seismic base motions are typically applied over the entire foundation;

blast loads resulting from a close-in explosion tend to impose higher intensity loads over

a more concentrated region. Although the total base shears may be nominally the same,

the lateral-resisting behavior is not. The usual rigid diaphragm action might not be

suitable in such a localized blast situation and a full three-dimensional analysis of the

building might be required.

Fig. 10. Diaphragm action

The ability of structures to resist a highly impulsive blast loading depends in great

measure on the structural detailing of the slabs, joists, and columns that provides for the

ductility of the load-resisting system. The structure has to be able to deform inelastically

under extreme overload (i.e., dissipate large amounts of energy) prior to failure.

Provisions have been established for the design of structures to resist seismic forces that

ensure both the ductility of the members and the capacity of the connections to undergo

large rotations without failing. For example, the provisions of Chapter 21 of the

American Concrete Institute 318 were devised to improve the behavior of reinforced

concrete structures subjected to large inelastic deformations.

In addition to providing ductile behavior, there needs to be a well-distributed lateral-load

resisting mechanism in the horizontal floor plan. The use of several shear walls

distributed throughout the building will improve the overall seismic as well as the blast

behavior of the building. If adding more shear walls is not architecturally feasible, a

combined lateral-load resisting mechanism can also be used. A central shear wall and a

perimeter moment-resisting frame will provide for a balanced solution. The perimeter

moment-resisting frame will require strengthening the spandrel beams and the

connections to the outside columns. This will also result in better protection of the

outside columns. For more information on seismic design, see WBDG Seismic Design

Principles.

Internal Partition Reinforcements

The walls surrounding loading docks, mailrooms, and lobbies—where explosive threats,

like a hand delivered package bomb, may be introduced prior to inspection and

screening—must be hardened to confine the explosive shock wave and permit the

resulting gas pressures to vent into the atmosphere. Specific modifications to the features

of these unprotected spaces can prevent an internal explosion from causing extensive

damage and injury inside the building. This hardening can be achieved by designing the

slabs and erecting cast-in-place reinforced-concrete walls, with the thickness and

reinforcement determined relative to the appropriate threat. The isolation of occupied

spaces from these vulnerable locations and any other unsecured spaces, such as

basements and underground parking garages, requires both adequate levels of

reinforcement as well as connection details capable of resisting the collected blast

pressures. These structural designs must be integrated with the remainder of the structural

frame to make sure they do not destabilize other portions of the gravity load-bearing

system.

Alternative Construction Materials to Resist Explosive Threats

A variety of materials, not traditionally used in building construction, may provide

alternatives to conventional blast hardening solutions. Among these alternatives there are

shock attenuating chemically bonded ceramics (SA/CBC), and composite systems

comprised of carbon, aramid and polyethylene fibers and resin. These materials are well-

developed systems currently in use for the prevention of sympathetic detonation of

explosives in munitions storage depots (SA/CBC materials) as well as in the seismic

retrofit of reinforced concrete columns in highway bridges in California (carbon fiber

wrapping). In the latter application, carbon fiber wrappings were found to have

advantages over conventional steel jacketing of columns due to problems with weld

seams and corrosion. Spray-on elasto-polymers have been demonstrated to protect

unreinforced masonry walls by providing a ductile membrane that enables these brittle

elements to sustain large deformations without fragmenting and throwing hazardous

debris.

In retrofit scenarios where conventional structural treatments may be too heavy or too

labor intensive, composite materials may be attractive alternatives because of their

lightweight and high tensile strength. However, full scale and component testing are

required to collect data on the performance of these materials in blast scenarios as well as

in different structural configurations. Ultimately, a set of analysis procedures and

structural engineering guidelines are needed in order for engineers to specify such

materials in both the retrofit of structures and in new construction.

Seismic Protection vs. Blast Protection

It is often stated that blast damage would be reduced if 'seismic-like' construction

standards were adhered to. However, this should not be taken to say that a structure

designed to resist the effects of strong ground motions would perform well in response to

an explosive loading. It is true that seismic building design details enhance the ductility

of structures and thereby increase their capacity to sustain plastic hinges and withstand

large rotations. Furthermore, for reinforced concrete structures, closely spaced stirrups

improve the confinement of the core and increase the shear capacity of the section. Yet, it

is important to understand that the nature of the blast loading and the structure's response

to it is very different from a seismic event.

The desirable features of earthquake-resistant design—that is, the provision for ductility

in member response and connection details, and redundancy in the ability to redistribute

extreme loads to lesser-loaded elements—are equally desirable in blast design. In both

cases, it is the obligation of the engineer to guarantee that the full capacity of the section

be realized and that no premature failure, resulting from inadequate confinement of a

reinforced concrete section or the local buckling of steel sections, prevents the structure

from transferring the loads to the foundation. Chapter 21 of the American Concrete

Institute 318 was developed to improve the behavior of reinforced concrete structures

subjected to large inelastic deformations. It is recommended that those provisions be

adhered to in designing the blast load resisting structural components. However, the

required extent of confinement and ductility, and the location of the stress concentrations

which form as a result of blast loading will not be the same as for structures subjected to

a seismic event. Furthermore, lateral loads resulting from strong ground motions are

proportional to the mass, which is distributed throughout the building. Conversely, blast

design relies, to some extent, on the inertial resistance of massive structural elements.

Finally, seismic resistance is distributed globally throughout the structure whereas blast

hardening must provide protection against localized explosive loads. Therefore, it should

not be assumed that a structure adhering to the governing building codes' recommended

provisions for seismic design or designed to withstand a strong ground motion is

sufficient to resist the prescribed blast loading or prevent subsequent progressive

collapse. For more information on seismic design, see WBDG Seismic Design Principles.

Nonstructural Components

Nonstructural building components, such as piping, ducts, lighting fixtures and conduits,

must be sufficiently tied back to structural elements to prevent failure of the services and

falling debris hazards. To mitigate the effects of in-structure shock, due primarily to the

infilling of blast over-pressures through damaged windows, these nonstructural systems

should be located below the raised floors or tied to the ceiling slabs with Seismic Zone IV

restraints.

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Relevant Codes and Standards

Federal standards and criteria are widely recognized as the primary source of guidelines

for the design of buildings to resist explosive threats. Because of the uniqueness of each

building's mission, functional requirements, and physical security design objectives, there

are limited codes and standards that apply to blast mitigation design.

Federal Guidelines

Department of Defense

o FM 3-19.30 Physical Security—Sets forth guidance for all personnel

responsible for physical security

o Unified Facility Criteria (UFC) 1-200-01, Design: General Building

Requirements

o Unified Facilities Criteria (UFC) 4-010-01, DoD Minimum Anti-

Terrorism Standards for Buildings—Establishes prescriptive procedures

for Threat, Vulnerability and Risk assessments and security design criteria

for DoD facilities.

General Services Administration (GSA)

o Facilities Standards for the Public Buildings Service, P100—Chapter 8,

Security

Other "official use only" documents may be obtained from the Office of

the Chief Architect

Department of State

o Architectural Engineering Design Guideline (5 Volumes) (limited official

use only)

o Physical Security Standards Handbook, 07 January 1998 (limited official

use only)

o Structural Engineering Guidelines for New Embassy Office Buildings,

August 1995 (limited official use only)

Private Sector Guidelines

Blast Effects on Buildings, 2nd Edition by David Cormie, Geoff Mays and Peter

Smith. London: Thomas Telford Publications, 2009.

American Concrete Institute 318, Chapter 21

Public Testing Institutions

ASTM International

Underwriters Laboratories (UL)

Private Testing Laboratories

Many private laboratories with expertise in protective glazing systems testing are

also available. Contact the Protective Glazing Council for additional information

and referral.