Perimeter security for historic buildings

Project Overview
Historically, the intended image of Federal public buildings was to be inviting and accessible to visitors while portraying the aura of importance of the Government in the everyday lives of its citizens. These government buildings sometimes continue to serve the public in their original capacity and sometimes get adapted for a more current function, while maintaining their design integrity. The General Services Administration is committed to upholding the architectural excellence of these important structures while keeping them accessible, functional and safe. Concerns for security at monumental Federal buildings have increased in the aftermath of the Oklahoma City bombing and the events of September 11, 2001. In many cases, grand historic government buildings, located in densely built urban districts, do not include setbacks from the streetline that would afford them adequate protection from blast damage. Where setbacks do exist, such as public plazas in front of monumental buildings, vehicles can easily approach without the presence of physical barriers. This report focuses primarily on perimeter vehicular barriers for Federal historic buildings. The goal of this pilot study is to meet the needs of perimeter security criteria in a sensitive manner such that the architectural integrity of the historic building and its urban context are maintained and the pedestrian experience be enhanced rather than diminished. In December 2000, KressCox Associates created a report entitled Culture and Commerce: Bridging the Federal Triangle for the U.S. General Services Administration. This report was to serve as the conceptual basis for the technical pilot study. In particular, the U.S. General Services Administration desired to test the “garden wall concept” presented in the KressCox report as a prototype through the development of construction document drawings, speciﬁcations and an estimate of associated construction costs. In addition, the U.S. General Services Administration sought concepts for alternate versions of the prototype elements for use at two other public buildings chosen to represent diverse historical styles and periods. The Howard M. Metzenbaum U.S. Courthouse in Cleveland, Ohio was chosen by the U.S. General Services Administration as the prototype project for the technical pilot. Built in 1903 to 1910, the Metzenbaum Courthouse, adjacent to Cleveland’s Public Square, is listed on the National Register of Historic Places. The special challenges of this particular facility include the proximity to the street, the vaults under the sidewalks, its prominence on Public Square, and the various amenities on the existing site. The proposed resolution of these issues is illustrated later in this report. Two other buildings chosen for alternate versions of the principal perimeter security elements are the Auditor’s Building and the U.S. Department of Housing and Urban Development Headquarters. Both are located in Washington DC, but vary greatly in materials and historical styles. The design process that evolved from the technical pilot study and the alternate versions has national application for providing perimeter vehicular barriers in a sensitive manner to historic Federal buildings, achieving GSA’s goals of preservation, performance, cost containment, public accessibility and design excellence.

Design Parameters
Design objectives and parameters developed by GSA and the design team include the following:

Types of passive perimeter security elements include the following: The Metzenbaum Courthouse prototype incorporates specially designed and structured planters as part of the anti-ram perimeter security. The landscaping at buildings should respond to the conditions of the site including location (urban, suburban, rural), climate, site conditions (drainage, hardscape areas, wetlands, forested areas, etc.), and maintenance operations. Selected plant materials should be suitable for the particular site including hardiness, sun exposure, habit and disease resistance. As many federal buildings are located on urban sites, chosen plant materials should be hardy enough to thrive even in the harsh conditions of urban areas which include salt, soil compaction and pollution. Site design conditions including project limit lines, how the site circulates, drainage and utility locations must be understood and coordinated, especially on renovation projects such as the Metzenbaum Courthouse. On large sites where the landscape is composed of extensive areas of lawn with trees, mowing may be a primary maintenance effort. In urban areas, typically the landscaping areas are smaller and more intensely planted. On a downtown urban block, such as the Metzenbaum Courthouse site, landscaping may be restricted to only planters and pots. Plantings may be rotated throughout the year for seasonal interest. Plant heights and shapes should be considered to ensure safety by maintaining views through the site. The level of maintenance that will be provided should be considered when choosing which plant material to use and how to install it. Young plants will require more maintenance to ensure survival that established plants. Irrigation, if budget allows, should be approached like other utilities and coordinated with building systems and access through the site. Irrigation is an initial capital cost for a project, but may pay for itself over a couple years in savings for maintenance. For urban locations with small areas of planting, hand watering is an option. Pruning, weeding and fertilizing are other areas that will require ongoing maintenance. Design cues for landscape design can be taken from the existing site. In addition to light conditions and orientation, existing plant materials may dictate a direction for the landscape design. At the Metzenbaum Courthouse, existing trees have shown a history of durability on this very exposed urban site. The landscape design solution for this application incorporates matching these existing trees. Another design parameter for the aesthetic aspects of the perimeter security elements relates to the historical context of the existing building. Taking cues, but not necessarily replicating, historical features, details and materials for perimeter security elements is part of the balance that occurs with any historic preservation project.
 * 1) Disguise the protection.
 * 2) Maintain accessibility to the public, i.e. permeability.
 * 3) Security design is part of urban design.
 * 4) Trees are not considered anti-ram.
 * 5) Light standards and other typical streetscape elements are not considered anti-ram unless engineered to do so.
 * 6) Elements can be combined.
 * 1) Bollards with foundations. Foundations to be tied together.  Spacing allows 4 feet clear maximum.
 * 2) Anti-Ram kneewalls with foundations. Three foot height minimum recommended. Can have open­ings, not greater than 4 feet clear.
 * 3)  Planters with foundations. Twelve inches below grade required for security protection.  Deeper required to be below frostline. Planters 3 foot height above grade.
 * 4) Surface-mounted planters. One-inch indent in slab minimum. Can be any shape or design.
 * 5) Bodies of water.
 * 6) Seating with foundations. Seat needs to be higher than axle of wheel.

General
The design of the technical pilot for perimeter security of historic buildings, using the Howard M. Metzenbaum U.S. Courthouse as the prototype, was a collaborative effort. The project was already in the working drawing phase for renovations to the Courthouse, so a design team familiar with the project and its site conditions was already in place. The technical pilot for perimeter security became an extension of that project. The U.S. General Services Administration, including the Ofﬁce of the Chief Architect and the regional ofﬁce, has been involved with decision-making, design issues and discussions with local authorities throughout the design process. Along with van Dijk Westlake Reed Leskosky, providing project management and architectural design, the design team consists of Sasaki Associates for landscapedesign, Hinman Consulting Engineers for blast engineering, Barber & Hoffman for structural engineer­ ing and Project and Construction Services for cost estimating. The team also closely collaborated with the United States Bacruptcy Court, Northern District of Ohio, the City of Cleveland City Planning Commission, Division of Engineering and Construction, Trafﬁc Engineering and the Greater Cleveland Regional Transit Authority.

Historical Context
The ﬁrst step in the design process was acquainting the perimeter security team with the historical and physical context of the Metzenbaum Courthouse. In 1901, architect Arnold W. Brunner of New York City won the competition to design the Cleveland Federal Building, once called the Old Federal Building and now known as the Howard M. Metzenbaum U.S. Courthouse and Federal Building. The structure is located in the heart of Cleveland’s central business district at the northeast corner of Public Square. Brunner’s commission places the project in the context of the emerging City Beautiful Movement and Cleveland’s Group Plan at the turn of the century. Brunner’s Federal Building was the ﬁ rst building of the Cleveland Group Plan to be built, and established the scale and style for the city’s subsequent important landmarks. Its site and approach were signiﬁcant to the city. The Public Library of 1925 directly across Third Street was intentionally patterned after the Federal Building and together the two form the inland terminus of the Group Plan Mall. Its prime site on the newly envisioned mall solidiﬁed the prominence and presence of the federal government, integrating public realm, urban design and architectural façade in one. Today, the Howard M. Metzenbaum U.S. Courthouse remains one of the most signiﬁcant landmarks within the downtown cityscape of Cleveland. The building is adjacent to Public Square and is a key element in anchoring the economic revival of the central core of Cleveland. It was listed in the National Register of Historic Places in 1974. The incorporation of perimeter security elements require design sensitivity to this important structure in its key urban setting.

Perimeter Security Zone
The Metzenbaum Courthouse site was analyzed for the application of anti-ram elements. Zones were created which dictated a variety of perimeter security elements. Clearly, a variety of types of elements is a more interesting design solution than using a single type of element, such as a bollard, around the entire site perimeter. All elements are designed to meet the anti-ram requirements previously established. The form and material of each element is designed to aesthetically compliment the style of the existing building and site conditions. The zones outlined below can and should be combined on various streetscapes.

Zone 1: Permeable. It allows physical pedestrian access to the site and is visually “lighter”. Bollards usually meet Zone 1 requirements. Several bollard styles were incorporated into the Metzenbaum project in a variety of locations where a more open feel was desired. Retractable bollards are also an option where vehicular access is required on a limited basis. Retractable bollards are incorporated into the Metzenbaum Courthouse on the north side at an access drive.

Zone 2: Partially Enclosed. This is a zone where site conditions allow planters or seating. These are more solid elements and they also add visual interest and public amenity to the site. These appear on the south and west sides of the Metzenbaum Courthouse.

Zone 3: Planting. This zone is located where there is a generous distance from the curb to the building. In the case of the Metzenbaum Courthouse, this occurs on the west side where there is already a deep zone accommodating existing locust trees.

Zone 4: Screen. This zone incorporates site amenities such as bus shelters, newspaper vending machines, post ofﬁce boxes, and trash receptacles. All sites, especially urban ones, have site amenities that need to be addressed and coordinated with perimeter security elements. It is advisable to discuss the requirement of the site amenities at a particular site with the local authorities. Sometimes they can be relocated to a different location. At the Metzenbaum Courthouse, the majority of these site amenity elements were grouped on the west side.

Zone 5: Enclosed. This is an articulated wall. It can be a combination of bollards and rails, or a more solid wall treatment. This is used to add variety to the perimeter in locations where pedestrian access is not required or desired.

The shape, detail and materials used for the Metzenbaum Courthouse perimeter security elements are addressed in the next section of this report. Copies of the construction documents are also included in the Appendix.

City Review Process
As most historic Federal buildings are located in urban environments, local authorities are key team members to the design process. For this technical pilot, the design team and representatives from the General Services Administration met with various individuals and commissions that would be involved with the review of the installation. In the City of Cleveland, this meant meeting with the members of the Planning Commission, Division of Engineering and Construction, Trafﬁ c Engineering and the Greater Cleveland Regional Transit Authority. Some site-speciﬁc conditions required close collaboration with City of Cleveland agencies. For example, two of the four streets require narrowing to meet the 20-foot standoff distance. At the Metzenbaum Courthouse, which has vaults under sidewalks on three sides, getting the foundations of the security elements into soil was a challenge. After extensive discussion, the City ofﬁcials agreed to this approach for the design of the technical pilot. The design team had discussions with the Regional Transit Authority about the location of the bus shelters on the site and the possibilities for relocating them. In addition, the City of Cleveland has utility duct banks that were either worked around or created in the areas that were affected.

The Tao of Blast Design

Lorraine Lin, Ph.D., P.E

Taoism

 * Taoism seeks to create harmony and balance with one’s environment. It is a metaphor for understanding blast design.

Blast versus Seismic Design

 * Blast engineering is a specialized field of structural engineering. Blast engineers deal with enormous pressures applied for fractions of a second typically to the outer bays of a building. Seismic engineers deal with cyclical loads applied through the base of structure as shear forces.
 * The small amount of overlap between blast and seismic engineering is in dealing with progressive collapse.

Rules of Thumb for Blast Design
DO maximize the standoff distance between vehicles and your building.
 * DON’T site your building so that there is a direct approach for fast-moving traffic.
 * DO use passive perimeter barriers to increase the standoff distance.
 * Bollards
 * Anti-ram kneewalls
 * Concrete planters
 * Benches
 * Moats
 * DO integrate perimeter security with the landscape architecture.
 * DO use active perimeter barriers for vehicle access points.
 * Rotating wedge system
 * Surface-mounted plate system
 * Retractable bollards
 * Crash gate
 * Crash beam
 * DO choose simple and convex building shapes.
 * DO set back the upper floors.
 * DO minimize the number of insets in the building façade.
 * DON’T design overhangs with vehicular traffic below.
 * DON’T use large transfer girders.
 * DO design your floor slabs for upward, as well as downward forces.
 * DO design your building with sufficient structural redundancy for progressive collapse.
 * DON’T locate loading docks and mail delivery areas within 50 feet of critical areas, such as occupied spaces.
 * DO locate high-density areas and essential personnel away from the perimeter of a building and above the ground floor.
 * DON’T allow unsecured parking in the basement or on the roof of your building.
 * DO place stairways for emergency egress as far away from vulnerable locations as possible.
 * DO allow these stairways to discharge away from lobbies, parking areas, or loading areas.
 * DON’T cluster your emergency egress routes.
 * DO provide areas of refuge in high-rise buildings.
 * DO located refuge areas in the inner bays of a building.
 * The best way to approach blast mitigation for new construction is early and with a multi­disciplinary blast mitigation team which includes the architect, structural engineer, blast engineer and landscape architect.
 * Retrofits are more expensive, more complicated, less effective and have greater uncertainty DO use ductile materials for your structure, such as steel or reinforced concrete.
 * DO design your floor slabs for upward, as well as downward forces.
 * DO design your building with sufficient structural redundancy for progressive collapse.
 * DON’T locate loading docks and mail delivery areas within 50 feet of critical areas, such as occupied spaces.
 * DO locate high-density areas and essential personnel away from the perimeter of a building and above the ground floor.
 * DON’T allow unsecured parking in the basement or on the roof of your building.
 * DO place stairways for emergency egress as far away from vulnerable locations as possible.
 * DO allow these stairways to discharge away from lobbies, parking areas, or loading areas.
 * DON’T cluster your emergency egress routes.
 * DO provide areas of refuge in high-rise buildings.
 * DO located refuge areas in the inner bays of a building.
 * The best way to approach blast mitigation for new construction is early and with a multidisciplinary blast mitigation team which includes the architect, structural engineer, blast engineer and landscape architect.
 * Retrofits are more expensive, more complicated, less effective and have greater uncertainty

Windows

 * DO minimize the size of your windows.
 * DO use strip windows.
 * DO design hazard mitigating window systems.
 * DO design cladding that is securely fixed to your structure.

Conclusions

 * Architectural measures can be as, if not more, effective than structural measures at mitigating blasts. They allow the possibility of aiming for invisible protection.
 * This requires that informed blast design decisions are made early in the design process.