Office Buildings in High Threat Situations

Services/Work Provided:

• Site Survey & Investigation
• Blast  Effects Analysis and Vulnerability Assessment (BEA/VA)
• Development of Mitigation Concepts and Costs.
• Report Documenting Work
• Development of Construction Drawings

Description:

Karagozian & Case has performed numerous blast and security related evaluations for facilities located throughout the world. K&C has been awarded several long term agreements with government agencies and NGO’s related to performing BEA/VA studies and the development of protective designs. 

The facility shown was evaluated by K&C as to its vulnerabilities to blast and other forms of security threats (e.g. forced entry/ballistic resistant (FE/BR) protection). This included performing BEA/VA studies; the results from one of the studies indicate the damage imparted to the curtain wall of the facility by a particular bomb scenario. Red sections indicate the sections of the building which are most vulnerable.

Blast Protection for Historic Buildings

Services/Work Provided:

• Blast Effects Analysis and Vulnerability Assessment (BEA/VA) studies
• Check for compliance with Security Criteria
• Design of anti-ram perimeter protection
• Protection for historic buildings

Description:

The blast protection of historically significant buildings is often more complicated than providing protection for other types of existing facilities since it is important that the upgrade measures not detract from the building’s existing appearance.  For buildings that are a part of the U.S. National Register of Historic Places, the required protection standards are performed in accordance with GSA standards/criteria which include a comparative evaluation against the Security Design Criteria for the protection level specified by GSA, a window vulnerability assessment, and development of a perimeter protection plan.

Such studies generally include evaluation of the blast loads striking the building from a bomb located along the perimeter of the building, which is depicted in the figure shown for a specific car bomb scenario. This kind of analysis is done with K&C’s own proprietary software and is generally done in the form of an envelope representing the threat of a car bomb located at any of the likely locations.  Given these blast loads, the performance of the building’s windows (shown in figures to the left) and walls can be computed.  This is accomplished by computing fragility curves for each type of window and structural component, which is done in the form of PI-curves and then generated from a variety of sources depending on the type of components involved. These curves are fed to K&C software that was specifically designed to perform a rapid visually based screening result to indicate to the client the extent of magnitude of the vulnerability. An example of this in terms of window vulnerability is shown, where red indicates a high hazard condition.

Blast Walls and Detonation Shields

Services/Work Provided

• Blast Effects Analysis and Vulnerability Assessment (BEA/VA)
• Design and Evaluation of Effectiveness of Blast Walls and Detonation Shields
• Perimeter Site Security Recommendations
• Design and Construction Drawings

Description

In the BEA/VA studies considered by Karagozian & Case in high threat regions, there is often a requirement for the use of blast walls and/or detonation shields. The design of these features is gradually predicated on the availability of local materials and the ability of the analyst to tailor the situation into a workable and effective solution. For protection purposes such walls/shields cover a large extent of the facility and must work in a severe blast and penetration environments because the blast/penetration threats they are likely to encounter will be severe.

K&C has performed blast vulnerability assessments and designs for blast walls and detonation shields at several facilities located throughout the world. For example, the facility indicated in the figure to the left is located in Baghdad, Iraq. It is four stories with a reinforced concrete frame structure and a building façade consisting of unreinforced masonry infill walls with window openings. The scope of work included:

• Reviewing available construction documents and photographs.
• Conducting a detailed Blast Vulnerability Assessment of the “as-built” facility.
• Developing retrofit concepts to enhance the level of protection of the facility.
• Providing analysis and construction details for retrofits and upgrades.

After reviewing construction drawings, K&C evaluated how the building responded to a range of charge weights and standoff distances. Retrofit options for the structural and non-structural components were provided to protect from vehicle-borne IEDs. Additionally, concept designs were developed for blast-resistant barriers to provide shielding to the structure. An overhead protection system (detonation/blast shield) was also installed to protect against indirect fire from mortars. 

Protection from a Pressure Vessel Rupture

Services/Work Provided:

• Explosive Safety
• Protection from Tank Rupture
• Vulnerability Assessment
• Mitigation Concepts
• Design and Construction Drawings

Description:

The rupture of storage tanks and pressure vessels and the resulting risks to nearby facilities and personnel have been addressed by K&C on several occasions for a wide range of circumstances. Upon rupture, gas pressures and vessel fragments and other form of debris emanating from the rupture can potentially damage equipment or injure personnel in the vicinity. To address such risks, K&C would generally perform a study to assess the situation and make recommendations.  The elements of such a study would include:

• Determining the type of explosion/rupture and amount of blast pressure/debris released.
• Calculating debris throw including: trajectories, amounts, and sizes.
• Assessment of the risks to the facility and personnel from air blast and debris.
• Designing alternatives and developing costs to mitigate the risks.
• Prepare design and construction drawings of the concepts chosen by the client.

There are several ways that pressure vessels might fail, and a variety of simplified and advanced methods for estimating the ensuing risks may be used depending on the complexities of a particular problem. In particular, the calculation shown was developed from a Computational Fluid Dynamics (CFD) analysis where the physics of the actual problem is modeled quite precisely.  Such precision is often needed to get realistic estimates of the threat because of the complexities involved in determining the consequences and threat environment represented by such events. In the case shown, the calculation indicates the gas pressure released when a small area of the tank’s wall failed, causing debris and high pressure gases to be relased. The magnitude of has pressure propagated and the debris thrown calculated with the model shown were used to design the walls surronding this space to protect personnel housed in adjacent spaces.

Refinery Equipment Damage

Services/Work Provided:

• Assessment of blast threat
• Vulnerability assessment of control room
• Design Mitigation Measures

Description:

Vulnerability assessment (VA) studies performed at refineries represent a quite different situation from that encountered in buildings.  Two major risks need to be considered: personnel on site will be protected during an accidental explosion and the protection of employees during a blast related attack.  Also one major concern here is the risks from secondary hazards that might result from an initial incident in the form of fire and the potential for vapor cloud explosions. 

In the VA studies, the vulnerability of structural, mechanical, and electrical systems under a variety of blast, impact, and penetration threats are considered. Each represents a broad range of risk factors that need to be effectively evaluated.

Given these complications, K&C often uses a variety of engineering tools and a broad set of risk scenarios to perform vulnerability assessment studies.

On occasion, K&C uses advanced simulation tools to evaluate the risks of tanks and process vessels to address concerns and quantify the risks associated with a terrorist attack. Calculations with computational fluid dynamics (CFD) models are shown to the left. They evaluate the risks for a specific type of vessel presented by satchel charges and rocket-propelled grenades (RPGs).

Curtain Wall Vulnerability Analysis Software

Services/Work Provided:

• Development of software to perform blast effects vulnerability analyses for curtain walls.
• Creation of LS-DYNA models to simulate blast response of curtain walls.
• Design a tool for enhancing the blast resistance of new curtain walls
• Present options to retrofit existing curtain walls. 

Description:

Determining the blast resistance of curtain walls (CW's) can be complicated because they are often quite complex and generally afford minimal resistance to blast.  Also, they are comprised of widely different forms that are not easily reduced to some form of simplified analytic model.  However, curtain walls are a major source of risks were a blast to occur and a key item whose improvement could afford much greater protection.

To address this risk, K&C created a computer code, BEA_CW (Blast Effects Analysis for Curtain Walls) that allows a user to rapidly enter the basic properties of a CW system and then generate an LS-DYNA finite element model for predicting its response to a blast load. This is done in such a way that the used LS-DYNA is transparent to the user.

Security upgrades generally involve retrofitting a building’s windows, CW's, and other façade components to enhance their blast resistance.  Several retrofit options provided by BEA_CW include the use of film and polymer panels, cable and fabric catcher systems, and the use of stronger mullions. 

K&C performed blast analyses of many CWs for this project to develop the modeling strategies employed in BEA_CW. K&C also validated the analysis capability afforded by BEA-CW by comparing experimented and analytic results to several types of CWs subject to blast loads. Based on the results, our team developed the necessary coding to implement the automated generation of the LS-DYNA models and the generation of CW upgrades. 

Review of Naval Hospital Building Collapse - Naha, Japan

Services/Work Provided:

• Progressive Collapse Analysis
• Tie Force (TF) Analysis
• Alternate Path (AP) Analysis
• Technical Report
• Redesign Recommendations

Description:

K&C uses high-fidelity physics based finite element analyses of building system in order to evaluate and mitigate collapse risks. These calculations allow us to simulate the actual behaviors of the structural system and the failure of their components. For the purposes of ensuring that the new naval hospital in Japan satisfied progressive collapse criteria, K&C was hired to review and evaluate whether or not it was in compliance the United Facilities Criteria (UFC) manual 4-023-03. The facility consisted of a four-story hospital building along with a two-story central utility plant. Both structures were designed as concrete frame structures.

Two forms of analyses were performed: Tie Force (TF) and Alternate Path (AP) Analysis. The TF analysis showed that only minor modifications to various reinforcement details were required to meet the requirements set forth in the UFC. Additionally, a nonlinear static analysis procedure was performed by using a standard structural engineering finite element model using the SAP code in order to check if the structural design satisfied the requirements. For the AP analysis, columns at several locations were removed to show that acceptability of the design.  As a result, several design revisions were necessary to enable the structure to span over the missing column. Recommendations for improving the design were then provided.