Protective Building Systems

The Science Behind Modular Blast Buildings

The Science Behind Our Buildings

The first engineered blast rated module (BRM) was built in the late 1990’s for a major Chemical Plant in Baton Rouge Louisiana. At the time, the conventional wisdom was that the buildings needed an anchoring device to prevent the building from turning over in a blast. Further engineering proved that the building would actually slide – not turn over.

Blast Building Insulation
Blast Resistant Duplex
Blast Building Interior

Being in the business of saving lives and having a commitment to quality. Mechanical Integrity removes the ambiguity of the building’s capability and consists of professionally stamped engineering structural drawing and calculations; all material traceability documentation, material tests and non-destructive test reports, MSDS sheets; and all fabrication certifications, including welding and construction process documentation.

Taking into consideration that a large portion of the industry deems our products as critical safety equipment and lines of defense, HMB provides the required documentation for OSHA Mechanical Integrity.

Multiple Modules:

Hallwood Modular Buildings uses a revolutionary process, changing the flexibility and installation of blast resistant buildings. There has been a significant amount of time and money invested in research and development to increase overall customer value by improving the design of our blast resistant buildings. One of the most valuable results of these efforts is a bolted system developed to drastically reduce the installation process for blast resistant modular buildings. The traditional method of installing these buildings involves a time consuming welding process, which is not only more costly and less flexible, but also has significant safety implications when working inside the process area of a refinery.

Our bolted system offers the following benefits:

When compared to the traditional welded method of installing a 24×40 complex, this method offers almost a 7 to 1 reduction ratio in installation time! In less than the time it takes to weld the interior and exterior seams, a building with this system can be completely installed and occupied. A recently completed project of a 36×40 blast resistant modular building comprised of three(3) 12×40 wide open modules was completed in 204 man hours using a 4 man crew. This included offloading the modules with a crane, mechanically fastening the modules together and completing all of the interior finish work required. If this building had been installed using the traditional welded method, this same scope of work would have taken an estimated 1350 man hours.

Engineering & Verification

HMB begins with the premise that its products are designed to save lives and protect critical equipment and is why the quality of engineering and design are so critical.  President Ronald Regan made popular the quote “Trust but Verify” and at HMB we say, “Engineer but Verify”. During the “verification” process, there have been valuable lessons learned and know how acquired that have been integrated into current designs.

BRM’s or blast rated buildings may look the same from the outside but what is behind the exterior wall and how it is constructed can make the difference between life and death. HMB has accumulated a vast library of engineering data, know-how and intellectual property not only on the exterior envelop of its buildings but also in the biodynamic analysis of the effects of its buildings occupants during blasts.   When you couple this data with vigorous QC/QA standards, the building is certain to perform to its expectations.

Depending on the application, HMB uses a variety engineering disciplines and computer programs to provide the best data possible this includes Single Degree of Freedom Analysis, Finite Element Analysis, Computational Fluid Dynamics and/or 3-D design modeling.

Finite Element Analysis Demos (click each video to play)

Steel-framed modular buildings may be designed using dynamic structural analyses ranging from the basic single degree of freedom analysis (SDOF) method to nonlinear transient dynamic finite element analysis (FEA). With fully welded connections between the exterior steel cladding crimped wall or flat plate panels and the structural frame members, as well as the frame member-to-member connections, modular buildings improve their blast capacity by providing a high level of continuity. This steel plate-member construction can be effectively modeled using either an SDOF or FEA approach. The analysis should account for tension membrane effects and plastic strain limitations, both of which can be more appropriately captured using the FEA approach.

Any structure, regardless of how simple its method of construction, posses more than one “degree of freedom”. However, many structures can be adequately represented as a series of SDOF systems for analysis purposes. The accuracy obtainable from a SDOF approximation depends on how well the deformed shape of the structure and its resistance can be represented with respect to time. Sufficiently accurate results can usually be obtained for primary load carrying components of structures such as beams, girders, columns, wall panels, diaphragms and shear walls.  However, it is very difficult to capture the overall system response if a building is broken into discrete components with simplified boundary conditions using the SDOF approach, with the result that the SDOF method may be overly conservative.

Nonlinear finite element analysis methods may be used to evaluate the dynamic response of a single building module or a multi-module assembly to blast loads. This global approach can remove some of the conservatisms associated with breaking the building up into its many components when using the SDOF approach. Geometric and material nonlinearity effects are normally utilized in such analyses. These analyses are typically carried out using a finite element program capable of modeling nonlinear material and geometric behavior in the time domain.  HMB has the capability to design buildings using either the ABAQUS or ANSYS finite element analysis programs.

Computational Fluid Dynamics

Blast loads on buildings can be determined through the use of computational fluid dynamics (CFD) computer programs. The basic premise of CFD modeling is to discretize the building and surrounding area encompassing the blast source and adjacent obstacles into small regular cells of finite volume and then solve the governing equations for conservation of mass, momentum, and energy within each cell, taking into account the effects of adjacent cells.

Among other uses, CFD is utilized to simulate the propagation of blast waves in an environment of obstacles, to simulate pressures on unusually-shaped buildings, to simulate leakage through openings into buildings, to simulate interior explosions, and to simulate near-field explosion effects. Where applicable, CFD can be used as an alternative to the more commonly used empirical methods. It should be understood that CFD results are sensitive to modeling techniques and the software used. CFD programs can employ a true first principles approach, which includes turbulence modeling and detailed combustion, or a semi-empirical approach where simplifications of the explosion source are made, based on test data and guidance, to simplify and speed the analysis. Phenomological models are sometimes used to simplify the analysis by using numerical modeling of selected explosion phenomena to capture important features of blast propagation. As with most simulations, the greater the detail of the model, the greater the potential accuracy of the result.

Testing | Verifying | Improving

Often times, people order BRM’s and simply request it to have a certain blast rating. That rating can be determined by engineering calculations on the exterior structural envelope of the building. However, HMB has taken this an added step to not only “verify” that the external structure comports to its blast rating but also verifies that its construction methodologies actually do protect lives.

Two BRM’s were actually tested. The exterior structures were identical but the interior framing systems were different.   Baker Risk designed one and the other was HMB’s design. Both buildings were fully outfitted with computers, wall mounted cabinets, microwave, refrigerator, dishes, etc. and had censored test dummies that provided a wealth of data.   This test proved that no two buildings are created equal and that there are factors other than the structural envelop that need to be considered when saving lives.