Engineering and Design are a critical component in the products that MBI provide. MBI utilizes multiple engineering disciplines and computer programs, as well as, 2-D/3-D design software. Along with this technology, MBI has developed the intellectual property that allows them to provide modular protective building systems that can protect against a complete array of threats.
Included in this section are details about the following:
- Single Degree of Freedom Analysis
- Finite Element Analysis
- Computational Fluid Dynamics
- 3-D design modeling
Single Degree of Freedom Analysis or Finite Element Analysis
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.
All structures, regardless of how simple the 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. Figure _____ shows a finite element model for a six-module complex. Doors and other openings can be explicitly modeled as shown. MBI 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.