A 3D Approach to Integrating Mining Structures with Process Equipment
When designing and building a facility as complex as a large mineral processing plant, good communications between the designers and owner are essential. The use of 3D modeling in the design process can facilitate efficient interaction among the various disciplines involved.
by Edward Nemetz, PE, SE and Troy Bernhardt, EIT
Unified Theory, Inc. (UTI) engineers are using a three-dimensional (3D) modeling approach to improve the design speed and quality of plant facilities. This allows engineers to address the complexity and short design schedules for projects while integrating mechanical and structural systems.
One of the many challenges for designers of facilities is the coordination of structural systems with the process equipment due to changes that occur during design development. Structures for mining facilities are a clear example of building types where the structural system conforms directly to the arrangement of process equipment. Due to accelerated design and construction schedules, engineers often begin structural design early in the project when the process layout is still conceptual and before the final equipment selection. This can lead to an inefficient design effort and costly changes during construction. Although the owner’s investment in the process machinery represents a substantial part of the capital cost, the structural systems must be integral to the equipment layout to achieve overall economy.
Often, the structural engineer must make critical decisions about materials, loading, and framing while the capacities and product flows for the process are still undefined. Mineral processing plant designs usually do not allow designers enough flexibility to assume repetitive column bays and story heights such as in manufacturing plants or commercial buildings. The design team and owners start with a general idea of how the structure relates to the overall process, and the structural engineer often has to proceed with the design of specific structural members long before adequate shop drawings and equipment mounting details are available to complete the design.
While engineers need to consider how equipment and structural members relate to each other in three dimensions, construction documents are typically drawn as two-dimensional floor plans and elevation views. This creates a challenge for the designers to provide enough information for decision makers to visualize the design at all stages of development.
A typical mineral processing plant expansion project might have a series of crushers, screens, and storage bins connected by material handling systems. The mechanical engineers would start by laying out the preliminary equipment sizes based on the specified system capacities along with descriptions of access needs and requirements for protection from the elements. At this point, the mechanical engineers would pass the general arrangements and preliminary cut sheets to the structural engineers, who use the rough layout to start designing buildings and support structures. However, the capacities of the process equipment could change, the exact mounting locations might be unknown until later in the project or the location and heights of the bins could change as designers develop the process details. Any of these changes can affect the routing of conveyors or chutes. The structural engineer might provide approximate sizes of beams and columns but then need to change them repeatedly as changes occur and more details are available.
In one case, the engineers might lay out the process and design the supporting framework only to find that the sizes of a series of floor openings must change in order to accommodate a rerouted conveyor system feeding a kiln. This seemingly minor change could require the redesign of several beams at each opening and the re-analysis of the major framing members within each affected bay. In another case, the floor height might have to change to add headroom for chutes at fixed flow angles or to increase the sizes of conveyors and dust collection equipment, which would then affect column and bracing designs.
The structural engineer is faced with choosing between two approaches:
1. Begin with a preliminary design and modify repeatedly throughout the refinement of the process arrangement. This is inefficient and can result in uneconomical designs or costly field changes.
2. Wait for relatively complete process equipment information before starting the design of structural members that provide support, required access, and shelter. While this approach appears to improve design efficiency, it reduces the ability to coordinate between disciplines and to communicate essential information to the owner and contractors. In addition, it is not feasible for the structural engineer to wait in cases where the owner’s schedule requires construction to start before the process flows are final.
To fully integrate the design of structural systems with the process equipment, engineers need to share conceptual information early in the project timeline when the process layout is still incomplete. Throughout the entire project, collaboration and flexibility are critical for accuracy and quality. It is necessary to continue to share information and to refine the structural design as the process layout evolves. In many cases, structural details cannot be finalized until after final certified equipment drawings are available late in the project or during construction.
Structural Design Development for Mining Facilities Plant Design
Structures for mining facilities support very heavy dynamic loads with complex framing arrangements designed to fit around the process. The framing must be economical but it also has to accommodate equipment footprints, bulk material handling systems, floor openings, and access for personnel.
Typically, the mechanical engineers begin with a conceptual process flow diagram and general arrangement drawings for review. At this point, the structural engineers lay out preliminary framing of beams, columns, and foundations to give a sense of how the structural system interacts with the process layout. The designers assemble cost estimates and continue design development by considering the numerous building, structural, mechanical, electrical, and site requirements. Active participation from the owner and other technical disciplines helps the team develop a more detailed design as the process equipment is specified and vendors submit shop drawings. At each step, the structural engineer performs calculations to determine beam and column sizes and then communicates the results through two-dimensional construction drawings that need to be updated and reissued at every phase of the design.
3D Modeling: Unified Theory’s Approach to Mining Structures Design
Structural engineers at Unified Theory, Inc. (UTI) use 3D modeling extensively in the design of new or retrofitted mining facilities. UTI had been using up-to-date structural engineering procedures and software for conventional building design but found that the geometries of buildings at mining sites sometimes became difficult to manage. These multilevel structures support machinery at each level that is interconnected vertically, horizontally and diagonally by conveyors, chutes, process piping, and dust collection ducts that cross the structural grid at all angles.
UTI engineers developed an approach to modeling the process equipment in 3D to show the required relationships between equipment and to look for interferences between mechanical components. By combining the structural and process layouts into a single 3D model, UTI creates a powerful design and communication tool that benefits the engineers and the owners.
As a communication tool, the 3D model facilitates coordination between the structural engineers, architects, and mechanical engineers. By sharing the same model, each discipline has an active role in coordinating its designs with the other team members. In addition, UTI uses the virtual 3D model to walk the owners through the overall design of the process and facilities at each phase and to develop visual responses to questions or requests.
3D Modeling Tools
UTI uses several different software programs for 3D modeling and structural design. Since each program on the market offers unique capabilities, UTI matches the appropriate tools to the project needs. The best solution usually means that the structural engineers need to apply multiple programs for structural analysis and design to accomplish different tasks. UTI designers also use several CAD programs to accomplish the transfer of 3D information to 2D documents.
After evaluating different software options, UTI chose RAM Structural System from Bentley for 3D modeling of mining structures. It has the ability to include the entire framing system in the model and to design individual members and connections for gravity and lateral loads. RAM Structural System also incorporates the analysis of seismic and wind loads, and floor vibration, and it checks vertical and horizontal deflections from the model.
For coordination between disciplines, UTI uses AutoCAD from Autodesk, Inc. to assemble all of the process and structural information into a single general arrangement (GA) model. Since the main intent of the RAM software is to model the structural geometry and properties from an analysis and design perspective, an additional step is required to convert the information in the model into AutoCAD objects.
Structural software offers great benefits for designing mineral processing plants. The model can easily accommodate other point loads or hanging loads such as process piping, electrical equipment, and cranes throughout the structure. Another benefit is the ability to obtain the steel takeoff at any time during the project. This can help with the tasks of creating cost estimates during the preliminary phase, ordering steel, and estimating the cost of proposed framing changes during later project phases.
Because of the dynamic nature of developing the process layout to satisfy project requirements, engineers have to deal with numerous changes. What appears to be the best solution at the start of the project will become very different by the end. Even if the engineers start with a preconceived conceptual design, the owner or members of the team may consider alternative concepts. It is quick and easy to explore different options in the 3D model and to produce a visualization to help with the selection of the best concept. Since the software also provides structural design results, the engineers can obtain a quick understanding of the structural requirements for each option and the effects on process equipment integration.
Since mining building structures usually fit closely to the process layout, additional challenges arise during the engineering phase. Process equipment presents complicated loading footprints which result in each beam receiving unique applied loadings. Structural software minimizes the computations necessary to distribute loading to other structural members and to verify assumptions about uniform loading applied to floor areas. When changes occur after the analysis is complete, the engineer can update the 3D model with the revised structural members and observe the effect on the entire frame. The structural engineer can use the structural software to easily adopt process changes that occur after analysis with reduced chances for error in determining tributary loads and reactions.
When all of the engineering disciplines combine their 3D models together they can see interferences between objects. Typically, the mechanical engineers design the process equipment and place it into the 3D model as a general arrangement (GA). After the process equipment is placed in the GA, the structural model is merged into the GA to create the 3D model for coordination.
While engineers use software to perform the calculations, they still must check a few things manually. One of the key items is to verify process equipment connections to the structural steel. Using the approved shop drawings from the equipment, engineers can easily determine if the bolted connections to the structural steel will fit correctly and make installation easier. It also is important to check for conflicts with smaller systems such as piping, conduits, and control panels that might be excluded from the model.
A 3D model in AutoCAD can present several issues. Each piece of process equipment can be modeled with inaccurate shop drawings. The result will be an inaccurate 3D representation of the equipment, which may result in some interference or conflict. This will lead to items in the field that require attention. Another possible issue is the method of installation. For example, a bucket elevator requires a certain amount of clearance in the floor openings; during installation it requires additional space to get everything to fit. This can easily be overseen while viewing the 3D model before construction begins
Other programs are available to help coordinate disciplines, but UTI has had the most success with AutoCAD and RAM Structural System. UTI uses the RAM software along with AutoCAD to produce 3D models that provide significant benefits for clients. After each project is completed in 3D, UTI conducts internal reviews for continuous improvement to develop a better understanding of modeling for future projects.
The application of 3D modeling to mining projects has helped UTI improve design quality and efficiency. 3D modeling is a tool that improves the overall design with better integration of process equipment and the structural system. The design tasks proceed quicker than traditional methods, which aids the engineers in producing functional 3D design information early in the project. The resulting 3D model is an excellent communication tool between the designers and the owners and for coordination between disciplines.
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Edward Nemetz, PE, SE has been practicing structural engineering for over 20 years for industrial manufacturing facilities. He has designed structures for chemical and minerals processing, industrial and consumer manufacturing, food processing, mining and transportation throughout the United States and internationally. Troy Bernhardt is an Engineer-in-Training (EIT) and a graduate of the University of Minnesota with a Bachelor of Civil Engineering degree. UTI is a full-service consulting and engineering firm that specializes in the design of industrial and institutional facilities, along with process design.
