BOWLING GREEN, KENTUCKY
Proposed Structural Steel Frame for the National Corvette Museum
Due in part to the efficiency of material, labor, and overall construction practices as well as countless precedents for both empirical and design inspiration, multi-story structural steel frames are commonly underrated feats of structural engineering.
For a class known as Steel II, the full Spring, 2021 semester was utilized to gain a greater understanding of how building loads are calculated, distributed, and ultimately used to size a structural steel frame for a ground-up building project. For this theoretical structural design project, the National Corvette Museum in Bowling Green, Kentucky was chosen for a total redesign proposal. In February of 2014, a massive sinkhole opened up beneath the Museum and, over the course of mere hours, consumed eight priceless Chevrolet Corvettes of various ages.
While the National Corvette Museum did successfully rebuild in the subsequent years along the lines of its original design, the case study created a perfect opportunity for a theoretical ground-up redesign proposal. The class instructor acted as the project architect and supplied students with schematic plans and elevations for initial structural designs. Once a design scheme was agreed upon as a class, the application of composite slab design, moment connections for cantilevers, and simultaneous types of Lateral Force Resisting Systems commenced.
Along with the "typical" tools such as the International Building Code (IBC 2018), ASCE 7-16 Minimum Design Loads for Buildings[...], and the AISC Steel Construction Manual (Fifteenth Edition) for old-school hand calculations, the project saw the introduction and consistent usage of three key digital tools: RISA Floor, RISA 3D, and AutoDesk Revit. The RISA software was utilized for load analysis and preliminary sizing while Revit was primarily used for the production of theoretical construction drawings.
RISA Floor - Gravity Design
The predominant area loads were decided upon using the ASCE 7-16 in conjunction with the architect's program for the project. These defined loads were applied to the RISA Floor model that was created in line with the final, agreed-upon structural scheme for the Museum. In order to maximize the economic and structural efficiency of the steel frame, it was decided that all elevated floors with exception of the roof were to be designed as 3.5" concrete slabs on 3" composite deck. A composite deck makes use of the inherent compressive strength of concrete as compared to hot-rolled steel. Because a simply supported beam experiences compression forces on the top chord and tension on the bottom, the biased strengths of both materials is combined to ultimately require a smaller, more economic size of steel.
The following shows a set of hand calculations for a single composite beam and highlights the necessity for such programs as RISA Floor for repetitive tasks and calculations:
The following slideshows depict the load cases and subsequent floor member sizes as recommended by RISA Floor. While the above hand calculations can be fun and rewarding in their own sense, the ability to produce dozens or hundreds of similar results in mere seconds is far more efficient.
Members that are modeled in RED are designated for Lateral design instead of gravity design. In essence, the members in these bays are to be designed to transfer lateral loads from seismic and wind forces as opposed to the primary dead and live gravity loads like the rest. Because RISA Floor is better suited for gravity design, these members were exported to RISA 3D to be analyzed.
RISA 3D - Lateral Design
Although the combined RISA Software were immensely helpful for solving for a suggested member size for an entire frame, they really are not much more than intricate calculators. Just like any calculator, RISA needs a proper input in order to produce results. Below is a sample of the calculations that an engineer must undergo for such results. More specifically, the following includes the Equivalent Lateral Force Procedure for seismic load calculations per the ASCE 7-16, Chapter 09.
As stated above, the usefulness of RISA Floor was invaluable for gravity design of composite floor slabs. However, the developers relegated design and analysis for lateral loads (seismic and wind forces) to the sister software RISA 3D. Once the class agreed on which bays to utilize for the Lateral Force Resisting System (LFRS), they could be designated as such in RISA Floor and then ported to RISA 3D for more appropriate modeling and analysis.
Ordinary Moment Resting Frames were chosen for the longitudinal direction of the building and Concentrically Loaded Ordinary Braced Frames in a Chevron pattern were chosen for the transverse direction. The isolated LFRS bays can be seen here, modeled in RISA 3D with applied loads in a load case-by-load case basis:
Although each Load Case must be considered, the standard design method for Steel construction (known as LRFD or Load and Resistance Factor Design) requires that each load case be factored in a series of Load Combinations described by the AESC 7-16. For this project, the Load Combinations required a separate Live Load A and Live Load B case to account for a complex design phenomenon known as Live Load Patterning. For brevity's sake, the resulting number of Load Combinations that must be taken into account for worst-case-scenario calculations is 61.
After manually checking, rechecking, and verifying the rechecks, the RISA 3D software analyzed the applied lateral loads in the 61 different combinations, complete with load factors for "overdesign" or "factor of safety," to finally suggest column, beam/girder, and chevron brace sizes in the LFRS bays.
AutoDesk Revit - Construction Documentation
After all load calculations, applications, and solutions were produced by both RISA Floor and RISA 3D, complete with upsizing for story drift and deflection limits, the final structural steel frame was ready to be drawn in Revit for "Construction Documentation." Although this building will not actually be built according to these designs, the exercise proved valuable for an increased understanding of how and why Construction Documents such as Foundation Plans, Framing Plans, and Details are created and laid out.
A comprehensive Project Manual that contains all applicable calculations and Design Criteria as well as Model Narratives for both RISA Floor and RISA 3D can be found here for the curious: