2021 Seismic Design Competition

Retrofitting of the existing structure is not permitted for deliverables #2 and #3. This will be one of the primary components of deliverable #4, so it may be beneficial to brainstorm retrofitting options in anticipation of deliverable #4 based on your current analyses.

We would prefer that your poster is 5 separate slides. This will allow for better viewing on a computer screen when you submit the 1-2 minute video overview of the poster slides.

The scoring document states that teams will have a maximum of 7 minutes for their presentations. Teams should mention architectural considerations that played a role in their design or may highlight an architectural challenge that their project responds to especially well. This would likely be beneficial when judges are scoring the presentation, but the focus of the scoring will be on the topics listed in the rubric.

Make sure you’re converting the time histories to .txt files separately for each scaled ground motion. They should be uploaded as separate time histories in SAP or ETABS. Otherwise, consider discussing with an advisor or looking at online resources to troubleshoot this issue.

Yes, this is correct. You do not need to consider the layout of the existing structure before the extension is added. However, the existing structure should be considered in conjunction with the extension after it is added. Because no prior layout is provided for the existing structure, it is up to the team to design the layout.

At the mid-height of floor one (3” elevation from the ground), there are no interior beams. The horizontal struts at the mid-height of floor one are only on the exterior of the structure in the locations shown on the elevations. Interior beams do intersect exterior beams and braces at all subsequent floors.

Just use the single Poisson’s ratio and assume that the balsa is isotropic. Although this is not entirely accurate, you may make this assumption for simplicity.

The best approximation may be to select the nodes at/closest to the Center of Gravity. This is one way of calculating the Center of Gravity:

The full time history analysis should be run for each ground motion.

You may assume a dimension lumber grade of No.1 for the purpose of determining the size factor.

Torsion should still be considered regardless of how diaphragms are defined. Torsion will likely appear in your mode shapes and it would be advantageous to attempt to
minimize torsion in your design.

Yes, you are correct that section 2.4.5 of ASCE 7-16 refers to the appropriate load combinations. Rather than calculating Ev and Eh using section 12.4.2, it is permitted to
simply input the time history as Eh and neglect Ev. Additionally, you may disregard overstrength.

Yes, but only members with the highest axial, bending, and shear forces must be reported. This should be easily obtainable by viewing member force diagrams or output
tables from the software. Note that in question 3, we are asking for the highest forces, but in question 5, the highest stresses will also depend on cross-sectional area, so we recommend that you find the peak forces in each type of member that has a different cross-sectional area.

There is no required format to your construction details. We are primarily interested in your thought process and reasoning behind your construction sequence. Diagrams would be a good way to convey your ideas but there is no required format.

Non-structural elements such as curtain walls are permitted to extend past the required footprint of the building. The plan dimensions specified in the design guide and
drawings are for the purposes of constructing your numerical model. Any architectural features may extend outside of these bounds. However, please keep non-structural elements within reason (if they extend far outside of the structural bounds, then they would likely require additional structure outside of the structural bounds).

For this deliverable, please just apply the 100% of the force in only one direction

The Addition should be on top of the existing building

E should be used in your ETABS or SAP2000 models. Emin should not be used in your numerical model, but may be used in addition to E when determining member capacities according to the NDS. Equations in the NDS explicitly call for E or Emin.

Please refer to “2021 SDC Structural Design Guide” for all the details regarding the extension building geometry, member sizes and spacing requirements.

This is something up to the designer; however, the addition should be constructed as fast as possible within a reasonable timeframe and ensuring that the existing hospital structure is functional.

Yes, all parts of the existing structure and the addition should be restricted to the set footprint of each floor, as outlined in the provided drawings.

For part 1 of the structural deliverable , your results should be based on your SAP/ETABS model for the existing structure only. For part 2, the addition should be
incorporated into your existing model and the two components should be modeled together. For any future questions about the additional structure, analysis should be conducted based on your SAP/ETABS model that has both the existing and the addition structure together.

No, please consider the addition and existing structure as a single building in part 2 of the structural deliverable. In reality, the additional structure will be put on the existing
building to perform together in an integral way

We would like you to design balsa wood connections for this part. The structural drawings in part 2, question 3 should all correspond to a balsa wood model.

Yes, this is correct. In this deliverable, we are asking for a preliminary design for the additional structure that you believe will perform well with the existing building once the
existing building is retrofitted.

The use of shear walls is allowed, however, as mentioned it should be connected to the existing building foundation (in the final version of the building).

Teams should say how they will apply the points mentioned in the scoreboard in the LEED official website in a practical way in their designs, not just tick or check the points in the scoreboard.

The scale of the architectural model is up to the discretion of the teams. The only requirement for the scale of the model is that the render and drawings fit on size 8 ½” x 11” paper.

For the architectural model, you can assume any material that you think would be appropriate for the members. Balsa wood is required for the structural model, but there is no specified material requirement for the architectural model.

For Deliverable #3, only architectural renders and schematic drawings are required. The floor plans for the addition is part of the structural deliverable.

The floor dimensions of the real building are up to the discretion of the teams. As an approximate range, you may consider about 2000 to 3000 square feet when deciding the layout of the internal floor plan. Include schematic drawings for whenever the layout of the floors changes. If you have a repetitive floor plan, simply label it with the floor levels it applies to. Teams may use their judgment to decide the number of schematic drawings needed to adequately convey their ideas.

There isn’t an exact linear scale of the model to the real building. When determining the internal layout of rooms, consider a floor area of approximately 2000-3000 square ft, but you will not be penalized for going outside this range.

Consider both the existing and extension parts when aiming for the LEED certification. You may make an assumption for materials or put more emphasis on LEED points that are independent of material type.

Your structural configuration should be taken into consideration when completing this part of the architectural deliverable. For example, you should consider where columns
and braces are located in the floor plan and where your access points are located. However, the dimensions of your access points in the real structure may be adjusted to accommodate the functionality and architectural interests of the hospital. Strict adherence to dimensions of your balsa wood structure is not required.

The site class of D was determined by performing additional in-situ tests after the liquefaction mitigation methods were performed.

The difference in choosing site class D (stiff soil) and the site class D (default) is stated in ASCE 7-16 section 11.4.3:”where the soil properties are not known in sufficient detail to determine the site class, Site Class D … shall be used unless the authority having jurisdiction or geotechnical data determine that Site Class E or F soils are present at the site”. The “default” selection (based on insufficient data) is typically more conservative in its values than the “stiff soil” selection (based on the available data). Because shear wave velocity data is available near the project site, it can be assumed that we have sufficient data.

Use Site Class D.

Please provide a screenshot of the deaggregation plot only. This is the 3D bar chart.

Please plot the “total” deggregation for the spectral periods that we specified in the deliverable (not at PGA).

These are all potential seismic sources that are mapped and considered in the hazard calculation. Interface and slab (sometimes labeled intraslab) sources indicate the location of a source relative to a subduction zone. Faults represent seismic sources from known or mapped faults. Grids indicate potential background seismicity not related to a known fault, and use an algorithm to smooth this data over gridded coordinates.

Details regarding gridded seismicity can be found here:
Frankel et al. (1996). “National Seismic-Hazard Maps: Documentation.” Open-File Report 96-532, Denver, CO. June 1996

The “other” category can be evaluated by leaving the deaggregation as “total.” All remaining percentages without an m and r value can be added to make up the “other” percentage.

Please just add them together and present the total only. There is no need to distinguish between these sources for this assignment.

That part of the assignment should only be referring to what appears on the webpage, not the downloaded report. Please keep those fault sources without m and r presented on the webpage (such as “Geologic Model Full Rupture”) in the Other category. These are expected to be minor sources and may not always represent actual mapped faults.

You are not expected to manipulate and /or data or modify the spreadsheet. The given seed motions’ period (T) and pseudo-spectral acceleration were obtained using a different  method than what PEER is using, hence the discrepancy in the T values. it is okay to use a different set of T values for the response spectrum obtained from PEER.

See answer to question below.

Yes, we did not foresee this issue with the geomean. Please use the period range provided by PEER for the response spectrum only. Still provide a plot with your scaled geomean using only the four provided seed motions.

An appendix with sample calculations and referenced tables will count towards the 12 page limit. We are primarily interested in seeing your final answers and/or recommendations to the stated questions, with only the necessary supporting information. The
reference section should only include citations of referenced resources.

Since this deliverable is not as graphic-heavy as later deliverables, the image can be considered as optional.

We would like you to use centerlines of perimeter beams when determining the total rentable floor area of the structure.

Yes, you may adjust other parts of the report as long as the total report is within the 11-page limit. Please only use 11×17 size pages for drawings (i.e. if you use fewer than three pages for drawings, you may not use an 11×17 page for the body of the report).

We would like you to stay within the specifications of the Design Guide for all parts of the addition. You are permitted to deviate from parts of the Design Guide for the existing structure because you’re restricted by the original design of the structure. With the addition, however, you have the ability to completely adjust the design of the addition and should therefore be able to come up with a configuration that meets the Design Guide criteria.

Yes, you are permitted to increase the column dimensions of the existing structure as part of the retrofit scheme. However, if you choose to do so, please describe how this represents a real retrofit technique.

Yes, this question in Deliverable 4 asks you to consider how the modal results will differ when you change the initial Deliverable 2 assumption and impose a rigid diaphragm.

Because you are assigning rigid diaphragms rather than semi-rigid diaphragms, the thickness that you assign to the slab element should have little consequence on the behavior of the structure. Rigid diaphragms have infinite in-plane stiffness rather than considering the actual in-plane stiffness, so the slab thickness would not affect the behavior.

If your retrofit scheme includes dampers, then yes, please provide information about the properties of the dampers that you input into the ETABS/SAP model and how those properties relate to dampers that could be constructed in a physical balsa wood tower and/or how the dampers are similar to dampers that are implemented in real structures. 

For any retrofits applied to the existing structure, you may deviate from the dimension limits of the Design Guide in order to simulate a real retrofit technique. When considering a BRBF-type member, you may choose to stray from the dimension limits for the entire composite member or for each of its components, but please provide justification for how this would relate to a real BRBF and/or how it could be constructed in a physical balsa wood tower. It may be more appropriate with BRBFs to adjust the material properties rather than go outside the dimension limits.

For this question, change the diaphragms from flexible to rigid for all the levels from the bottom floor up to the 10th floor (roof of the existing structure). Keep the diaphragms of the extension (11th floor to roof level of the addition) flexible. You are asked to compare mode shapes of this configuration to mode shapes of the structure with all flexible diaphragms.

The 8 pcf value is the weight per unit volume for the balsa wood members. This is similar to mass per unit volume but expressed as a specific weight rather than a density. Make sure that in addition to this self weight of the balsa wood members, you apply a dead load of 1.44 psf to all floor areas. This dead load should be included in the seismic mass of the structure and therefore be activated as a lateral force when conducting a modal analysis or running a ground motion. If the 8 pcf self weight of the balsa wood is the only load considered in the analyses, your results will have very low displacements and forces. This could be the issue, but also keep in mind that a small-scale balsa wood model would have much lower displacements and forces than a real structure. 

Because this was not clear in the instructions and the question and response were posted very close to the submission deadline, either of the above checks will be acceptable. However, we would prefer option (2) as a more direct comparison between the unretrofitted and retrofitted conditions.

For the sake of simplicity, we would prefer that this reduction due to overlapping connections is not taken into account when determining the weight of the structure. Also, consider that if you’re measuring lengths of members from centerline to centerline of perpendicular members, the overlapping member volume on the inside corner of the connection would be picked up by the missing volume on the outside corner of the connection so it would be more accurate to not include any reductions. This calculation becomes more complicated for braces and non-orthogonal geometries and it may be more accurate to apply the reduction for redundant volumes in these cases. If you do reduce weights because of overlapping volumes, we just ask that you clearly state this in your report and provide any example calculations to prove the accuracy of your reduction.