Notification, Q & A

Notifications, Q&A

Question 1: I have a question about the bottom conditions: is there a waterproofing membrane that goes around the bottom and physically separates the soil mass from the shaking table? Do you have a detail of the base before starting pouring the soil?

Answer: Yes, we did use a membrane to contain the model ground since the laminar soil box is not waterproof.

Question 2: Is there any measure of the horizontal stresses in the soil? Did you perform CPTs or dilatometers before the test?

Answer: No, we did not measure horizontal stresses. We performed DCP prior to the shaking to confirm our target relative densities.

Question 3: I’m assuming the following filling steps: 1) dense send; 2) loose sand; 3) water up to - 0.6; 4) foundation; 5) crust; 6) top load in the foundation block; 7) shaking.

Answer: This construction sequence looks reasonable and is consistent with our model construction method.

Question 4: The signal has essentially zero acceleration up to 2-3 sec and again almost zero acceleration after about 18 seconds. The shaking is essentially about 16 seconds. Are the benchmark displacement measured after 80 seconds or after the significant motion?

Answer: The benchmark displacements (i.e. permanent settlements) used to evaluate the accuracy of blind prediction are measured at 80 seconds. This information has been added to the “Rules” document.

Question 5: I’m assuming a density of the concrete of 2.4 ton/m3. Is this ok?

Answer: The density of concrete is 2.616 ton/m3 (2616 kg/m3). This information has been added to the “Model Ground” document as well.

Question 6: There are a few discrepancies about the RD of the layers depending on the method used to measure it. Which one should we consider for the analysis?

Answer: The target relative density for each layer is presented in the “Model Ground” document. However, the achieved values were slightly different depending on the method used to measure as presented in the slides posted on the PEER website.

Question 7: Can I use a numerical modeling approach to predict the settlement response or strictly it should be 2D or 3D analytical model?

Answer: As you can notice in the submittal spreadsheet, you need to enter time histories of the predicted settlements as well as the calculated permanent settlements at 80 seconds which are the basis to evaluate the accuracy of predictions. It is up to the participant to select the approach to perform these predictions. Please check updated information in the “Rules” document.

Question 8: Am I correct in assuming that the blue steel frame is not connected to the laminar box? Looking at the picture it looks like there is a gap. I just want to be sure about it.

Answer: That is correct. The blue frame is not connected to the laminar box.

Question 9: We are trying to understand the construction sequence outlined in Question 3 of the 10/31 update Q&A set, and your response: after water was filled up to -0.6m, to the top of the thick loose sand layer, surely 200mm of ‘crust’ was placed on top of the thick loose sand layer prior to the placement of the foundation? The remaining 400mm of crust was then placed around the foundation? Was the 200mm of crust placed across the full width of the box prior to placement of the foundation?

Answer: Yes, we initially placed 0.2m of crust across the full width of the box, then placed the foundation, and finally completed the remaining crust.

Question 10: It is not clear whether or not we can filter the input ground motion or not. There are a lot of high frequency components shown but a typical mesh will filter these out if we are to complete the simulation in a reasonable time.

Answer: It is up to the participants to decide whether filter the input motion or not. We provided the unfiltered table (input) motion and to be consistent will use the unfiltered measured settlements to gauge the prediction accuracy.

Question 11: Are the teams to be comprised of just students, or can they include professors?

Answer: The teams can include students, professors, and practicing engineers, no limits! They are all encouraged to participate.

Question 12: Could you please let me know the center of mass on the superstructure, or the height of superstructure?

Answer: Up to 13 steel plates, each with thickness of 0.0635m, were evenly placed on the footing to achieve the target contact pressure. The height of superstructure was 0.8255m above the footing surface.

Question 13: Is the load value of 41.6 KPa applied on the footing, so the contact pressure will be 41.6 KPa + weight of the footing, or is it that value (41.6KPa) the value of the absolute contact pressure (load + footing weight)?

Answer:  The indicated value for contact pressure (i.e. 41.6 kPa) is indeed the absolute contact pressure (superstructure load + footing weight).