Q & A
Questions on the prediction can be submitted to Jack Moehle and Jerry Zhai (with the subject line Thick Foundation Contest Questions) and selected questions with answers will be posted here.
Question 1: Are there any more recent concrete strength data?
- Answer: 28-day measured strengths have been added to the Provided Information.
Question 2: Can you provide stress-strain test data for the No. 9 bottom bars and the No. 5 shear reinforcement?
- Answer: Those data should be available during the week of 9/20/21. Please check back then.
Question 3: As I read the contest rules, I saw that a team could be disqualified for not guessing the correct failure mechanism. The spreadsheet names several failure mechanisms, and a team should pick one of those. Now, I think there could be a grey area between 'diagonal tension" and "flexure-diagonal tension" failures that could lead to ambiguity in selecting either failure mode. This is especially relevant for those using simplified methods to make the prediction. It may be useful to give a concise explanation of the metrics the judging team will use to differentiate one failure mode from the other.
- Answer: We agree that there are gray dividers between some of the failure modes. We mainly want to guard against someone guessing an answer and winning based on the guess. We plan to have a panel of non-competing experts judge the first question and give fair leeway for the identified failure mechanism.
Question 4: Please describe the lateral bracing system.
- Answer: Three laterally braced steel frames are provided around the test specimen, one located at midspan and two located near the support points located 31.5’ from the midspan. Telescoping steel arms extend from the braced frames to the test specimen, one near the top of the test specimen and one near the bottom of the test specimen. At the location of each telescoping arm, a ¾” piece of plywood is epoxied to the test specimen and a 1/8” steel plate is epoxied to the plywood. A 1/8” thick brass plate, greased both sides, sits between the telescoping steel arms and the steel plate to provide a low-friction sliding plane. The bracing will remain during the tests. Should excessive out-of-plane motion occur, we will stop the test and adjust the system as necessary.
Question 5: What is the horizontal location of the bottom two longitudinal bars?
- Answer: Within the flexural tension steel, the two bars located in the bottom layer are spaced 4” apart, centered on the cross section at the indicated elevation.
Question 6: Please provide improved quality drawings such that the dimensions can be more readily identified.
- Answer: A pdf of the construction drawings can be found here.
Question 7: What is the nominal maximum aggregate size?
- Answer: As indicated on the drawings and the mixture design, the maximum nominal aggregate size is ¾”.
Question 8: How are the bars anchored at the ends?
- Answer: The bonded bottom longitudinal bars terminate with Lenton D16 threaded terminators (4X net bar area), with the following exception. In Span 1, where five of the bottom bars are ungrouted for Phase 1 testing, the bars project from the end of the beam without any anchorage device; in Phase 2 testing those five bars will be grouted using SikaGrout 528 SF. Top longitudinal bars terminate without heads. All longitudinal bars are made continuous using staggered A32K high strength Lenton couplers. Transverse reinforcement is anchored using Lenton threaded terminators (10X bar area).
Question 9: Are concrete tensile, modulus of rupture, or split cylinder strength results available?
- Answer: No. If time and materials permit, we will provide sample results, but we cannot promise that we will be able to do so in time for this contest.
Question 10: What are the inverted U-shaped items spaced 2’-6” along the top of the beam?
- Answer: These are lifting hooks that will be used to lift segments of the test specimen onto a truck after the testing is completed and the test specimen is cut into manageable lengths.
Question 11: In what sequence were the four concrete trucks placed in the test specimen?
- Answer: The trucks were placed 1-4 sequentially from the bottom up, each filling about one quarter of the test specimen.
Question 12: It is stated that, after failure of Span 1, it will be repaired using external shear reinforcement and any other remedies as required. Can you describe these?
- Answer: The failed section will be strapped with pairs of high-strength reinforcement in the form of paired XXX diameter Dywidag threadbars post-tensioned with about YYY tons on each bar against two steel stub sections that sandwich the specimen from above and below. Positioning of the paired threadbars will depend on the failure location. Stressing is intended to bridge and close the primary failure crack. Additional measures, to be determined in real time, may be applied if necessary.
Question 13: Is it possible that out-of-plane deformation of the compression zone due to lateral torsional buckling will limit the capacity of the test specimen, and, if so, will additional measure be taken?
- Answer: The intent is for out-of-plane failure to be restrained by the bracing system. Should it become necessary, additional bracing will be added such that out-of-plane failure does not control the strength of the test specimen. Consequently, predictions should not include primary out-of-plane failure.
Question 14: What are the properties of the grout?
- Answer: The grout is SikaGrout 528 SF. Interested parties can find typical product details online.
Question 15: Please provide additional details for the splitting control reinforcement.
- Answer: The bars are shown in details 1 and 2 of the drawings. The bars are No. 3.
Question 16: There is some ambiguity in the six failure mechanisms. Please elaborate.
- Answer: See behavior mode worksheet in the provided prediction submittal spreadsheet.
Question 17: What is the unit weight of the concrete?
- Answer: Based on measurements, it is 150 pcf.
Question 18: Please provide the stress-strain relationship for the A1035 Grade 120 No. 9 bars.
- Answer: See below.
Question 19: Please provide the stress-strain relationship for the A615 Grade 60 No. 5 bars.
- Answer: See below. Note: Stress-strain relationships for all bars are from original bars (not machined) using nominal cross-sectional areas.