04.1 - BSRB BCER URS Resp to WJE comments Table 2023-10-20 — original pdf

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Job No.: CLMP167 Title: Bridge Concept Engineering Report (BCER) Peer Review PEER REVIEW COMMENTS Date: October 10, 2023 Preparer: URS/AECOM Reviewer: WJE – Brian D. Merrill, PE Responder:   URS / AECOM Discipline: Bridge/Structures Status: ☐Criteria ☐100% ☐90% ☐60% ☐30% ☒Draft Report Review Purpose: ☒Independent Peer Review ☐Discipline ☐Project Approach Review ☐Interdiscipline ☐Other: Action Code: A ‐ Agree, will comply D ‐ Delete comment1 E ‐ Exception taken Commen t No. 1 2 3 4 5 6 7 Drawing,  Spec, or Page No. Pdf 7 Pdf 7 Pdf 8 Comment Action/Response2 The statement highlighted is possibly overstated. Neither TxDOT nor the City have performed additional inspections/assessments over  time that aren’t related to the current efforts. The condition ratings for the deck, superstructure, and substructure are all 6  (Satisfactory condition) and have been that way for the many years. TxDOT has not increased the frequency of safety inspections. We do agree that at almost 100 years old, the original portions of the bridge may be approaching the end of their useful life. Given the desire for the “next” bridge to last 75+ years, keeping the original poses some challenges. We propose to revise the highlighted statement as follows, "The condition of the structure has  progressively deteriorated over its lifespan and this points towards more detailed inspection  and condition assessments looking forward ." Comment acknowledged. Rehab Options 2 & 3 appear to address a similar approach taken for the Congress Ave bridge over Lady Bird Lake and SH 29 at S. San  Gabriel River in Georgetown. These designs both left the arches and spandrel columns in place but not acting as part of the structural  system. This bridge’s skew and the location of the spandrel columns makes adding a new substructure on the existing foundations  more challenging, if not impossible. Agree this concept was considered. Comment acknowledged.  The retrofitted spandrels are intended to be engaged for vertical  loads. Pdf 9 Phase 2 of the Preliminary Selection and Concept Eng. Process was not provided to WJE for review. Deliverables for Phase 2 were transmitted by URS/AECOM to the City of Austin.   Pdf 12 The CoA streel “levels” (per CoA Street Design Guide) for Bartron Springs were not mentioned. We suggest it likely falls under level 3 –  but the lane widths shown in Section 2.2 Geometric development, are too narrow for this street level. Comment acknowledged.  These lane widths were a product of coordination with Austin  Transportation Department.  The lane widths are compliant with TCM Sect. 2.7.1 in the  constrained condition for level 3 streets with curb and gutter.  The bridge deck is much larger  than these lanes would imply.  Design team will investigate wider lanes as part of the design  process. Pdf 15 Pdf 26 The above comment (3) describes the Congress Ave treatment where the spandrel columns and arches were retained but were no longer engaged as part of the new structural system. See response to Comment 3. There are no fabricators we are aware of in TX that have forms for the AASHTO Type VI (72” deep) girder section. The closest TxDOT  shape is the TX70 (Bulb T), which would need to be modified to accommodate the post‐tensioning ducts. An additional concern is the  wide girder spacing (14’‐1”) might require very high concrete strengths which should be avoided as the mitigation methods for ASR  need to be met. Additionally, if the girders are to be made continuous, the middle span is normally set to be 25‐30% longer than the end  spans both for structural efficiency (balancing positive and negative dead load moments) and aesthetic reasons. U40 beams can be  spaced at 16'‐7" per TxDOT for a 75' span. The suggested 72” deep girders are very deep relative to the span length. Thinner girders are  usually suggested to help the bridge be more visually pleasing. We see potential benefits in investigating other beam types including U‐beams during the next  phase of design.  U‐beams may not offer considerable cost savings over the post‐tensioned I‐ beams since they are more expensive than I‐beams.  The proposed span arrangement currently  shown has attempted to avoid existing foundations.  Alternative span arrangements,  considering constraints, may present an opportunity to better balance forces and will be  investigated during the next phase of design. 8 Pdf 26 The 9” thick deck, relative to the proposed wide girder spacing, is very close to the 1/20 limit where AASHTO suggests using a prestressed deck. This would drive up construction costs. The l/d limit for the current concept is 14.08'/0.75' = 18.8 which gives some margin to the 1/20  limit.  For bulb tees, designs generally consider the slab is supported an appropriate distance  away from the centerline of the beam to account for web thickness and top flange depth.   Thus, considering those items the l/d ratio would be reduced further.  We intend to reevaluate  the beam type selection and spacing and slab depth further in the next phase of design. 10/20/2023 1 of 6 Job No.: CLMP167 Title: Bridge Concept Engineering Report (BCER) Peer Review PEER REVIEW COMMENTS Date: October 10, 2023 Preparer: URS/AECOM Reviewer: WJE – Brian D. Merrill, PE Responder:   URS / AECOM Discipline: Bridge/Structures Status: ☐Criteria ☐100% ☐90% ☐60% ☐30% ☒Draft Report Review Purpose: ☒Independent Peer Review ☐Discipline ☐Project Approach Review ☐Interdiscipline ☐Other: Action Code: A ‐ Agree, will comply D ‐ Delete comment1 E ‐ Exception taken Commen t No. Drawing,  Spec, or Page No. 9 Pdf 26 Comment Action/Response2 The wider than normal overhangs cannot be accommodated by traditional or customary formwork systems. The span lengths are not  very long, In fact, for this span, TxDOT would recommend a much shorter girder as the most economical solution. Were the TxDOT U‐ beams considered? They can easily span this distance and allow more conventional forming systems (including TxDOT’s precast deck  panel system) to be used. In addition, they could offer an aesthetic advantage in that their sloping webs do not provide a roosting  place for birds – that is not the case for the bulb T girders. They also appear to be able to accommodate the project phasing, but the  beams may not have uniform spacing.  App. C‐1 shows that U‐beams were considered at some point, but it is not clear why they were  not carried forward as a viable solution. The overhangs currently shown are not considered to be problematic nor unfeasible.  Per the  response to Comment 7, we see potential benefits in investigating other beam types including  U‐beams during the next phase of design. 10 Pdf 26 The service life of the MLPO system is only 7‐10 years. A Polyester Polymer Concrete overlay (PPC) has a much long expected service  life (25+ years) but at greater cost. Is an overlay needed? TxDOT constructs most of its bridge replacements in phased construction  and doesn’t typically use overlays to cover the phasing joints. With construction joints needed for phased construction and accommodating the pinning of  temporary barriers to the deck, an additional layout of protection for the deck was felt  warranted.  If the City of Austin chooses to eliminate or enhance the overlay system, this  decision will affect cost and service life and can be reviewed during the next phase of design.  11 Pdf 28 The contractor may need to use some portion of the existing half‐section or the new north section to stage demolition equipment. Maintaining 4 lanes of traffic during this operation may be challenging ‐ could a reversible middle lane be  used for peak traffic periods? 12 Pdf 29 Does the water depth in Barton Creek, and access points for barges, support on‐water equipment? On‐ water equipment was used in  1990 for the South First Street Widening but access and water depth in the lake we likely better than in Barton Creek. On‐water  equipment will also significantly affect water use by the public. 13 Pdf 29 Have the creek bank slopes and access points been evaluated for crane access for the trestle? If the span lengths are adjusted (balanced, per prev. comments), it may be possible to drill all the shafts at one time. 14 Pdf 30 The drill rig needed to drill 8ft diameter shafts into bedrock may require a barge set‐up so large that it effectively closes the creek to public access. 15 Pdf 32 Figure 6‐3 shows traffic along the new north bridge section (which will eventually be sidewalks/bikeways). How will this traffic  transition to the existing Barton Springs Road lanes configuration at the ends of the bridge? There are no lanes there currently off the  bridge ends and no indication of temporary lane construction. It is expected a temporary trestle will be used to access the interior portions of the bridge  during demo of the existing bridge and construction of the new bridge.  Access may be  augmented by barges.  Both trestle and barge access will be affected by permitting  requirements. Construction access will ultimately be determined by the Contractor.  During later design  phases, attention will be given to provide the Contractor with flexibility to build the bridge (by  barge, trestle, causeway, ect.) while addressing agency and public needs.  The overall  construction and attendant safety considerations are anticipated to affect public access; there  has been some discussion with PARD RE this, which will continue in the design phase. During later design phases, attention will be given to provide the Contractor with flexibility to  build the bridge (by barge, trestle, causeway, ect.) while addressing agency and public needs. 8 ft. diameter shafts were considered advantages as they would not require a cofferdam to  construct the foundation caps needed for smaller diameter elements.  During later design  phases, attention will be given to provide the Contractor with flexibility to build the bridge (by  barge, trestle, causeway, ect.) while addressing agency and public needs. There will need to be temporary pavement and temp retaining walls to facilitate the shifting of  traffic onto the new structures.  We have developed plan views and coordinated the  preliminary MOT design (and Temporary works) with City of Austin Staff.  The plan views were  ultimately left out of the BCER given their complexity and the  audience that would read the  report.  We will share the TCP plan views with WJE to address this comment. 10/20/2023 2 of 6 Job No.: CLMP167 Title: Bridge Concept Engineering Report (BCER) Peer Review PEER REVIEW COMMENTS Date: October 10, 2023 Preparer: URS/AECOM Reviewer: WJE – Brian D. Merrill, PE Responder:   URS / AECOM Discipline: Bridge/Structures Status: ☐Criteria ☐100% ☐90% ☐60% ☐30% ☒Draft Report Review Purpose: ☒Independent Peer Review ☐Discipline ☐Project Approach Review ☐Interdiscipline ☐Other: Action Code: A ‐ Agree, will comply D ‐ Delete comment1 E ‐ Exception taken Commen t No. Drawing,  Spec, or Page No. 16 Pdf 32 Comment Action/Response2 Figure 6‐3 also shows one lane of eastbound traffic using the existing north arch structure – but this traffic will have to cross over the  construction zone for the 1945 south arch structure – this could create a traffic or work‐zone safety issue. 17 Pdf 33 The WB lane on the new north section will have to cross the construction zone for the N. Interior section. It's generally best not to  split traffic in this manner. 18 Pdf 322329 Barton Spgs. must be widened to accommodate temp. traffic during staged construction. See comment 15 19 Pdf 349356 The Condition Ratings for the Deck, Superstructure, Substructure are all 6’s = Satisfactory Condition. (Refer to App. B) 20 21 22 23 Pdf 394401 Spliced Ty VI girders (not made in TX) will be more expensive than U‐beams considering that the wide beam spacing proposed  excludes the use of PCP deck panels ‐ so deck construction is also more expensive. Pdf 394401 There should never be a reason to use stainless reinforcing steel in Austin. Pdf 394401 Why were FDOT prices used? TxDOT has good construction cost history. Pdf 395402 It appears that TxDOT U‐beams could be used at the same locations as the proposed Type VI bulb tees, with reduced construction costs. This is an accurate statement and the design team is aware of the impacts that this will have on  construction.  One of the main objectives of the TCP is to maintain 2 lanes of traffic in either  direction.  This plan would do that and the impacts to the construction effort is the concession  that has to be made.  We will further explore the TCP setup in design but this will be the design  starting layout. We will share the TCP plan views with WJE to address this comment. Comment acknowledged.  Referring back to our previous response.  Keeping 4 lanes of traffic is  one of the main objectives.  Moving the lanes on the available bridge deck is a necessity to  make this work.  We will work to better the lane assignments thru design but this layout will be  our base starting point.  Plan views of the TCP will be shared with WJE but not included in the  BCER. Comment acknowledged.  A small segment of Barton Springs will have to be widened  temporarily to accommodate vehicle traffic on what will be ped facilities ultimately.  Plan views  of the layout will be shared. A footnote will be added to this page to indicate "Fair"  revised to "Satisfactory" with  clarification that the floorbeams, edge girders and vertical were below satisfactory. Agree Deck,  Superstructure, and Substructure are rated 6 = Satisfactory. Channel is rated 5 = Fair. While the  channel does not directly affect the structure, channel deterioration had begun to undermined  walkways below the bridge and could potentially lead to undermined bridge abutment. We  also note the floorbeams, edge beams, and vertical spandrels generally have "minimum  ratings" far below 6. The statement reflects these assumptions, but does not appear to affect  overall recommendation for replacement structure. We see potential benefits in investigating other beam types including U‐beams during the next  phase of design.   Final cost estimates have used black rebar. TXDOT and FDOT prices have both been used for developing cost estimates to give cross‐ checks to one another in the high inflationary period we are currently experiencing. We see potential benefits in investigating other beam types including U‐beams during the next  phase of design.   10/20/2023 3 of 6 Job No.: CLMP167 Title: Bridge Concept Engineering Report (BCER) Peer Review PEER REVIEW COMMENTS Date: October 10, 2023 Preparer: URS/AECOM Reviewer: WJE – Brian D. Merrill, PE Responder:   URS / AECOM Discipline: Bridge/Structures Status: ☐Criteria ☐100% ☐90% ☐60% ☐30% ☒Draft Report Review Purpose: ☒Independent Peer Review ☐Discipline ☐Project Approach Review ☐Interdiscipline ☐Other: Action Code: A ‐ Agree, will comply D ‐ Delete comment1 E ‐ Exception taken Commen t No. Drawing,  Spec, or Page No. Comment 24 Pdf 427434 Condition Ratings are all 6 = Satisfactory Condition per TxDOT Coding Guide for Bridge Inspections ( 5 = Fair) 25 26 Pdf 428435 Agree with the statement regarding any proposal to re‐use portions of the existing bridge. Pdf 428435 The remaining service life estimate before significant repairs appears to be overstated given the condition ratings (6). There was no  data in the condition assessment to support this. 27 Pdf 433440 The Type VI girders are to be spliced with Post‐Tensioning per Section 5.4 ‐ Preferred Bridge Concept Action/Response2 A footnote will be added to this page to indicate "Fair"  revised to "Satisfactory" with  clarification that the floorbeams, edge girders and vertical were below satisfactory. Agree Deck,  Superstructure, and Substructure are rated 6 = Satisfactory. Channel is rated 5 = Fair. While the  channel does not directly affect the structure, channel deterioration had begun to undermined  walkways below the bridge and could potentially lead to undermined bridge abutment. We  also note the floorbeams, edge beams, and vertical spandrels generally have "minimum  ratings" far below 6. The statement reflects these assumptions, but does not appear to affect  overall recommendation for replacement structure. Acknowledged. Statement was based on understanding of carbonation intrusion data from detailed inspection  report for this structure. Carbonation levels appear to be reaching concentration levels   favorable to reinforcement corrosion. While visible deterioration may not be evident at this  time, it is likely carbonation intrusion has continued to increase globally on the structure, and it  is possible reinforcement corrosion has initiated or will initiate in the near term. Statement  does not appear to affect overall recommendation for replacement structure. Footnote will be added to the statement "Longitudinal post‐tensioning of the girders and  transverse post‐tensioning of the diaphragms is eliminated." Footnote will read "Longitudinal  post‐tensioning of the girders is considered. Transverse post‐tensioning of the diaphragms is  eliminated." 28 Psf 574581 the wider than normal spacing of the Bulb‐tee girders will increase the deck construction costs as compared to a more "normal" girder  spacing. We see potential benefits in investigating other beam types including U‐beams during the next  phase of design.   Comments from Introductory Letter BCER Comments WJE is also generally supportive of the selected replacement bridge type, three‐span concrete girder bridge, but we offer the following (and attached) comments or suggestions: *     The suggested use of an AASHTO Type VI (bulb‐tee) shape is unusual given we are not aware of any girder  fabricators in Texas that have forms for this shape. The best available TxDOT shape is the TX70 girder  which is 2 inches shorter than the Type VI girder. The TX70 shape can be modified to accommodate  the suggested post‐tensioning. Comment acknowledged. We see potential benefits in investigating other beam types during the next phase of design.   10/20/2023 4 of 6 Job No.: CLMP167 Title: Bridge Concept Engineering Report (BCER) Peer Review PEER REVIEW COMMENTS Date: October 10, 2023 Preparer: URS/AECOM Reviewer: WJE – Brian D. Merrill, PE Responder:   URS / AECOM Discipline: Bridge/Structures Status: ☐Criteria ☐100% ☐90% ☐60% ☐30% ☒Draft Report Review Purpose: ☒Independent Peer Review ☐Discipline ☐Project Approach Review ☐Interdiscipline ☐Other: Action Code: A ‐ Agree, will comply D ‐ Delete comment1 E ‐ Exception taken Commen t No. Drawing,  Spec, or Page No. Comment *     The use of spliced, post‐tensioned girders for this bridge is also unusual and structurally unnecessary.  Post‐tensioned girders are typically used when the span lengths exceed that of normal simple‐span girders.  That is not the case for these relatively short spans. The additional costs for post‐tensioning likely offset  any savings due to a reduction in the number of girders in the cross section. Action/Response2 We see potential benefits in investigating other beam types including U‐beams during the next  phase of design.  U‐beams may not offer considerable cost savings over the post‐tensioned I‐ beams since they are more expensive than I‐beams.  The proposed span arrangement currently  shown has attempted to avoid existing foundations.  Alternative span arrangements,  considering constraints, may present an opportunity to better balance forces and will be  investigated during the next phase of design. *     Using three equal span lengths for a continuous structure—based on the post‐tensioned girder concept is structurally inefficient. An efficient, continuous three‐span superstructure will have a longer middle span,  typically 25 to 30 percent longer than the end spans. A longer middle span is also an aesthetic consideration. The proposed span arrangement currently shown has attempted to avoid existing foundations.   Alternative span arrangements, considering constraints, may present an opportunity to better  balance forces and will be investigated during the next phase of design. *     The girder depth and overall superstructure depth are greater than needed for the span lengths.  This is a potential waste of funds for the larger girders and has a negative impact on the Bridge’s aesthetics. *     The suggested wider‐than‐normal girder spacing and deck overhangs increase construction costs due to the need for special deck and overhang formwork. The girder spacing also increases the loads supported by  individual girders, possibly increasing their required concrete compressive strength to levels that could challenge the ability to conform to the alkali‐silica reaction (ARS) mitigation methods   employed by TxDOT for girder fabrication. We see potential benefits in investigating other beam types during the next phase of design.   The beam spacings and overhangs currently shown are not considered to be problematic nor  unfeasible.  Phased construction was carefully considered in developing beam spacing. Per the  response to Comment 7, we see potential benefits in investigating other beam types during the  next phase of design. *     The BCER mentions that TxDOT U‐beams were considered, at some point, for the superstructure. It is not clear why this beam section was not considered in the final recommendations. The U40 shape could be an ideal section  for this bridge, as it can easily span the distances between the piers without the need for post‐tensioning;  can accommodate the project phasing; has an improved aesthetic appearance compared to a bulb‐tee section;  allows for conventional, less expensive, deck and overhang forming; and the sloped girder webs do not provide a roosting place for birds, as opposed to a bulb‐tee section. We see potential benefits in investigating other beam types including U‐beams during the next  phase of design.  U‐beams may not offer considerable cost savings over the post‐tensioned I‐ beams since they are more expensive than I‐beams.  The proposed span arrangement currently  shown has attempted to avoid existing foundations.  Alternative span arrangements,  considering constraints, may present an opportunity to better balance forces and will be  investigated during the next phase of design. Aesthetics Considerations WJE reviewed the AASHTO Publication, Bridge Aesthetics Sourcebook (November 2010), for guidance during   our review of the aesthetic components of the proposals for the Bridge. This document presents practical ideas  to improve the aesthetics of short and medium span bridges. The elevation view of the proposed Bridge is very  similar to Figure 1‐3 in this document. The document describes four Keys to Success for bridge aesthetics: simplicity; good proportions   and emphasis on thinness; clear demonstration of how the structure works; and fitting its surroundings. Comment acknowledged. Comment acknowledged. 10/20/2023 5 of 6 Job No.: CLMP167 Title: Bridge Concept Engineering Report (BCER) Peer Review PEER REVIEW COMMENTS Date: October 10, 2023 Preparer: URS/AECOM Reviewer: WJE – Brian D. Merrill, PE Responder:   URS / AECOM Discipline: Bridge/Structures Status: ☐Criteria ☐100% ☐90% ☐60% ☐30% ☒Draft Report Review Purpose: ☒Independent Peer Review ☐Discipline ☐Project Approach Review ☐Interdiscipline ☐Other: Action Code: A ‐ Agree, will comply D ‐ Delete comment1 E ‐ Exception taken Commen t No. Drawing,  Spec, or Page No. Comment The Bridge’s geometry is dictated by the confines of Barton Creek, Zilker park, the connecting roadways,   and the need for shared‐use facilities for pedestrians and bicyclists. The following points taken from this  document appear to be relevant to the Bridge: *     Generally, thinner structures with longer spans are more visually transparent and less bulky. *     When more than two spans are used, the interior spans should be longer than the exterior spans      if the same girder depth can be used. *     An odd number of spans is often preferrable. *     Slender column or supporting elements that minimize the silhouette are preferred to minimize the         visual impact of the structure. *     Open railings lighten the structure visually. WJE agrees that most of the above‐listed points are met by the proposal for the Bridge, except for girder depth  and span lengths. Action/Response2 Girder depths will be examined further during the 30% design refinement process. There is a  desire to create open viewsheds through to bridge when viewed from the creek.  In addition,  the design should not create any obstructions in the middle of the creek for users on the water.   Therefore, the span lengths are set by the desire to preserve openness across the center of the  creek (no piers located in the center of the creek).  Conclusions The BCER was a very large file detailing several years of work given that the project for the Bridge has started   and stopped due to political decisions, funding issues, input from external stakeholders, the Pandemic, among others.  The document appears to include sufficient information and detail to help the City make an informed decision,  but we suggest the City consider our comments as we feel they offer an improvement to the suggested bridge concept presented in the BCER. Comment acknowledged. 10/20/2023 6 of 6