Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 15
15 Of the five jurisdictions reporting use of high-strength cally stated that they were satisfied with the results versus cost reinforcing steel, three report only the use of steel up to 75 ksi, of high-strength steel when compared to 60 ksi although they and two report use of steel having a yield strength greater than had concerns over crack width with higher yield strength 100 ksi (Question #2). Respondents indicated that high- (paraphrased by authors of this report). strength reinforcement is not excluded from use in any appli- cation and, indeed, has been applied in all applications cited We advertised one project where high-strength bars [A1035] were allowed as an alternative to epoxy-coated rebar. The con- in Question #3 except "spirals in piers." One jurisdiction tractor elected to use epoxy-coated bars. We would only allow reporting use of steel having fy greater than 100 ksi reports its the rebar to be designed for up to 75 ksi, until AASHTO has spec- use as only "main flexural reinforcement in beams," although ifications to account for higher strength bars. it is apparently "permitted" elsewhere. The second such juris- diction reports its use as only slab reinforcement. The reasons 1.4.1 Survey of Use of Stainless Steel for incorporating this steel (Question #4) are reported as Reinforcement in Bridge Structures being to "improve durability by enhancing corrosion resist- ance of reinforcement." Both jurisdictions having used fy A similar, abbreviated survey (Appendix J) addressing the greater than 100 ksi in flexural applications report this use as use of stainless steel was also conducted. In this case, 28 being on an "experimental/trial" basis. Three jurisdictions responses were received. Thirteen jurisdictions reported the report fewer than 10 structures having high-strength steel use of stainless steel reinforcing bars; in all but one case for reinforcement while one reports between 10 and 50 struc- slab reinforcement and in most cases on an experimental tures (Question #5). basis. Design for stainless steel bars was apparently a one-for- Design using high-strength reinforcement was facilitated one substitution for conventional reinforcing bars. by the engineer of record's best judgment (Question #6). Three of the five respondents reported simply using AASHTO 1.4.2 Reported Use of A1035 Reinforcing design methods for 60 ksi reinforcement and replacing the Steel in Highway Bridge steel, one-for-one, with high-strength steel bars. In one Infrastructure response, high-strength steel is simply used in place of 60 ksi steel for areas requiring corrosion resistance; nonetheless, MMFX Inc., the only supplier of A1035 reinforcing steel, increased lap lengths are prescribed in this case. A comment reports 25 U.S. and 4 Canadian jurisdictions that have used from this respondent follows (identifying information has A1035 reinforcing steel in at least one bridge project as of been removed): December 2009. Most applications have been bridge decks. According to MMFX, most applications are simply one- [This jurisdiction] has mainly used [A1035] steel to aid with to-one replacement of A615 with A1035 in order to take corrosion. We have been very conservative with its usage. Usu- advantage of the improved corrosion resistance of the latter. ally designing as if we are using 60 ksi rebar or in some instances Nonetheless, there are 17 known projects where a value more. Then we will use longer development lengths to assist with ultimate capacities. Codes [are] not fully written to use such greater than fy = 60 ksi was used in design; these are listed in high-strength rebar properties; therefore [this jurisdiction] hasn't Appendix J. Design values of fy of 75, 80, and 100 ksi are generally designed for maximum strength usage in bars. How- reported, although most were 75 ksi (thus, presumably tak- ever, we do look at ultimate bending capacity and increase laps if ing advantage of the upper limit on fy prescribed by AASHTO deemed prudent. We have built about five slab bridges using specifications). [A1035] entirely. We have used it in some bridge decks--three Cross-referencing existing projects with the survey indicate to seven. Then we use it in our P/S girders for shear reinforcing [bars] in the ends of girders and as shear reinforcement between that most projects were experimental "demonstration" proj- the girders and the bridge deck--substitute it for 60 ksi rebar-- ects. It is further noted that not all jurisdictions reported to assuming 60 ksi properties. have erected structures returned the survey. Additionally, five jurisdictions reporting in the survey no projects with high No problems or impediments to design were reported by performance steel are revealed by the project list to have, in any respondents (Questions 7 to 9). One respondent specifi- fact, one or two existing demonstration projects.