Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
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 9
9 using 100 ksi steel at the tension-controlled strain limit of ments; therefore, it is not unexpected that experimental inves- 0.0066 exhibited ductility behavior (as measured by steel tigations of A1035-reinforced decks exhibit no significant strain and section curvature) similar to that exhibited by a differences in behavior (particularly under service loads) 60 ksi design having a strain limit of 0.005. They demon- compared to A615-reinforced counterparts (Rizkalla et al. strated that the ratio of nominal to service deflections was 2005, Hill et al. 2003). indeed greater for the higher strength steel reinforced sec- tions. In addition, due to the higher tension strain in the 1.3.4 Shear Reinforcement high-strength reinforcement under service loading condi- tions, the beams may exhibit larger crack widths than if rein- The shear behavior of reinforced-concrete beams is not forced with conventional steel. However, as shown in Mast well understood and calculation of the shear strength is et al. (2008), previous testing indicates that the measured based on semi-empirical relationships. As a result, the cal- crack width under service loading conditions is only slightly culated shear strength can vary significantly (up to 250%) larger than the (so-called) acceptable crack widths for beams among different code approaches (Hassan et al. 2008). Sim- reinforced with conventional steel. It is proposed that since ilarly, it is unclear whether current design approaches for some high-strength steels have improved corrosion resist- shear may be extended to members having high-strength ance, the increased crack widths may be acceptable as long as steel reinforcement. One concern is whether the high stress these are not aesthetically objectionable. levels induced in the reinforcement may cause excessive Based on this work, Mast et al. proposed variation of the cracking in the concrete resulting in degradation of the con- flexural resistance factor, , between 0.90 and 0.65 at strain crete component of shear resistance. Sumpter (2007) sought limits greater than 0.009 and less than 0.005, respectively. to determine the feasibility of using high-strength steel These limits correspond to the tension-controlled limit of 0.005 as shear reinforcement for concrete members, particularly and compression-controlled limit of 0.002 presently used for focusing on the member behavior under overload condi- 60 ksi steel in AASHTO (2007). To help prevent compression- tions where the steel experiences high stress levels. Sumpter controlled failure, they suggest providing compression rein- reports tests of beams having shear span to depth ratios of forcement having a design yield strength, fy < 80 ksi. This limit approximately 3 alternately reinforced with A615 or A1035 is based on the maximum stress that can be developed at a longitudinal and transverse steel. Stirrup spacings used strain of 0.003, which is the ultimate concrete strain at the reflected the minimum and maximum permitted and an extreme compression face of the concrete beam. additional intermediate spacing between these limits. Due to A number of experimental studies (Seliem et al. 2006, the stiff nature of shear-critical sections, little differences McNally 2003, Malhas 2002, Vijay et al. 2002, Florida DOT between specimen behaviors were noted at service loads. As 2002) of the flexural behavior of members reinforced with expected, observed capacity of these shear-critical members A1035 reinforcing steel support the conclusions of Mast reflected the amount of shear reinforcement present. Mem- et al. (2008). These studies all indicate that flexural members bers having A1035 shear reinforcement exhibited marginally designed using the same simplified approach (i.e., elastic- greater capacity than those with A615 shear steel. Sumpter perfectly plastic steel behavior at higher values of fy) will have concludes that most observed behavior was dominated by flexural characteristics comparable to members having con- concrete behavior and that stress in the shear reinforce- ventional reinforcement grades. Where reported, cracking ment in any specimen never exceeded 80 ksi; thus, the high- and deflections at service loads are only marginally greater strength steel (fy > 100 ksi) was not fully utilized, whereas the when using A1035 steel. One study (McNally) indicates a 60 ksi steel was. A study reported by Florida DOT (2002) reduction in overall ductility when using an earlier formula- draws the same conclusions with respect to the stress that tion (since changed) of A1035 reinforcement. Other studies may be developed in shear reinforcement. Sumpter also (Seliem and Florida DOT) report a marked increase in duc- reports that all shear crack width values at service loads tility likely resulting from the lower reinforcement ratio that were less than the ACI-implied limit for flexural cracking of may used in conjunction with the high-strength flexural 0.016 in., regardless of the reinforcement grade or details. reinforcement. Indeed, Sumpter reports smaller crack widths in comparable members having high-strength steel than those with conven- tional steel. He attributes this behavior to enhanced bond 22.214.171.124 Applications in Bridge Decks characteristics of A1035 steel resulting from differences in Most extant applications of A1035 steel have been in bridge rib configuration. This conclusion is curious because there is decks and its use is typically as a one-to-one replacement for typically no difference between the rib configuration of A615 less corrosion-resistant "black" steel. Bridge deck design is and A1035 reinforcing steels, and Sumpter does not report a based more on serviceability criteria than on strength require- difference in his test program.