Reinforcing bar physical properties are main determinants for reinforcing-bar seismic demands. Consequently, seismic codes set appropriate single upper or lower limits on reinforcing bar yield strength and tensile/yield ratio, but they do not consider the variable-parameter effects of the shape of the reinforcing-bar stress-strain curve on what tensile/yield ratios and ductilities should realistically be required of reinforcing bars in seismic-resistant structures. Therefore, a theoretical study was performed to evaluate the effect of range of allowable steel yield strength, shape of steel stress-strain curve (strain and tangent modulus of elasticity at onset of strain hardening), and beam slenderness (S/d, where S is the clear span length and d is the effective depth to the reinforcing bar centroid, Figure 1) on the minimum values of steel tensile/yield ratio and useful ductility that are necessary to accommodate 2% seismic drift by plastic hinging at the end of beams, Figure 1, of concrete rigid frames reinforced with Grade 60 steel reinforcing bars.

This Symposium Publication provides engineers and contractors with up-to-date information on new technologies that are available to improve the performance of reinforced concrete structures, especially in zones of high seismicity and to make design and construction more cost effective. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP184

Headed reinforcement uses one or more anchorages, called heads, attached to the ends of steel reinforcing bars. Such heads serve to develop a bar in a relatively short distance, and can also better confine the interior concrete. For over a decade, headed reinforcement has had extensive field use in major structures subjected to cyclic fatigue and dynamic loading, as well as thorough laboratory testing on both bare steel bars as well as on concrete members with headed reinforcement. Such test have also demonstrated the superior performance of headed reinforcement under seismic loading conditions, even in high moment zones, and joint regions. This paper addresses both: (I) aspects of design and detailing with headed reinforcement for seismic resistance, and (ii) aspects of the concrete material performance as it is modified by headed reinforcement. Specific advanced design tools are discussed including empirical equations, strut-tie modeling procedures, a new membrane stress theory, and a new cyclic reinforcing bar bond-slip theory, together with design examples for bridge structures. Currently, ACI 349, CSA 474, and several overseas codes provide design rules for headed reinforcement. Where necessary these rules may be supplemented by experience, engineering judgment, empirical guidelines, and test results. New standards, regarding the use of headed reinforcement in concrete, are pending with both ASTM and ACI 318; which when incorporated should further facilitate the design process.

Eight years ago, when this engineer began in the welded wire industry, it was unclear what the capabilities of welded wire reinforcement were, let alone what the strength of materials and mechanical properties or testing methods were all about. Test books at that time placed WWR in a low strength and low ductility category. Until recently, WWR was a lesser extent, for structural applications. Now, with the latest technology and practices of cold-working rod to wire plus controlling speed and temperature of wire welding, the industry is producing reinforcement with much higher strengths and higher ductilities for more structural concrete applications. There has been excellent growth in this industry in recent years in structural WWR. It's being specified and used in many more building and bridge structures today. This paper deals principally with high strength steel reinforcement recognized and documented in the latest ACI 318 Structural Building Code and the latest ASTM Standards, A 82, A 185, A 496 and A 497. Reinforcing yield strength today are up to 80,000 psi (550 Mpa) Since AASHTO/LRFD and ACI specifications coincide for the most part, ACI references will be discussed. Being associated with the Wire Reinforcement Institute, this paper makes reference more to welded wire reinforcement. The paper will address code provisions related to all types of steel reinforcement in general. The name of the successful project game is to use the most readily available and most efficient reinforcing materials. There has been a considerable amount of performance research on reinforced slabs and paving done in recent years. Luke Snell of Southern Illinois University has done work on this subject. His paper, titled: "Cover of Welded Wire Fabric in Slabs and Pavements" was presented at another ACI Technical Session in Seattle, Washington on Jobsite Quality, Part 1. It implies that performance is achieved when steel reinforcement is placed and located property.

Theoretical moment-curvature analyses were performed in this study for analyzing the effects of cyclic behavior of reinforcing steel on seismic performance of reinforced concrete members. Cyclic stress-strain relations for reinforcing steel were estimated from an analytical model proposed in the literature and considering the onset of buckling of a steel rebar defined according to an approach proposed in this study. The ACI318-95 provisions for evaluating probable flexural strength are used for relating interstory drift and strain demands in longitudinal reinforcement of typical sections of reinforced concrete members subjected to earthquake loading.