High-strength Steel Reinforcement Research Articles

Case Study on the Effect of 690 mpa (100 ksi) Steel Reinforcement on Concrete Productivity in Buildings

High-strength steel reinforcement in buildings had previously been limited to specialized applications, but recently published design guidance allows expanded use. A case study, conducted to investigate productivity benefits of using 690 mpa (100 ksi) versus 414 mpa (60 ksi) reinforcement, found that there was little to no benefit in using 690 mpa (100 ksi) steel in slabs, post-tensioned girders, and columns, but the beam reinforcement weight was reduced by 36%. The 2010 material cost ratio of 690 mpa (100 ksi) to 414 mpa (60 ksi) reinforcement was two, outstripping the weight reduction. However, labor cost is a function of weight, bringing the overall cost of 690 mpa (100 ksi) reinforcement to within 35% of 414 mpa (60 ksi) reinforcement cost. The material cost ratio will presumably decrease over time; if it drops by 30% or more, 690 mpa (100 ksi) reinforcement will be more economical. Labor costs, which vary by location, strongly influence the productivity benefits of 690 mpa (100 ksi) reinforcement. The use of 690 mpa (100 ksi) reinforcement is more favorable in expensive labor markets and it appears to be currently competitive in some. The paper’s primary contribution to the overall body of knowledge is the quantitative understanding of the economic factors that influence the ability of 690 mpa (100 ksi) steel reinforcement to have a productivity advantage over the use of conventional 414 mpa (60 ksi) steel reinforcement. Practitioners, designers, and researchers can use this information to understand the cost and productivity impact of high-strength reinforcing steel.

Bond Characteristics and Shear Behavior of Concrete Beams Reinforced with High-Strength Steel Reinforcement

This paper evaluates the bond behavior of high strength (HS), steel reinforcing bars and highlights the effect of various key parameters believed to affect the bond characteristics. Nine reinforced concrete spliced beams were constructed and tested. The beams had different splice lengths and levels of confinements. The applicability of different hypotheses for development of conventional steel bars was examined for the HS bars. The study is extended to examine the behavior of the reinforcing bars as shear reinforcement for concrete beams by testing twelve concrete beams reinforced with HS steel stirrups under static loading conditions. The main variables in the study included steel type, concrete compressive strength, web reinforcement ratio and shear span-to-depth ratio. The applicability of various building codes and standards for concrete beams with HS shear reinforcement was also evaluated.

Development Length of Unconfined Conventional and High-Strength Steel Reinforcing Bars

The development length equation specified by ACI 318-08 and the similar equation recommended by ACI 408R-03 are based on extensive test results using conventional reinforcement conforming to ASTM A615/A615M and A706/A706M. With the development of new ASTM A1035/A1035M high-strength steel reinforcement, several studies have been conducted to examine whether the current equations are applicable for the new high-strength reinforcing steel. These studies have shown that the current equations could, in some cases, overestimate the bond strength of high-strength steel bars. This paper proposes a new equation for the bond strength of unconfined reinforcing bars for all three types of steel. The proposed equation for high-strength steel is compared to extensive test data reported in the literature and is found to be more accurate than ACI 318-08 and ACI408R-03 equations specified for conventional reinforcement.

Punching Shear Behavior of Two-Way Slabs Reinforced with High-Strength Steel

The punching shear behavior of slabs reinforced with high-strength steel reinforcement was studied and compared with that of slabs reinforced with conventional steel reinforcement. The high-strength steel selected for this research conforms to ASTM A1035-07. The influences of the flexural reinforcement ratio, concentrating the reinforcement in the immediate column region, and using steel fiber-reinforced concrete (SFRC) in the slab on the punching shear resistance, post-cracking stiffness, strain distribution, and crack control were investigated. In addition, the test results were compared with the predictions using various design codes. The use of high-strength steel reinforcement and SFRC increased the punching shear strength of slabs, and concentrating the top mat of flexural reinforcement showed beneficial effects on post-cracking stiffness, strain distribution, and crack control.

Mechanical Properties of Concrete and Reinforcement

Sub-working group 1 of the Japan Concrete Institute (JCI) committee on Utilization of High-Strength Concrete (HSC) and High-Performance Concrete (HPC) (JCI-TC063A) has been working on collecting information from research on HSC and HPC as well as their practical use. The committee published a report in 2006 in Japanese. The objective of the report is to present state-of-the-art information on concrete with strengths in excess of about 60 MPa and high-strength steel reinforcement such as prestressing steel, excluding concrete made with atypical materials, such as fibers, or uncommon techniques. It primarily addresses the mechanical properties of high-strength concrete and high-strength steel reinforcement. A concise digest of the report has already been published as a keynote paper in the proceedings of 8th International Symposium on Utilization of HSC and HPC in October 2008 in Tokyo. This paper is based on the keynote paper with additional information on High Strength Steel, HSS, reinforcing bars in Japan.

Influence of longitudinal reinforcement strength on one-way slab deflection

The CSA A23.3 standard for reinforced concrete design provides both an implicit check of deflection control based on minimum member thickness requirements and a direct computation method for deflection. This paper reports on an analytical study that compared maximum span-to-depth ratios from the implicit deflection provisions against ratios determined from direct deflection calculations. Emphasis was placed on the deflection performance of lightly reinforced one-way slabs, including those with high-strength steel reinforcement. The results indicated that maximum span-to-depth ratios should decrease as the span length increases, as the design load increases or as the cracking moment decreases. In contrast to the current implicit provisions, the design strength of the longitudinal reinforcement did not have a significant effect on the minimum slab thickness required to satisfy common deflection criterion. Design aids were proposed, with implications for design presented through a case study of a multispan one-way slab system.

Enhancing the performance under close-in detonations with polymer reinforced CRC

Compact Reinforced Composite, CRC, is a high-strength cement-based composite possessing an enormous flexural and energy-absorbing capacity due to close-spaced high strength steel reinforcement and a high-strength cement-based fiber DSP matrix. The material has been used in various construction projects including as protection for explosion hazards. In connection with explosive impact, the fraction of shear reinforcement needed to obtain full flexural capacity is controlled by the stand-off distance. For close-in detonations, a high fraction of shock reinforcement is needed to obtain full flexural capacity without breaching. This paper introducesan efficient method for implementing high fractions of polymer shock reinforcement into a CRC element. Experimental tests and a preliminary finite element analysis were performed to assess the potency of this material.

Bond Characteristics of High-Strength Steel Reinforcement

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Some controversial aspects of the seismic design of reinforced concrete building structures

Significant differences exist between the recommendations for seismic design of the codes and guidelines for reinforced concrete of different countries. Performance criteria for building structure to avoid unacceptable damage during various levels of earthquake hazard need to be refined. More accurate recommendation for the effective flexural rigidity of reinforced concrete members are required for linear elastic structural analysis to enable better estimates of the periods of vibration and the lateral deflections of statically indeterminate structures including the effects of cracking of concrete. Current code recommended values for flexural rigidity will generally lead to estimates of the periods of vibration and lateral deflections, which are on the low side. The capacity design approach to ensure the most appropriate mechanism of yielding will occur in the event of a severe earthquake is generally recognized by codes but to varying degrees of clarity, and the degrees to which capacity design is incorporated in each code varies significantly. High strength concrete and high strength non-prestressed steel reinforcement can be used in the design of buildings but the brittle behaviour of high strength concrete and the unusable yield strength of high strength steel reinforcement need to be considered. Important differences between codes exist in the rules for the quantity of confining reinforcement placed in reinforced concrete columns to ensure ductile behaviour. Significant differences also exist between the quantities of shear and confining reinforcement required in beam-column joints and in the anchorage of length of longitudinal reinforcement passing through beam-column joints. Precast concrete structures can be designed successfully for earthquake resistance but design codes in seismic regions contain provisions for precast concrete to varying degrees.

A conceptual design of the international thermonuclear experimental reactor central solenoid

One of the central solenoid (CS) designs for the International Thermonuclear Experimental Reactor (ITER) superconducting magnet system is presented. The CS part of this magnet system will be a vertical stack of eight modules, approximately 16 m high, each having approximate dimensions of 4.1-m o.d., 2.8-m i.d., and 1.9-m h. The peak field at the bore is approximately 13.5 T. A cable-in-conduit conductor with Nb/sub 3/Sn composite wire will be used to wind the coils. The overall coil fabrication will use the insulate-wind-react-impregnate method. Coil modules will be fabricated using double-pancake coils with all splice joints located in the low-field region on the outside of the coil. All coils will be structurally graded with high-strength steel reinforcement which is cowound with the conductor. Further details of the CS coil design and analysis are described.

Effects of hoop reinforcement in steel and reinforced concrete composite sections

A new version of steel and reinforced concrete (SRC) structural system is proposed. It consists of H-shaped high strength steel, concrete and hoop reinforcement. Longitudinal reinforcement is not used. Experiments were carried out to study the restoring force characteristics of the proposed SRC, with emphasis on the effects of hoop reinforcement. Hoop reinforcement improved the compressive behaviour of the concrete and protected the H-shaped steel from local buckling. The proposed SRC system showed a large energy dissipating capacity as well as a large deformation capacity.

Fatigue testing and performance of steel reinforcement bars

The methods of testing and the fatigue performance of six types of high strength steel reinforcement have been studied. Effects of bar diameter and butt-welding have been evaluated with an emphasis on long endurances. There is no evidence of the commonly assumed endurance limit at around 2×106 cycles and fractures occurred at up to 97×106 cycles. The performance can be represented by the expression σr9N=K, where σr is stress range and N is cycles to failure. The value of K is dependent on type of test, bending or axial, and bar diameter. It is concluded that it is appropriate to design using the performance for axial testing in air. The method of expressing performance is uniform with classification of welded connections and gives a safe representation of behaviour.

Uses and Limitations of High Strength Steel Reinforcement

Uses and Limitations of High Strength Steel Reinforcement