High-strength Steel Reinforcement Research Articles

High-cycle fatigue of bond in reinforced high-strength concrete under push-in loading characterized using the modified beam-end test

In this paper, combined experimental–numerical investigations of the bond behavior between high-strength concrete and steel reinforcement under monotonic, cyclic and fatigue loading are presented. A modified beam-end test specimen is used to study the bond behavior under push-in compressive loading. The bond length, the concrete strength as well as the bar diameter have been varied in the test program consisting of 56 beam-end test specimens. The bond behavior has been tested under several loading scenarios and the results have been compared with the results of the pull-out tests. Push-through and combined push-through × splitting failure modes have been observed in the test program. Moreover, a bond fatigue model based on a cumulative measure of inelastic slip developed by the authors has been used to demonstrate how to identify the model parameters for a test exhibiting a pure push-through failure. The tests including three design parameters and four distinct loading scenarios will serve for further detailed theoretical research on the bond fatigue phenomenology governing the behavior of reinforced concrete structures.

Flexural behavior of high-strength, steel-reinforced, and prestressed concrete beams

To study the flexural behavior of prestressed concrete beams with high-strength steel reinforcement and high-strength concrete and improve the crack width calculation method for flexural components with such reinforcement and concrete, 12 specimens were tested under static loading. The failure modes, flexural strength, ductility, and crack width of the specimens were analyzed. The results show that the failure mode of the test beams was similar to that of the beams with normal reinforced concrete. A brittle failure did not occur in the specimens. To further understand the working mechanism, the results of other experimental studies were collected and discussed. The results show that the normalized reinforcement ratio has a greater effect on the ductility than the concrete strength. The cracking- and peak-moment formulas in the code for the design of concrete (GB 50010-2010) applied to the beams were both found to be acceptable. However, the calculation results of the maximum crack width following GB 50010-2010 and EN 1992-1-1:2004 were considerably conservative. In the context of GB 50010-2010, a revised formula for the crack width is proposed with modifications to two major factors: the average crack spacing and an amplification coefficient of the maximum crack width to the average spacing. The mean value of the ratio of the maximum crack width among the 12 test results and the relative calculation results from the revised formula is 1.017, which is better than the calculation result from GB 50010-2010. Therefore, the new formula calculates the crack width more accurately in high-strength concrete and high-strength steel reinforcement members. Finally, finite element models were established using ADINA software and validated based on the test results. This study provides an important reference for the development of high-strength concrete and high-strength steel reinforcement structures.

Experimental seismic behavior of ultra-high performance concrete columns with high strength steel reinforcement

Ultra-High Performance Concrete (UHPC) is an advanced cementitious composite material that exhibits high ductility and durability with superior mechanical properties, e.g. compressive strength in excess of 22 ksi (150 MPa) and sustained post-cracking tensile strength greater than 0.7 ksi (5 MPa). These characteristics have promoted UHPC to be considered for new construction applications specially for next-generation bridge structures. Currently, UHPC is commonly used in limited structural applications, such as joints and connections between precast structural elements. However, there is a growing interest in larger UHPC applications and new designs of full structural members as the UHPC market keeps growing and material becomes more available. One potential application for structural elements is full UHPC columns, which is the focus of this study. This paper presents an experimental investigation of the structural and seismic behavior of large-scale full UHPC columns reinforced with conventional and high strength steel reinforcement. The UHPC columns were tested under combined axial and quasi-static cyclic lateral loading at the University of Nevada, Reno. The testing program included four columns where the seismic performance of three different columns with grade 100 reinforcement is compared with a reference UHPC column with regular grade 60 reinforcement. Thus, the varied experimental parameters included the longitudinal reinforcement ratio and grade as well as the transverse reinforcement ratio. Results demonstrate that UHPC columns have reasonable ductility and drift capacity. Moreover, higher reinforcement ratio or grade is needed to better utilize the superior mechanical properties of UHPC and recommended to inform future design.

Accelerated testing of super lightweight UHPC waffle deck under heavy vehicle simulator

A super lightweight deck can enhance load rating and functionality of a bridge, especially those identified as structurally deficient. This study was aimed to develop and experimentally validate a novel bridge deck as an ultra-lightweight low-profile waffle slab of ultra-high-performance concrete (UHPC) with either carbon fiber reinforced polymer (CFRP) or high strength steel (HSS) reinforcement. The proposed system lends itself to accelerated bridge construction, rapid deck replacement in bridges with load restrictions, and bridge widening applications without the need to replace girders. Performance and failure modes of the proposed deck were initially assessed through extensive lab experiments and finite element analysis, which together confirmed that the proposed deck panel meets the AASHTO LRFD requirements. The proposed deck system is not susceptible to punching shear of its thin slab and fails in a rather ductile manner. To evaluate its long-term performance, the system was further tested under the dynamic impact of wheel load at the Accelerated Pavement Testing (APT) facility of the Florida Department of Transportation using a Heavy Vehicle Simulator (HVS).

Shear capacity of reactive powder concrete beams using high-strength steel reinforcement

Reactive powder concrete (RPC) is a special type of concrete with a microstructure optimised by precise gradation of all particles in the mix to yield the maximum density. Therefore, RPC exhibits ultrahigh strength and durability. High-strength reinforcement has both high strength and good plastic deformation properties, so a combination of RPC and high-strength reinforcement can fully exploit their respective advantages. At present, there is little research on the shear capacity of beams made from RPC reinforced with high-strength steel, neither are there design guidelines for this type of structure. This paper reports on 32 full-scale shear tests of RPC beams containing high-strength steel reinforcement. The parameters affecting the shear capacity of this type of structure were studied and the major failure modes due to shear were identified.

Seismic fragility assessment of bridge piers incorporating high-strength steel reinforcement and concrete under near-fault ground motions

Design codes in the United States and Canada limit the use of high-strength steel (HSS) and high-strength concrete (HSC) to bridge components that are expected to remain elastic during a seismic event. Although HSS and HSC have higher tensile and compressive strengths, respectively, their lower inelastic strain capacities impose for such restrictions. To assess the seismic performance of HSS and HSC, the pier of an existing bridge is redesigned using concrete compressive strength of 50 and 80 MPa, and reinforcement yield strength of 420, 690, and 830 MPa. Static pushover and nonlinear dynamic time-history analyses were performed to generate force–deformation and seismic fragility curves. Bridge piers incorporating HSS and HSC attained the maximum load capacity yet were the least ductile. They were less seismically vulnerable than those incorporating conventional materials at minimal and repairable damage states, but not at extensive and probable replacement damage states.

Development of performance limit states for concrete bridge piers with high strength concrete and high strength steel reinforcement

Current design codes and guidelines do not permit reinforcing the plastic hinge region of bridge piers using high strength steel (HSS) rebars. This is due to the lack of adequate research on the seismic response of HSS reinforced bridge piers. The objective of this study is to develop analytical expressions for predicting the drift at the onset of different performance limit states for high strength concrete (HSC) bridge pier reinforced with HSS reinforcement. Utilizing damage data obtained from incremental dynamic analysis of HSC circular bridge piers reinforced with HSS, this study developed drift ratio relationship accounting for the aspect ratio, concrete and steel material properties, axial load ratio, and reinforcement ratio, using validated finite element models. Analytical equations are developed for estimating the drift at the inception of rebar yielding, concrete spalling, and bar buckling using multivariate regression analysis. The proposed equations showed reasonable precision when corroborated against experimental results.

Influence of steel fibers on the static and blast response of beams built with high-strength concrete and high-strength reinforcement

This paper presents the results of a study examining the influence of steel fibers on the static and blast performance of beams built with high-strength concrete (HSC) and high-strength steel reinforcement. As part of the study, a series of fiber-reinforced HSC beams designed with Grade 690 MPa ASTM A1035 reinforcement are tested under static and blast load conditions using a shock-tube. The performance of the beams is compared to that of a control set of specimens built with plain HSC and high-strength bars. In addition to the effects of the steel fibers, the effects of reinforcement type (Grade 690 MPa vs. 400 MPa) and high-strength steel ratio (ρ = 1–2.2%) are also investigated. Under static loads the provision of fibers is found to significantly enhance the ductility of the high-strength reinforced concrete beams. Under dynamic conditions, the use of fiber-reinforced HSC leads to important enhancements in blast behavior, including better control of displacements, increased blast capacity and improved damage resistance. As part of the numerical study the blast response of the beams is predicted using 2D finite element (FE) modelling.

Effects of detailing on the blast and post-blast resilience of high-strength steel reinforced concrete (HSS-RC) beams

This paper examines the influence of reinforcement detailing and fibers on the static and blast performance of beams built with high-strength concrete (HSC) and high-strength (HS) steel reinforcement. The beams in this study had dimensions of 125 mm × 250 mm × 2440 mm (b × d × L), and were built with HSC and Grade 690 MPa ASTM A1035 reinforcement. Longitudinal reinforcement in tension consisted of either 2-No.4 or 2-No.5 high-strength bars (ρ = 1% or 1.5%), while transverse reinforcement consisted of closed ties or open-stirrups made from 6 mm wire arranged at various spacing (s). Group A beams (6 specimens) were designed according to modern blast standards, with top continuity bars and closely spaced ties at s = 50 mm (d/4) throughout the beam span, while Group B beams (2 specimens) were designed with high-strength fiber-reinforced concrete (HSFRC) and a larger tie spacing of s = 100 mm (d/2). The performance of the beams is compared to that of a control set of singly-reinforced beams with “nominal detailing” consisting of open-stirrups spaced at s = 100 mm (d/2) in the shear spans only - Group C. Blast tests were conducted using a shock-tube with companion beams tested under quasi-static four-point bending. The use of blast detailing in Group A is found to significantly enhance the ductility of the high-strength steel reinforced concrete beams under static loading, allowing for full utilization of the high-strength bars in tension. Improved detailing also leads to important enhancements in blast behavior, including better control of displacements, increased blast capacity and high damage tolerance when compared to the Group C control specimens. Moreover, the results from Group B demonstrate that fibers can be used to relax transverse steel detailing without compromising ductility or performance under both static and blasts loads. The ability of high-strength steel to reduce steel requirements is also demonstrated. Moreover, the post-blast performance of the beams is assessed through residual static testing of the blast-damaged beams. The results show that blast detailing and fibers allow for significant residual post-blast resistance and energy-absorption capacity. As part of the analytical study the blast response of the test beams is predicted using 2D finite element (FE) modelling. The results show that the FE procedure which employed the Disturbed Stress Field Model was able to accurately capture the peak load and failure mode of the beams under static conditions. Under blast loading, the model also captured the displacement response of the beams up to first peak, however the accuracy reduced at subsequent cycles, with the results found to be sensitive to the choice of damping coefficients.

High-Strength Steel Reinforcement (ASTM A1035/A1035M Grade 690): State-of-the-Art Review

AbstractHigh-strength steel (HSS) and ASTM A1035 Grade 690, in particular, have been gaining popularity in the last two decades due to its considerably higher strength and corrosion resistance comp...

Structural behaviour of prestressed concrete beams with high-strength stirrups

Many studies related to high-strength concrete material have been conducted, but relatively few studies have considered high-strength steel reinforcement. Four current design codes – ACI 318-14, Eurocode 2, CSA A23.3-04, and JSCE-07 – limit the yield strength of transverse reinforcement to control diagonal crack width, and to ensure yielding of transverse reinforcement prior to brittle failure mode. ACI, Eurocode 2 and CSA A23.3-04 limit the yield strength of transverse reinforcement to 420, 600, and 500 MPa, respectively; while JSCE-07 limits the yield strength to 800 MPa, when the compressive strength of concrete is higher than 60 MPa. The implementation of high-strength transverse reinforcement in prestressed concrete (PSC) and reinforced concrete (RC) beams has been determined in this study. A total of 16 beams were strengthened using higher yield strength stirrups than the code limitations, and were monotonically loaded to failure. All the beams were designed to experience shear failure prior to flexural failure. Most of the test results showed yielding of the stirrups, and narrower crack width than the code limitations even though the specimens were strengthened with higher than 420 MPa stirrups. The test results imply the feasibility of using high-strength stirrups for PSC beams with regard to serviceability.

Flexural performance of steel-reinforced engineered cementitious composites with different reinforcing ratios and steel types

Reinforced engineered cementitious composites (ECC) flexural members fail either after a dominant crack forms (i.e., crack localization) or after gradual strain hardening of reinforcing steel. These two failure paths represent distinct ductility ranges and load reduction mechanisms that have not been fully characterized. This study experimentally investigates the two failure paths of flexural members with different reinforcing ratios (0.53%–2.10%), two types of reinforcing steel (A615 Grade 60 and A1035 Grade 100), and under monotonic and cyclic loading conditions. A total of twelve simply-supported beams are tested including two conventional concrete beams for baseline comparisons. Based on the experimental results, a recently-developed flexural strength prediction method is validated. Results show that (1) the two failure paths are affected by the reinforcing ratio and steel type, (2) ECC sustains a maximum compressive strain that is larger than 1.0% before crushing, (3) ECC effectively restrains crack width opening for flexural members using high strength (Grade 100) steel reinforcement, and (4) a recently proposed flexural strength prediction method is able to predict the experimentally observed flexural strength of the beams with an error less than 5%.

Numerical Analysis of RC beam with High Strength Steel Reinforcement using CDP model

The article is based on preliminary research on use of high strength steel for RC elements. A reinforced concrete beam with a span length of 5700 mm has been subjected to four-point bending test. The bottom reinforcement of the beam was made of SAS670/800 high strength steel. This type of steel has no specific yield point. The yield limit declared by the manufacturer is specified as 670 MPa and the ultimate strength is equal to 800 MPa. The aim of the research was to establish a numerical model that would render properly the real beam behaviour. The model was created in the ABAQUS software using the CDP (Concrete Damage Plasticity) material model for concrete. The paper analyses the influence of several parameters on the results of numerical computations. The author’s aim is to define values of the dilation angle that should be implemented in the model. Generally, the value of this parameter is established a priori, without any justification. The analysis reveals that in a situation when the dilation angle is greater than or equal to 25 deg, the numerical model predicts properly the damage obtained in the experiment. For lower values of the dilation angle, the failure mode is not consistent with the actual beam behaviour in the experiment. Another issue is whether and how the results from the model are influenced by the choice of specified concrete tensile behaviour. In the CDP model, this property may be set in three ways: by giving the stress - displacement relation, stress - cracking strain relation or determining the fracture energy. All three alternatives are analysed and compared. Another aspect described in the paper, is the difference in load application through force control and displacement control as well as the influence of the amount of shear reinforcement. In order to analyse mesh size sensitivity, the results obtained for models with various mesh densities were compared.

Behavior of concrete columns reinforced with high-strength steel rebars under eccentric loading

In this study, high-strength steel (HSS) reinforcement with a yield stress of about 600 MPa was used in reinforced concrete columns to reduce both the reinforcing bar congestion and the construction costs. For this purpose, 16 square concrete columns reinforced with either the conventional normal-strength steel (NSS) or HSS rebars were subjected to axial and eccentric compression loads. The primary test variables included longitudinal reinforcement with two strength grades, axial load eccentricities, two different concrete compressive strengths, and different longitudinal reinforcement ratios. The structural response of the columns reinforced with reduced HSS rebars (Grade 600) was compared with that of the columns reinforced with grade 420 MPa rebars in terms of their load-carrying capacity, failure mechanism, axial force-bending moment (P-M) interaction, and ductility. Experimental results showed that although the amount of longitudinal steel reinforcement was reduced by about 34% in columns containing grade 600 MPa rebars, their load-carrying capacity and P–M interaction diagrams were comparable to those of the reference columns containing conventional NSS rebars. It was also concluded that simultaneous use of high-strength rebars and high-strength concrete below a balanced point would lead to slightly higher values of ductility index (by up to 4%) than when normal concrete strength and conventional reinforcement steel rebars of Grade 420 MPa are used.

Drift capacity of high-strength concrete columns with mixed-grade longitudinal reinforcements

A unique reinforced concrete column design method which aims to improve the ductile behavior of reinforced concrete columns by utilizing various steel grades for longitudinal reinforcements is evaluated in this article. Six large-scale reinforced concrete columns were tested, with the columns subjected to axial load and cyclic forces under reversed bending. The parameters varied in the test program including the axial loading level and the ratio and strength of longitudinal steel reinforcement. It was found from the test results that utilizing longitudinal high-strength steel reinforcement by the ratio of 30%, 50%, and 100% of the total longitudinal reinforcement in a column section will increase the lateral loading drift capacity by 18%, 26%, and 55% on average, respectively. Parametric studies via nonlinear finite-element approach were performed to study the influence of various design parameters on the ultimate drift capacity of reinforced concrete columns. The correlation between the ultimate drift capacity and the confinement level, the axial loading level, and the ratio and grade of longitudinal high-strength reinforcing bars was investigated. Design charts for various ultimate drift levels in terms of other design parameters were developed.

Enhancing the performance of UHSC columns intersected by weaker slabs

This paper presents strategies for enhancing the transmission of ultra-high-strength concrete (UHSC) column loads through normal-strength concrete (NSC) slabs in the joint of slab-column connections. Parameters of the investigation were the ratio of column concrete strength to slab concrete strength (fcc′/fcs′), as well as the placement of steel fiber-reinforced concrete, and the installations of high-strength dowel bars and special structural steel inserts in the weak slab joint. The beneficial effects of using high-strength dowel bars and high-strength structural steel inserts on the ability to transmit axial loads from the UHSC columns through the weaker slabs were demonstrated. The benefits of placing steel fiber-reinforced concrete in the joint are not as significant as the additional high-strength steel reinforcement. Predictions of the effective concrete strengths using current code approaches and using equations proposed in the literature were compared to the experimental results. The results indicate that the design approach in the CSA Standard (CSA A23.3-14) and the method proposed by Kayani (1992), which is based on the a data fitting approach, provide reasonable lower bound predictions of the effective strength for the UHSC columns with weaker slab layers.

Novel UHPC-CFRP Waffle Deck Panel System for Accelerated Bridge Construction

AbstractA novel deck system is developed as an ultralightweight low profile waffle slab of ultrahigh-performance concrete (UHPC) reinforced with carbon-fiber-reinforced polymer (CFRP) bars. The proposed system lends itself to accelerated bridge construction, and has great potential for deck replacement in bridges with load restrictions, and as well for bridge widening. A total of seven specimens at two different overall depths, with single or multiple ribs and in simple or two-span configuration, were tested in two consecutive phases in this study. The results were compared to similar deck panels with high-strength steel (HSS) reinforcement from previous studies. The study confirmed that the proposed deck panel with only 102 mm overall depth and a self-weight of 0.9 kN/m2 meets the demand for a 1,219-mm stringer spacing. The flexural behavior and failure modes of the deck are in general similar to the UHPC-HSS deck. The deck is not susceptible to punching shear of its thin slab and fails in a ductile man...

Seismic Performance of High-Strength Steel RC Bridge Columns

AbstractThis paper presents the results of a testing program developed to assess the performance of circular RC bridge columns constructed with ASTM A706 Grade 80 [550] high-strength steel (HSS) reinforcement. Two pairs of columns were tested (four columns in total). The columns were subjected to lateral cyclic loading to determine the effects of steel reinforcement grade (yield strength) and of moment–shear span ratio on column performance. Each pair consisted of one column constructed with Grade 80 [550] HSS reinforcement and a control column constructed with Grade 60 [420] reinforcement. The first pair had a moment–shear span ratio of six (6), and the second pair had a moment–shear span ratio of three (3). All four columns were designed to have similar nominal bending-moment capacities. Results indicate that the columns constructed with Grade 80 [550] HSS reinforcement achieve similar resistance, similar maximum lateral displacements, and similar curvature ductility values when compared with the contro...

Seismic Performance of Beam-Column Subassemblies with High-Strength Steel Reinforcement

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Flexural Members with High-Strength Reinforcement: Behavior and Code Implications

High-strength steel reinforcement provides various benefits to the concrete construction industry, including a more efficient use of high-performance concrete, reduction of reinforcing bar congestion, and materials savings. Prior to the 2013 interim revisions of the AASHTO LRFD Bridge Design Specifications, the value of reinforcing steel yield strength used in design was limited to being no greater than 517 MPa (exceptions were permitted with owner approval for cases with a yield strength of less than 414 MPa). In 2007, National Cooperative Highway Research Program Project 12-77 was initiated to evaluate the AASHTO specifications with respect to the use of high-strength reinforcing steel and other grades of reinforcing steel having no discernible yield plateau. Among the objectives of this project was the investigation of ductility and crack control of flexural members using high-strength reinforcement. This research led to a number of recommendations that were subsequently incorporated into the 2013 interim revisions of the specifications. The flexural behavior and design of members reinforced with high-strength steel are presented. This paper also provides the background information for the AASHTO specification revisions related to strength reduction factors for flexure. The research demonstrates that the strain limits for high-strength reinforcement must be changed to achieve the curvature ductility comparable to that implicit with the current use of Grade 414 reinforcing steel. Moreover, the service load stresses in steel should be limited to 60% of the yield strength.