American Concrete Institute Building Code Research Articles

Assessment of concrete shear resistance of lightweight SCC beams containing scoria aggregates

Lightweight self-consolidating concrete (LWSCC) has become a construction material that combines the benefits of lightweight concrete (LWC) and self-consolidating concrete (SCC). However, this combination may affect the shear resistance of structural members made with such concrete. This paper evaluates the shear resistance and performance of LWSCC beams. Eight full-scale beams without stirrups were fabricated and tested to failure. Seven beams were constructed using LWSCC and one was cast using normalweight self-consolidating concrete (NWSCC). Natural lightweight coarse and fine scoria aggregates were used in preparing the concrete mix. The beams were tested over a simply supported span in a two-point loading configuration. The test parameters comprised the type of aggregates, the reinforcement ratio of longitudinal steel bars, the shear span-to-depth ratio, and the depth of the beam. The experimental results showed that employing scoria aggregates in the mix resulted in beams with a reduced self-weight, where the obtained unit weight of LWSCC was 1800 kg/m3. Compared to the beam with NWSCC, the counterpart beam with LWSCC showed 25% lower shear strength. Additionally, the LWSCC beam experienced a reduction of 20% in the flexural cracking load while the beam showed a larger number of cracks at failure. The shear strength of the beams was predicted using the relevant shear design provisions of the American Concrete Institute building code ACI 318, the Canadian standard CSA-A23.3, and Eurocode 2. The ACI 318 method provided more reliable and conservative estimates for the shear capacity of the tested beams.

Local Behavior of Lap-Spliced Deformed Rebars in Reinforced Concrete Beams.

Twelve full-scale reinforced concrete beams with two tension lap splices were constructed and tested under a four-point loading test. Half of these beams had shorter lap splices than that recommended by American Concrete Institute Building Code ACI 318-19; they failed by bond loss between steel and concrete at the lap splice region before rebar yielding. The other half of the beams were designed with a lap splice length slightly exceeding that recommended by ACI 318-19; they failed by rebar yielding and exhibited a ductile behavior. Several strain gauges were attached to the longitudinal bars in the lap splice region to study the local behavior of deformed bars during loading. The strain in a rebar was maximum at the loaded end of the lap splice and progressively decreased toward the unloaded end because the rebar at this end could not sustain any load. Stress flow discontinuity occurred at the loaded end and caused stress concentration. The effect of this concentration was investigated based on test results. The comparison of bond strengths calculated by existing equations and those of tested specimens indicated that the results agreed well.

Axial load limit considerations for 14 in. square prestressed concrete piles

The 2018 International Building Code and American Concrete Institute Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318R-19) have adopted axial load limits that prohibit the use of some 14 in. (350 mm) square prestressed concrete piles in areas of moderate to high seismicity. This paper presents the results of a study that examined the development of these axial load limits, their appropriateness as an attempt to ensure reliable seismic performance, and the expected seismic performance of commonly used 14 in. (350 mm) square prestressed concrete piles when the axial load limit is increased to levels commonly used in seismic design practice. Results of the study suggest that the axial load limits established by previous researchers are overly conservative and do not ensure reliable seismic performance. This paper recommends that reduced nominal moment strength be used in lieu of axial load limits for consistency with codified approaches already used in the United States and to help ensure reliable seismic performance when appropriate.

EXPERIMETNAL INVESTIGATION ON THE LOAD-DEFLECION BEHAVIOUR OF CRACKED CONCRETE BEAM BY PARTIAL REPLACEMENT OF COARSE AGGREGATE WITH CINDER

Rapid industrial growth, Environmental pollution, Scarcity of natural resources, Economic design of structural elements, Adoptability and suitability of new materials, Disposal problems, Cost effective projects, Usage of many industrial wastes for use in cement concrete applications have initiated the present investigation. The measure of soot squanders is entirely expansive in India for use as a total in cement. Ash is delivered amid blazing of coal in numerous businesses. It is the material sintered at high temperatures. There are no hurtful chemicals in soot. Squashed ash total is a material particularly proposed for the building built in hot atmospheres. The targets of this study are to show the consequences of test study and investigation on the conduct and the quality of typical quality strengthened solid pillars (NSC) and fortified solid bars with ash totals and connects their outcomes. Trial blends were made to accomplish a legitimate blend for the solid of M40 evaluation with appropriate workability to cast the bars. With the right blend extent accomplished, pillars were thrown, measurements of each being 2800mm x 100mm x 145mm. The support of the shafts differed from 0.84%, 1.31% and 1.88%. The bars were cured for 28 days. Following 28 days, all the bars were tried for flexure under two point stacking in a stacking casing of 50tonnes limit. The heap was connected by method for a100kN water driven jack, through a steel I-area, bolstered on two steel rollers. The result obtained was then plotted as graphs. The experimental results are compared with IS 456:2000 provisions. The analytical work involved the calculation of deflections of test beams using the methods currently available in the literature. In addition, the design provisions contained in the American Concrete Institute Building Code ACI 318-2010, British Code BS 8110 and Euro Code EN 1992 are used to calculate the strength of all the beams.

Evaluation of new spiral shear reinforcement pattern for reinforced concrete joints subjected to cyclic loading

Using continuous spiral reinforcements can greatly improve the seismic performance of reinforced concrete columns, in terms of ductility and energy dissipation capacity. The simultaneous incorporation of this method in beams and columns might influence the behaviour of beam–column connections as wide spectrums of brittle failure were observed in this region. A new proposed beam–column connection introduced as ‘twisted opposing rectangular spiral’ was investigated in this research in both experimental and numerical manners along with comparing its seismic performance with both normal rectangular spiral and conventional shear reinforcement systems. The design of three full-scale beam–column connections was performed according to Eurocode (EC8-04) for high ductility classes, and the quasi-static cyclic loading recommended by American Concrete Institute Building Code (ACI 318-08) was hired to conduct the seismic tests. Finally, the experimental results were validated by numerical results obtained from the finite element analysis of the three specimens. The results revealed improved ultimate lateral resistant, energy dissipation capacity and ductility for the new proposed connection.

Experimental study on transfer length of an eco-friendly prestressed concrete sleeper

This study focuses on investigating transfer length in a newly developed eco-friendly concrete prestressed concrete sleeper. A next generation prestressed concrete sleeper was developed at the Korea Rail Research Institute (KRRI) in order to improve structural performances of the current prestressed concrete sleepers while addressing some environmental issues such as CO2 emissions and a lack of natural resources. The authors used ground granulated blast furnace (GGBF) slag and electric arc furnace (EAF) oxidizing slag to reduce the amount of Portland cement (III) and natural sand. To ensure the safety and structural integrity of the newly developed sleeper prior to a mass production and installation in the field, the structural performances of this newly developed eco-friendly concrete sleeper ought to be studied. One of important structural performances of prestressed concrete members which should be measured is transfer length. Unlike other civil engineering fields, no design guidelines for transfer length in prestressed concrete sleepers have been established in the railway industry. For example, the American Concrete Institute Building Code and the American Association of State Highway and Transportation Officials Bridge Design Specifications specify the required transfer length in prestressed concrete beams or girders depending on the size of prestressing wires or strands. Therefore, this study examines transfer length in the newly developed eco-friendly concrete sleeper and compares that with the transfer length in traditional prestressed concrete sleepers. Four sleepers are manufactured for each concrete, and the transfer length in each sleeper is monitored at the day of prestress release, and 7, 28 and 90days. As monitoring the behavior of the sleepers over 90days, the long-term effect on the transfer length is also investigated. The study demonstrates that the transfer length in the eco-friendly concrete sleepers is not only shorter than that of the traditional prestressed concrete sleepers, but also found to be more desirable since the prestress is fully developed prior to the railseat area.

Evaluation of tension lap splices for code provisions

Six real-size beams were tested in order to examine the reliability of tension lap splices for the minimum requirements of clear cover, spacing between bars and transverse reinforcement. The beams were prepared in accordance with the minimum provisions of the American Concrete Institute building code requirements for structural concrete (ACI 318–08) and the Turkish standards on requirements for design and construction of reinforced concrete structures (TS 500). Results showed that all beams prepared in accordance with ACI 318–08 showed satisfactory behaviour. Since the specimen prepared according to TS 500 with 26 mm diameter bars failed due to bond, it can be concluded that the TS 500 clear cover is insufficient for spliced bars equal to or greater than 26 mm in diameter. In order to evaluate the ACI Committee 408 new proposal and Eurocode 2 provision for tension lap splices, a case study was also conducted. According to the results of the case study, while the ACI 318–08 requires unnecessarily longer splice lengths for bars of greater than 19 mm diameter, Eurocode 2 always gives the smallest lap splice length which leads to safety concerns.

Observations from the February 27, 2010, earthquake in Chile

On February 10, 2010, Chile was struck by an 8.8-magnitude earthquake, followed by hundreds of aftershocks. This article summarizes findings from a reconnaissance team from the Precast/Prestressed Concrete Institute that visited the region in April 2010 to assess damage. The team found that most structures performed acceptably or better, with the number of deaths and the amount of property loss proportionate to the severity of the earthquake. Precast concrete building systems generally performed well. The absence or weakness of diaphragm framing did result in local failures. Although bridges experienced shaking that was much more intense that the bridges were designed to handle, most precast concrete bridges performed well. However, the bridges that suffered the most damage were those that were designed based on a recent (1990s) practice that eliminated or reduced diaphragms providing lateral support between beams. These bridges experienced lateral displacements at the bearings, failure in end stoppers and overturning of some beams. Steel-girder bridges constructed with similar end details experienced similar failures. As a result of the earthquake, changes were made to Chile’s building code. Similar changes are being considered for possible inclusion in the American Concrete Institute Building Code 318-08 section 21.9 on special structural walls and coupling beams.

Shear Strength and Drift Capacity of Fiber-Reinforced Concrete Slab-Column Connections Subjected to Biaxial Displacements

Results from the tests of three large-scale slab-column subassemblies subjected to combined gravity load and biaxial lateral displacements are presented. The main purpose of the experimental program was to investigate the use of randomly oriented steel fiber reinforcement as a means to increase connection punching shear strength and deformation capacity. The connection of Specimen SB1 was reinforced with regular strength (1,100 MPa) fibers, 30 mm long and 0.55 mm in diameter, while the connection of Specimen SB2 featured high-strength (2,300 MPa) fibers, 30 mm long and 0.38 mm in diameter. Both types of fibers were targeted at a 1.5% volume fraction. The connection of Specimen SB3, on the other hand, was reinforced with shear studs, designed according to the 2008 American Concrete Institute Building Code. All three connections were subjected to a gravity shear ratio of approximately 1/2 during application of biaxial lateral displacements. The use of fiber reinforcement in the connection region resulted in...

Cyclic response of non-seismically detailed interior RC beam–column connection with varying column tributary area

The current paper presents a test of non-seismically detailed reinforced-concrete (RC) beam–column connections under reversed cyclic load. The tested specimens represented those of the actual mid-rise RC frame buildings designed according to the non-seismic provisions of the American Concrete Institute building code. The evaluation of ten existing RC frames was conducted to identify key structural and geometrical indices. It was found that there was correlation among structural and geometrical characteristics and the column tributary area. Hence, the column tributary area was chosen as a parameter for classifying specimens. The test results showed that specimens representing small and medium column tributary areas failed by brittle joint shear while specimens representing large column tributary areas failed by ductile flexure, even though no ductile seismic details were provided. The local bond deterioration and joint shear distress accounted for the pinched hysteretic loops. The detailed failure mechanism was investigated through a nonlinear finite element analysis. In the finite element analysis, the two-dimensional reinforced concrete plate element was used to model beam and column whereas the one-dimensional discrete joint element was used to model the interface between beam and joint face. The finite element analysis revealed that the joint shear failure of specimens representing a small to medium column tributary area resulted from the collapse of the principal diagonal concrete strut.

Fly ash-based geopolymer concrete: study of slender reinforced columns

The objectives of this paper are to present the results of experimental study and analysis on the behaviour and the strength of reinforced geopolymer concrete slender columns. The experimental work involved testing of twelve columns under axial load and uniaxial bending in single curvature mode. The compressive strength of concrete for the first group of six columns was about 40 MPa, whereas concrete with a compressive strength of about 60 MPa was used in the other six columns. The other variables of the test program were longitudinal reinforcement ratio and load eccentricity. The test results gathered included the load carrying capacity, the load-deflection characteristics, and the failure modes of the columns. The analytical work involved the calculation of ultimate strength of test columns using the methods currently available in the literature. A simplified stability analysis is used to calculate the strength of columns. In addition, the design provisions contained in the Australian Standard AS3600 and the American Concrete Institute Building Code ACI318-02 are used to calculate the strength of geopolymer concrete columns. This paper demonstrates that the design provisions contained in the current standards and codes can be used to design reinforced fly ash-based geopolymer concrete columns.

Tension development length and lap splice design for reinforced concrete members

AbstractThe key factors that govern development (anchorage) and splice performance of reinforcing bars in tension are described. The bond design provisions of the AASHTO (American Association of State Highway and Transportation Officials) LRFD (Load and Resistance Factor Design) Bridge Design Specifications, the American Concrete Institute Building Code Requirements for Structural Concrete (ACI 318‐05), ACI Committee 408, CEB‐FIP Model Code 1990, and Eurocode 2 are summarized and compared with test results. In terms of the key factors, the bond strength of bars not confined by transverse reinforcement is proportional to the concrete compressive strength to the ¼ power. The contribution of transverse reinforcement to bond strength increases with the area of the transverse reinforcement per bar and the relative rib area and diameter of the bar being developed or spliced and has been found to be proportional to the concrete compressive strength to a power between ¾ and 1.0. For deep members or for high‐slump (conventional and superplasticized) concrete, the effect of bar placement may be greater than accounted for in current design provisions. Of the five design procedures compared in this paper, those developed by ACI Committee 408 provide the best match with test results for both developed and spliced bars. For developed bars, the other four design procedures result in a high percentage of tests for which the test to calculated strength ratios (T/C) are less than 1.0, with the greatest percentage of low T/C values resulting from the AASHTO requirements. The relative safety of the latter four design procedures improves for lap splices. A provision in ACI 318‐05 that allows a 20% reduction in development and lap splice length for bars smaller than 19 mm appears to be unsafe and should be removed or modified.

Evaluation of the seismic performance of a three‐story ordinary moment‐resisting concrete frame

AbstractThis study focuses on the seismic performance of Ordinary Moment‐Resisting Concrete Frames (OMRCF) designed only for gravity loads. For this purpose, a 3‐story OMRCF was designed in compliance with the minimum design requirements in the American Concrete Institute Building Code ACI 318 (1999). This model frame was a regular structure with flexure‐dominated response. A 1/3‐scale 3‐story model was constructed and tested under quasi‐static reversed cyclic lateral loading. The overall behavior of the OMRCF was quite stable without abrupt strength degradation. The measured base shear strength was larger than the design base shear force for seismic zones 1, 2A and 2B calculated using UBC 1997. Moreover, this study used the capacity spectrum method to evaluate the seismic performance of the frame. The capacity curve was obtained from the experimental results for the specimen and the demand curve was established using the earthquake ground motions recorded at various stations with different soil conditions. Evaluation of the test results shows that the 3‐story OMRCF can resist design seismic loads of zones 1, 2A, 2B, 3 and 4 with soil types SA and SB. For soil type SC, the specimen was satisfactory in seismic zones 1, 2A, 2B and 3. For soil type SD, the OMRCF was only satisfactory for seismic zones 1 and 2A. Copyright © 2004 John Wiley & Sons, Ltd.

Factors Affecting Anchorage Bond Strength in High-Performance Concrete

The objective of this investigation was to observe the effect of the compressive strength of concrete, reinforcing bar size, thickness of concrete cover, and amount of web reinforcement on the anchorage bond strength and on the bond behavior of reinforced high-performance concrete. For this purpose, eccentric pullout bond tests were conducted under monotonic loading on high-performance concrete specimens. Some of the specimens were reinforced by one and some by two deformed steel bars. Results indicated that the bond strength between reinforcement and concrete increased with increasing concrete strength, cover thickness, and amount of web reinforcement, while it decreased with increasing bar size. Using the test data, the variation in the average bond strength with respect to each of the stated parameters is formulated. The trend of variation for each parameter is compared with the associated trends inherent in the development length expressions of the American Concrete Institute Building Code and the Eurocode 2. An expression for the required development length, enveloping all the tested specimens, is presented.

Side-Face Reinforcement for Flexural and Diagonal Cracking in Large Concrete Beams

The current American Concrete Institute (ACI) Building Code and American Association of State Highway and Transportation Officials (AASHTO) Bridge Code requirements for side-face reinforcement are meant to control flexural cracking in the webs of large concrete beams and may not provide adequate diagonal crack control for certain exposure conditions. Twenty-one large concrete beam elements with 1,200-mm deep webs were tested in a specially constructed apparatus to study the influence of amount and arrangement of side-face reinforcement in controlling both flexural and diagonal cracking in large concrete beams. The amount of side-face reinforcement was varied from 50% to 300% of what is required by the current ACI Building Code and AASHTO Bridge Code. Deformed reinforcing bars, welded wire fabric, and hooked steel fiber were included in the study. Over 11,000 crack widths were measured with a microscope on the 21 specimens, and an analysis of the crack data revealed the relationship between crack width and average strain and the ratio of maximum to average crack widths. A procedure is presented for estimating diagonal crack widths in the webs of large beams caused by service level shear stresses, and a general design procedure is presented for the amount of side-face reinforcement needed to control both flexural and diagonal cracking in the webs of large concrete beams. The required spacing of side-face longitudinal reinforcing bars depends on the maximum acceptable crack width, strain of the longitudinal reinforcement on the flexural tension side, magnitude of the applied shear stress, amount of transverse reinforcement, and the diameter of and cover to the side-face reinforcing bars. A design example illustrates the proposal.

Shear strength of members without transverse reinforcement

The variable angle truss model is extended to members without transverse reinforcement by introducing concrete tension ties perpendicular to concrete compression struts. The modified compression field theory approach of limiting the shear transfer across diagonal cracks is combined with the variable angle truss model to develop equations for the shear capacity of members without transverse reinforcement. These equations are the theoretical basis of tabulated values for members without stirrups in the general shear design method of the 1994 Canadian concrete code. This paper also presents the results from an experimental study in which 27 narrow (beam-like) wall elements, with significant longitudinal reinforcement and little or no transverse reinforcement, were subjected to combined axial tension, bending moment, and shear. The experimental results are compared with predictions from the 1994 Canadian concrete code, as well as the American Concrete Institute building code. Key words: building codes, reinforced concrete, shear strength, structural design, tension, tests, truss model.

Tests of Large Partially Prestressed Concrete Girders

Six large beams with overhangs and various levels of post-tensioning and stirrup reinforcement were tested. The results were compared to predictions given by the modified compression field theory, truss model design approach, and the current American Concrete Institute (ACI) Building Code. The comparison showed that both the modified compression field theory and the truss model approach yielded results that were consistent with the specimen behaviors. The current ACI Building Code overestimated the flexural capacity of the beams and underestimated their shear capacity with respect to the applied loading conditions.

Reduced Strand Spacing in Pretensioned, Prestressed Members

Pretensioned, prestressed concrete girders are used widely in bridge superstructures in the United States. Predominantly, 0.5-in. (12.7-mm)-diameter prestressing strand is used in these girders at a center-to-center spacing of 2 in. (50.8 mm). This corresponds to the four-strand-diameter center-to-center spacing, which is the American Concrete Institute (ACI) 318-89 minimum requirement for pretensioned, prestressed members. In the past, however, several states have used a center-to-center strand spacing of 1.75 in. (44.5 mm) with success. The purpose of this paper is to report the results of laboratory tests designed to determine if the closer strand spacing has a detrimental effect on prestressed girder performance. Twelve test specimens were cast for the study. The experimental results from this research were compared to results in the literature and the provisions of the ACI Building Code (ACI 318-89). It was concluded that the closer strand spacing has no significant effect on transfer length, development length, or nominal moment capacity.

Parametric study of composite column strength variability

The study reported herein investigates the effects of different variables on the variability of the ultimate strength of steel—concrete composite columns in which steel shapes are encased in concrete. The ultimate strength of a number of typical composite columns was studied in terms of the ratio of ‘theoretical’ strength based on an accurate description of strength and probability distributions of variables affecting the strength to a ‘nominal’ strength based on design expressions of the American Concrete Institute Building Code (ACI 318-83) and the specified properties of the variables. This was done to non-dimensionalize the strength and to simplify the comparison of strength for different columns. The major conclusions drawn from the analysis of results reported in this study are: (a) the residual stresses play an appreciable role in the strength of composite columns; (b) the concrete confinement provided by the lateral ties produces a beneficial effect on the strength of composite columns, and (c) the specified concrete strength, end eccentricity ratio, and slenderness ratio are the major parameters affecting the variability of composite column strength.

Concrete Encased Steel Columns—Design Tables

Tables for the design of columns composed of concrete-encased structural steel shapes are presented. The design loads and slenderness provisions fulfill the requirements of the American Concrete Institute Building Code (ACI 308-71). The tables include all A36 rolled shapes shown in the American Institute of Steel Construction Manual, with nominal depths from 6 to 14 in. and weights less than 114 lb/ft encased in lightweight concrete. Tables are both English and SI units.