International Concrete Abstracts Portal

Three large-scale reinforced concrete rectangular slender structural walls were subjected to cyclic displacement demands to establish whether, and under what conditions, mechanical splices can be used with Grade 100 (690) bars where yielding is expected. These tests were conducted because ACI 318-19 prohibits both lap splices and mechanical splices for high-strength longitudinal reinforcement (Grade 80 (550) and higher) in special structural walls where yielding is expected. Three mechanical splices were used that differed in connection type (one type per wall) and overall splice length. The mechanical splices were all placed starting 2 in. (50 mm) from the wall base. Mechanical splices satisfying the specified minimum tensile strength criterion of ACI 318-19 Type 2 mechanical splices resulted in better wall behavior than reported for lap splices, but satisfying Type 2 requirements alone did not prevent bar fractures at the mechanical splice. Thus, Type 2 mechanical splice requirements are not recommended as the sole qualification criteria where yielding is expected. Test results also showed that mechanical splices with a strength not less than the actual bar tensile strength, such that bars systematically fail in direct tension tests away from the splice and therefore develop their actual uniform elongation, perform well, and are recommended for use where yielding is expected in special structural walls.

Compression development and lap splice length provisions in ACI 318-19 §25.4.9 and §25.5.5 are reexamined after an example is used to show that existing provisions can produce unexpected results in some design conditions, such as compression lap splices longer than tension lap splices. A historical review of ACI Building Codes shows existing compression bond length provisions are largely based on provisions adopted before test data were available. The provisions in ACI 318-19 are compared with a database of 89 test results, and are shown to poorly fit the data. Several compression and tension bond equations are also examined that fit the data better. It is shown that compression development and lap splice lengths can be based on a number of expressions available in the literature for tension development length, with minor modification, including the ACI 318-19 equation for tension development length. Using this approach would simplify design by eliminating the use of different expressions to calculate tension and compression development lengths, prevent calculated lengths from being longer in compression than in tension, and provide a better fit to available data.

The ACI 318-19 Building Code does not allow the use of headed bars larger than No. 11 (No. 36) due to insufficient experimental data. Thirty large-scale simulated beam-column joint specimens containing high-strength No. 11 (No. 36), No. 14 (No. 43), or No. 18 (No. 57) headed bars were tested to investigate the effects on anchorage strength of key factors, including bar stress at failure, bar size, bar spacing, embedment length, transverse reinforcement, concrete compressive strength, and loading condition. Specimens exhibited concrete breakout, side splitting, or a combination, with four exhibiting a shear-like failure. Anchorage of larger bars is noticeably influenced by joint shear demand and loading condition. Descriptive equations developed based on 164 tests accurately characterize anchorage strength for headed bars up to No. 18 (No. 57). They indicate that anchorage strength is proportional to concrete compressive strength to a power close to 0.2 and that the contribution of parallel ties for large headed bars is lower than that observed for smaller headed bars.

Design codes such as ACI 318-19 and AASHTO LRFD permit the use of high-strength steel in specific provisions. Particularly, reinforcing bars with yield strength of 100 ksi (689 MPa) and size as large as No. 11 (No. 36) are permitted for use in tension lap splices. However, the test data using larger-diameter bars, especially No. 11 high-strength bars, is limited. In this study, four largescale reinforced concrete beams with No. 11 bars were tested in four-point bending. The beams were grouped in two groups: one used Grade 60 (420) steel while the other used Grade 100 (690) steel. Within each group, one beam had continuous bars, while the second beam had spliced bars. Test results showed that splicing No. 11 (No. 36) high-strength reinforcing bars had adequate load-carrying capacity; however, the crack width may not be adequate. Therefore, test results indicate that using No. 11 (No. 36) high-strength reinforcing bars in tension lap splice applications should be used with caution.

Reinforced concrete walls are commonly used in low- and mid-rise construction because they provide high strength, stiffness, and durability. In regions of low and moderate seismicity, ACI 318 Code requirements for minimum reinforcement ratio and maximum reinforcement spacing typically control over strength-based requirements. However, these requirements are not well-supported by research. The current study investigates requirements for the amount and spacing of reinforcement using experimentally validated nonlinear finite element modeling. For lightly reinforced concrete walls subjected to out-of-plane loading: 1) peak strength is controlled by concrete cracking; and 2) residual strength depends on the number of curtains of steel. Walls with very low steel-fiber dosages were also studied. Results show that fiber, rather than discrete bars, provides the most benefit to wall strength, with fiber-reinforced concrete walls achieving peak strengths more than twice that of identically reinforced concrete walls.