![]() Crack width is a function of steel strain and consequently steel stress (Nawy 1968). The limits on yield strength also serve to control of crack widths at service loads. The limits on yield strength are required to ensure adequate ductility of a section and are related to the prescribed limit on concrete compressive strain of 0.003. Both ACI and AASHTO limits have been written and interpreted to not exclude the use of higher strength grades of steel, but only to limit the value of yield strength that may be used in design, thus, reducing the efficiency of using these materials. The AASHTO LRFD Bridge Design Specifications (AASHTO 2010) similarly limit the use of reinforcing steel yield strength in design to no less than 414 MPa (60 ksi) and no greater than 517 MPa (75 ksi), although exceptions are permitted with owner’s approval. Currently, ACI 318 (2011) permits design using steel reinforcement with yield strength not exceeding 552 MPa (80 ksi). Design with steel having higher yield strength values is permitted although the yield strength used in strength calculations is limited. The design of reinforced concrete structures in the United States is dominated by the use of steel reinforcement with yield strength, f y, equal to 414 MPa (60 ksi). This approach, however, affects the flexural stiffness, as measured by the effective moment of inertia, I e, of a cracked reinforced concrete member and results in different deflection and cracking behaviors. Finally, coupling high-strength steel reinforcement with high-performance concrete should result in a more efficient use of both materials. Reducing reinforcement quantities may also reduce congestion problems leading to better quality of construction. Using a higher strength reinforcing steel could provide various benefits to the concrete construction industry by reducing member cross sections and reinforcement quantities, which would lead to savings in materials, shipping, and placement costs. Concrete members reinforced with high strength steel reinforcement have different behavior due to the expected higher service loads, compared to concrete members reinforced with conventional steel bars. The material strength of steel reinforcement and concrete, bond characteristics, size of a member, and amount of reinforcement are all factors affecting the development of cracks in reinforced concrete members. Although the service checks are generally conservative-based on limiting stresses in the structure at service loads-the adoption of higher strength materials suggests potential problems under service conditions. A design example illustrates the proposal.Reinforced concrete members are typically designed based on strength at ultimate limit state and subsequently checked for deflection and crack control at serviceability limit state. 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 trans-verse reinforcement, and the diameter of and cover to the side-face reinforcing bars. A procedure is presented for estimating diagonal crack widths in the webs of large beams due to service level shear stresses, and a gen-eral design procedure is presented for the amount of side-face rein-forcement needed to control both flexural and diagonal cracking in the webs of large concrete beams. Over 11,000 crack widths were measured with a microscope on the 21 specimens, and an analysis of the crack data reveals the relation-ship between crack width and average strain, and the ratio of maxi-mum to average crack widths. Deformed reinforcing bars, welded wire fabric, and hooked steel fiber were included in the study. 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. Twenty-one large concrete beam elements with 1200 mm (47 in.) 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 current ACI Building Code and 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. Keywords: beams (supports) cracking (fracturing) flexural strength girders reinforced concrete shear properties ![]() Title: Side-Face Reinforcement for Flexural and Diagonal Cracking in Large Concrete BeamsĪuthor(s): Perry Adebar and Joost van Leeuwen ![]()
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