Throughout the past decade, committee members and key industry players attending meetings held by leading organizations [Concrete Reinforcing Steel Institute (CRSI), American Concrete Institute (ACI) and others] frequently engaged in unofficial discussions centered around what changes needed to be made to advance the reinforced concrete construction industry and to improve constructability and job site efficiencies.
非官方讨论转化为几个月的委员会会议和研究，涉及来自全国各地的专家，包括Lou Colarusso，Michael Ugalde和来自Nvent Lenton（以前的Erico Lenton）的克雷格的家伙。供应商，建设者和研究机构之间的伙伴关系孜孜不倦地勾结，以嫁给整体行业的需求与可用的技术。在全国各地行业志愿者的努力工作之后，对ACI 318-19进行了严重变化，该从业者将制造和设计过程更加高效。在本文中，将在改善设计钢筋混凝土结构的情况下，研究对ACI 318守则的一些重要变更。
High-Strength Rebar Comes of Age
One of the most significant additions to ACI 318-19 was the broadening of the approved uses for high-strength rebar (HSRB), commonly understood to be reinforcing steel with a specified yield strength of 80,000 psi or greater (e.g., Grade 80 and Grade 100). When working with prior versions of ACI 318, designers and builders had the option of using HSRB, but the uses were more restricted as the material standards did not provide the right framework around which such reinforcement could be specified—resulting in an inefficient process for designing and building with HSRB.
As engineers find new ways to use HSRB, design, supply and construction become more efficient. HSRB means less rebar to cut, bend, couple, anchor, tie and place. Labor cost is reduced and construction accelerated, allowing owners and end users to more quickly generate revenue. Most importantly, HSRB can improve the structural integrity of the building and increase floor space as columns and other concrete elements can be reduced in size.
机械剪接消除了大型HSRB LAP拼接开发长度（ACI 318-19，第25.4.2节）
The traditional and most common method of transferring loads between reinforcing bars has always been the lap splice. One of the difficulties with lap splicing HSRB is that calculated development lengths per ACI 318-19 Section 18.104.22.168 increase rapidly with the new ѱg rebar grade modification factor. As the strength of the rebar enters the Grade 80 and Grade 100 realm (Section 22.214.171.124), the modification factor jumps to 1.15 and 1.3, respectively.
Structural engineers, architects and specifiers continue to discover that mechanical splicing rebar has many advantages over the conventional method. Not only do mechanical splices solve the development length challenge, but mechanically splicing also improves the structural integrity of the building by making the strength of the mechanically spliced rebar equivalent to one continuous bar.
Designing for anchorage with larger-diameter HSRB prior to the release of ACI 318-19 was challenging due to the difficulty in bending HSRB and the inconveniently long hook lengths required for development. Replacing a hook with a mechanical head presented its own obstacles when designing to prior versions of ACI 318, as Section 126.96.36.199 prohibited the use of the simplified development length formula in 188.8.131.52 with any rebar strength above Grade 60. Granted, designing for mechanically headed HSRB was a possibility by using Chapter 17 of ACI 318-14 (formerly Appendix D), but the process was viewed as complex and inefficient for design engineers.
幸运的是，在2014年和2019年的尊敬机构的研究中进行了研究[堪萨斯大学;普渡大学;加州大学伯克利;加利福尼亚大学洛杉矶;和德克萨斯大学]并由CRSI，Pankow基金会和ACI等组织赞助，为在ACI 318-19中制定了机械领导的HSRB，提供了基本的测试。该研究证实，头部的杆和钩子受到类似参数的影响，如盖子，限制，产量和混凝土抗压强度。然而，在开发钢筋方面更有效。使用ACI 318-19的头部钢筋设计的工程师现在可以通过使用第184.108.40.206节中的修改开发长度公式来轻松计算头部HSRB的开发长度。
Headed Rebar Spacing Requirements Relaxed (ACI 318-19, Section 25.4.4)
Dr. David Darwin at the University of Kansas, in conjunction with colleagues across the country, spearheaded research and code provisions that enabled a significant change to ACI 318-19 regarding the spacing requirement for headed rebar of all grades (Section 220.127.116.11). ACI 318-14 (and prior) restricted clear spacing between headed bars to 4 bar diameters (db) and greater. ACI 318-19 is updated and now allows center-to-center spacing between headed rebar of 3 db. In terms of clear spacing, the change is from 4 db to 2 db, representing a 50 percent reduction. In terms of center-to-center spacing, the change is 5 db to 3 db, representing a 40 percent reduction.
The changes to ACI 318-19 discussed in this article were realized through an industrywide collaboration and were the culmination of more than a decade of discussions and committee meetings. Designers now have more options when working with HSRB, headed HSRB and headed rebar in general—options that streamline design, supply and placement; reduce construction cycle times; and, provide overall cost savings. Though seemingly small on the surface, the code changes are an enormous step forward, opening a gate to new paths for the industry to blaze. —Lou Colarusso is Sales Director and Samuel Barker an Engineering Technologist with Solon, Ohio-based nVent LENTON, a specialist in concrete reinforcing steel connections.
Typical installations using mechanical versus lap splicing. The additional space required for lap splicing along with overall installation complexity exceed what is needed for mechanical splicing.