Proponents of two historic code changes—one to allow taller mass-timber buildings and the other to allow use of higher-strength reinforcing steel—are optimistic after recent ballots at two different meetings moved the proposals closer to acceptance by code officials and standards developers.
9月17日在拉斯维加斯，负责监督ACI 318的ACI 318的美国混凝土研究所委员会对在几种地震应用中使用高强度钢筋的使用初步批准。
"For now, the hardest part of the journey has been cleared," says Andres Lepage, an engineering professor and director of laboratories in the department of civil, environmental and architectural engineering at the University of Kansas.
Structural engineers who support the changes are particularly interested in the proposed increase in allowable steel yield stress for seismic design of shear-wall and moment-frame seismic-force-resisting systems. The changes would be a game changer for seismic design and reinforcement detailing of structural concrete buildings, they say.
Reduced Rebar Congestion
The approval of high-strength steel for seismic zones would reduce rebar congestion and could permit the construction of stronger walls, beams and columns without increasing their size.
根据该提案，2019年ACI 318代码将首次允许80 ksi加强地震应用和非主体应用。该代码还将允许使用100 ksi进行非主体应用。对于地震应用，只允许剪切壁100 ksi加固。
If the proposal gets passed, the maximum grade of reinforcement allowed would continue to be 100 ksi but it would be able to be used as transverse reinforcement, including confinement, and longitudinal reinforcement for nonseismic applications, says Lepage.
100级将继续被允许的reinforcement, however, the design for shear and torsional forces would continue to be limited to 60-ksi reinforcement, except in seismic shear walls where shear design can take advantage of a yield strength equal to 100 ksi, he adds.
1963年，该法规将产量强度限制在75 KSI。在1971年，允许的最高成绩为80 KSI钢筋，应用有限。在2005年，100 KSI是允许的最高成绩，但仅用于限制非视觉应用中的加固。在2008年，还允许100 KSI进行地震应用，但仅用于限制强化。
Lepage was the co-lead investigator oftests on high-strength rebar, conducted at the university. ACI is using the data from the research to support the increase in the allowable limit on rebar grade in seismic zones.
Still ahead is a review by ACI's technical advisory committee, followed by a public discussion period.
Lepage说：“时间至关重要。”“这些活动需要在非常紧张的时间表中进行”，以便将提案包括在2019年版的ACI 318中，该提案将通过参考将其引用到2021年国际建筑法规（IBC）中，该法规（IBC）由国际法规委员会（ICC）发表（ICC））。
Mass Timber
The other historic change would be the adoption of provisions, also in the 2021 IBC, to allow mass-timber framing in residential and office buildings as tall as 270 ft. On Oct. 24, at the ICC's final action hearings in Richmond, code officials voted 220 to 103 to increase the height limits for mass timber buildings, according to Mike Pfeiffer, ICC's senior vice president of technical services.
The ICC's online voting, which runs for two weeks beginning mid-November, will determine whether the primary proposal, called G108--along with the other 13 related proposals on mass timber also approved on Oct. 24--will actually be included in the 2021 IBC. Preliminary results of the online tally will likely be announced in mid-December.
在国际刑事法院验证委员会称为技术活动委员会之后，官方业绩直到2月中旬才宣布，审查了建议和对在线投票的外部审计，并向ICC标准委员会报告。董事会有最终决定权。
ICC’s ad hoc committee on tall wood buildings (TWB) "studied mass timber construction for two years prior to introducing these code change proposals, including conducting numerous fire performance tests," said the American Wood Council (AWC), in a statement released after the Oct. 24 vote. "The result of that rigorous process is that each of the new proposed construction types has had its fire and life safety performance confirmed, resulting in a robust building performance."
TWB正在引入三种用于建筑物IV型分类的新型构造，每种建筑物都基于占用分类和质量磁带系统的设计，每个建筑物都有不同的高度可能性。
Structural elements of Type IV construction are primarily composed of solid, built-up, panelized or engineered wood products, such as cross-laminated timber, that meet minimum cross-section dimensions. None of the new types of construction proposed permit use of light-frame construction.
18个故事
For top-of-the-line IV A residential and office-building construction--which would have a three-hour fire rating and the timber totally encapsulated in gypsum board rather than exposed--the code would allow a height up to 18 stories, which is equivalent to 270 ft, according to Stephen DiGiovanni, TWB's committee chairman and the fire protection engineer for the Clark County, Nev., Dept. of Building and Fire Protection.
For IV B residential and office construction, which would have a two-hour fire rating and the timber mostly but not completely encapsulated, the limit would be 12 stories or 180 ft.
For IV C construction, which would have a two-hour fire rating and totally exposed mass timber, the limit would be 85 ft or nine stories.
当前的津贴for heavy timber buildings is 85 ft. That translates to five stories for residential occupancies and eight for office. For IV C, TWB is not proposing an increase in height but is proposing an increase in the number of stories allowed--to nine for both occupancies.
For IV C, "we were very conservative," says DiGiovanni.
