The new Sixth Street Viaduct, when completed next year, will be hard to miss. Ten pairs of continuous arches will create a sinuous profile as the 3,060-ft-long, 100-ft-wide viaduct soars over the 101 Freeway, several railroads, the LA River and the downtown Los Angeles arts district.
The structure replaces a 3,500-ft-long, 46-ft-wide viaduct that served as a backdrop for dozens of movies, TV shows, music videos and video games. The $588-million project is the largest infrastructure effort underway in the city of Los Angeles.
The unique design and construction challenges have pushed back the schedule by 18 months, but work is on track for a mid-2022 completion, says Gary Lee Moore, Los Angeles city engineer. “The viaduct is about 65% complete,” he says. “By the end of January, we’ll have 2,000 linear feet of superstructure up to the deck level. Construction for the first of our six out of 20 arches will be complete by the end of February.”
Skanska美国民事和Stacy and Witbeck（SSW）的建筑经理/总承包商（CM/GC）团队正准备平均每个拱门以最高4个垂直ft的速度降低300立方英尺Skanska项目主管Jerry Iniguez说，大量数量。混凝土倒入完成后，“我们将过渡到电缆 - 安装衣架支架，并从拱形到混凝土甲板，”他说。
Crews have completed concrete pours of up to 200 cu yd each for the Y-shaped columns, which are 80 ft wide and 30 ft tall. SSW is hitting the peak of construction activity with up to 32 crews and 200 craftworkers, says Iniguez.
迈克尔说，这些柱子和拱门将创建一个“光丝”的图像，该图像在博伊尔高地和市中心的东洛杉矶街区之间延伸，该图像是目的地以及多模式的链接以及改变城市景观的动力。Maltzan是由HNTB领导的设计团队工作的建筑师，该团队赢得了设计比赛，以取代2012年的旧高架桥。
原来的高架桥不得不被拆除,因为of alkali silica reaction, a form of concrete “cancer” that began plaguing the four-lane vehicular-traffic structure just two decades after its completion in 1932. It was also functionally obsolete in terms of national bridge design standards, and seismically vulnerable.
Maltzan说：“有必要从技术和安全的角度将其降低，但是社区在情感和文化上与桥梁有很多投资的社区有很多推动力。”“ [我们需要]创建一座新的桥梁，具有与原始桥一样强大的桥梁，这是一个捕捉城市的野心和精神。”
Built To Last
如此标志性的是原始的高架桥，在2016年2月被拆除之前，洛杉矶市以一系列的公民活动标记了其未决的灭亡，包括现场音乐和“油脂”放映。Angelenos带回家1,300份混凝土残余物作为纪念品。
HNTB的团队是shortliste六9d for the design competition and one of three given a stipend for further design. The team has since implemented minor changes to accommodate construction staging, such as adding construction joints at key locations, says Michael H. Jones, senior civil engineer with HNTB. Along with the aesthetics of the design, the team added measures aimed at minimizing maintenance costs and enhancing the 75-year service life, he adds.
琼斯指出：“上层建筑在横向和纵向上进行了张紧，以减少开裂。”“混凝土混合物具有聚合物纤维和混合物以减少收缩。”为了增加地震抗性，团队消除了高架桥中的所有扩展关节。结构钢被镀锌，拱形吊架支架将具有锌 - 铝合金涂层，预计将具有传统锌涂层的设计寿命三倍。
The unique design has brought with it unique construction challenges—requiring 27 million lb of falsework not only supporting the new deck, but falsework on the deck supporting the Y-shaped columns that will support the arches, and the use of customized lock-up devices to support each column during construction, eventually serving as shear keys in case of a seismic event.
The project scope includes demolishing 13 buildings, relocating five systems of overhead power lines and improving 10 local street intersections. The city will also create a 12-acre park beneath the viaduct.
The viaduct is supported on 10-ft-dia cast-in-drilled-hole piles up to 165 ft deep. The 10 arch spans will each be about 300 ft long, with 388 hanger cables and post-tensioning in edge girders and floor beams.
船员们用巨大的边缘大梁倒了横向横梁，然后将其张紧张开。虚假工作将通过电缆安装保留。钢板和螺栓在施工过程中保持圆柱稳定。一旦形成并放置了甲板，横向和边缘的大梁，船员还将afor架上的夫人竖立在拱门的顶部。
Erection engineer COWI designed unique lock-up devices that hold the Y bents in place during construction. The devices will eventually serve as shear keys that will accommodate anticipated changes in the alignment of the continuous cast-in-place structure due to creep and shrinkage over 10 years, notes Julie Allen, principal engineer with the city of LA.
The viaduct is designed to withstand a 1,000-year seismic event, adds Allen. Earthquake Protection Systems, Vallejo, Calif., developed and patented friction-pendulum bearings as well as second-generation triple-pendulum bearings that will rapidly stiffen after an earthquake, allowing for the activation of the secondary system.
艾伦说：“根据计算的运动，轴承朝任何方向偏移了几英寸。”“桥可以允许在任何方向上移动30英寸。”
SSW worked with the city and design team to address rebar congestion, says Iniguez. “As you come out of these wide Y arms, the bridge is post-tensioned, so we had to create enough room for the stressing ducts to fit.” That required more modeling and design tweaks. Also, the concrete mix was adjusted to be more self-consolidating.
The city and SSW agreed to a new completion date in mid-2022. “Right now, the contractor is on schedule,” says Moore. The contract includes $40,000 a day in potential liquidated damages or an early completion incentive of $200,000 a day up to $20 million, he says.
Moore补充说，SSW还将实现联邦目标，即处于弱势企业企业的参与为23.95％。“这是6000万美元的机会。”
When complete, the new Sixth Street Viaduct will allow motorists, cyclists and pedestrians to traverse between East LA and downtown, and potentially create the impetus for public spaces such as athletic facilities and plazas. “It’s not simply a bridge crossing the river; arguably that’s one of the smallest parts of the exercise,” says Maltzan. “It was more important to not celebrate this as a line dividing the city, but as a way to knit it together.”
