ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/768999
STATE NEVADA by Jessen Mortensen, Nevada Department of Transportation As the Nevada Department of Transportation (NDOT) approaches its 100-year anniversary, there is a continuing effort to explore more economical and innovative methods of maintaining and expanding the state’s infrastructure while keeping the traveling public safe and connected. Nevada is fortunate to have the lowest percentage of deficient bridges in the nation, as ranked by the American Road and Transportation Builders Association. However, like other states, many of Nevada’s bridges were constructed as part of the interstate system and are quickly approaching the end of their original service lives. While the state has managed to reduce the number of deficient bridges in recent years, it will become more difficult to maintain this trend as approximately 38% of the stateowned bridges currently exceed 50 years of age. Concrete Bridges in Nevada Concrete bridges have always played a major role in Nevada’s infrastructure and while it continues to utilize precast concrete and steel girders, cast-in-place (CIP), post-tensioned concrete box-girders are the most commonly constructed bridge type throughout the state, and have been since their first use in the early 1970s. Widespread use of CIP post-tensioned concrete box-girder bridges may seem foreign in other parts of the country where precast concrete beams are a more economical option. However, a problem somewhat unique to Nevada is the lack of girder fabricators in the state. Historically, all steel and precast concrete beams have been supplied by out-of-state contractors in Utah, Arizona, or California. Shipping often contributes to the additional cost associated with these superstructure types. Cost analysis of many of our bridges has shown CIP concrete box girders to be the most economical, followed by precast concrete and steel. In the past, precast concrete girders had limited use throughout the state. Records indicate the occasional construction of precast concrete box-beam and girder bridges dating back to the 1930s, with the highest concentration in the 1960s. Only in the last 10 years has there been a resurgence in the use of precast concrete structures, primarily in designbuild jobs. Several factors have contributed to this increase. The larger design-build projects have included improvements to major arterials in urban areas where falsework is not feasible. In these locations, steel girders were the previously preferred alternative because of the price associated with precast concrete girders. However, with standardized shapes leading to quicker designs, increased speed of construction, and more competition amongst suppliers, precast concrete girder prices have become more competitive, and in some instances, more economical than steel girders in Nevada. Segmental construction has been utilized only once in Nevada while building the Las Vegas Spaghetti Bowl, a project that included several large flyover structures. Very few other projects in the state have had the size or number of structures to prove economical for this type of construction. Although there has been more diversity in the recent construction of bridges in the state, CIP post-tensioned concrete box girders continue to be widely used because of the many benefits they offer. The bridges have proven to be lowmaintenance, durable structures that exhibit excellent seismic performance. They are an economical option that local contractors are familiar with and know how to build, and the majority of the work is performed by local laborers, supporting the state’s economy. Current Trends There is currently a substantial increase in the pace of construction of bridges in the state, primarily attributed to three large projects underway in the Las Vegas valley. Over the next few years, Project NEON and the two phases of the Boulder City Bypass will add nearly 50 bridges to the state’s structural inventory of approximately 2000 bridges. More than 40 of these structures are precast or CIP concrete. While this may not seem significant to many