September 1995 Table of Contents

Features Forming Bridge Pier Shafts

Obround, elongated hexagonal, and elongated octagonal piers have long been used at river crossings for hydraulic purposes. Now such shapes are increasingly being chosen over circular or rectangular columns simply for the aesthetic effect. To form these pier shafts, contractors must choose from a wide variety of systems after carefully evaluating such criteria as bridge design, jobsite conditions, existing supply and expected reuse of formwork, and availability of lifting equipment. Among the most common choices are job-built wood systems, manufactured steel systems, and combinations of the two. Read more

Features Investigating Effects of Concrete Handling on Air Content

A 1994 study examined the effects of concrete handling methods on normal air-entrained concrete. Concrete for a large parking lot and driveway project was placed by pump, crane and bucket, truck-mounted conveyer, and directly from the chutes of ready mix trucks. The primary goal of the test program was to determine how air content, air-void system parameters, and freeze-thaw durability of air-entrained concrete are influenced by placement and consolidation methods. Read more

Features Concrete Canoes Paddle It Out on the Potomac Canoe Competition

Between June 29 and July 1, 1995, 22 teams of civil engineering students from universities across the country met on a rain-swollen Potomac River in Washington D.C., to put their engineering (and paddling) skills to the ultimate test: racing canoes they designed and built from concrete in the 1995 American Society of Civil Engineers National Concrete Canoe Competition. Read more

Features Reducing Transverse Cracking in New Concrete Bridge Decks

Most concrete bridge decks develop transverse cracks soon after construction. The authors recently completed a study for the National Cooperative Highway Research Program (NCHRP) that examined the causes of transverse cracking in new concrete bridge decks. They found that a combination of shrinkage and thermal stresses causes most transverse deck cracking, not traffic loads and vibrations before or during concrete hardening. Read more

Features Chesapeake & Delaware Canal Bridge

A sterling example of precast concrete segmental bridge construction, the Chesapeake & Delaware (C & D) Canal Bridge proves that this construction technique can produce economical bridges even in an area of the country in which steel bridges have been predominant. The economy resulted from innovative design and construction techniques, which allowed the 4,650-foot-long, cable-stayed bridge to be built very rapidly. All the precast structural bridge elements were cast and erected within three years of the notice to proceed. Read more

Problem Clinic Forming Curved Walls

We were asked to build a curved concrete retaining wall for a homeowner. The curve of the wall has a radius of 4 feet. Can we produce this curve using job-built forms? Read more

Close X