Balanced Cantilever Method Research Articles

STRUCTURAL BEHAVIOR MONITORING AND ADJUSTING SYSTEM USED IN SUPERSTRUCTURE CONSTRUCTION OF PRESTRESSED CONCRETE CABLE-STAYED BRIDGE, YOBUKO-OHASHI BRIDGE

The Yobuko-Ohashi Bridge, located in Yobuko Town, Saga Prefecture, is a 3-span continuous prestressed concrete cable-stayed road bridge with a center span of 250m, which connects an isolated island, Kabejima Island, to Kyushu. It is the longest-span concrete bridge in Japan. In construction of the superstructure, the girders were constructed by cast-in-place balanced cantilever method using travelers. And the deflection of girders, tensile forces in stay cables and stresses in girders, which are essential for prestressed concrete cable-stayed bridges, were monitored and adjusted rationally and promptly with the help of a new system using microcomputer. This report outlines the system used in this bridge construction project.

Effects of time-dependent concrete properties on prestress losses

Prestress losses were calculated for a segmental concrete box-girder bridge. Results were based on the time-dependent investigation of the Kishwaukee River Bridge constructed by the balanced cantilever method. Instruments were installed in the bridge during construction to measure the time-dependent deformations. Short- and long-term properties of concrete used in the instrumented segments were measured. With the actual construction schedule and the measured concrete properties, time-dependent nonlinear analyses were performed. Prestress losses were calculated for each construction step. Time-dependent variations of prestress losses during and after construction are presented. Comparisons between design concrete properties and measured values and between analytical prestress losses and design values were made. Key words: mechanical properties, creep properties, shrinkage, prestressing, losses, prestressed concrete bridges, measurement, analysis.

The Twelve Mile Creek bridges—Design and construction

The two bridges featured are precast segmental concrete box girders built by the balanced cantilever method. Crossing a hydro tailrace, this $11 million project forms a part of the new Highway 406 through St. Catharines, Ontario. Several unique features of the structures are highlighted. These features include transverse rib beams employed at each segment face to support the deck slab; flaring of the deck slabs to accommodate on and off ramps; and twisting horizontal alignment of the highway. Both bridges have a depth-to-span ratio of 1:27, which results in one of the most slender precast box girder bridges built by the balanced cantilever method. The construction phase of this project is reviewed with particular attention to the casting operation and to the erection of the segments employing a steel launching truss. Design- and construction-related problems encountered are presented and reveal that the more perplexing problems are generally those not related to the complexities of the segmental form of construction but rather to the more mundane aspects of posttensioned concrete bridge construction. Key words: precast segmental concrete box girder bridges, balanced cantilever methods, steel launching truss, short line casting bed.