Of the nearly 1100 architectural precast concrete wall panels that Universal Concrete Products (UCP) fabricated for the facade of 255 E. 77th St. in New York, N.Y., 339 panels were delivered with factory-installed windows. It was the company’s largest order for preglazed window wall panels at the time.
Using precast concrete as both building enclosure and wind tunnel flow circuit for its Flight Dynamics Research Facility in Virginia saved NASA millions of dollars in construction costs while delivering a testing facility that will outlive the required 30-year life cycle. Tindall Corp. of Petersburg, Va., cast solid wall panels with the airflow-facing side down in forms. Eleven horizontal wall panels, all wider than they are tall with gently inward-angled sides, were delivered for each of the tower’s four sides. EDI Precast LLC of Upper Maryland, Md., used a 230-ton (209-tonne) crawler crane to lift and stack panels weighing up to 40 tons (36 tonnes).
This paper evaluates procedures from design specifications and the literature for predicting strand stress at the nominal flexural capacity of prestressed concrete beams with combined (bonded and unbonded) strands and with only unbonded strands. Flexure test data were compiled for 39 beams with combined strands and 296 beams with only unbonded strands. For beams with only unbonded strands, design specifications procedures based on a bond reduction coefficient, collapse mechanism, or empirical approaches had similar accuracies and predicted the unbonded strand stress well. While conservative, assuming the unbonded strand stress is equal to the effective prestress resulted in inaccurate predictions. For beams with combined strands, predictions were the most accurate when unbonded strand stresses were predicted using the American Association of State Highway and Transportation Officials’ AASHTO LRFD Bridge Design Specifications 10th edition expression meant for beams with only unbonded strands and when bonded strand stresses were predicted using the AASHTO LRFD specifications 10th edition expression meant for members with only bonded strands.
Multicell box-girder bridges are traditionally constructed using precast concrete segmental or cast-in-place methods. Although cast-in-place construction accommodates complex geometries, it can involve lengthy schedules, traffic disruptions, and substantial on-site labor. Fully precast concrete systems offer an attractive alternative by accelerating construction and improving quality control. This paper presents prestressing, erection, and assembly considerations for unsymmetrical precast concrete box-girder components assembled to form full-bridge-width multicell box girders. The approach enables construction from manageable precast concrete components while maintaining the structural efficiency and appearance of a closed box-girder system. Key construction challenges include prestressing unsymmetrical sections, lifting and placement stability, torsional behavior during erection, alignment of adjacent segments, temporary support requirements, and sequencing of bottom closure pours to achieve a continuous flat soffit. Practical methods for addressing these challenges are discussed based on their implementation in several bridges, including the King Abdullah Financial District access road network project in Riyadh, Saudi Arabia.
