Long-term lateral deflection of precast, prestressed concrete spandrel beams

Slender precast concrete spandrels that span long distances are being used to increase the cost effectiveness of precast concrete parking structures. They are efficient because they reduce the number of column lines required in a building floor plan as well as the number of elements to transport and erect. However, increasing spandrel slenderness reduces sectional stiffness, making the spandrels prone to larger deflections. Moreover, because of the eccentric loading transferred from the deck double-tee beams, both vertical and lateral deflections should be considered in design. This paper provides realistic estimates of long-term deflections for slender spandrels and examines the parameters that affect these deflections. A numerical study was conducted using high-fidelity, nonlinear finite element analyses of L-shaped and pocket spandrels for different span lengths (48 and 60 ft [15 and 18 m]) and web thicknesses (8, 9, and 10 in. [200, 230, and 250 mm]). The sensitivity of long-term deflections to parameters such as spandrel type, span length, beam width, concrete curing, creep, shrinkage, and load eccentricity and magnitude is presented. The results indicate that long-term lateral deflections are less than the corresponding long-term vertical deflections and in all cases long-term deflections were below a threshold of the lesser of length/500 and 1 in. (25 mm).