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minimizing distortion | pnu’s apm unsymmetrical beams
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3-D solid element modeling of the unsymmetrical precast pre-tensioned beam at transfer 3-D solid elements are adopted to model the precast unsymmetrical pre-tensioned beam. The output normal stress results at transfer at mid-span range from 3.06 to 3.10 MPa for top fiber and are equal to almost 24.55 MPa all over the bottom beam fiber. The lateral displacement is about 1.1 mm, insignificant considering a 34.8 m beam span. 1-D frame element modeling of the unsymmetrical precast pre-tensioned beam at transfer One-dimensional frame elements used to model the precast 34.8 m span unsymmetrical pre-tensioned beam yielded maximum longitudinal, transversal and vertical displacements at mid-span, at transfer of 6.3, 1.2 and 44.5 mm, respectively. Optimum selection of transverse pre-stressing eccentricities resulted in a negligible 1.2 mm maximum transverse displacement of the beam at mid-span and only significant camber and axial displacement.
The pre-casting concrete technique used had a positive impact on ease of construction resulting in major time cutting. It ensured a higher concrete quality than the cast in-situ method of construction which relies on traditional scaffolds and would have taken much longer to complete. The tendency of the unsymmetrical precast beam to distort during transfer was made negligible by use of proper arrangement of pre-stressing strands. Only camber deformation is expected and recorded after pre-stressing transfer. The two finite element models developed guaranteed the validity of the non-distorted behavior of the unsymmetrical beam at transfer. The bridge’s box section with its two precast unsymmetrical sections produced elegant and elongated guideways adding a visual element to the already well-designed campus.
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1 Maximum displacements at mid span for the unsymmetrical precast beam at transfer using solid element model 2 Normal stress distribution at mid-span for the unsymmetrical precast beam at transfer using solid element model 3 Displacement results for the one dimensional frame element model
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