e-mosty March 2019 Long Span and Multiple Span Bridges - Page 27

Figures 7 and 8: Central Pylon foundations on piles Each of the two pile caps is supported by 18 piles to support two of the four inclined pylon columns. Pile lengths vary between 82.5 and 86 meters for the North Pylon, and between 50.5 meters and 54.7 meters for the Central Pylon. Voided linkages connect the twin pile caps, resulting in a total of 36 piles under the Central Pylon. As with the North Pylon, the Central Pylon pile cap has a bottom elevation of +4.5 MSL The on-shore South Pylon pile foundations and the abutment pile foundations also use 2.5 meter- diameter drilled shaft foundations. Connections between the piles and pile caps are critical in developing sufficient resistance to seismic and other design demands. However, steel casings are not required for construction or to resist design demands. Anticipated large soil movements during the MPE event resulted in concerns related to permanent displacements at the South Pylon foundation. The connection design is based on a combination of pile casing embedment into the pile caps, welded studs on the pile casing exteriors, and reinforcing steel. As a result, the South Pylon pile lengths are 60 meters long. Abutment pile lengths vary between 35 and 45 meters to resist design demands. Pylon pile caps depths vary between 6.0 and 9.0 meters. Post-tensioning is used in addition to reinforcing steel to resist pile cap design demands. PYLON PILE CAPS The North and South Pylon both use an 18-pile arrangement to support pile caps of similar dimensions. PYLONS The North and South Pylons have very similar arrangements of two reinforced concrete columns with a slight transverse inclination and two transverse cross beams connecting the columns. An arrangement of 9 piles and a solid pile cap sections are located under each of the two pylon columns, and a voided section of the pile cap connects the two solid pile cap sections. One cross beam is located directly under the bridge deck and the other near the pylon top elevation. The North Pylon pile cap soffit is located above the tidal zone with a bottom elevation of +4.5 MSL, while the on-shore South Pylon pile cap has a bottom elevation of +21.0 MS. The South Pylon column heights above the pile cap are 127.7 meters, while the North Column heights are 182.4 meters. In contrast, the Central Pylon pile cap consists of two linked pile caps, each cap having similar dimensions to the North Pylon and South Pylon pile caps. The column base dimensions are 5.8 meters x 5.5 meters for the South Pylon, and 7.5 meters x 6.0 meters for the North Pylon, while the top dimensions are 5.1 meters x 5.5 meters for the South Pylon, and 5.4 meters x 6.0 meters for the North Pylon. 1/2019