ahmd8201

Can you also advise what a typical pile raft connection would be like?

Salam, please find attached drawings of the proposed structure. The raft slab is proposed to have movement joints every 10m. Is the movement joint (dowel anchored on one end of the slab and on a sleeve/debonded on other side) therefore only transmit shear? Also the raft (~35m wide) will be by supported on piles at approx 12m intervals to 35m raft. As the raft is 2m deep and the piles are 1.2m dia. I have assumed the piles will modelled as simply supports. Is this a reasonable assumption? See attached drawings

Assalamualaikum dear forum members, I am currently designing a 35m span prestressed precast I beam bridge. The deck is formed from 300 rc insitu slab and the beams are 1.8m deep precast I beams. These span simply supported onto bearings shelf/abutment. Due to a high watertable, a secant pile wall option is used to form the abutments (with a hard/soft pile configuration). There is also a raft to form the underpass and act as a prop to the secant walls. The secant walls are formed from 1200mm diam. piles and the raft is currently 2m deep. Apparently another engineer (quite senior) advised to have the raft dowelled into the piles, i.e. maybe 3 dowels per pile in the secant and then continued into the raft at an appropriate anchorage. The 35m span deck is supporting a curved road on top and the underpass is supporting 6 lanes of traffic. The whole bridge is designed to AASHTO I have a few issues which are troubling me which I would like to ask for opinions on; 1) The prestressed I beams at ULS are sagging as they are simply supported. At SLS the ends are hogging; is this due to the prestressing force being too much? The secant pile wall is being designed by geotech. I assume that under any limit states as the deck is supported on bearings, the forces transferred to the secant will only ever be axial forces and shears ie. fx, fy, fz? 2) The raft/ secant pile wall connection does not sound particularly convincing to me. The actual secant pile wall is very long and is about 480m. The raft slab therefore has movement joints every 10m or so. I thought that the raft plus secant could either be considered as an inverted portal frame or as a wall with a lateral prop. The senior engineer want to assume this is acting as an inverted portal frame but how can we have fully fixed moment connection with 3 dowel bars! Also if the abutment was actual wall, the raft could be detailed with rebar to be cast as a full moment connection, but with the secant the rebar will be very congested and I do not know an easier way to achieve this full moment connection of the raft with the secant. Please advise.

Hi Uzair, Thanks for your prompt response. I have tried to buy the CRSI guide but they only post out hard copies and that takes a minimum of 2 weeks. I kind of need to do it by this evening (12 hours). Do you have a copy of that guide? are there any specific equations for voided slab. With a voided slab the compression block is smaller and i dont know how to derive the equation for fc. basically the slab is a 20m span integral frame and 1.5m deck with 0.8m void. i have looked at the PG software but this is for precast and it discusses using tendons etc. i have tried to look at aashto and ACI 318 but im struggling...

This bridge is insitu. All the references are for precast prestressed or post tensioned Using strands and not rebar

Hi how do I design a 20m integral bridge deck? 1.5m thick with .8m voids.designed to assshtO.i can't find any design guidance for this voided rc.