huangyhg

expansion joint required?
is an expansion joint required for long piers.
a pier constructed of ppc piles, cast in place pier caps, a system of precast planks supporting a road and townhouses, will be 80' wide and 430' long. the location will be maryland, over water. do you feel an expansion joint is required?
i appreciate your comments
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first look to the code if any applies. if not, introducing expansion joints is usually thought to be good thing in general, maybe because making the designs more controllable use to forfeit the thermal expansion phenomena that when not present you will have to deal expressly with. so if the free standing height of the piles is big and so can be understood flexible, or you provide (and accept as good) slipping superstructure, it may be worth thinking a bit on doing without joints and making some estimates of the structural effects and their significance to the design.
if it is straight -friction non forbidding, which likely not at these length- you may really think on the sliding superestructure, maybe the challenge then being the contraptions used as vertical and lateral restraints, for even without taking earthquake loading the mere waving action will introduce dynamical effects.
then if you want to make the thing without joints and with fixity at least to the main superstructure you may think in using h piling with on weak axis bending for the pier expansion, to enhance its flexibility without damaging the structure, whilst delivering bigger stiffness on the transversal direction. unequal faces' tube piles may also be arranged to have akin properties.
hi mjohan,
i can't quite visualize the project. expansion joints are not required if the design of the system accounts for secondary effects from shrinkage, creep and temperature.
however, this looks like a very large structure and i would modularize as much as possible.
regards
vod
i think expansion joint can be omitted in the lateral direction where it is only 80ft wide.
longitudinally i would worry about the house superstructure. there is no need to worry about the road as it made of precast planks which are difficult to link together to contract and expand as one body. to support the concrete planks longitinal beams have to be cast between pile caps. the whole superstructure is free to expand and contract and horizontal restriants are only provided by the sway of the piles so one can risk not having expansion joint in the 430 flt length. if cracking does occur it will be on the beams linking the pile caps.
the house superstructure will be fairly rigid and liable to crack if the thermal movement is not controlled.
for my money i would have some beams arranged as simply supported between the pile caps. say using 86ft span and in 5 equal bays and have the central span simply supported on both sides and the two twin bays on both ends monolithic.
thank you all for your responses.

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