huangyhg

creep in bridge rope
i'm looking for information that provides the estimated long-term creep in either bridge rope - 6x7 wsc or bridge strand (class a coating). i have information that gives me the e, and the max. tensile strength of various diameters, but nothing on long term creep.
as in high-strength prestressing strand, there is a long-term loss of prestress due to relaxation of the strand. looking for ways to estimate this for the rope or strand over time in similar fashion.
i believe your problem is usually overcome by prestretching the rope. this will eliminate the creep. there is good information on this in an old bethlehem steel publication,"bethlehem wire rope for bridges, towers, aerial tramways and structures", if you can find a copy.
redhead - thanks for the post. yes, i have that document. and it does talk about prestretching the rope. that takes out much of the slack in the rope and raises the effective modulus of elasticity. however, what i'm looking for is any information regarding creep in the rope after restretching and due to permanent tensile load on the rope. similar to relaxation in high strength strands for precast.
i have some information from a wire rope manufacturer (haggie) in south africa. they report a relaxation loss at 10 000 hour of 10% at initial stress of 80 % uts and a relaxation loss of 3 % at initial stress of 50 % uts.
if you send me your fax number i can fax the graphs and data to you. my email :
safety factors in cables without taking into account the incurvation at pulleys or seats may range 5 to 6, (source; apuntes de maquinaria auxilar de obras, jose juan aracil segura, etsiccp, madrid, lesson 35, p.22) what must mean low average tensile stress elsewhere outside the seats, and then low relaxation.
taking incurvation into account, 1.66 to 2 safety factors seem be the equivalent ones, by the same source. but you then need very accurately evaluate the stresses at details., one must infer from the difference of safety factors with or without.
ribeneke: i tried your email but it didn't allow me to send it (it said "no provider")
the relaxation in stress may not be significant in general applications of bridge rope. unlike prestressing strand which is stressed to to 80 percent of ultimate, working stresses in bridge strand are normally well below 50 percent of ultimate. also, i believe the percent of relaxation with time is related to the initial ratio of working stress to ultimate, hence it is more significant in prestressing strand.
i just found out that the particular cable i'm checking is bridge strand (not rope). the strand is 1" diameter, class a finish, and is under 60,000 lbs. constant dead load stress. ultimate capacity of the strand is 122,000 lbs.
any other info on relaxation would be greatly appreciated.

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