how to model cable suspended bridge in SAP2000

[pphawk]

Hi, I am modelling a 220m suspended bridge. the cable geometry was defined by including a 22m vertical sag; it gives a 27438 kgf of horizontal tension. then I want to draw the tensor so i decided to modify the cable geometry by dividing it into 72 parts, but each section has changed the horizontal compount of the cable and I dont know how to keep the horizontal tension in the 72 sections as the theory says. (H is constant in the cable).
my second question is that the target force could be set at the both ends (I or J) but the 72 parts have differents forces because of the angle.
please help me, thsnks

 

[IRstuff]

Is this for school?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[pphawk]

no, it isn't for school. I designed it by myself but I want to check the design using this software

 

[JStephen]

I'm not sure I understand the question entirely. But it sounds more like a How-Do-I-Use-This-Software problem than anything else, and in that case, you might check with other users of the software.

One idea is to make sure that you are defining the gravity loads as vertical, not normal to the cable. If the loads were applied normal to the bowed cable, the horizontal component of tension would vary along the length.

It strikes me also that potentially the bigger problem here would be dealing with wind, seismic, and vibration issues, rather than just a static analysis, in which case a good bit more insight from someone used to designing suspension structures might be in order.

 

[paddingtongreen]

Did you make the shape of the cable as a catenary or a parabola. The bridge weighs much more than the cable so it should be more parabola than catenery. I presume you made the 72 parts pin connected. If you model the bridge as equal dead loads at each junction, you should find the natural curve, then add the bridge as members to replace the imposed dead loads.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[edward1]

I designed a 200 feet long suspended bridge 3 years back on STAADPro and used a parabola to get points along the cable. I used CABLE for the members and put initial tension on cable of 33 kips. The final tension on the CABLE from abutment to support tower was 93 kips due to dead load and live load. After the cable passed over support tower the tension was 62 kips on first cable member and then it was constant at about 58 kips until the 62 kips at the next support tower. SAP 2000 should have a member to use for the cable. Good luck!