How to Calculate the Load for a Small Bridge

Hey Bruce, Using your original math, and a safety factor of 5, which I believe is standard for structural members, (more for seismic loads), gives me a total point load of 1346.66# , or 6.8 tons. Since the load is spread on two axles, 7 tons is a reasonable load, and forget it if the load sways.

Carl

Carl,

I used a safety factor of 1.5, not 5. Where does the 1346.66# come from? And 6.8 tons?

The question was what is the safe axle load on the bridge. I believe the answer is 9000 kg or 9 Tonnes but that is providing the load in centered on the beams. Some care should be exercised in ensuring that the wheels are centered over the beams. For lighter axle loads, it would not be quite so important.

I'm with ya on this ba/ael the support material is insufficient for the given conditions.

Fuzzey math? I just rounded off everything.

Thanks, I'll know better next time.

Bruce,

Thankyou for your time and knowledge in responding to my question, I appreciate your assistance greatly.

I take on board your concerns about centering a fully laden light-truck over the beams although as previously mentioned this would be an infrequent occurence.

I have spent most of today cutting and preparing the beams ready for their installation but the installation side of things is on hold for I guess the next 3-4 days as we a expecting a very active rain depression starting here overnight and by tomorrow my work area will be awash.

Regards John

I take on board your concerns about centering a fully laden light-truck over the beams although as previously mentioned this would be an infrequent occurrence.

All it's going to take is one time.

take on board= acknowledge

infrequent = not often

not often = you have time to check and double check that things are OK

negative = not positive

coastal: I think a minimum factor for live load is 1.70. Also, how can we be sure your rectangular tubes have a tensile yield strength of 350 MPa? Some rectangular tubes might have a tensile yield strength of Sty = 315 MPa. Could some even be only mild steel? Could you give us the material specification for your rectangular tubes? Using FS = 1.70 and Sty = 315 MPa, I get a maximum allowable mass per axle of 7850 kg. I will let you work out the percentage of truck mass distributed to each axle, keeping in mind that some two-axle trucks perhaps have up to 80 % of their mass on the rear axle.

aeon, Thankyou for your positive input on this matter, as the rectangular tube that I have is of unknown origin, I have checked it for any markings that may identify it. Unfortunately I can offer no further information about the tube but even if I use your more reserved load figures I am happy with the safety factor that I have, bearing in mind the use this "bridge" will get.

I also acknowledge your concerns about load sharing of front and rear axles on commercial vehicles