Seismic Calc’s on pole

[Johnny 630]

Do I need to calculate for seismic for a 25’ light fixture that will be placed on a concrete bridge? Pole weights 170lbs & carries 55lbs lights. It will be embedded into concrete using 4 epoxy anchors and 16x16x.25” baseplate.

Pole is less than 25% of the weight of the bridge as it says in asce 7 ch 15. Do I just need to calculate for wind loads and dead loads(self weight & lights) & not seismic? In California.

 

[r13]

The light pole need not to be included in the seismic weight of the bridge for the earthquake effect analysis and design, but the light pole should be analyzed, and the connection designed for its own earthquake reactions. The bridge structure and the light pole have very different seismic response, which is the base for separate analysis and design. However, the wind load case may control the design, as the pole is so light weight.

 

[JLNJ]

You will probably have meet seismic code minimums for design of the anchor bolts, regardless of wind load.

The prescriptive bolts shown by the light pole manufacturer may not be sufficient.

 

[HTURKAK]

...Pole is less than 25% of the weight of the bridge as it says in asce 7 ch 15. Do I just need to calculate for wind loads and dead loads(self weight & lights) & not seismic? In California.

The wind load case may control the design. However the seismic load also should be checked.

The seismic design force shall be calculated using the formula (13.3-1) and the force shall be applied at the pole’s center of gravity. The applicable requirements are; General Design Requirements (Section 13.2), Force and Displacement Requirements (Section 13.3),Attachment Requirements(Section 13.4) and electrical component Requirements (Section 13.6).

Seismic Coefficients should be taken from TAble 13.6-1 and i will suggest ap=2.5 and Rp=3.0

 

[Agent666]

The light pole need not to be included in the seismic weight of the bridge for the earthquake effect analysis and design

I'm not sure I agree with this in general terms, you should be allowing for the mass of the entire bridge including any attachments. The mass used for the determination of seismic loading needs to reflect what is present during the event, and the distribution of mass should represent what is present during the event. Usually the mass of all ancillary/secondary attachments might simply be accounted for in a superimposed dead load smeared all over the bridge. In a way allowing sufficient allowance to cover anything now and in the future (like light poles being replaced in the future which could have a completely different mass).

But I'm reckoning the poles themselves are a fairly small mass in comparison to the overall mass/weight of the bridge (fractions of a fraction of a percent), so whether the mass of a small elements is correctly accounted for or not it will likely not make a scrap of difference to the global response of the bridge.

The wind load case may control the design. However the seismic load also should be checked.

Definitely agree with this, there are often different limits, different loading directions to consider and so forth. Also the only way you are going to know if one load case truly governs over another in all possible aspects is if you check both cases!
For people that argue otherwise I like to state the case of checking a simply supported steel span for a moving point load, if that load is in the center of the span it will result in the max bending load, but for shear you need to consider cases where that load might be nearer the end, but if you consider bending and shear interaction, the critical point might be somewhere completely different. So you need to check all possibilities to determine the critical case. Similar for assessing and combining different types of loads, snow, seismic, wind, water, traffic, etc within the bounds of the load cases your code requires you to assess.