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Thank you guys. I feel much better now. I just have never used this thick back fill under fundation. Therefore do not feel confident. By the way, if I assume the subbase under this thick back fill is strong enough. What kind of bearing capacity I can expect for this 95% compacted select...

I need to back fill a 50’x50’x12’ (deep) pit and build a pre-engineering building. The max load from each column (Total of 8) is 50 kip. I specify the select structure fill as backfill material. Backfill are required to be compacted (95%)every 8”. However, I am still afraid that this thick...

Thanks for help. The safty factor should remain the same as 1.5 for sliding and 2 for overturning?

I need to design a concrete retaining wall. In the design, the seismic load has to be considered. I did design a dam which considered seismic load from water behind but I have never designed such a retaining wall which seismic load from earth behind need to be considered. I use similar idea to...

Unless specific indicated by engineer, usually shop drawing will not supersede the contract drawing.

cntw1953, what is suspend support system, could you please give more detail? Hokie66, You are right, it might not have problem. However, I cannot rule out the possibility. Therefore, I still need to consider it in the design.

Thanks guys. The unit has to be installed here and Pipe can be adjusted. Estimated movements come from the following: Horizontal movement: The existing expansion has a 6” gap (say, joint filer material 2” under pressure). I therefore assume that existing building is designed for 4” expansion...

Estimated movement: lateral: 4" vertical, 3"

Hvac unit is located on the top of roof

Jike, Columns are existing. No other structure member can be used to support the HVAC unit. Ron, it is difficult to support a independent system by 2 column on each side. Unit size is 25'x21'.

I need to design a steel dunnage support for a HVAC unit. Four supporting posts will be sat on four existing building columns which located at both sides of an expansion joint. (2 columns on one side of the joint and the other 2 columns on the other side of the joint). I am afraid of either...

Thank you NUTTE. I am glad there are a lot of knowledgeable engineers here. Is any book or website list all update items for Edition 13? Some other engineers in my office still use edition # 9. I would like to show them the difference. Actually I find web available strength in edition 13 is...

I just got an AISC 13th edition manual. Comparing table III Framed beam connection in AISC 9Th (P4-26) and table 10-2 Bolted dbl angle connection in 13th edition (P10-46). It gives such a big different result for the same connection. I can not figure out why. Is there anybody can help me? For...

Thanks guys. I guess 271828 is right. I need to spend more time to be familiar with edition 13.

I used to use 9th edition AISC manual of steel construction. A few days ago, our office just bought a 13th edition. I went over it a few times. It seems to me that 9th is much handier. Most importantly, 9th edition give many examples which explain manual very well. While the new one (new to me)...

I am designing a shear connection for steel beams. One beam is coped. Is it required by any code to check web buckling for all coped beams? Is it necessary? I could not find any example in AISC manual. Any quick way to do that? Please help.

AlmostPE said: you shouldnt be looking at horizontal wall deflection if you use a ridge beam But why not? If ridge beam deflect, the only way this structure deform accordingly will be this way: peak of roof settle and the top of wall move outwards horizontally. There is no any force to prevent...

Thanks AlmostPE. The collar beams are needed for the vaulted ceiling so that gym. Board can be secured on them. If I used ridge beam, collar beams do not have their structural function. However, if I treated rafters + collar beam as a truss, I believe that it will act as a horizontal member to...

Sorry I did not descript my geometry clearly. I try to explain more clearly here. The room is 16’ x16’. Roof is about 7’ (16x 5/12, say 7’) high. Collar beam (same direction as rafter)is 2/3 of 7’ from the peak and 1/3 of 7’ from the top of wall. It is about 2.3’ above the top of the wall...

Thank you guys. I did think of both solutions (ridge beam and truss) but have questions for both. Ridge beam: The mid point of my 16’ ridge beam will allow l/240= 0.8” settlement. Because roof is 5:12 slope, 0.8” settlement in the middle means the wall in the middle of building will move out...