I'm not sure there is a correct answer to this but a little advice would help. I have a metal building where the owner has mezzanines to the far left and right hand sides of the building. In the middle is a 50 foot length of clear space. There are stairs up to the right mezzanine and plans for future stairs up to the left mezzanine. I have a catwalk that spans 50 feet clear from mezzanine to mezzanine. Also at the middle of the catwalk are two other catwalks that span perpendiculary to the primary 50 foot catwalk. These other catwalks are inconsequental except they limit my options as I will explain later. Initially it will be the only access to the left mezzanine so I have designed it for a LL = 100 psf since I believe functionally it will be a corridor at first. The two beams under the catwalk which is only 4 feet wide meet deflection criteria. However when I analyzed it with the footbridge method for vibration it fails miserably and only truly outrageous sized beams will work. Futhermore the current plans are for metal grating welded to the beams to be the floor not concrete or anything like that.
Originally the architect wanted to add a hanger support near midspan with would connect to the bottom of the metal building wind frame above. I didn't want to do this since the perpendicular catwalks attach to beams spanning between metal building columns at the perimeter of the metal building. My thought is that once I had the vertial post the combinations of wind frame, vertical post, and the perpendicular catwalks will when acting together will attempt to restrain the drift movement of the metal building. So I thought it better to keep the systems seperate.
So I have a light walkway with heavy beams and a far span. How should I approach the risk liability that the owner will complain of vibration. Of course I plan on discussing with the architect the need to prepare the owner for the possibility of vibration as people walk across. But on my plans what kind of note should I add? A verbal agreement does not seem to be enough.
Or should I simply go with W24x176 type beams (verus W24x68 or was it W24x62).
Basically the construction they want to use isn't good if you want to limit vibration. They are expecting light catwalk construction. I'm thinking of simply convincing the architect to put the other set of stairs up to the left mezzanine now. That way the catwalk will only be used as an observation deck for training and would probably never have more than 5-8 people up there at a time.
Any advice would be appreciated. The beams are large as it is and the actually deflection will be low even at 100psf loading. Just not sure how to best set the expectations of the owner.
John Southard, M.S., P.E.
Originally the architect wanted to add a hanger support near midspan with would connect to the bottom of the metal building wind frame above. I didn't want to do this since the perpendicular catwalks attach to beams spanning between metal building columns at the perimeter of the metal building. My thought is that once I had the vertial post the combinations of wind frame, vertical post, and the perpendicular catwalks will when acting together will attempt to restrain the drift movement of the metal building. So I thought it better to keep the systems seperate.
So I have a light walkway with heavy beams and a far span. How should I approach the risk liability that the owner will complain of vibration. Of course I plan on discussing with the architect the need to prepare the owner for the possibility of vibration as people walk across. But on my plans what kind of note should I add? A verbal agreement does not seem to be enough.
Or should I simply go with W24x176 type beams (verus W24x68 or was it W24x62).
Basically the construction they want to use isn't good if you want to limit vibration. They are expecting light catwalk construction. I'm thinking of simply convincing the architect to put the other set of stairs up to the left mezzanine now. That way the catwalk will only be used as an observation deck for training and would probably never have more than 5-8 people up there at a time.
Any advice would be appreciated. The beams are large as it is and the actually deflection will be low even at 100psf loading. Just not sure how to best set the expectations of the owner.
John Southard, M.S., P.E.
