Walkway design! 4

[luu]

hi all!
i am required to design a walkway to provide all weather access between a surgical building of a hospital and a multi-level carpark. The carpark and the surgical building are both constructed from reinforced or prestressed concrete. The walkway is to span 30m across an ambulance access road between the buildings (this access road is not to be completely closed at anytime). The walkway is to have 2 levels: the upper level is to provide access from level 3 of the surgical building to the helipad on the rooflevel of the carpark; the lower level is to join levels 2 in both buildings. the clearance between floors of the carpark is 7m and of the surgical building is 5.5m. The floors of the carpark are strong enough to be able to directly support the walkway. However, the floors of the surgical building arent that strong.
I have 2 options as follows:
+ a truss spanning 30m ( with no column support at the middle since the access road is to remain open all the time -> would cause difficulties to the construction of the middle columns). One end of the truss will be directly connected to the floor of the carpark, the other end will be sitting on an additional column due to the fact that i cannot connect the truss to the beam or column that are existing in the surgical building.
+ the other opion is to build one level of the walkway and a system of rollers to bring the walkway to the rooflevel of the helipad when some patients are to be transfered since the clearance between floors is different between two buildings.
However, I do not have much experience in designing walkways. I will need heaps of help to accomplish this. Can anyone help ?
thanks in advance.

 

[Rich2001]

Notes for a 30m Truss design -
1. Get a copy of the AASHTO Pedestian Bridge design specifications, it has an complete design example around this size.

2. A copy of this book <B> GUIDE TO STABILITY DESIGN OF METAL STRUCTURES</B> Theodore V. Galambos (Editor),T. V. Galambos (Editor) / Hardcover / Wiley, John & Sons, Incorporated / June 1998. The HOLT procedure for pony truss design is either in chapter 15 or 17.

 

[Qshake]

Rich2001, my thoughts exactly!

 

[Ron]

One other point in addition to the excellent advice from Rich and Q...stay away from mechanical walkway/ramping/roller designs, particularly where disabled access is important, and in this case, perhaps emergency access. Unimpeded access is critical for functionality and for your liability.

A stuck roller could become a life-threatening issue in a case like this!

 

[gradstoodent]

Search for and read about the Hyatt Regency Walkway Collapse to learn what not to do in your design.

 

[Qshake]

The Hyatt Regency isn't about what not to do in the design process but rather what not to do in following up on site changes, shop drawings, and communicating with the rest of the design team.

If you believe this to be an original design error, please go back and review the information.

 

[gradstoodent]

You are correct, however, I never said it was part of the original design.

 

[malaysian]

The problem of not using columns to support the 30 m walkway is easily solved by using additional cantilever supports at the ends such as the Petronas twin tower walkway. But clearly the difference in clearance levels between the two will give your design some problems. And to the best of my imagination, if you were to build two levels of walkway, both will not be in parallel, and you'd result in a weird funky shaped walkway.

Because I'm not a bright person, I would not recommend the mechanical version of using rollers between the two levels due to its complexity in terms of construction and servicability.

I would however, question the importance of building the two level walkway. Personally, the I can see the reason for the link between the helipad and the surgical building, but why between the 2nd floor for of both buildings? Why not build just one walkway on 3rd floor, and replacing the need for a second walkway by using a lift access between the 2nd and 3rd floor of both buildings (that is if there are lifts in these buildings..)? And above all, if people just want to get accross both buildings, it's only the 2nd and 3rd floor you're talking about... ever considered staircases instead??

 

[ishvaaag]

I am an architect but for buildings in Spain we are as well the structural designer. It is clear that as a structural designer you are being interfered by an architectural problem. So since I assume the options are clear, more or less, make management decide what option wants, then you do the calculations, inclined, cantilevers, column or not.

For the pony truss you have also a sheet for free download in Mathcad. In any case I don't see the convenience of a pony truss where I assume there will be roof and maybe as well an intermediate floor; this you will perform far easily with the help of a FEM program, of course under your close scrutiny. If in doubt, model initial geometrical imperfections directly AND ensure any real initial geometrical imperfections at the site remain under the worst assumptions you have made.

 

[evelrod]

Just a little note, not ment to ruffle your feathers, gentlemen. The Hyatt Regency skywalks were designed to be supported by continuous steel rods. Somewhere along the line they were changed (I won't point any fingers, the past is the past, lets just not repeat it) The asbuilts show that the support rods were replaced with individual hanger rods on EACH level which were capable of supporting each individual level, but not ALL levels. During the grand opening, the skyway bridges were filled to capacity with the uppermost walkway supporting all the lower walkways. The individual hanger rods pulled out of the concrete and the lower walkways fell with catastrophic results.
Litigation went on for years and I am not sure how it all turned out, but I'll bet the spin doctors and lawyers got rich.


Rod

 

[FrankHartzell]

Regarding the Kansas City Hyatt Regency walkway failure:

In addition to the increased load on the hanger rod-floor framing connection at each level due to the substitution of individual hanger rods between levels for continuous rods, the hanger rod-floor beam connection itself was, I believe, unsatisfactory. The beams consisted of a pair of channels seam welded toe to toe to form a box beam. The hanger rods were inserted in holes through the center of the box beam top and bottom flanges. There were no stiffeners or other means to prevent channel flange bending or web bending/buckling or to prevent tearing of the toe to toe seam weld. Intuitively, it looked pretty easy for the rods to pull through the built-up box beam. Frank Hartzell
Jacobs Engineering
Conshohocken, PA
frank.hartzell@jacobs.com