CMU block walls with Hollow Core slab - how high??? 1

[slapjack]

Just curious - how many stories tall have you built using CMU block load bearing walls with a Hollow Core slab system? We are looking at an 8 story hotel and wondering if this type of construction is feasible for such heights.

 

[JedClampett]

I've never done it, but my "Reinforced Masonry Engineering Handbook," Fifth Edition, by Amrhein has an example of a seven story building.

 

[csd72]

Do a calculation using maximum reinforcement, all cores filled and site wind load at ground level.

Then calculate the maximum allowable axial capacity concurrent with the wind load.

Divide this by 1.5 to allow for doors/windows e.t.c. and then figure out how many stories that will support.

This will give you a preliminary design.

Rules of thumb only get you so far.

csd

 

[jike]

This sounds feasible but will be affected by the architectural concept, the framing scheme and the amount of lateral load determined by basic wind speed, exposure, and seismic parameters.

Can all of the bearing walls be carried to the ground? Are all floor to floor heights the same?

Normally, the precast spans the long way of the hotel over two rooms, about 28 feet. Intermediate walls between rooms are non-load bearing stud walls. This can provide for doors between pairs of rooms.

Do some prelim. calculations as csd72 suggests to determine structural feasibility.

 

[jike]

You might also look at using precast with steel framing. Will your masonry be affected by winter construction?

 

[JAE]

Also check out the IBC (or ASCE 7) if you are in seismic areas as Table 1617.6 has height limits for bearing wall systems.

 

[jike]

Another idea is to look at hollowcore with precast bearing walls.

 

[JS15]

In a similar scenario, I have discovered cold formed steel studs to be a much more cost effective alternative to the block and plank system. The cold formed SigmaStud easily builds eight stories and works well with a hollow core plank floor system. The foundations are able to be reduced by the reduced weight, and base shear is much less. Shear forces are resolved using a flat strap shear wall system.

 

[concretemasonry]

Not hollow core, but - The highest I have seen was about 20 stories of 6" (140 mm) block. The project consisted of a number of building ranging from 15 to 20 stories. The building was in Brasil. Since quality high strength 6" block were available, there was no justification to go to 8" walls.

They used four or five different strengths of block depending on the floor level. The walls were partially reinforced with very little extra vertical reinforcement on the upper floors beyond the normal reinforcement for doors and windows. The masonry walls were generally designed in accordance with ACI 530 or the predecessor design standard (NCMA "green book").

The floors in Brasil were two-way cast in place slabs and were about 5" thick if I recall correctly.

It was a typical loadbearing apartment building with both exterial and most interior walls loadbearing. Room sizes were in the range of 9x12 to 10x20.

There was a large amount of engineering that went into creating the excellant drawings and details. There was also a great deal of coordination between designers, suppliers and contractors in comparison U.S. projects. The amount of engineering involvement and attention to details was very impressive. Because of the quality control and inspection practices implemented, very few prisms were cast on the site and all units were identified and pre-qualified at the plant because 5 to 10 buildings were undergoing construction at the same time using different strength units.

There are numerous 8 to 12 story loadbearing buildings in California and the Excalibur in Las Vegas is 28 stories. Most of the were constructed using 8" block and lift slabs and 4000 f'm block. The lift slabs were generally chosen because of speed of contruction and scheduling crane time.

The maximum height of you building with hollow core plank will depend on the efficiency of the bearing/shear wall layout and the spans. With a reasonable building shape and wall layout, spanning two hotel rooms with a single hollow core is very reasonable on an 8 story building.

Which ever type of floor system you use, find out from the local supplier what maximum block prism strengths (f'm) are available. The Excalibur was 4000 psi and the company I was with offered a 4500 psi f'm unit in our product line, but could have gone a little higher.

Dick