high masonry wall design

huangyhg

high masonry wall design
i am doing a structural design of a 3-storey with roofdeck reinforced concrete building. the building is irregularly shaped and a portion of the structure is to have an l-shaped footprint of masonry wall (which will serve as firewall) with dimensions of 7.5m by 10m and height of 14m from ground. the  masonry wall stands vertically upright with no roof/truss above it. i would like to know:
a.) if there are special design consideration for this type of wall aside from gravity and lateral loads due to wind.
b.) what frame system is appropriate for this considering that the wall is situated within the perimeter and only cantilever footing and wall footing is possible?
thank you and i hope anyone can help me on this.

this is a cantilevered 45ft high masonry wall exposed to exterior wind?
the wall does not seem to be a major design problem for a reinforced masonry or concrete element. i have seen several similar walls built for large masonry homes in russia.
the plan dimensions (7.5 m x 10m) of the "l" shaped element relative to the height (14 m) provide a relatively robust structural element. the torsion will make it somewhat interesting depending on your simplifying assumptions.
i assume the element will be partially reinforced masonry (for descriptive purposes). critical portions will be the vertical steel at the ends of the walls and somewhat at the wall intersection. obviously, some intermediate bond beams(8" or 16" deep) will be required for shear depending on the wind/seismic loadings).
the vertical steel and grout spacing in the "field" of the wall will be relatively widely spaced.
constructability of the design will be critical. concerns should be selection of masonry unit shape, spacing of bond beams and selection of masonry unit strengths and grout strengths. if your local code still requires visual observation/clean-outs, this will be a factor.
avoid the primative approach of dumping the wall full of high strength grout into every core to create a robust structure. - it is unprofessional sign, wasteful and contrary to good engineering. the grout strength should not greatly exceed the masonry unit strength. - you want the outer fibers (the masonry) to be stronger than the core fill material that does not see the stresses.
dick
what is the out of plane load?
thanks for the reply.
the element will be partially reinforced masonry with columns and bond beams intermediately spaced. i am thinking of having the columns and beams as my primary system (to resist gravity and horizontal loads - wind or eq). do you think this is a good approach? i am trying to eliminate stresses on masonry because high strength blocks is not available in our locality.
haynewp,
yes cantilevered about 45ft exposed to minimal wind because adjacent to it is a 5-storey bldg. earthquake will probably be considered because of the wall height. no other loads on the wall other than its selfweight.
why do you think you need high strength block? - you are not building a 20 story building out of 6" block are you? an "l" shape structure is reasonably efficient.
a mixture of columns, bond beams and masonry is very inefficient compared to an element designed out of masonry. the minute you break a strucrual element up into microscopic elements of units, mortar, beams and columns, you are adding complexity and assumptive errors.
look to aci 530 and treat the "l" shaped wall as another structural element.
you must design the wall as if the other 5 story building is not there.  don't shield it from wind forces due to the presence of that structure.  things could change.  buildings are torn down resulting in vacant lots.  cya.
mike mccann
mccann engineering
that seems awfully tall to be free standing and exposed to full wind load. why can't you tie it to the structure for stability?
at each leg end is already the bldg structure also at same height. yes, it will be tied together since it will also serve  as the building perimeter fence and fire wall.
thank you everyone for your reply. its very helpful.