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  • 1.  Rooftop Pool

    Posted 07-06-2018 01:43 PM
    Edited by Tirza Austin 08-09-2018 10:24 AM
    Hello everybody,

    I'm starting to plan a design of a 19 stories (74.5 m) above ground RC Hotel building + 4 underground.   Not very large in terms of plan area ( 600 m² = 6456 sq ft the rooms tower), but with a rooftop pool and social area. I live in a moderate to high seismic area (Ss = 0.95g, S1 =0.55g) and we don't have much experience with relatively tall buildings with roof top pools in our country.  I would appreciate any suggestion(s) and/or advise to consider for the structural treatment of such building, especially things to keep in mind and be aware of in terms of modeling for analysis and detailing of the pool.
    Pool size is 5 x 10 x 1.20 deep meters ( 16' x 32' X 4' ) , so it adds some 60 metric ton of weight to the top level toward one side of a near square floor plan.   I'm  concerned of vertical mass, torsional irregularities, and other problems.
    Building Lateral resisting system would be SRMF with a special reinforced wall elevator/stair core.

    Thanks in advance for your comments.

    Ramses Sanchez Aff.M.ASCE
    Santo Domingo, Dominican Republic

  • 2.  RE: Rooftop Pool

    Posted 09-05-2018 05:25 PM
    Edited by Tirza Austin 09-05-2018 05:24 PM

    Hi Rames,

    Can you clarify the code under which you are designing?

    At first glance - and if I was designing under IBC - I would be concerned if you can get enough lateral resistance (moment frames and shear walls) both for strength and drift given the fairly small footprint. Also related to drift, if the building was an addition to an existing one or immediately adjacent to other buildings, consideration of the distance between the two structures would be needed, especially if the building is on a property line.

    Also because of the small footprint and height of the building, careful attention should be paid to the foundations related to overturning moment/uplift. 

    Given that you have 4 levels of underground parking, consider how you expect construction to be sequenced for the retaining walls as you are likely to have a construction condition that results in more than one story of <g class="gr_ gr_26 gr-alert gr_gramm gr_inline_cards gr_run_anim Grammar only-ins doubleReplace replaceWithoutSep" id="26" data-gr-id="26">unbraced</g> length of retaining wall that would need to be designed for. You would also need to check your retaining wall foundations to determine if there is enough frictional resistance for sliding at the base or, alternatively, if the diaphragm at each level would need to be designed for the horizontal force of the wall in addition to the seismic and gravity forces. With four stories of <g class="gr_ gr_27 gr-alert gr_gramm gr_inline_cards gr_run_anim Grammar only-ins doubleReplace replaceWithoutSep" id="27" data-gr-id="27"><g class="gr_ gr_28 gr-alert gr_gramm gr_inline_cards gr_run_anim Punctuation only-ins replaceWithoutSep" id="28" data-gr-id="28">wall</g></g> you will very likely need beams to resist the force requirements unless you design the slab on grade as a diaphragm also. You might even need to add beams at the elevated garage floor levels or increase the slab thickness to accommodate depending on the building layout.

    I've put a large water fountain/assembly area/gardens on top of 20 story buildings (haven't done a pool), and for <g class="gr_ gr_25 gr-alert gr_gramm gr_inline_cards gr_run_anim Punctuation only-ins replaceWithoutSep" id="25" data-gr-id="25">those</g> we put a waterproofing admixture in the concrete. There was also a much larger floor-to-floor height between the last occupied level and the roof to accommodate the equipment needed for the fountain; I assume it would be similar with a pool.

    One other thing I ran into the first time I designed a building of this height was the use of much higher strength concrete and also making sure I allowed enough room in my column sizes and shear wall thicknesses to accommodate rebar lap splices, both for constructability and to avoid exceeding maximum rebar requirements at the splices.

    Hope this helps and I look forward to hearing others' thoughts on this.

    Stephanie Slocum P.E., M.ASCE
    Engineers Rising LLC
    State College PA