American Towers at 48 W Broadway, Salt Lake City Structural Investigation of Rooftop Hot Tub Structures (North & South Towers)

Transcription

1 12 October 2011 Mr. Joseph Toronto General Manager American Towers Owner s Association 48 W Broadway, Suite 100 Salt Lake City, UT RE: American Towers at 48 W Broadway, Salt Lake City Structural Investigation of Rooftop Hot Tub Structures (North & South Towers) On Monday, October 3 rd, at your request, and per the recommendation of Kraig Clawson from Innovative Building Envelope Consultants, Inc. (IBEC), Cambria Flowers, from Canyons Structural Consulting, Inc. (CSC), made an observation site visit to 48 West Broadway, Salt Lake City, UT. The structures examined were the hot tub support frames located on the rooftop level of both the North & South Towers. Water damage has occurred to the structural framing members of both of these structures. The purpose of this site visit was to: (1) determine the current adequacy of the damaged elements; (2) provide demolition, repair, or replacement recommendations; and (3) assess structural costs for those recommendations. EXECUTIVE SUMMARY The evident presence of moisture within the rooftop hot tub structures of both towers has led to deterioration of many of the structural steel framing members. The north tower s hot tub structure displays the greatest amount of damage, but both structures have enough damaged steel that repair options are not recommended. The present condition of these structures represents a safety hazard to anyone who might access or utilize the hot tubs. In the immediate future, our advice would be to empty the tubs, rope them off, and remove the concrete benches above. Alternatively, you could provide temporary shoring to stabilize the deteriorating steel frames & metal decks until demolition or replacement options are pursued. The two options that we recommend for consideration are: 1. complete demolition & removal of the hot tubs, concrete access stairs, and steel support structures 2. demolition and replacement of the steel support structures only (keeping the tubs, equipment, and access stairs) A general fee assessment for each of these options can be accessed later in this report. See Table 1. OBSERVATIONS All observations during the site visit were done by sight, with a camera, or with a tape measure: no testing, destructive or otherwise, was conducted. Mrs. Flowers had previously oriented herself on the project with some photos and a site layout that were ed to her by IBEC. Also present on the rooftop during the visit was Jose, with property management. The rust damage to the steel-framed structures appears to have been caused not only by condensation underneath from the hot tubs & their equipment, but also from exposure to the outside elements, because the cladding skirts were not built to be waterproof. Had the steel elements been properly waterproofed initially with galvanizing or painting procedures, these steel frames would have been quite suitable support systems for the hot tubs & the seating areas above.

2 A list of our observations with associated photograph references follows: 1. The formed concrete stairs appear to be structurally sound. See Figures 1 & The metal guard rails & light posts around the hot tubs top surfaces appear to be structurally sound, but their connectors will need to be replaced if new decking is placed & a new concrete topping is poured. See Figures 1 & The cementitious cladding skirt surrounding each the hot tub structure was bolted on. From the outside, it appeared to be relatively sound; however, the bolted attachments to the structure were quite rusted. See Figures The metal formdeck displayed rust damage and some delamination. A lot of the damage was concentrated at the perimeter. Adequacy of the puddle welds holding the formdeck to the support structure is suspect due to the amount of visible damage. See Figures 4 & Many structural columns displayed rust damage and some delamination. See Figures 3, & The 3 and 3-1/2 diameter concrete piers at the bases of the columns and wide-flange beams appeared to be sound. The attachment methods used to attach the columns to the piers were concealed, so knifeplate and welded connections most likely were used. Similar attachment of any replacement columns will be considered. See Figures The steel angles and steel channels, both parts of the structural frames were rusted and damaged. See Figures 9 & The steel wide-flange beams supporting the bases of the hot tubs were rusted. See Figures 11 & 12. RECOMMENDATIONS Our observations showed that the greatest amount of rust damage is present in the hot tub structure for the North Tower. However, there is sufficient damage in the South Tower to render the steel-framed structures unsafe and unsuitable at present. We would not advise trying to re-use any of the structural steel for either of the structures, and this includes the metal formdeck which supports the concrete walking surface above. Because of the safety threat that these elements currently pose, we strongly advise that the tubs be emptied and that the access surface be roped off as soon as possible. An alternative to this would be building some temporary shoring to stabilize the hot tubs and frame structures underneath until a more suitable solution can be implemented. The two different permanent solutions to this situation were listed previously, and we will explore them a little further at this time. Complete Demolition & Removal of Rooftop Hot Tubs & Their Structures- This scenario would make sense if the current usage of the hot tubs is minimal. From what was indicated at the site visit, only 20% of the tenants living at the American Towers complex are using the tubs. A rough estimate on fees for demolition & material removal for this option is just over $8,000. This represents no additional cost for engineering, because it would not be required. All removal must be from the roof surface upward, so any connectors penetrating the rooftop concrete surface must be sawcut. It is understood that re-roofing procedures are being considered for both towers, and this effort would need to take place prior to the re-roof process. Demolition & Replacement of the Steel Frame Structures Only- While this effort might be more costly than the one just described, it will enable tenants to continue to have hot tubs for their use. Since the hot tubs, concrete stairs, the hot tub equipment, the guardrails & surface

3 lampposts, and the cladding skirt and doors all appear to be in good working order and are structurallysound, we feel that they can be re-used. The tubs & stairs would need to be temporarily shored up. The lighting under the hot tubs needs to be disconnected. Then, the steel frame, metal deck, and overlying concrete slab would need to be carefully demolished and removed. Replacement with new framing elements, matching the layout and sizes currently in place, if approved by the engineering, would need to take place; however, this replacement steel must be pre-treated with waterproofing methodologies. Galvanizing has been included with the cost estimate, but waterproof painting procedures can also be considered. Welded connections make the most sense with the steel-frame elements used here, and that has also been included in the cost estimate. The steel frame can also bear on the cylindrical concrete piers that are currently in place. As such, those should not be removed with the demolition. Once the steel frame is constructed and in-place, the metal deck can be placed, and the concrete slab can be poured and formed, allowing for proper connection to the concrete stairs and allowing for the upper surfaces of the hot tub to be supported. New lighting will then need to be installed under the tubs. The cladding & doors can be re-hung on the steel frame, and the guardrails & lampposts re-installed. Care should be made to include water-resistant connectors. Total cost for this effort is estimated to be just over $32,000. This does include engineering allowance for the structural design of the frame elements and connections, as well as structural consulting during the construction process. Other Considerations Made that are not Recommended- Prior to seeing the existing steel frames, we thought that re-use of some of the un-rusted elements could be considered. However, as none of the existing steel has been adequately waterproofed, any of it that is reused would not be warranted against future water damage. Plus, the construction logistics of keeping some steel elements and replacing others would prove to be a lot more difficult than total steel replacement. The added labor costs would not make this effort worthwhile. Another option that was briefly considered was replacing the existing tubs and support structures with freestanding, self-supported hot tub units. However, per communication with a local supplier, replacement tubs would have to be lifted in-place somehow. Due to the height of these towers, the cost of helicopters or other hoisting mechanisms would prove to be quite cost-prohibitive. As such, this option was not pursued further. We have attached some figures breaking down the fees for the options considered. See Table 1. Detailed copies of the cost estimate spreadsheets can be made available upon request. Please contact us with any questions. We hope that this analysis will provide you with adequate information to arrive at desired solutions for the hot tubs & their supports. In the mean time, again, please do whatever necessary to prevent any life-safety concerns by draining the tubs or shoring up the structures. Sincerely, Cambria M. Flowers, P.E., S.E. Vice President CC: Kraig Clawson & Susan Hanson, IBEC

4 Figure 1: Sound concrete stair & cladding elements for North Tower hot tub. Metal guardrail & lamps also sound. Figure 2: Sound concrete stair & cladding elements for South Tower hot tub. Metal guardrail & lamps also sound. Figure 3: Section view of concrete cladding & rusted tube steel column for South Tower hot tub.

5 Figure 4: Rusted framing elements & delamination of the metal decking. Rusted cladding connectors also visible. (North Tower) Figure 5: Rusted metal decking at the perimeter. (South Tower) Figure 6: Rusted & delaminating pipe column at base (North Tower).

6 Figure 7: Rusted tube columns near hot tub. (South Tower) Figure 8: Rusted pipe column & steel angle at top. (North Tower) Figure 9: Rusted channels & angles. (North Tower)

7 Figure 10: Rusted channels & angles. (South Tower) Figure 11: Rusted W6 beams under hot tub. (North Tower) Figure 12: Rusted W6 beams under hot tub. (South Tower)

8 TABLE 1: BREAKDOWN OF FEES FOR BOTH OPTIONS COMPLETE DEMOLITION (BOTH TOWERS) DUMPSTER RENTAL & DUMP FEES* $3,590 SALES TAX (6.85% ON RENTALS & DUMPING) $246 LABOR (FOR LABORERS & PROJECT MANAGER)* $3,966 EQUIPMENT* $291 TOTAL $8,093 20% PROFIT & OVERHEAD $1,601 SUB-TOTAL $9,694 CLEAN UP (0.3% OF $9,964) $29 PERMITS (1% OF 9,964) $97 CITY INDEX (13.5%) & POOR ECONOMY(5%) REDUCTION ($1,793) ENGINEERING $0 GRAND TOTAL $8,026 DEMOLITION & REPLACEMENT OF STEEL STRUCTURES (BOTH TOWERS) DUMPSTER RENTAL & DUMP FEES* $1,750 MATERIALS* $12,683 SALES TAX (6.85% ON RENTALS & MATERIALS) $989 LABOR (FOR LABORERS & PROJECT MANAGER)* $12,178 EQUIPMENT* $1,295 TOTAL $28,895 30% PROFIT, OVERHEAD, & CONTINGENCY $8,287 SUB-TOTAL $37,182 CLEAN UP (0.3% OF $37,182) $112 PERMITS (1% OF $37,182) $372 SPECIAL INSPECTIONS (WELDING) $283 CITY INDEX (13.5%) & POOR ECONOMY(5%) REDUCTION ($6,879) ENGINEERING (INCLUDES (1) CONSTRUCTION VISIT) $975 GRAND TOTAL $32,045 * These initial values are based on national averages. A city index reduction factor of 13.5% is applied later.