HIGH PERFORMANCE SELF-CONSOLIDATING CONCRETE FOR NORTH AMERICA S TALLEST REINFORCED CONCRETE BUILDING: TRUMP INTERNATIONAL HOTEL AND TOWER, CHICAGO

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1 HIGH PERFORMANCE SELF-CONSOLIDATING CONCRETE FOR NORTH AMERICA S TALLEST REINFORCED CONCRETE BUILDING: TRUMP INTERNATIONAL HOTEL AND TOWER, CHICAGO William F. Baker (1), Matthew R. Houson (2), D. Stanton Korista (1), Dane S. Rankin (1), and Robert C. Sinn (1) (1) Skidmore, Owings & Merrill LLP, Chicago, Illinois, USA (2) Skidmore, Owings & Merrill Inc., London, United Kingdom Abstract When completed in 2009, Trump International Hotel and Tower, Chicago will rise to a height of 345 metres (415 metres including the spire). Designed by Skidmore, Owings & Merrill LLP (SOM) the 92-story Trump Tower will be the tallest concrete building in the United States, and the tallest building built in North America since the completion of Sears Tower in New ground is being broken through a series of high performance concrete mixes designed by Prairie Material Sales, Inc. and employed by SOM on the project. Local areas in the outrigger zones require 110 MPa concrete at 90 days. Since this 110 MPa concrete is also located in areas of high reinforcement congestion, self-consolidating concrete has been specified for the mix. It is also necessary to limit the heat gain during the hydration process as this concrete is used in the massive outrigger elements. It is the first application of 110 MPa self-consolidating concrete pumped and placed to an elevation up to 200 metres above grade. The high performance SCC mix includes multiple cementitious constituents including slag cement, fly ash, silica fume, and ordinary portland cement. 1. INTRODUCTION When completed in 2009, the Trump International Hotel & Tower, Chicago will rise to a height of 345m (415m including the spire). The building is currently being constructed on the north side of the Chicago River, between Wabash Avenue and Rush Street, at the site of the recently-demolished Chicago Sun Times building (Figure 1). The tower s 240,000 m 2 of floor space will incorporate 472 condo units, 286 hotel units, a health club, parking for 1000 cars, and 9300 m 2 of retail space. Encased in stainless steel and glass, the tower shaft will rise from a newly landscaped plaza that will include a new 925

2 riverwalk that will link the pedestrian level with the retail shops. The building will feature setbacks at Levels 16, 29, and 51 that correspond to the top elevations of prominent neighboring buildings, providing visual continuity with the building s surroundings. Figure 1: Computer rendering, Trump International Hotel and Tower, Chicago 2. STRUCTURAL SYSTEMS SYNOPSIS A core and outrigger system provides the lateral stability for the Trump Tower. Large outrigger elements tie the concrete core to perimeter columns, significantly increasing the building s lateral stiffness as well as its resistance to overturning due to wind. The core is located at the center of the building and consists of four I-shaped and two C- shaped walls. The webs of these I- and C-sections are oriented in the north-south direction, are 460mm thick, and are 12.5m long. The flanges of the sections are oriented in the east-west direction, are 1.2m thick, and range from 2.7 to 6.7m in length (Figure 2). Above the entries to the elevator cores at each level, 1.2m wide by 0.8m deep reinforced concrete link beams connect the flanges of adjacent walls. The outrigger effect is most pronounced in the narrow direction of the building (northsouth), as the width of the lateral system increases from 15 to 43m when the perimeter building columns are engaged. The outriggers are massive reinforced concrete wall-beams (up to 1.7m wide and 5.3m deep) that extend from the wall flanges to the exterior columns at three of the double-height mechanical floors in the tower (Levels 28-29, 50-51, and 90-91). Perimeter belt walls at the roof and the three setback levels provide additional torsional stiffness and redundancy, as well as serving to equalize column loads along the perimeter. 926

Figure 2: Typical residential floor plan Tower columns are typically 600 by 1200mm rectangular sections at the top of the building and 1800mm diameter circular sections at the base.

3 Figure 2: Typical residential floor plan Tower columns are typically 600 by 1200mm rectangular sections at the top of the building and 1800mm diameter circular sections at the base. Typical residential floors are 230mm thick flat plates spanning up to a maximum of 9.1m without perimeter spandrel elements. This construction minimizes the structural depth of the floor, allowing higher ceiling heights. A 3m thick concrete mat under the core walls transfers their enormous loads into a grid of 3m diameter drilled shaft rock caissons that extend about 25m down where they are socketed 1.8m into solid Chicago bedrock. The tower columns are also supported by rock caissons up to 2.4 m in diameter and stabilized by a series of caisson caps and grade beams. 3. THE NEED FOR HIGH PERFORMANCE SELF-CONSOLIDATING CONCRETE Because of the scale of the outrigger elements and the magnitude of the applied loads, the structural engineering design for these elements was unique and extremely challenging. Large tie forces are resisted by top and bottom longitudinal reinforcing and vertical ties. The heavy longitudinal reinforcing steel must pass from the thicker outrigger through the thinner core wall web to transfer forces between the columns and core. To reduce congestion, all primary reinforcing bars in the outrigger levels are U.S. Grade 75 (520 N/mm 2 yield strength). Further, in three especially-tight locations, high strength structural steel plates with welded shear studs are used in lieu of reinforcing bars to transfer the necessary forces through the core wall web (Figure 3). A series of high performance concrete mixtures, specified by SOM and designed by Prairie Material Sales, Inc., are advancing the state-of-the-art. Up to Level 51, concrete strengths of 83 MPa at 90 days have been specified for all vertical column and wall elements. Local areas in the outrigger zones, however, require 110 MPa concrete at 90 days. Because the 110 MPa concrete is located in areas with high reinforcement congestion, self-consolidating concrete (SCC) with a minimum flow spread of 600mm has been specified. Further, to reduce the heat gain in the massive elements, the high performance SCC incorporates slag cement, fly ash, and silica fume as well as portland cement. 927

4 Figure 3: Outrigger wall reinforcing To meet the occupant motion perception criteria, the stiffness of the concrete is critical. The modulus of elasticity of the high strength concrete was therefore specified to at least achieve the modulus of elasticity values indicated in ACI 318 equations. To meet this as well as the minimum strength requirements, the producer is using dense limestone coarse aggregate, with a topsize aggregate size of 12mm. In contrast to the stringent minimum strength requirements in ACI 318, concrete modulus of elasticity may be specified on an average basis. Somewhat lower modulus values in local areas are therefore acceptable as long as the average value remains as specified. Further, such modulus values may be obtained at a much later date for example, 180 or 365 days as the motion perception criteria are long-term serviceability issues and won t be critical until the building is completed. To date, testing for the 83 MPa concrete in the lower story walls and columns indicates that the modulus of elasticity is somewhat higher than predicted using equations from ACI CAISSON MAT FOUNDATION SCC The 3m deep caisson mat slab at the base of the core walls represented a major milestone in the construction of the Trump Tower. The choice of SCC for the mat was based on the ease of placing concrete and finishing in a confined, subgrade area. The mat slab was poured in late-september, 2005 to the following concrete specifications required by SOM: 69 MPa cylinder compressive strength (minimum) at 56 days 41 GPa static modulus of elasticity (average) at 56 days Self-Consolidating Concrete Concrete temperature at time of placement not to exceed 80 0 F Concrete temperature in place during hydration process not to exceed F Mazimum differential temperature between any two points in the mat 40 0 F 928

The mat pour represented some 3,800 cubic metres of self-consolidating concrete over the plan dimensions of 60m x 18m in a single continuous pour.

5 The mat pour represented some 3,800 cubic metres of self-consolidating concrete over the plan dimensions of 60m x 18m in a single continuous pour. The pour was accomplished in a period of 22 hours and required over 30 ready mix trucks making a total of 600 trips to the job site. The concrete was placed by conveyor (Figure 3). Concrete was dispatched from the batch plant at a distance of approximately 2.5 kilometers. The concrete flow from placement was on the order of up to 15 metres. Figure 4: Mat foundation construction The mix design for the mat foundation concrete included the following constituents and design properties: Blend of 12mm and 20mm topsize coarse aggregate (crushed dolomitic limestone) Natural sand fine aggregate Trenary mix of Type II portland cement, slag cement and Class C fly ash Type D chemical retarder Polycarboxylate HRWR admixture and Viscosity Modifying Admixture (VMA) Target flow spread 66 to 71cm Target J-Ring 61 to 69cm Water / Cementitious Ratio 0.26 to 0.28 After completion of the mat pour, the top surface of the mat was topped with rigid insulation planks and plywood to limit the heat loss through the exposed top surface. The sides of the pour were against steel sheeting retaining the mat excavation below the level of the adjacent Chicago River. The peak temperature within the interior of the mat pour was recorded at F at approximately 72 hours after the pour. The maximum differential between mid-height and top surface of the mat was 28 0 F. At 56 days, concrete cylinder tests indicated compressive strengths at nearly 100 MPa and static modulus of elasticity at 47 GPa. It is believed that the mat foundation pour for the Trump Tower represented the largest single SCC placement in North America to date. Subsequent core samples taken from the in-place 929

6 mat concrete indicated uniform aggregate dispersion throughout the samples without segregation. 5. SUPERSTRUCTURE SCC Trump Tower is not only a very tall building, it s quite slender, as the aspect ratio of the tower (measured as the overall height divided by the smaller base dimension) exceeds 8 to 1. Such slender buildings are known to be significantly influenced by the dynamic nature of the wind and its interaction with the building structure. Movements under wind load are affected by a building s stiffness, mass, and damping as well as the local wind environment and geometry of the tower shaft. Concrete was chosen as the primary structural material for the Trump Tower to take advantage of its ability to provide a highly massive frame with high damping. The high lateral stiffness of the tower was accomplished by using high modulus of elasticity concrete in the massive column, wall, and outrigger elements. Inherent damping of the designed concrete frame is on the order of 50% higher than in a comparable steel scheme. All of these factors resulted in predicted peak accelerations at the topmost occupied floors that are comfortably within the ISO criteria applied to residential buildings. Both 83 and 110 MPa strength SCC mix designs have been developed for the special, highly reinforced local outrigger zones at the building setbacks. Concrete from these mix designs will be pumped with Putzmeister equipment as high as 340 metres above grade without horizontal staging. The 110 MPa design calls for a quadrenary cementitious mix composed of microsilica, slag cement, and fly ash in addition to ordinary portland cement. Target water / cementitious ratio is Combinations of mid-range and high-range water reducers, retarder, and VMA are included in the mix design. Locally available limestone aggregate from the Thornton quarry up 20mm topsize is being used for the pumped mix. 6. CONCLUSION Project completion is scheduled for spring of 2009; however, based upon the phasedoccupancy plan, the hotel will be operational in late 2007, well before the scheduled topping out of the structure in mid To date, project milestones met have included the demolition of the existing Sun Times building in March of 2005, completion of the rock caissons in August of 2005, and the 3360m 3 continuous 22 hour placement of SCC for the core mat on September 29, Also, as part of the development, the Trump Organization replaced the adjacent 1920 s era Wabash Viaduct, completed on November 19, As of February 2007, the Trump Tower structure has risen to the second setback zone (Level 25). 930

7 7. ACKNOWLEDGEMENTS Developer: Structural Engineer: Architect: Construction Manager: Concrete Contractor: Concrete Supplier: SCC Admix. Supplier: Figure 5: Current construction progress 401 North Wabash Venture LLC (The Trump Organization) Skidmore, Owings & Merrill LLP Skidmore, Owings & Merrill LLP Bovis Lend Lease LMB, Inc. James McHugh Construction Co. Prairie Material Sales, Inc. Degussa Admixtures, Inc. REFERENCES [1] Trump International Hotel and Tower, William Baker, Stan Korista, Robert Sinn, Karl Pennings, and Dane Rankin. Concrete International, July 2006, [2] Trump Update: Tower Making Its Climb Toward Chicago s Skyline, Midwest Construction, October 2006, [3] Prairie Sets SCC Record in the Heart of the City, Concrete Products, November 2005, p. 6. [4] New Tower Trumps Others as the Tallest Reinforced Concrete Structure in North America, Putzmeister Marketing article, February,

Council on Tall Buildings. and Urban Habitat CAYAN TOWER CTBUH BEST TALL BUILDING MIDDLE EAST & AFRICA

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