ENGINEERING ETN-D-5-18 Concrete Reinforcing Steel Institute Technical Note Structural Design projects arealsoprovided. was assumedinbothoptions. floortoceilingheightof9 A typical ft-0 in. crete optionaregiven inFigures3and4. tively. Similarviews for thereinforced con- option aregiven inFigures1and2,respec- erated fromthisstudy). section below for thereportthatwas gen- & Company, Seattle, WA (seetheReference structural Kopczynski engineering firm Cary concrete. The study was performed by the timber (CLT) andcast-in-placereinforced Pacific Northwest usingcrosslaminated 10-story residentialbuildinglocatedinthe of thestructural frameofahypothetical of arecentstudy thatcomparesthecost Overview shorter insome areasthanthosefor the ceed 16 ft-0 in. at thecornerunitswhere floorspans ex blies, with9-5/8-in.-thick 7-lam assemblies 6-7/8-in.-thickare typically 5-lam assem- U.S.-manufactured CLT). The floorpanels grade softwood size timber(astandard for ing 1-3/8-in.-thick laminationsofstructural 6-7/8-in.-thick 5-lamassemblies,assum- and lateralloads(seeFigure2). Walls are system where thewalls resistbothgravity CLT Option ing thelatestmaterialdesignstandards. us- designed for strengthandserviceability andlateralforce-resistingity systems were governed thedesign. Membersofthegrav SEI 7-10). Itwas assumedthatwindloads for BuildingsandOtherStructures (ASCE/ the 2010 editionofMinimumDesignLoads of theInternationalBuildingCode(IBC)and mined in accordance with the 2015 edition Reinforced Concrete Structures Timber (CLT) andCast-in-place Cost Comparison ofCross Laminated Design loadsfor thebuildingswere deter Additional for cost data some actual CLT Axonometric and plan views of the CLT This Technical Noteprovides asummary Spans selected for the CLT option are The CLT optionutilizes abearing wall - - - nents attached tothebuildingframe. the floorslabsorpre-manufactured compo- were assumed tobeeitheranextension of load bearing and non-structural. Balconies and exterior walls were assumed tobenon- cores. Except for theshear walls, allinterior cast-in-place reinforced concrete optionis range from$2to$6persquare foot. and fireprotectioncosts are expected to dampening andfireprotection. Acoustical square foot excluding costsfor acoustical was estimated to be $48 to $56 per gross of thestructural frameintheCLT option edgeable inCLT construction, thecost Cost Comparison tem consistsof9-in.-thick slabs(ƒ throughout thestructure. The flatplatesys- 60 ASTM A615 reinforcement areutilized option, normalweight concreteandGrade Cast-in-place ConcreteOption to thebuildingframe. be pre-manufactured componentsattached CLT Balconies framing. were assumedto anddonotrequire to benon-loadbearing, south sidesofthebuildingwere considered (SCL) beam. Exterior walls on the northand solved withastructural compositelumber integrated intothewall assemblies,orre- Wall openingswere assumedtobeeither and wall panelstotransfer lateralloads. screw anchors were usedbetweenfloor also beutilized for fireresistance. with aconcretetoppingslab,which may bemitigated Floor vibrationcantypically vibration potentialfor CLT floorsystems. cast-in-place concreteoptionduetothe (ƒ sists of12-in.-thick concreteshearwalls ft-0 in.oncenter(seeFigure4). psi), which arespacedatamaximumof25 psi) and16 in.by 24in.columns(ƒ c The costofthestructural frameinthe Based ona surveyofcontractorsknowl- In thecast-in-placereinforced concrete Steel angleclipsfastened withstructural The lateral force-resisting system con- ’=6,000 psi) around the stair andelevator psi)aroundthestair ’=6,000 c c ’=6,000 ’=6,000 ’=5,000 Figure 1 – Axonometric View of the CLT Option.

Figure 2 – Plan View of the CLT Option.

2 Cost Comparison of Cross Laminated Timber (CLT) and Cast-in-place Reinforced Concrete Structures [ETN D-5-18] Figure 3 – Axonometric View of the Reinforced Concrete Option.

Figure 4 – Plan View of the Reinforced Concrete Option.

CRSI Technical Note 3 estimated to range from $42 to $46 per gross square cores, and the wood superstructure is supported by a re- foot. Additional cost for acoustical dampening may be inforced concrete podium slab at the first elevated level. required, which is estimated to be in the range of $1 to $2 per square foot. Conclusion

It is evident from the results of this study that The results from this study clearly show that CLT struc- the cost of the structural frame for the CLT option tures cost significantly more than cast-in-place reinforced is about 16 to 29% greater than that of the cast-in- concrete structures. Square foot costs of some actual place reinforced concrete option. CLT projects are also greater than comparable reinforced concrete structures based on national average structure Additional CLT Cost Data costs. It is expected that the costs would be even great- er for CLT projects outside the Pacific Northwest where Cost information for the structural frame of CLT proj- the majority of CLT production facilities are located. ects located in North America is given in Table 1. Reference Typical bay sizes in the Brock Commons Student Residence are 9.4 ft by 13.1 ft. Floor framing consists of Cary Kopczynski & Company, 2018, Cross Laminated 6.7-in.-thick CLT members. It is assumed that these bay Timber Feasibility Study - A comparison between cross sizes were used so that beams would not be required; laminated timber and cast-in-place concrete framing for using beams would have significantly increased floor-to- mid-rise urban buildings. Seattle, WA. floor heights and overall cost. Seismic forces are resist- ed solely by 18-in.-thick reinforced concrete walls in the

Table 1 - CLT Cost Data

Project Description Location Cost Information Notes

Square foot cost does not include cost One-story industrial building Rockwood, TN $55/square foot for fireproofing

Square foot cost does not include cost Two-story commercial building Whitefish, MT $60/square foot for fireproofing and acoustical damping

Square foot cost does not include cost Four-story commercial building Eugene, OR $54/square foot for fireproofing, acoustical damping, and concrete topping slabs CLT framing cost approximately $26 / 18-story college dormitory Square foot cost for CLT framing Vancouver, BC square foot (US) more than cast-in- (Brock Commons Student Residence) includes cost for fireproofing place reinforced concrete framing

Some of the mass timber structure is 12-story mixed-use building (Framework) Portland, OR $65/square foot unprotected

Contributors: The principal author of this publication is David Fanella, PhD, PE, SE, FACI, FASCE. Concrete Reinforcing Keywords: Buildings, CLT, cost, cost comparison, reinforced concrete Steel Reference: Concrete Reinforcing Steel Institute – CRSI [2018], “Cost Comparison of Cross Lami- Institute nated Timber (CLT) and Cast-in-place Reinforced Concrete Structures”, CRSI Technical Note ETN- 933 North Plum Grove Rd. D-5-18, Schaumburg, Illinois, 4 pp. Schaumburg, IL 60173-4758 p. 847-517-1200 • f. 847-517-1206 Historical: None. New Technical Note. www.crsi.org Note: This publication is intended for the use of professionals competent to evaluate the signifi- cance and limitations of its contents and who will accept responsibility for the application of the Regional Offices Nationwide material it contains. The Concrete Reinforcing Steel Institute reports the foregoing material as A Service of the Concrete Reinforcing Steel Institute a matter of information and, therefore, disclaims any and all responsibility for application of the stated principles or for the accuracy of the sources other than material developed by the Institute. ©2018 This publication, or any part thereof, may not be reproduced without the expressed written consent of CRSI.