Shallow Flat Sofﬁt Precast Concrete Floor SystemSimanjuntak [“System for joining precast...

Shallow Flat Soffit Precast Concrete Floor SystemEliya Henin, Ph.D., S.M.ASCE1; George Morcous, Ph.D., P.E., A.M.ASCE2; and

Maher K. Tadros Ph.D., P.E., M.ASCE3

Abstract: It is a key economic criterion for multistory residential and office buildings to have a shallow floor that minimizes floor height andsaves in the cost of architectural, mechanical, and electrical systems. This paper presents the development of a new precast concrete floor systemthat eliminates the need for column corbels and beam ledges while being shallow. The proposed system can achieve a span-to-depth ratio of 30and flat soffit while being consistent with prevailing erection techniques. The proposed system consists of continuous precast columns, pre-stressed rectangular beams, hollow-core (HC) planks, and cast-in-place composite topping. The paper presents the construction sequence ofthe new system and focuses on testing HC-beam connections without ledges in a full-scale specimen. Testing results indicate that a 30-cm-deepflat soffit precast floor system has adequate capacity to carry gravity loads (including 488 kg/m2 live load) in a 9.14- 3 9.14-m bay size. Also,testing shows that shear capacity of the proposedHC-beam connections without ledges can be accurately predicted using the shear friction theory.DOI: 10.1061/(ASCE)SC.1943-5576.0000135. © 2013 American Society of Civil Engineers.

CE Database subject headings: Precast concrete; Floors; Beams; Columns; Multi-story buildings.

Author keywords: Precast concrete; Flat soffit floor; Hollow-core; Shallow beam; Beam ledge; Column corbel.

Introduction

Conventional hollow-core (HC) floor systems consist of HC plankssupported by inverted-tee (IT) precast, prestressed concrete beams,which are, in turn, supported on column corbels or wall ledges.These floor systems provide a rapidly constructed solution to mul-tistory buildings that is economical, fire-resistant, and that has ex-cellent deflection and vibration characteristics. The top surface ofHC floor systems can be a thin nonstructural cementitious topping orat least 5-cm-thick concrete composite topping that provides a lev-eled and continuous surface. Despite the advantages of conventionalprecast HC floor systems, they have two main limitations: (1) rela-tively low span-to-depth ratio; and (2) presence of floor projections,such as column corbels and beam ledges. For a 9.14-m-bay size,a conventional precast HC floor systemwould require a 71-cm-deepIT plus a 5-cm topping, for a total floor depth of 76 cm, which resultsin a span-to-depth ratio of 12 (PCI 2010). In addition, this floorwould have a 30-cm-deep ledge below theHC soffit and a 14-in.-deepcolumn corbel below the beam soffit.

In contrast, posttensioned cast-in-place concrete slab floor sys-tems can be built with a span-to-depth ratio of 45 and a flat soffit,which results in a structural depth of 8 in. for the 30-ft-bay size (PTI2006). If the structural depth of precast floor systems can come closeto that of a posttensioned cast-in-place concrete slab system, then

precast concrete could be very favorable because of its rapid con-struction and high-product quality. Reducing the depth of thestructural floor results in reduced floor height, which, in turn, createssavings in architectural, mechanical and electrical (AME) systemsand may allow for additional floors for the same building heightwhen height restrictions exist. The cost of AME systems is ap-proximately 75–80% of the total initial and operation cost, and anysmall savings in these systems would have a significant impact onthe building life cycle cost.

Although the use of column corbels and beam ledges is thecommon practice in parking structures and commercial buildings, itis not aesthetically favorable in residential buildings (e.g., hotels).False ceilings are used in these applications to hide the unattractivefloor projections, which results in reduced vertical clearance.Elimination of floor projections combined with shallow structuraldepth will improve the building aesthetics and overall economics.

The main objective of this paper is to present a flat soffit shallowprecast floor system for multistory residential and office buildings.The developed system should minimize the limitations of existingprecast floor systems with regard to span-to-depth ratio and floorprojections, while maintaining speed of construction, simplicity,and economy of conventional precast floor systems. To achieve thisgeneral objective, the following specific three goals were identifiedfor the proposed system:• Has a span-to-depth ratio of at least 30 to reduce the floor height

and save in AME costs;• Eliminates the column corbels and beam ledges to provide addi-

tional space and flat soffit for residential and office buildings; and• Consists of easy-to-produce and erect precast/prestressed com-

ponents with minimal cast-in-place operations to ensure practi-cality, economy, quality, and speed of construction.The paper is organized as follows: first, a review of the existing

precast concrete floor systems is presented; second, the developedsystem and its construction sequence are discussed; third, the maindesign concepts of the developed system are explained; fourth, theexperimental investigation conducted to evaluate the shear capacityof HC-beam connections is presented; and finally, research con-clusions are summarized.

1Structural Engineer, Ebmeier Engineering, LLC, 58187 250th St.,Glenwood, IA 51534.

2Associate Professor, Durham School of Architectural Engineering andDesign, Univ. of Nebraska-Lincoln, Omaha, NE 68182 (correspondingauthor). Email: [email protected]

3Principal, econstructUSA, 11823 Arbor St., Omaha, NE 68144; andEmeritus Professor of Civil Engineering, Univ. of Nebraska-Lincoln,Omaha, NE 68182.

Note. This manuscript was submitted on September 28, 2011; approvedon July 20, 2012; published online on July 27, 2012. Discussion period openuntil October 1, 2013; separate discussions must be submitted for individualpapers. This paper is part of the Practice Periodical on Structural Designand Construction, Vol. 18, No. 2, May 1, 2013. ©ASCE, ISSN 1084-0680/2013/2-101–110/$25.00.

PRACTICE PERIODICAL ON STRUCTURAL DESIGN AND CONSTRUCTION © ASCE / MAY 2013 / 101

Pract. Period. Struct. Des. Constr. 2013.18:101-110.

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http://dx.doi.org/10.1061/(ASCE)SC.1943-5576.0000135

mailto:[email protected]

Precast Concrete Floor Systems

Low et al. (1991; 1996) developed a shallow-floor system formultistory office buildings. The system consists of HC planks, 2.44mwide and 40-cm-deep prestressed beams, and single-story precastcolumns fabricated with concrete cavities at the floor level. Thecolumn reinforcement in this patented system is mechanicallyspliced at the job site to achieve the continuity [M. K. Tadros andS. Low, “Concrete framing system,” U.S. Patent No. 5,507,124(1996)]. The beam weight and the use of single-story columns werediscouraging to US producers, although the system has been ex-tensively used overseas. Thompson and Pessiki (2004) developeda floor system of ITs and double tees with openings in their stemsto pass utility ducts. This floor system may be more appropriate foroffice buildings, because it does not provide either the shallow flooror flat soffit required for residential buildings. It is also challengingto coordinate IT openings with double tee space between stems.Hanlon et al. (2009) developed a total precast floor system for theconstruction of a 9-story flat-slab building. This system consistsof precast concrete stair/elevator cores, prestressed concrete beam-slab units, prestressed concrete rib-slab floor elements, variable-width beam slab, and integrated precast concrete columns witha column capital. The need for special forms to fabricate thesecomponents, the challenges of shipping column/floor pieces, and thelack of multistory precast columns are possible limitations of thissystem. Developed the Dycore floor system, which consists of ashallow soffit beam, Dycore floor slabs, and continuous cast-in-place/precast columns with block outs at the beam level. In thissystem, precast beams and floor slabs act primarily as stay-in-placeforms for major cast-in-place operations required to complete thefloor system. Dependence on the cast-in-place composite toppingmay be a disadvantage inU.S. practice as it slows down constructionand create inter-dependence between the two trades in the field.Simanjuntak [“System for joining precast concrete columns andslabs,” U.S. Patent No. 5,809,712 (1998)] developed a shallow-ribbed slab configuration without corbels. This is accomplished bythreading high-tensile steel wire rope through pipes embedded in thefloor system and holes in the columns. This system would requirea false ceiling to cover the slab ribs. Wise [“Composite concreteconstruction of two-way slabs and flat slabs,” U.S. Patent No.3,763,613 (1973)] introduced a method for building RC floors androofs employing composite concrete flexural construction with littleformwork. The bottom layer of the composite concrete floor isformed by using thin prefabricated concrete panels laid side by sidein place with their ends resting on temporary or permanent supports.The panels are precast with one ormore lattice-type girders or trussesextending lengthwise from each panel with their bottom chordsfirmly embedded in the panel and with the webbing and top chordsextending above the top surface of the panel. This system generallyrequires shoring during construction.

Filigree Wideslab System is presently used under the name ofOMNIDEC (Mid-State Filigree Systems, Inc. 1992). It is similar tothe Wise system previously described. Bellmunt and Pons (2010)developed a new floor system that consists of a structural grid ofconcrete beams with expanded polystyrene (EPS) foam blocks inbetween the beams. The grid has beams in two directions every0.81 m. The floor is finished with a light paving system on top anda light ceiling system underneath. This system hasmany advantages,such as lightweight, flat soffit, and thermal insulation. However,some of its disadvantages include a relatively large floor thicknessand a unique fabrication process. The Deltabeam is a hollow steel-concrete composite beam made from welded steel plates with holesin the sides (Peikko Group 2010). It is completely filled withconcrete after installation on site. Deltabeam acts as a composite

beam with the HC planks and the cast-in-place concrete. TheDeltabeam height varies based on the required span. For a 9.75-mspan, the Deltabeam can be 58 cm (53-cm-deep beam 1 5-cmtopping). Although this is 13 cm less than the conventional 28 in.deep precast/prestressed concrete IT, it requires shoring for erection.It also requires addition of shims, to the base plate to allowmatchingthe top of the 8 in. hollow core plank with the top of the Deltabeam.As will be seen in the following sections, the proposed system oversa shallower, less expensive, more corrosion and fire protected beamsthan the Deltabeam.

Proposed Precast Flat Soffit Floor System

The proposed floor system consists of precast continuous columns,precast rectangular beams, precast HC planks, and cast-in-placecomposite topping. The precast components can be fabricated us-ing the facilities readily available to precast producers in the UnitedStates. Fig. 1 presents the layout of an example building and thecomponents of the proposed floor system.

Fig. 2 shows a three-dimensional schematic representation of theconstruction sequence of the proposed system. The constructionsequence consists of the following steps, which are presented inFig. 2 in the same order [Henin et al. (2011)]:a. Multistory continuousprecast columns are erected and temporary

corbels are installed at each floor level. The temporary corbelscan be steel angles that are anchored to the column using high-strength threaded rods through sleeves in the precast columns.

b. Precast rectangular beams are placed on the temporary corbels.Steel angles are welded to the steel plates on top of beams andplates on column sides to torsionally stabilize beams duringHC erection.

c. Temporary beam ledges are installed to support the HC planks.These ledges can be steel tubes anchored to the beam soffitusing bolts and preinstalled coil inserts, or angles welded toplates embedded in the beam sides.

d. HC planks, which have the same thickness of the beam, areplaced on the temporary ledges for the entire floor to providea flat soffit.

e. Specially shaped steel bars (called hat bars and loop bars) areplaced in the HC keyways and preformed slots. Also, beamcontinuity reinforcing bars are placed in the beam recessthrough the column opening.

f. Flowable concrete is used to fill the HC keyways, beamrecesses, shear keys between HC planks and beam sides,and gaps between the beam ends and column sides.

g. Additional layers of beam continuity reinforcement are placedon top of the beam through the column opening and on eachside of the column. Also, topping reinforcement is installed.

h. Cast-in-place topping is placed to provide a composite, leveledfloor surface.

i. Temporary corbels and ledges are removed after the toppingconcrete reaches the required strength. This will provide a flatsoffit without projections. The temporary corbels and ledgescan remain in place if the owner prefers that; however, thestructural capacity of the floor system does not depend on thesetemporary attachments.

Design Concepts

Three key concepts were used to achieve the structural capacity ofthe proposed floor system under gravity loads:1. Increasing the beam width accommodates a large number of

prestressing strands in one row, which maximizes prestressing

102 / PRACTICE PERIODICAL ON STRUCTURAL DESIGN AND CONSTRUCTION © ASCE / MAY 2013


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Fig. 1. Layout of the example building (1 ft 5 0.305 m)

Fig. 2. Construction sequence of the proposed system



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eccentricity while minimizing the beam depth. Also, use of15-mm-diameter strands allows for higher prestressing forceusing fewer strands.

2. Achieving beam continuity for topping weight and live loadsimproves the beam resistance to gravity loads and eliminatesthe need for column corbels. This continuity requires havingopenings in the precast column at the beam level to allow thereinforcement in the beam recess to go through the column.This reinforcement, in addition to the reinforcement in thecast-in-place topping, resists the gravity load negative mo-ment. Beam continuity reinforcement, combined with a pre-formed shear keywill also provide adequate vertical supportfor the beam as it creates a hidden corbel.

3. The use of shear key on the beam sides eliminates the need forbeam ledges to support HC planks. Reinforcing bars used

across this connection allows for the transfer of the verticalshear from the HC planks to beam using shear friction theory.

Fig. 3 shows the cross sections of the precast, prestressed rect-angular beam designed for the example building floor shown inFig. 1. Cross sections in Figs. 3(a) and (c) present, respectively, themiddle and end sections of the beam with shear key, whereas crosssections in Figs. 3(b) and (d) present, respectively, the middle andend sections of the beam with hidden ledge. Fig. 4 shows the re-inforcement details of the beam-column connection (i.e., hiddencorbel) and HC-beam connection (i.e., shear key) for the examplebuilding floor. It should be noted that the design of these con-nections is conducted using the shear-friction design methodof ACI 318-11 Section 11.6.4 (ACI 2011). Grade 60 reinforcingbars and cast-in-place concrete are used to create shear-transfermechanism between the precast beam and column components,

Fig. 3.Middle and end sections of the beam with different HC-beam connections; (a) beam with shear key midspan section; (b) beam with hiddenledge midspan section; (c) beam with shear key end-span section; (d) beam with hidden ledge end-span section (1 ft 5 0.305 m; 1 in. 5 2.54 cm)

Fig. 4. Reinforcing details of beam-column and HC-beam connections (1 ft 5 0.305 m; 1 in. 5 2.54 cm)



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and between the precast HC and beam components. A coefficientof friction equal to 1.0 is used between the cast-in-place con-crete placed against the hardened precast concrete, because thecontact surface is intentionally roughened. HC-beam connection ismodeled as a hinge connection, whereas the beam-column con-nection is modeled as a moment-resisting connection because thecontinuity reinforcement extends beyond the negative momentregion. Flexural capacities of both midspan and end-span sectionsare calculated using the strain compatibility approach for the fol-lowing loading conditions:

• Simply supported noncomposite beam for prestressing force andbeam and HC self-weight;

• Continuous noncomposite beam for topping weight; and• Continuous composite beam for live load and superimposed dead

load.The resistance of the proposed floor system to lateral loads, such

as wind and seismic loads, was investigated.Wind and seismic loadswerecalculatedaccording toASCE7-05 (ASCE 2005) for the buildingshown in Fig. 1, assuming it was 21.9 m-high (6-story) buildingthatwas located in theMidwest region of theU.S. (i.e., wind speed of

Fig. 5. Plan view of the precast components of test specimen (1 ft 5 0.305 m; 1 in. 5 2.54 cm)

Fig. 6. Details of the tested four HC-beam connections (1 ft 5 0.305 m; 1 in. 5 2.54 cm)



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145 km/h and seismic category B). The building was analyzed usingtwo-dimensional frame models for both the beam and the HC direc-tions. Analysis results and design calculations showed the adequacyof the proposed system for lateral load resistance in the beamdirection. However, shearwalls would be needed in theHCdirectionfor lateral load resistance. For more information on lateral loadanalysis, please refer toHenin (2012) andMorcous andTadros (2011).

Experimental Investigation

The experimental investigation presented in this paper was carriedout to evaluate the shear capacity of four different HC-beam con-nections and the flexural capacity of the shallow rectangular beam.The flexural capacity of the beam for resisting gravity and lateralloads, flexural capacity of composite HC planks for resisting lateralloads, and shear capacity of beam-column connection without acorbel (i.e., hidden corbel) were evaluated through testing in ear-lier investigations (Morcous and Tadros 2011; Henin 2012). Thefull-scale test specimen shown in Fig. 5 consists of a 8.53-m-long,25-cm-thick, and 1.22-m-wide precast rectangular beam andtwelve 1.83-m-long, 25-cm-thick, and 1.22-m-wide HC segments.In the shown test setup, the beam was supported by three rollersupports (i.e., two end supports and one middle support) tominimize beam deflection while testing the capacity of HC-beamconnections. The beam was fabricated with two different alter-natives for HC connections: shear key and hidden ledge. For eachalternative, two temporary ledges were used to support HC planksduring construction: (1) steel tubes (HSS 1023 1023 6) wereattached to the beam soffit using 19 mm threaded rods, and coilinserts were embedded in the precast beam and removed after thetopping hardened; and (2) steel angles (L 43 33 3=8) werewelded to preinstalled beam side plates and remained in the spec-imen during testing. Fig. 5 shows the four different combinations ofbeam-HC connections tested in this investigation: hidden ledge withangle (north-west side), shear key with angle (north-east side),hidden ledge without angle (south-west side), and shear key withoutangle (south-east side). Fig. 6 shows the dimensions and reinforcingdetails of each of the four connections. HC planks used in this speci-men have two 30-cm-long and 38-mm-wide slots in the top surface, asshown in Fig. 7, to allow placing connection reinforcement.

Fig. 8(a) shows the specimen before placing the 5-cm-thick, cast-in-place concrete topping. The reinforcement ofHC-beamconnectionsconsists of the hat bars and loop bars shown in Figs. 8(b and c). Thehat bars were placed over the beam in the HC slots and keyways toresist the vertical shear between the beam and HC planks. The loopbars were placed in the HC slots to resist the horizontal shear be-tween the HC planks and the topping. Twenty-four strain gaugeswere attached to the reinforcement (six strain gauges in each con-nection), which are classified as follows: three gauges to the hat bars

and three gauges to the loop bars. After grouting the HC keyways,slots, and shear keys, topping reinforcement was installed. Eightstrain gauges were attached to the topping reinforcement (two ineach connection). Finally, concrete topping was poured, and tem-porary ledges were removed after reaching the specified strength.Table 1 shows the specified and attained concrete strength at the timeof testing for precast, grout, and topping concrete.

Fig. 7. Cross section and dimensions of the used HC segments (1 ft 5 0.305 m; 1 in. 5 2.54 cm)

Fig. 8. a) Installation of HC-beam connection reinforcement; b) hatbar; c) loop bar



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The following subsections present the test program that includestwo tests:1. Testing HC-beam connection

a. Hidden ledge with angle (north-west);b. Shear key with angle (north-east);c. Hidden ledge without angle (south-west);d. Shear key without angle (south-east); ande. Hidden ledge without angle by loading HC as a cantilever

(south-west)2. Testing beam flexural capacity.

Testing HC-Beam Connection

The purpose of this test is to evaluate the shear capacity of the HC-beam connections under gravity loads. The HC planks were loadedat their midspan in one side while clamping the other side of thebeam to maintain specimen stability. Testing was performed usingtwo jacks applying two concentrated loads to a spreader steel beamto create uniform load on the HC planks at 0.914 m away from theHC-beam connection. Loading continued to failure whilemeasuringthe deflection under the load using a potentiometer attached to thesoffit of the middle HC plank. The HC-beam connection was testedin two stages. In the first stage, HC planks were loaded up to 445 kN(222.5 kN each side), which created a shearing force at the con-nection of 73.4 kN per HC. This value is the ultimate shearing forcedue to factored dead and live loads. In the second stage, HC plankswere loaded up to the failure. The shear capacity of the HC-beamconnection using shear friction theory was predicted to be 930 kN(465 kN each side, which is 155 kN per HC). Also, the capacity ofthe composite HC planks in flexure and shear were predicted to be1,401 kN (700.5 kN each side, which is 233.5 kN per HC) and 1,068kN (534 kN each side, which is 178 kN per HC), respectively. Fig. 9shows the test setup.

Hidden Ledge with Angle (North-West)Two 578-kN jacks were used to test the connection. In the first stageof loading, the specimen performed well under ultimate design load,with no signs of failure or cracking. In the second stage, HC planks

were loaded up to 1,148 kN (574 kN each side). The test was stoppedafter reaching the ultimate load capacity of the used jacks. The ap-plied load creates a shearing force at theHC-beam connection of 191kN. This value is almost 2.6 times the demand and 23.2%more thanthe design capacity of the connection. At that load, the connectiondid not crack, whereas small shear cracks were observed in the otherend of the HC.

Shear Key with Angle (North-East)Two 1,780-kN jacks were used in this test. The specimen performedwell under ultimate design loadwith no signs of failure or cracking. Inthe second stage,HCplankswere loaded up to 1,068 kN (534 kNeachside) without even cracking the connection. The test was stoppedbecause of the shear failure of theHCplanks. The applied load created178 kN shearing force on each HC. This value is almost 2.4 times thedemand and 15% more than the design capacity of the connection.

Hidden Ledge without Angle (South-West)Two 1,780-kN jacks were used in this test. The specimen performedwell under ultimate design loadwith no signs of failure or cracking. Inthe second stage, HC planks were loaded up to 908 kN (454 kN ineach side)without even cracking the connection. The test was stoppedbecause of the shear failure of theHCplanks. The applied load created151-kN shearing force on each HC. This value is almost 2.1 times thedemand and equal to the design capacity of the connection.

Shear Key without Angle (South-East)Two 578-kN jacks were used in this test. The specimen performedwell under ultimate design loadwith no signs of failure or cracking. Inthe second stage,HCplankswere loaded up to 1,010 kN (505 kNeachside) without even cracking the connection. The test was stoppedbecause of the shear failure of theHCplanks. The applied load created168-kN shearing force on each HC. This value is almost 2.3 times thedemand and 8% more than the design capacity of the connection.

Fig. 10 presents the load deflection relationships of the fourtested connections, and Fig. 11 shows the typical mode of failure,which is the shear failure of the HC planks at the other end.

Testing Beam-HollowCoreConnection byLoading theHollowCore as a CantileverThe four previous tests were done by applying the load at themidspan of the HC, and the failure occurred in the HC withouteven cracking the proposed HC-beam connections. Therefore, toinvestigate the full-shear capacity of these connections, the HCwas loaded as a cantilever. Fig. 12 shows the test setup, whereHC planks were loaded on the free end (south-west side) while

Table 1. Specified and Actual Concrete Compressive Strength at Timeof Testing

Component Specified strength (MPa) Actual strength (MPa)

Precast beam 55.2 64.7Grout 27.6 55.4Topping 24.1 39.1

Fig. 9. Test setup for HC-beam connection (1 ft 5 0.305 m)



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clamping the other end (south-east side) to maintain specimenstability. Testing was performed to the hidden ledge connectionwithout angle by applying a uniform load on the cantilevered HCat 1.22 m from the center of the beam, while measuring thedeflection at midspan of the HC. The clamped side was clampedat 1.52 m from the center of the beam. Fig. 13 plots the load-deflection relationship. This plot indicates that the three composite

HC planks in the south-west side were able to carry 623 kN, whichcorresponds to a total shear force of 657 kN and includes the self-weight of the HC and topping (219 kN per HC). This is almost threetimes the demand and 40%more than the design capacity of the HC-beam connection. Fig. 14 plots the load-strain relationships forconnection reinforcement, which indicate that the topping rein-forcement and hat bars reached the yield stress. The test was stoppedbecause the shear failure of the HC at the clamped side and severecracking of the connection. Table 2 shows all HC-beam connectiontest results.

Testing the Beam Flexural Capacity

The purpose of this test is to evaluate the positivemoment capacity atthe midsection of the composite beam. One 1,780-kN jack was usedto apply a concentrated load on the beam at 4.19m from the centerlineof roller supports, up to failure, whilemeasuring the deflection underthe load. Fig. 15 shows the load-deflection relationship. The load-deflection relationships show a linear behavior up to the crackingload, which was approximately 222 kN. This plot indicates that thebeam was able to carry a load up to 405 kN, which corresponds toa positive moment capacity at the critical section of 765 kN.m(including the moment caused by the self-weight of beam, HC, andtopping). The ultimate positivemoment caused by factored dead andlive loads was calculated to be 765 kN.m (demand), which is 30%below themeasured capacity. The nominal capacity of the compositebeam predicted using strain compatibility approach was found to be976 kN.m, which is very close to the actual capacity. It should benoted that the point load equivalent to live load is approximately 218kN, and the corresponding final deflection is approximately 19 mm,whereas the allowable deflection equals 24 mm.

Summary and Conclusions

A common option for constructing flat soffit shallow floors in mul-tistory buildings is using posttensioned cast-in-place concrete flatslab. The system being proposed here is less complicated, less ex-pensive, and most importantly, less dependent on site construction.Current conventional precast concrete floor systems are relativelythick and require the use of beam ledges to support HC planks andcolumn corbels to support beams. The proposed floor system

Fig. 10. Load-deflection relationships for the four HC-beam connection tests (1 in. 5 2.54 cm; 1,000 lb 5 4.45 kN)

Fig. 11. HC shear failure for one of the tested connections

Fig. 12. Test setup for loading the HC-beam connection as a cantilever(1 ft 5 0.305 m)



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Fig. 13. Load-deflection curve for the HC-beam connection loaded as a cantilever (1 in. 5 2.54 cm; 1,000 lb 5 4.45 kN)

Fig. 14. Load-strain relationships for HC-beam connection reinforcement (1,000 lb 5 4.45 kN)

Table 2. Summary of HC-Beam Connection Test Results

Test ID Test titleMeasured capacity

per HC (kN)Design capacityper HC (kN)

Demand perHC (kN)

Shear capacityper HC (kN) Observation

A Hidden ledge with angle(three-point loading)

191.3 155.2 73.4 177.9 Test stopped because ofreaching the capacity of theloading jacks

B Shear key with angle(three-point loading)

177.9 HC shear failure

C Hidden ledge without angle(three-point loading)


D Shear key without angle(three-point loading)


E Hidden ledge without angle(HC loaded as a cantilever)

218.9 HC shear failure and severalcracks in the connection

Note. ID 5 identification.



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combines the shallowness of the posttensioned cast-in-place floorsand the superior speed and quality of the conventional precast system.The paper summarized the main features of the proposed system.Construction sequence, and themain design concepts are covered. Full-scale testing of four HC-beam connections without ledges was con-ducted to evaluate the behavior and shear capacity of these connec-tions. Based on the test results, the following conclusions can bemade:1. HC-beam connections made of the proposed shear key and

hidden ledge with and without temporary support anglesperformed very well. Their shear capacity exceeded the pre-dicted values and significantly exceeded the demand. None ofthese connections failed because the tested HC planks failed inshear before the failure of the connections.

2. The capacity of the proposed HC-beam connections can beaccurately predicted using the shear friction theory.

3. Because the shear capacity of the HC-beam connections withoutsteel angle was adequate, steel angles are considered to betemporary ledges that donot affect thefire rating of the building.

4. The results of testing full-scale specimen do not only indicatethe efficiency of the proposed system but also the consistencyof its performance.

5. The flexural capacity of the shallow prestressed beam exceededthe demand and was accurately predicted using the straincompatibility flexural theory.

Acknowledgments

The writers wish to acknowledge EnCon, Denver, CO and ConcreteIndustries Inc., Lincoln, NE, for specimen donations.

References

American Concrete Institute (ACI). (2011). “Building code requirementsfor structural concrete and commentary.” ACI 318-311, FarmingtonHills, MI.

ASCE. (2005). “Minimum design loads for buildings and other structures.”ASCE 7-05, Reston, VA.

Bellmunt, R., and Pons, O. (2010). “New precast light flooring system.”3rd Fib Int. Congress, Precast/Prestressed Concrete Institute (PCI),Chicago.

Finforck Industries. (1992). “Composite dycore office structures.”Companyliterature, Orlando, FL.

Hanlon, J. W., Dolan, C.W., Figurski, D., Deng, J., and Dolan, J. G. (2009).“Precast concrete building system components for the Westin ResortHotel: Part 1.” PCI J., 54(2), 88–96.

Henin, E. (2012). “Efficient precast/prestressed floor system for build-ing construction.” Ph.D. thesis, Univ. of Nebraska-Lincoln, Lincoln, NE.

Henin, E., Morcous, G., and Tadros, M. (2011). “Construction of a shallowflat soffit precast floor system.” 47th ASC Annual Int. Conf., AssociatedSchools of Construction (ASC), Windsor, CO.

Low, S., Tadros, M. K., Einea, A., and Magana, R. (1996). “Seismicbehaviour of a six story precast concrete office building.” PCI J., 41(6),56–75.

Low, S., Tadros, M. K., and Nijhawan, J. C. (1991). “A new framing systemfor multi-story buildings.” Concr. Int., 13(9), 54–57.

Mid-State Filigree Systems, Inc. (1992). The Filigree Wideslab method ofconcrete deck construction: Company literature, Mid-State FiligreeSystems, Inc., Cranbury, NJ.

Morcous, G., and Tadros, M. K. (2011). “Shallow hollow-core floor sys-tem.” Technical Rep. 07-08, Charles Pankow Foundation, Claremont,CA.

Peikko Group. (2010). “Delta beam composite beams.” Peikko News,Æhttp://www.peikko.comæ (Jun. 12, 2010).

Pessiki, S., Prior, R., Sause, R., and Slaughter, S. (1995). “Review ofexisting precast concrete gravity load floor framing systems.” PCI J.,40(2), 70–83.

Post-Tensioning Institute (PTI). (2006). Post-tensioning manual. 6th Ed.,PTI, Phoenix.

Prestressed Concrete Institute (PCI). (2010). PCI design handbook, 7th Ed.,PCI, Chicago.

Thompson, J. M., and Pessiki, S. (2004). “Behaviour and design ofprecast/prestressed inverted tee girders with multiple web openingsfor service systems,” ATLSS Rep. 04-07, Lehigh Univ., Bethlehem, PA.

Fig. 15. Load-deflection curve for the beam flexural test (1 in. 5 2.54 cm; 1,000 lb 5 4.45 kN)



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http://www.peikko.com

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