Annabel B. Shephard1, Erica C. Fischer2, Andre R. Barbosa3, Arijit Sinha4

1 Graduate Research Assistant, School of Civil and Construction Engineering, Oregon State University2 Ph.D., P.E., Assistant Professor, School of Civil and Construction Engineering, Oregon State University3 Ph.D., P.E., Associate Professor, School of Civil and Construction Engineering, Oregon State University4 Ph.D., Associate Professor, Wood Science and Engineering, Oregon State University

OBJECTIVEInvestigate the fire performance of timber-concrete compositefloors under service loading conditions for both cross-laminatedtimber (CLT) and nail-laminated timber (NLT).

BACKGROUND AND MOTIVATIONNorth America is rapidly adopting the use of mass timber productsin mid- and high-rise building construction, especially CLT, whichlends itself to:

• Offsite prefabrication,

• Greater precision in production,

• Decreases construction time,

• Provides for lighter foundation systems, and

• Reduced seismic demands.

In many mass timber buildings, floors are constructed with aconcrete topping to improve the acoustic, vibration, or fireperformance. Engineers have begun to design mass timber floorsto be composite with a concrete topping to span longer distances.

Mass timber high-rise building construction is currentlyhindered by the confines of the building codes[1]. The timber-concrete composite systems have an improved fire performance ascompared to the timber only floor systems. This improvementcould lead to taller code-allowed mass timber buildings.

RESULTS

ACKNOWLEDGEMENTSThis work is in collaboration with our industry partners actively working on mass timber buildings. These include KPFF, Skidmore Owings & Merrill, Katerra, Arup, and Forest Products Laboratory. This work is funded by the TallWood Design Institute.

CCE3

TIMBER-CONCRETE COMPOSITE FLOORS• Composite action achieved through mechanical connections

• Can increase the stiffness and strength of the timber floorsystems

• Gap in knowledge of the fire performance of composite floorsystem results in conservative design, not accounting for theaddition of concrete

STATE-OF-THE-PRACTICECurrently, mass timber construction is categorized ascombustible. This limits the height of a timber building [1].

• Timber construction is categorized as Type III, IV, and Vconstruction in the International Building Code [1].

• Types III and IV construction can have a maximum height of 85feet with an increased level of fire protection and structuralperformance [1].

• For high-rise mass timber structures to be characterized asType I category, the primary structure must be non-combustible, and therefore requires an alternative engineeringapproach to structural fire engineering [1].

• Type I construction represents a large market for theOregon timber industry. This research project will reducethe burden on project teams and facilitate the use of timberin many more projects around Oregon and the UnitedStates.

Figure 1: CLT and NLT specimens, right and left respectively, prior to the concrete pour. The mechanical connections, (screws for CLT and plates for NLT) that will achieve the

composite action of the floor system are visible.

Figure 6: Temperature-dependent moment capacity of CLT-concrete composite floor specimen [3] , [4]

FIRE PERFORMANCE OF TIMBER-CONCRETE COMPOSITE FLOORS

Figure 2: Cross-section of CLT specimens

TESTING METHODOLOGY• Testing occurred in a gas-fire furnace at the National Research

Council in Ottawa, Canada

• Heating procedure adhered to the ASTM E119 standard firecurve, shown in Figure 6

• Service loading conditions was applied with hydraulic ramssimulating a distributed loading

• Temperature distributions through the cross-section weremeasured with Type K thermocouples

• Panel ends were simply supported by rollers during testing

• Failure was defined as the loss of load carrying capacity

Figure 4: (a) Hydraulic rams suspended above panels prior to testing (b) Specimens being heated from below. NLT on the left, CLT on the right (c) End of test, specimens being removed from furnace. Structural failure of the CLT specimen is shown on the left and

the NLT specimen is on the right.

SPECIMEN DESCRIPTIONSCLT• 5-PLY V2

• Spruce-Pine-Fir

• 15’-9” x 4’-0”

• 2-¼” NW Concrete

• 6” Spline

Composite Connectors

• Fully-Threaded Screws

• ASSY VG CYL

• ⁄3 8” x 7- ⁄7 8”

• 12” o.c., at 45˚

• Embedded:

• 4- ⁄1 5” into timber

• 1- ⁄3 8” into concrete

Figure 5: Plotted temperature distributions through the cross section for CLT, left, and NLT, right, at selected points of time during the test.

APPLICATIONSExperimental tests are essential for demonstrating the fundamentalbehavior of timber-concrete composite systems. These testsdemonstrated that timber-concrete composite floor systems canhave significant fire resistance. Future work to be done includes aseries of push-out tests to quantify the force-slip behavior of thecomposite connections used in these tests. The complied results ofboth tests will be a cohesive package of data demonstrating theperformance of TCC systems.

REFERENCES[1] ICC, International Building Code (IBC). Washington D.C.: International Code Council, Inc., 2018.[2] ASTM, “Standard test methods for fire tests of building construction and materials (ASTM E119-18a),” West Conshohocken, Pennsylvania, 2018.[3] CEN, Eurocode 5-design of timber structures-Part 1.2: general rules-structural fire design. CEN ENV 1993-1-2, 2005.[4] Frangi, A; Fontana, M, “Elasto-Plastic Model for Timber-Concrete Composite Beams with Ductile Connection” Structural Engineering International, 12:1, 47-57, 2003

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Table 1. Resulting char rates (average)

Location (in)

Charring rate (in/hr)

CLT NLT

1.38 1.55 1.60

2.75 1.89 1.36

4.13 1.42 1.50

Table 2. Unloading time and remaining thickness

CLT NLT

Unloaded at 105 min 187 min

Thickness at end of test (187 min)

~1.0 in ~1.5 in

a b

c

NLT• No.2 Visual grade

• Spruce-Pine-Fir

• 15’-9” x 4’-½”

• 3” NW Concrete

• 1-½” Expansion Gap

Composite Connectors

• Truss Plates

• Mitek MT-20

• 10” x 5”

• 24” o.c.

• Embedded:

• 3” into timber

• 2” into concrete

Figure 3: Cross-section of NLT specimens

*Specimen was

unloaded after

105 minutes*

CLT unloaded at 105.33 min

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