texas’ first hybrid clt office building: designing class a ... · and character, progression and...

Disclaimer: This presentation was developed by a third party and is not funded by WoodWorks or the Softwood Lumber Board.

Texas’ First Hybrid CLT Office Building: Designing Class A Office Space with Modernity & CharacterStructural Considerations in Hybrid Mass Timber Construction

Presented by:Michael Dupras, PE, SE, LEED Green AssociateBart Whatley, AIA

“The Wood Products Council” is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider #G516.

Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request.

This course is registered with AIA CESfor continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.

______________________________Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

901 E 6th Street in Austin is a unique 5-story project—and the first commercial structure in Austin to utilize cross-laminated timber (CLT). Creating Class A Office space in a neighborhood as special as East Austin requires integration of modernity and character, progression and heritage, and CLT helped to accomplish these goals.

This presentation will discuss the design decisions that led to the use of CLT, and the lessons learned along the way—from building official interaction, to design and detailing strategies for a steel/CLT hybrid structure, to construction administration, and more.

Additionally, structural considerations when designing hybrid mass timber structures will be discussed, and a number of sample projects will be referenced.

Course Description

1. Highlight the recent use of mass timber in a hybrid steel/timber office building in Austin.

2. Consider the unique design criteria associated with mass timber office buildings, including programmatic layout and code compliance.

3. Review detailing techniques for CLT structures that result in cost-effective solutions that meet code requirements for fire and life safety, structural performance, and acoustics.

4. Discuss approaches to designer/building official interaction needed to realize successful mass timber commercial projects in Texas.

Learning Objectives

Bart is an Architect with the design firm for the 901 East 6th Street Office Building. Bart

has a background in mixed-use, office and adaptive re-use projects, and has been a

project architect on some of the first mixed-use, urban infill projects to be developed in

the East Side area of Austin. Recently Bart has been working on the first CLT commercial

office structure to be built in Texas. Community design involvement includes past

experience on the Austin Downtown Commission, the AIA Austin Board, and present

membership on the City of Austin Design Commission.

Michael is an Associate with DCI Engineers and a licensed Professional Engineer in Texas

(PE) and Washington (SE). Michael is experienced in mass timber design including

projects in Texas. Michael leads the sustainability effort for his firm and is a strong

advocate for mass timber as a sustainable alternative to traditional steel and concrete

structures. Prior to becoming a structural engineer, Michael proudly served in the United

States Marine Corps.

Presenter biographies

1. Project introduction: Context, scale, purpose and how/why mass timber was chosen.

2. Why a hybrid structure? Advantages, disadvantages from a design and construction standpoint.

3. Structural Considerations of a hybrid structure. Design Drivers. Lesson’s Learned. Other hybrid systems.

4. Design particulars: Building department approval. Fire ratings, acoustics, details. Coordination with the contractor and CLT manufacturer.

Sections

901 E 6th Street in Austin is a unique 5-story project—and the first commercial structure in Austin to utilize cross-laminated timber (CLT). Creating Class A Office space in a neighborhood as special as East Austin requires integration of modernity and character, progression and heritage. CLT helped to accomplish these goals. Features of the 130,000 sf building include efficient floor plates, 14-ft floor-to-ceiling heights with 9 ft and taller windows outdoor terraces & other functional common areas, bike storage, and underground parking.

Introduction: 901 East 6th Street Office Building

The use of mass timber floor plates and steel allowed the project to achieve long spans from core to perimeter, eliminating columns within the open office floor space.

This presentation will discuss the design decisions that led to the use of CLT, and the lessons learned along the way—from building official interaction, to design and detailing strategies for a steel/CLT hybrid structure, to construction administration, and more.

901 East 6th Street Office Building

1. Architect- TB/DS – THOUGHTBARN / DELINEATE STUDIO LLC, led by partners Bart Whatley AIA, Robert E Gay, and Lucy Begg AIA.

2. The Owner’s Design Team was comprised of Will Marsh, Bryce Miller, Richard Kooris and Dennis McDaniel.

3. Structural Engineering- LEAP! Structures

4. MEP Engineering- Bay & Associates

5. Landscape Architecture- DWG Landscape Architecture

6. Civil- LOC Civil

7. Fire Engineering- Arup

8. Contractor- DCA Construction

9. CLT Panel Manufacturer- Structurlam

Building design leadership

East Austin. The Saltillo TOD, a city initiated transit oriented development started in 2007 planned for infill development while seeking to maintain a place for artisans in the area. Development started in a significant way in 2014 with multifamily and offices mostly catering to high tech.

Project context

The design and character of this building is informed by our admiration for the elegant and functional use of wood, steel and masonry in classic industrial factories built at the dawn of the Industrial Age. This building seeks to reimagine those manufacturing halls with a contemporary execution of high ceiling open floorplates, filled with natural light and the muscular exposure of the steel and wood structural materials.

The building explores new sustainable approaches utilizing mass timber within the office building typology.

Inspiration & design

The lobby is conceived as an extension of the street with a large bi-fold door at the entrance while wrap-around balconies on the second level and operable windows encourage a lively street-facing facade.


The raw wood/steel interior, reminiscent of early 20th century warehouses, is complimented by an exterior cladding of tapered mild steel that will patina over time.


Much like the formation of a tree, Cross Laminated Timber derives its strength from layer upon layer of smaller wood fibers to become a larger scale structural element. The wood ceiling above you is the bottom surface of seven inch thick CLT.

Materiality

This feature wall was created by stacking 243 individual salvaged off-cuts of the CLT decking used in the construction of this building. The undulating screen design allows viewers to examine the exposed laminations of the CLT system that are normally hidden from view as a building material, while appreciating the play of light on the timber.

Materiality

1. Mass timber selected for its materiality and ability to create a warm, quality ceiling. The material also fit within team sustainability goals.

2. What ultimately allowed mass timber to become a reality for this project was shared values amongst the team and a willingness of the developer to take a chance.

3. A shared focus on design supported a creative process of considering innovative materials & systems.

4. Leasing broker feedback has been that CLT helped generate interest, assisted in faster leasing, and helped support higher lease rates.

Materiality

Evaluation of structural systems.

1. The project started out with a Design/Build process.

2. The contractor and structural engineer assisted with bay size studies for all mass timber and for hybrid structural systems.

3. Shafts have a different rating than the frame, so steel braces were used for lateral support.

4. Speed of construction was considered but the main consideration became bay sizes.

Hybrid structure

Why a hybrid structure?

Steel allowed longer spans for an open floor plan with minimal columns.

Hybrid structure

While the developer was willing to use an innovative material, they did not want to push past the norm of what leasing brokers and tenants were used to seeing for an office layout.

Hybrid structure

.

Structural considerations

Topics

- Why Steel/Timber Hybrid

- Lessons Learned

- Other Timber Hybrid Systems

Three Takeaways

- Keep the Timber Columns

- Detail for Field Adjustability

- Focus on Value

Structural Considerations

Why Introduce Steel into Timber System?

• More Open Layout (Developer or Parking Driven): Steel can achieve longer spans with less weight.

§ Don’t underestimate the positive impact of timber columns within space

§ You can have timber columns with steel framing

• Shallower Structural Depths (Design Driven): Steel can achieve shallower sections for same span (30” glulam vs. 24” WF beam)

§ Lower floor-to-floor heights/higher ceilings

§ More space for MEP systems

§ Various steel beam capacity at same depth

Structural Considerations: Why Hybrid


• Structural Efficiency (Engineering Driven):

§ Steel can be structurally complementary to timber and is often used in areas of highly concentrated forces – connections, braces, columns, trusses

§ Steel sometimes needed for demand – long spans, transfer beams, ductility (seismic)

• Aesthetics (Architecturally Driven): Steel can be aesthetically complementary to timber

§ Connections, braces, trusses


Flatiron PDX


http://www.woodworks.org/wp-content/uploads/CS-Bullitt.pdf


§ Cost vs. Value (Process Driven): When can steel add value to a timber project?

§ When it cost less? When it’s faster? When it’s familiar?

§ Focus on adding value: defining benefit vs. cost

Ø Understand project goals (aesthetics, sustainability, function, schedule, occupant experience, etc.)

Ø Collective team decisions to balance needs/goals


Timber/Steel Hybrid Lesson’s Learned:

Fire Rating: If intent is to leave steel exposed, target an un-protected (zero-hour) construction type.

Timber/Steel Trade Sequencing (GC): Lead/communicate to integrate sequencing of trade partners to prevent delays. Recommend GC self-perform CLT installation.

Tolerances: Timber tolerances not always defined and may vary by manufacturer. Detail for field adjustability. Recommend connections be shop fitted by timber supplier prior to delivery.

Structural Considerations: Lessons Learned


Type I Type II Type III Type IV Type VA B A B A B HT A B

Height Limit UL 160’ 65’ 55’ 65’ 55’ 65’ 50’ 40’Primary Struct Frame 3 2 1 0 1 0 HT 1 0Bearing Wall - Exterior 3 2 1 0 2 2 2 1 0Bearing Wall - Interior 3 2 1 0 1 0 HT 1 0Floor Construction 2 2 1 0 1 0 HT 1 0Roof Construction 1.5 1 1 0 1 0 HT 1 0

Key Exposed: Requirements:0 Yes No restrictions1 Yes Buy down w/ sprinklers, or check char2 Yes Fire treated wood and must check char

HT Yes Complete Type IV requirements apply.0 Yes HT member sizes required1 Yes HT member sizes required

Timber/Steel Hybrid Lesson’s Learned.

BIM/Prefabrication: Steel industry already familiar with 3D modeling/BIM/advanced shop fabrication. Easy to marry up CLT prefabrication benefits with steel.

Nailer: Nailer can provide convenience for attaching timber decking elements and conduit pass-thru.

Connections: Timber/steel connection not standardize. Understand scope break-up and request feedback from subs. Detail based on capability and prefabrication sophistication of trade partners.

Recommend you spec steel connections be shop fitted prior to delivery.



Beam Camber: Can create fit-up and connection issues – particularly with wider panels. Can be a challenge with glulam beams as well (r<3500 ft).

Recommendations: Avoid steel camber if feasible. Recommend ¾” maximum (steel industry minimum). Do not fully fasten spline until all DL is on beam.



Moisture Effects: Wood shrink/swell with moisture change - steel does not.

Recommendations: Provide regular expansion joints. Detail for field adjustability. Develop

construction moisture management plan (GC). Restrain (sheath) nominal lumber systems

(NLT, T&G) as soon as possible. Protect CLT panel ends and panel joints: properly tape

spline/joint seams, shelter space if possible, cover CLT (poly or roofing underlayment).

Squeegee standing water. If expansion occurs, allow wood to return to normal moisture

content before making connections.

Thermal Effects: Steel expands/contracts with temperature change – wood does not.

Recommendation: Provide regular expansion joints. Detail for field adjustability.


Proprietary Hybrid Systems:

Structural Considerations: Other Hybrid Systems

SHALLOW

FLAT-PLATEDIVERSAKORE

DELTABEAMGIRDER-SLAB

NO TIMBER COLUMNS! L

Design particulars

Austin was under 2012 IBC at time of permitting.

No mention of CLT in the 2012 IBC and hybrid construction precluded Type IV.

The city could have considered an

Alternative Method of Compliance for CLT in Type IV with the 2015 code out, but for

Type III, the city saw no precedent for exposed CLT in a rated floor assembly.

Design particulars: Codes and permit approval

78’ tall 5 story Group B building with steel required Type III-A, fully sprinklered construction.

Type III-A. Non-combustible exterior & interior elements any material. 1 hour primary structural frame, 1 hour floors.

Solution. Fire-resistive material on steel, CLT thickness for 1 hour performance.

Structural steel was rated with an intumescent coating to allow the steel to present itself in a more pure form than with a cementitious coating.


Challenge. To recognize CLT for 1 hour, Austin would have accepted a U.S. or Canadian UL witnessed fire test.

Rating to Canadian UL S101 standards test at the time was to UL Canada standards, but not witnessed by UL Canada, which was an obstacle for the city accepting an Alternative Method for the material based on fire tests available.

Calculated fire resistance of the material was required.

Design particulars - Codes and permit approval

When wood is exposed to fire, the outer layer burns and turns to char. The char layer acts as an insulation, slowing down the burn rate.

Permit solution- Alternative Method

An Alternative Method of Construction is requested per IBC 2012 104.11 for use of Cross Laminated Timber (CLT) floor

panels. CLT floor panels are proposed to be used in a floor/ceiling assembly with an exposed underside in a Type III-A

building (1 hour floor/ceiling). It is requested that consideration is given that the building frame will be fire-resistive

steel. Additionally fire sprinklers will be provided not only for fire resistance, but also for exposed CLT floor panel

ignition resistance. Concealed spaces that may not otherwise require sprinklers will include sprinklers or CLT floor

panels will be covered with 5/8" type X gypsum boards in these locations.

The floor panels will be supported on a steel frame with a rating as required by the construction type. CLT floor decks

in a 5 ply, 7" nominal thickness have been tested to over 60 minutes of fire resistance. CLT has been tested to Canadian

UL rating to S101 standards (“Standard Methods of Fire Endurance Tests of Building Construction and Materials“) (NRC

fire laboratory test). ULC S101 is equivalent to UL 263 and thus ASTM E119. The 2012 IBC Section 722 allows for

calculated fire resistance for wood members per the 2015 National Design Specifications for Wood Construction. This

request for recognition of a 1 hour fire resistive rating is based on calculated fire resistance.


US CLT Handbook

Design/Build Contractor & Crosslam Timber Solutions

Woodworks

American Wood Council

Arup Fire Engineering

Structurlam

Design & permitting assistance

Design goal: Capitalize on wood as a natural material for occupant comfort.

Biophilia- A hypothetical human tendency to interact or be closely associated with other forms of life in nature.

The girder and joist directions were aligned such that the most wood could be seen when entering a floor from the elevator or stairs.

Design goals, details, lessons learned

Acoustics.

1. A tenant will not likely ask about

acoustics of floor assemblies unless the

building is a unique structure.

2. Lack of testing data for the designed

floor assembly.

3. Acoustic engineer modeled the

assembly to estimate STC & IIC ratings.

4. Estimated rating for 3” concrete on ¼”

acoustic mat, 7” CLT- 55 STC, 45 IIC

versus 52/29 with just 5” concrete slab.

Details, lessons learned

Planning utility routing.


Roof drains.

Tieback anchors.


CLT manufacturer assistance.

1. Design assistance.

2. Structural coordination.

3. Shop drawings.


Construction. Contractor installation. Weather protection.


Lobby designed to connect with the street through a large bi-fold door. Art showings & events will expose people to the beauty and sustainability of the Cross Laminated Timber.

Community & art

The works of art on the back wall of each elevator are three distinct relief prints created from wood cuts by Connecticut artist Bryan Nash Gill that artistically complement the foundational focus on wood in this building.

Community & art

“I found that the inside of things was more beautiful and complex than what was visible from the outside… You’ll never know what you’re missing if you don’t find some way to get inside and look.” © Bryan Nash Gill, Artist

1. Ash "Art is (or should be) an authentic experience, which brings you closer to understanding yourself in relation to your surroundings."

2. Leader "The nature around us displayed beautiful and complex qualities. Patterns, texture, and color were everywhere. This sense of discovery has been a governing force throughout my life."

3. Willow "Strict concentration on the making, the process, is more important than the result."

Community & art

This concludes The American Institute of Architects Continuing Education Systems Course

QUESTIONS?

Bart Whatley, AIA

TB/DS – Delineate Studio

[email protected]

Michael Dupras, PE, SE, LEED Green Associate

DCI Engineers

[email protected]

texas’ first hybrid clt office building: designing class a ... · and character, progression and...

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