Challenges of Using Steel Staggered Truss Challenges of Using Steel Staggered Truss Challenges of Using Steel Staggered Truss Challenges of Using Steel Staggered Truss Framing Systems in High Seismic Regions: Framing Systems in High Seismic Regions: Behavior Issues and Possible Solutions Behavior Issues and Possible Solutions Behavior , Issues, and Possible Solutions Behavior , Issues, and Possible Solutions Shih Shih Ho Ho (Simon Simon) Chao Chao Shih Shih‐Ho Ho (Simon Simon) Chao Chao Assistant Professor of Civil Engineering, University of Texas, Arlington, TX Presentation at Quake Summit NEES and MCEER Annual Meeting Presentation at Quake Summit, NEES and MCEER Annual Meeting, Buffalo, New York, June 10, 2011
Transcript
Challenges of Using Steel Staggered TrussChallenges of Using Steel Staggered TrussChallenges of Using Steel Staggered Truss Challenges of Using Steel Staggered Truss Framing Systems in High Seismic Regions: Framing Systems in High Seismic Regions:
Behavior Issues and Possible SolutionsBehavior Issues and Possible SolutionsBehavior, Issues, and Possible Solutions Behavior, Issues, and Possible Solutions
ShihShih HoHo ((SimonSimon)) ChaoChaoShihShih‐‐Ho Ho ((SimonSimon)) ChaoChaoAssistant Professor of Civil Engineering, University of Texas, Arlington, TX
Presentation at Quake Summit NEES and MCEER Annual MeetingPresentation at Quake Summit, NEES and MCEER Annual Meeting,
Buffalo, New York, June 10, 2011
NEESRNEESR--CR: Steel Truss Systems with Enhanced CR: Steel Truss Systems with Enhanced Seismic Safety and Performance (CMMI: 0936563)Seismic Safety and Performance (CMMI: 0936563)
The University of Texas at Arlington
Research Team:Research Team:
Shih-Ho Chao, PISanputt (Pat) Simasathien, Doctoral StudentChatchai (Chad) Jiansinlapadamrong Doctoral StudentChatchai (Chad) Jiansinlapadamrong, Doctoral StudentXuejian Liu, Postdoctoral Research FellowBrandon Price, REU Undergraduate Student ResearcherR h l Si REU U d d S d R hRachel Simer, REU Undergraduate Student Researcher
Valparaiso University Michael Hagenberger, Co-PI
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What is Staggered Truss Framing (STF) System?
STF was developed at MIT in the 1960s.STF was developed at MIT in the 1960s.
Has been widely used in lowHas been widely used in low--seismic regions for seismic regions for yy gghotels, apartment buildings, dormitories, office hotels, apartment buildings, dormitories, office buildings, and hospitals; 5buildings, and hospitals; 5--40 stories.40 stories.
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Features of Staggered Truss Framing (STF) System
StoryStory--High Steel Trusses are StaggeredHigh Steel Trusses are StaggeredCentral Vierendeel Truss Panel used toCentral Vierendeel Truss Panel used toA d t idA d t idStoryStory High Steel Trusses are Staggered High Steel Trusses are Staggered Accommodate corridorAccommodate corridor
PostPost
Transverse DirectionTransverse Direction
Large ColumnLarge Column--Free SpaceFree Space Hanger TrussHanger Truss
Hanger TrussHanger Truss
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Precast Prestressed HollowPrecast Prestressed Hollow--Core Planks Core Planks Span from Bottom Chord of Truss to Top Span from Bottom Chord of Truss to Top Chord of Adjacent Truss/FrameChord of Adjacent Truss/FrameLongitudinal DirectionLongitudinal Direction
Features of Staggered Truss Framing (STF) System (cont’d)
The Lateral and Gravity ForceThe Lateral and Gravity Force--Resisting Systems in Resisting Systems in the Transverse Direction are One and the Samethe Transverse Direction are One and the Samethe Transverse Direction are One and the Samethe Transverse Direction are One and the SameWeakWeak--Axis Bending of Columns in Axis Bending of Columns in
the Transverse Directionthe Transverse Direction
Transverse DirectionTransverse Direction
Moment orMoment orBraces Frames are Braces Frames are Required at the Ground Required at the Ground St i TSt i T
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Story in Transverse Story in Transverse DirectionDirection Conventional Moment or Braced FramesConventional Moment or Braced Frames
in Longitudinal Directionin Longitudinal DirectionLongitudinal DirectionLongitudinal Direction
Benefits of Staggered Truss Framing Systems
•• Low floorLow floor--toto--floor heights (typically 8'floor heights (typically 8'--8” ~ 10’ trusses in demising8” ~ 10’ trusses in demisingLow floorLow floor--toto--floor heights (typically, 8floor heights (typically, 8 --8 10 , trusses in demising 8 10 , trusses in demising walls; floor slab is the only structural depth that needs to be walls; floor slab is the only structural depth that needs to be accommodated). Lower floor height accommodated). Lower floor height cost savings (cladding, cost savings (cladding, heatingheating--andand--coolingcooling--energy consumption etc.);energy consumption etc.);
•• Large columnLarge column--free spaces (as much as 60 feet in each direction with free spaces (as much as 60 feet in each direction with columns often only appearing on the perimeter of a structure); columns often only appearing on the perimeter of a structure);
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•• Less foundation formwork is required because the vertical Less foundation formwork is required because the vertical loads are concentrated at a few column points;loads are concentrated at a few column points;
R d d d d l d (d t li ht t l f d t tR d d d d l d (d t li ht t l f d t t
Benefits of Staggered Truss Framing Systems (cont’d)
•• Reduced dead load (due to lighter steel frames as compared to concrete Reduced dead load (due to lighter steel frames as compared to concrete systems) systems) reduced seismic load;reduced seismic load;
•• Reduced weight of the superstructure results in savings in foundationReduced weight of the superstructure results in savings in foundation•• Reduced weight of the superstructure results in savings in foundation Reduced weight of the superstructure results in savings in foundation work; work;
•• Increased design flexibility due to fewer columns (especially for atriumIncreased design flexibility due to fewer columns (especially for atriumIncreased design flexibility due to fewer columns (especially for atrium Increased design flexibility due to fewer columns (especially for atrium placement and floor plans); good quality concrete plank floor structure placement and floor plans); good quality concrete plank floor structure yields a dry, semiyields a dry, semi--finished ceiling that requires little or no finishing; finished ceiling that requires little or no finishing;
•• Faster, allFaster, all--weather erection reduced time and save money; the need for weather erection reduced time and save money; the need for applied fireproofing is reducedapplied fireproofing is reduced.
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Truss Frame (Stiffer)Truss Frame (Stiffer)
Transfer Paths of Seismic Forces in Staggered Truss Framing Systems
Transfer Paths of Seismic Forces in Staggered Truss Framing Systems (cont’d)
9Long and Staggered force transfer paths
Preferred Yield Mechanism in Staggered Truss Framing Systems
Plastic hinges within central Vierendeel panels (similar to that in the “Special Segments” of STMFs)
Vierendeel Panel
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Special Truss Moment Frames (STMFs)
Issues of STFs subjected to Strong Earthquakes
No test data available; very limited analytical studies (none of them No test data available; very limited analytical studies (none of them considered the diaphragm issues).considered the diaphragm issues).
The increasingly large diaphragm shear force in the lower stories brings The increasingly large diaphragm shear force in the lower stories brings di th li b h i f di hdi th li b h i f di h tt ttconcerns regarding the cyclic behavior of diaphragmconcerns regarding the cyclic behavior of diaphragm--toto--truss truss
High inHigh in plane forces in the precast diaphragmsplane forces in the precast diaphragms High inHigh in--plane forces in the precast diaphragms. plane forces in the precast diaphragms.
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Issues of STFs subjected to Strong Earthquakes (cont’d)
Large openings in the diaphragms that accommodate stair cases and Large openings in the diaphragms that accommodate stair cases and g p g p gg p g p gelevatorselevators How this would affect the shear transfer across the How this would affect the shear transfer across the diaphragms?diaphragms?
The lateral and gravity systems in the transverse direction are one and The lateral and gravity systems in the transverse direction are one and thth St bilit f it t ft th i iSt bilit f it t ft th i i ff i tii ti
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the samethe sameStability of gravity systems after the seismicStability of gravity systems after the seismic--forceforce--resisting resisting members yield/fail?members yield/fail?
Proposed SolutionsProposed Solutions
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Use Horizontal Steel Trusses as Diaphragms to Transfer Large Shears
T i ffi i t t t l f tT i ffi i t t t l f t Truss is an efficient structural form to Truss is an efficient structural form to transfer large shear;transfer large shear;
Truss members primarily carry direct tension Truss members primarily carry direct tension or compression;or compression;or compression;or compression;
Use typical steel connections to transfer the Use typical steel connections to transfer the diaphragm shear to diaphragm shear to STFsSTFs..
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Gravity Loads Applied outside the Central Vierendeel Panel
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Proposed Modifications to STF Systems
Large “kink” in columns at the Large “kink” in columns at the flexible “nonflexible “non--truss” level truss” level under lateral loadsunder lateral loads
Diagonal braces (“kickers”) are added at the non-truss levels to alleviate the demand on
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columns.
Proposed Modifications to STF Systems
Observations:
The Vierendeel panels experience large rotation at the ends of the chord members if the ratio of Ls/L is small This will in turn limit the overall drift capacity of the structure.Ls
L
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Proposed M difi tiModifications
to STFSystemsSystems
Vierendeel panel was modified to span over three panels of the truss.
The horizontal trusses are shifted towards the ends of the STFs to
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avoid the direct gravity loading on the Vierendeel panels.
Pushover Results on a 6-Story STF Model
3000
4000
5000
e (kips)
1000
2000
Lateral force
0
0 0.5 1 1.5 2 2.5 3 3.5 4
Drift (%)
Pushover curvePushover curve
Deformation of the STFs at 2% roof driftDeformation of the STFs at 2% roof driftLoading direction parallel to Loading direction parallel to STFSTF s (transverse s (transverse direction of the building)direction of the building)
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SS
11 Using staggered truss framing (STF) systems inUsing staggered truss framing (STF) systems in
SummarySummary
1.1. Using staggered truss framing (STF) systems in Using staggered truss framing (STF) systems in seismically active areas is challenging seismically active areas is challenging due to the due to the complicated load transfer paths and other issues such complicated load transfer paths and other issues such
th di hth di h tt t ti d t bilit ft ti d t bilit fas the diaphragmas the diaphragm--toto--truss connections and stability of truss connections and stability of gravity systems (which is also the LFRS). gravity systems (which is also the LFRS).
2.2. Modifications to conventional STFs are proposed and Modifications to conventional STFs are proposed and further design/analyses are underway.further design/analyses are underway.
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AcknowledgementsAcknowledgements
National Science Foundation (George E. Brown, Jr. Network for Earthquake Engineering Simulation); Grant No. CMMI 0936563
Kevin Moore, Principal, Certus Consulting, Inc.
T i hi Ok ki A i t P f H kk id U i it Taichiro Okazaki, Associate Professor, Hokkaido University
