Precast concrete buildings in seismic · PDF filePrecast Frame Systems Reference is made to the different types of precast frame systems and guidance is pro- ... Precast concrete buildings

CPI – Concrete Plant International – 6 | 2015 www.cpi-worldwide.com160

PRECAST CONCRETE ELEMENTS

Spyros Tsoukantas, Athens, GreeceSatyendra K. Ghosh, Palatine, USA

Basic Principles of Earthquake –Resistant Design

In this chapter, the main principles and phi-losophy of seismic design are briefly re -viewed with reference to performance re -quirements, seismic actions, design conceptetc., with emphasis on precasting and rele-vant ductility properties of precast framestructures.

Basic Principles of Conceptual Design

This section emphasizes the major impor-tance of the first step of the seismic designprocess, the so-called conceptual design. Itis pointed out that every analysis has to becarried out on a preconceived structuralsystem; several decisions have to be made

prior to any analysis being carried out, soas to minimize uncertainties related to theseismic response of the structure.

Structural simplicity, vertical uniformity –regularity, bi-directional and torsional resist-ance together with proper stiffness andadequacy of foundations, should governthe architectural – structural concept forany structure subject to seismic excitations.

Precast Frame Systems

Reference is made to the different types ofprecast frame systems and guidance is pro-vided to the selection of the force-responsefactors.

Precast Frame Systems with HingedBeam-To-Column ConnectionsSuch frame systems are used in low-risebuildings in areas of low or moderate seis-

micity. However they may also be integrat-ed as gravity – dominated systems in build-ings where the lateral loads are principallycarried by fixed-connection frames, or bylateral force-resisting systems of other types,such as shear walls or dual systems (com-bining walls and frames). Emphasis is given on the behaviour ofhinged beam-to-column connections (seefig. 1 and fig. 2) in seismic situations, basedon most recent experimental and theoreti-cal research.

Precast Frames with Moment-ResistingConnections (FCF)In this chapter various types of equivalentmonolithic moment-resisting beam-to-col-umn connections are presented by meansof descriptions, connection details, con-struction steps, photos and comments withreference to relevant experimental re -search.

Precast concrete buildings in seismic areas Practical aspects

This report provides a short summary of work done by Task Group 6.10 of fib Commission 6 (Prefabrication) in collaboration with PCI. A moreextended report on the work will be available in a joint fib/PCI publication that is expected to be issued by the end of 2015. It has been devel-oped by selected experts from around the world and therefore combines a variety of precast experiences, design philosophies and con-struction techniques. The Task Group was convened by S.Tsoukantas. S.K.Ghosh, serving as liaison between fib Commission 6 and PCI,together with other distinguished PCI members and members of fib T.G. 6.10, ensured consideration, throughout the document, of U.S. designand construction practice for precast concrete structures. The general overview contained in the fib/PCI document intends to provide engi-neers, architects, clients, and end-users with a better appreciation of the wide range of applications that modern precast concrete technol-ogy is capable of in various types of construction from industrial to commercial as well as residential. Lastly, the emphasis on practicalaspects, from conceptual design to connection detailing, aims to help engineers move away from blindly following prescriptive codes in theirdesign to basic principles, in order to achieve a more robust understanding, and thus control, of the seismic behavior of the structural system as a whole, as well as its components and individual connections.

Fig. 2: Hinged beam-to-column connection with two parallel dowels.a) Actions in the plane of the frame b) Actions perpendicularly to the plane of the frame

Fig. 1: Typical hinged beam-to-column connection with two parallel dowels (other reinforcements not shown for clarity).

DowelGrout

Precast beam

Bearing pad

Precast column

Dowel Dowel

Grout Grout

Precastbeam

Precastbeam

Bearingpad

Bearingpad

Precast column

Precast column

a) b)

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Dr. Spyros Tsoukantas, shares his professional activities between experimen-tal research, academic teaching and consulting work on the design and behav-iour of R.C.precast structures under seismic situations. He is author of numeroustechnical papers and co-author of books for University students. He was theintroducer with Prof. Tassios of the Greek Precast Code (1999), which is stillvalid in Greece. As head of the M.E.C.S. structural design consulting firm inAthens, he designed and supervised a great number of R.C. and precast struc-tures. [email protected]

Dr. S. K. Ghosh is President, S. K. Ghosh Associates Inc., Palatine, IL andAliso Viejo, CA. He and the firm specialize in seismic and building code consult-ing. He is a Fellow of the American Concrete Institute and the Precast/Pre -stressed Concrete Institute and serves on ACI Committee 318, StructuralConcrete Building Code, the ASCE 7 Committee, Minimum Design Loads onBuildings and other Structures, and the Masonry Standards Joint Committee. Hehas served on the Boards of the American Concrete Institute (ACI) and theEarthquake Engineering Research Institute (EERI). [email protected]

Fig. 3: Classification of FCF considering in-plane lateral force resistance: a) one-way frame; b) one-way frame with pin-endedtransverse beam; c) two-way frame

Fig. 4: Schematic representation of a moment-resisting connectionusing U-shaped precast beams (construction steps and typical reinforcement).

Pin-ended connection

Reinforcement ofthe beam core

(according seismiccodes for in-situ

frames)

prestressedsteel

rough internalconcrete beam

faces

Moment-resistingconnection






For example:

Figure 4 shows a beam-to-column connec-tion using U-shaped precast beams.

Figure 5 shows a beam-to-column connec-tion with inverted T-shaped precast beam.

Figures 6, 7 and 8 show a system in whichthe beam-to-column connections are madeas follows: multi-story precast concretecolumns are fabricated, each of which hasan open gap at each floor level. The longi-tudinal bars are continuous and run throughthe gaps. Precast beams are placedbetween columns, seated on the cover con-crete of the columns or on column corbels.The open gaps allow for the arrangementof the bottom and top beam reinforcement

together with stirrups inside the joint core. A brief reference to hybrid frame and wallsystems is also made (see fig. 9).

Different types of column-to-foundation con-nections are presented as, for example, theones shown in fig. 10 and fig. 11 and arecommented on.

Wall Systems – Large Panel Systems

Precast large-panel wall systems are mainlyused in cases where there is no need forlarge open spaces, such as in apartmentbuildings, office buildings, hotels, housing,educational and administrative buildingsand similar structures. Such systems arecomposed of precast large-panel load-bearing walls and precast concrete slabs.

Usually, walls are story-high and both wallsand slab panels are room-size. Walls mightalso be multi-story.

Alternatively, floors and roofs can be com-posed of precast components of other typessuch as hollow-core units, solid concreteunits, plank-floor units, etc. In all cases,diaphragm action of the floors needs to bemobilized. This can be achieved by properconnections between precast slab elementsand their supports or by using topping ofproper thickness, or a combination of theabove.

The seismic behaviour and structural integri-ty/robustness of such systems are dis-cussed, together with possible mechanismsfor dissipation of seismic energy.

Fig. 5: Construction steps of a beam-to-column connection with inverted T-shaped precast beams. a) Step 1: Placement of the columnb) Step 2: Placement of one beam resting on the columnc) Step 3: Placement of two beams resting on the columnd) Step 4: Placement of the column ties into the joint and proper arrangement of the negative reinforcement of the connection

Fig. 6: A precast project (Cummins) under construction in Pune,India, (courtesy of Precast India Infrastructures PVT LTD; photo byNagesh Kole).

Fig. 7: Lifting of a column with two gaps after demolding, ready fortransport, Cummins project, Pune, India (courtesy of Precast IndiaInfrastructures PVT LTD; photo by Nagesh Kole).

column stirrups

a) b) c) d)




Fig. 8: A column with two gaps in its finalposition, Cummins project, Pune, India(courtesy of Precast India Infrastructures PVT LTD; photo by Nagesh Kole).

Fig. 9: Jointed precast “hybrid” frame and wall systems developed in the PRESSS-Program(modified from fib, 2003; NZS3101:2006).

Fig. 10: Schematic representation of a socket foundation.

Requirements concerning details betweenprecast walls (horizontal and vertical joints)are presented and commented on, coveringtechniques that are usually used in Europe(see fig. 12) and in the United States (seefig. 13).

Figure 14 shows an application of largepanels by KEF Infra Precast Company forthe construction of a nine-story-high resi-dential building in Mangalore, India, usingthe U.S. technique.

Wall Frame Systems

Dual systems consist of a combination ofshear walls and moment frames. A dual sys-tem is commonly used when the moment-resisting frames alone do not provide desir-able lateral stiffness.

However, a probable lack of deformationcompatibility in both elastic and inelastic

Non prestressed(mild) steel

Cast in-situ foundation

Cast in-situfoundation

Precast socket vertical stirrups

Precast socket horizontal stirrups

Plain cementconcrete (PCC)

Infill concrete

Precast column

Precast column

Infill concrete

Horizontal stirrups

Precast socket

Precast socket

Vertical stirrups

Vertical stirrups

Horizontal stirrups

unbounded post-tensioned tendons

Fibre reinforcedgrout pad

Energy dissipationdevices

Plain

Section

post-tensioned tendons




ranges between walls and frames shouldbe visualized during the design; this isbecause walls and frames do not deformequally under normal or severe lateralloads. On the other hand, for the design ofa lateral-force-resisting system for a pre-cast/prestressed concrete building (whichis made of precast walls and precastframes), it is important that the characteris-tics of the connections between walls andframes be such as to accommodate the dif-ferent behavior of the two systems (wallsand frames). Typically, the desired primary ductile be -havior of precast shear walls emulating

cast-in-place detailing is flexural yielding atthe wall base (see fig. 15).

Because a small rotation in a wall will cre-ate a large bar elongation, the ductility atbase is important. Ductility can be in -creased significantly by debonding barsinto and out of the foundation, so that theycan deform inelastically over a longerlength, thus resulting in greater rotationalductility (see fig. 16).

Reinforcing steel specified for special wallsshould be ductile and have controlledstrength properties.

Reference is also made to distinctionsamong categories of structural walls andmoment frames according to ACI 318-11and Eurocode 8 (1998).

Typical connections in structural wall sys-tems according to United States experienceare shown.

Floor Framing Systems

Floor systems play a key role in the lateralresistance of precast structures by providing“diaphragm action” which serves to: - transfer lateral loads at each level to

the lateral force-resisting system (walls,frames, dual systems); and,

- combine individual lateral force-resist-ing elements into a single lateral force-resisting system.

Generally speaking, design and construc-tion of floor systems in precast constructionsshall meet the basic requirements of serv-iceability and strength typical of any con-struction system. Serviceability refers prima-

Fig. 11: Column-to-foundation connections using corrugated metal ducts (other details not shown for clarity).

Fig. 12: Typical transverse reinforcement ina closed vertical shear connection and typi-cal reinforcement of the precast panels(shown in one panel only).

Fig. 13: Location of tensile ties in large-panel structures according to ACI 318 (2011)a) Cross wall structure; b) Spine wall structure. (T = transversal, L = longitudinal, V = vertical, P = peripheral)

Fig. 14: A nine-story large- panel building under construction in Mangalore, India (courtesy of KEF Infra; photo by A.Dienst).

Column

In-situ concrete

Section A–A

Precast concrete

Shims

Rebaroverlap

Corrugated duct

Foundation

Pre-bed seat withnon-shrink grout

with thickness ≈ 50mm slightly morethat shim stack

a) b)




rily to limitations on flexural deformation. Strength requires verifica-tion of the following:- diaphragm action, which should be effective and in accor-

dance with the design assumptions;- adequacy of end supports of the slab units, which must accom-

modate the earthquake- induced displacements (satisfy com-patibility) including beam elongations in frame systems anduplifting in lateral force-resisting wall systems, or combinationof the above; and

- slab action (flexural and shear strength), which should bemaintained under gravity and seismic (horizontal and vertical)loads.

Aspects of diaphragm behaviour in precast floor systems are treat-ed by means of design rules, pictures and connection details (seefig. 17, fig. 18 and fig. 19) together with reference to displacementincompatibility issues between lateral force-resisting systems andprecast floor diagrams (see fig. 20).

Fig. 15: Dual building with rotation of the shear wall at each floor(ACI 550.1R-01).

Fig. 16: Dual building – ductile yielding of partially debonded bars between foundation and shear wall boundary elements (ACI 550.1R-01).

Fig. 17: Shear and moment on diaphragm. Compression and ten-sion forces due to moment. Shear along the precast member joints.Shear along the supports of the diaphragm due to horizontalactions.

Precast shearwall

Hinges atcolumns

Precast shearwall

Horizontal actions Compression

Shear on diaphragm

Moment od diaphragm

Tension

Shear along the joints

Hinges atcolumns

Visit us!stand # N351

Visit us!stand # 879




Double-Wall Systems

Double-wall precast systems are used forboth low- and high-rise buildings such asresidential and office buildings, housing,hotels, educational and administrativebuildings.

Double-wall systems are normally builtusing an industrialized automatic produc-tion process. These are walls composed oftwo concrete layers, each usually 5 cm to 7cm thick, with a gap of about 8 to 20 cm(see fig. 22). The two concrete layers are internally con-nected by means of reinforcement in theform of lattice girders at a spacing of about40 to 80 cm. One layer of welded wirereinforcement is typically provided in eachlayer of the double-wall and acts as themain wall reinforcement. The gap betweenthe two precast concrete layers is filled bycast-in-place concrete during construction,after placement of additional connectionreinforcement where needed, and afterplacement of the installations.

Details of such systems are presented forexample in fig. 23 and fig. 24. Advantages of the double-wall system arespeed of construction, fire resistance, andeconomy. From a structural point of view,the main advantage is monolithic behaviorunder vertical and horizontal loads, whichresults in more or less uniform distribution ofthe seismic loading in all directions of thebuilding, minimizing story drifts.Compared with monolithic cast-in-placeconcrete walls, less visible cracking isobserved in precast double-walls due totheir production process. The ease of on-siteplacement of the hydraulic and electricalinstallations that precede the on-site place-ment of the cast-in-place infill concrete, isalso worth mentioning.

Fig. 18: Typical details for a topped hollow-core slab to ensure full transfer of longitudinalshear across the interface with precast units.

Fig. 19: Typical flange weld connection (concept according to PCI, 2010) – a) plan; b) forces; c) connection detail.

Fig. 20: Schematic example of vertical displacement incapability between floor and framesystems (modified from Matthews et al., 2003; NZS3101:2006).

Reinforcing mesh

Reinforcing mesh

Reinforcing mesh

Cast in-situ topping



Precast hollow-core-slabs

Precast hollow-core-slabs Precast hollow-core-slabs

Precast hollow-core-slabs

Precast hollow-core-slabsIn-situ infill

In-situ infillSection A–A

Section B–B

Welded steelplate

Welded steelplate

WeldingsWelding

Steelangels Steel angels

Steelangel

Edge ofmember

Anchorbar

Anchorbars

Weldings

Seismic action

Displacement incompatibilitybetween frame and precast

floor unit

Beam in whichfloor units sit

Plastic hinge ofthe beam

Precast floor unit in its original position Frame deforms in double

curvature forcing the precastfloor unit to follow

Displacement incompatibilitybetween frame and precast

floor unit

a) b) c)



Precast Cell Systems

Precast cells are industrially produced,completely finished, and fitted out at theprecasting plant and delivered to the build-ing site and installed in the building (see fig.

25). They are typically placed in one verti-cal line and usually form a self-supportingtower when properly connected together.

Precast cell systems are also used for theconstruction of different types of buildings

such as residential buildings, office build-ings, hotels, educational facilities, correc-tional facilities, etc.

The cell units are completely constructed inthe precast plant, ready for use after assem-bly on site, satisfying structural requirementsand incorporating plumbing, electrical, andmechanical installations.

Fig. 21: Schematic representation of the deformation demand on and damage to a hollow-core unit sitting on a beam, due to the elongation of a plastic hinge and rotation of supporting beam under seismic excitation.

Fig. 22: Precast double-wall: (–) reinforcement during production

Seismic action Elongation in beam hinge (M)

Section a–a

Section b–bDisplacement due to

rotation of column




Fig. 25: Horizontal connection between closed cell units using dry connections at the top of the slabs (other reinforcement not shown for clarity) (Manolatos et al., 2003).

Fig. 23: Connection of interior walls. Horizontal section: (–) Reinforcement in precast members (–) Additional reinforcement in cast-in-place concrete

Fig. 24: Interior wall and floor connection. Vertical section:(–) Reinforcement in precast members (–) Additional reinforcement in cast-in-place concrete

Cell systems are presented by means oftexts and figures; fig. 25 is an example.Such systems are very suitable in caseswhere dismantling of a building is requiredfor rebuilding at another location.Prestocked precast cell units are sometimesused to accommodate people after naturaldisasters. Advantages of cell systems are:- short construction time and good quali-

ty, since cells are finished andequipped at the factory;

- structural integrity of the final buildingif cell units are properly connected hor-izontally and vertically with eachother;

- minimum risk of progressive collapseunder accidental loading;

- good insulating properties; and- cost savings due to industrialization of

the production.Main disadvantages of cell systems are:- restriction on the sizes of the cell units,

mostly on their widths, which are limit-

Proper anchorage length

Joining reinforcement

Precast plank floor

Positive slab reinforcement

Negative slab reinforcementConnecting (wall) reinforcement

longitudinal reinforcement withproper overlapping

Precast plank floor

Recommended

Acceptable

Z-axis

X-axis

X-axis

Y-axis

Y-axis

Anchors

AnchorsFillingconcrete

Precast slab

In-situ concreteat the factoryBolts

Metal plate

Metalplate

Section 1-1 Section 2-2

Non-acceptable

Strip foundation

Transverse slab reinforcement

Transverse slab reinforcement

Proper anchorage length

c = proper cover

c = proper cover

Supporting reinforcement

lattice girder height

Upp

er w

all

Low

er w

all

c = proper cover

c = proper cover

lattice girder height

h = total thicknessof the double wall

prop

er a

ncho

rage

leng

th

Detail “A”




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ed to about 3.6 m due to constraints on transport from the pre-cast plant to the site;

- high self weight of the cell units, which may cause difficultiesduring transportation and erection; and

- limited architectural flexibility.

Appendices

The fib/PCI document containsthree Appendices, as follows: Appendix A: Structural ductility of precast frame systems Appendix B: Behavior factors of precast frame systems Appendix C: Design example of a one-story industrial building

using Force-Based or Displacement-Based Design approaches

Conclusions

In this report, a short summary of the fib/PCI Bulletin of the sametitle is presented, in order to draw attention of the readers of this arti-cle to the variety and extent of the precast topics that are coveredin the fib/PCI Bulletin. It is expected to be published by fib and PCIby the end of 2015.

Acknowledgements

To all those who participated in fib/PCI Task Group 6.10 �

References

fib/PCI Bulletin : “Precast concrete buildings in seismic areas-Practical aspects”(to be publishedby the end of 2015).


Documents

Precast concrete buildings in seismic · PDF filePrecast Frame Systems Reference is made to the different types of precast frame systems and guidance is pro- ... Precast concrete buildings