Precast-concrete Details

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COLLEGE OF ARCHITECTURE AND PLANNINGDepartment of Architecture and Building Sciences

Dr. Mohammed Ghonim

3. PRECAST CONCRETE IN DETAIL

ARCH 436Contemporary Building Construction Methods

Lecture Objectives

Upon completion of this lecture, the student will be able to:

1. Differentiate between architectural precast and structural precast concrete.

2. Compare between total precast and mixed Precast Construction.

3. Explain how to connect precast structural elements.

4. Draw sketches for the connections between precast structural elements.

5. Describe the installation process of precast concrete structural elements.

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Lecture Content

• Introduction.

• Architectural Precast & Structural Precast Concrete.

• Total Precast Vs. Mixed Precast Construction.

• Precast Concrete Joints.

• Slab to Slab Connections.

• Slab to Beam Connections.

• Slab to Wall Connections.

• Beam to Column Connections.

• Panel to Panel Connections.

• Column to Column Connections.

• Column to Foundation Connections

• Precast Concrete Extra Details.

• Precast Concrete Construction Process.

IntroductionThe considerations for design anddetailing of structural and non-structural precast elements includingjoints and connections for buildingsand building works are introduced inthis lecture.

Also, it is important to mention thatprecast concrete buildings should bedesigned wherever possible to utilizestandardized precast concreteelements, while most buildings will beunique and site specific.

At the conceptual design stage, a basiclayout plan should be developed whichachieves a balance betweenarchitectural / aesthetic requirementsand a high degree of standardisation .

Therefore, close collaboration amongstdifferent design parties is essentialduring conceptual design to achievethe optimum standardisation.

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Architectural Precast & Structural Precast ConcretePrecast concrete members are classified as; 1- architectural precast concrete and 2-structural precast concrete. Architectural precast refers to concrete elements that are usedas nonstructural cladding elements, and their most common use is in precast concretecurtain walls.Structural precast concrete, includes all elements of a building’s structural frame floors, roofsslabs, columns, and walls. Although an entire room or assembly of rooms can be precast,most structural precast concrete is used in standard elements that are assembled on site toform spaces.

Structural Precast Concrete Elements.Architectural precast wall panels.

Total Precast Vs. Mixed Precast ConstructionA building can be constructed of allprecast concrete members in which allstructural components; columns, walls,and floor and roof slabs are made ofprecast concrete. This system isreferred to as total precast concreteconstruction.

In mixed precast construction, someelements of the building are made ofprecast concrete members, while theothers are made of cast-in-placeconcrete, steel, or masonry. It combinesthe benefits of both precast andconventional construction.

In mixed precast, precast concrete isused only in floor and roof slabs. Usingprecast concrete floor/roof slabs yieldssignificant savings because a largepercentage of the cost of materials andformwork in a concrete structureis embedded in floor and roof slabs.

A total precast concrete parking under construction.

Mixed precast concrete construction consisting of a steel-frame structure with hollowcore slabs.

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Precast Concrete JointsIn precast concrete buildings, joint designs play a pivotal role in ensuring that concretecomponents act as one piece. In most cases, sealing the joint space is necessary to preventinfiltration of groundwater and exfiltration of liquids carried by the structure.

Well detailed and constructed joints play a vital part in maintaining the integrity of theexternal envelope of the building, ensuring it is weatherproof and meeting any otherrequirements such as fireresistance and acoustic performance.The function of the joint between precast elements is to provide physical separation betweenthe units and prevent -in conjunction with joint sealants- the ingress of water and air into thebuilding; and, if required, fire resistance.

Slab to Slab Connections

Grout keys provide structural continuitybetween floor slab units.

Connections between hollow-core slabs andsupporting members are made using site-castconcrete fill and reinforcing steel. In addition tothe concrete fill used for connections, a site-castconcrete topping is generally used over the slabs.The topping provides structural integration of slabunits and increases the floor’s fire resistance andsound insulation. It also functions as a levelingbed, particularly with units with uneven camber.Topping, when used, is generally about 2 inchesthick and reinforced with welded wirereinforcement (WWR).

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Slab to Beam Connections

Precast hollow core slabs connected attheir ends to a rectangular precast beamby steel ties.

Grout

H.C. slabs

Bearingpads

Steel barsthrough thegrout keys

Slab to Beam Connections

A double-tee floor unit being flown into position in a precast building.The setbacks in double-tee stems reduces floor height.

Setback

Double tee slabs supported over arectangular beam.

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Slab to Wall Connections

Projections in precast concrete walls tosupport the inverted-tee beams or thedouble-tee floor slabs.

Beam to Column Connections

ProjectingBracket

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Panel to Panel ConnectionsPrecast panels are connected to each others or to floor and roof elements by using metalplates and angels, they are fastened by welding or bolting. Connections may be projected orrecessed to provide flush finishing surface.

Different cases of precast panel to panel connections.

Column to Column ConnectionsPrecast concrete columns are connected togetherthrough bolting, the top of a lower-floor columncontains threaded bolts projecting out, while thebottom of an upper-floor column has an embeddedbase plate containing holes to engage the bolts. Theblock-outs in the column above the holes are filledwith concrete after the connection has been made.

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Column to Foundation ConnectionsThe method of connection to the foundation and to thecolumn above will vary with manufacturer. Foundationconnection may be via a base plate connected to the columnor by reinforcing bars projecting from the end of the columnpassing into sleeves that are subsequently filled with grout.Alternatively, a column may be set into a preformed hole in afoundation block and grouted into position.Column to base connections may be by threaded rods joinedwith an appropriate connector; with concrete subsequentlycast round to the dimensions of the cross-section of thecolumn.

Precast Concrete Extra Details

Partial precast concrete hollow core slabover metal hanger to provide an opening.

Lifting hooks are very important component in precastconcrete units.

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Precast panels installation process requiretemporary support.

Precast double tee slab lifted by a crane to its positionover l-shaped precast beams.

Total precast construction

TemporarySupport

TemporarySupport


Double tee slabs does not require temporarysupport because they are stable.

Precast beams contain grooves to hold double tee ribsto provide more neat beam to roof connection.

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Various solutions for beam to columnconnection.

Precast Concrete ConstructionThe construction process of a total precast building has much in common with structuralsteel construction; that is, members are brought into position using a crane, and areconnected together either through welds or bolts. Steel embeds are included in precastmembers to facilitate member bolting and/or welding.

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Summary• Also, it is important to mention that precast

concrete buildings should be designedwherever possible to utilize standardizedprecast concrete elements, while mostbuildings will be unique and site specific.

• Total precast concrete construction refersto those cases where all structuralcomponents are made of precast concrete.

• In mixed precast construction, someelements of the building are made ofprecast concrete members, while theothers are made of another materials.

• In precast buildings, joint designs play apivotal role in ensuring that concretecomponents act as one piece. In mostcases, sealing the joint space is necessary.

• The construction process of a total precastbuilding has much in common withstructural steel construction; that ismembers are brought into position using acrane, and are connected together eitherthrough welds or bolts.

References

Allen, EA. (2009) Fundamentals of building construction materials and methods, John Wiley & Sons.

Ching, Francis (2008) Building Construction Illustrated, John Wiley & Sons. Emmitt, S.& Gorse, C. (2006) “Barry’s Advanced Construction of Buildings”, Blackwell Publishing.

Garrison, Philip, (2005) “Basic Structures for Engineers and Architects”, Wiley-Blackwell. http://en.wikipedia.org/wiki/Precast_concrete. https://fp.auburn.edu/heinmic/ConcreteHistory/Pages/timeline.htm

http://www.concretenetwork.com/precast-concrete/advantages.html http://youtube.com

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Lecture ActivityEach student is required to prepare a brief but informative internet-based research about one of the topicsrelated to this lecture (Precast Concrete in Detail); i.e., new developments, successive and local casestudies or important details. The research should be presented in only one A4 sheet.

Design

Precast-concrete Details