Category STRUCTURAL CONCEPT FOR PRECAST CONCRETE SYSTEMS

Section 1-І

WELDING AT TOP

Figure 5.61 Beam-Load Bearing Wall

1. Wall

2. Beam

The beam-wall assembly соuld consist of either a dowel-hole, or stirrup or a welded connection as shown in Section 1-І.

1. Wall

2. Beam

As shown in Section 1-І, assembly could be done using a dowel-hole connection or protruding stirrups in cast in-situ joints.

Figure 5.63

1. Edge beam

2. Plank

3. Cladding

4. Structural topping

The cladding is fixed using dowel-hole connections which are locked to the structural topping.

Figure 5.64

1. Edge beam

2. Plank

3. Cladding

4. Structural topping

The cladding is fixed using embedded steel profiles and via placed – on-site steel angles.

Figure 5.66

1. Edge beam

2. Plank

3. Cladding

4. Structural topping

The lightweight cladding shown can be fastened to the beam and finished floor slab using steel angle profiles.

Figure 5.67 Beam-Panel Connections

Statically determinate connections should be chosen if possible. Load reactions are shown as a response to panel weight and to wind pressure.

Vertical forces are transmitted through the horizontal joint. Horizontal forces are carried by the steel plate and reinforcement anchorage.

Schematic solutions for positioning of joints.

A. Panels are fastened to floor slab

B. Joints are placed at floor slab and beam

C. Cross walls on panel plus beam joint

D. Corbels on panel plus beam fixing

E. Corbels on panel plus steel bracing

Figure 5.70 H. C.SIab-H. C. Slab

1. Hollow core slab with reinforcement bar placed in joint

Figure 5.71 And 5.72: H. C.SIab-H. C.Slab

2. Beam, wall or frame

3. Edge of HCS without void

4. Locking rebars and dowels in joint

It is important to reinforce structural joints, for instance as shown with interaction between dowel in beam, reinforcement from slab joint and locking bar screwed into insert.

To create structural continuity in the floor slab system, it is important to anchor joint reinforcement in all adjoining members.

1. Beam as inverted T

2. Precast or cast in-situ members

3. Hollow core slab

4. Joint reinforcement anchored to insert

5. Double T-slab component

6. Structural topping

Figure 5.77 H. C.Slab-Double T

1. Double T-slab component

2. Hollow core slab 1

3. Steel anchor in edge of hollow core slab

4. Structural topping

Normally, the double T-support is secured by a welded connection. Structural continuity between different types of slabs is obtained by cast in-situ structural topping anchored to precast members.

Figure 5.78 H. C.SIab-Load Bearing Wall

1. Load bearing wall

2. Hollow core slab, load bearing support

3. Slab joint reinforcement

4. Dowel screwed into steel insert

Figure 5.79 H. C.SIab-Load Bearing Wall

1. Load bearing wall

2. Hollow core slab, load bearing support

3. Slab joint rebar to be locked in wall joint

4. Dowel screwed into steel insert

5. Hollow core slab, non-load bearing support

Crossing reinforcement bars are locked together in the wall-slab joint. Wall in next storey (if any) is shown dotted.

Figure 5.80 H. C.Slab-Cladding

1. Hollow core slab, non-load bearing edge

2. Cladding component

3. Steel angle bolted to hollow core slab and cladding

4. Joint material

The slab component has been reinforced along the edge to absorb vertical as well as horizontal forces from the cladding.

1. Hollow core slab, non-load bearing edge

2. Facade

3. Steel anchor plate

4. Edge beam reinforcement in hollow core slab

Facade weight is transmitted via the horizontal facade joint. The facade is anchored for horizontal forces using a steel plate bolted to the floor slab structure.

1. Supporting wall or beam

2. Plank

3. Reinforcement protruding from plank

4. Locked bar in joint

5. Structural topping

Figure 5.82 shows the connection along the non-load bearing edge while Figure 5.83 the connection between planks and supporting member. Protruding reinforcement bars from the planks are to be connected and locked in a joint cast in-situ together with the structural reinforced topping.

Figure 5.84

1. Double T-slab

2. Plank

3. Welded connection

4. Structural topping

Normally, steel plates are cast-in per

1.2 rib along the edge of double T’s. Protruding rebars from planks could be welded to the plates and covered by the topping.

1. Supporting wall

2. Plank

3. Structural topping

4. Joint reinforcement locked to assembly bolt

Protruding rebars from planks are locked using joint reinforcement and assembly bolts from the wall.

Figure 5.86

1. Structural topping on planks

2. Cladding component

3. Steel angle bolted to plank and cladding

As the cladding is lightweight, the steel angle must be designed to transmit vertical as well as horizontal forces.

Figure 5.87

1. Structural topping on planks

4. Facade component

Vertical forces are transmitted from facade to facade whereas horizontal loads go from assembly bolt via cast-in steel insert to reinforcement in the structural topping.

1. Supporting Wall

2. Double T, the rib

3. Structural topping

Welded connection between wall and ribs together with the structural topping locked to the plate create continuity in the floor slab structure.

1. Double T, the rib

2. Cladding components

3. Connecting steel bar

The cladding components are placed on top of each other, horizontal forces are transmitted to the floor slab structure via steel anchors.

1. Facade components

2. Double T, the rib

3. Structural topping

The rib-facade joint is welded. A recess in the plate over the ribs allows the double T to rotate at the support.

1. Solid precast wall

2. Cast in-situ joint

3. Reinforced cast in-situ joint

Sketch A shows the standardised vertical joint between two wall components with castellated vertical edges. Sketch В shows a T-shaped wall connection which is normally reinforced like the L – shaped wall connection shown in Sketch C.

Figure 5.93 Load Bearing Wall – Load Bearing Wall

1. Standardised wall component

2. Grouting with cement mortar

The horizontal wall-to-wall joint is shown as a simple concrete joint with assembly bolts.

Figure 5.94 Load Bearing Wall – Load Bearing Wall

1. Standardised wall components

2. Hollow core slab

3. Plank

4. Structural topping

The wall-to-wall joint is often connected to slab structures as well. Reinforcement bars from adjoining members are locked using the structural topping.

1. Load bearing and bracing walls

2. Concrete joint between walls and floor slabs

3. Bolted connection

4. Cast-in reinforcement bars

5. Welded connection

In Sketch F, the assembly bolt forms the tensile connection to the next wall. Sketch G shows reinforcement bars placed-on-site in corrugated pipes. Protruding rebars are welded together in Sketch H allowing tensile forces to be transmitted from wall to wall.

Figure 5.96

1. Wall component

2. Cladding

3. Non-load bearing joint

As cladding components are normally fastened to floor slabs, the joint must be designed to resist sound and fire.

Figure 5.97

1. Facade wall

2. Floor slab structure

3. Cladding

4. Steel angle to fix the cladding

Vertical forces are absorbed in a locked dowel-hole connection at the top of the cladding. Horizontal forces are transmitted to the floor slab via a steel anchor.

1. Facade wall

2. Plank

3. Standardised facade

4. Joint reinforcement

5. Structural topping

The assembly bolts in facades and walls act as connecting devices between the facade components and the structural

topping.

Figure 5.100

1. Facade component

2. Fixing point, if any

3. Grouting with cement mortar

4. Partly open facade joint

5. Reinforced castellated concrete joint

Normally, the facade-joint is designed according to the two – step principle: Airtightness inside and watertightness outside. Figure 5.100 shows a concrete joint inside and an open joint or a neoprene strip as an outside protection against the rain.

Figure 5.100 Facade-Facade

Figure 5.101

1. Frame

2. Beam placed in frame plane of symmetry

3. Beam placed perpendicular to frame

Figure 5.102

1. Frame

2. Beam

A normal dowel-hole solution is shown with reinforcing stirrups near the narrow support area.

Figure 5.103

1. Frame

2. Beam

To get the components flushed, the whole width of the frame is used as supporting area. A dowel-hole connection is chosen.

1. Frame

2. Plank

3. Protruding rebar

4. Casting on site

The connection is able to support the plank and absorb horizontal shear as well.

Figure 5.107 Plank-Frame

1. Frame

2. Double T-slab

3. Welded connection

4. Structural topping

Cast-in steel plates in frame and in ribs make it possible to execute a welded supporting connection.

320

Frame

1. Standardised wall component

2. Frame, beam and column

3. Reinforced castellated joint

This horizontal section shows the use (it a normal rough vertical joint in both the.^йИ and frame column.

Figure 5.110

1. Frame, beam and column

2. Cladding component

3. Soft joint material

4. Ventilated space/neoprene strip

The connection is considered only as a climatic joint. All forces are transmitted to the floor slab structure.

Figure 5.112

1. Frame component

2. Plank

3. Facade

4. Cast in-situ joint

5. Structural screed

Self weight from facade components is transmitted direct from facade to facade. Horizontal forces go to the floor slab structure using assembly bolt, steel plate and dowel.

Figure 5.111

1. Frame component

2. Plank

3. Cladding

4. Steel angle

5. Rebar protruding from cladding

The cladding is fastened at the top using a steel angle device and, at the bottom using rebars to be cast into the structural topping.

1. T-shaped frame

2. V-shaped frame

A two-dimensional load-bearing and bracing frame system can be created by using T – and V-shaped frame components. The T-shaped frames are placed longitudinally while the V – shaped frames are placed in the transverse direction.

Figure 5.113 shows the reinforced and rough joint between T-components while Figure 5.114 features the narrow bearing support between the two frame types. These bearings are reinforced by cast-in steel plates.

Precast building systems without beams may create problems due to very small support areas between slabs and columns.

Figure 5.115 provides a solution to this: A column head supports the narrow slabs, which are, in turn, supported by the main floor slabs.

1. Column

2. Cladding

3. Cast-in steel plate

4. Steel angle welded to plate

5. Dowel-hole connection

6. Dowel as assembly bolt

Vertical movement can take place at the top of the cladding components. Vertical and horizontal forces are transmitted via the welded steel connection.

1. Cladding components

2. Steel bar welded to the cladding components

3. Reinforcement in cast in – situ column

Precast cladding components are used as a finished surface and a form panel for cast in – situ structures.

1. Cladding component

2. Cast in-situ column

Precast cladding is used as shuttering in a skeleton main structure.

1. Column components

2. Balcony slab

3. Soft packing

4. Joint cast in-situ

5. Mastic joint

The designer must ensure a sound transfer of the vertical load and check on temperature movements in the balcony structure.

Slab

1. Beam or frame

2. Balcony slab

3. Soft bearing, for instance, neoprene

4. Dowel-hole connection

Temperature movements between beam and slab have to be considered.

Figures 5.121 and 5.122 have been designed to eliminate

coldbridges and to allow temperature movements to take place.

1. Beam, frame or wall

2. Hollow core slab

3. Balcony slab

4. Embedded steel section

5. Locking stirrups protruding from slabs

6. Vertical support

1. Beam, frame or wall

2. Hollow core slab

3. Balcony slab

4. Support cam or nib

5. Dowel in nib plus locking stirrup

6. Vertical support

1. Wall 1. Balcony slab with fixed support

2. Balcony slab 2. Balcony slab with movable

3. Cast-in steel plate support

4. Soft Joint material

1. Beam, frame or wall

2. Plank

3. Balcony slab with nibs

4. Bearing, for instance, neoprene

5. Nib with protruding reinforcement

6. Structural topping

The balcony slab is considered as fixed-ended in Figure 5.125

1. Facade wall

2. Hollow core slab

3. Balcony frame

4. Balcony slab

The balcony slabs are simply supported on the frame which is locked to the assembly bolt in the facade.

1. Load bearing wall

2. Balcony parapet

3. Balcony slab

4. Assembly bolts

The assembly bolts with nuts allow temperature movements from the right hand parapet to take place, but do not allow movements from the parapet to the left.

1. Load bearing wall

2. Balcony slab

3. Balcony parapet

4. Neoprene bearing

5. Bolt into cast-in steel insert

Temperature movements in the parapet have to be considered before designing the parapet joint.

1. Landing component

2. Flight component

3. Loose steps

4. Supporting steel studs

5. Bolted connection between flight and landing

Staircase System 1/2/3

1. Load bearing wall

2. Landing component

3. Loose dowel in steel section socket

4. Soft support, for instance, neoprene

5. To be grouted

Figure 5.133

Half-beam joints are used between landings and flights.

Figure 5.134

1. Load bearing wall

2. Landing component

3. Support nib

4. Soft material, for instance, neoprene

5. To be grouted

Figures 5.133 and 5.134 are both related to the staircase system shown here which uses a hollow core slab as landing and a normal solid plate as flight component.

Figure 5.135 Column-Column Socket

1. Bottom plate

2. Socket wall

3. Ring reinforcement

4. Vertical stirrups

5. Steel plate placed in cement mortar

6. Precast column component

7. Casting on site

The column socket could be cast-on-site or it could be produced as a precast component. The column can be designed as a fixed-ended column.

Figures 5.136, 5.137 and 5.138 Column Sockets

1. Thick cast-on-site socket walls

2. Precast column

3. Thin cast-on site socket wall with rough surfaces

4. Precast column with rough surface

5. Cast-in-situ rough joint

6. Ring reinforcement and stirrups

7. Precast column socket with very thin walls and fins

8. Precast column with castellated surface

Figures 5.136, 5.137 and 5.138 show the development of the column socket from very solid concrete boxes cast in-situ to more light precast structures with thin walls supported by fins.

[1] x 3.70 x 36004 x 12

[2] =——————————————-

384 x28x 103 x 1000 x 1453 = 1.1 mm

= 1/3272 < 1/350 (d.3.2.1.2, Part 2) OK

Joints Used In European Countries

The details indicated in the table below cover the most commonly adopted structural joints in European countries. For external joints in facades, the two-step open joint principle is chosen.

Types of Joints Used In European і Countries

Column

E

ffl

HC Slab

і і

Plank

Double T

Load Bearing Wall

Cladding

c

O.

І

Balcony Slab

Balcony

Parapet і

Staircase

: Column

5.32 to 5.37

5.38 to 5.45

5.115

5.116 to 5.117

5.118

5.119

! Beam

5.46 to 5.49

5.50 to 5.54

5.55 to 5.56

5.57 to 5.59

5.60 to 5.62

5.63 to 5.66

5.67 to 5.69

5.101 in 5.103

5.120

5.131 to 5.134

: HC Slab

5.70 to 5.72

5.73 to 5.75

5.76 to 5.77

5.78 to 5.79

5.80

5.81

5.1041-‘

5.103

5.121 to 5.122

j Plank

5.82 to 5.83

5.84

5.85

5.86

5.87

5.107

5.125

і Double T

5.88

5.89

5.90

5.91

5.106

Load Bearing Wall

5.92 to 5.95

5.96 to 5.97

5.98

5.109

5.123 ІО 5.124, 5.126

5.129 to 5.130

I Cladding

5.99

5.110 to 5.111

Fagade

5.100

5.112

; Frame

5.113

5.114

Baloony Slab

5.127

5.128

Column Socket

Figure 5.32 Column/Column Dowel Connection

1. Column with cast-in assembly bolt at the top

2. Column with cast-in steel plate and recess at the bottom

3. Grouting with cement mortar

4. Assembly bolt with nut

The simply supported column is temporarily placed on the assembly bolt. The grout will transmit the compression force.

1. Column with protruding rebars at the top

2. Support shims

3. Column with protruding rebars at the bottom

4. Steel angle welded to rebars protruding from columns

5. Grouting with cement mortar

As the main reinforcement bars are welded together, the column acts as fixed-ended.

1 – Column with assembly bolts at the top

2. Column with steel plate at the bottom

3. Bolts fastened to steel plate

4. Grouting with cement mortar

5. Steel plate welded to column bars

The four assembling bolts and the embedded steel plate form a fixed-ended column.

1. Column with assembly bolt at the top

2. Precast beam

3. Hollow core slab

4. Column with steel plate support and recess

5. Grouting with cement mortar

6. Dowel-hole connection

1. Column with corbels and assembly bolt

2. Column with steel plate and recess

3. Grouting with cement mortar

4. Precast beam

5. Hollow core slab

6. Dowel-hole connection

The assembly detail shows a normal column-to-column joint and two simply supported beams.

Figure 5.39 Column/Beam Connection With In-Situ Jointing And Looped Bars

1. Column with anchor insert at the top

2. Steel plate as support

3. Precast beam with protruding stirrups

4. Dowel screwed into insert

5. In-situ concrete or grouting

The two beams are restrained by the use of protruding stirrups and locking dowel.

1. Column with cast-in steel plate and protruding dowels at the top

2. Reinforced neoprene rubber bearing

3. Beam with dowel holes

4. Grouted dowel-hole connection

5. Non-grouted connection

To the left, a movable bearing is shown; to the right, a fixed bearing is used.

Figure 5.41 Column-Beam

1. Column with corbels and anchor insert with dowel

2. Bearings: steel or neoprene

3. Beam with stirrups

4. Column-beam joint cast in-situ

Figure 5.42 Half Joint Column/Beam Connection

1. Column with corbels and cast-in dowels

2. Precast beam with half joint

3. Grouted dowel-hole connection

4. Dowel protruding from column

In Figure 5.42, the components are placed on top of each other. Using a beam with half joint, the corbels can be hidden and the structural height can be reduced as shown in Figure 5.42.

Figure 5.43 Column-Beam With Moment And Shear Continuity

1. Column with anchor insert

2. Steel bearing plate

3. Beam with protruding stirrups and rebars at the top

4. Welded connection using steel angle

5. Reinforcement bar

6. In-situ concrete or grouting

Figure 5.44 Edge Column/Beam

Connection With Moment And Shear Continuity

1. Column with corbel and cast-in dowel

2. Steel bearing plate

3. Beam with stirrups and protruding rebars at the top

4. Welded connection

5. Reinforcement bar or bolt

6. In-situ concrete or grouting

The beams can be connected to both the bottom and top by stirrups, locking bars or welding.

Figure 5.45 Column/Beam Connection With Temporary Steel Section Supports

1. Column component with anchor insert

2. Steel angle bolted to column

3. Beam with embedded steel section

4. Connection using protruding stirrups and reinforcement placed on site

5. Casting on site

In Figure 5.45, a combination of a temporary and a permanent column-beam support is shown. First the embedded steel profile acts as support, later the stirrups and locking bars take over.

1. Prestressed main beam with anchor inserts at the top

2. Secondary beam or purlin with protruding stirrups

3. Dowel screwed into insert

4. Stirrup-dowel connection

5. Cast in-situ joint

The connecting detail is simple, cheap and easy to execute.

1. Prestressed beam

2. Secondary beam

3. Dowel protruding from beam

4. Grouted dowel-hole connection

With the use of beam half joints, a more aesthetic solution has been obtained.

Figure 5.48 Secondary To Main Beam Half Joint Connection

1. Prestressed main beam

2. Transverse beam as double corbel

3. Secondary beam with half joint

4. Dowel-hole connection

To decrease the total construction height, double corbels can be used.

1. Beam with half joint

2. Cantilevered beam

3. Dowel-hole connection, half-beam joint

Two half-beam joints have to be considered.

1. Beam with anchor inserts at the top

2. Hollow core slab

3. Dowel screwed into insert

4. Reinforcement in slab joint

5. In-situ concrete or grouting

Figure 5.51 Beam-H. C.Slab

1. Precast beam

2. Hollow core slab

3. Stirrups protruding from the top of beam

4. Joint reinforcement

5. Casting on site

Figure 5.53 Beam-H. C.Slab

1. Precast beam

2. Hollow core slab

3. Dowel in insert

4. Locking stirrups

5. Casting on site

Figure 5.51 shows modular slabs and a neutral zone; Figure 5.52 uses non – modular slabs. Both solutions result in a wider cast-on-site joint.

Figure 5.54 Beam-H. C.Slab

1. Precast beam: half inverted T

2. Hollow care slab

3. Anchor insert

4. Joint reinforcement screwed into insert

5. Casting on site

It is important to anchor the joint reinforcement to, for instance, edge beams.

1. Precast beam

2. Plank

3. Stirrups protruding from beam

4. Reinforcement placed on site

5. Cast in-situ structural topping

1. Precast beam t~T j

2. Plank I

3. Reinforcement protruding j

from beam j

4. Reinforcement placed on J

site j j

5. Cast in-situ structural,

topping _ !

L

The combination of precast and cast in-situ structures gives good opportunities for the transmission of forces in the main structural system.

1. Beam: inverted T

2. Double T-slab

3. Structural topping

Normally the double T-slabs are produced with cast-in steel plates in the ribs for a welded support, and with protruding stirrups in the plate for the cast in-situ structural topping.

As double T’s are normally long-spanning components, moments and movements in the joints have to be considered in the structural design.

Figure 5.60 Beam-Wall Connections

1. Wall

2. Beam placed in the wall plane of symmetry

3. Beam placed perpendicular to the wall

Joints Used In Singapore Projects

The table below shows a compilation of connection and jointing details commonly used in Singapore. These details have been used in various projects such as private residential buildings, public housing, commercial and industrial buildings.

Types Of Joints Used Locally

C

£

3

0

о

Beam

Slab/Plank

Wall

Stump

Precast

Panel/Fagade

Staircase

Column

5.9» 5.11, 5.12

5.9,5.11, 5.12

5.17, 5.18

5.9,

5.10

Beam

5.1, 5.3, 5.4, 5.5, 5.6, 5.8, 5.14

5.20

iW s’""-‘-‘ . –

Slab/Plank

5.1, 5.2

5.7, 5.8, 5.15, 5.16, 5.20

! 5.27, 5.28, 5.7,5.16 ; 5 29, 5.30, 5.31

Wall

5.21,5.22, 5.23,5.24, 5.25, 5.26

Ш j……………….. ;

1. Tie beam

2. Links

3. Steel mesh

4. Concrete topping

5. Hollow core slab

6. Shear links (if structurally required)

1. L shape T10 or R10 at 600c/c

2. Steel mesh

3. Concrete topping

4. Hollow core slab

5. Foam or cement/sand block – out

1. Reinforcement to engineer’s design

2. Neoprene strip

3. PC/RC beam

4. Hollow core slab

5. Steel mesh

1. Reinforcement to engineer’s design

2. Shear links —I r~

3. Steel mesh

4. Plastering

5. Reinforcement in pour strip

6. Hollow core slab

7. Concrete topping

8. PC/RC beam

9. 20mm recess in beam lab

1. PC external wall

2. 20mm dry pack under external wall

3. Backer rod

4. Reinforcement (from PC wall)

5. Plank

6. In-situ topping

1. Sand/cement mortar or grouting

2. Steel mesh

3. Plank

4. PC beam / wall

5. Dowel bars

Column And Column/Beam Connection

1. Pilecap

2. Links loop round steel bars

3. Cast in-situ concrete

4. In-situ beam bars

5. Column steel bars to extend above floor for grouted pipe sleeve column connection

6. Steel dowel for site safety

Stages of Construction

A. Construct foundation and 1st storey RC work

B. Erect precast columns

C. Grouting of column base

D. Launch precast beams and floor slab elements

E. Cast in-situ RC work

F. Launch precast beams and floor slab elements

G. Cast in-situ RC work

1. The gap is to be formed by seating precast column onto shimming plates (with the adjusting bolts screwed down to the lowest position).

2. Template to position bolts

3. Ground slab

4. Grouting

5. Nuts and washer plates

6. Base angle

7. Base plate (recessed from column faces)

8. Precast column

9. Bars welded to base plate

10. Column bars

11. Pilecap

1. Neoprene strip

2. Horizontal loop at beam ends

3. PC beam

4. Corbel reinforcement to engineer’s design

5. PC column

6. Column bars

7. Bend-up beam reinforcement

8. In-situ reinforcement

9. Column links

Figure 5.12 Column / Beam Connection Without Corbel

1. Precast beam

2. Cast-in end plate with horizontal welded bars in PC beam

3. Cast-in steel plate with vertical welded bars at column face

4. Site welding to prevent beam toppling

5. Shear friction steel

6. Precast column

7. In-situ placed reinforcement

8. Bend up beam reinforcement

9. Upper floor precast column

10. Pipe sleeve

11. Starter column bars from lower precast column

12. 25 thick non-shrink grout

13. Column links

14. In-situ concrete

Figure 5.13 Typical Section Of A Precast Building (Section And Details To Refer To Figures 5.14 To 5.20)

This is a typical section of a precast concrete structure for a dormitory. The precast members consist of single storey high column and beam with integrated partition walls. A cantilever beam is incorporated: in the outer frame at the corridor which is column free. Hollow core slabs are used as internal floor; structure and profiled precast planks incorporating perimeter beams are used at the corridor. Ail internal and external walls are precast with architectural features of window sills, copings, drips etc. The precast components are simple pin-connected both vertically and horizontally with either cement/ sand mortar or grouted joints. An in-situ 75mm thick concrete topping throughout the floor will bind all members together to provide the necessary structural action to resist horizontal forces.

Reinforcement added on site

Steel mesh Cast in-situ concrete Rebar from precast plank Cantilever beam from precast frame

1. Reinforcement added on site

2. Steel mesh

3. Precast wall

4. Drypack cement mortar

5. Reinforcement to engineer’s design

6. Concrete topping (75mm – 100mm)

7. Dowel bar

8. Corrugated pipe sleeve (to be grouted)

Figure 5.16

1. Precast wall

2. Backer rod

3. Drypack cement mortar

4. Reinforcement

5. Concrete topping

6. Precast hollow core slab

7. Open horizontal joint

8. Steel mesh

Figure 5.17

1. Precast wall

2. Cottering reinforcement (placed on site)

3. Precast column

4. Reinforcement to engineer’s design

5. Plastering

6. Column and wall joint to be cast in-situ

7. Recess in wall for plastering

Figure 5.18 Column/External Wall Connection

1. Precast wall

2. Reinforcement to engineer’s design

3. Precast column

4. Cottering reinforcement (placed on site)

5. Column and wall joint to be cast in-situ

6. Backer rod

Figure 5.19 Column To Column Vertical Joint

1. Column

2. Vertical castellations

3. Grouting

Figure 5.20 Hollow Core

Slabs Beam/Wall Connection

1. Precast wall

2. Drypack cement mortar

3. Dowel reinforcement to engineer’s design

4. Concrete topping

5. Steel mesh

6. Hollow core slab

7. Precast beam

1. Joint rebar

2. Pipe sleeve

3. Steel mesh

4. Space bar

5. Edge castellation

6. Reinforcement

Procedures for connecting internal walls using pipe sleeves

A. Levelling blocks are placed

B. Lower the upper member Into position

C. Grouting of horizontal joint

Procedures for connecting external walls using pipe sleeves

D. Levelling block is placed

E. Lower the upper member into position

F. Grouting of horizontal joint

1. Cast in-situ slab

2. Rebar embedment; dowel installed in factory

3. PC Wall

4. Rebar embedment; dowel installed in factory

5. Grouting

1. PC wall panel

2. Watertightness sealing strip

3. Aluminium or stainless steel flashing

4. Backing

5. Sealant or mortar

6. Baffle strip

7. Design gap

1. PC wall panel

2. Recess profile for baffle strip

3. Baffle strip

4. Backing

5. Sealant or mortar

6. Drained and ventilated air space

The close and open joints have both been successfully used to ensure watertightness in the joints of precast wall panels.

The close joint adopts a single stage sealing using either polysulphide mastic or silicone sealants to prevent the penetration of air and water. The open joint has a 2-stage sealing feature namely a front protection baffle and a rear air-tight seal. Water penetrating the front baffle will be drained away in the airspace between the 2 seals.

Most failures in close joints involve aging, loss of surface adherence or elasticity of the sealant material. For good performance, it is necessary, therefore, to note the followings:

1. good workmanship preferably by specialists

2. good sealant material with correct proportioning or resin and inert materials

3. sufficient joint dimensions with enough width and depth for proper joint filling

4. regular and plain joint edges to ensure good surface adherence

5. seal should be set back in the joint for protection from weather elements

The watertightness of open joint depends critically upon the effectiveness of the air-tight seal at the rear of the joint. Damages to the seal may be due to the movement of the wall panels, loss of adherence of air-tight sealant or dropping off of the mortar or grouting. The loss of front baffle may arise from inadequate end stoppages which cause the baffle to fall out of the joint or from simple vandalism. Compared with close joint, the placement of open joint sealing features is carried out during the erection of the panels. It is thus necessary to check that the insert grooves for baffle in the adjoining panels run relatively parallel to each other at the joint. A further disadvantage of the open joint is that it is difficult to inspect and maintain the joint particularly at the intersections of the horizontal and vertical joints. Repair of leaking joints is also difficult. Despite these shortcomings, the open joints are less exposed to the weather than close joint and movement of the panels does not generally affect the effectiveness of the joints. Most open joints are found to give little trouble in service.

1. Cement mortar (10-15mm thick)

2. Roughened contact faces

ASSEMBLY

5.1 General

5.2 Joints Used In Singapore Projects

5.3 Joints Used In European Countries

Chapter 5 PRECAST CONCRETE ASSEMBLY

5.1 General

A complete statical evaluation of prefabricated buildings includes the following phases:

1. load assessments

2. formulation of a model of the main structural system

3. description of load paths

4. design of structural members

5. design of connections

Construction drawings for a prefabricated building project will normally consist of architectural sketches, modular details, general modular drawings, production drawings and assembly details.

For designers not familiar with prefabicated building designs, there will be considerable confusion with the selection of the appropriate methods of jointing and connections of precast components. With the exception of some common ones, the development of connection details is often on a project to project basis. Even the same details may be subjected to various modifications as dictated by the different structural and architectural requirements.

Despite the different manners in which a connection detail may be executed, the type of joint details must fulfil the following requirements:

1. compatibility with adjoining structural members

2. economy of materials

3. manufacturing and erection techniques

4. ease of assembly and speed of construction

5. final aesthetic joint appearances

There are basically three different types of connections used in precast concrete structures, namely, the cast in-site joint including grouted pipe sleeves, mechanical joint by bolting or welding, or a combination of both. Generally, the cast in-site type is the cheapest and it fits well into the craftsmanship already available on the building site. Bolted connections are easy to execute with both skilled and unskilled labour, whereas welding operations call for skilled labour or specialists. In terms of execution, bolted and welded joints normally need closer supervision and higher quality control.

This chapter presents an overview of the various jointings and connections of precast components which may assist the designer and architect in the design of prefabricated buildings. The details represent a cross-section of some of the proven techniques used locally in residential buildings, public housing, commercial and industrial buildings. As the local construction industry is relatively new to precast construction techniques, a selection of connection details from overseas are also included to provide readers with a wider spectrum of the connection techniques.

The details should be used a guide instead of as a design manual. It must be emphasised that the responsibility for a proper connection fulfilling all relevant performance requirements rests with the structural designer and the architect working often in close consultation with the precaster and contractor in an integrated approach during the design, development, fabrication and construction of the precast buildings.

Design Information

thick, 3 m long and is designed as braced structure with pin-connection at the floor levels. The wall is erected with a 20 mm thick horizontal joint which is to be grouted. Vertical ties from foundation to roof are provided at intervals along the wall length.

a. Loading:

Total statical floor area carried by the wall is determined to be about 25 m2. Dead load :

Say N = 14840 kN

nw = 14840/3 = 4947 kN/m

b. Vertical load capacity

Effective wall height la = 1,0lo

= 1.0 x (3.2-0.175)

= 3.025 m

Slenderness ratio Jb = 3025/250 = 12.1

The wall is considered a short wall under Part 1, clause 3.8.1,3. CP65.

From equation 42 (Part 1, clause 3.9.3.6.1) of the Code, the vertical load capacity is given as : nw < 0.35fcuAc + 0.67Ascfy

nw = 4947 kN/m

Asc = (4947 X 103 – 0.35 x 45 X 1000 X 250) / (0.67 x 460)

= 3275 mm2/m

Per face = 1638 mm2/m

Use T16 -125 c/c per face (As= 1675mm2/m)

c. Vertical structural ties

Vertical tie force per floor = 1.05 x 331.9 + 0.33 x 37.5 = 360.9 kN

Tension steel area As = 360.9 x 103/(460)

= 785 mm2

Use 3 numbers of T20 (£AS = 943 mm2) with one at each end of the wall and one number at the middle section

d. Horizontal joint capacity

Joint thickness t„ = 20 mm

Permissible concrete compressive stress (Part 1, clause 5.2.3.4) = 0.6fcu Net area for vertical load transfer (Part 1, clause 5.3.6 of the Code) = 75%AC

nw = 4947 kN/m and nw = 0.6fcu x 0.75AC

Minimum concrete strength required for the joint infill:

fcu = 4947 x 103 / (0.6 X 0.75 X 1000 x 250)

= 44 N/mm2

Use fcu = 45 N/mm2 as joint infill

e. Connection details

Some typical connection details of the wall W1 and floor are shown in Figure 4.14 to Figure

4.16.

f. Production details

Typical production details for the precast wall W1 are shown in Figure 4.17.

3xT20 lapped with grouted pipe

>

/ .

250 thk precast wall

3×065 corrugated pipe to be grouted

SFL

}

j::: :::::;:.::: ::: . $ ,

II": ї | i::- ::: ::: j i

:::::: ::: :у i ::: : r:’ ::: з i ::: • .і i

<::: ::: ::: . і i і: :::;::: ::::::.::::::: ::..3 i

250 thk precast wall

i – T

3xT20

S s’ _

-■■■■■■ ::: :::

/

3000

/

Л 7

Figure 4.15 Vertical Ties

Structural System

The structural system shown in a typical layout in Figure 4.13 consists of cast in-situ prestressed flat plates of typically 175 mm thickness. The floor is supported by a series of precast load bearing walls which are generally 200 to 250 mm thick depending on the gravity loads the wall carries. The precast walls are located at the gable ends of each living unit as well as in between rooms. In areas where precast walls are not possible due to architectural reasons, the floor plates are supported by cast in-situ beams of typically 250 x 600 mm deep. The precast walls are braced in two directions by a cast in-situ stabilising lift and staircase cores which are 300 mm thick. They are assumed to carry all lateral loads.

Residential Block

1. Project Description

The project consists of four blocks of 30-storey residential apartments with basement carparks. There are four units on each floor which includes a common passenger lift, fire lifts and two staircases. Floor to floor height is typically at 3.2 m. For design illustration, only a typical floor structural system is presented. It is assumed to carry all lateral loads.

Design of supporting Nibs

Reaction at supporting nibs V = 44.50/2

= 22.25 kN/m

a„ = 90 + 30

= 120 mm

Bending moment at section X = M = V x a,

= 22.25 x 0.12 = 2.67kNm/m

95-20-5 70 mm

Bending Steel

0.5 + 10.25 -(————- )

N .9bd2f„./

F bt = 0.87fyAs

= 0.87 X 250 X 28 X 10‘3

= 6.09 kN

Minimum bending radius

Г

F h, x 1 + 2(0/ab)

0 2fcu

0

6 mm

ab

150 mm

fcu

=

40 N/mm2

r

>

6.09 x 103 x 1 + 2(6/150)

6 2×45

>

12.2 mm

2.03 0

provided r = 2.75 0 > 2.03 0

Check shear

V =

22.25 kN/m

V =

22.25 x 10s

1000×70

=

0.32 N/mm2

rs =

188 x 100%

1000 X 70

=

0.27%

Vo =

°-84 (rs)1/3 (400/d)V4 (fcu/30)V3

Йщ

8m =

1.25

Vc =

°-.84- (0.27)1/з (400/70)1/4 (45/30)

1.25

=

0.77 N/mm2 > 0.32 N/mm2

SECTION 2-2

SECTION 3-3

TOP VIEW ЗА

Figure 4.12 Mould And Reinforcement Details Of Precast Flight (12-Storey Office Block)

Design Of Structural Integrity Ties

Basic design data : Total number of floor

Average UDL dead load

Average UDL live load Basic tie force Ft = 20 + 4n„

= 20 + 4×12 = 68 kN > 60kN Hence Ft = 60 kN/m

1. Horizontal ties (Part 1, clause 3.12.3.5,)

a. Periphery ties

Design tie force = 1.0 F,

= 60 kN

Steel area As = 60 x 103/460

= 130 mmz

b. Internal ties

Case 1 : Tie force = 0.0267(gk + qk) F, lr

= 0.0267(7.6 + 3.0) x 60 x 8.0 = 135.8 kN/m Case 2 : Tie force = 1.0 F,

= 60 kN/m

Hence Case 1 governs.

Using steel mesh as floor ties,

As = 135.8 x 103/485
= 280 mm2/m

Use D6 mesh (фб @ 100 c/c both ways, As = 283 mm2/m) within the 65 mm thick topping. This provides automatically the required quantity of floor ties in the other direction as the spans between the bays are similar in both directions.

c. Column ties

Internal columns are tied by D6 mesh in both directions and all corner columns are automatically tied as the adjacent floors are cast in-situ. Hence only edge columns need to be checked.

Case 1 : Tie force = 2.0F, (ls F,/2.5 is less critical)

= 2.0 x 60 = 120 kN

Case 2 : Tie force = 3% of ultimate axial column load

At 2nd storey, ultimate column axial load for edge column is conservatively estimated (allowing for brickwalls) to be :

N = (1.05 X 5768.4 + 0.33 x 1152.0) x 2/3 = 4291.3 kN

Hence tie force = 3 x 4291.3/100 = 128.7 kN

Therefore Case 2 governs the design.

As= 128.7 x 103/460 = 280 mm2

= 35 mmz/m over 8m bay width

The D6 mesh is anchored to the perimeter beams and hence no separate edge column horizontal ties are required.

2. Vertical ties

The vertical ties in the columns have been considered in the design of column joint connection.

Vertical tie requirement

Maximum axial load per floor = 1.05×480.7 + 0.33×192.0 = 568.1 kN

Vertical tie reinforcement As= 568.1 x 103/460 = 1235 mm2

Total provision of bolt (root area) = 362 x 6

= 2172 mm2 > 1235 mm2 OK

Total provision of welded bars to base plate = 8T16

= 1609 mm2 > 1235 mm2 OK

Vertical column tie requirement is satisfactory at the column to column joint.

4. Design of corbel

a. Check shear stress

V = V/bd

= 430.8 x 103/(500 x 275)

= 3.13 N/mm2 < 0.8Vfcu = 5.66 N/mm2

adopt max. vc = 5.00 N/mm2 OK

і. Main steel

0.9(z/d)(ayd)(1 – z/d)
(a„/d)2 + (z/d)2

v/fcu = 3.13/50 = 0.063
a„/d = 125/275 = 0.454

Hence (z/d)2 – 0.866(z/d) + 0.0276 = 0 z/d = 0.833

200 (z/d – 0.55) / (1 – z/d)

200 (0.833 – 0.55) / (1 – 0.833) 339 N/mm2

Ft = V x ajz

= 430.8x 125/(0.833×275) = 235.1 kN > V/2

Figure 4.10 Reforcement Details Of Precast Column (12>Storey Office Block)

Beading Reinforcement

Assuming no effective restraint at support: Ultimate bending moment at mid-span

= 44.50 X 3.49/8

= 19.41 kN/m

153-25-5 123 mm

Say d =

120 mm

z

0.5+ 10.25-f M

d

У V0.9bd2fcu/

=

0.5+ / 0.25-/ 19.41 x 106

V .9 X 1000 x 1202 X 45/

0.965

use -5- =

0.95

z =

114 mm

A,

M

0.87fyz

=

19.41 x 106

0.87x460x 114

=

425 mm2/m

Use T10-150 c/c. provided A, = 523 mm2/m

Deflection

M

19.41 x 106

bd2

1000 x 1202

=

1.35

f„

5/8 fy X Ag req / As prov

=

5/8x460x425/523

=

234 N/mmz

Tension modification factor

(477-fv)

0 =

0.55 + о

120 (0.9 + M/bd )

477 – 234

0.55+ ———————-

120(0.9 + 1.35)

Cl.3.10.2.2, Parti, CP 65,

basic span/depth ratio of staircase flight =

£

0 x (span/depth ratio)

3490

1.45 x 23

=

105 mm< 120 mm