Design of Precast Elements
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Transcript of Design of Precast Elements
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Under the Guidance of: Dr. Aswath M.U.
Presented by- Rahul Das Biswas
USN: 1BI14CSE14,
M.Tech (Structural Engineering)
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Contents Introduction
Advantages
IS Recommendations
Materials
Prefabrication Systems
Types according to IS
Design Requirement as per IS
Progressive Collapse
Design of Ties
Design of Vertical Pillars (Walls, Diaphragms, Cores)
Frame installation
Conclusion
References
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Introduction
WHAT ?
WHY ??
HOW ???
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“What”
Precast:
Produced in Factories
Transported to Site
Assembled at Site
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“Why”Advantages of Precast:
Partial or total saving of materials
Multiple using of shuttering
Better accuracy of workmanship
Less Man Power Required
Interruption in concreting can be omitted
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“Why”
Advantages of Precast:
Fewer expansion joints
High capacity
Shorter construction time
Independent of adverse weather conditions
during construction
Continuing erection in winter time until -20 °C
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“Why”
Advantages of Precast:
Opportunities for good architecture
Reduced energy consumption
Safety in construction
Low shrinkage with high strength
High modulus of elasticity
Very little micro cracks
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“Why”
Advantages of Precast:
Resistance to chemical attack
Toughness and impact resistance
Volume stability
Durability against chloride attack
Reduced maintenance cost
Higher Strength at earlier ages and low heat of hydration
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“How”
From Structural Engineering Point of view:
Material
Aspect
Type of Construction
Design (With all Safety Concern)
Detailing
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IS CODES TO BE FOLLOWED
IS 15916: Precast Construction
IS 875: Design Loads
IS 456: Concrete
IS 1893 and IS 13920: Seismic Design
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Characteristics of Material
Recommended by IS: 15916: 2011
• Easy Availability
• Light- Weight
• Thermal Insulation Property
• Easy Workability
• Durability
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Characteristics of Material
Recommended by IS: 15916: 2011
• Non-combustibility
• Sound insulation
• Easy assembly and compatibility to form a complete
unit
• Economical
• Any other special requirement required for particular
application
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Aspects to be considered as per the
Recommendation of IS: 15916: 2011
Effective utilization of spaces
Straight and simple walling scheme
Limited sizes and numbers of components
Limited opening in bearing walls
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Aspects to be considered as per the
Recommendation of IS: 15916: 2011
Regulated locations of partitions
Standardized service and stair units
Limited sizes of doors and windows with
regulated positions
Structural clarity and efficiency
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Aspects to be considered as per the
Recommendation of IS: 15916: 2011
Suitability for adoption in low rise and high rise
building
Ease of manufacturing, storing and transporting
Speed and ease of erection and
Simple jointing system
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Types of Precast System according to
IS: 15916: 2011
Prefabrication System
Open Prefabrication
System
Partial Prefabrication
System
Full Prefabrication
System
Large Panel Prefabrication
System
Staircase Systems
Precast Floors Precast Walls
Box Type Construction
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Design Requirement as per IS: 15916: 2011
Progressive Collapse
(A Major Threat to Safety of Structure)
Collapse or Failure of the major part
Due to the damage of small areas or
Failure of single element
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Precaution: Against Progressive Collapse
1) All buildings should be capable of safely
resisting the minimum horizontal load of 1.5% of
characteristic dead load applied at each floor or
roof level simultaneously.
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2) All Buildings Shall Be Provided With Effective
Horizontal Ties1) Around The Periphery
2) Internally (In Both Directions) &
3) To Columns & Walls.
3) All Buildings of Five or More Storeys Shall Be
Provided With Vertical Ties.
Precaution: Against Progressive Collapse
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Design of Ties
(Peripheral Ties)At each floor and roof level an effectively continuous tie should be
provided within 1.2 m of the edge of the building or within theperimeter wall.
The tie should be capable to resisting a tensile force of Ft equal to 60 kNor (20 + 4N) kN whichever is less, where N is the number of storeys(including basement).
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Design of Ties
(Internal Ties)
These are to be provided at each floor and roof level in two directions
approximately at right angles. Ties should be effectively continuous
throughout their length and be anchored to the peripheral tie at both
ends, unless continuing as horizontal ties to columns or walls.
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Design of Ties
(Internal Ties)
• The tensile strength, in kN per meter width shall be
the greater of-
• gk + qk = Avg. characteristic D.L. + L.L in kN/m2
• lr = Greater of-• The distance between the centre of columns
• Frames or walls supporting any two adjacent floor spans in the
direction of the tie under consideration.
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Design of Ties
(Internal Ties)
The bars providing these ties may be distributed evenly in the
slabs or may be grouped at or in the beams, walls or other
appropriate positions but at spacings generally not greater
than 1.5 lr.
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Design of Ties
(Horizontal ties to column and wall)• All external load-bearing members such as columns and
walls should be anchored or tied horizontally into the structure at each floor and roof level. The design force for the tie is to be greater of-
a) 2 Ft kN or ls × Ft × 2.5 kN, whichever is less for a column or for each metre length if there is a wall. ls is the floor to ceiling height, in meter.
b) 3 percent of the total ultimate vertical load in the column or wall at that level.
• For corner columns, this tie force should be provided in each of two directions approximately at right angles.
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Design of Ties
(Vertical ties)
Should be provided for buildings of five or morestoreys
Each column and each wall carrying vertical loadshould be tied continuously from the foundation to theroof level. The reinforcement provided is required onlyto resist a tensile force equal to the maximum designultimate load (dead and imposed) received from anyone storey.
In situation where provision of vertical ties cannot bedone, the element should be considered to be removedand the surrounding members designed to bridge thegap.
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Design of Vertical Pillars
(Walls, Diaphragms, Cores)
Indian Standards for Designing Precast is
unavailable
Adopt any code of practice which is-
Safe
Durable
Economical
Reliable from Past Experience
Methods of mounting precast structures used in Russia will
be discussed
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Primary Load-bearing Members of the Building
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Optimal Configuration
The frame members to securely perform their
functions without “extra” efforts. This means that
the columns operate only for compression, floor
structures operate only for bending, with no
forces in the plane of the slab (the membrane
group of efforts), pylons take horizontal forces
ensuring the necessary rigidity of the building.
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Optimal Configuration
• The principle of concentration of material isobserved. To reduce the material consumption theload should be transmitted through the minimumnumber of elements.
• The main feature of the framework is the abilityto ensure the integrated operation of all itselements: columns, pylons, floor slabs, foundationslab, piled and/or soil foundation. Proper use ofthese features can improve the designcharacteristics of the building frame whilereducing the consumption of its materials.
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Rules of the Pylons Distribution
(Rule No. 1)
• All of the pylons should not be
intersected by straight lines on
which they are rested at one
point
• All of the pylons should not be
parallel
Building plan (slab & pylons)
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Rules of the Pylons Distribution
(Rule No. 2)
The pylon should be sufficiently hard with a height of the
cross section equal to 1/10 – 1/5 of the building height.
With a smaller size the pylon will be more flexible and
will transmit a significant portion of the horizontal load
onto the columns or originate the need for more pylons.
If several flat diaphragms are connected to one core, the
height of their cross section can be reduced by virtue of a
more rigid joint operation with respect to the total
cumulative individual work.
It is necessary to strive for the minimum number of
pylons in the building.
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Rules of the Pylons Distribution
(Rule No. 3)
Determining efforts in the plane of the slab
aab 5.26
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Rules of the Pylons Distribution
(Rule No. 4)
If one looks at the aggregate of all the diaphragms of the
building combined with floor structures, it is possible to
find the shear center of the building. If the shear center
does not coincide with the center of gravity, the building
will have additional bending stresses. If the resultant
wind load does not pass through the shear center, the
building will be subject to additional twisting forces. The
configuration in which all three centers coincide will be
optimal. The easiest way to achieve is to prepare a
symmetrical in the two axes building plan with a
symmetrical arrangement of the pylons.
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Frame installation
(Column)
Schemes Of Installation of Multi-story Columns Using A Set of Individual Installation
and Mounting Devices and Tooling a — the location of columns and accessories, b — securing columns by knees, c — clamp for
securing knees in the column; 1 — foundation socket, 2 — readymade mount, 3 — column, 4 —
clamp 5 — knee, 6 — drawbar of the knee, 7 — wedges, 8 — anchoring device, 9 — crimping
rope
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Frame installation
(Cross beams)
Cross beam installation: a — applying an axial mark
on the column pillar; b — installing cross beam; c —
column pillar alignment
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Frame installation
(Pylons)
Installation of interior walls — diaphragm plates — in a framed building: a —
installation, b — temporary fastening; 1 — knee-piece, 2 — diaphragm with a
cantilever replacing a collar beam, 3 — a universal sling, 4 — movable L-
clamp with a rack.
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Frame installation
(Slab panels)
Laying bracing (spacing) (а) and lintel (b) floor slab panels
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Conclusion
Considering its huge advantage, Technology
should be adopted in India
Safety should be the 1st concern
Past Hazards should be analyzed and
precautions to avoid it should be taken
Indian Standard Code required for Design
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References
• http://en.wikipedia.org/wiki/Precast_concrete
• IS: 15916: 2011
• IS: 13920: 1993
• “DESIGN RULES FOR PRECAST CONCRETE:
VERTICAL PILLARS (WALLS, DIAPHRAGMS,
CORES)” By- Mark P. Son & Denis V. Konin, Redecon
2014, Bangalore
• “Design and Construction of Multi-Storey Residential
Buildings with Precast Concrete” By- Dr. H S Lai ,
Redecon 2014, Bangalore
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