Analysis and Design of One-way Slab System

45 Pages·2016·4.54 MB·English

by  Aamir Raza

Department of Civil Engineering, University of Engineering and Technology Peshawar
Lecture-02
Analysis and Design of
One-way Slab System
(Part-I)
By: Prof Dr. Qaisar Ali
Civil Engineering Department
UET Peshawar
www.drqaisarali.com
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Topics Addressed
 Concrete Floor Systems
 Analysis and Design of Slabs
 Basic Design Steps
 Example: Design of 90′ x 60′ Hall
 References
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Concrete Floor Systems
 Beam Supported Slabs
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Concrete Floor Systems
 Flat Plate
 Punching shearisatypical probleminflatplates.
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Concrete Floor Systems
 Flat Slab
 DropPanel:Thickpartofslabinthevicinity ofcolumns
 ColumnCapital:Columnheadofincreased size
 Punching shear can be reduced by introducing drop panel
andcolumncapital
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Concrete Floor Systems
 One-wayJoist
 Joist construction consists of a monolithic combination of
regularly spaced ribs and a top slab arranged to span in
onedirectionortwoorthogonal directions.
Rib
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Concrete Floor Systems
 Two-wayJoist
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Analysis and Design of Slabs
 Analysis
 Unlike beams and columns, slabs are two dimensional
members. Therefore their analysis except one-way slab
systemsisrelatively difficult.
 Design
 Once the analysis is done, the design is carried out in the
usual manner. So no problem in design, problem is only in
analysis ofslabs.
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Analysis and Design of Slabs
 Analysis Methods
 Analysis usingcomputersoftware(FEA)
 SAFE,SAP2000,ETABSetc.
 ACIApproximate MethodofAnalysis
 StripMethodforone-wayslabs
 MomentCoefficientMethodfortwowayslabs
 DirectDesignMethodfortwowayslabs
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Analysis and Design of Slabs
 One-Way and Two-WayBehavior
 Aslabwhenloadedinflexuremaybendinoneorbothdirections
One-Way Behavior Two-Way Behavior
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Analysis and Design of
One-Way Slab Systems
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Strip Method of Analysis for
One-way Slabs
 For purposes of analysis and design, a unit strip of one way
slab, cut out at right angles to the supporting beams, may be
consideredas arectangular beam of unit width, with a depth h
andaspanl asshown.
a
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Applicability of Strip Method
 The strip method of analysis and design of slabs having
bending inonedirection isapplicable onlywhen:
 Slabissupportedononlytwosidesonstiffbeamsorwalls,
 Slabissupportedonallsidesonstiffbeamsorwallswithratioof
largertosmallersidegreaterthan2.
 Note:Notapplicabletoflatplatesetc.,evenifbendingisprimarily
inonedirection.
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Basic Design Steps
 Basic Steps for Structural Design
 Step No. 01: Sizes:-Sizes of allstructuraland nonstructural
elements aredecided.
 Step No. 02: Loads:-Loads on structure are determined
basedonoccupationalcharacteristics andfunctionality(refer
Appendix Cattheendofthislecture)
 Step No. 03: Analysis:-Effect of loads are calculated on all
structuralelements
 Step No. 04: Design:-Structural elements are designed for
therespectiveload effectsfollowing thecodeprovisions.
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Basic Design Steps
 Sizes: ACItable7.3.1.1givestheminimumonewayslabthickness.
Table 7.3.1.1–Minimum Thickness of Non-PrestressedBeams or One-Way Slabs Unless
Deflections are Computed
Minimum thickness,h
Simply Oneend Both ends
Cantilever
supported continuous continuous
Members not supporting or attached to partitions or other
Member
construction likely to be damaged by large deflections
Solid one-way slabs l/20 l/24 l/28 l/10
Beams or ribbed one-way
l/16 l/18.5 l/21 l/8
slabs
l=Spanlength,definedonthenextslide.
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Basic Design Steps
Slab
 Sizes(DefinitionofSpanLength,l) Beam
h
Wall
l l
n n
lc/c lc/c
1) l= l ; for integral supports such as beams and columns with l ≤ 10′
n n
2) l= Minimum of [(l +h) or c/c distance] ; for non-integral supports such as walls
n
with any distance & for integral supports (beams and columns) with l > 10′
n
• l (span length) is used in calculating depth of members.
• ln(clear span) is used for determining moments using ACI coefficients.
• lc/cis (center to center distance) is used for analysis of simply supported beam.
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Basic Design Steps
 Loads:
 According to ACI 5.2 — Service loads shall be in
accordance with the general building code of which this
code forms a part, with such live load reductions as are
permittedinthegeneralbuilding code.
 BCP SP-2007 is General Building Code of Pakistan and it
refers to ASCE 7-10 for minimum design loads for buildings
andotherstructures.
 One way slabs are usually designed for gravity loading
(U=1.2D+1.6L).
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Basic Design Steps
 Analysis:
 Chapter 8 of the ACI addresses provisions for the analysis
anddesignofconcretemembers.
 According to ACI 6.5.1, as an alternate to frame analysis,
ACI approximate moments shall be permitted for design of
one-way slabs with certain restrictions, which are as
follows:
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Basic Design Steps
 Analysis: ACI 6.5.1
Uniformly distributed load (L/D 3)
Prismatic
1.2n n members
Two or more spans
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Department of Civil Engineering, University of Engineering and Technology Peshawar
Basic Design Steps
w
u
Integral with Simple
support support
  
n n n
1/14 1/16 1/11 Positive
Moment
x w  2
u n
Spandrel
1/24 1/10* 1/11 1/11 1/10* 0 Negative
support
Moment
Column 1/16 *1/9 (2 spans) xw  2
support u n
* 1/11(on both faces of other interior supports)
* 1/12 (for all spans with l < 10 ft)
n
Note: For simply supported slab, M = w l2/8, where l= span length (ACI 2.2).
u
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