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Northern Technical University Technical College of Mosul Building & Construction Technology Engineering Dept.
Analysis & Design of Reinforced Concrete Structures (1)
THIRD CLASS
Lecturer: Dr. Muthanna Adil Najm ABBU
2015-2016
Analysis & Design of Reinforced Concrete Structures (1) Introduction Lecture .1
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Dr. Muthanna Adil Najm
Design of Reinforced Concrete
Text Books:
1- Design of Concrete Structures (13th Edition) by: A. H. Nilson; D. Darwin &
C. H. Dolan
2- Building Code Requirements for Structural Concrete ACI 318-05
References:
1- Reinforced concrete Design (7th Edition) by: C. K. Wang , C. G. Salmon &
J.A. Pincheira
2- Design of Reinforced Concrete (7th Edition) by: J.C. McCormac & J.K. Nelson
Units
SI Metric British
Force
N
kN = 1000 N
1 kg = 9.81 N
gm
kg = 1000 g
Ton = 1000 kg
lb
kip = 1000 lb
1 lb = 4.448 N
Length
mm
m = 1000 mm
mm = 0.1 cm
cm
cm = 10 mm
m = 100 cm
in
ft = 12 in (˝)
1 in = 25.4 mm
Stress
Pam
N
Area
ForceStress
2
kPam
kN
2
MPamm
N
2
2cm
gm
2cm
kg
2m
Ton
psiin
lb
2
psiksiin
kip1000
2
MPaksi 895.61
Kilo Pascal = kPa = 103 Pa
Mega Pascal = MPa= 106 Pa
Gega Pascal = GPa = 109 Pa
Tera Pascal = TPa = 1012 Pa
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ACI building Code:
Whenever two different materials , such as steel and concrete, acting together, it is
understandable that the analysis for strength of a reinforced concrete member has
to be partial empirical although rational. These semi-rational principles and
methods are being constant revised and improved because of theoretical and
experimental research accumulate. The American Concrete Institute (ACI), serves
as clearing house for these changes, issues building code requirements.
Design Philosophy:
Two philosophies of design have long prevalent.
• Working stress method focuses on conditions at service loads.
• Strength of design method focusing on conditions at loads greater than
the service loads when failure may be imminent.
The strength design method is deemed conceptually more realistic to establish
structural safety.
Strength Design Method:
In the strength method, the service loads are increased sufficiently by factors to
obtain the load at which failure is considered to be “imminent”. This load is called
the factored load or factored service load.
Strength provide is computed in accordance with rules and assumptions of
behavior prescribed by the building code and the strength required is obtained by
performing a structural analysis using factored loads.
The “strength provided” has commonly referred to as “ultimate strength”.
However, it is a code defined value for strength and not necessarily “ultimate”.
The ACI Code uses a conservative definition of strength.
Safety Provisions:
Structures and structural members must always be designed to carry some reserve
load above what is expected under normal use.
strength required to strength provided
carry factored loads
Fundamentals
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There are three main reasons why some sort of safety factor are necessary in
structural design.
[1] Variability in resistance.
[2] Variability in loading.
[3] Consequences of failure.
Variability of the strengths of concrete and reinforcement.
Differences between the as-built dimensions and those found in structural
drawings.
Effects of simplification made in the derivation of the members resistance.
Loading:
Specifications:
Cities in the U.S. generally base their building code on one of the three model
codes:
Uniform Building Code
Basic Building Code (BOCA)
Standard Building Code
These codes have been consolidated in the 2006 International Building Code.
Loadings in these codes are mainly based on ASCE Minimum Design Loads for
Buildings and Other Structures (ASCE 7-98) – has been updated to ASCE 7-02.
Dead Loads:
Weight of all permanent construction
Constant magnitude and fixed location
Examples:
Weight of the Structure
(Walls, Floors, Roofs, Ceilings, Stairways)
Fixed Service Equipment
(HVAC, Piping Weights, Cable Tray, Etc.)
Can Be Uncertain….
pavement thickness
earth fill over underground structure
Live Loads:
Loads produced by use and occupancy of the structure.
Maximum loads likely to be produced by the intended use.
Not less than the minimum uniformly distributed load given by Code.
Minimum concentrated loads are also given in the codes.
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Dr. Muthanna Adil Najm
Structural System Overview:
1. Building system primary functions
2. Types of load
3. RC structural systems
4. RC structural members
1. Basic Building System Functions:
Support gravity loads for strength and serviceability during:
1. Normal use (service) conditions
2. Maximum considered use conditions
3. Environmental loading of varying intensities
2. Types of Load
Lateral
Wind
Earthquake
Soil lateral Pressure
Thermal
Gravity:
Dead
Live
Impact
Snow
Rain/floods
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4. RC Structural Systems
A. Floor Systems
B. Lateral Load Systems
A. Floor Systems:
Flat plate
Flat slab (w/ drop panels and/or capitals)
One-way joist system
Two-way waffle system
Flat Plate Floor System: Slab-column frame system in two-way bending
Advantages:
Simple construction
Flat ceilings (reduced finishing costs)
Low story heights due to shallow floors
Lateral deflection (sway)
Wind or
earthquakes
ertical deflection (sag)V
Dead, Live, etc.
Performance-Based Design: Control displacements within acceptable
limits during service loading, factored loaded, and varying intensities
of environmental loading
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Flat Plate w/Spandrel Beam System:
Advantages:
Same as flat plate system, plus
Increased gravity and lateral load resistance
Increased torsional resistance
Decreased slab edge displacements
Flat Plate w/Beams Floor System:
Advantages:
Increased gravity and lateral load resistance
Simple construction
Flat ceilings (reduced finishing costs)
Plan Elevation
Plan
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Flat Slab Floor System: Flat plate with drop panels, shear capitals, and/or column
capitals.
Advantages:
Reduced slab displacements
Increased slab shear resistance
Relatively flat ceilings (reduced finishing costs)
Low story heights due to shallow floors
One-Way Joist Floor System: Ribbed (joist) slab : (One-way bending)
Advantages:
Longer spans with heavy loads
Reduced dead load due to voids
Electrical, mechanical etc. can be placed between voids
Good vibration resistance
Gravity and lateral load frames
Plan Elevation
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Two-Way Joist Floor System: Waffle slab : (Two-way bending)
Advantages:
Longer spans with heavy loads
Reduced dead load due to voids
Electrical, mechanical etc. can be placed in voids
Good vibration resistance
Attractive Ceiling
• 2’ or 3’ cc. – Joists
• 4’ or 6’ cc. – Skip joists
• 5’ or 6’ cc – Wide-module joists
Top of Slab
1:12 Slope, type
8-24” for 30” Modules
16-24” for 53” Modules
14-24” for 66” Modules
Width varies
4”, 6” or larger
Typical Joist
2D lateral frames
Floor joists, type
2D gravity or lateral
frames
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B. Lateral Load Systems:
Frame Overview
Flat plate (& slab)-column (w/ and w/o drop panels and/or capitals) frame
systems
Beam-column frame systems
Shear wall systems (building frame and bearing wall)
Dual systems (frames and shear walls)
Frame: Coplanar system of beam (or slab) and column elements dominated by
flexural deformation
2D lateral frames
Waffle pans, type
Planar (2D) Space (3D)
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Basic Behavior:
Frame Advantages:
Optimum use of floor space, ie. optimal for office buildings, retail, parking
structures where open space is required.
Relatively simple and experienced construction process
Generally economical for low-to mid-rise construction (less than about 20
stories)
In Houston, most frames are made of reinforced concrete.
Frame Disadvantages:
Generally, frames are flexible structures and lateral deflections generally
control the design process for buildings with greater than about 4 stories. Note
that concrete frames are about 8 times stiffer than steel frames of the same
strength.
Span lengths are limited when using normal reinforced concrete (generally less
than about 40 ft, but up to about 50 ft). Span lengths can be increased by using
pre-stressed concrete.
Gravity Load Lateral Loading
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4. Structural Members:
Beams
Columns
Slabs/plates/shells/folded plates
Walls/diaphragms
Beam Elements: Members subject to bending and shear.
Shear Wall Lateral Load Systems
Shear wall
Elevation
Edge column
Interior gravity
frames
Shear deformations
generally govern
Gravity frames
Shear walls
Coupling beams
Elevator shaft configuration
Hole
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Column Elements: Members subject to bending, shear, and axial.
Slab/Plate Elements
Defn: Members subject to bi-directional bending & shear
Elastic Properties:
) (bending)n( EI/L f= bk = My/I (normal stress)
= GA/L (shear) sk = VQ/Ib (shear stress) v
(load, support conditions, L, E, I) (bending) f= b
V
V L
E,I,A M M
Elastic Properties:
= EA/L (axial) ak = F/A (normal stress) a
) (bending)n( EI/L f= bk l stress)= My/I (norma b
= GA/L (shear) sk = VQ/Ib (shear stress) v
(load, support conditions, L, E, I, A) (normal) f= b
V
V
L
M E,I,A M
F F
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Wall/Diaphragm Elements
Defn: Members subject to shear