lec.1 introduction

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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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



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

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