BUILDING LOADS

Design

Strength

Loads

ReinforcementRatio

Member Dimension

DESIGN PROCESS

Design is the determination of the

general shape and all specific

dimensions of a particular structure

so that it will perform the function

for which it was created.

So , good design must be safe and

economic.

Building Codes

Buildings must be designed andconstructed according to the provisions of abuilding code, which is a legal documentscontaining as requirements related to suchthings as structural safety, fire safety, plumbing,ventilation, and accessibility to the physicallydisabled.

A building code has the force of law and isadministered by a government entity such as acity, a county, or, for some large metropolitanareas, a consolidated government.

Building codes do not give designprocedures, but they do specify the designrequirements and constraints that must besatisfied.

i.e. For structural engineer the prescription of minimum live loads for buildings.

Three National Code Organizations

• Uniform Building Code (west of Mississippi)

• Standard Building Code (southeastern states)

• BOCA National Building Code (northeastern country)

where BOCA stands for Building Officials and Code Administrators)

Unified building code- International Building Code

Design SpecificationsGives more specific guidance for the design ofstructural members and their connections.They are periodically revised and updated by theissuance of supplements or completely neweditions.

For steel;

1. American Institute of Steel Construction (AISC)- design of steel buildings and their connections.

2. American association of State Highway and Transportation officials (AASHTO) – covers the design of highway and bridges related structures. It provides for all structural materials normally used in bridges, including steel, reinforced concrete, and timber.

3. American Railway Engineering and Maintenance-of-Way Association (AREMA)-covers the design of railway bridges and related structures.

4. American Iron and Steel Institute (AISI)- deals with cold-formed steel.

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Types of Loads

• Determination of loads for which a given structure may be designed for is a difficult problem.

Questions to be Answered:

• What loads may structure be called upon during its lifetime?

• In what combinations these loads occur?

• The probability that a specific live load be exceeded at some time during lifetime of structure?

SCOPE OF THE LECTURE

• Types of loads.

• Static and dynamic loads.

TYPES OF LOADS

Loads are classified as static and dynamic . Static loads are independent from

time but dynamic loads are function of time.

Dead and live

loads are types of

static loads.

Dead loads are

those have

unchangeable

locations in

structure and their

values are certain

and constant .

Live loads are those

movable and their

values are uncertain.

Dead loads are calculated easily using structure dimensions and material density .

Live loads are movable and their values are uncertain , so they can not be

calculated directly and local or international specifications shall be consulted.

International Building Code IBC 2009 published live load values dependent on

types of building occupancy.

80 psf

50 psf

100 psf

Dynamic loads

The other group of loads is the dynamic loads , and the following are types of such loads:

Wind load Blast load

Impact load Flood loadSeismic load

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1. Dead load

Dead Loads consist of the weight of all materials and fixed equipment incorporated into the building or other structure.

– Weight of structure

– Weight of permanent machinery etc.

– Dead loads can be reasonably estimated if the member dimensions and material densities are known.

Types of Loads

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2. Live load:

Live loads are those loads produced by the use and occupancy of the building or other structure and do not include dead load, construction load, or environmental loads.

– Weight of people, furniture, machinery, goods in building.

– Weight of traffic on bridge

Types of Loads

CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan15

Live loads for various occupancies

Occupancy Live load,psf

Residential 40

Libraries(reading room) 60

Mercantile 75-125

Heavy manufacturing 125-150

Light storage 120-125

Heavy storage 250 minimum

Types of Loads..

2. Live load: (UBC Table 16-A)

Load Example: Live Load in Ballroom

Live Load = 100 lb/ft^2Ballroom

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The 40psf L.L specified by code for Residential Buildings is too

Conservative to account for the uncertainties in structural actions

Such as impact, fatigue, temp. effects etc.

Types of Loads2. Live load:

Types of loads

3. Environmental Loads

Environmental loads include wind load, snow load, rain load, earthquake load, and flood load.

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SEISMIC LOADS

Seismic loads on buildings are caused by movement in foundations . The acceleration of this

movement is very rapid and its value

is highly increased with height.

Earthquake Loads

• Structure loaded when base is shaken

• Response of structure is dependent on the frequency of motion

• When frequencies match with natural frequency of structure - resonance

Load Example: Earthquake Load

Base Motion

Earthquake Load

Earthquake Load

Seismic load is applied as horizontal shear at the building base. The shear force is

proportional to the building weight (W) and calculated from :

V = Cs . W

Cs is the seismic response coefficient which is found from :

Cs = SDS / ( R/I)

R is the response modification factor , which is dependent on the type of structure and

can be found from the table below.

I is the importance factor ,which is dependent on the occupancy category and is taken

1.25 for building designed for more than 300 person and 1.0 for ordinary building.